THE EFFECT OF CORNCOB MIXTURES AND MULCHES ON THE GROWTH OF THE ROSE By WILLIAM JOHN CARPENTER, JR. A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1953 ProQuest Number: 10008275 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10008275 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 ACKNOWLEDGMENTS The author is indebted to Dr. Donald P. Watson for valuable suggestions and direction throughout the conduction of this study. He deeply appreciates the respected counsel of Dr. Alvin L. Kenworthy. An expression of deep gratitude is directed to Professors Kirkpatrick Lawton and A. Earl Erickson, of the Department of Soil Science, for their valuable help. THE EFFECT OF CORNCOB MIXTURES AND MULCHES ON THE GROWTH OF THE ROSE By WILLIAM JOHN CARPENTER, JR. AN ABSTRACT Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science In partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture Year 1953 Approved ■/ * Within the past five years the application of ground corncobs^.as ja mulch for roses has been extensively adopted in commercial greenhouse production. The lack of adequate research and the conflicting reports concerning the value derived from ground corncobs were stimuli for the initia­ tion of the present experiment.. The first experiment Included 96 rose plants of the variety Peter's Briarcllff planted in 12-inch pots contain­ ing a media of 600 cubic inches. Three treatments received one to four inch depths of ground corncobs on the surface of the Miami clay loam soil. The media of the remaining five treatments varied from 100$ soil to 100$ corncobs with three Intermediate mixtures. The second experiment consisted of 3^0 rose plants of the variety Better Times planted in two greenhouse benches subjected to the following five treatments: 2 and L inch depths of ground corncobs as surface mulches, 10 and 20$ ground corncobs mixed with the soil by volume, and a soil treatment. The data collected Included monthly records of the number of flowers produced, the number of centimeters of linear growth and the fresh weight of the vegetative growth In grams. The use of I.B.M. cards was employed to acceler­ ate the collection and summarization of these data.. An evaluation of soil fertility, aggregation, moisture, aeration and temperature was made in an effort to explain plant growth differences between the various treatments. Immediately following the application of freshly ground corncobs as either surface mulches or soil mixtures a large reduction in the nitrate level of the soil occurred. The data from the aeration study indicated that the oxygen content of the soil air was also very low at this time. Growth records showed that a reduction in the amount of linear growth waC m&de b^ the plants of the mulch treatments after 'applying the fresh corncobs. The aeration study indicated that although the percent­ age of aggregation, average diameter of the aggregates, total porosity and percentage of non—capillary pore space were increased in a soil beneath a surface mulch of ground corncobs, the percentage of the oxygen in the soil atmosphere was less than the oxygen content in the soil of the non-mulch treatments. Fluctuations in the soil temperature were greater In the soil of the non-mulch treatment than in the soil of the mulch treatments, X*Jt.% -v'< A * d 3 V*f> Moisture retention was much greater in tbe soil of the mulch treatments ...than those of the non-mulch treatments. The plfints in the outside rows produced 39$ more flowers during the summer period and 24$ more flowers during the win­ ter period than did the plants of the center rows. results were found for linear growth. Similar The plants along the southern and northern edges of the benches produced 49.4 and 47*9$ more flowers during the summer than the same plants produced during the winter*. The center rows of plants produced 38.0 and 41.9$ more flowers in the spring than In the winter* In both the first and second experiments the largest production of flowers, linear growth and weight ©f vegetative growth were made by plants grown in the sell with mulch treatments. The growth and flower production of the 10 and 20$ mixture treatments exceeded those of the soil treatment. The thesis contains 17 tables and 9 figures*. TABLE OF CONTENTS Page INTRODUCTION ......................................... 1 REVIEW OF LITERATURE.................................... 3 Soil F e r t i l i t y .................................... ^ Soil Aggregation . . . . . . . . . ............... Soil Moisture................................. 6 . Soil A e r a t i o n................. Soil Temperature 9 11 . . ............................. 13 EXPERIMENTAL PROCEDURE Experiment O n e .........* . . . . . . 1? Experiment Two Treatments........... 20 Description of methods and materials... ....... 