NITROGEN CARRIER INDUCED CHANGES IN, CHEMICAL MINERALDGICAL AND MICROBIAL PROPERTIES OF A SANDY LOAM SOIL Thesis for the Degree of Ph. D. MICHIGAN STATE UNIVERSITY JOHN W. SCHAFER, JR.. 1968 This is to certify that the thesis entitled VHF-.033}: ”“12er 3:23:33 CHANGES III C‘FT—‘ICALW I’ITIEPALOGICAL AID ViI’VPf‘TfiTfiT FUC'T-‘T‘PmTV—xr‘ Ch A Jekfiw SA‘ZD‘L’ LCA“? SOIL presented by J03"I W. SCIL‘XFYCR, JR. bo“ has been accepted towards fulfillment of the requirements for n 'fi‘Vv" C“ l ... ’ l.‘ J»’ 4.4 ..V\JL.J TY PM 9 degree {1.30-}. x/flfifl Major professor Date VA" 111., 1969. 0-169 .Y' rammed-c BY I HMS & SONS’ . 800K BINDERY INC. LIWRY BINDERS mmmr mama! _“- m. ‘4" ABSTRACT NITROGEN CARRIER INDUCED CHANGES IN CHEMICAL, MINERALOGICAL AND MICROBIAL PROPERTIES OF A SANDY LOAM SOIL By John W. Schafer, Jr. Residual effects of eight nitrogen carriers were studied after nine annual applications of 300 lb N per acre on a sandy loam soil. Carriers included Ca(NO3)2, NaN03, anhydrous NH3, urea, ureaform, NHANOB' NH#CI and (NHh)2504. Adequate P and K For corn were supplied each year. Half of the plots were Ihned in the seventh and'eighth years. The rate of acidification of the soils was rapid and dramatic. By the third year soils receiving NHuCl and (Nquzsoh were near pH h.0 and Mn levels of plants exceeded toxic levels., In general, the extent of acidification was related to the residual acidity of the carrier. Two years after liming, the pH of soils receiving residually acidic carriers was less than expected. Soil receiving the two most acid carriers, had a pH near 5.0. Nitrogen rates were in excess of plant needs. High (xmcentrations of carrier ions increased mobility of cations r'eplaced by protons released during nitrification. All soils John W. Schafer, Jr. below pH 5.0 showed considerable inseason fluctuations of pH, potential acidity and nutrient levels. These fluctuations coincided with weather patterns conducive to rnovement of water and solutes between the surface and ssubsoil. Cationic iron hydronium complexes were probably ‘the dominant mobile component of potential acidity. The 'Failure of liming to correct this acidity or to increase exmhangeable Ca to expected levels suggests that iron complexes are precipitating in the alkaline micro- environment of the lime particle, restricting its solubilization and neutralization value. Solubilization of Ca from lime was more retarded than the release of Mg. Acidification depleted exchangeable Ca and Mg. Exchangeable K and P levels were only moderately affected, indicating weathering of K and P bearing minerals under acid conditions. The level of certain soil and plant nutrients seemed to be related uniquely to characteristics of certain carrier ions. Calcium suppressed Mg; sodium associated preferentially with leaching anions, reducing dePletion of other cations; sodium and NH3 displaced inter- Iayer K from illitic minerals. The slow, concurrent release CW HCO3' and NH“. from ureaform dissipated the protons John W. Schafer, Jr. released by nitrification and reduced residual acidity relative to urea or NH3. With NH4N03, retention of protons resulted in residual acidity in excess of expected values. Sulfate complexation by sesquioxides led to extreme soil acidification but promoted reversal with lime. With acidification, foliar levels of Si, Fe, Al, Zn and Mn increased. The most striking nutritional imbalance was the high concentration of Mn in the tissue from all unlhned plots receiving residually acidic fertilizers. Liming reduced foliar Mn to below the 400 ppm toxic level. Levels of N, Mg, and P were deficient with certain treatments. It was impossible to pinpoint any specific cause for reduced yfields on any single nutrient tested for in the plow soil or hi foliar analyses. Subsoil nutrition influenced yields. ' Nitrification rates and evolution of C02 in soils below Wlh.5 indicated little microbial activity. Reduction in cation exchange capacity and alterations himineralogy of the clay fraction of the soil were indicated. Hmreases in Fe, Al, Si, Mn, and Zn, and their slow reduction with Inning, plus the failure of the lime to increase pH as expected, indicate drastic alteration of soil colloidal systems below pH 5.0. John W. Schafer, Jr. Implications of this project include: (I) Simultaneous independent changes in soil systems below pH 5.0 are modified by interactions and equilibria in the complex and continuously changing chemical environment. (2) Specific ion effects are important in this environment. Mass action effects of each fertilizer species with increased application rates in modern agriculture further complicates the equilibrium. (3) High rates of application of fertilizers on lightly buffered soils without adequate leaching will eventually result in excessive soil acidity. There is no evidence yet that this is reversable. If it is, complete restoration of soil productivity will be a slow and expensive process. NITROGEN CARRIER INDUCED CHANGES IN CHEMICAL, MINERALOGICAL AND MICROBIAL PROPERTIES OF A SANDY LOAM SOIL By John W. Schafer, Jr. A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Soil Science I968 ACKNOWLEDGMENTS The author wishes to express his sincere appreciation to Dr. A. R. Wolcott for his guidance, support and encourage- ment during the course of this investigation. His allowance of freedom is conducting the research and his assistance in the preparation of this manuscript were an invaluable learning experience. The author also wishes to express his appreciation to Dr. H. D. Foth for introducing the author to the need for this study and eSpecially for his enthusiasm, interest and desire in promoting high quality undergraduate teaching. It was his example that encouraged the author to undertake' this degree program. He is thankful to Dr. E. P. Whiteside, and to Drs. IL M. Miller and J. K. Kinsinger for their assistance on his guidance committee. The author also wishes to express appreciation to Dr. G. Benson Jones of the Ohio Agricultural Research and Devel0pment Center in Wooster, Ohio, for his assistance in the plant analysis; to Mrs. Nelly Galuzzi for assisting in the statistical analysis; and to Carl Kaechele and James LkBride for their assistance with the first incubation Study. Many thanks are due to the professors and graduate students of the Soil Science Department for their advice, encouragement and friendship during the course of this study. And finally, and especially, the author expresses thanks for the encouragement, assistance and patience of Ifls wife, Grace. TABLE OF CONTENTS PAGE INTRODUCTION . l IJTERATURE REVIEW. A Historical Aspects. 4 Acid PrOperties of Nitrogen Fertilizers 7 Basic Carriers 8 Ammonia Carriers 8 Ammonium Carriers. . . . . . . . . . . . . . . 9 Soil pH and Nutrient Availability . . . . . . . . lO Soil pH. . . . . . . . . . . . . . . . . . . . IO Calcium and Magnesium. . . . . . . . . . . . . l3 Molybdenum . . . . . . . . . . . . . . . . . . ' IA Manganese. . . . . . . . . . . . . . . . . . . l4 Aluminum . . . . . . . . . . . . . . . . . . . IS Other Inorganic Nutrients. . . . . . . . . . . l8 Mineral Nitrogen . . . . . . . . . . . . . . . l9 Clay Minerals and Amorphous Materials . . . . . . 20 Cation Exchange. . . . . . . . . . . . . . . . 2l Buffering Curves . . . . . . . . . . . . . . . 22 Clay . . . . . . . . . . . . . . . . . . . . . 23 Amorphous Material . . . . . . . . . . . . . . 24 PAGE EXPERIMENTAL PROCEDURES AND METHODS OF ANALYSIS. . . . . 25 History of the Field Trial. . . . . . . . . . . . . 25 Macronutrient Soil Tests. . . . . . . . . . . . . . 26 Micronutrient Soil Tests. . . . . . . . . . . . . . 28 Plant Analysis. . . . . . . . . . . . . . . . . . . 3l Soil Mineralization Studies . . . . . . . . . . . . 3l' Seasonal Changes in Mineral Nitrogen. . . . . . . . 33 Clay Studies. . . . . . . . . . . . . . . . . . . . 35 Amorphous Material. . . . . . . . . . . . . . . . . 36 Cation Exchange Capacity. . . . . . . . . . . . . . 37 Other Investigations. . . . . . . . . . . . . . . . 38 Statistical Analysis. . . . . . . . . . . . . . . . 39 RESULTS AND DISCUSSION l. Soil and Plant Analysis. . . . . . . . . . . . . . #2 Changes in Soil pH and Lime Requirement Since 1959. . . . . . . . . . . . . . . . . . . . . 42 Macronutrient Soil Tests. . . . . . . . . . . . . . #8 pH . . . . . . . . . . . . . . . . . . . . . . .' #8 Lime Requirement . . . . . . . . . . . . . . . . 50 Calcium. . . . . . . . . . . . . . . . . . . . . 52 Magnesium. . . . . . . . . . . . . . . . . . . . 5h Potassium. . . . . . . . . . . . . . . . . . . . 55 Phosphorus . . . . . . . . . . . . . . . . . . . 57 PAGE Micronutrient Soil Tests. . . . . . . . . . . . . 59 Zinc . . . . . . . . . . . . . . . . . . . . . 59 Manganese. . . . . . . . . . . . . . . . . . . 59 Iron . . . . . . . . . . . . . . . . . . . . . 63 Copper and Aluminum. . . . . . . . . . . . . . 6h Sulfur and Sodium. . . . . . . . . . . . . . . 65 Foliar Analyses . . . . . . . . . . . . . . . . . 66 Nitrogen . . . . . . . . . . . . . . . . . . . 66 Phosphorus . . . . . . . . . . . . . . . . . . 66 Potassium. . . . . . . . . . . . . . . . . . . 68 Calcium. . . . . . . . . . . . . . . . . . . . 68 Magnesium. . . . . . . . . . . . . . . . . . . 7l Manganese. . . . . . . . . . . . . . . . . . . 72 Zinc . . . . . . . . . . . . . . . . . . . . . 7h Aluminum . . . . . . . . . . . . . . . . . . . 75 Iron . . . .-. . . . . . . . . . . . . . . . . 77 Silicon. . . . . . . . . . . . . . . . . . . . 78 /Copper . . . . . . . . . . . . . . . . . . . . 83 Barium . . . . . . . . . . . . . . . . . . . . 83 Carrier Anion x Lime Interactions . . . . . . . . 8% Other Micro-elements . . . . . . . . . . . . . 90 Plant Performance . . . . . . . . . . . . . . . . 92 Plant Performance in Relation to Soil and Plant Analyses. . . . . . . . . . . . . . . . . . 9h 2. Major Nutrients. . Secondary Nutrients. Micronutrients and Other Elements. Seasonal Fluctuations in Soil Tests. Soil pH . . . . . . Soil Nitrate. Soil Sulfate. . . . . Extractable Ammonium. Exchangeable Calcium. Exchangeable Magnesium. Exchangeable Potassium. Lime Requirement. Soil Phosphorus Implications of Seasonal Study. Incubation Studies Incubation Experiment I Incubation Experiment ll. Mineralogical Studies. Cation Exchange Capacity. Clay Minerals Amorphous Material. . . . Organic Matter. . . . . . . . . vi PAGE 95 97 99 lOZ lOZ llh Il7 ll7 l20 l2l l22 l23 l24 l25 l27 I30 I33 I35 I35 l39 IA6 lh8 Summation . 5. Subsoil Studies. . . . . . . . . . . . . Texture of the Subsoil. Soil Test Variation with Depth. The Influence of Treatment on the Subsoil Subsoil Influence on Crop Response. SUMMARY AND CONCLUSIONS. Effect of Nitrogen Carriers on Soil Acidity . Effects on Elements of Soil Fertility . Effects on Crop Nutrition . Cr0p Response . Effects on Microbial Activities Ionic Effects of Carriers Ionic Mobility. Effects on Soil Colloids. . . . . . . . . . Implications. . . . . . . . . . . . . LITERATURE C I TED . APPENDIX . vii PAGE lh8 ISO ISO lSl I55 I65 I67 I67 I69 I73 I75 I77 I77 l80 l8l 183 I86 20l TABL_EI LIST OF TABLES Fertilizer and lime treatments in the field experiment . Changes in soil pH since I959 as influenced by nitrogen carriers and lime. Changes in lime requirement since I959 as influenced by nitrogen carriers and lime . Annual rainfall for the l960-l967 sampling years. . . . . . . . . . . . . . . . . . . Effects of nitrogen carriers and lime on pH and lime requirement in the plow layer. Effects of nitrogen carriers and lime on exchangeable calcium‘ and magnesium in the plow layer . Effects of nitrogen carriers and lime on exchangeable potassium and Bray extractable phosphorus in the plow layer . Effects of nitrogen carriers add lime on extractable zinc in the plow layer . Effects of nitrogen carriers and lime on extractable manganese and iron in the plow layer . Effects of nitrogen carriers and lime on foliar nitrogen and phosphorus . . . Effects of nitrogen carriers and lime on foliar potassium . Effects of nitrogen carriers and lime on foliar calcium and magnesium . viii PAGE 27 43 45 46 A9 53 56 60 6I 67 69 7O LABL_EI lL3 ll+ If; l€5 l7' L8 I9 20 2l 22 23 2h 25 Effects of nitrogen carriers and lime on foliar manganese and zinc. Effects of nitrogen carriers and lime on foliar aluminum and iron . Effects of nitrogen carriers and lime on foliar silicon . Effects of nitrogen carriers and lime on foliar copper and barium . Effect of nitrogen carriers and lime on several micro-elements in corn tissue. Effects of nitrogen carriers and lime on corn yields. . . . . . . . . . . . . Comparison of observed ranges and deficient, normal and toxic levels of nutrients in corn leaves. Effect of nitrogen carriers and lime on seasonal variation of soil pH in the plow layer in I967. . . . . . . . ,., . . Effect of nitrogen carriers and lime on seasonal variation of lime requirement in the plow layer in I967. Effect of nitrogen carriers and lime on seasonal variation of exchangeable potasssium in the plow layer in I967 . Effect of nitrogen carriers and lime on seasonal variation of exchangeable calcium in the plow layer in I967. . . . . . -Effect of nitrogen carriers and lime on seasonal variation of exchangeable mag- nesium in the plow layer in I967 . Seasonal variation of sulfate-S in the plow layer on ammonium sulfate treated plots without lime . . . . . . . . . PAGE 73 76 79 82 9I 93 96 I03 ION l05 lO6 lO7 l08 TABLE PAGE 265 Ammonium and nitrate in the plow layer (O-IO“) on July 3|, I967 . . . . . . . . . l28 2J7 Ammonium and nitrate in the plow layer (O-IO") on September 28, I967. . . . . . . l29 223 Changes in mineral N (NH4* and N03’) durin two weeks' incubation in Experiment I. . . l3l 25? Changes in mineral nitrogen and evolution of C02 during two weeks' incubation in Experiment II. . . . . . . . . . . . . . . I32 3() Effect of nitrogen carriers and lime on cation exchange capacity of plow layer and its pH dependence. . . . . . . . . . . I37 3l Interpretation of x-ray peaks in the clay analyses. . . . . . . . . . . . . . . IAO 32 Effect of nitrogen carriers and lime on sodium hydroxide soluble SiOz and Al203 and an estimation of all0phane in the clay fraction of the soil. . . . . . . . . IA6 33 Variation of soil pH with depth in the profile. . . . . . . . . . . . . . . . l52 3H Variation of lime requirement with depth in the profile . . . . . . . . . . . . . . 152 35 Variation in soil phosphorus with depth in the profile . . . . . . . . l53 35 Variation in soil potassium with depth in the profile . . . . . . . . . . . . . . l53 37 Variation in soil calcium with depth in the profile . . . . . . . . . . . . . . ISA 38 Variation in soil magnesium with depth in the profile . . . . . . . . . . . . . . ISA 39 Effect of nitrogen carriers on soil ‘ ammonium at three depths . . . . . . . . . I57 x TABLE MI) tel 1+2 1+3 AJI 1+5 1+6 Effect of nitrogen carriers on soil nitrate at three depths. Effect of nitrogen carriers on soil pH at three depths . . Effect of nitrogen carriers on lime requirement at three depths. . . . Effect of nitrogen carrier on soil phosphorus at three depths . . . Effect of nitrogen carriers on soil potassium at three depths. . . . . Effect of nitrogen carriers on soil calcium at three depths. Effect of nitrogen carriers on soil magnesium at three depths. xi PAGE I57 l58 l58 l59 I59 I60 I60 FIGURE l LIST OF FIGURES PAGE Apparatus for titration under C02 free conditions. . . . . . . . . . . . . . 3A Residual effects on soil and plant para- meters for ammonium chloride (solid line) and sulfate (dashed line) relative to other acidifying carriers two years after liming . . . . . . . . . . . . . . . . . . 87 Rainfall distribution for summer I967, East Lansing, Michigan . . . . . . . . . . l09 Seasonal fluctuation of ammonium and nitrate nitrogen on soil receiving only basal fertilizer . . . . . . . . . . . . . lIO Seasonal fluctuation of ammonium and nitrate nitrogen on calcium nitrate treated soil . . . . . . . . . . . . . . . Ill Seasonal fluctuation of ammonium and nitrate nitrogen on ammonium nitrate treated soil . . . . . . . . . . . . . . . Il2 Seasonal fluctuations of ammonium and nitrate nitrogen on ammonium sulfate treated soil . . . . . . . . . . . . . . . ll3 X-ray diffraction tracings of oriented soil clay films from the unlimed basal and ammonium sulfate treated soils on porous ceramic plats. Treatments: A, Mg-saturated, glycerol-solvated, no heat treatments; B, K-saturated, no heat treat- ment; C, K-saturated and heated to 330 C; D, K-saturated and heated to 550 C. Scale of horizontal axis is linear for degrees 29. Vertical axis is radiation intensity at a scale factor of 8 . . . . . . . . . . lAI xii INTRODUCTION The early civilizations of man in the Tigris and other river valleys recognized the value of the yearly flooding of the land in renewing the fertility of the soil. In contrast, depletion of soil fertility in medieval EurOpe, in the revolutionary war period of the United States, and today in much of the tropical regions of the world, cause man to move from one location to another. Natural Processes will often gradually restore the soil to some basal fertility leveL and then,man can move back for a few mona years of cultivation before the soil is again depleted 0f its available nutrients. As technology has advanced, particularly in the last 5O‘Years, man has put higher and higher demands on the soil. He has depleted the natural fertility level of the soil "MCI! faster than natural processes can restore it. Some OFIhan's activities, such as irrigating with poor water, haVe ruined the productivity of some soils. 0n the other ham3|,new techniques for maintaining high fertility and recllamation of unproductive soils have been developed. Fertilizers are used to provide nutrients needed for intensive cr0pping and to maintain a proper nutrient tmlance in the soil. Today's high analysis fertilizers are often highly acidic. Some fertilizers are acidic because of the nature of the carrier. Other fertilizers may undergo chemical or biological transformations in the soil, resulting in an acidic residue. So that, while adding a beneficial input; nutrients we may also be adding something to our soils that is potentially very harmful, namely, acidity. Thus, a fertility paradox results whereby man may destroy soil productivity by adding plant nutrients. This project was undertaken to investigate several aspects of this paradox related to the acid nature of some nitrogen fertilizers: I. How is soil pH affected by different fertilizer nitrogen sources applied at high rates and repeated annual applications over a period of time? 2. What effect will pH changes have on the fertility status of the soil as reflected by soil tests? What effect will changes in soil pH have on crOp nutrition as reflected in plant tissue tests? How will these changes effect cr0p yields? If extreme acid conditions result, are colloidal soil materials destroyed or their surface properties altered? LITERATURE REVIEW Historical Aspects The fertility value of the silt deposited by annual floods was recognized by the early civilizations between the Tigris and the Euphrates rivers. It is not known when man first began to add amendments to improve soils, but the practice of adding manure to soils is mentioned in Homer's Odyssey which dates back to about 800 B.C. The early dwellers of Aegina dug marl and applied it to their fields. The use of marl was common among the Romans, the Greeks, and the Gauls before them. Pliny was one of several early writers to discuss the value of various types ofinarl. The use of limestone on sour soils was first investigated systematically in the United States. Early investigators included Edmund Ruffin and Benjamin Franklin (82) . The first long term field trials on nitrogen carriers vmwe established in England in I877 (70) and in Pennsylvania h11882,(58). Each ran for more than A0 years. In both, NaNOBIand (NHh)2504 were used as two of the treatments. ”\England animal manure was used as a third treatment while irlPennsylvania, dried blood was used. In the former, wheat ..