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'..' ! .kc‘l ' L.‘ - o a. . .‘c'... ‘ (‘ {hm‘fi THE RELATION BETWEEN A NITRATE-NITROGEN INCUBATION SOIL TEST AND GREENHOUSE AND FIELD RESPONSE OF CROPS TO ADDED NITROGEN BY Toshiaki Kinjo “K. AN ABSTRACT Submitted to the College of Agriculture of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Soil Science Year 1955 Approved (R L. M , g b Toshiaki Kinjo 1 ABSTRACT This study was undertaken to determine if a rapid laboratory nitrate-nitrogen incubation soil test could be correlated under Michigan conditions with crop response to added nitrogen and from different crop rotations. Eight soils of varying texture and organic matter content were collected from.central Michigan. Three of these soils were from plots of a rotation involving the use of green manure crops in growing sugar beets and field beans. The preliminary analyses were made for tex- ture, soil reaction, phosphorus, potassium, residual ni- trate, and organic matter content. The procedure of the nitrate-nitrogen incubation soil test developed in Iowa was followed with slight modification. Soils were incu- bated in the laboratory for a period of eight weeks under controlled conditions of moisture and temperature, and tests for nitrate-nitrogen were made every two weeks. The quantity of nitrate-nitrogen released on moist incubation was found to be closely related to the organic matter content of the soils. There was a direct relation- ship between soil texture and release of nitrate-nitrogen on incubation; namely, the finer the texture, the greater the amount of nitrate produced. In the greenhouse the response of the tomato, wheat, and field bean plants in terms of increased dry weight to Toshiaki Kinjo 2 added nitrogen was not significantly related to nitrate- nitrogen released on incubation. In addition, the correla- tion between the nitrate-nitrogen test values and the dry weight of crops grown on soils receiving no nitrogen was net significant. The nitrate-nitrogen released from the soils on moist incubation was more closely related to the quantity of nitrogen taken up by the several crops than to their dry weights. However, only in the case of the wheat crop of the first series was a significant positive correlation coefficient obtained. A negative relationship was found between laboratory nitrate-nitrogen incubation tests and nitrogen absorption response on all crops. However, correlation was not signi- ficant when all the soils were considered. Yield response of corn grown on three different rotations to added nitrogen in the field in l95u was not related to the nitrate-nitrogen incubation tests of soils from.these rotation plots. THE RELATION BETWEEN A NITRATE-NITROGEN INCUBATION SOIL TEST AND GREENHOUSE AND FIELD RESPONSE OF CROPS TO ADDED NITROGEN By Toshiaki Kinjo A THESIS Submitted to the College of Agriculture of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Soil Science 1955 ACKNOWLEDGMENTS The author would like to express his deep appre- ciation to Dr. Kirk Lawton for his help, suggestions, and interest shown during the period the research work was carried and while this manuscript was being written. In addition, the suggestions and criticisms of Drs. R. L. Cook, M. M. Mortland, and R. Swanson in reviewing the thesis are sincerely appreciated. 38667.2 TABLE OF CONTENTS INTRODUCTION . . . . . . . . . . . . . REVIEW OF LITERATURE . . . . . . . . . MATERIALS AND METHODS . . . . . . . . . Soils Used . . . . . . . . . . . Laboratory Studies . . . . . . . . Greenhouse Studies . . . . . . . . RESULTS AND DISCUSSION . . . . . . . . SUMMARY AND CONCLUSIONS . . . . . . . . SELECTED BIBLIOGRAPHY . . . . . . . . . Page 12 12 13 17 20 1+7 51 LIST OF FIGURES FIGURE 1. 2. 3. 7. The production of nitrate-nitrogen in soils of first series during successive moist incubation periods 0 e e e e e e e e e e e e e e e e e 0 Relationship between organic matter contents of the eight soils and pounds per acre of nitrate- nitrogen produced in eight weeks . . . . . . . Relationship between the production of nitrate- nitrogen and total nitrogen absorbed by wheat plants of check pots of first series . . . . . . Relationship between the production of nitrate- nitrogen over an eight-week period and total nitrogen absorbed by tomato plants of check pots of first series . . . . . . . . . . . . . . The production of nitrate-nitrogen in soils of second series during successive moist incubation periods 0 e e e e e e e e e e e e e e e e e e 0 Relationship between the production of nitrate- nitrogen over an eight-week period and total nitrogen absorbed by wheat plants of check pots of Second series 0 e e e e e e e e e e e e e 0 Relationship between the production of nitrate- nitrogen over an eight-week period and total nitrogen absorbed by field bean plants of check pots or Second series 0.0 O o e e e e e e e e 0 PAGE 22 23 27 3O 37 no #3 TABLE I. II. III. IV. V. VI. VII. VIII. X. LIST OF TABLES PAGE The sand, silt, and clay content of soils used in the eXperiment . . . . . . . . . . 1h Analyses of eight soils for soil reaction, phosphorus, potassium, nitrate-nitrogen, and organic matter 0 e e e e e e e e e e e 15 The production of nitrate—nitrogen in soils of first series during successive moist incubation periods . . . . . . . . . . . . 21 The dry weight, nitrogen content, total nitrogen absorbed, and nitrogen absorption response of wheat plants of first series . 25 The dry weight, nitrogen content, total nitrogen absorbed, and nitrogen absorption response of tomato plants of first series . . . . . . . 28 Analyses of soils for nitrate-nitrogen left in soils after growth of wheat plants and tomato plants of first series . . . . . . . 3h The production of nitrate-nitrogen in soils of second series during successive moist 1DCUbat10n periods 0 e e e e e e e e e e e 36 The dry weight, nitrogen content, total nitrogen absorbed, and nitrogen absorption response of wheat plants of second series . 38 The dry weight, nitrogen content, total nitrogen absorbed, and nitrogen absorption response of field bean plants of second 801’1080000000 eeeeoeeeeee “.1 Corn yield, nitrate-nitrogen produced in an eight-week incubation period, and yield response of corn to added nitrogen from rotation l, h, and 6 . . . . . . . . . . . AS INTRODUCTION Nitrogen, an essential element for plant growth, plays a most important role in the fertility of soils and thereby in crop production. The need for additions of nitrogen to soil for continued high yields of crops has been emphasized in the last twenty-five years. For more than a century it was known that much of the bene- fit derived from animal manures and other organic residues applied to soils was due to their nitrogen content. During this time a general relationship between soil organic“ matter and plant requirements for nitrogen in the form of organic or mineral fertilizers was noted. Although numerous exceptions are evident, crop response to nitro- gen is generally greater on soil low in organic matter. Because ammonification and