20 Growth measurements ......................... 22 Soil temperature, moisture, and aeration . . . . 23 RESULTS Experiment O n e ................................ 25 Fertility level and pH of s o i l ...............25 Aggregation and water penetration of soil . . • 2? Quantity and quality of flowers and growth. . . 29 Experiment Two Nitrogen level of the soil and Increase ......................... 31 in linear growth Page Moisture retention of the soil and soil d r a i n a g e ........................... .32 Aeration of the soil . ......................... 34 Temperature of the soil and Increase in linear g r o w t h ........................... . 37 Plant variability due to position within the bench . . . . . .................... 42 Linear growth differences between treatments............... 45 Fresh weight differences between treatments . ................. 45 Flower quality and yield ................... .48 DISCUSSION.............................................53 S U M M A R Y ........................... 59 APPENDIX TABLES 6l ..................................... BIBLIOGRAPHY...........................................62 LIST OF TABLES TABLE Page 1. Soil Nitrogen in Various Combinations of Soil and Corncobs........................... 25 2 Soil pH in Various Combinations of Soil and Corncobs........................... 2? 3 Soil Aggregation as Influenced by Various Depths of Corncob Mulches 4 5 ............ 28 Water Penetration as Effected by Various Combinations of Soil and C o r n c o b s ......... Total Number of Flowers, Amount of Linear Growth and Fresh Weight, as Influenced by Mulches and Mixtures of Ground Corncobs . . . . . 29 30 6 The Delayed Effect of Corncobs on Linear Growth ........................... 32 7 Part I: Oxygen Content of Soil Solution .... 35 Part II: Oxygen Diffusion H a t e ................. 35 8 Part I: Oxygen Content of Soil Solution . . . . 36 Part II: Oxygen Diffusion R a t e ............... . 3 6 9 Daily Soil Temperatures in Various Combinations of Soil and C o r n c o b s ............. 37 10 Yield of Flowers and Linear Growth . . . . . . . 40 11 Flower Production, Variability Between Seasons and Treatments . . . . . ............. 43 Linear Growth, Variability Between Seasons and Treatments ............ 44 12 13 . . . . . . Linear Growth as Influenced by Soil Mulches or Mixtures of Ground Corncobs . ............. 46 TABLE 14 15 1 2 Page Weight of Vegetative Growth as Influenced by Soil Mulches or Mixtures of Ground Corncobs ................... 4? Quality and Yield of Flowers Influenced by Soil Mulches of Ground Corncobs and Mixtures of Soil and Ground Corncobs . * . . . 49 Appendix Table: Mineral and Dry Weight Content of Several Organic Mulches . . . • • • Appendix Table: Effect of Corncobs on Aggregation and Porosity . . . . . ........... 6l 61 LIST OF FIGURES FIGURE I II Page The Greenhouse Bench and Wooden Shelf to Support P o t s .......................... 19 The Ratio of Corncobs to Soil In the Mixture Treatments.......... . • • • . 19 III The Planting Plan of the B e n c h e s ............... 21 IV Moisture Retention After Saturation with Water . ........................ 33 V Soil Temperature Along the Southern Row of the Bench ............................ 39 VI VII VIII IX Soil Temperature Beneath Mulches In the Winter After Saturation with Water • . • . Al Weight of Vegetative Growth of the Mulch and Mixture Treatments in Excess of the Soil Treatment ............ 50 Length of Vegetative Growth of Mulch and Mixture Treatments in Excess of the Soil T r e a t m e n t ........ ............ . . 51 Number of Flowers of Mulch and Mixture Treatments in Excess of the Soil Treatment................................... 52 INTRODUCTION Decaying plant material is the primary source of organic matter in the soil. The roots of plants are an im­ portant source of organic matter, but the residue of the above ground parts of the plant must be returned to the soil if an adequate organic content is to be maintained. Plant residues cannot be permitted to remain on the surface of greenhouse soils when their presence stimulates the devel­ opment of infectious diseases and insects. Animal excrement, usually cow manure, was the primary source of organic material applied to greenhouse soils be­ fore and during the early part of the twentieth century. The red^"ednnurmber of animals on the farm and in the cities has increased the cost of animal manure and limited its use as a source of organic matter to greenhouse soils. There has been an increasing trend in recent years toward apply­ ing plant residues as organic matter. Ground corncobs have been one of the many materials recently tested. Within the past five years the application of ground corncobs as a mulch for roses has been extensively adopted in commercial greenhouse production. The value of applying this material has been questioned within the past few years. 