‘ and barley were grown while in the latten a corn-oats- wheatrhay rotation was used. It took l6 years in Pennsylvania and 20 years in England before any marked treatment effects were observed at annual rates of 2A or A8 lbs N per acre per year. The effect of a given treatment depended on the crop grown. After 30 years in England, wheat yields on the (NHA)250A treated plots were significantly reduced relative to NaN03 while barley simply would not grow. After four decades, the group in Pennsylvania Iimed their plots and were able to bring yields of all treatments to the same level. Early work in Alabama on cotton (8i) showed similar chferences between NaNO3 and (NH4)ZSOA. The addition of lime eliminated differences in yield and soil pH between treahnents. 'The recognition that certain nitrogen carriers reduce SOIllfli has lead to attempts to predict the extent of this reduction. One of the first to attempt this was Pierne (62). From the calCulated basicities and aCiidities of the cations and anions in the fertilizer and fine effected biological alteration of ions by soil Organisns, he predicted the amount of lime needed to maintain the SOil pH. Twenty years later in I95A, using Pierre's data, Andrews (6) concluded that the predictions of Pierre were too low and that the effects of the various carriers were more acidic than Pierre estimated. In an earlier paper (7) Andrews and Cowart accurately predicted the effects of acid fertilizer on the soil, but to arrive at these valuesthe/measured and allowed for nitrogen uptake by cotton plants. Hiltbold and Adams (35) have shown considerable variations in pH between soil samples receiving the same nitrogen source. By accurately accounting for all forms of nitrogen before and after an incubation period, they were able to relate these differences in pH to the amount of nitrogen volatilized. It is generally held today that soil acidity that deveLOps from a fertilizer is not a calculable constant for each fertilizer. It depends on: soil characteristics, thelerpping system, the environment; whether nitrogen is removed by plants, or leached as an anion, cation or molecule,or lost by volatilization; as well as,.onthe natune of the fertilizer (3). Volk (9A) compared urea andiflmnonium nitrate. These theoretically have the same Potential acidity. He found that the resulting soil pH was higher for surface applied urea than for NH4N03. This was attributed to higher volatilization rates of urea, and to its leaching and/or absorption by plants in molecular form. These:processes could take place without altering soil pH. It has also been shown that higher rates of fertilizer application usually result in more acidity per pound because oflnore leaching and less efficient use of the fertilizer by plants. Ammonium sulfate may be an exception to this (I). Recent field trials in Ireland (ll), Puerto Rico (72), the southern United States (2), Brazil (28) and Russia (IOS) have explored the acidic effects of fertilizers, particularly nitrogen. Wolcott, Foth and their associates at Michigan State University (IOO, lOl, IOZ) have established experiments to investigate the acidic effects of certain nitrogen carriers. In one of these, heavy rates of nitrogen from several sources have been applied to a sandy loam soil annually since I959. The yield of corn has been dramatically FEduced by the more acidic carriers. The availabilityiof sewera] nutrients in the soil seems to be well correlated wiflw fertilizer treatment (lOl). Acid Properties of Nitrogen Fertilizers The final acidic effect of any fertilizer depends on more than the nature of the carrier itself. But a relative \Cl AI. ranking of the carriers according to their chemical acidity is frequently useful. Table l (page27) lists the residual acidity for eight common nitrogen carriers. These values are average values calculated from several sources (6, (SA 82, lOl). They represent the pounds of CaCO3 needed to neutralize that amount of carrier which contains one pound of nitrogen. §§§ic Carriers Even though they leave a basic residue, calcium nitrate (residual acidity of -],3) and sodium nitrate (-I.8) have an initial acidic effect on the soil due to direct displacement of exchangeable H+ by Ca+2 or Nal to form HN03.The absorption of the nitrate by the plant,leaves an excess 0f<:alcium or sodium and the final effect on the soil iS‘then basic. Ammorfia Carriers Anhydrous ammonia (I.8), urea (I.9) and ureaform (I.9) all have an initial basic effect on the soil. Urea is quCkly hydrolyzed by urease-synthesizing microorganisms to Form NHAOH. Anhydrous ammonia hydrolyzes to NHqOH in the presence of soil moisture. Ureaform is a urea formaldehyde Polymer which is more slowly hydrolized. The biological oxidation of NHL: to N03'releases hydrogen ions to the soil system. The net effect of these fertilizers is acidic. During the initial hydrolysis of anhydrous ammonia or urea,the soil pH in the micro-environment near the point of application may reach 9.5. At this high pH, nitrification is strongly inhibited. Oxidation begins at the periphery of this microenvironment where conditions are more favorable. High levels of nitrite may form temporarily that are toxic to nematodes, fungi and bacteria. The anhydrous ammonia can react with nitrous acid formed under these conditions QIVlng the reaction: NH3 + HN02——9 NH4N02._9 N2 I 2H20. This reaction,plus the direct loss of ammonia vapors,can result in considerable loss of applied nitrogen. Aimonium Carriers Ammonium chloride (5.3) and ammonium sulfate (5.5) have an initial acidic effect on the soil due to hydrolysis and exchange reactions leading to the formation of hydrochloric (N'sulfuric acids. The low percentage of nitrogen in these ComPOunds results in a high application of the anion per unit of nitrogen. This Enitial acidic environment is responsible for the slower oxidation of ammonium under acid soil conditions, when compared to anhydrous ammonia. Oxidation I0 cm ammonium is a further source of acidity. Thus these two carriers have the highest residual acidity of the common nitrogen fertilizers listed in Table l. Monoammonium phosphate (5.9) tends to leave an even greater residue of acidity because of the lower solubility and greater retention of phosphate in soil, as compared with chloride or SLHfate. The residual acidity of diammonium phosphate (3.6) is intermediate between these carriers and those which supply only nitrogen, as ammonia, urea or ammonium nitrate. Ammonium nitrate (l.8) contains nitrogen in both the ammonium and nitrate forms. It is acidic both initially and residually but the total acidity is not as great as the other ammonium carriers (A, 5, 2A, 25, A8, 7l, 73, 82, lOl). Soil pH and Nutrient Availability Soil EH The pH test is probably the most common and most useful C” all soil tests. Yet we do not really understand what is be- inSmeasured *when we measure soil pH. We define pH as the negative log of the hydrogen ion activity and it is ll commonly measured with a glass electrode. For clear solutions the glass electrode probably does measure hydrogen ion activity in solution. But in a soil suspension the pH value obtained is influenced by several factors. Among them are the soil to water ratio, soluble salts and atmOSp- heric C02 (2l, 6l). In addition, the pH value will vary depending on the position of the glass electrode and whether the suspension is in motion or has settled (l8). This so-called suspension effect is not well understood, but two theories are suggested. It may be due to the charged nature of the clay particles in the suspension or to leakage across the fiber plug of the calomel electrode. Either of these theories should give the observed decrease in (PHIMhen a glass electrode is lowered from the solution into the soil (2l). Schofield and Taylor (76) found that pH was independent CW electrolytic concentration if a weak CaCIZ extractant was used. The suspension effect could be avoided if pH waSIneasured in the clear supernatant. What they were actually measuring,howeven was a function of (pH-l/ZpCa) rather than pH. This corresponds to the activity of Ca(OH)2 mulwas thus called the lime potential. e.- l2 Turner and Nichol (87) showed that the amount of added CaClz influenced (pH - l/2pCa) but not the expression (pH - l/2(CaeM9)). They suggested that lime potential should consider both calcium and magnesium. They further suggested that since this expression was a constant at a given pH, a more meaningful value for pH could be obtained by measuring (Ca + Mg) and the constant. Then the pH could be calculated frmn the expression K a pH - l/2p(Ca + Mg). Over the next seven years a series of papers came from the laboratory of Turner and his associates (83, 8A, 85, 86, 88, 89, 90) as they studied various aspects of potential measurements. Their final conclusion was that lime potential is influenced by aluminum activity. As they and ,Linsey, Peach, and Clark (A6) have shown, activity of alwninum in soils is extremely variable. So the potential cnncept has been abandoned as a practical way to determine soil pH. Many studies have been conducted to investigate the effect of the hydrogen ion on plant growth. These have been rather unsuccessful. In soil systems it is impossible uldrOp the pH to A.0 without influencing all other nutrients Ulthe soil and usually the toxicity or deficiency of some runrient becomes more important in controlling plant growth than the hydrogen ion concentration (A2). It". .5 e - u b I3 Jackson (A2) has listed calcium, magnesium, molybdenum, nmnganese and aluminum as the inorganic elements which most often are responsible for reduced plant growth under strong acid conditions. In addition to these, other nutrients are knm~n to play an important role in acid soil infertility under local conditions. Calcium and Magnesium Calcium, magnesium and hydrogen usually comprise more than 90 percent of the exchangeable cations in the soil. Thus a marked increase in acidity will be accompanied by a decrease in available calcium and magnesium. Neither of these ions seem to form compounds under acid conditions that render them unavailable to plants. Calcium is involved in ion uptake from the soil by Plants and seems to be important in protein synthesis. A deficiency of calcium results in failure of both terminal buds and apical root tips to deveIOp prOperly. Magnesium is an essential part of the chlorophyll molecule and seems to be important in phosphorus metabolism. It is mobile in plants and the deficiency shows up as a chlorosis of the lower leaves (A2, 82). filo an. n.» I. IA Molybdenum Molybdenum is usually found in the soil as the anion MoOhfz. Sometimes soils are low in native Mo, but usually a nmalybdenum deficiency is associated with low soil pH. Lhning will usually correct the problem. Molybdenum is Hnnolved in nitrate reduction in the plant and is particularly hnportant in plants that fix nitrogen. The plant will show nitrogen deficiency symptoms when Mo is deficient (42. 82). Mgnqanese Divalent Mn is the form taken from the soil by plants. The ratio of divalent to Mnl'Ll increases as the pH is reduced. Toxicity usually occurs only in soils below pH 5.5. Aluminum does not give characteristic toxic symptoms in plants. Since Al and Mn toxicity often occur together, Ihltoxicity symptoms may show up when Al toxicity is responsible for plant retardation. This may have led to some incorrect conclusions in earlier work. Toxicity of Mn can occur however at a slightly higher pH than aluminum toxicity. ' The toxic level of Mn in the soil has not yet been determined. In solution culture the toxic level of Mn l l I ll - . . a ~ .. e: ... a n . .p. .p- ..~ » . . L. . .p. r a p p . . a u . - . n v n . s . . s .e. .u u u s c .e .i. .lh .x. .. a . I. .u . In. .u .u a.- I5 depends on the concentration of the other salts in solution. “we toxic level of Mn in dilute nutrient solutions is lower than the toxic level in more concentrated nutrient solutions. 'Hua determination of specific levels of toxicity is further hampered by the fact that drying a strongly acid soil at room temperature will increase the extractable Mnlz. Thus, air dry soils may not reflect the true field Situation. The toxic effect of manganese on plants seems to be due in part to an induced iron deficiency and in part due to an amino acid imbalance (3, A2). Aluminum Jenny (A3) has referred to the history of agronomic concepts concerning the role of aluminum in soil in the United States as the merry-go-round. Coleman and Thomas (21) in summarizing the state of our knowledge concerning ahmfinum and pH have stated that aluminum is involved in complex ion-exchange and hydrolysis reactions which have a definite influence on pH, but they have not been adequately evaluated. Part of the problem has been the failure to understand soil systems. The role of aluminum in soil acidity was first postulated by Veitch in the early l900's. In I909 l6 Hue concept of pH was defined and techniques perfected to imxasure it. For the next AO years researchers generally unuared aluminum,and aluminum was given no importance in soil systems (A3). It gradually became apparent, and today is universally accepted, that the H-clays studied during this period were actually (H,Al)-clays. The aluminum is believed to come from an acidic attack and breakdown of the crystal lattice of clay minerals. The resulting clay is primarily a (H,Al)-clay but contains some Mg, Fe, and Other cations released upon degradation of clay (IO, 20). Soil pH measures the hydrogen ion activity in the System when the liquid and solid phases are in equilibrium. The hydrogen ion associated with the permanent charge of the clay is the most active form of soil acidity. But hydrogen associated with the hydrolysis of organic functional groups, hydroxyl-aluminum monomers, polymers and other acid-producing ions such as Fe and Mn are also important. The pH does not measure the activity of the metal ion itself, although these ions have a marked effect in buffering the soil system (50, IOA). The problem in studying aluminum is the almost infinite variety of aluminum compounds in the soil. It can occur in either tetrahedral or octahedral coordination in the crystal l7 Iatrtice. It can be crystalline, or form sols or gels. It H5 found in, between, or on the surface of the clay lattice. Alunfinum forms compounds with many anions and forms complexes witrlboth organic and inorganic constituents in the soil. It also polymerizes (39, 93). Each of these forms has its own solubility equilibrium and the intermediates and complexes have corresponding intermediary pK.values. This makes it almost impossible to define the system or to prepare an artificial system that is analogous to a soil system. Soluble aluminum ions in the soil are octahedrally hydrated as Al(H20)6l3. The first step in the hydrolysis of this gives Al0H(H20)5‘2. The pK value for the first stage of hydrolysis of aluminum is around 5.0. It is well established that there is an increase in soluble soil aluminum when the soil pH falls below 5.0. As the number of hydroxyls increases with further hydrolysis, there is a tendency for this to polymerize (2l, 37, 39, A7, 5l). Since this polymer is positively charged, it can react with the negative surface of soil colloids. This complexed Al can block exchange sites and it also serves as a cementing agent for clay and clay-organic matter complexes (l5, I7, 30. 67). l8 Aluminum has been shown to both stimulate and reduce ttie growth of corn (2l). Undoubtedly aluminum toxicity is a major factor of infertility in many acid soils. But sc>il conditions that result in aluminum toxicity have not ‘yet been defined precisely enough for universal application. Altmfinum level in soil has been reported as solution Al, exchangeable Al, or percentage Al saturation of the cation exchange. Experiments often show good relationships between measured aluminum and plant growth when the experi- ments are considered separately. When the experiments are considered collectively, inconsistencies between them are apparent. Toxicity has been reported for soils with as little as l.2 ppm solution AI, 0.2 meq of exchangeable Al/ l00 g. of soil and at A percent Al saturation of the soil exchange (3. 33, l03). Other Inorganic Nutrients The nutrients zinc, c0pper and boron are often found to be deficient under alkaline soil conditions; however, they are usually very soluble under strongly acid conditions. The availability of sulfur increases with addition of lime. Phosphorus forms aluminum and iron phosphates under acid conditions. These are unavailable to plants (3. 82). l9 Iron, like aluminum, becomes soluble under acid ccn1ditions and forms various amorphous products that can neact with clays and may eventually crystallize (80). Iron may be deficient at high pH, in the presence of high anounts of phOSphorus, when high levels of metallic ions such as copper and manganese are present, and under conditions of high moisture or cool temperatures (82). Mineral Nitrogen In describing the effects on the soil of nitrification processes, Alexander has said “it is clear that nitrifi- cation is a mixed blessing and, possibly, a frequent evil.” Nitrification can be considered a self-inhibiting reaction: NHL,t i 202—) No3‘ -l H2 ) - 2H‘. The microorganisms (predominantly bacterial of the genera Nitrosomonas and Nitrobacter) that carry out these processes are acid sensitive. The reaction is acid producing and without lime to reverse this acidic drift, the products of reaction can inhibit the nitrifying autotrophs that carry it out. For reasons yet unclear, nitrogen oxidation stands out among biological processes in the soil for its sensitivity to pH. A pH of 5.0 is considered the minimum pH needed for significant activity of these organisms (A). .. I II a — LC an» a. ii .i. r ... .C .. . . . r: l a .C .. . A V . . r e \ AI. . .. ~ ~_- . u 3 s .x. AI.» . - s.\ p v r . LC . . p u a w - . . v :5 Alw .e an. ac I o a . . ~ - .iv .\. .\. v s y .e . u . .