nitrification, the processes leading to the production of nitrates, are biochemical in nature, no great degree of success has been achieved using chemical soil tests to estimate the nitrogen supplying power of soils. Even biological tests are subject to con- siderable error since microbial activity in soils is in- fluenced to a great extent by moisture and temperature. Thus, seasonal fluctuations of these factors are important reasons why empirical tests for nitrogen needs of field soils are often inaccurate. IMM’I" ‘ffi'fl Nevertheless, agronomists have spent considerable effort in attempting to develop reliable methods of deter- mining nitrogen availability in soils. A reasonably rapid nitrogen incubation test has recently been developed by the Iowa Agricultural Experiment Station. The results of this test have been correlated with the response of corn to added nitrogen. The purpose of this study is to determine whether such a nitrogen incubation test under Michigan conditions can be correlated, first with crop response to added nitro- gen fertilizers, and secondly, with different crop rotations in which the nitrogen needs of specific crops are quite different. REVIEW OF LITERATURE Many studies of the influence of nitrate-nitrogen on crop production have been carried out since the beginning of the twentieth century. In 1917, Lipman and Burgess (19),working on the problem of ammonification versus nitrifiability as a test for the relative availability of nitrogenous fer- tilizers, concluded that the nitrate form of nitrogen was of paramount importance for the nutrition of most plants. Agronomists both in.Europe and America at that time came to this same conclusion. Hence nitrifiability was adopted as the criterion of availability of organic nitrogenous fertilizers rather than ammonifiability in normal soil con- ditions. As Gainey (13) pointed out, ammonia accumulates under conditions such as poor drainage or water-logging. Experimenting on Hawaiian soils in 1918, Burgess (8) attempted to determine the possibility of predicting, with some degree of accuracy, crop yields from microbiological data. Criteria used in routine and comparative tests were ammonification, nitrification, and nitrogen fixation. Re- sults of these experiments showed that the nitrification process was by far the most accurate available biological measure for evaluating soil fertility conditions and predicting future crop yields. It was concluded by Gainey (13) that those conditions which tend to promote rapid nitrification are closely identical with those which result in maximum.crop yields, though active nitrification may not be the cause of high fertility. The idea of nitrification or nitrifying power of a soil at Gainey's time was a little different from the present concept. In previous years, the nitrifying power of a soil was measured by the potentiality of the soil to nitrify added organic matters, such as dried blood and alfalfa meal under optimum.conditions for incuba- tion. with the old concept of the nitrification, Gainey (13) stated that productivity in infertile soils, in so far as nitrogen was the limiting factor, was not lumited by the process of nitrification. Several types of procedure for determining nitrogen availability in soils have been advocated. The method Woodruff (29, 30) has described is based on the amount of easily oxidizable soil organic matter. He stated that each percentage of organic matter in the surface plow depth of soil corresponded to about 1000 pounds of total nitrogen per acre. If all organic matter were alike, Uoodruff con- cluded that the liberation of nitrogen from.organic matter in a form.available to plants would be preportional to the amount of organic matter in the soil. The fraction that decomposes to liberate nitrogen for a particular crop depends upon such factors as the season of the year in which the crop grows, the temperature and moisture condi- tion of the soil throughout the growing period of the crop, and the textural and structural condition of the soil. Thus, it is necessary to know how much nitrogen is released from.organic matter under specific environmental conditions. Another group of methods involves the chemical extrac- tion of a fraction of the soil nitrogen. Truog (26) proposed a procedure involving alkaline oxidation of soil organic material. A third procedure, which has received recent widespread attention, is that of biological mineralization of nitrogen from.soil during a controlled incubation period (10, 25). Since nitrification is biochemical in nature, many- complex and interacting factors have an influence on the rate of nitrate production. Such factors are amount and kind of organic matter, nature of the residue of the pre- vious crep, moisture and temperature fluctuation patterns, nature of soil microflora, aeration, soil reaction, mineral nutrient status, and other biotic properties of soils. One of the most important factors which influences the production of nitrates is the presence of nitrifying bac- teria as well as ammonifying bacteria. Fortunately, it has been shown by Gainey (l3) and others that all cultivated soils under normal conditions contain active nitrifying .‘i organisms. Specific organisms responsible for nitrate- nitrogen formation from ammonia are two groups of bacteria called Nitrosomonas and Nitrosococcus. Bacteria of the group known as Nitrobacter carry out the formation of nitrate from nitrite compounds. E” Nitrifying bacteria are aerobic organisms. They ob- tain their energy by the oxidation of certain elements and compounds. Thus, the amount of nitrate formed is affected in part by the amount of oxygen available in soil air. waksman (2?) pointed out that the quantity of oxygen con- sumed during nitrification was closely related to the amount of nitrogen nitrified. The data obtained by Fathi and Bar- tholomew (9) from.studies on influence of oxygen concentra- tion of oxygen for nitrification in soil is about that con- tained in ordinary air, that is, approximately 21 percent by volume. Approximately half as much nitrate was produced when the oxygen concentration was maintained at 2.1 percent as at 20 percent. Reducing the oxygen concentration from about 20 to 11 percent had only a negligible influence upon the rate of nitrification. Jodidi and‘Wells (17) found that several Iowa soils, when soil air was analyzed in July, 1911, contained 20.39 percent of oxygen in the soil air at 7-inch depth, while data by Boynton (S) on a New York soil showed it to have 11.60 percent of oxygen by volume at 6-inch depth when tests were made after frequent showers in July. Thus, oxygen is not a ltmiting factor for nitrification under normal soil conditions. Another major factor affecting the numbers and activities of nitrifying organisms is soil moisture. Major fluctuations in soil moisture primarily govern soil aeration. The nitri- fication process is retarded by very low as well as by very high moisture conditions (20). According to Fitts, Bartholo- mew, and Heidel (12), 100 centimeters of water tension pro- vided