2 The lack of adequate research and the conflicting reports concerning the value derived from ground corncobs were stimuli for the initiation of the present experiment. REVIEW OF LITERATURE Preparation of greenhouse soils has been found to be especially important because de-terioration of soil structure was accelerated by the intensive soil cultivation. Optimum environmental conditions for plant growth have favored the decomposition of organic matter. The degree of soil aggrega­ tion has been found to be closely associated with aeration and water retention of the soil (Baver, 19^8 ). The use of organic mulches on soil or mixtures of soil and organic matter in the production of greenhouse crops has been a common commercial practice for many years (Chadwick, 19^ 8 ), While cow manure has been the most common material used, others such as peat moss (Laurie, 1930), straw and hay (Chadwick, 19^8 ), leafmold and blue grass (Laurie, 1939) have been substituted frequently. Chadwick (19^8 ) found that ground corncobs were an exceptionally fine mulching material for both greenhouse and garden roses. The major effects of heavy applications of organic mat­ ter to greenhouse soils, as mulches and mixtures, have beens conservation of moisture (Brase, 1937)> temperature regulation (Shanks and Laurie, 19^9)> increased quantity of available nutrients (Galle and Chadwick, 19^8), and improvement in aer­ ation (Boiler and Stephenson, 19A6 ). Soil Fertility Applications of fresh organic mulches of straw to orchard soils have been shown to greatly increase the quan­ tity of several of the essential nutrient elements (Havis and G-ourley, 1935)* They found that readily available phos­ phorous was increased 7 to 8 times over that found in the surface 6 inches of cultivated soil and twice that found in the 6 to 12 inch level. Potassium was increased 3 to ^ times at all levels to depths of Zk Inches. Exchangeable calcium was shown to have increased in the surface 6 inches, and mag­ nesium in the surface 12 inches as a result of straw mulch. Mulches also prevented the fixation of potassium. The potas­ sium which they applied to the surface of the cultivated soil was often fixed in the upper few inches because of the pres­ ence of free aluminum and the effect of alternate wetting and drying of the surface layers. There has been little information dealing directly with the accumulation of nitrogen under mulches, but Proebsting, 1937> indicated considerable increase over a three year period. It was probable that an initial reduction in soil nitrogen occurred under some organic mulches because of bac­ terial action (Stephenson and Schuster, 19^5)• When materials high in carbon and low in nitrogen {such as straw, cornstalks, or corncobs) were applied to the soil or incorporated in it, soil bacteria were greatly increased in number due to the in- crease in carbohydrate (Chadwick, 19^8 ). These bacteria utilize nitrogen which otherwise would be available to the crop. Although this effect was only temporary, Chadwick rec­ ommended that care should be exercised to avoid nitrogen starvation. Chadwick (19^-8) believed that it was not advis­ able to mix fresh corncobs with soil because this mass of raw organic matter was so great it would be difficult to add enough nitrogen to satisfy the requirement of the microorgan­ isms without causing injury to the plants. In contrast to Chadwick^s conclusions, Eastwood and G-ianfagna (1951) reported that no decrease in the nitrate level of the soil occurred immediately after applying a mulch of fresh corncobs. Their records showed no significant dif­ ference in the amount and kind of fertilizer required by a crop of greenhouse roses grown with or without a corncob mulch. Bell (1936) found evidence that alfalfa, when applied as a mulch, had an inhibitory effect upon the growth of chrysan­ themums. Lack of nitrogen was not given as the cause of re­ duced weight of plants grown with a mulch treatment but, in­ stead, Bell postulated that the readily decomposable organic matter produced toxic substances which inhibited growth of chrysanthemums. Over a period of 7 years, 19*40-^6, pine straw and oat straw as surface mulches had no effect on the acidity of orchard soil while cornstalks Incorporated In the soil had a slightly alkaline effect (Johnson and Ware, 1950). 