\. tu- n i n v \ § 20 There is some evidence that other heterotrophs also taroduce nitrite at pH values below 5.0 and that a non- t>iological oxidation of nitrite to nitrate may take place below pH 5. But the importance of these in the soil has not yet been evaluated (9l). Weber and Gainey (95), have shown nitrate production in soils as low as pH A. They suggested either an acid tolerant strain was present,<3r some component in the soil protected organisms from acidity that is fatal in nutrient solutions. As the soil becomes progressively more acid, the microbial population that mineralizes organic matter shifts from one dominated by bacteria and actinomycetes to one dominated by fungi. MineraliZation of organic matter is less sensitive to pH,and thus,ammonium accumulates in a soil of low pH, while nitrate accumulates in soils above 6.0 (23, A2). Below pH A.O, 002 production,hence release of ammonium by mineralization,is reduced, apparently because of increased solubility of aluminum. Organic matter-aluminum complexes are very slowly decomposed by microbes (57). Clay Minerals And Amorphous Materials Nutritional problems associated with the low soil pH can perhaps be alleviated by prOper liming and fertilization 2l prwactices. The question that does arise is: What happens tc> the colloidal prOperties of the soil under extremely ac:id conditions? Can strong acids destroy or alter clay ininerals, amorphous materials, or their surface prOperties? Cation Exchange The cation exchange capacity of soils has been successfully correlated with the amount of organic matter and clay in the soil. More recent work has shown that amorphous material also makes a significant contribution to the exchange capacity (22, 32, 3A, 55, 75, 99). As the pH of a soil decreases,the measurable cation exchange capacity also decreases. This decrease equals the amount 0f pH dependent exchange acidity (6A, 98, lOl). This appears to be a revershble phenomenon, but it may not be if at some point the exchange surface is altered or destroyed. In the ordinary ranges of soil pH (5.0-7.0), exchange capacity due to clay is relatively unaffected by soil pH (3A, 69). In this same range the bulk of the pH dependent sites have been traditionally ascribed to organic matter (64). But amorphous materials in the soil are also strongly PH dependent in their exchange properties and they are probably more important in the soil than previous believed (8, 40, 5A). .e ..- » i . u a — §- - .s. l 22 At low soil pH, (5.0 and below) clay appears to exhibit pH dependency in its exchange prOperties (2l, 3A). Also in this region, alumino-hydronhunions exhibit prOperties of hydrogen exchange as a result of their hydrolysis (39). Buffering Curves The titration curves of clays and soils are one of the oldest tools in studying soil prOperties. Titration curves of solutions, resins and clays have been compared in an effort to understand some of the complexities of the soil system. Because of its complex nature, most work related to soil has dealt with pure clay systems. It was first believed that a hydrogen clay was like a weakly ionized acid. Later it was shown that a true hydrogen clay behaves like a strong acid. The weak acid character of clays is due to the presence of aluminum (2l, A3). Schwernnann and Jackson (77) have shown three buffer ranges in a H-vermiculite. The first is below pH A and is the result of the presence of hydronium (H30*). A second buffer range in the region of pH A.0-S.6 is due to exchange- able alumino-hexahydronium ions. A third buffer range (pH 5.6-7.6) results from the neutralization of non- exchangeable hydroxy aluminum produced by hydrolysis and polymerization of aluminum. This aluminum results from 23 an acidic attack on the vermiculite structure at low pH. This third range is weakly exhibited in a freshly prepared H-vermiculite, but as the H-vermiculite ages,it becomes stronger. These aluminum polymers exist as coatings in the interlayers and on the surface of clays. They account for most of the pH-dependent buffer capacity (exchange sites) that has been attributed to clay. This source, plus organic exchange sites, provide most of the buffering capacity of soils between pH 5.5 and 8.0 (2l). Elél A variety of laboratory tests on clay minerals,involving various solutions, temperatures and pressures, indicate in general, that clays are somewhat soluble in acids and unaffected by bases (3l). The acidic breakdown of clays has been previously discussed. There appears to be no work with regard to the importance of this degradation under field conditions. Will the aluminum recrystallize to form fresh clay if an acid soil is limed? If so, how long will it take? If the clay contains large amountsof magnesium which can be leached or absorbed by plants, will the new clay be the same type as the original? Wolcott and others (lOl) have presented indirect evidence that clays in a soil will be destroyed under highly acid conditions. But they did not investigate the effect of liming on these soils. . . .e . . .. ._. . . . e s .c . v ... . . s r. .\. a . o .—~ ... a» - a .—. L. ... u 9 ...~ - e n « ~n- - .s— In . u a .\u n.. ... o . ~ - e . nun .b a I. .t. s .1- a . 2A Amorphous Material All0phane is rigidly defined to include only amorphous colloidal alumino-silicates, but more generally the term refers to all amorphous silica, aluminum, iron and alumino- silicates in the colloidal fractions of the soil. This general connotation includes the aluminum polymers discussed above that are found as coatings on the clay particals. The important consequences of the prOperties of all0phane in the soil are not emphasized in the literature,because methods for accurate characterization have not yet been deveIOped (A9). The general prOperties of all0phane are rather broadly and vaguely defined. Procedures for isolating and estimating all0phane have been established. These procedures generally give good results. However, no one really knows just what is being measured (8, 29, A0, 68). It is generally held that crystalfine materials are acid soluble and amorphous materials are alkali soluble. Amorphous material is readily subject to alteration by treatment,and any attempt to isolate or study it may in part alter or destroy it (54). .\< use EXPERIMENTAL PROCEDURES AND METHODS OF ANALYSIS History Of The Field Trial In I959 an experiment was established on the Soil Science Experimental Farm at Michigan State University to study the effects of nitrogen carriers on the soil and on plant growth. Ten treatments were replicated four times in a randomized complete block design. Each plot was IA by 25 feet. Corn (Zg§_may§) has been grown continuously year after year. Michigan A80 and in recent years Michigan 300 hybrids, have been used. In the early years of the experiment, corn was planted in A2 inch rows. In I967, 28 inch rows were planted. An initial plant population of 25,000 plants per acre was established. This was thinned to l6,000 plants per acre when the plants were two feet high. Simazine was used for weed control. The soil was first described as a Hillsdale Sandy Loam (Typic Hapludalf) (lOl). In a recent reclassification, it has been tentatively called a Hodunk Sandy Loam (Ochreptic Fragudalf) (See appendix for description) (7A, 96). The treatments are shown in Table I. The basal fertilizer treatment was applied before plowing. Some years the plots were plowed in the fall, and in other years, they were plowed in the spring. The supplemental nitrogen fertilizer was applied just before planting each year at the 25 or. .- w ,'l AI s: l. 26 rate of 300 pounds of nitrogen per acre and disked in. In I96l, the anhydrous ammonia was not applied. In the spring of I965, the center two replications were uniformly limed with the equivalent of two tons of dolomitic limestone per acre. In the spring of I966, additional dolomitic limestone was applied to the same two replications, so that total limestone applied on each treatment was equal to twice the lime requirement test for that treatment. The totals used in I966 are indicated in Table I. In I967, the urea fertilizer intended for plot #7 in one unlimed replication was accidentally placed on the adjacent plot #6. This plot also received 300 pounds of nitrogen as anhydrous ammonia five weeks later. The urea plot (#7) received no nitrogen other than that in the basal fertilizer in I967. Macronutrient Soil Tests Soil samples from the plow layer have been taken each fall since the initiation of the experiment. Samples were taken periodically throughout the I967 growing season. 27 Table l. Fertilizer and lime treatments in the field experiment ==E_ Treatment Base Supplemental Relative Limestone nwnber fertilizer nitrogen %N residual applied treatment source acidity in I966 * # ** tons per acre ## 1 None None -- -- 2 2 5-20-20 None -- -- h 200 lbs 3 ” Sodium nitrate l6.0 -l.8 2 h “ Calcium nitrate l5.5 -l.3 2 5 ” Anhydrous ammonia 82.2 1.8 h 6 ” Urea h6.0 1.9 6 7 ” Ureaform 38.0 l.9 6 8 " Ammonium nitrate 32.5 1.8 6 9 ” Ammonium chloride 28.0 5.3 8 I0 ” -Ammonium sulfate 20.5 5.5 l0 *Total N+P+K = l0+l8+33 per acre per year beginning in I959. #Annually, 300 lbs. N per acre per year beginning in I959. **Lbs. of CaC03 one pound of nitrogen. to neutralize a weight of carrier containing ##This is in addition to the 2 tons of lime applied to each of these plots in I965. .\a or our a. - 28 Soil pH (glass electrode, I:I water suspension), available P (0.025 N_HCI in 0.03 N_NHhF, l:8 soil-to-extract ratio), and K, Ca, and Mg exchangeable with IN_NH40Ac were determined by routine procedures of the soil testing labonatory at East Lansing. Lime requirement was estimated using p-nitrOphenol, triethanolamine buffer of Shoemaker et al. (78). Micronutrient Soil Tests Soil samples were taken from the plow layer for micro- nutrient analysis on October 25, I967, using plastic and stainless steel equipment. Zinc was extracted using a procedure deveIOped for IHchigaryscnls by Melton (52). Forty grams of dry soil meregnlaced on Whatman No. 3 filter paper that had been Prevkanly rinsed with deionized water. The soil was leached With 25 ml. of deionized water. When the first 25 ml. fwd draained through, a second 25 ml. was added in small alkflfllts, allowing the soil to drain between aliquots. The Ieachate:was analyzed for zinc on a Perkin-Elmer Model 303 Atomic Absorption Spectrophotometer. Manganese was extracted using the method of Hoff and Mederskr (36), which Pailoor (60) found best suited for ‘- o . --- .hv - n 'w . A . u ', u . . \ ca. 1 u . . I ., - -_~ '.l . -I ‘ - Q o “ ‘- p Ill Ll! 29 Michigan soils. Five grams of soil, with 50 ml. of 0.] N.H3P04: 7 drops of 0.l N_silver nitrate, and a quarter teaspoon of activated carbon was placed on a shaker for ID minutes. The solution was filtered through Whatman No. 40 filter paper. The filtrate was analyzed for manganese on a Perkin-Elmer 303. Iron was extracted from the soil using the method suggested by Olson (59) as an availability index for iron. A flask with l2.5 g. of soil and 50 ml. of l.0 fl_ammonium acetate was shaken for 30 minutes. The suspension was filtered and the filtrate analyzed for iron on a Perkin- Elmer 303. Aluminum was determined according to the method of Laflamme (#5). Ten grams of soil was shaken for 30 minutes in l00 ml. of l.0 N_KCI. The mixture was filtered and 50 ml. was placed in a centrifuge tube. Two ml. of I000 ppm iron solution and two drops of phenol red indicator were added. Ammonium hydroxide was added drop-wise until the color changed from yellow to red. The solution was centrifuged for 20 minutes at 3000 rpm, decanted, and the precipitate dissolved in 5 ml. of 4.N HCI. The solution was diluted to l00 ml. and aluminum determined on the Perkin-Elmer 303. 30 Copper was determined using the method suggested by Fiskell (27) for available c0pper. Fifty grams of air dry soil was shaken for one hour in I00 ml. of 0.] N ammonium nitrate. The suspension was filtered through Whatman No. 3 filter paper and c0pper determined on the leachate using the Perkin-Elmer 303. Sulfate was determined using the method of Bardsley and Lancaster (9). Ten grams of soil was shaken with 25 ml. of ammonium acetate extracting solution for 30 minutes. Then, 0.25 g. of charcoal was added. The mixture was shaken for 3 minutes and filtered through Whatman No. 42 filter paper. To l0 ml. of filtrate was added I ml. of 20 ppm K250“. It was swirled and 0.5 g. of BaClz added. After one minute it Was swirled till crystals dissolved. Within 2 to 8 minutes after the crystals dissolved, turbidity was read on a spectOphotometer at 420 mu. The method of Pratt (66) was used to determine soil sodium. Ten grams of soil and 25 ml. of l.0 N, pH 7.0, NHAOAc were placed in a centrifuge tube. After I0 minutes of shaking,it was centrifuged until clear. Sodium was determined on the supernatant on a Coleman Model 2l flame photometer. Z. 3] Plant Analysis On July 31, I967, when the corn was in the tasseling stage, leaf samples were collected. The leaf below the ear leaf was removed. Ten leaves per plot were taken and dried at l50O F. One sample was lost in the drying process. The samples were then ground in a Wiley Mill with stainless steel screens. The samples were sent to Ohio State University where they were analyzed for potassium, phos- phorus, calcium, magnesium, manganese, iron, boron, c0pper, zinc, aluminum, strontium, molybdenum, cobalt, sodium, silicon, barium and nitrogen. Soil Mineralization Studies Two soil mineralization rate studies were conducted. The first was conducted on duplicate samples from the plow layer of all ho plots. Samples were brought moist from the field on August I, I967. Each sample was analyzed for ammonium and nitrate nitrogen using the microkjeldahl techniques of Bremner (13). Two grams of moist soil plus l0 ml. of 2.E KCI and approximately 0.I g. of MgO were placed in the distillation flask. A 50 ml. graduated Erlenmeyer flask containing 5 ml. of two percent boric acid plus indicator was placed under the condensing tube, our ya .x. 32 and 25 ml. of condensate was collected. Following the distillation, the condensate was titrated with standard 0.005 N_H2504 to determine ammonium-nitrogen. At the completion of the first distillation, about 0.2 g. of ball-milled Devarda's alloy was added to the distillation flask and 25 ml. of condensate was collected in a second Erlenmeyer flask containing 5 ml. of boric acid plus indicator. This was titrated with the standard acid to determine nitrate-nitrogen which had been reduced to ammonium. A sample of the soil was dried to determine soil moisture. The mineralization study was a modification of the method suggested by Bremner (l4). A weight of moist soil, equivalent to ten grams of dry soil, along with 30 grams of clean 30- to 60-mesh quartz sand were placed in a bottle. Sufficient (NH4)2C03 solution (0.I mg. N per ml.) was added to bring all the soils to the same ammonium level (0.2 mg. ammonia-N per 9. soil). Sufficient distilled water was added so that the total liquid (moisture in the soil 4 ammonium carbonate solution + water) equalled 6.0 ml. The bottles were capped with a piece of plastic held in place with a rubber band. The bottle was placed in a 30 C constant temperature room for l4 days. After incubation, l00 ml. of . .ap I 'I I a- II! (I‘ (I: 1 n" .‘u‘ 33 2 N KCI was added to each bottle, they were stOppered, shaken for one hour and allowed to settle for 30 minutes. Then 20 ml. of supernatant was distilled to determine ammonia and nitrate using the procedure outlined above. The second incubation was carried out on samples taken on September 28, I967. This time four replications of only six of the ten treatments were used. The procedure was the same as outlined above with the following changes. The total amount of liquid, soil, sand and ammonium level was increased by a factor of ten. A small vial of 0.5 N NaOH was placed in the jar to absorb 002. The jars were sealed with an airtight cover and periodically the vials of NaOH were removed and fresh ones inserted. Barium chloride was added to the base and titration carried to the phenolphthalein end point with 0.25 N HCI under COZ-free conditions, using the apparatus depicted in Figure I. At the end of the lh-day incubation period, the soil samples were shaken for one hour with 300 ml. of h.N KCI. Ammonium and nitrate was determined as described above. Seasonal Changes In Mineral Nitrogen In order to study the effect of carriers on the ammonium and nitrate nitrogen level in the soil at different times f-f' ling burette (0.25N HCl) 5 m 3 Air exhaust (hose to drain may be attached in case of overflow) Burettc tip centered in stopper 5mm into titration chamber (3/16” polyethylene) Titration chamber l” x 8” tube (0r about 30 ml volume below burette tip) r\V\/\p/ Air inlet tube extended M‘Igfi C0 -free air I” Wd’l f/unaer 3 to 5 lbs. -‘ pressure 2-hole stopper I #3 Circulating tub; (3/l6” polyethylene "i Tr V 1.5.2... 3-hole stopper ———9 #3 H C02 collection vial (h dram capacity with plastic snap cap) 5m]. 0.5N NaOH l/2 teaspoon BaCIz 2 drops phenol- pthalein Air inlet tube cut at sharper angle so air will bleed into it but not into circulating tube Figure l. Apparatus for titration under C02 free conditions a\v -h 35 during the season, plow layer soil samples were taken periodically during the I967 growing season. Only the four replications of treatments 2, h, 8, and IQ were used in this study. Ammonium and nitrate nitrogen were determined on moist samples by the microkjeldahl method of Bremner (I3) as described above. Air dried soil samples were sieved through a 20-mesh screen and sent to the soil testing lab. Lime requirement, pH, Ca, Mg, K, and P were determined by the methods previously described. In addition, on October 25, I967, these plots were sampled at 0-l0, l0-IS, and l5-20 inch depths and the above analyses were made. Clay Studies Composite samples of both replications of the unlimed starter, ammonium nitrate, and ammonium sulfate plots, and the limed ammonium sulfate plots were prepared for x-ray analysis using standard methods. Salts, organic matter, and free iron were removed and the clay fraction separated, using sedimentation techniques (4h, 97). The samples were x-rayed after magnesium saturation, potassium saturation, heating to 300 C and heating to 550 C. The method suggested by Pratt (65) was used to determine total potassium in order to estimate the amount of illite 36 in the clay fraction of the soil. A 0.I 9. sample of clay was placed in a platinum crucible. Perchloric acid (I ml.) and hydrofluoric acid (5 ml.) were added and the sample evaporated to dryness on a sandbath. The residue was dissolved by heating in 5 ml. of 6 N HCl and 20 ml. ofiwater. The sample was diluted to l00 ml. and potassium determined on a Coleman Flame Spectrophotometer Model 2l. Amorphous Material All0phane was estimated using the method described by Jackson (#1). A 0.I 9. sample of clay was wetted in a nickel beaker with a small amount of 0.5 N_Na 0H. Then 200 ml. of boiling 0.5 N NaOH was added and the suspension boiled for 2.5 minutes. After rapid cooling and centrifu- gation, the supernatant was decanted and stored in a plastic bottle. Silicon was determined by placing l0 ml. 0F I5 percent ammonium molybdate solution, 30 ml. of distilled water, 5 ml. of 6 N HCl and 5 ml. of extract into a 50Inl. volumetric. The solution was made up to volume and the absorbance determined 30 minutes later on a Bausch S-Lomb Spectronic 20 colorimeter at #20 mu. Aluminum was determined by placing l0 ml. of pH 4.2 ammonium acetate buffer solution, 30 ml. of water, l0 ml. of 0.0h% aluminon reagent and 5 ml. of extract in a 50 ml. volumetric. The 37 solution was made to volume and the absorbance at 520 mu. was determined after 30 minutes on a Bausch 8 Lomb Spectronic 20 (38). The percent all0phane in the soil was estimated to be l.2l times the sum of the percentage of Si02 plus the percentage of Al203 in the sample. Cation Exchange Capacity The cation exchange capacity of the soil was determined using the conductometric technique adapted for estimating pH dependency by Chodan (I6) from the method developed by Mortland and Mellor (56). Ten grams of soil was placed in a 250 ml. beaker. To this was added l00 ml. of l N BaOAc buffered to the desired pH with acetic acid. The suspension was stirred on magnetic stirrer for two hours while nitrogen gas was bubbled through the system. ~The pH of the suspension was then adjusted with Ba(0H)2 to the original buffer pH and stirred for another two hours. This was continued until the pH of the suspension was equal to the original buffer pH of the BaOAc. The suspension was then filtered through a Buchner funnel (Whatman No. 42 filter paper) and washed with 50 ml. of l N BaClz. The soil was washed with 30 ml. increments of deionized H20 until the leachate was chloride free using the silver nitrate test. The soil was .