the Optimum.moisture for the production of nitrates under laboratory conditions. Depending on the texture of the soils the tension resulted in 25 to 35 percent moisture. This was found to be slightly above the field capacity. These Iowa workers also pointed out that adjustment to 25 percent moisture gave lower and less consistent results than wetting and removal of excess water by tension. With soils of widely varying texture, the uniform percentage adjustment would be expected to be even less favorable. The effect of temperature on production of nitrates is also very striking. According to Waksman (27) nitrate formation was noticeable at 5° C, became prominent at 12° C, and reached a maximum at 37° C. Higher temperatures, such as h5° C, exerted an injurious effect. Panganiban (21) and Russell,iJones, and Bahrt (22) found the optimum temperature for nitrification to be 35° c. It is known that activities of the nitrifying organisms are to some extent dependent upon the pH of the medium.in which they function. The limiting acidity for the develop- 'ment of these organisms, as Haksman (27) concluded, is pH 3.7 to n.0, whereas their optimum.reaction is at pH 6.8 to f 7.3. Ca1cium.carbonate is generally used as the compound to neutralize acid soils. However, Brown and Hitchcock (7) . found that presence of an excess of calcium.carbonate in. I E concentrations up to 1.5 to 6.0 percent proved toxic in normal Hyoming soils. Halvorson and Caldwell (15), studying factors affecting the nitrate producing power of some Minne- sota soils, also came to the conclusion that the presence of a large amount of calcium.carbonate inhibited nitrification. Baldwin, Walters, and Schmidt (3) noted that nitrifi- cation in some normal soils was stimulated by the addition of phosphate and potash. This stimulation was still greater when nitrogen was used in combination with phosphorus and potassium. In regard to nitrification of organic matter, Whiting (28) stated that, even with carbon in a resistant condition, nitrate was formed rapidly if organic or inorganic nitrogen was added. About the same time Brown and Gowda (6) recog- nized that sodium nitrate increased the nitrate content of the soil and enhanced its nitrifying power. Organic matter, applied as animal manure or green manure, definitely influences nitrification process, ac- cording to Brown and Gowda (6), and Kubota, et a1 (18). In studies by Brown and Gowda (6), the nitrifying power of a soil was increased by manure applications up to 36 tons per acre, but nitrate accumulation was not propor- tional to the amount of manure used. These investigators found that clover hay had little effect on the nitrate con- tent of the soil, but it increased the nitrifying capacity. Gainey (1h) reported a specific instance wherein the ability of a soil to accumulate nitrate-nitrogen rapidly under laboratory conditions appeared to be more intimately associated with a certain small fraction of soil nitrogen than with the total quantity. He worked on the problem of total nitrogen as a factor influencing nitrate accumulation in soils. Gainey (1h) found that wnen the nitrogen con- tent and the nitrate producing power of a large number of soils were determined and the data grouped on the oasis of the nitrogen content of the soils, and averaged, an almost perfect direct relationship appeared to exist between total nitrogen content and the accumulation of nitrates. However, when the data were studied in detail, it was evident that there were a large number of irregularities in the direct relationship between total nitrogen and nitrate production. It was found that the nearly perfect correlation coefficient of 0.988 1 0.006 obtained from average values was reduced 1; a 10 to a non-significant value of 0.368 1 0.052 when it was cal- culated from the individual samples. Jensen (16) stated that no correlation could be established between total nitrogen and nitrate content in soils. Gainey (1h) concluded that as long as the quantity of easily nitrifiable nitrogen varied _ in soils, a perfect correlation could not exist between total nitrogen and nitrate accumulation, at least during a limited incubation period. Yet, Allison and Steeling (l) maintained that wide variations between total nitrogen and production of nitrates of many individual soils were due, in part, to the use of natural soils without additions of microorganimms, lime, phosphate or other substances that may be limiting for microbial growth. In their work, nitrate formation from soil organic matter was directly correlated with total soil nitrogen at all incubation periods in both limed and unlimed soils. Allison and Steeling (l) emphasized that the quantity of organic matter in a soil was a more important factor than either quality or source of organic matter. Recently, a nitrate-nitrogen incubation soil test was developed.at Iowa Agricultural Experiment Station as a means of evaluating the nitrogen supplying power of a soil and predicting the magnitude of crop response from nitrogen application. Although there was considerable seasonal variability, the data obtained from the work of Fitts, Bar- tholomew, and Heidel (11) showed that nitrification rate, 11 as determined by their incubation soil test, gave results that were correlated with response to application of nitro- gen fertilizer on corn when the stand count was considered. The regression coefficient between nitrification rate and response of corn to nitrogen fertilizer on fields with thin stands was found to be -O.630, significant at the one per- cent level. MATERIALS AND METHODS Soils Used Eight different surface soils varying in organic matter content and texture were used for this experiment, including Oshtemo sand, Hillsdale sandy loam, Conover loam, Miami sandy loam, Brookston loam, and three samples of Sims The three Sims soils’were obtained from different loam. experimental rotation plots at the Ferden farm in Saginaw The purpose of the rotation experiment on the farm County. was to compare seven systems of farming at two fertility One-half of each rotation plot was at low fertility levels. level, and 800 pounds of 5-20-10 fertilizer per acre was The other half of each rotation plot was applied in 1951. at high fertility level, and 1600 pounds of 5-20-10 ferti- lizer per acre was applied in 1951. The five-year crop sequence for rotation l was alfalfa brome, alfalfa brome, corn, beets, and barley. Ten tons of manure per acre for corn or beans was applied in rotation on plots of rotation 1. In rotation Li, the crop sequence was oats, alfalfa brome, corn, beets, and barley, and seven tons of manure per acre was applied for corn. The crop sequence for rotation 6 was beans, wheat, corn,'beets, and barley. This is a cash crop rotation without green manure crops, and with no manure 13 applied, although straw was plowed under. All the remaining soils were collected from farm areas in lower Michigan and were in storage in an air dry condition at the college barn. Oshtemo sand, Conover loam, and Miami sandy loam soils came from the Rose