6 Waksman (1932) showed that organic acids formed from polyand mono-saccharides, proteins, and their derivatives, when neutralized, were utilized by bacteria and fungi. The decom­ position of these acids resulted in the formation of alkali carbonates which led to an alkaline reaction of the medium. Appendix Table 1 (after Chadwick, 1948) gives the Com­ parative mineral and dry weight content of several organic materials. On the basis of the analysis given, ground corn­ cob mulch would be expected to be less effective than straw, hay and hops in building up the mineral content of the soil. Soil Aggregation Soil structure has been defined as the arrangement of particles of soil into certain definite patterns. The type of this arrangement varied with the amount and nature of the secondary particles or aggregates (Baver, 1948). Yet the de­ gree of soil aggregation was closely associated with the or­ ganic matter content of the soil and microbial activity (Mar­ tin and Waksman, 1940). Martin and Waksman (1940) observed that the growth of microorganisms led to a binding together of soil particles that increased soil aggregation. The extent of aggregation was found to be dependent upon the nature of the microorgan­ isms and the nature of the substrate. The type of organic matter Influenced the effectiveness of organisms in their ability to alter the aggregation of the soil. Organic matter 7 containing a high sugar content was a better source of energy for growth of microorganisms than was one high in cellulose. The more readily the complex organic materials decomposed, the greater was the degree of aggregation of the soil parti­ cles. McCalla (19^2 ) observed that adding sucrose to the soil increased the development of mycelia which greatly increased the stability of aggregates. In addition to the direct me­ chanical effects of the mycelia, the suggestion was made that the organisms apparently produced gums or waxes. He suggest­ ed that these may have coated the soil particles and rendered the individual aggregates impermeable to water. In 19^, it was shown by Ray that with roses grown in greenhouse benches, additions of sugar at the rate of two pounds to 100 square feet greatly Increased granulation of the soil. This was more effective on old soils than those which were more recently placed in a greenhouse bench. He concluded, however, that such applications were too costly for practical use. The effect of ground corncobs on soil aggregation and soil porosity was investigated by Chadwick (19^8). He filled five-gallon glazed crocks with steam sterilized silt loam soil. Treatments were made contrasting two inch surface mulches of old and new corncobs. After 2-§- months the soil was analyzed for aggregation and porosity. The results (Ap­ pendix Table 2 ) indicated that some substances were being leached from the fresh corncobs and either directly or indi­ rectly brought about the increase in soil aggregation. The chemical composition of corncobs on a dry weight basis as re­ ported by J. H. Salisbury (19^8) was as follows: sugar 6 .8$; resin 0 .9$; fiber 63.8$; extract from fiber 22.7$; albumin 0 .8$; casein 0 .1^$; dextrine 1 .15$; glutinous material 3#7$> and starch, a trace. G-ourley and Havis (1935) found that an organic matter mulch gradually increased the organic content of the soil di­ rectly beneath the mulch. By applying a mulch of wheat straw in an orchard and comparing the amount of organic matter in the soil beneath the mulch with that in a similar cultivated soil, Godrley and Havis showed a range of 4.3$ of organic matter in the upper two inches of soil compared to only 1 .9$ in the upper two inches of a cultivated soil. The increased quantity of organic matter under a mulch of ground corncobs was indicated for garden roses by Chadwick (19^8). A comparison of the amount of organic matter present after three years showed 20$ under ground corncobs, 7 «2-5$ un­ der a sod of Chewing9s fescue, 11$ under a peat moss mulch, and 8 .5$ where cultivation was practiced. Soil Moisture The conservation of soil moisture has resulted from ad­ ditions to the soil surface of innumerable organic materials. A reduction In the amount of moisture lost from the soil has been shown as a result of the use of surface mulches of straw walnut leaves and sawdust (Boiler and Stephenson, 1946); var­ ious grass sods and straws (Langford, 1937); paper (Thompson and Platenius, 1931); peat moss (Turk and Partridge, 1941); sawdust, seaweed, and meadow hay (Latimer and Percival, 1944) Lespedeza serlcea hay and farmyard manure (Mooere, Washko and Young, 1946); and corncobs (Chadwick, 1948). Stephenson and Schuster (1945) found that a straw mulch retained a moisture equivalent to 2 or 3 inches of rainfall during a dry growing season, a moisture saving that was prin­ cipally in the upper 2 feet of soil. Eser (1884) reported that 8 times more water was lost from a bare soil than from the soil under a 2 inch surface mulch of chopped straw, beech leaves, pine needles, or fir needles. He concluded that a mulch protecting the surface from the direct rays of the sun and from x?ind currents, reduced the soil temperature. Peat moss had such a great absorptive capacity for water that percolation of