\v ~-- A q-v K .—v O-' .V. a.- .5- A\- nab 38 washed from the filter paper into a 250 ml. beaker with exactly l00 ml. of deionized water. This was stirred for one hour and allowed to set overnight with nitrogen bubbling through the system. Then 50 ml. of absolute ethyl alcohol was added and the suspension stirred for one-half hour. The suspension was titrated with 0.4 ml. increments of 0.2 N MgSOu. After each addition the system was allowed l0 minutes to equilibrate before the conductivity of the suspension was measured. If the suspension was not at equilibrium after ten minutes it was stirred for an additional five minutes and the conductivity again determined. The cation exchange capacity was determined on eight' composite samples. The two replications of the starter,. calcium nitrate, ammonium nitrate and ammonium sulfate treatments were each mixed. This was done for both the limed and unlimed plots. To measure the pH dependency of the exchange capacity, it was determined at pH 4.0, 5.0, 6.0, 7.0 and 8.0 by appropriate adjustment of the BaOAc buffer. Other Investigations During the summer of I966, soil samples were taken by increments to a depth of 66 inches on several plots. It was 39 originally planned to determine ammonium and nitrate on these samples. However, the samples sat, moist and at room temperature, for several weeks, so these determinations were not made. The samples were subsequently dried and sent to the soil testing lab for routine analysis. Samples taken from the 40 plots at a l0-l5 inch depth in the fall of I966, were analyzed for percent sand, silt and clay using the method of Bouyoucous (12). One hundred grams of soil, with 60 ml. of Calgon solution (50 g./l.) were placed in a dispersion cup along with sufficient distilled water to fill the cup half way. The suspension was stirred on a mechanical stirrer for IS minutes and then transfered to a sedimentation cylinder. The cylinder was filled with water, shaken, and hydrometer and temperature readings taken at 40 secOnds and 2 hours. Statistical Analysis IVhere apprOpriate, analysis of variance was performed on tfua results, using facilities of Michigan State lknvearsity's Computer Center. The experimental design was a randomized complete block design, biased slightly so that all fcnn anhydrous ammonia treatments were in line for ease oflapplication. In I965 and I966, the two center replications 40 were limed. Although this resulted in systematic disposition of the main plot factor, lime, the data were treated as in a Split plot design. The original four replications were treated as two replications of two lime treatments: unlimed and limed. The carrier treatments were treated as sub-effects.v One of the plant samples was lost during drying. Values for this plot were estimated using standard procedures for calculating missing plot values. If the F test from the analysis of variance indicated signficance at the 5 percent level, an LSD .05 was determined. Where appr0priate, the results were arrayed and grouped into ranges of equivalence, using Duncan's multiple range procedures (I9, 26, 79). In the split plot analysis of two replications, two lhne levels and ten carriers, degrees of freedom were distributed as fol lows: Source Degrees of Freedom Replication Lime Error A Carrier Carrier-lime interaction Error 8 Total N— \OCDKOKO—H—H" 4] Because there was only one degree of freedom for lime and one for replication, the basis for statistical inferences regarding lime effects was very weak. It must be emphasized that real effects of lime may have been statistically significant if an experimental design with more replication had been used. An attempt is made in the discussion to put the lime effect in prOper perspective. RESULTS AND DISCUSSION I. -SOIL AND PLANT ANALYSIS Changes in Soil pH and Lime Requirement Since I959 Table 2 shows the history of the changes in soil pH of the various fertilizer treatments. The initial pH for the experimental area was 6.2. No soil samples were taken after the I959 or I960 growing seasons. By l96l, the ammonium chloride and ammonium sulfate treated soils were already below pH 5.0 -- a surprisingly rapid change. ' After l96l, there was a general decline in soil pH on the unlimed plots. The I964 pH values were consistently higher on unlimed plots than in either I963 or I965. There is no apparent explanation for this. Liming increasefl soil P”. but not to the extent expected for the double lime requirement rates used. The urea, ammonium chloride, ammonium sulfate, and ammonium nitrate treated soils, after liming, still- had a pH below 6.0 in I967. Theoretically, a mi near 7.0 could have been expected on all limed plots by this time. (Lime requirements are calculated to raise soil pH to 6.5 to 6.8 in a traditional 7-inch plow layer. A double lime requirement with a lO-inch plow layer should raise the soil pH to above 7.0. 42 Table 2. 43 Changes in soil pH 5 by nitrogen carriers ince l959l3as influenced and lime Soil pH by years Fertilizer Lime treatment treatment l96l I962 I963 I964 I965 I9667 I967 No fertilizer No lime 5.9 5.7 5.7 6.0 5.2 6.0 .5 Lime 5.8 6.4 6.6 Basal ‘fertilizer N0 lime 5.7 5.9 5.9 6.l 5.6 5.9 5.4 Lime 6.3 6.8 6.7 NaN03 No lime 5.9 6.0 6.2 6.5 6.2 6.4 6.4 Lime 6.2 7.0 7.0 Ca(N03)2 No lime 5.7 5.8 5.8 6.l 5.6 5.7 5.4 Lime 6.2 6.6 6.l NH3 No lime 5.2 5.4 5.l 5.6 5.6 5.l 4.5 Lime 5.l 5.7 5.8 Urea No lime 5.1 4.9 4.9 5.2 4.8 4.6 4.6 Lime 4.6 5.6 5.8 Ureaform No lime 5.4 5.3 5.0 5.2 5.0 4.8 4.4 Lime 5.0 5.6 6.0 NHANO3 No lime 5.4 4.8 4.8 5.l 4.4 4.4 4.0 Lime 5.0 5.5 5.8 NHgCI No lime 4.9 4.6 4.4 4.6 4.3 4.0 3.7 Lime 4.5 4.5 4.8 (NHq)2504 No lime 4.5 4.2 4.0 4.4 4.l 3.9 3.5 Lime 4.2 4.4 5.4 lInitial lime requirement not reported 2Supplemental nitrogen carriers applied at the rate N per acre each year, beginning I959 3Two tons per acre dolomite in I965. for each fertilizer treatment of 300 lbs. Additional dolomite in I966 to total twice the lime requirement by soil buffer test 44 Lime requirement was not determined on these soils until l96l. The lime requirement increased in I962 and I963, as shown in Table 3. In I964 the lime requirement of all treatments decreased nearly 50 percent. This paralleled the pH increase between I963 and I964 and also cannot be explained. It does not appear to have been a systematic error in measurement. Soil pH values in I965 were again in line with earlier and later years; whereas, it took two or three years before the lime requirement of most of the soils returned to the I963 level. And even in I967, the lime requirement of most unlimed soils were still lower than the I963 values. Annual rainfall since I960 is given in Table 4. It is reported on an October to September basis, rather than a January to December basis. This better correSponds to the sampling dates. Rainfall data alone does not explain the change in lime requirement and pH noted. If the number of rains over 0.40 inches can be taken as an index of the number of leaching rains, there is an increase in I964 over the two previous years. This may help to explain the changes noted. Soluble acids may accumulate during dry periods and be leached in wet periods. This would be reflected in soil pH and lime requirement measurements. A study of natural runoff and 45 Table 3. Changes in lime requirementI sjnce I959 as influenced by nitrogen carriers. and lime Lime requirement (ppt CaCO3) by years Fertilizer Lime 4 L treatment treatment l96l I962 I963 I9644 I965"I l9665l967 No fertilizer No lime l. I.5 I.5 2.2 Lime I.8 .5 Basal No lime l. I.8 I.5 I.8 fertilizer Lime .8 0 .8 NaNO3 No lime 2. .8 I.5 l.0 Lime l.2 O O Ca(N02)2 No lime I. I.5 2.2 2.2 Lime .8 .5 l.O NH3 No lime 3. I.8 3.5 4.5 Lime I.8 I.8 I.5 Urea No lime 2. 3.8 4.0 3.8 Lime 3.2 I.8 I.5 Ureaform No lime 2. 3.5 5.0 4.5 Lime 3.0 I.5 I.5 NH4NO3 No lime 2. 4.2 4.5 5.0 Lime 2.2 2.5 I.5 NHhCl No lime 3. 3.5 5.0 . 4.5 Lime 3.8 3.2 2.8 (NHA)2504 No lime 4.6 6.2 7.6 4.0 5.5 5.0 7.0 Lime 5.2 4.0 I.5 lInitial lime requirement not reported 2Supplemental nitrogen carriers applied at the rate of 300 lbs. N per acre each year, beginning I959 3Two tons per acre dolomite in I965. Additional dolomite in I966 to total twice the lime requirement by soil buffer test for each fertilizer treatment hMaximum value reported by Soil Test Lab: 5.5 ppt SMaximum value reported by Soil Test Lab: 5.0 ppt 46 'Hable 4. Annual rainfall for the I960-I967 sampling years *# Year rl‘ifiiéi I ISTRSro‘V’Sr 0.40 inches inches I960 3l.02 l5 l96l 23.2l 17 I962 2l.45 8 I963 22.30 l0 I964 23.44 l4 I965 23.84 IO I966 28.28 ll I967 26.19 I6 * Sanmfling year defined as October I, of previous year to September 30, of year listed in table. # REiinfall data through December 3|, I966 from EasstLansing Horticulture Farm Weather Bureau Located about one-third mile east of Rainfall data for I967, from East Station. Plots. Larwjng 3SE Weather Bureau Station. abcmt one mile south of plots. Located 47 infiltration on this site might be helpful but these data are not available. Lime requirements tabulated in Table 3 were subject to policy changes in the soil testing laboratory. Beginning in I964, maximum lime recommendation reported was 5.5 tons per acre, regardless of how low the value of buffer pH. In I966, a maximum of 5.0 tons per acre was established. In the fall of I967, this restriction was removed for research samples. Only a few of the values in Table 3 were restricted by these policy changes. These were the unlimed plots of (NH4)2504 in I965 and unlimed ureaform, NHhCl and (NH4)2504 in I966. Substantial fluctuations in lime requirement can be expected because soils are highly responsive to their environ- ment. The organic component of soil buffering systems varies in quantity and exchange activity with rates of return of crOp residues and their rate of decomposition. In soils below 5.0, soluble aluminum compounds contribute significantly to active and potential acidity, hence lime requirement. These compounds will tend to accumulate in dry periods and can be rapidly leached in a wet period. For these and other reasons not yet fully understood, the lime requirement of a soil changes considerably in 48 response to climatic changes and management between and within seasons. Macronutrient Soil Tests Tables 5-7 show the values for soil pH, Ca, Mg, K, P, and lime requirement of samples taken on July 3l, I967, for the various treatments. EN Table 5 shows the soil pH values. Lime effect was significant only at the 7.5 percent level, although there was a full pH unit difference between the means for unlimed and limed plots. Carrier effects were highly significant. The interaction was not significant. Sodium nitrate resulted in the highest pH. The two controls, and NH3 treatments formed a second group not significantly different from sodium nitrate. The last three were also not different from the calcium nitrate or ureaform treatments. The ammonium chloride and sulfate treatments resulted in the greatest soil acidity. The pH associated with use of ammonium nitrate was between these and that for urea and ureaform, and was not significantly different from either group. These results fall in line with the known acidic nature of the fertilizers, except for anhydrous ammonia. Plot #6, an unlimed anhydrous ammonia plot, accidentally received 49 pcmmzo;u Lea mucma u uaa%% poueoaoc pad o.m mo o:_m> E:E_xmza« _o>m_ ucoocoa o.o~ um UoE__:: Eocm ucmcomm_o >_ucmo_m_cm_m% _o>o_ ucoocoa m.n um toE__c: EOLm ucmcomm_p >_ucmo_m_cm_m« 6m. 6m._ 6m._ mm. me. me. mt6_eemo tee magma o.~ 46.. o.m m.m eo.6 o.m memmz m.m o.~ o.m :.: _.m m.m :ommxezzv :.m m._ o.m m.: o.m 6.: _e:Iz m.~ m._ N.: m.: 6.m _.: mozqzz m.~ m._ N.: :.m N.6 6.: Eeoemme: m.~ m._ m.m N.m k.m m.: met: :._ N._ m._ 0.6 _.6 m.m m:z m. o m._ m.m :.6 e.m Nxmozvmo m. o m._ 6.6 m.6 N.6 mozmz o._ o o.N m.6 w.6 m.m L6N___eeme .mmmm m. o m._ N.6 k.6 m.m e6~___ueee 62 odd uaa afiuaa ommuo>< ooE_4 poE__c: ommco>K. moE_4 noE__c: «aucoeoc_sooc oE_4 IQ __0m Lo_ccmu Lo>m_ 30.6 ecu c_ ucoEoL_:Uoc oE__ ocm Id :0 oE__ 6cm mco_cemo comoLu_c mo muoommm .m o_nmh 50 600 lbs. of nitrogen in I967 as previously noted (p. 26). Both this plot and the adjacent urea plot (#7), which received no nitrogen in I967, often gave results other than expected for each treatment. In this case, the average pH value for the two unlimed NH3 plots was 5.9. This is an average of 6.6 (plot #6) and 5.2 (its replicate in block 2). If the 5.2 is truly representative of the effects of this carrier, than the overall carrier average (ignoring lime) would be 5.5. This is approximately the same as the pH of the ureaform plot, and is what would be expected considering the residually acid nature of anhydrous ammonia. It will be shown later (p. l27) that the urea and anhydrous ammonia applied to plot #6 resulted in a soil exchange with a high percentage of ammonium ions. This fact helps to explain the high pH value, as well as some of the other discrepancies that show up for this treatment. Lime Requirement As was true for pH, there was no statistical significance to the effect of lime on lime requirement (Table 5). In both cases, this must be attributed to the inadequate design of the experiment. The consistent direction and magnitude of changes in both of these measurements provide reasonable quantitative estimates for real effects of lime. 5l The effect of carriers was significant, and the plots were separated into two groups. The anhydrous ammonia treat- ment is grouped with the no fertilizer, basal, and the sodium and calcium nitrate plots. The low lime requirement for the basic, basal and no fertilizer treatments was expected since they did not contain acid forming materials. The lime requirement of plot #6 was zero. The anhydrous ammonia treated soil in block two had a lime requirement of 3.0. This would group anhydrous ammonia with the other acid forming fertilizers that form the second statistical group. As was true for pH, there was no significant carrier x lime interaction. Each limed carrier treatment received twice the amount of lime needed, as indicated by the buffer test, to raise pH into the 6:5 to 6.8 range. It would be expected that dolomite would react quicker in more acid soils. Actually, the change in pH and lime requirement was less than expected for all acidifying carriers. The greatest discrepancy occured with the two most acidic carriers, NHACI and (NH4)2504- Ten and twelve tons per acre of dolomite, respectively, had raised soil pH to only 5.0 or 5.l after two years. It must be concluded that residual acidity from these materials has drastically altered the character of buffering systems in the soil. 52 Calcium Exchangeable calcium (Table 6) was influenced by lime. The lime plots contained more exchangeable calcium than the unlimed plots. The calcium nitrate plot contained the most exchangeable calcium. It had received calcium with the carrier through the nine years of the experiment, as well as the lime applied in I965 and I966. The two no-nitrogen treatments and the sodium nitrate treatment resulted in less exchangeable calcium than the calcium nitrate plots. The three ammonium carriers and ureaform resulted in the least soil calcium. The anhydrous ammonia and urea plots had an intermediate level of calcium, significantly different only from the calcium nitrate plot. There was no statistically significant carrierxlime interaction. However, the exchangeable calcium on the limed plots, as shown in Table 6, is inversely related to the quantities of limestone applied (Table I). The release of calcium from dolomite, or its exchangeability after release, was suppressed by soil conditions associated with stronglyiacidic carriers. Whether this may have been an artifact due to inadequate buffering of the exchange extractant was not investigated. 53 _o>o_ ucoocma _ um _o>o_ ucoocma m um ooE__c: Eocm ucoLomm_U >_ucmu_m_cm_m§ poE__c: EOLm ucotmmm_c >_ucmo_m_cm_me 63 M6 m6 6k~ .mm .mm mte_eemu toe moems 6m_ emea :6 :_m «ok__ mm6 memmz .k. emNm 3. 6mm eNmm gem somaxezzv 66. eema mm 6:6 eNmm mNm .6612 Ne. e6mN 6N 6:6 eNmm mNm m 2:12 Ne. eNJN N: omk «Nmm mom steemmt: JR. awmm 6m New «m_N_ mom mot: 66. e6mN :6 N66 em~__ kmm mzz 6m 6:. N: on_ «m_m_ 6a.. Nxmozcmo k6. 66a 6N. :66. mN__ 646. M6sz N6. e_:N Nm NN__ e_mm_ m66 e6~___6eme _mmmm :6. :mw 6m. :66. 6a.. 666. L6N___6eme 62 Emma .ENQQ ENQQ Emma Ewan Emma ommtm>< ooE_4 poE__c: ommco>< voE_4 poE__c: m: o_bmomcmLUXu mu o_nmmmcm:oxw Lm_ccmo Loam. eo_e 666 em e3_m6emme 6:6 E:_o_mo 6_emmmcm;6xm so me__ 6cm mcm_eemo ammotu_c Lo muomeeu .6 6_6me 54 Magnesium The effect of treatment on magnesium in the soil is shown in Table 6. The effects of lime, carrier and their interaction were all significant. The limed plots had considerably more exchangeable magnesium than the unlimed plots. This is to be expected since the limestone added was dolomitic. The overall carrier effect separated the calcium nitrate plot from all the others. The low level of magnesium for this treatment suggests that the exchangeability of magnesium was suppressed by the calcium added with the carrier and lime. This suppression was expressed in limed and unlimed plots. The mechanism is not apparent. The effect of lime within carriers was not significant for the unfertilized check, sodium nitrate or calcium nitrate treatments. These plots received two tons of lime in I966; all other plots received more than two tons. Ranking carriers within limed plots gives an order generally reflecting the amount of lime added. .When they are ranked within unlimed plots, the order is essentially reversed. As pH was depressed by carrier, the magnesium level drOpped. Low pH resulted in low magnesium level and high lime requirements. When dolomitic limestone was applied, those with the lowest level of soil magnesium received the highest amount of dolomitic limestone. So carriers with 55 lime show a trend opposite to that exhibited by carriers without lime. The calcium nitrate treated plots are an exception to this, containing less magnesium than would be expected if only the acidic properties of the fertilizer were considered. This is true whether or not lime effects are considered. It is apparent that the magnesium released from the dolomite, particularly in very acid soils, appears in the soil in forms having very different exchange prOperties than calcium released under the same conditions. Potassium Table 7 shows the potassium levels for the various plots. Only the carrier effect was significant at the 5 percent level. The lowest K level was in the check plot which received no potassium fertilizer. All other plots have received potassium each year. The acid forming carriers, in general, have similar K levels which are significantly higher than the check in the unlimed series. The exchangeability of K in plots receiving the basic fertilizers or the two control treatments were unaffected by lime. The addition of lime consistently reduced exchangeable K in plots receiving acidifying N carriers, and this effect was more pronouned with the ammonium carriers. With the 56 ucmo_m_cm_m U: muuommo 66.4% 66 o: 66 km 66 ,66 6.6.6666 to. 6666. 