Lake Experiment Station, the R. Miller farm, and the R. L. Cook farm, respectively, in Clinton county. A sample of Brookston loam was taken from the Britten farm in Lenawee county. Hillsdale sandy loam soil was collected from the K. Lawton farm in Ingham county. The texture of each soil was determined with the hydrometer method developed by Bouyoucos ((4.). The results are shown in The soils were analyzed for pH, available phos- Table I. phorus, available potassium, nitrate, and organic matter. The results are shown in Table II. Laboratory Studies Laboratory experiments consisted of three parts: (a) preliminary analyses of the eight soils, (b) nitrate- ni trogen incubation soil tests, and (c) determination of the total nitrogen content of greenhouse crops by the Kjeldahl procedure. Soil reaction values were determined using a 1:1 Avail- soil to water suspension and a Beckman pH meter. able phosphorus and potassium were measured according to Estimates the reserve method of Spurway and Lawton (2h). _ ' In - . r. i '9 .. P TABLE I THE SAND, SILT, AND CLAY CONTENT OF SOILS USED IN THE EXPERIMENT Soil Series peggggt pegeezt pegezgt Textural Class A Oshtemo 89.67 9. 3O 1. O3 sand E Hillsdale 69.31 23.12 7.57 sandy loam Brookston h6.01 3h.62 19.37 loam Conover 52.h0 32.39 15.21 loam Miami 56.16 31.22 12.62 sandy loam Sims h8.22 29.93 21.85 10mm (rotation l) ' Sims h6.71 29.n2 23.87 loam (rotation h) Sims h6.21 29.39 2h.h0 loam (rotation 6) TABLE II 15 ANALYSES OF EIGHT SOILS FOR SOIL REACTION, PHOSPHORUS, POTASSIUM, NITRATE-NITROGEN, AND ORGANIC MATTER Soil Type pH _P* If" N0; 32%??? (pounds per acre) (percent) Oshtemo sand ,5.8 113.6 1AA. 1.2 1.30 Hillsdale sandy loam 5.3 28.0 156 h.h 1.86 Brookston loam 6.h 2h7.5 22h, 7.2 6.89 Conover loam 7.2 H7.5 10h 27.6 3.92 Miami sandy 10m 6 OS 19. 0 90 27 .6 2.118 Sims 10m 606 8105 188 1011.14. 11.86 (rotation 1) Sims loam 6.6 127 .5 191;. 1.20 11.67 (rotation u) Sims loam ‘ 6.7 110 .o 170 0.1;8 a. 18 (rotation 6) *Spurway reserve test 16 of nitrate-nitrogen were obtained using the phenoldisulfonic acid procedure, which was modified by Fitts, et a1.(12) to speed up the operations of the old procedure. Organic matter content was determined by dry combustion method. The re- sults of these analyses are in Table II. The nitrate-nitrogen incubation tests were carried out using the procedure developed by Hanway and Stanford (25). at Iowa State College. Thirty-five milliliter Gooch crucibles were used instead of thirty milliliter glass tubes. Gooch crucibles were kept in a desiccator, which had one inch of water at the bottom in order to maintain Optimum moisture of the soil-vermiculite mixtures. The desiccator was placed in an oven maintained at a tempera- ture of 35° C 1 2° C. The soils were aerated three times a week to supply sufficient oxygen for Optimum nitrifica- tion. After leaching and suction, these soils were stirred with a pin to prevent compaction and to maintain soil structure. By so doing, it was much easier to leach out soils without any puddling after a two-week period of incu- bation. The total incubation period was limited to eight weeks because the production of nitrate-nitrogen was negli- gible after this time. Production of nitrate-nitrogen was measured every two weeksuby the phenoldisulfonic acid method. Duplicates of all soil samples were used, and the average results calculated. m ,1 17 For the determination of the total nitrogen content of greenhouse crops, Gunning's modified method of the Kjeldahl procedure was followed. One gram portions of ground plant tissue dried at 65° C were used for the deter- mination of total nitrogen. The amount of total nitrogen absorbed by the plants in each pot was calculated by multi- plying the value of dry weight by percent of total nitrogen. Greenhouse Studies Two pot experiments were carried out in the greenhouse to determine the response of several crops to added nitro- gen. Three levels of nitrate were obtained by using two rates of added nitrogen, 50 and 150 pounds of nitrogen per acre and a no nitrogen treatment. Ammonium nitrate, applied at the rate equivalent to a two million pounds per acre of 6-inch depth soil, was used to supply the nitrogen. An amount equal to two hundred pounds per acre of P205 and K20 in the form of 0-20-20 fertilizer was thoroughly mixed with the soil in each pot to supply opthmum amounts of phosphorus and potassium. A Three replications of each treatment were set up in one-gallon glazed jars. The position of the jars was ro- tated several times during the experiment. These jars were filled with screened, air-dry soil to within one inch of the top. The amount of soil of each type varied, and 18 fertilizers were applied accordingly, on a two million pounds per acre surface soil basis. Spring wheat and tomato seeds were planted on the 10th of November, 19514, for the first series of greenhouse tests. - K1 .. l Eight plants of spring wheat per pot and one plant of tomato per pot were grown. Since vegetative growth was more important than seed or fruit formation, the wheat plants were cut close to the soil when they started to head out, and the tomato plants were harvested at about the. time flowering began. Plants harvested from each pot were put in separate bags and dried in an oven at 65° C. In the second series of greenhouse studies, field beans were grown in those soils which had previously grown spring wheat, and spring wheat was grown in these soils which had grown tomatoes. The same rates of nitrogen appli- cation as in the first series of tests were used. However, the amount of phosphorus and potassium was reduced to one- half of the previous application. Before planting the second series, soils from all pots were dumped out, and the large roots were removed to avoid addition of organic matter to the soils. Eight plants of spring wheat and four plants of field beans per pot were allowed to grow until they flowered, at which time the entire above ground parts of the plants were harvested. 19 Before the second series of greenhouse experiments were set up, the soils, in which the first series of crops were grown, were analyzed for nitrate-nitrogen left in the soil. 20 RESULTS AND DISCUSSION The results obtained from the first series of nitrate- nitrogen incubation soil tests are given in Table III. Easily nitrifiable nitrogen was mineralized to a great ex- tent in a two-week period of incubation under controlled After this period, nitrogen in more optimum conditions. resistant compounds was nitrified slowly in small amounts without much variation over the rest of the incubation period. The Brookston loam, which contained a relatively large amount It did not of organic matter, provided the only exception. fit into the pattern of nitrification of the rest of the It can be noted that a rather large amount of soils. nitrate-nitrogen was liberated from Brookston loam soil Figure 1 shows the trend of over the period of four weeks. nitrification of each soil during an eight-week period of successive incubation. In order to evaluate the relationship between the organic matter content and the production of nitrate- nitrogen in each soil after eight weeks of success incuba- a graph (Figure 2) was plotted with the values of tion, total nitrate-nitrogen produced in terms of pounds per A acre against the organic matter content of each soil. close relationship between the organic matter content and 21 TABLE III THE PRODUCTION OF NITRATEQNITROGEN IN SOILS OF FIRST SERIES DURING SUCCESSIVE MOIST INCUBATION PERIODS P‘ Soil Type ‘ Incubation Period I ; 2nd week Lith week 6th week 8th week Total Nitrate 1 in 8 weeks H 2 (pounds per acre of nitrate-nitrogen) E é Oshtemo sand 902 9.6 “.08 (4.08 280“» I I Hillsdale sandy loam 13.6 5.6 5.6 7.8 32.6 BrOOkBton 10am 5502 29.6 12.