water through the soil and loss from sur­ face drainage were reduced (Turk and Partridge, 1941). They also found after light rains or very long Intervals between rains that evaporation from a mulch was enormous and this limited the amount of water which reached the soil. Under garden conditions, Chadwick (19^8) found ground corncobs to be more effective than peat moss in conserving soil moisture. The cobs ground into 3/8 to 3/^ inch irregu­ lar shaped pieces did not have the tendency to compact as much as some other types of organic mulches but provided a more uniform distribution of water applied to the surface* The effects of the organic matter content of the soil upon water absorption and availability by plants was found in the data of Feustel and Byers (19365* They reported that mix­ tures containing equal parts of soil and peat moss were capa­ ble of absorbing from *K) to 50 percent more moisture than the soil alone, but the increased evaporation rate and the great­ er moisture content at the wilting point largely counteracted the initially higher moisture-holding capacity* They have recommended that, except on sandy soils, peat should not be used for the sole purpose of conserving a supply of available soil moisture* Smith, Brown and Russell (1937) found that soils high in organic matter have more than double the rate of water pene­ tration of soils with a low organic matter content. It was found by Dudley and Russell (19^1) that crop residues left on the soil surface were much more effective in increasing the Infiltration of water and decreasing evaporation than was the same amount of organic matter plowed into the soil. 11 Soil Aeration Gillespie (1920) devised an electrical method for meas­ uring the amount of redox in the soil. His apparatus con­ sisted of gray platinum wire sealed into glass tubing xvhich was pressed into the soil. A liquid contact was made between the soil and a calomel cell by laying a capillary tube filled with potassium chloride solution on the soil in order to meas­ ure the potential against the calomel electrode. Since an intimate relation has been found to exist between pH and Eh, it was agreed to adapt a value of 0.060 volts per unit of pH change. Gillespie found that when small quantities of dex­ trose ranging from 0.25 to 2.0 grams had been mixed with 200 grams of a loam soil, and when this soil had been kept moist for four days, that even the smallest quantity of dextrose produced a very large reducing effect upon the soil. This indicated a substantial decrease in the oxygen content of the soil. Burrows and Gordon (1936)> adapting Gillespie^s appara­ tus, showed that additions of carbohydrate materials reduced the value of the electrical potential whereas casein had the opposite effect. Andreasen (1951) employed an apparatus similar to that of Haney (19^9)* It consisted of a diffusion chamber that could be inserted to a desired depth in the soil and the chamber flushed and filled with nitrogen at atmospheric pres­ 12 sure. By means of a suitable valve arrangement the lower end of the chamber was opened to the soil atmosphere and the gases were allowed to diffuse Into and out of the chamber for 10 minutes. The chamber was again closed, and the oxygen content of the gas determined by use of a Beckman Oxygen Analyzer. Andreasen (1951) found that applications of organic fer­ tilizers and mulches could cause serious oxygen deficiencies immediately after soils had been heavily watered because the organic materials furnished a substrate for the soil micro­ flora. Andreasen concluded that roots of the higher plants used in his experiment may have been impaired from oxygen de­ ficiency as a result of active competition for oxygen on the part of soil fungi and bacteria. Seeley (19^9) found that the growth of rose plants was not affected initially when the roots were exposed to gases containing 5 > 10 , and 21 percent oxygen in the soil but at the end of 37 days there was a very significant reduction in shoot growth with the lowest concentration of oxygen in the aerating gas. After almost 3 months plants with their roots exposed to a gas containing 5$ oxygen were considerably smaller than those plants at the 10 and 21$ oxygen concentra­ tions. No significant difference was found in the amount of growth produced at the 10 and 21$ oxygen levels. The data of Boicourt and Allen (19^1) revealed that by forcing air through the tile in the bottom of the bench for one hour per day the linear growth of greenhouse roses was 13 nearly double that obtained in the ssjne soil without soil aeration. This great difference in growth resulted from only slight differences in soil oxygen content. Soil Temperature The effect of soil temperature upon growth and flower production has been determined for numerous floricultural crops. Laurie (1939) reported that poinsettias, roses, gar­ denias, gerbera, African violet and other plants benefited from additions of water heated to 70°F. Increased number of flowers per plant and longer stem lengths of calendula and snapdragon were obtained as a result of increasing soli tem­ peratures to ?2°F. (Allen, 193*0* Allen found that the num­ ber of flowers per plant of columnar stocks was not influ­ enced by soil temperature, but flowering was delayed at the 72°F. temperature. A soil temperature of 7^°F. was found by Davidson (itykl) to result in the highest flower production and the least bud drop of gardenias. Soil temperatures of 58°, 66° and 82°F. decreased the number of flowers per plant and increased the bud drop. He concluded that a warm air temperature tended to off­ set the inhibiting effects of a low root temperature and that a cool air temperature reduced the harmful effects of high root temperatures. Ik Kohl, Fosler and Weinard (19^9) reported that a high soil temperature range of 75° to 85°F. significantly reduced the number of roses per plant. Water at 80°F., when applied to the soil in which the roses were growing increased the soil temperature from 66° to 73°F. and resulted in a slight reduction in the average number of flowers produced per plant (Pfahl, Qrr and Laurie, 19^9)• A bench of roses grown in gravel culture with grade B "Haydite" {expanded mica) as a medium showed inhibiting effects upon growth within 17 days after the solution was heated to 90°F. (Pfahl, Orr and Laurie, 19L9 ). Shanks and Laurie in 19^9 conducted an experiment on greenhouse roses in which the root temperatures were varied at k degree intervals from $6° to 72°F, The optimum root temperature for vegetative growth of the top was found to be 6k°F. and there was a decrease in the amount of roots pro­ duced for each plant as the soil temperature increased from 56° to 72°F. Injury to the leaves and the fruit of cucumber was shown to be caused by soil temperatures of 55°F. or lower, (Schroeder, 1937)- He concluded that the cucumber plant was unable to obtain sufficient water at these temperatures to replace that lost through transpiration. Jenny (1928) working with prairie soils reported that the total nitrogen content of soils throughout the United States decreased from north to south; the average nitrogen 15 content decreased by 50 percent with every 18°F. fall In the mean annual temperature. King and Whitson (1902) compared the rate of nitrification at constant temperatures of 35°> ^8°, 68° and 90°F. and found that the rate of nitrification at 90°F. was 6.3 times more rapid than 35° and 68°F. and was about twice as rapid as at ^8°F. At high soil temperatures, Eid, Black and Kempthorne (1951) reported that organic phos­ phorus was rapidly wmineralized” and readily served as a source of supply for the crop, while at low soil temperatures mineralization was limited. Mulches have been found to exert a pronounced effect up­ on soil temperature. Wollny (1883) made comparisons between the daily temperatures of bare soil and soil that was covered with grass. He found that the major fluctuation in tempera­ ture of the subsurface of the grass-covered soil was about 3.5°c.; that of the bare soil was about 11°C. Chadwick (19^8 ) reported that temperatures are more uniform under mulches and during the hot summer months may be as much as 10-15 degrees cooler. He indicated that under outdoor con­ ditions a mulch of ground corncobs was not as effective in reducing temperatures as peat moss or a live cover of Chew­ ing® s fescue or bluegrass. Mooers, Washko and Young (19A6) concluded that the effectiveness of some mulches was reduced more than other mulches the second and third year after appli­ cation. Turk and Partridge (19^7) found that the effective­ 16 ness of an artificial mulch varied greatly with the kind of mulch, type of soil, and climatic conditions. EXPERIMENTAL PROCEDURE Experiment One Ninety-six rose plants of the variety Peter®s Briarcliff were removed from five-inch pots, the soil washed from the roots, and placed in storage at Ao°F. for three weeks. The plants were then pruned and weighed so that they could be placed into groups consisting of eight plants of approx­ imately equal weight. The inside of the twelve-inch clay pots was painted with an asphalt emulsion paint and a glass Jar five inches in height fitted against the opening in the bottom to collect the leachate. of six-hundred cubic Inches. Each pot contained a media The roses were planted in the pots August 23, 1950. Treatments consisting of 1, ground , and A inch depths of corncobs applied as surface mulches, as well as 16, 33, and 66 percent corncobs by volume were prepared. Treat­ ments consisting of soil with no additions of ground corncobs and corncobs with no additions of soil were added