6m. 66. 6:. 66. 6:. 66. «6:66: 66. mm. :6. :6. 66. k6. 6666.6126 mm. 66. 66. NJ. 66. 6k. .6612 mm. 66. mm. .m. 6N. 6k. 662612 6:. 66. km. Na. 66. mm. 566666.: .66. me. 66. Na. 66. mm. mat: .66. 66. :6. .66 N6. 666 6:2 6m. 66. .6. mm. mm. .6. 6.662666 km. 6.. 6:. 666 New 666 m6sz :6. .6. :N. 66. k6. 6k. eaN...etme .6666 .6 Na 66 66 66 66 66N...6emc oz .ENQQ Ewan fmaa Emma Ewan Ewen ommcm>< poE_u. moE__c: ommto>< UoE_4 poE_Pc3 a >mLm x o_nmmmcmcoxM Lo_tcmo ) .563. 26.6 65 E 63938.3. 6332“..on xmgm Dcm E:_mmmuoa m_pmomcm;uxo co oE__ pcm mLo_LLmu comotu_c mo muuommm .m o_nmk 57 most acid treatment (ammonium sulfate), exchangeable K after liming; was the same as in the unfertilized check. Two treatments, anhydrous ammonia and sodium nitrate, seemecl to behave anomalously. They contained more exchangeable K.thari would be expected. Potassium is a common impurity in soclium compounds and this may have contributed to higher soil KL with NaN03 fertilization. However, both sodium and ammoniaa can replace interlayer potassium in illite. It will be shovvn later (p. l39) that illite is present in the clay fracti<>n of this soil. One ammonia treated plot (#6) received an exceeptionally high application of ammonium in I967. The K level of plot #6 was 282 lbs. while the correctly treated duplicaate plot had IS9 lbs. This in itself suggests dis- Placement of K by ammonia. Assuming the IS9 value to be a fibre Eiccurate reflection of the effect of anhydrous ammonia, the a\Ierage K level (ignoring lime) would be I70 pounds. This is St ill higher than would be expected from its acidic ten- denci<35 alone. In nine growing seasons, both NaNO3 and NH3 COUld have replaced considerable interlayer K from illite. Elm—Swag Table 7 shows the effects of treatment on phosphorus eXtractable with 0.025 N HCI in 0.03 N_NH4F. A very significant 58 carrier effect was expressed. This was due mainly to the 2- to 3-fold increase in phosphorus in all fertilized plots over the unfertilized check. This was true whether the plots were limed or not. Extractable phOSphorus was consistently higher in all unlimed plots receiving supplemental nitrogen treatments than in those receiving basal fertilizer alone. This increase was statistically significant with NH3 and (NH4)2504. These two carriers, ureaform and the two basic materials, showed a tendency for phOSphate to be depressed with the addition of lime. Although this effect of lime was pronounced, neither the main effect of lime nor the carrierxlime interaction was statistically significant. The tendency for phosphate extractability to increase with decreasing pH and to be decreased by the addition of lime in this acid pH range (Table 5), are contrary to what one might expect. Phosphorus availability generally decreases in acid soils. Below pH 5.5, phosphorus often becomes deficient due to the formation of iron and aluminum phosphates. If the apparent anomalies in this experiment are, in fact, real phenomena, it could be due to accelerated weathering of certain phOSphate minerals at low soil pH; 59 and also, to the associated anion exchange and mass action efFeects of the sulfate, nitrate, chloride, hydroxyl and bicaarbonate ions introduced with the various nitrogen carwriers. If the products of such reactions at low pH COLIchbe identified, the apparent depression effect of lime migflwt well be explained by pH-solubility product relationships. Micronutrient Soil Tests Liming the plots significantly decreased the level of zinc in the soil as shown in Table 8. The effect of carriers was also significant. In general, the more acid carriers resulted in a higher level of zinc in the soil. The unlimed ammonium carriers promoted a significantly higher zinc level than the others. Soil pH with these carriers was 4.l or I95$ (cf. Table 5). Since zinc becomes soluble in the soil at low pH, these results are as expected. Man anese Table 9 shows the effect of treatment on soil manganese. OnLy the effect of carrier was significant. Ammonium Chlor'ide and sulfate had significantly less manganese in the 50“ than the other unlimed plots. Liming tended to increase 60 ItatDIe 8. Effects of nitrogen carriers and lime on extractable zinc in the plow layer Extractable Zn Carrier Unlimedfii [imedl Average Ppm ppm ppm NC) fertilizer .03 .06 .04 Basal fertilizer .06 .04 .05 NaNO3 .08 .05 .06 Ca(N03)2 .07 .04 .06 NH3 .IO .06 .08 lJrea .I6 .06 .ll Ureaform .IO .05 .07 NH4NO3 .68 .05* .36 NHqu .60 .l2* .36 (NH4)2804 .50 .07* .28 Means .24 .06* .15 LSD£35 for carriers .35 .35 .24 *Significantly different from unlimed at 5 percent level 6l _o>o_ ucoocoa m um UoE__c: EoLm “cocomm_p >_ucmo_m_cm_ma : m m m. 66 6N 666.6660 Low magma 6. «6. 66 6.. 6.. 2.. 66662 66 «66 66 66 66 -66 2666.6226 66 «.6 22 .6 66. 66 .6622 .6 66. 66 66. 26. 66. 662222 6. a6 6. 66. 66. 66. EL66.665 6. «6. 6. 6.. 66. 2.. . 66.2 6. e6 6. 66. 66. 6.. 622 6 «a 6. 66. 6.. 6:. 6.662666 6 a 6 6.. 6.. 6.. 66262 6 «6 6. .‘2.. 6.. 6.. L66:366.. .6666 6 6 6. 66. 66. 66. . t66...6666 62 End Ema Eda EQQ Ema Ema ommco>< 665.4 poE__c3 uwmco>< .on_4 mewbc: on o_nmuomcuxM cz o_nmuomcuxm Lm_ctmu co>m_ 30.6 ecu c. cot. 6cm omocmmcme o_nmuomcuxo :0 me.— ocm mtm_tcmo comoLu_c mo 6600mmm .m 6.666 62 due rfln level with these two treatments. The solubility of NH1 compounds and the ratio of Mn’2 to other valence fornms.increases rapdily below pH 5.0. This often results in txaxic effects of Mn in the plant. Abnormally high Mn in tflne corn tissue was the first nutritional imbalance to appear in this experiment, as the soil pH declined with treatment since I959. Toxic levels of Mn (400 ppm or more) were already prwasent in the third season on plants receiving NHhCl and (NH4)2504. The extraction procedure used here failed to show'this relationship to pH in the soil. Hoff and Mederski (36) have shown good relationships between Mn extracted with this method and plant response. They, too, were unable to Show any relationship between pH and extractable Mn in the soil. Perhaps the form of manganese extracted with Phosphoric acid is not the form responsible for the toxic el:Icects noted. On the other hand, it may be that these results are accurate. Mn toxicity may not be due simply to high levels CW s<>luble Mn in the soil. It is possible that the total manQilnese in the soil has been extensively depleted over the 7 or 8 years in which soil pH in the unlimed NH4CI and INHglzsoh plots have been belOW 5.0. The lime applied in 63 the seventh growing season may have reduced this rate of depletion during the last two years. Or it may have promoted release from some, as yet unrecognized, complexes which may form at low soil pH. 1593 Table 9 shows that lime, carriers and their interaction significantly affected extractable iron. Lime decreased extractable soil iron. The effect of lime within carriers was significant for all fertilizer treatments except the unfertilized check and sodium nitrate treatments. Except for calcium nitrate, all plots showing a significant decrease in iron received more than two tons of lime. Unlimed plots receiving no nitrogen or those which received nitrogen from basic carriers showed the lowest level of iron. All acidifying carriers showed a significantly higher level than the basal fertilizer treatment. In the case of ammonium nitrate, chloride, and sulfate, there was a highly significant stepwise increase related directly to increasing acidity over the range from pH 4.6 to 3.8 (Table 5). When the plots were limed, extractability of iron was reduced for all treatments; although in the ammonium chloride and sulfate treated plots, it remained significantly higher than for the other treatments. 64 Ten to twelve tons per acre of lime have been applied to the plots receiving these strongly acidifying carriers (Table I). The failure to reduce iron extractability to levels comparable to the other treatments supports the inference made earlier that buffering systems have been altered by long exposure to low pH in these soils. Qgpper and Aluminum All plots contained less than 0.03 ppm c0pper. This is too low a level to detect differences between plots. Like zinc, copper becomes soluble at low pH but usually at lower values. Either the pH was not low enough to affect solubility of copper compounds, or the soil was too low in c0pper minerals to bring about an increase in extractable copper. The aluminum analysis also gave extremely low results. The unlimed ammonium sulfate, chloride and nitrate plots averaged about l.25 ppm Al. The unlimed urea and ureaform plots averaged about 0.90 ppm Al. All other plots contained no detectable aluminum. This was similar to the results for iron except the amounts present were less. Although the differences were small and hard to detect, they were probably 65 real. This adds further evidence to the contention that soil buffering systems have been materially altered by pro- longed use of acidifying carriers. The effects of ammonium carriers on extractable zinc (Table 8), iron and manganese (Table 9) serve as further evidence of such changes. Sulfur and Sodium The level of sulfate S in the soil varied somewhat throughout the season in the ammonium sulfate treated plots. This variation will be discussed in a later section (p. II7)- All other plots showed sulfate levels of less than 2 ppm S. Sulfur in the ammonium sulfate treated plots ranged from 5 to 25 ppm during the season. The limed ammonium sulfate plots showed a slight, but consistent, reduction in sulfur than the unlimed plots (Table 25). All treatments except the sodium nitrate treatment showed less than 20 ppm of sodium in the soil. The sodium nitrate treated plots averaged about I30 ppm of sodium and showed no effect of lime. 66 Foliar Analyses Nitrogen The level of nitrogen in plants, as shown in Table IO, was affected only by carrier. The NH3 plot which received 600 lbs. of nitrogen by mistake in I967, had a foliar nitrogen content equal to the plot receiving 300 lbs. of nitrogen. Phosphorus Table IO also shows the phosphorus content of corn leaves for the various treatments. Differences in phosphorus were small, but the carrier effect was significant. The plots that received no supplemental nitrogen and those that received ammonium sulfate resulted in the lowest phOSphorus content and the differences between these treamtnets were not significant. The anhydrous ammonia treated plots had the most plant phOSphorus, but it was significantly different only from the above three treatments. The differences in foliar P did not closely reflect differences in soil P. In general, the three ammonium carriers resulted in less plant P, but higher soil P, relative to the other treatments (cf. Table 7). 67 ucmo_m_cm_m 60c muooemo oE_46 66. 66. 66. .6. 66. 66. 666.6666 .62 66666 66. 66. 66. 66.6 66.6 66.6 «66662 66. 66. 66. 66.6 66.6 66.6 6666.6226 66. 66. 66. .6.6 66.6 66.6 .6622 66. 66. 66. 66.6 66.6 66.6 662622 66. 66. 66. 66.6 66.6 66.6 56666662 mN. mm. 0m. 0:.N 6:.N mm.~ mot: 66. 66. 66. .6.6 66.6 66.6 622 66. 66. 66. 66.6 66.6 66.6 6.662666 66. 66. 66. .6.6 66.6 66.6 66262 66. 66. 66. 66.. 66.. 66.. e66...6e66 .6666 66. 66. .6. 66.. 66.. 66.. L66...6666 62 .x & N ii & & NVI momco>< moE_4 coE__c: mmmcobn moE_4: poE.bc: a Lm__om z tm__ou Lo_tcmo 6360566056 6cm comoLu_c cm__0e c0 68.. new mco_ccmo comotu_c mo muoommm .o_ o_nmp 68 Potassium The unfertilized check and the ammonium sulfate treated plants contained the lowest amount of K (Table II). The basal fertilizer, and the base forming nitrate carriers, resulted in the highest levels of plant K. There was a highly significant difference for lime treatment. The plants receiving lime were lower in potassium. The largest reduction‘was for the urea treatment. This was due primarily to the high K level in the plants which mistakenly received no nitrogen fertilizer in I967. The array of treatments according to contents of soil K and plant K gave a similar order of treatments. Calcium The data in Table l2 shOw no significant average effect 0f l ime on calcium content of corn leaves. Thereiwas h(Never, a very highly—significant (P = O.l percent) carrier lime interaction. The average effects of carriers were also very highly significant. Without lime, calcium content was significantly increased bY C6(NO3)2 relative to the basal fertilizer. It was signifi- cantly reduced by NHACI. The reduction by NaNO3 and (Nthzsm, approached significance at 5 percent. 69 Table II. Effects of nitrogen carriers and lime on foliar potassium . Carrier Foliar K Unlimed Limed 77AVer§ge % %7' 7% N0 femtilizer 2.37 2.04 2.20 Basal fertilizer 3.24 3.l0 3.l7 NaNO3 3.49 3.l9 3.34 060403)2 3.08 2.98 3.03 NH3 2.84 2.75 2.79 Urea 3.98 2.85* 2.9l Ureaform 2.74 2.58 2.66 NH4N03 2.56 2.7I 2.64 NHQCI 3.08 2.6l* 2.84 (NHL,)230L+ 2.62 2.47 2.54 Means 2.90 2.73# 2.8l LSDOS for carriers .43 .43 .37 ¥ *Significantly different from unlimed at 5 percent level :#Significantly different from unlimed at l percent level 70 _m>o_ 6:60.66 m 66 >_co ucmo_m_cm_m muoommo .m...mu ommto>o_ 6:60.66 _.m_ 66 poE__c: So.» 6co.omm_p >_ucmu_m_cm_m% _o>o_ HCoULoQ m 66 poE__c: Eo.m uco.omm_p >_ucmo_m_cm_ma 66. 6.. 6.. 6.. 6.. 6.. 6.6...6U .6. 66662 66. 666. 66. 66. 666. 66. 66662 66. 666. 6.. 66. 666. .6. 6666.6226 66. 666. 6.. 66. 666. 66. .6622 66. 666. 66. 66. 666. 66. 662622 66. 666. 66. 66. «66. 66. E.6666... 66. 666. 66. 66. 66. .6. 66.2 66. 666. .6. 66. «66. 6.. 622 66. 666. .6. 66. 66..—- 66. 6.662666 66. 66. 66. 66. 66. 66. 66262 66. 66. 66. 66. 66. 66. .66...6.6. .6666 .6. 666. 66. 66. 66. 66. 666...6.66 62 ommw6>n mom_4 mem_c2 ommWo>< pom_u pmew_:: 62 .6..6. 66 .6..o. .6...66 E:.mmcme 6cm E:_o_mo .m__om :0 6E._ 6cm m.m_..mo Como.u_: mo muommmu .N. 6.6m» 7l The addition of lime increased foliar calcium with most carriers, notably with Ca(NO3)2 and the two most acid carriers. Lime significantly reduced leaf calcium when combined with the NH3 treatment. This was not_due to the mistaken application of fertilizer as the two plots had similar leaf calcium levels. Calcium levels in the plants with NaN03 were signifi- cantly lower than with basal fertilizer, regardless of lime treatment. One suspects that the high levels of soil and plant K assoclated with this treatment, plus high concentra- thons of Na available to the plant from the carrier itself, may haveipromoted an imbalance leading to reduced uptake of Ca. Magnesium The magnesium content of corn leaves is shown in Table l2. Average effects of carriers were significant at the 7 Percent level of probability. The average effect of lime W35 ESIgnificant at the 4 percent level. The significance levefl for the interaction of these two effects approached ‘ Percent. Lime increased plant Mg as it had soil Mg. Plant m99nesium levels showed non-significant responses to lime only for the sodium nitrate and basal fertilizer treatments. 72 Soil magnesium showed no significant differences for lime in the sodium nitrate, calcium nitrate and the unfertilized check treatments. The foliar magnesium levels were lowest for the unlimed ammonium chloride and sulfate treatments. This is similar to the results for plant calcium. Sodium nitrate, unlimed, gave the highest magnesium content. This is in contrast to the fact that this treatment gave the lowest foliar calcium content when compared to other treatments. But it twaflects the high soil Mg level. The low level of plant Mg, “from unlimed ammonium carrier plots, reflects the low soi l Mg test for these treatments. Manganese The effects of treatment on plant‘ manganese shown in Table l3 are very striking and distinct. The average lime effect approached significance (P = 0.55) at the 5 percent level. The average effect of carriers and the carrier lime interaction were both very highly significant (P4.000S). The toxicly high Mn content of corn growin in acid soils wfithout lime was directly related to increasing acidity bahmu pH 5.0 (cf. Table 5). This result is in contrast to SOiI Mn (cf. Table 9). The lowest soil tests for available 73 _o>o_ 6:60.66 _.6 um co£__c: Eo.m 6co.mmm.c >_6cmo_m_cm_m66 _o>o_ 6:60.06 m.m um cuE__c: 50.» 6co.omm_c >_ucmo_m_cm_m% _o>o_ 6:60.66 m um coE__c: so.» 6co.omc_c >_6cmo_m_cm_m6 6 6. 6. 66 66. 66. 6.6...66 66.666 mm «60m mm mum _%6m_ m_: mcmoz 66 66 66 666 66.6 666 6666.6226. 66 666 66 666 6666 666 .6622 66 666 66 666 666. 666 662622 66 666 66 666 666 6.6 e.6.66.6 0: 66m 6: mm: 666. can mot: 66 666 .6 666 666 666 622 66 66 66 66 66 66 66662666 66 .6 66 66 66 66 66262 .6 6. 66 .6 66 66 .66...6.6. .6666 66 66 66 66 66 66 .66...6.6. 62 e66 266 e66 566 266 266 oomto>< coEnq . coE_—c: omm.o>< coE_4 mweppc: 66 .6..62 62 .6..6. .6...66 oc_N ccm omocmmcme .m__0w co oE__ ccm m.o_..mo comOLuhc mo muommww .m_ m_nmh 74 Mn were in the most acid soils where ammonium chloride and sulfate had been used. This relationship between soil pH and plant Mn is (nansistent with the expected effect of pH on Mn availability. 'The low soil tests for Mn under acid conditions must be ascmibed to Mn depletion of the soil, to formation of Mn complexes in the soil or to laboratory artifacts, which \uere not detectable by the analytical procedure used. Where lime was applied, plant Mn was reduced. The reduction~with all acidifying carriers was large and very I1ighly significant statistically. The reduced levels in Ihned plots were, however, more closely related to soil PFI (cf. Table 5) than to the soil tests of Mn (cf. Table 9). Zlnc Average effects of lime were significant at six percent and highly significant carrier and interaction effects were evident in foliar Zn contents presented in Table I3. Without lime, Zn in leaves of corn grown with acidifying car-r-iers was significantly higher than for Ca(NO3)2, NaN03 0" the two control treatments. The addition of lime reduced plant Zn significantly wltkw four of the acidifying carriers. With NHhCl there was 75 a significant increase in leaf anwith addition of lime; with (NHMZSOL, thererwas no lime effect. The high levels of Zn found in the unlimed soil with the use of the three most acidifying nitrogen carriers would have led to the prediction of high plant Zn. However, the high plant Zn content associated with the other acid carriers was not anticipated. Liming significantly reduced the level of Zn in the soil where the three ammonium carriers were used. But of these three, only the use of lime with ammonium nitrate significantly reduced foliar Zn. Foliar Zn actually increased by liming the NHACI plots and was unaffected by lime on the ammonium sulfate treated soils. As in the case of Mn, foliar Zn was more closely related to soil pH (cf. Table 5) than to the soil test for available Zn. Frequently Zn uptake has been found to be closely and inversely related to soil P. There was no evidence of such a relationship here (cf. Tables 7 and I0). Ailmfinum Aluminum content of corn leaves was influenced signi- ficantly by carrier and carrier lime interaction (Table I4). The array of foliar Al values for unlimed carriers raltlected increasing residual acidities of the carriers. 