“. 120(4- 10906 Conover loam. 20.0 8.0 8.u 6.h h2.8 M181n1 sandy 10m 280).]. 906 6.8 502 5000 $1318 10” 3302 706 302 762 51.2 (rotation 1) Sims loam ‘ 29.2 6.1;. 5.2 8.8 149.6 (rotation k) Sims 10m 2596 800 106 (4.08 (4.000 (rotation 6) 22 60 I no 30- 20- Pounds of nitrate-nitrogen per acre 10" Oshtemo sand Hillsdale sandy loam Brookston loam - Conover loam Miami sandy loam Sims loam (rotation 1) Sims loam (rotation h) Sims loam (rotation 6) \.\ O 0 o I O -a»o O Fig. 1. I I l ; 2nd nth 6th 8th Time of incubation in weeks The production or nitrate-nitrogen in soils of £irst series during successive moist incubation periods. ic \JI \" A \J Percentawe of “\y' Efu“ ? ‘ : Vw ") k- y=O.688+0.06lX ryx=O.833 J l l 1 a 20 0 Lu; 9: oc- 70 so 9 o 1 o u up Pounds of nitrate-nitrogen pt? acre Fig. 2. Relaticnship between vrganic matter contents of the eight soils and poqncs per acre or nitrate—nitrogen pwcduce in eight weeks. the amount of nitrate-nitrogen produced from the soils was apparent. A correlation coefficient of 0.833, significant at the one percent level, verifies the relationship. In their studies of Marshall silt loam in Iowa, Andharia, Stanford, and Schaller (2) found a highly significant cor- relation between the nitrate-nitrogen and the organic matter content. Table IV shows the results of the first series of the greenhouse experiment on wheat plants, including the average dry weight per pot, average nitrogen content per gram of plant sample, average total nitrogen absorbed per pot, and the response of wheat plants in terms of nitrogen absorption to additions of 50 pounds and 150 pounds of nitrogen per acre. Wheat plants grown on all soils, except Miami sandy loam with.l§0 pounds per acre of nitrogen application, and Sims loanl(rotation l) with 50 pounds per acre of nitrogen, responded in.yie1d to added nitrogen, though the degree of response varied with each soil. The restricted root development due to compactness of the soil may have resulted in the non-response in yield of the above-stated two soils. But in the case of Sims loam.soil (rotation 1), treated with 50 pounds per acre of Iritrogen, the nitrogen absorption was greater than for the non-treated soils. Growth and nitrogen absorption response to 150 pounds per acre of nitrogen application for Hillsdale sandy loam, 25 TABLE IV THE DRY WEIGHT, NITROGEN CONTENT, TOTAL NITROGEN ABSORBED, AND NITROGEN ABSORPTION RESPONSE OF WHEAT PLANTS OF FIRST SERIES Soil Type Rate of Average Average Average Nitrogen. Nitrogen Dry Weight Nitrogen Total Absorption Content Nitrogen Response Absorbed 5,1 lbs/acre gms/pot mg/gm. mg/pot mg/pot E . I Oshtemo 0 8.63 16.h96 1h2.360 --- sand 50 9.15 21.968 201.007 58.6 7 I 150 9.52 26.967 256.726 11h.3 6 . Hillsdale 0 8.73 25.69u 121.533 --- c j sandy loam 50 5.38 28.700 15h.729 33.196 5? 150 h.78 29.136 139.270 17.737 Brookston 0 11.39 25.857 289.955 --- 10am 50 12.06 26.165 315.589 25.598 150 11.83 26.213 310.100 20.1h5 Conover 0 5.23w 2%.8h5 129.9h0 --- loan 50 6.19 2 .071 161.379 31.h39 150 5.85 2h.986 lh6.188 16.2h8 Miami 0 6.11 25.17h 153.813 --- sandy loam. 50 6.68 26. 01 176.359 22.5h6 Sims 108m 0 5.51 230807 1310177 -"" (rotation 1) 50 5.23 28.335 1h8.192 17.015 150 7.20 28.807 207.h10 76.233 Sims loam. 0 6.82 17.959 122.u80 --- (rotation u) 50 7.19 27.250 195.928 73.%88 .150 7.77 30.128 23u.095 111. 15 Sims 10am. 0 %.85 17.062 82.751 --- (rotation 6) 50 .05 23.85h .317 61.566 150 6.29 29.090 1 2.976 100.225 26 lfiwokston loam, Conover loam, and Miami sandy loam soils, umre less than that of 50 pounds per acre of nitrogen ap- plication. Wheat on the remaining four soils showed a greater response to an application of 150 pounds of nitro- gen per acre than to the lower rate. A study of the relationship between the production of nitrate-nitrogen and the total nitrogen absorbed by wheat plants in the check pots of the first series was made by plotting pounds of nitrates produced during an eight-week incubation period against total nitrogen recovered by wheat plants. This relationship, which is graphically presented in Figure 3, does not appear to be entirely satisfactory though the correlation coefficient of 0.9126, statistically significant at the one percent level, was obtained. Values for the Oshtemo sand and Sims loam (rotation 6) did not fall close to the line of best fit. However, a greater number of soils with a wider range in nitrate incubation values are needed to establish the validity of the relationship. The results of the first series of the greenhouse experiment with tomato plants are given in Table V, including dry weight, nitrogen content, total nitrogen absorbed, and nitrogen absorption response. The dry weight of tomato plants grown on all soils increased with added nitrogen. In Conover loam and three Sims loam soils (rotations 1, h, and 6), the response of plant growth to 150 pounds per acre P pct ‘ H 4 nitrOgen absorbed p total 3C0 250 150 100 D.) ‘xJ' yz33.575+2.240x ryx=o.9|26 I l‘ 1 1 cl 4J2 4 l l 10 .3 30 ht 50 CA) (0 00 9%; ltO 110 tunes par acre of nitrate-nitrogen Fig. 3. Kala ticnship between the prccuction of 1trate-nitrogen ans total nitrogen absorbed by wheat plants of Check pots cf irst series. —rl'r 1 "I 2 ‘2.) 1 p. ‘IJ Li!" '- 28 TABLE V THE DRY WEIGHT, NITROGEN CONTENT, TOTAL NITROGEN ABSORBED, AND NITROGEN ABSORPTION RESPONSE OF TOMATO PLANTS OF FIRST SERIES Rate of Average Average Average Nitrogen 3°11 Type Nitrogen Dry Weight Nitrogen Total Absorption Content Nitrogen Response Absorbed lbs/acre gms/pot mg/gm mg/pot mg/pot Oshtemo 0 9.912 13.833 137.113 --- sand 50 11.639 19.3 8 225.191 88.078 150 11.111 31.3 1 359.158 222.015 Hillsdale 0 10.137 10.778 109.257 --- sandy loam. 50 10.668 20.263 216.166 106.909 150 7.869 37.700 296.661 187.101 Brookston 0 13.981 21.221 296.796 --- loam. 50 18.651 18.890 352.371 55.578 150 11.013 30.103 121.833 125.037 Conover loam 0 13.899 18.752 260.631 --- 50 12.835 23.833 305.897 15.263 150 16.013 28.363 151.177 193.513 Miami 0 0733 190898 2930157 "" sandy loam. 50 1 .186 22.689 371.051 80.89 150 15.588 30.790 179.955 186.79 Sims loam 0 7.735 11.196 112.127 -—- Crotation 1) 50 8.905 19.050 169.610 57.513 150 10.531 31.796 331.939 222.812 Sims 10m 0 80150 130672 111.127 "" (Imitation 1) 50 12.105 12.911 156.651 15.221 150 12.190 22.232 271.008 159.581 Sims 16am 0 5.987 .519 86.925 --- (Imitation 6) 50 10.159 1 .396 171.186 81.561 150 9.372 21.151 226.371 139.116 29 of nitrogen application was greater than that of 50 pounds per acre of nitrogen application. In the rest of the soils, the growth response of tomato plants was less with 150 pounds per acre of nitrogen treatment than with 50 pounds per acre of nitrogen treatment. However, in every instance, the nitrogen absorption response of tomato plants to 150 pounds per acre of nitrogen application was far greater than that of 50 pounds per acre of nitrogen application. One explana- tion for this phenomenon would be that a greater dry weight production was obtained using tomato plants, thereby in- creasing the absorption of nitrogen at the 150 pounds per acre level. The relationship between the production of nitrate- nitrogen and the total nitrogen absorbed by tomato plants grown at the zero level of nitrogen in.the first series was poor. In this case the correlation coefficient was 0.593, not significant at the five percent level. The data from the Miami sandy loam and Conover loam.soils, especially, appear to be at variance with the relationship as it is shown in Figure 1. Tomato plants absorbed as much nitro- gen from Miami sandy loam as from Brookston loam soil, though the amount of nitrate-nitrogen produced during in- 3 \ .1 L 0. \JV; 'r_4 : r. -n1.t1“ugt:n pPCCPJCt11n1 \ v- . 1... g. ‘ ' A‘.AAL'- ‘- —. ‘. “|\ .- .I‘ ‘ ‘ t I; J 'L.’ .‘ 3‘1 :16. (.4. L3 ‘11. lirtt .1; 110 "'Jl v 1'}: 31 Conover loam soil was noted. According to the data in Table II, Miami sandy loam and Conover lowm soils contained large amounts of residual nitrates. It is possible that this accounts for lack of relationship in Figure 1. This nitrate fraction was leached out before incubation studies were started. Correlation between the nitrate-nitrogen incubation soil tests and the increase in nitrogen absorption by wheat and tomato plants for the first series when 50 pounds and 150 pounds per acre of nitrogen applications were compared with no nitrogen application was not satisfactory in all cases. The coefficient of correlation between the amounts of nitrate-nitrogen produced in the first two-week incu- bation period and the values of nitrogen absorption response of wheat plants to 50 pounds of nitrogen application in eight soils was -0.311, non-significant at the five percent level. In the case of 150 pounds per acre of nitrogen application for wheat plants, the correlation coefficient was ~O.238, also non-significant at the five percent level. When the total amount of nitrate-nitrogen produced in an eight-week incubation period was correlated with the response of wheat plants to 50 pounds per acre of nitrogen application, the correlation coefficient was -0.361. With response of wheat plants to 150 pounds of nitrogen application, the coefficient 32 of correlation was -0.332. None of these coefficients are significant at the five percent level. The reasons for lack of significance are not evident unless nutrient intake may have been restricted in such soils as Hillsdale sandy loam, Miami sandy loam, and Conover loam by a surface crust formation. The caking of soil and the formation of a puddled surface layer may have reduced air diffusion to a level where oxygen was deficient for root respiration and microbial activity. A higher degree of correlation was obtained from the experiment with tomato plants. The amounts of nitrate- nitrogen produced in a two-week incubation period were cor- related with the nitrogen absorption response of tomato plants to 50 and 150 pounds of nitrogen applications. These correlation coefficients were -O.517 and -0.671, respectively. When the total amount of nitrate-nitrogen produced in an eight-week incubation period was correlated with the response of tomato plants to the 50 and 150 pounds per acre of nitro- gen applications, the correlation coefficients were -0.170 and -0.629, respectively. These values are not significant, since with only eight pairs of figures a significant corre- lation coefficient must be above -0.707 at the five percent level. One of the reasons for the lack of significance in the correlation coefficients may be the small number of samples. Fitts, et a1. (11) correlated the nitrate-nitrogen 33 produced during a three-week incubation under controlled laboratory conditions with the yield response of corn to the nitrogen application in field eXperiments. These workers found a correlation coefficient of -0.630 to be significant at the one percent level. When wheat and tomato plants of the first series were harvested, the nitrate-nitrogen left in the soils was de- termined. The results of these analyses are shown in Table VI. The amount of nitrate-nitrogen recovered from the soils on which tomato plants were grown was much lower than that from.the soils planted to wheat. This situation would be expected since tomato plants absorbed more nitrogen than did wheat plants, except in the case of the Sims soils from the Ferden rotation plots. Approximately 30 to 10 pounds per acre of nitrate-nitrogen was recovered from the soils where wheat plants were grown after receiving 150 pounds per acre of nitrogen, except in the case of Oshtemo sand. The residual nitrate-nitrogen in Oshtemo sandy soil was lower than that found in other soils mainly because of a greater uptake by the wheat plants. The second series of experiments were carried out with the same soils which had been used in the first experiment with wheat and tomato plants. The amounts of nitrate- nitrogen produced from each soil, which had previously re- ceived no nitrogen, was much less than that obtained during 31 TABLE VI ANALYSES OF SOILS FOR NITRATE-NITROGEN LEFT IN SOILS AFTER GROWTH OF WHEAT PLANTS AND TOMATO PLANTS OF FIRST SERIES 3011 Type 33:63:. Pounds pm acre of nitrate-nitrogen Applied after after lbs/acre wheat harvest tomato harvest Oshtemo sand 0 0.1 0.80 50 0.6 0.10 150 11.8 ‘1.28 Hillsdale sandy 16am. 0' 1.2 0.72 50 8.% 1.00 150 10. 16.80 Brookston loam 0 6.8 1.00 50 6.2 5.60 150 29. 