for compar­ ative purposes. All treatments were replicated twelve times and randomized throughout the bench. A special wooden shelf was constructed on the greenhouse bench to support the pots (Fig. I) which were contiguous in rows four inches apart resulting in plant spacing of twelve by sixteen inches. Fig. II shows the ratio of corncobs to 18 soil in the mixture treatments. The prescribed proportions of corncobs and soil were mixed before planting the roses, the mulch applications were applied immediately after planting. The mulches were in excess of the six-hundred cubic inches of soil, therefore requiring the height of the pot be increased to contain the organic material. As a guide to the amount of soil nutrients required by each plant in each treatment, a preliminary trial was con­ ducted using the same sterilized Miami clay loam soil in the following manner. Twenty-four 200 gram samples of a previous­ ly sterilized Miami soil were placed in 500ml beakers. Various amounts of chemically pure sodium nitrate, potassium sulfate, and monocalcium phosphate were applied in an effort to find the amounts of these fertilizers necessary to increase the fertility level of the soil to 50 ppm. nitrate, 10 ppm. phos­ phorous and 30 ppm. potassium. The beakers were covered after moistening the soil to field capacity and left one week. A soil sample was then taken from each beaker and the nitrate, phosphate and potassium levels determined by the modified Spurway Method (Spurway and Lawton, 19^9)• Soil samples were taken before planting, at weekly in­ tervals for ten weeks and bimonthly thereafter. The result of each analysis was used as a basis to maintain soil fertil­ ity within the desired range. Distilled water was applied during the first six months and tap water during the second half year. All leachates were re-added. Fig. I THE GREENHOUSE BENCH AND WOODEN SHELF TO SUPPORT THE POTS Fig. II THE RATIO OF CORNCOBS TO SOIL IN THE MIXTURE TREATMENTS 19 20 The weight and linear measurement of the individual plants were obtained at the time of planting and the measure­ ment of linear growth was obtained at the end of each month. The number of flowers produced, the length of the peduncle and the weight of the flower were recorded. Fifty days after planting, samples of soil were removed from the check and mulch treatments for an aggregate analysis of the soil. Determinations of the soil pH were made period­ ically by the use of the glass electrode. Experiment Two Treatments. As a result of the first experiment a more extensive, yet more refined procedure was adopted for the second experiment. The following five treatments were included: 1} a twoinch depth of ground corncobs as a mulch, 2) a four-inch depth of ground corncobs as a mulch, 3) ten percent by volume of ground corncobs mixed with the soil, 4) twenty percent by volume of ground corncobs mixed with the soil and 5) onehundred percent soil. The mixture and mulch treatments were replicated four times and the soil treatment was replicated only twice; each replication consisted of twenty plants. (Fig. III). Material. The 360 dormant rose plants of the variety Better Times used in these treatments were selected from kOO plants, each of which was weighed individually and grouped BENCH PLANTING- PLAN 21 o dJ s -=J- o CM iH *H O CQ « CM O H 5- Cvl O H O CM s O iH o CM -3- ■3- O CM H •H O CQ — CM O i—I i- 1____ 2 o _ CM fQ «) PQ 22 into lots containing plants weighing from; 20.0 to 2^.9 gms, 25.0 to 29.9 gms, 30.0 to 3^.9 gms, 35.0 to 39.9 gms, *K>.0 to ^ . 9 gms, U5.0 to ^9.9 gms, 50.0 to 5^-9 gms. Plants for each treatment were selected so that there was the same num­ ber of plants from each weight group and the total weight of plant8 per plot was approximately equal. Method. The planting was in a Conover loam soil on April 4, 1951 according to the plan shown in Fig. Ill, The plants were syringed twice daily xvith water until growth was renewed. Greenhouse temperature regulation, ventilation and other cultural practices were followed as required for best plant development. During the first two months all buds were removed including a part of the stem and the uppermost fivefoliolate leaf. Corncob applications were made at six month intervals to maintain the desired depths of mulch; no corn­ cobs, other than the original applications, were added to the mixture treatments. Immediately after the applications of ground corncobs either as mixtures or mulches, biweehly soil testing (modified Spurway Method, 19^9) was made to study the modifying effect upon the fertility level of the soil. The first flowers were cut on July 1, 1951 and cutting continued until the termination of the experiment on October It 1952. Growth measurements. The collection of data was accel­ erated by the use of Individual record cards, one