76 _o>o_ 6:60.66 m.0N um coE__c: Eo.m 6co.omm_c >_ucmo_m_cm_m%% _o>o_ 6:60.06 m.m um coE__c: 50.6 6co.omm_c >_6cmu_m_cm_m% _o>o_ 6:66.66 m 66 coE__c: E0.m 6co.owm_c >_ucmo_m_cm_ma .o...mo .06 modm2 66 66 66 66 66. 66. 66. 6666. 666 66. 666 66. 66662 666 66. 666 6.6 666 666 666666226 666 66. 666 66. 666. 666 .6622 66. 66. 666 66. 666 66. 662622 66. 66. 66. 66 66 6.. E8.66.2 66. 66. 6.6 66. 66 66. 6662 6.6 666 666 66. 66. 66. -,622 mm_ cm. 66. mm mm mm NAmozvmu 66. 66. 66. 66 66 66 66262 66. .6. 66. 66. 66 6.. .66...6.6. .6666 66. 66. 66. 66 66 66 .66.._6.6. 62 Eda Eaa Eda Ema Ema Ema omm.o>< 665.4 coE__c: .wmm.o>< coE_2 me__c: 6. .6..6. .6 .6..6. .6...66 cOL_ Ucm E:c_E:_w .m__0m c0 08.. ocm m.®_ctmo cmmoLumc mo muummmm .¢_ m_QMh 77 Although, only with NHhCl and (NH4)2504 were Al contents significantly higher than the basal treatment. The addition of lime significantly reduced plant Al, with the three ammonium carriers, to levels statistically the same as for all other limed carriers. Iron content of corn foliage is shown in Table I4. Onl‘y the carrier effect was signficant. Iron in plants witflnout lime increased with the acid nature of the carrier iri.an array very similar to that for aluminum. The increase over the basal fertilizer was significant for NH3, urea, and the three ammonium carriers. As was true for aluminum, plarit iron was generally reduced by lime. Although for Fe. theses reductions were statiStically significant only at the 20 percent level. In the limed series, foliar iron was significantly higheu‘ with NH3 treatment than with the basal fertilizer treatirnent. A similar effect of NH3 was expressed in limed p"mach foliar Al. There the effect on Al was large but “0t Significant statistically. 78 Silicon Table l5 shows the silicon content of the plants. Carrier effects were highly significant (Pride treated soil was an exception to this. The unlimed annuanium chloride and sulfate treatments resulted in the higl1est foliar silicon. The use-of ureaform (without lime) gave: results more like the basic carriers than the ammonia carriers. Ureaform has the same theoretical residual acidity as Lirea. Foliar silicon, aluminum and iron (cf. Table I4) hlt>lants receiving ureaform were consistently, although not allways significantly, less than in plants receiving urea. Perhaps the slow release of nitrogen from ureaform is associated with a slow release-of acidity and the soil buffer'ing system is better able to handle this acidity when It lS introduced over a longer period of time. This difference between ureaform and urea was not found in soil extractable Iron (cf. Table 9). The lime requirement was higher and the pH lower (not significantly) for the soils receiving Ureaform when compared to those receiving urea (Cf. Table 5)- 79 Table l5. Effect of nitrogen carriers and lime on foliar silicon Foliar Si Carrier Unlimed Limed Average %' %' % bk) fertilizer .34 .22* .28 Basal fertilizer .36 .26* .3I NaNO3 .20 .l8 .l9 Ca(NO3)2 .22 .22 .22 er3 .34 .20* .27 UI‘ea .40 .23* .32 Ut'eaform .26 .20* .23 NH4N03 .36 .I8* .27 NH1+CI .44 .42 .43 (NHLQZSOL, .50 .3I* ' .40 Means .34 .24# .29 [-80.05 for carriers .07 .07 .IO *Significantly different from unlimed at 5 percent level :#Significantly different from unlimed at l6.l percent level 80 This would tend to weaken the argument that ureaform acidity is more easily handled by the soil buffering system. These apparent differences between urea and ureaform may reflect mass action effects or rate of carbonate release on dissipation of hydrogen ions through hydrolysis of carbonic acid to C02 and water. Ammonium carbonate is released rapidly by the hydrolysis of urea, much more shmuly by hydrolysis of ureaform. The transiently high cmmcentrations of ammonium and carbonate which accompany unaa hydrolysis would promote more extensive displacement of Fl‘ released during nitrification and its dissipation as H20 ‘through hydrolysis of carbonic acid. The increased solubility of iron and aluminum with incrweased soil acidity is clearly indicated by soil tests. This is reinforced by the observed influence of nitrogen carr'iems, hence soil pH, on foliar Al, Fe, and Si. Foliar lnnw, aluminum, and silicon were reduced by the application 0f lirne. Foliar Al and Si were reduced with the use of basic: carriers. Ammonium chloride and sulfate fertilizers, when Luwlimed, resulted in the highest levels of foliar Si, Al.lancl Fe, and the highest amounts of soil extractable iron and altuninum. 8l At low pH, Jackson (39) refers to the decomposition of primary and secondary crystalline minerals as the "ultimate” buffering mechanism in the soil. It is accompanied by the release of cationic species of Al and Fe. The hydrated hydronium complexes of Al and Fe formed are themselves potent pH buffers. The ability of sesquioxides to neutralize bases is well recognized and is the basis for the use of various buffering systems to estimate lime requirement of soils. The influence of nitrogen carriers on soil and foliar Al , Fe, and Si contributes more evidence to the conclusions drawn fromother soil and plant parameters (pp. SI and 65) that the nature of the soil buffering system, as well as, capacity has changed with declining soil pH. The reduction in plant Si, Al and Fe, when the soil is limed, indicates that polymers or other insoluble complexes have been formed. Perhaps Ca is coordinated with, or trapped by, these polymeric or complexed species and this may explain the "disappearance" of the Ca (cf. Table 6) applied as lime to the acidic ammonium sulfate plots and the failure of the pH and lime requirement (cf. Table 5) to give the eXpected response . 82 .o>o. 6:66.66 ~.m_ um coE._c2 Eo.m 6cm.omm.c >.ucmo.c.cm.m%a 6:66.66 06 um 6cmo.m.cm.m no: 666666 08.2% 6.6 ..6 ..6 6.. 6.6 6.6 6.6...66 .6. 66.26. 6.6 66..6 6.6. 6.6. 6..6. 6... 66662 6.6 6.6 6.6 6... 6.6. 6... 6666.622. 6.6. 6.6 6... 6.6 6.6 6.6. .6622 6... 6.6 6.6. 6... 6... 6... 662622 6... 6.6 6.6. 6.6. 6.6. 6.6. 6.6.66.2 6.6. 6.6 6.6. 6.6. 6.6. 6.6. 66.2 6.6 6.6 6... 6.6. 6.6. 6.6. 622 6.6 6.6 6.6 6.6. 6.6. 6.6. 6.662.66 6.6 6.6 6.6 6.6. 6.6. 6.6. 66262 6.6 6.6 6.6. 6... 6.6. 6.6. .66...6.6. .6666 6.6 6.6 6.6 6.6. 6.6. 6... .66...6.6. 62 Eng Ema Ema Ema Ema Eaa .mmm.o>< .lpoE.2 coE..c: omm.o>< coE.2 coE._c: 66 .6..6. 26 .6..6. .6...66 E3..mn pcm .oaaoo .6.—o» co oE.. 6:6 6.6...66 :mmo.u_c mo muumemm .6. 6.66H 83 Copper The solubility of c0pper in the soil is expected to increase at very low pH values. Table I6 indicates that liming did not appreciably alter foliar copper. There was a general increase in foliar copper over the checks with the application of either basic or slightly acidic nitrogen carriers. The highly acidic carriers (NHACI and (NH4)2504) resulted in a plant c0pper content similar to the checks. Whether this was a result of carrier affect on soil copper (N' due to the contribution of the supplemental nitrogen. in basic or moderately acidic forms, on the general health of the plant, is not known. Barium In unlimed soils, the use of basic or highly acidic earn—iers tended to depress foliar barium. Moderately acidic car1'iers (urea, ureaform and NH4N03) significantly increased fol Lar barium over both controls and (NH4)2$06. When limed, foliar Ba was reduced with all carriers. The imesulting level with (NH4)2504 was significantly lower than for NHQCI. This differential response to liming for the two most acidiliying carriers again indicates that more than just the acidifying effect of the carrier was involved. At these high 84 it appears that the non-nitrogenous If rates of application, cation or anion is also influencing the soil system. only the direct contribution by carriers to soil acidity were of importance, then liming these soils with appropriate ramounts of lime should result in soils with similar chemical and nutritional characteristics. In this particular case it is probably simply due to solubility products of the salts involved. Carrier Anion x Lime Interactions It was noted during earlier years of this experiment, that decreases in soil pH and exchangeable bases, and increases in lime requirement occurred most rapidly with amnuanium sulfate (lOl). It is known that divalent anions are ' sorbed moreextensively by soils than are monovalent anions. The isorbed anions themselves contribute to titratable acidity. Anion sorption mechanisms include replacement of hydrwaxyl in hydrous sesquioxides ("anion penetration”). The Complexes formed with Fe and Al at low pH are polymeric catiCNTS. Those formed by divalent anions are more basic (weaken' in acidic character) than are those formed by mono- valent anions (39). Thus charged sesquioxide-SOL, species 85 would be more effective in displacing metal cations from exchange sites than are cationic sesquioxide-Cl and ses- quioxide-NOB species. The acidifying carriers (NH3, urea, ureaform, NH4N03, NHhCl and (NH4)2504) have in common the fact that none supply a stable‘cation to neutralize the nitric acid produced when anmonium is nitrified. The first four of these differ in the chemistry of their reactions in the soil by reason of the anions which are associated with ammonium after solution or hydrolysis (hydroxyl, carbonate or nitrate). Urea and ureaform both form ammonium carbonate on hydrolysis, but the rate .of hydrolysis and the associated concentrations of ammonium and carbonate aremuch lower with ureaform. Some of the observed differences in residual effectof these four carriers must be ascribed to mass action effects of specific anion concentrations associated with solution or hydrolysis. With these four carriers, as well as with NHACI and (NW4) 2501,, all of the nitrogen applied either as ammonium or nitrate appears as HNOB as soon as the ammonium is nitrified: NHL,+ 6 N03' _?.°_2_, 2 N03- + 2 H+ 6 H20 86 The major difference, then, between the four moderately aci.66.6. 6:6 30.66 66:.6> c. 666.366. 6666.36 6cm 6c..0.;0 ' r“ i ,------L--------- | | I I I L___ r------ r---‘------ V'f p. ""'t§| r---------- Fa E:.cOEE< ‘EHN ‘ Jo; 95UEJ eaJn aAlnelau ‘wJOJ €0NVHN pue ‘eaJn \ 63 --6: :2 .__I% IS. "’IS _%3 p. [Z ..lgl--- "lSI -_1¥|---------- ---.--:;E1 k3 I0. BE 3; ---. ---- In) ---1---- ---. ---.le: LJ 6.666E6cma 6:6.6 6.66656cma ..0m 6mc6. 6>.um.6. 6:6 6>066 m6:.6> C. 666—366. 6666.36 6cm 66..0.;0 Esvcoeea mc.E.. .6666 m.66> 036 6.6...60 mc.>m.c.06 .6260 06 6>.um.6. 66c.. 66:666. 6666.36 6:6 .62.. e..66. 62..o.26 22.66556 .66 6.66656.66 626.6 626 ..66 no 6666666 .626.662 .6 6.26.. 88 vvas significantly lower. Foliar Fe and Mn also tended to be i1igher with the chloride than with the sulfate. Exchangeable Mg was uniquely higher with ammonium ‘sulfate, exchangeable K was uniquely lower. Soil Mn, 'foliar K and final yield were depressed to a greater extent by the sulfate than the chloride. The complexity of soil solution chemistry precludes aany simple explanation for these data. A number of possible rnechanisms may be operating in these systems. Jackson (39) has noted that divalent sulfate promotes the polymerization of monomeric aluminum. Hydrolytic anlymerization of monomers and low polymers of Fe and Al is also promoted by increasing pH from below 5.0. Exchangeable Ca after liming was much lower with all acidifying carriers than in the fertilized or unfertilized controls, whereas exchangeable Mg was higher, notably with ammonium sulfate. This would suggest that Ca is trapped in forming polymers of hydrated iron and aluminum. A steric effect might be involved, since the hydrated calcium ion is larger than the hydrated magnesium ion. However, the marked‘ differential effect of sulfate on the exchangeability of these 89 two cations could as readily be understood in terms of the different solubilities of their reSpective sulfate salts. Plant Al, Mn, Zn and Si were higher with the two most eacid carriers than with the four moderately acid carriers. 'The latter three elements were higher in ammonium chloride ‘treated plants than in ammonium sulfate treated plants. 'These differences may be partially explained in terms of suolubility product relationships among the sulfate and cflwloride salts of the cations. With reference to Si, a higher auztivity of Cl' than of $04" in the soil solution can be irrFerred, leading to greater diSplacement of silicic acid by'tnass action equilibria. The higher activity of Cl' would der'ive partly from the greater solubility of many of its sal ts and partly from its lesser tendency to form complexes witrw hydrated iron and aluminum. These data clearly illustrate the important role of fEttilizer anions in soil acidification. The processes involved are obviously complex and it is not possible to Pin-1aoint specific mechanisms for each of the phenomena Obse=l"‘ved. The solubilities of compounds, the activities of ions,, their tendencies to complex and polymerize, and mass aeti<3r1 equilibria among diverse species present are certainly involved. 90 Below pH 5.0, qulitative changes occur which greatly accelerate the retention of titratable acidity and the associated decline in soil fertility. It is probable that some of these changes can be reversed by liming. However, it is apparent from the data that unusual amounts of lime are required and that recovery will, at best, be slow. There is no evidence, as yet, that there may not be residual effects which lime alone cannot correct. This is both a warning for practical soil management and a challenge for further research. __§her Micro-elements With three exceptions, the foliar sodium level from a] l treatments was less than 0.0l percent. The unlimed Cfueck in block two had a sodium level of 0.01 percent while true two unlimed sodium nitrate plots resulted in foliar Scndium levels of 0.0] and 0.02 percent. Boron, strontium, molybedenum and cobalt were also measured in the plant tissue. None of these elements were afffiacted by nitrogen carrier or lime treatment. Table I7 Shcwvs the probabilities for treatment effects, the mean VallJessand the range for each of these elements in the Ussue. Talole l7. Effect of nitrogen carriers and lime on several micro-elements in corn tissue El<3ment Significance level of F test Mean Range Lime Carrier Interaction PPm PPm Cc>balt .627 .599 .651 2.86 l.6-h.66 Bc>ron .500 .l2h .600 l0.2 6.5-l5.0 Mc>lybdenum .3l3 .299 .356 l.81 l.00-3.12 Strwantium .304 .MOM .l20 27.8 23-32 92 Plant Performance Yields of corn in Table 18 are expressed in two ways -— as the weight of the dried ear in metric tons per hectare and in bushels of grain per acre, adjusted to 15.5 percent moisture. Lime, carrier and their interaction effects were all significant. Lime, ignoring carrier, resulted in an average yield increase of 15 bushel. A comparison of lime within carrier treatments showed that lime was significant in increa- sing yield in only three treatments, the three most acid nitrogen carriers. ‘Corn on unlimed plots of these three treatments was severely reduced in stand and vigor by nutritional imbalances which could not be identified by visible symptoms with any Particular nutrient. With (NHMZSOL, treatment only a few SCattered, chlorotic, severaly stunted plants survived a'ltter- the plants reached about three inches. Survival was only slightly better with NHQCl. With NH4N03 treatment, the plants were distinctly more vigorous but stands were spotty, ranging from £10 to 80 percent of a perfect stand. A Uniform stand was achieved on all other plots (including Ii"19d plots of these three treatments) by thinning to 16,000 Sta] ks per acre. 93 _o>m_ ucoocmo m um omE__c: EOLL ucmLomm_U >_ucmo_m_cm_m« :m._ me._ me._ ~.- a.m~ o.mN mtm_ttmo tea mo.omu me.m «.m.: N~.m m.mm «:.mm ~.m: mama: mm._ «mm.N no. m.- «o.:: 0.. somafisxzv om.~ «mo.: em. m.om a:.mm m.:_ _o::z Nm.m «:N.m me._ m._m «N.Ne :.6N m02:12 mm.: 6N.: mm.: :.No m.Na o.NN etoemmt: mo.: _:.m we.: o.mm N.om o.m6 mat: oe.m m:.e we.s m.Nm n.sm 3.0“ m12 :N.m ma.m mk.m 6.3m m.mm m.mm NAmozvmu _m.: “N.m mm.: m.o~ 6.Nn N.:6 mozmz mm.m m_.m :6.m m.m: N.oa 6.mm tmN___utmL .mmmm oa.~ m6.~ RN._ :.~m m.mm 0.6N tm~___utmc oz wmoco>< ooE_4 omE__c: oemuoog com mcou u_cuoz >+mrco>o .cLoo me ommco>< ooE_4 ooE__c: ocom Loo m_m;m:m oczum_0E1&m.mbi.c_mLU cLoo mo mp_o_> Lo_ccmu mu_o_> cLoo co oE__ pcm mco_ccmo :mmoLuNc mo muumukm .m~ m\£flk 94 On limed plots, the fullness of leaves and diameter of sstalks were reduced, but not plant height, with (NH4)2504 arwd NH#Cl. A mild chlorosis was maintained through the ggrowing season. These plants looked more vigorous all season ‘than the limed checks which were also chlorotic but showed ssevere midrib firing characteristic of nitrogen deficiency. F’inal yields on the limed plots were not significantly clifferent between the checks and the ammonium chloride and Stilfate treatments. The large reduction in the stand and yield with the urilimed plots for the three most acidic carriers was respon- s it>le for the significant limexcarrier interaction. In unlimed plots, the only significant yield increase Fc>r carrier over basal fertilizer at the 5 percent level vwas; with Ca(N03)2. In limed plots, increases for Ca(N03)z NH4N03 and MH3 were significant. Plant Performance in Relation to Soil and Plant Analyses Relationships among the various soil and plant para- mEters presented in previous sections are being investigated by e=>onm mcm_ccmo comoLu.c o.o.um mc.>_oooc muo.a owe..c: ..oom muo.a 668.. ..< .mN. 30.66 Low...ucom o: ocm mozmznmwmmmwwmuo.a omE..c: ..<: om. m>onm ~.mozvmo ame__ acm mzz >.com .mo.~-~m.~ mtmguo __< .mm._-~m._ axomcoa ..mmv..m no occo.m mom. 96 N_.m-oo._ o. m-m. m. ”v gag N. Encmnn>_oz o.m_-m.6 N .v Ema A. cot0m_ m.m_-m.m om _A o~-m a v 2am a. twaaou Jem-0m. 00mumm om V. Eng J. coL_ ooim. 00m.A oo.-o: m. V Eda m. oc_N m6.5-mm co: A oom-0m ma v Eaa m. mmmcmmcmz :Qm.-m_. ma. v a N. e:_mmcmmz N...-m:. N. v & N. E:.o.mo mm.m-:o.~ o..v a __ s:_mmmuoa mmm.-oN. mm~._v & o. msco;omo;m Nmo.N-~m._ om.m-mm.~v. x o. ammota_z u.on .mELoz >oco.u.mmo . ucoE.coaxm 6.660 EoLm momcmm m.m>o. .mo.u.Lu mu.c: mococmmom ucoEm_u 41 . . w.mo>mo. cLoo c. mucm_cu:: mo m—m>m_ o_x0u ccm .mELOC ucm_u_mmv vcm omcmc oo>Lomoo mo 20m.Lszou .m. o.omh 97 (observed on the two most acid treatments but it did not seem to be a major reason for reduced plant growth. A strong NxP interaction was apparent. There was no increase in foliar P from the application of P in the basal fertilizer unless supplemental nitrogen was also added. Based on the yield goal of 95 bushel, and the soil test for potassium, only 1/4 to 1/2 of the recommended K \Nas actually applied. The limed plots were lower in soil K than the unlimed plots. However, the foliar analysis for K indicates that the plants contained adequate amounts of K. 