1.21 Conover loam 0 115.2 0.80 50 1 .8 1.00 150 31.2 11.20 Miami sandy loam 0 13.2 0.60 50 19.8 0.72 150 32.0 18.10 Sims loam O 12.6 21.80 (rotation l) 50 8.2 15.60 150 32.0 9.20 Sims 16am 0 5.1 2.20 (rotation 1) 50 2.1 2.88 150 38.1 23.20 Sims loam 0 0.8 2.88 (rotation 6) 50 1.0 1.18 150 38.0 1.10 35 the first series of experiments (Table VII). This decrease in production of nitrate-nitrogen was undoubtedly due to. the mineralization of some.of the organic nitrogen during the growth of wheat and tomato plants, and its subsequent absorption. The only exception to this trend was with Oshtemo sand, which produced as much nitrate-nitrogen as in the first series of incubations. A graphic presentation of the production of nitrate-nitrogen for each soil is given in Figure 5. The pattern of nitrification closely follows that of the first laboratory experiments. Data of dry weight, nitrogen content, total nitrogen absorbed, and nitrogen absorption response of wheat plants of the second series are listed in Table VIII. The appli- cation of nitrogen fertilizer at 50 and 150 pounds per acre rates increased the yields of wheat plants of the second series in all soils except in Hillsdale sandy loam. In this instance the yield of wheat plants decreased as the application of fertilizer increased. This phenomenon.may be attributed to the effect of the rather large quantity of residual nitrate-nitrogen in the soil. The Hillsdale sandy loam soil, which received 150 pounds per acre of nitrogen fertilizer, had the highest residual nitrate- nitrogen (Table VI). Nitrogen absorption response of wheat plants to 150 pounds per acre of nitrogen application was generally more TABLE VII THE PRODUCTION OF NITRATE-NITROGEN IN SOILS OF SECOND SERIES DURING SUCCESSIVE MOIST INCUBATION PERIODS Soil Type “‘1 ~7— Oshtemo sand Hillsdale sandy loam Brookston 10mm Conover loam Miami sandy loam Sims loam (rotation 1) Sims loam (rotation 1) Shms loam. (rotation 6) Incubation Period 2ndwnxm: ludxweek (Sflnwefl: 8&1week Total Nitrate in 8 weeks pounds per acre of nitrate-nitrogen 17.10 16.60 36.10 21.10 21.10 28.20 12.20 17.10 1.10 2.10 8.10 1.56 6.20 11.28 5.60 1.60 3.88 2.80 6.32 5.18 3.52 5.80 5.10 2.20 3.12 1.88 3.20 1.92 1.28 0.88 1.72 0.72 28.80 23.68 51.32 33.36 35.10 16.16 21.92 21.92 5.1:. 37 Oshtemo sand Hillsdale sandy lo Brookston loam. am) Conover loam .1..- Miami sandy loam Sims loam (rotation 1) Sims loam (rotation 1) Silas loam (rotation 6) :m l 501 4:- O 1 Mo 0 l Pounds of nitrate-nitrogen per acre '8 f H O #T 0 1 14 1 2nd 1th 6th 8th Time of incubation in weeks Fig. 5. The production of nitrate-nitrogen in soils of second series during successive moist incubation periods. 38 TABLE VIII THE DRY WEIGHT, NITROGEN CONTENT, TOTAL NITROGEN ABSORBED, AND NITROGEN ABSORPTION RESPONSE OF WHEAT PLANTS OF SECOND SERIES I I 311 T Rate of Average Average Average Nitrogen ° ype Nitrogen Dry Weight Nitrogen Total Absorption Content Nitrogen Response Absorbed lbs/acre gm/pot mg/gm mg/pot mg/pot (mtemo sand 0 7.025 13.780 96.805 --— 50 8.088 20.389 161.906 68.101 150 8.122 25.798 209.531 112.726 Hillsdale 0 5.572 15.188 81.628 --- sandy loam 50 1.807 23.856 111.676 30.018 150 3.807 27.691 105.131 20.803 Brookston 0 8.019 15.233 122.153 --- loam 50 9.615 21.267 201.182 82.329 150 12.057 27.185 327.770 205.617 Conover loam. 0 3.017 22.723 69.237 --- 50 1.630 21.752 100.712 31.175 150 1.586 26.116 121.281 52.011 Miami 0 (4.0 92 02110 630966 0'-- sandy loam. 50 5. 76 2 .121 118.263 81.297 150 1.767 29.705 111.601 77.638 Sims loam 0 7.082 16.598 117.517 --- (rotation 1) 50 8.115 21.613 199.978 82.131 150 8.660 23.995 207.797 90.250 Sims 1081“ 0 60852 130821]. 911.0722 O-- (Imitation 1) 50 10.570 16.9 5 179.109 81.387 150 9.352 26.5 1 218.398 153.676 811118 1081“ 0 50618 130176 7110023 C-- Crotation 6) 50 6.990 20.313 112.198 68.175 150 9.153 26.723 252.613 178.590 7’ 39 than twice that of the 50 pounds per acre of nitrogen application, with the exception of Hillsdale sandy loam and Miami sandy loam. The relationship between the production of nitrate- nitrogen and the total nitrogen absorbed by wheat plants from.soils not treated with nitrogen is shown in Figure 6. A rather poor relationship is observed. The correlation coefficient of 0.619 is non-significant at the five percent level. In Table IX, the dry weight, nitrogen content, total nitrogen absorbed, and nitrogen absorption response of field bean plants in the second series are shown. The in- crease in yield of field bean plants due to the nitrogen fertilizer application was rather remarkable in Brookston soil. But for the rest of the soils, the yield of field bean plants at three levels of nitrogen application showed little variance. Field bean plants responded in terms of nitrogen absorption to nitrogen application in all soils with the exception of Sims loam, rotation 1, which was treated with 50 pounds of nitrogen per acre. In all soils, the nitrogen absorption response of the 150 pounds per acre 0f nitrogen application was greater than that of the 50 pounds Per acre of nitrogen application. The relationship between the production of nitrate- nitPOgen and total nitrogen absorbed by field bean plants 1.113333" 1;... -. 00'} . ‘~V1 “k1; >\ ‘. s o ‘x -/ y = 47.546 +1.262x ryx=O.6496 «.117 n 1- " 7 5 A AKA. '4 fl 1 .1 ' .1' .1. - \ r' '\ - 1“ ‘ '.- 1' in mm: It 4 l f 7‘ FA- .)\_1 “1’ . , " Io ,. ‘¢- 11.2»; .1 :._Ltz‘:ntt-. ”.1“- 11 TABLE IX THE DRY WEIGHT, NITROGEN CONTENT, TOTAL NITROGEN ABSORBED, AND NITROGEN ABSORPTION RESPONSE OF FIELD BEAN PLANTS OF SECOND SERIES Rate of Average Average Average Nitrogen 3°11 TYP° Nitrogen Dry Weight Nitrogen Total Absorption Content Nitrogen Response Absorbed lbs/acre sm/pot ms/em. ms/pot ma/pot 08111261710 0 6 e 088 2)." 21+; 1117 0 60h. -"-' sand 50 8.001 21.776 171.230 26.626 150 6.113 30.111 193.313 15.709 Hillsdale 0 1.131 11.286 59.058 --- sandy loam 50 1.713 23.000 108.399 19.311 150 1.336 10.837 177.069 118.011 Brookston 0 10.368 26.121 270.823 --- loam. 50 12.306 23.070 283.899 13.076 150 15.157 25.012 386.610 115.787 Conover 0 5.261 23.070 121.110 --- loan. 50 5.229 28.110 117.519 26.109 150 6.2 1 32.010 200.699 79.259 Miami 0 606 0 21.960 1%5081‘.‘ CO- sandy loam 50 6.1 5 28.711 1 5.617 39.803 150 6.202 31.762 196.988 51.171 Sims loam 0 6.165 22.913 1.370 --- (rotation 1) 50 6.522 25.059 1 3.135 22.065 150 7.018 30.930 217.995 76.625 Sims loam. O 7.783 28.618 222.731 --- (I‘Otation h») 50 80223 230672 19110655 -280079 150 9.611 31.139 302.255 79.521 Sims 10m 0 60158 260353 1620282 “'- (rotation 6) 50 6.907 23.995 165.731 3.152 150 7.120 32.085 238.071 75.789 12 in the check pots of the second series was very slight as shown in Figure 7. The correlation coefficient was 0.513, which is non-significant at the five percent level. Lack of relationship may have been due to differences in fixation of atmospheric nitrogen by field beans in each soil. The correlation coefficients between the nitrate-nitrogen incubation tests and the nitrogen absorption response of wheat and field bean plants in the second series to the added nitrogen resulted in positive figures, whereas in the first series of experiments, negative correlation coef- ficients were obtained. In the case of the first two-week incubation test and the nitrogen absorption response of wheat plants to 50 and 150 pounds per acre of nitrogen ap- plications, the correlation coefficients were 0.322 and 0.122, respectively. When the total nitrate-nitrogen pro- duced in an eight-week incubation period was correlated with the response of wheat plants to 50 and 150 pounds of nitrogen per acre, the coefficients were 0.271 and 0.319, respectively. For field bean plants, the correlation coef- ficients between the first two-week incubation soil test and the nitrogen absorption response to 50 and 150 pounds of nitrogen application per acre were 0.215 and 0.281, respec- tively. When the total nitrate-nitrogen-produced in a period of eight weeks was correlated with the response of field bean plants to 50 and 150 pounds of nitrogen per pot per 80$0Tb60 nitrogen u) C) C "D ‘J F.) '1 O r 2).») C‘ F— I 150 100 L y = 58.584 + 2.955X 50' ' ryx=O.5|28 1 l 1 1 10 20 30 10 rounds per acre of nitrate-nitrogen D \ C'— helationship between the productior of nitrate-nitrogen over an ei'nt- ' '7’ y ‘7 . - f ‘1 fl - . ~ Oh" A} ‘r'Ctr’. ‘utfripfl (.XTIC. tL'tZAJ. {111,1 126L711 r-‘r - ~\ -‘ ‘.