'They contained 25 to 50 percent more potassium than the critical level needed for good growth. High levels of K resulted in values of .19 to .55 for' the foliar ratio of (Ca+Mg)/K. Potassium deficiencies are «Jsually associated with values greater than 3.5. High levezls of soil K can, however, suppress the uptake of calcium. iscondary Nutrients Foliar calcium levels indicate that calcium was not lhniting for any treatment. F1ichigan recommendations (53) call for the use of dolomi tic limestone to supply Mg to acid sandy loam soils 98 when the soil test for Mg is below 75 pounds per acre. All unl imed treatments except the checks and sodium nitrate (cf. Table 6) were below this level. All limed plots were well above the critical level. Foliar Mg levels revealed the identical relationship: Unlimed treatments were below, I imed treatments were above the critical level for foliar Mg . The only exception to this was the uni imed basal tI‘eatment, where soil Mg was just above the critical level While foliar Mg was just below the critical level. Typical Mg deficiency symptoms were observed on scattered Plants. But generally, chlorosis and decline in viigour Were more prevalent and served to indicate that the poor state of health, as the result of some treatments, was due to more than just Mg deficiency. The ratio of K to Mg is much more critical in the soil than is the absolute level of Mg. The ratio K/Mg in soil 1:0r unlimed plots of NH4N03, NHQCI, and (NH4)250L, was 6.2, 5.0 and 10.5, respectively. All others were less than 4.0. Soil additions of Mg are recommended in Michigan when this ratio exceeds Li.0. Reductions in yield where lime was not applied were Partilly due to deficiencies of Mg in the plant. But the acidifying nature of the carrier may also have unfavorably 99 altered the ratios of K:Mg:Ca. In specific instances, the level of one or more of these elements in the soil and/or in the plant was altered, not because of the acidifying nature of the carrier, but because of the effect in the soil of the cation or the anion of the carrier. The depressing effect of NaN03 on the K level of the soil is an example of this. Micronutrients and Other Elements The most striking nutritional feature of corn on the unlimed plots receiving acidifying nitrogen carriers was the high leaf content of Mn. All were in excess of 400 ppm »vvhich is considered to be toxic for corn. Mechanisms of antoxicity are not understood. There sseems to be a critical interaction with Fe. Specific iron (deficiency is usually associated with foliar Fe levels l3elow 30 ppm. All treatments showed Fe levels well above this. No toxic concentrations of Fe are recognized. The observed chlorosis and reduced vigor associated \Nlth toxic levels of Mn may actually be due to an induced Fe deficiency. Plants may contain sufficient iron, but it is in a form that is unavailable for the metabolic processes 0f the plant. 100 It is significant that there was a general tendency for major and secondary nutrients (P, Ca, Mg) to decline in the plant and for micronutrients and nonessential elements (Si, Mn, Fe, Zn, Al) to increase in the plant as the soil pH declined. Only the high levels of Mn or the low levels of Mg, P and N assockated.with some treatments can be (considered to be specifically toxic or deficient, respectively. Idowever, the declining soil pH imposed by the treatments was aassociated with changes in the total supply or activity of {all elemental constituents. Specific changes with declining pH in the form or activity of a given element are unique to that element. These simultaneous, independent changes aare further altered by interactions and equilibria within ‘the changing chemical environment of the soil solution and vvith the chemically active surfaces of soil colloids. Soil manganese serves as an indicator of declining soil cud. This is probably due to its dynamic redox character vvhich becomes very important below pH 5.0. Plant content (of Mn may be a more sensitive indicator of the changing rwutritional status of the soil than is pH. However, by the time the Mn levels of aplant, growing in a natural soil, reaches levels known to be toxic by nutrient solution studies, 101 it is unlikely that excess Mn is solely responsible for the associated poor state of health of the plant. It is simply symptomatic of a generally unfavorable nutritional environ- ment, involving the deficiency, toxicity or imbalance of a whole suite of mineral nutrients. Thus these data suggest no straightforward explanations for the reduced plant growth observed in association with aacidifying nitrogen fertilizers and low soil pH. RESULTS AND DISCUSSION: 2. SEASONAL FLUCTUATIONS 1N SOIL TESTS Tables 2 and 5 both present values for soil pH for the year 1967. Yet parts of the two tables do not agree. Table 2 contains values for samples taken on September 28 while data in Table 5 are for samples taken on July 31. Similar discrepancies in lime requirement data for these two samplings are apparent in Tables 3 and 5. These apparent discrepancies were not due primarily to random variation in sampling or analysis. Tables 20 to 25 record analytical data obtained for periodic samplings made throughout the season. These may be compared usefully with rainfall distribution in Figure 3 and with the seasonal distribution of ammonium and nitrate in limed and unlimed {blots in Figures 4 to 7. Soil pH Soil pH values for the four selected treatments which “Kare sampled periodically are given in Table 20. There “was less variation during the season on plots which received CNle basal fertilizer than on those receiving supplemental N fertilizer. 102 Effect of nitrogen carriers and lime on seasonal variation of soil pH in the plow layer in 1967 Table 20. Date Treatment NO‘lime Lime Izér Basal fertil WM: mm 4'0 UMO No lime Lime C8(N03)2 103 JW“ 3WD CHD 3WD ON: mm —I'\ JLn CMO 3WD NH\ awn «no 3WD awn dun awn awn awn JWn mu— dWO No lime Lime NH4N03 [\l\ mm UL: mm FWD «hi wo— mm CH3 "Mn CH3 -¢Ln o— -¢Ln CL: -:Ln Gun «HA —~¢ -¢Ln 0H0 No lime Lime (NH4)2504 10h .L6>m. 30.6 56:. 5 Low 6.06 L6a mcouv pcmmDOLu L6o mucmo u poem o.m 663 o6ucoo6c 6:.6> E:E.xmz~ o6Locm. 6L6; m.o 6>onm m6:.6> Io c6mmam. I m._ m._ m._ o.~ m._ ~.~ ~.~ m._ 6.. m._ m.~ me_u m.: No.m No.m No.m N.: m.m m.: 0.: No.m No.m No.m ms_. oz :82.52. m._ m._ m._ m._ N._ ~._ N._ -m._ I m._ N._ N._ me_u m ~.: :.: No.m ~.: ~.m w.m m.m m.: m.: m.m m.a me__ 02 02:12 - - m. - - - m. m. m. m. - me_u m.~ ~.N 6.. 6.. m._ N.N m._ m.~ 6.. 6.. m._ me__ oz N.moz.mo - w. a. - - - m._ m. a. m. m. me_u t6~___utoa N.~ 6.. ~.~ o.~ m._ M.~ 6.. 6.. 6.. m._ m._ me__ 02 .mmmm muao wao. mNNm mwxm .mim, m.mm mxm .N\m :.\mtmxm .mNMIOFNM 6umo 6:6Eu66ch mom. c. c6>m. zo.o 6:» c. u:6E6c.:o6c 65.. mo co_um_cm> .mc0666m :0 65.. new mc6.ccmo,c6moLu.c mo 666mmm ..N 6.66h 105 oo. mm oo. No. mo. :~.. mm. m.. mm. :6. ... 62.. .m. oz. mo. .3. .m. oz. 6m. oz. om. am. as. oE..oz som~.:zz. mm. 6.. ma. wN. am. oo. ..N , mam .m. mma m.~ 65.. m mm. :N. m:. a.. mo. mm. ... mo. om. om. :o. 6:.2 oz ozazz mm. m:. ms. mm. mm. om. oma mma .a~ oma Naa oe.. 6:. am. m:. .m. .m. am. saw mom mma new emu 62.. oz N.3on Na. oz. mm. .m. om. moa NmN ‘ Nma ooa Nam cmN 62.. toN...ooo. om. .m. m.. 3.. 6.. N». :Na oau oNN mmm oaa 65.. oz .omom ENQQ mwxahi -mmxm. mwxw .mxs m.\N, wwx .Nxm :.\01 N\m1.mxm 0.xm 6umo 0:6E066Lh mom. c. L6>6. 30.0 650 c. E:.mmmu00 6.066@:6:0X6 .0 co.um.zo> .6:0666m c0 68.. 0:6 6.6.ccmu c6m0cu.c .0 u06mmm .NN 6.06h 106 om. 6.6 6.6 Nmm m.. 666 .Nm mo.. ma. omm mam 65.. .m .m m.. o.~ om. mam mom one ... mm mm 65.. oz .omN.:zz. mo. ..6 6.6 Nmm 666 Nmm Nmm a... ma. ..6 m~. 65.. o.. .m .mN mam oaa mam mom mom m.~ mo. m.~ 65.. oz mozazz 6m.. m.~. sea. m.m. oom. 6N6. oooa mooN mmm. mmoN mas. 65.. m N6. ma. ma. m~.. w~.. mow amo. 66:. .MN. m... mam 65.. oz N. oz.oo .mm .66 N66 .mm. .~.. :om. omm. mm.. am.. 36m. Nm.. 65.. .6N.....6. Nam on. mom mom .mm m.. .mm mom. 6mm mam ..m 65.. oz .mmom Ewan m~\o. maxm, m~\6 .m\m. m..w. memwl.~\6 zexm 15.6 .msma ormm 6060 u:6Eu66.h Rom..c. L6>6. 30.0 620 c. E:.0.60,6.nm6mcmzoxo 60 c0.06.L6> .6c0666m :0 65.. 0:6 mc6...60 :6m0c0.c mo 006mmm .mm 6.06h 107 0N. mom 60m 0.. ..m .6. 0mm mm. mm. .m. 0.. 65.. 0m 0m mm a. z. 0. 0. s. N. N. m. 65.. oz 00m...:z. 0.. mm. .0. 0m. 0.. N6. 0.. 0m. m0. 0.. .0. 65.. 0 .m m. mm 0. 0m m. N. a. 0m 0. 0m 65.. oz M02 :2 ma. 0m. 00 ms. -0.. om. 0.. .m. .m. 0.. .m. 65.. 0. pm m0 m. .m mm .m mm .0 0m .0 65.. oz N$02.60 m.~ :m. m.. N0. 0.. mm. .0. m.. m.~ 0.. m.~ 65.. .6w.....6. 00. 0.. m0. N6 00. mm .0. m0 00. 00 00 65.. oz .mmom Euoo m~\0r. 0N.m m~.0 .m.. a... m.mi .~.0 ...0 .w.0 .m.m 650m 606a . uc6Eu66.h Nom— c. .6>6. 30.0 6:. c. E:.m6cm6E 6.666mC6;UX6 mo co.u6..6> .6c0666m :0 6E.. 6:6 6.6...60 :6mo.u.c mo uo6mmm .JN 6.06» 108 lkable 25. Seasonal variation of sulfate-S in the ! plow layer on ammonium sulfate treated plots without lime Date Sulfur 1967 PPm 5/10 1.8 5/31 15.8 6/7 21.8 6/14 20.0 6/21 21.8 7/5 . 12.5 7/19 15.0 7/31 16.8 8/23 24.2 9/28 10.3 lO/25 . 7.3 109 26m.£o.z .mc.mC6. .m6m .mom. .6EEDm .0. c0..:0..um.0 ..6mc.6m .m 6.:@.. .000 .uo6m .m:< >.:w 6:36 >62 N UIBJ jo saqoul llO .6N...0.6m .6660 ..co mc.>.6o6. ..06 co :6m0.0.c 606.0.c 0:6 E:.coEE6 mo co.06:00:.. .6c0666m .: 6.3m.. .000 .0o6m .m:< >.:n 6:36 >62 om ON 0. o o 0 0m N a. pm ON 0 .0 ON 0. 0 0w 0. I III I II . _, I __ IIII I 5 I . 0. i I I!lfl.. IIIII, III i:om . I II I :00 d . d w w N . N. I I , I I I L.00. . . +0.. _ w . I 50:. m .00. I... II... 4...: z-..zz OEHA OEHH OZ 0%. lll . ..Om 06066.0 606.0.c E3.0.60 :0 :6mo.0.: 60600.: 0:6 E3.:0866 .0 :0.063003.. .6:0066m .m 603m.u .000 .0Q6m .m3< >.30 6:30 >62 00 0. 0. 0m 0.. ..6. 0m. 0m... 0. 0.m 0.. 0.. 0.m a. 0. 0.m 0.. 0.. ( HHMHHI‘IHLII Oi\..I1nl.l.|l’l.\. “Hui , IQI'I'?II®I$\4$ _ -0. IO... I00 now .0 d w III00.N I Ii.... .0... I I #10 616 z-.zz 00. 6504 mfiHH oz 112 —_Om DmummLu MHMLH_C E3_COEEM :0 :6mo:0.: 606.0.: 0:6 E3.:05§6 .0 :o.063003.m .6:0666m .0 6:30.. 000.. .0a6m .m3< >.30 6:30 >62 Om 0N om cm ON o. 0% om m. cm 0N or 0% ON 0. , -IIIoII -III- .0. . .0 o/ . V . r. I _ . /@./I /I /o / 00. .ON. 6 II I III.0... I I z-moz W I III06. ‘11.. @Iil¢ 2:312 6800 6&0. 02 cm. N wdd 113 ..Om 06066.0 6060.36 E3.:OEE6 :0 :600.0.: 606.0.: 0:6 E3.:08€6 .0 m:0.063003.. .6:0666m .m 6.30.. .000 .0o6m .m3< >.30 6:30 >62 0m 0w 0_ omI 0w 0. pm fiN 0. 0m 0m 0. 0M 9N 9. 0% ON 0. 0 ./I/ 3W . . . . . ~ A ’ \/ 11‘ IIL ON 0: 00 00 00. ON. 0:. 00. 00. N wdd 114 The first samples were taken on May 10, just before the supplemental nitrogen materials were applied on the surface ~and disced in prior to planting corn. With all treatments, except the limed basal fertilizer, there was a sharp dr0p in pH over the next two samplings. This is the usual I'salt effect" due to displacement of exchange acidity by fertili- zer cations. The numerical decrease in pH was greater for calcium nitrate and unlimed basal fertilizer than for either ammonium nitrate or ammonium sulfate. However, actual displacement of exchangeable H+ into solution was much greater for the ammonium carriers because the pH range was an order of magnitude lower. It took four to five weeks for this salt effect to express itself fully. This is the time required for the surface-applied fertilizers to approach an equilibrium with the bulk of the soil. This is apparent from the increasing recoveries of sulfate in Table 25 and of nitrate and/or ammonium in Figures 5, 6, and 7 over this same period. Later pH fluctuations followed rather closely the seasonal fluctuations in nitrate and sulfate. Soil Nitrate ’With the basal fertilizer treatment (Figure A) negli- gible quantities of nitrate-accumulated and only minor variations in soil pH were encountered. 115 With supplemental nitrogen treatments, large fluctua- tions in nitrate after the initial peak in June were clearly related to two main factors: (1) crop removal, and (2) the distribution of rainfall. With Ca(No3)2 and NH4N03 in Figures 5 and 6, there was a rapid disappearance of nitrate from the plow layer after the initial peak in June. This coincides with the period of rapid vegetative growth and rapidly increasing demand for nutrients by corn. It also occurred during a period of frequent and moderately heavy rains in 1967 (Figure 3). 1n the case of (NH4)2504, the June peak in nitrate and the succeeding draw-down period was clearly expressed only in limed plots because nitrification and plant removal was very greatly retarded at the low pH of the unlimed plots (Fig. 7). Later seasonal peaks of nitrate accumulation occurred during July or August. This was a long, droughty period when scattered light rains served to maintain capillary contact with the surface and promote mass flow of water and solutes from the subsoil into the plow layer. These later peak accumulations of nitrate were much reduced by cr0p removal in Ca(NO3)2 plots (Figure 5). They ‘were greatly exaggerated in NH4NO3 and (NHA)ZSOQ plots. 116 Crop removal was less with these two carriers, particularly on unlimed plots where stands and vigor of corn were severely reduced. However, reduced cr0p removal cannot account for totals of NHL,+ and N03' encountered in these plots in August. In the unlimed (NH4)ZSO4 plots, the total NHul plus N03" in the surface 10 inches on August 23 was equivalent to 760 pounds of N per acre (2 x (173 + 95) x 10/7). In NH4NO3 plots without lime, the total was 510. Only 300 pounds was applied in 1967. It must be assumed that large quantities of nitrate and ammonium had been retained in the subsoil from previous years and had moved with capillary water into the plow layer. After the August 23rd sampling, nitrate declined with all carriers to the end of the season. Here disappearance must be ascribed principally to leaching by heavy rains on August 27 and September 21 and by the frequent rains which followed through the cold month of October. As will be shown in a later section (p. 156), large accumulations of nitrate were encountered in the-subsoil to a depth of 20 inches on October 25, with evidence that additional quantities had leached to greater depths. 117 Soil Sulfate The seasonal distribution of sulfate in unlimed ammonium sulfate plots (Table 25) showed the same relationship to rainfall pattern as did nitrate on other plots. Its fluctuations followed very closely those of ammonium in the same plots (cf. Figure 7). As in the case of nitrate, on October 25 there was evidence of downward displacement of sulfate into the subsoil (p. 156). Extractable Ammonium As noted in the previous paragraph, ammonium fluctua- tions in unlimed (NH#)2804 plots followed very closely the seasonal fluctuations in sulfate. In unlimed NH4N03 plots (Figure 6), fluctuations in ammonium tended to follow fluctuations in nitrate. 1n the section on soil nitrate (p. 114) it was observed, that total mineral N in the plow layer (O~10 inches) in August exceeded by a factor of approximately 2 the actual 1967 application of N in these two carriers. Is the assumption that this apparent excess must have moved upward from the subsoil by capillarity unfounded? These-apparent recoveries may have been analytical artifacts. 118 Several independent observations argue against such gross analytical errors. In plots receiving only basal fertilizer (Figure 4), ammonium levels rarely exceeded 2 or 3 ppm, a characteristic level for cultivated soils (13). In Ca(NO3)2 plots (Figure 5), ammonium levels during the June flush of microbial activity were somewhat higher, notably in unlimed soil. This is consistent with the much higher yield history and higher N content of corn residues (cf. Table 10) associated with this treatment as compared with the basal fertilizer control. Organic sources of N in the soil would be quantitatively greater and ammonification rates higher when soil temperatures become favorable for microbial activity in the early part of the summer. There is no evidence of extremely erratic fluctuation during the initial equilibration periodwhenNHL,l and N03” were increasing precipitously to the first seasonpeak in June. Nevertheless, totals for Nqu -N plus NO3'-N in the lO-inch plow layer of unlimed plots at the time of the June peak in Figures 5, 6, and 7 were #96, 420 and #96 for ICa(NO3)2, NH4N03 and (NH4)2804, respectively. In limed plots these totals were #53, 537, and 368 pounds N per acre. 119 In the case of the Ca(N03)2 plots, up to 40 pounds of N might have been contributed to this total by minerali- zation of organic matter (2% organic matter containing 5% N amnonified at the rate of 2% per year). The contribution from organic sources would have been less in NH4N03 and (NH4)2$04 plots because of much lower corn yields and rate of residue return in previous years and the unfavorably low pH for rapid decomposition. This leaves unaccounted for in these June peaks up to 200 pounds of N per acre for the limed NH4N03 plot (537 lbs. total less I+0 lbs. mineralized less 300 lbs. applied). Errors of this magnitude are not inherent in the distillation procedure used for NHLfl' and N03". It must be assumed that substantial quantities of amnonium and/0r nitrate moved into the plow layer from subsoil horizons. The long dry period between May 11 and June 7 would have promoted extensive upward movement of water and solutes by capillarity (Figure 3). Ammonium could have moved upward in company with Chloride, nitrate or sulfate (cf. Table 25). Nitrate could have mOved up in association with ammonium or any number of 5°” cations including K, Ca, Mg, and hydronium complexed. With Al or Fe. 120 In the sections which follow it will appear that mobility of Ca was closely associated with mobility of nitrate and sulfate in both limed and unlimed soils. Magnesium may have contributed to anion mobility in limed soils. Downward movement of K may have been associated with downward movement of nitrate or sulfate, but there was little evidence of upward movement back into the plow layer. In very acid soils there was evidence that components of buffer acidity (lime requirement) moved extensively in both directions in association with nitrate and sulfate. Exchangeable Calcium Data for exchangeable Ca in Table 23 show an early season increase to seasonal maxima in the period from June 7 to June 21., This increase is less marked for limed plots of Ca(NO3)2 amd the basal fertilizer than for other treatment combinations. The increase on unlimed (NH#)2804 plots is dramatic and parallels the increase in sulfate rover the same period (Table 25). In the case of unlimed (NHQZSOL, and both '1 imed and unl imed plots of Ca(N03)2 .and NH4N03, the seasonal peak in exchangeable Ca coincided with the June-peak in soil nitrate (cf. Figures 5, 6 and 7). 