\~' ' ’- ' F {‘5‘ - r~ \p CAUSL‘I‘LIQ‘LA u‘y liclu UL c111 Plants C1 czeox pots of second series. acre, the coefficients of correlation were 0.085 and 0.235, respectively. All the correlation coefficients obtained from the second series of experiments were non-significant at the five percent level. In Table X, the corn yields in 1951 and the nitrate- gfifiahnh nitrogen incubation test values of soils from rotation 1, 3‘ 1, and 6 are shown. Since composite soil samples were taken from high and low levels of fertilizer application for the experiments, corn yields were calculated by averaging yields obtained from high and low fertility levels for each plot. The average corn yield of high and low fertility levels is regarded as that receiving no nitro- gen. The increase in yield due to 10 pounds of nitrogen per acre as a sidedressing is considered to be the yield response to added nitrogen. The corn yield from plots of rotation 6 was about one-half of that of the other two rotations. This decrease in yield was due to the exclusion of green manure in rotation 6. Plots of rotation 1, which had one year alfalfa-brome, produced a little more corn than those of rotation 1, which had two years of alfalfa- brome. The yield response of corn from rotation l was greater than that of the other two plots, though the yield response to 10 pounds of nitrogen per acre as a sidedressing was rather small in three plots. It is believed that the lack of precipitation after nitrogen sidedressing was largely 15 TABLE X CORN YIELD, NITRATE-NITROGEN PRODUCED IN A 8-WEEK INCUBATION PERIOD, AND YIELD RESPONSE OF CORN T0 ADDED g’.‘ ~Z""“.- 52 til-.1 -‘ 13.2-n.— NITROGEN FROM ROTATION 1, 1, AND 6 Nitrate-Nitrogen Corn Yield Yield Rotations giggzfiegeiiogn No N* aifiggrgasingizsiggzz pounds/acre bushe1/acre Nitrogen 1 51.2 86.8 89.1 2.3 1 19.6 92.9 91.9 -l.0 6 10.0 17.1 18.1 1.0 emean yield of high and low fertility plots 16 responsible for the lack of response in 1951. In 1955. a very significant yield increase was found for sidedressed nitrogen, especially for rotation 6. When the nitrate-nitrogen incubation tests of these ' u? an. soils were compared with the differences in yield between the plots sidedressed with 10 pounds of nitrogen and the plots receiving no sidedressing, little relationship could be observed. However, it should be pointed out that these soil samples were taken after the corn was harvested. “Lg, Therefore it may have less validity than if it were taken before planting time. No effort was made to determine a correlation coefficient simply because the number of samples was small. 17 SUMMARY AND CONCLUSIONS The purpose of this study was to determine whether a nitrogen incubation soil test developed by Hanway and Stanford (25) at Iowa State College could be correlated under Michigan conditions with crop response to added nitrogen fertilizers and different crop rotations in which the nitrogen needs of specific crops are quite different. Greenhouse experiments and laboratory incubation studies were conducted using eight field soils varying in organic matter content and texture. Three of these soils were obtained from different experimental rotation plots at the Ferden farm in Saginaw county. From this study the following conclusions were drawn: 1. Marked differences in the quantity of nitrate- nitrogen produced after a two-week period were obtained from.the eight soils. A similar trend was evident for total nitrate-nitrogen produced during an eight-week period. In general, the higher the organic matter content and the finer the texture, the greater was.the nitrogen released from soils during moist incubation. A highly significant correlation coefficient of 0.83 was obtained between nitrate-nitrogen released on incubation and the organic matter content of the soils. 18 2. No significant relationship was observed between the dry weight yield of the wheat and tomato plants of the first series where no nitrogen was added and the nitrogen released upon incubation. Lack of such a relationship was also noted for the wheat and field bean crops in the second greenhouse series. 3. The yield response of wheat, field beans, and tomato plants to either 50 or 150 pounds per acre of nitro- gen in greenhouse experiments was not significantly related to the nitrate-nitrogen released during incubation. Lack of response to added nitrogen on specific soils is believed to be due to soil physical conditions detrimental for plant growth. 1. A significant direct relationship was found be- tween the amount of nitrogen absorbed by wheat plants of the first series when no nitrogen was applied and the nitrate-nitrogen released on incubation. In the case of tomato plants of the first greenhouse series and both crops of the second series, non-significant correlation coeffi- cients were obtained. 5. Correlation between the nitrogen absorption response to the added nitrogen fertilizer by wheat and tomatoes of the first greenhouse series and the nitrate- nitrogen released from soil during laboratory incubation was negative, but less than that required for significance 19 at the five percent level. For the wheat and field bean crops of the second series, the coefficients were of low positive value, indicating a direct relationship between the nitrate incubation values and the yield response to added nitrogen fertilizer. 6. The yield response of corn grown in the field under three crop rotations to sidedressed nitrogen was not correlated with nitrate-nitrogen released by the incubation test. 7. It is apparent that the nitrate-nitrogen incuba- tion soil test as conducted did not clearly reflect the need for or the ability of crops to absorb nitrogen under greenhouse conditions. A preliminary observation also indicates it was not correlated with the yield response of corn to the added nitrogen under field conditions. The small number of soils and crops studied suggests that fur- ther experiments are needed to evaluate the present nitrate- nitrogen incubation test or some modified procedure. Since the nitrification test is an empirical one, it is possible that an incubation temperature of 35° C is too high to reflect the nitrogen supplying power of soils for crops grown under Michigan conditions. In addition, it is possible that soil physical conditions limited crop response to added nitrogen in both greenhouse and field experiments. An empirical nitrogen incubation test 50 can be evaluated only if all growth factors except nitrogen are not limiting. 1. 2. 3. 1. 5. 9. 10. 11. 51 SELECTED BIBLIOGRAPHY Allison, F. 8., and L. D. Steeling. Nitrate formation from soil organic matter in relation to total nitrogen and cropping practices, Soil Science, 67: 1919. 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