121 Immediately after the June 21 sampling, a total of 3.56 inches of rain fell over a period of four days, and this was followed by humid weather and light rains totaling 0.5 inches just prior to the July 5 sampling (Figure 3). Nitrate and sulfate moved extensively out of the plow layer (cf. Table 25 and Figures 5, 6 and 7). Disappearance of these anions was accompanied by sharp decreases in exchangeable Ca,-notably in unlimed soils (Table 23). Further declines in exchangeable Ca were associated with the massive disappearance of nitrate from all supplemental nitrogen plots after August 23. Exchangeable Magnesium Seasonal fluctuations in exchangeable Mg (Table 20) in plots which received basal fertilizer only, or Ca(N03)2, were not great and appeared to be random. The same was true for the much lower levels found in unlimed plots of NH4N03 and (NH4)230}+. In limed plots of these two strongly acid carriers, however, there was a distinct early season rise to a maximum on June 21, similar to that observed for exchangeable Ca. Whethem this increase was due to movement from the subsoil or to dissolution of dolomite cannot be said with any certainty. However, levels found on July 5 were distinctly 122 lower, which suggests that some magnesium may have accompanied nitrate or sulfate into the subsoil. A sharp decrease in exchangeable Mg in the last sampling (October 25) also suggests downward movement out of the plow layer and is consistent with the subsoil enrichment actually observed on this date (p. 163). Exchangeable Potassium There was not evidence of movement of exchangeable K (Table 22) from the subsoil into the plow layer during the May-June period of nitrate and sulfate accumulation. A sharp drop in level of K in the July 5 sampling for most treatments,and again at the end of the season for the unlimed-NHANO3 and (NH“)2804,suggests that downward movement may have occurred in these very acid soils. (Subsoil enrichment was not as clearly expressed on October 25, however, as was true for magnesium (p. 163)). The decrease in soil K between June 21 and July 5 was only of the order of #0 to 60 pounds. This would represent a reasonable level of uptake by corn during this period of growth. There was essentially no change in unlimed (NHn)ZSOQ plots where there wereonly a very few stunted plants and a change of only 16 pounds in unlimed 123 NH4N03 plots where stands and growth were also restricted, though not as severely. Thus the decrease in exchangeable K at this time was more likely due to uptake rather than leaching. This would ~not have been true for decreases observed at end of the season. Plant uptake certainly contributed also to in-season disappearance of nitrate and exchangeableCa and Mg. However, the quantities of nitrate and calcium which disappeared greatly exceeded any reasonable level of uptake. Lime Requirement In general, seasonal variations in lime requirement (Table 21) appeared to be random. However, the values for the unlimed plots of NH4N03 and (NH4)2$0q show a miduseason drop followed by an increase to maxima in August which tend again to drop off in the last sampling. This pattern follows those for nitrate (Figures 6 and 7) and sulfate (Table 25). These data lend support to the view that components of buffer acidity at low pH are highly mobile if suitable anions are present to accompany them in the soil solution. 120 The dominant cationic components of buffer acidity are generally considered to be hydrated Al—hydronium complexes. However, soil tests in this study showed Fe to be much more readily extracted than Al. During dry weather, iron was deposited in striking, dark brown, cemented crusts on the surface of plots where soil pH was below 5.0. Cationic species of iron were certainly associated to a significant extent with the observed mobility of nitrate and sulfate. It appears likely that hydronium complexes with Fe rather than Al may have dominated the mobile components of buffer acidity (lime requirement) in the soil of this experiment. Soil Ph05phorus Soil phosphorus data for this seasonal study are not given. variation over the season was less than 20 pounds ffixxn the respective mean values for the basal fertilizer, NH4N03 and (NHh)ZSO,+ plots. Where Ca(N03)2 was applied, the variation was greater but still appeared to be at ranckxn. It appeared that the calcium added with the carrier altered phosphate equilibria and the larger fluctuations reflected adjustments to this addition. 125 Implications of Seasonal Study The observedmobility of calcium was greater than for magnesium or potassium. This may have been only a super- ficial observation. Continuing release from decomposing primary and secondary minerals may have served to mask movement of K and Mg. The great mobility of calcium associated with nitrate and sulfate would lead one to expect that large losses of calcium could have occurred from the lime applied two years earlier. However, by no stretch of the imagination could it be supposed that the 12 tons per acre applied on the (NH4)2804 plots had been depleted to the same level as in the unlimed basal fertilizer plots. Yet the levels of exchangeable Ca were essentially the same (Table 23). By contrast, levels of exchangeableMg were 2 to 3 times higher (Table 24). Similar relationships hold for the limed NH4N03 plots. It may be suggested that this low recovery of exchange- able Ca from very acid soils after liming was a laboratory artifact. However, the fact that soil pH and nutritional restrictions on corn yields had not been corrected argues against this. 126 It is possible that some complexing mechanism, rather specific for Ca, was Operating to block its release from’ dolomite or to inactivate it after release. On the other hand, the lime inactivating mechanism may have been merely the precipation of soluble iron compounds in the alkaline vicinity of lime particles, with the result that the lime has become embedded in iron concretions. Investigations regarding the latter pr0posal were not carried out. RESULTS AND DISCUSSION 3. Incubation Studies Two incubation experiments were conducted to observe nitrification rates in soils taken from the field experiment. In the first experiment, soils from every plot were used. In the second experiment, samples from the two replicate plots of six selected treatments were used. Samples for the first incubation were taken July 31; those for the second incubation were taken September 28, 1967. Ammonium and nitrate in the soils at sampling time are shown in Tables 26 and 27. In the July sampling (Table 26), very high levels of ammonium and total mineral nitrogen were present in unlimed soils from plots receiving NH3 and the three ammonium salts.. The levels were still high for NH3 and (NH4)ZSO4 in September (Table 27). The unusually high values for unlimed NH3 were due to the fact that one of the plots received 300 pounds per acre of N,as urea,by mistake in May, in addition to the same amount of N,as NH3,in June. Total mineral nitrogen for several treatments exceeded the 10.5 mg N per 100 g soil which would be equivalent to 300 pounds N per acre distributed through the 10 inch plow layer. Prdbable reasons for this have been discussed in a l . previous section (p. 116). 127 128 0.6...60 .0 006..6 0:60...:m.m 020 65.. .o 006..6 0:60...:0.m 020% 0:60.60 m 06 0:60...:0.m 006..6 6E.0« 0.. :.0. «0.0 N.: 000.. N.0 0:665 68.0 N... 0.0. 0.0. 0.0 0.. ..0 0000.012. 0.0. 0.0. 0.0 0.0 ..m 0.0 .0022 0.0 ..0. 0.0 0.0 N.. ..0 m020:2 ..m 0.0 0.. ..m m. 0. 5.o.66.0 N.w 0.0 m.. 0.: .. 0.N .66.: 0.0. ...m ..m 0.. 0.0 0.0. m12 0.0 0.0 ..0 0.0 0. 0. N$02.60 0.0 0.0 0.0 0.. 0. 0. m0262 0.. 0. 0. m. 0. m. .6N.....6. .6060 0.. 0. 0.. m. 0. m. .6N...0.6. oz 0 00..z 05 0 000.2 05 0 00..2 05 065.. 065..e0 065.. I065..e0 065.. 065..00 -moz 03.0 0012 606.0.2 E3.:0&E< 0 .6...60 >00. ..m >.30 :0 .z0.-0. .6>6. 30.0 600 :. 606.0.: 0:6 E3.:OEE< .0N 6.06. 129 0:60...:0.m 0o: 65.. .0 m006..m% - - ..0 ..0 02 02 0.6...66 to. 00.00. ..m 0.0 m.: 5.: 0. N.: 06:668 68.0 ..0 m... ... 0.. ... ..0 0000.022. ..0 0.0 ..0 0.0 0. 0.. M02002 0.. m.. 0.. 0.m :. m.N 66.: 0.0 m... ... 0.. 0.. 0.0. m22 0.. 0.. 0.. 0.. N. m. N.m0z.60 .. 0. 0. 0. N. .. .6N...0.6. .6660 - 0 00..2I05 0 00..zim5 0 00..z 05 665.. 665..e0 065..I, 065~.00 065.. 665..00 -moz 03.0 0012 606.0.2 E3.:OEE< .6...60 .00. .0. .60560060 :0 .20.-0. .6>6. 30.0 600 :. 606.0.: 0:6 E3.:0&E< .NN 6.06h 130 Incubation Experiment I It had been the intent to bring all samples to a common ammonium level before incubation. Errors in calculation resulted in the initial ammonium concentrations shown in Table 28. For comparing treatment effects, ammonium and nitrate recovered after a two week incubation were converted to percentages of initial mineral N. The data confirm the field observation that nitrification was greatly retarded in unlimed acid soils. In soils which had been limed, there were no effects of carriers on the net disappearance of ammonium. The retardation of nitrification in unlimed soil with ureaform was much less than would have been expected. The pH of this soil was as low as for the urea or NH4N03 plots. This retardation may be attributed to the continuing release of NH3 which serves to maintain a pH more favorable to the nitrifiers in the immediate microenvironment of the slowly hydrolyzing ureaform particles. The hydrolysis of ureaform during the incubation resulted in a ho percent increase in total mineral nitrogen. This was equivalent to about 60 pounds per acre, or l/5 of the annual application of ureaform nitrogen in this experiment. In contrast with this net mineralization release of N from ureaform, 25 percent of the ammonium which disappeared l3l 0.0.mcoamo. mm; co.u.oom om.m.:o.mo c. coccm .08.. mo poommo ommco>m ucmo.m.cm.msoZ% .ucoocoa m um ucmo.m.cm.m co...mu c.:u.3 pummmo oE..« .m.o>o. mc.ucmum 5200.53-50: 20m .moowfidzzv mc.oom Loumm E:.cOEEm .m.u.c_~ m00N.022. 00 00000 .022 000 .-002 ..00 .0022 ..00 0000.00. 2 .0000.5 .0.0.c_. N..N N..N 0.0. m.m. 02 ..0. 02 02 0.0Wm.00 00. 0m. m+ 0+ mo. mm 0 RN m.m m.m #05005 05.. m. m- «00. mN «N .0 0.0 0... 0000.022. 0. .+ 0.0. 00 00 0. N.. 0... .0022 N. mN- «00. 00 «m 0N 0.0 0.0. 002022 00. 00. 0mm. 00. 00 N. 0.0 0.m .55000000 .+ N+ 0mm .m 0m mu m.: m.m woe: m.+ .. 0... m. 00 Nm 0.0 0..m m22 0. .+ .0. mm m 0 0.0 ..0 N202.00 0. m- 00. 00 0 0 0.0 0.0 00202 m. 0. 00. 00 00 0. ..0 0.0 500.....00 .0000 0- 0.. 00 .0 0 m. 0.0 0.0 L00:300.. 02 xi 0 0 0r .0 N, 0 00.x2 05 005.. 00050000 005.. 005..:0 005.. 005..:0 005.. 005..:0 C0_umn_30r__ MHMLH .2 E3_COFF:F NEzchEm mc.L:n .m.u.c_ .m.cemo z .mcoc.E mm co.umn:oc_ Loumm acommca c. omcmco .z .m.oc_E .m.u_c. mo ucouLom _ ucmE.LoQXu c. co.umn:oc. .mxooz ozu mc_.so Aumoz ocm +:Izv z .mcoc_E c. momcmso .ww o_nmh flaw-.03 A034 0.9.m -..;v Raynv .00 P55... a. .-..A.0\/.L ~0~:u .Lf.~.ac ..u .0 P. .90.-..0P5m0: 25‘ Liv-nx~z§shu ufivN. 1..\.»\F...h .ucoogoa m 00 ucmo_m.cm_m muommmo mE_.* .co.umn:oc_ mo mc_cc_mon 020 um z- :12 m oo_\mE o. m o>.m 00 mOUNAJIzv 20.3 omucoEmzm mm: 00.0800 o_o_m c. z E:.cOEE<_ I32 - - 02 02 00.. .0.. 02 00.. . 050.0500 500 00. 00. - - 0.- 0- 00.0 0.0 «0.0 0.0 0:005 05.. .0 0 0.- 0- 00.0 0.- 00.0 0.0 0000.022. 00 0. 0.- 0- 00.0 0.0 «0.0 0.0 002022 0. n 0.- m- «0.0 0.. 0m.m 0.~ 00.: 00 00 0- 0- 00.0 0.0 0..0 0.0 022 «N .N m- on «0.0 m.: *N.w m.m uhmozvmu 0. 0. 0.- 0.- 00.0 0.0 «0.0 0.0 t0~...0000 .0000 0 00.x0 05 0 i0, 0 00002 05 0 00.\2 05 005.. 005..:0 005.. 005..:0 0050., 005..:0 005.. 005..:0 co_u:_o>o co.umnsoc. mc.L:o z oumgu_c E:.cOEEm L¢.LL¢Q Nob .m.o:.E c. omcmzo c. ommogoc_ c_ ommogooo . .li::::::ii\\ii __ ucoE_.oQXm c. co_umn:oc. .mxooz 030 mc.L:o N00 00 co_u:_o>m pcm com00u.c _mLoc.E c. momcmco .mN 0.0mh 133 from the unlimed NH4N03 soil failed to appear as nitrate. This cannot be ascribed to microbial immobilization or denitrification because of the low organic matter content of the soil. It could have been due to loss of N2 or N20 from reactions of nitrous acid which is an intermediate in nitrification and unstable at low pH. If this were true, there is no apparent reason why it should not have occurred also at the even lower pH of the NHhCl and (NH4)250h soils. Incubation Experiment II In the second incubation experiment, soils were incubated in glass jars so that 002 could be collected in alkali as a measure of general microbial activity. The data are presented in Table 29. All soils were adjusted to a common initial ammonium level, except for soil from the one erratic NH3 plot which ’ contained l8 mg. N per lOO g. . The essential relationships were the same as in the first incubation. Nitrification was increasingly inhibited as soil pH was lowered by acidifying carriers. Where lime had been applied, there were no differences in the extent to which ammonium disappeared in two weeks. Notall of the ammonium coverted appeared as nitrate. Unlike the first experiment, there was a net loss of mineral l3h nitrogen with all treatments. This may have been due to the presence of a greater concentration of fine root debris in the September samples. This would have promoted immobilization. However, there is no correSpondence between the extent of N disappearance and the level of microbial activity as reflected in C02 evolution. It is of interest to note that the unlimed (NH4)2504 soil is approaching sterility as indicated by its failure to nitrify and the near absence of respiratory activity. This further reinforces observations made throughout this study that the effect of pH changes in the soil below pH 5.0 are of a much different nature than those changes taking place above pH 5.0. RESULTS AND DISCUSSION 4. Mineralogical Studies Cation Exchange Capacity Cation exchange capacity and its dependency upon pH were estimated conductometrically after potentiometric titration in BaOAc buffer with Ba(OH)2 or HOAc to equilibrium at various reference pH's. In the conductometric procedure described by Mortland and Mellor (56), CEC is estimated graphically from the intersection of the horizontal baseline, which represents displacement of exchangeable Ba by Mg, and the linear increase in conductivity resulting from concentration of the titrant M9504 in solution after the exchange complex has been Mg saturated. Barium chloride was used as a final saturating wash and disappearance of CI' in subsequent distilled water washes was used as the criterion for removal of soluble salts. With soils in this study, this criterion was not fully adequate. Insufficient washing and excessive washing with distilled water both resulted in baseline conductivities higher than the desired minimum. However, it was found that neither the slope or the horizontal displacement of the rising leg of the conductance curve varied appreciably with additional washing 135 136 after chloride could no longer be detected with silver nitrate. To avoid the variability associated with floating baselines, the endpoint was estimated by extrapolating the rising leg of the conductance curve to zero. Cation exchange values obtained in this way are presented in Table 30 for limed and unlimed soils from four selected field treatments. The range of values is not great, but consistent trends associated with treatment and equilibrium pH can be noted. The exchange capacity decreased with decreasing equilibrium pH and decreasing pH associated with acidifying carriers. Such pH dependency is characteristic for organic matter and for amphoteric clay minerals such as all0phane and t0*a lesser extent kaolinite. However, it must be observed that the degree to which this relationship to soil pH was reversed by liming was very different for the different carriers and at different equili- brium pH's. The largest increases in CEC after liming occurred with Ca(N03)2 and basal fertilizer. These increases ranged from 0.h to 0.9 me at equilibrium pH's of S to 8. With the two strongly acidifying carriers which had reduced soil pH in the field to the vacinity of h.0, liming had had little effect. In fact, with these two carriers, as well as with Ca(NO3). liming tended to suppress exchange sites active at an equilibrium pH 137 ..m 0.m o.m m.— o.. 0.0 0.0 ..m 0.0 ..0, 0.0 ..m m.0 0mm.0>< 0.0 0.0 0.0 0.. 0.. 0.0 0.. 0.0 0.0 0.0 0.0 0.0 0.0 0000.022. m.0 m.0 m.0 0.. 0.. m.. 0.. 0.0 0.0 0.m 0.0 m.0 m.0 m02012 0.0 0.0 0.0 0.. 0.. 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.002.00 0.m m.m m.0 m.— 0.. o.m 0.0 0.m ..m 0.0 m.m 0.m o.m .00._.0.0m .0000 m 0o. .00 we I mu n0 1. nu 1. n. 1. n” 1. fix” 1. .1 nu A I. u I. u I. u I. u I. n I. u a w I. w I. w I. w .l w u w .l J a I. a I. a I. a .1 a I. a I. E P w 0- w p w p w 0- I. P w I. a a a a w a .l D: D- P D. 8 D. D. 0mm.0>< 0.: o.m 0.0 0.0, ohm.. .0...mo 20 50......000 0000000000 :0 0.. 0:0 .0>m. 30.0 00 20.00000 0mcmzox0 50.000 :0 05.. 0:0 0.0...00 :0m0.u.c mo pummmu .om 0.000 138 of h.0. It should be pointed out that the samples used here were taken in the Spring of 1906, only one year after lime application. The pH values of the unlimed basal, calcium nitrate, ammonium nitrate and ammonium sulfate and the limed basal, calcium nitrate, ammonium nitrate and ammonium sulfate treated soils were 5.9, 5.8, n.8, h.h and 6.5, 6.6, S.h and h.5, respectively. It would appear that long exposure to high rates of the two very strongly acidifying carriers has resulted in irreversible loss of pH dependent exchange materials which become active in the pH range of S to 6. As a result, one year after liming, the CEC of these soils was 0.8 and 1.2 me lower than in soils which had received basal fertilizer alone or with Ca(N03)2. The difference was less at equilibrium pH's 0f 7 and 8. (The determination of CEC at pH 7.0 was difficult to duplicate because the titration curve for Ba(OH)2 vs HOAc is very steep in this region. Barium acetate is probably an inappropriate buffer for estimating CEC at pH 7.0 if the potentiometric method for barium saturation is used.) The observed reduction in CEC with declining pH is a third factor contributing to the great mobility of cations observed in these soils and described in a later section 139 (p. 155-165). The roles of hydrogen ions formed during nitrification and the associated anions will be discussed at that time. A question yet to be considered is: what is the nature and fate of exchange materials which appear to have been altered or removed in the process of soil acidification? The apparent pH dependency suggests that they include organic matter and amphoteric clay minerals. Increases in activity of AI, Fe and Si were indicated by soil tests and foliar analysis and have been offered in evidence that crystalline clay minerals were also breaking down. Clay Minerals Figure 8 shows the x-ray diffraction pattern for clays isolated from the unlimed basal treated soil and the unlimed ammonium sulfate treated soil. X-ray patterns were also obtained from clays isolated from the unlimed ammonium nitrate and the limed ammonium sulfate plots but are not shown here. The soil samples were taken in the spring of 1966. The peaks at 3.3 R and h.3 X indicate the presence of quartz. Part of the quartz is in the sample,and part is contained in the device used to hold the clay during analyses. The peaks at 3.2 and 3.8 R are due to feldspars. The former may be due to any feldspar while the latter is usually due only to plagioclase feldspars. IMO Table 31. Interpretation of x- ray peaks in the clay analyses Peak at Due to 001 001 lh.2 001 001 10.0 7.0 001 002 002 002 002 5.0 4.7 003 003 L. . 3 3 .8 3.5 and 3.6* 002 oot. 004 3 .3 003 003 chlorite vermiculite (prior to heating to 330)# illite vermiculite (after heating to 330) kaolinite (prior to heating to 550) chlorite vermiculite (prior to heating to 330) illite vermiculite (after heating to 330) chlorite vermiculite (prior to heating to 330) quartz plagioclase feldspars kaolinite (prior to heating to 550) chlorite vermiculite (prior to heating to 330) uartz Tllite vermiculite (after heating to 330) feldspars *Reason for shadow at 3.6 not known #Pure vermiculite will collapse without heating. Soil vermiculite usually requires heating. Figure 8. lhl X-ray diffraction tracings of oriented soil clay films from the unlimed basal and ammonium sulfate treated soils on porous ceramic plates. Treatments: A, Mg-saturated, glycerol-solvated, no heat treatment; B, K-saturated, no heat treatment; C, K-saturated and heated to 330 C; D, K-saturated and heated to 550 C. Scale of horizontal axis is linear for degrees 29. Vertical axis is radiation intensity at a scale factor of 8. “+2 ‘— _ _ _ «Nd. «0.0. «..h . _ _ «Qmfi «00 «Ev «on «a «a.» . ._.__ ‘ ‘ «we. «0.9 J