for each 23 plant, to facilitate the use of International Business Ma­ chines (IBM). Cards were clamped to each flower before cut­ ting it from the plant so that the weight of the flower and length could be recorded on the card as well as the monthly linear growth measurement of the plant. At the termination of each month the information was transferred to standard I.B.M. cards for rapid summarization. Weight and length of non-flowering growth removed in a gradual cutback, final meas­ urement of length and weight of each plant as well as weight of roots at the end of the project were recorded in a similar manner. Soil temperature. Soil temperature studies were con­ ducted in January and August to determine the effect of the various treatments upon the temperature of the soil under ex­ treme greenhouse and water temperatures. Thermometers were placed in each plot; the bulbs were inserted 2 inches below the soil surface and after saturation of the soil, tempera­ ture readings were taken at regular time intervals for the following 2k hour period. Soil moisture. Bouyoucos nylon moisture blocks buried in each plot, (Bouyoucos, 19^2), provided moisture retention comparisons between treatments. The percentages of available moisture were obtained by use of the Bouyoucos electrical re­ sistance bridge at 12 hour intervals after saturation of the soil. Water retention studies were also conducted in conjunc­ tion with soil aeration. 2k Soil aeration. An apparatus for soil aeration study was patterned after the one used by Erickson and Lemon (1952). Platinum microelectrodes of Pyrex glass tubing, k mm in diam­ eter, were drawn to a taper with a short 25-gauge platinum wire sealed Into the glass to allow *4- mm of exposed wire to protrude from the sealed end* A mercury-copper wire contact was made in the usual way with the platinum wire inside the glass tubing. This electrode was then forced into the soil to a depth of 2 inches. The large calomel cell with a ground glass joint attached was slightly but firmly pressed into the surface of the soil to make good contact with the moisture films of the soil. The leads from the calomel and platinum electrodes were connected to a voltage of 0.8 volts across the two electrodes to measure the current flow when the cir­ cuit was closed. In the soil aeration study two readings were made from each electrode. The original reading, which was recorded im­ mediately following Insertion of the electrodes into the soil, reduced the oxygen in the soil solution at the platinum wire surface. This reading lacked the accuracy of the second read­ ing because if the k mm of exposed wire protruding from the sealed end of the electrode was lodged in a large non-capil­ lary pore a higher reading would be obtained than if this did not occur. The second reading (after 5 minutes) measured the reduction of the quantity of oxygen which had diffused into the area of the exposed platinum wire during a 5 minute inter­ val following the initial reading. RESULTS Although similar results were obtained from experiment one and experiment two, the results are presented separately to emphasize definite phases of the results. Experiment One Fertility level. Equivalent quantities of chemically pure nitrate, phosphate, and potassium compounds were applied to the soil in each of the 96 pots. Soil samples were re­ moved and tested August 23» 1950» "the day before the applica­ tions of corncobs and the planting of the roses. The extent of the nitrate reduction was revealed upon testing the soil samples taken one week later, (Table 1). Table 1 SOIL NITROGEN IN VARIOUS COMBINATIONS OF SOIL AND CORNCOBS (Average of Twelve Soil Samples) Treatment Day before planting After one week After five weeks ppm Soil ppm 52 36 ppm k6 1N mulch 5^ 19 38 2^w mulch 52 15 35 55 13 30 mulch 26 Table 1 - continued Treatment After one week After five weeks Soil ppm 52 ppm 36 ppm 46 16$ mixture 59 11 37 33$ mixture 56 7 32 66$ mixture 56 8 25 Day before planting Chemically pure 3odlum nitrate at the rate of 2.75 a-n(33.20 grams respectively was added to each plant containing a surface mulch and each plant of the mixture treatments. Five weeks after planting the bi-weekly sodium nitrate applications had increased the nitrate level of the soil. The original pH of the soil was 6.5* Two and one-half weeks after planting the soil pH had increased as shown in Table 2. Additions of ammonium and iron sulfates had partially reduced the alkalinity to produce the pH readings listed in Table 2 "after five weeks." Table 2 SOIL pH IN VARIOUS COMBINATIONS OF SOIL AND CORNCOBS (Average of Three Soli Samples) Treatment After two and onehalf weeks After five weeks Soil 6.7 6.3 1M mulch 7.2 6.7 2iM mulch 7.1 6.6 mulch 7.1 6.9 16$ mixture 7.6 7.0 33$ mixture 8.1 7.2 66$ mixture 8.3 8.0 Corncobs 8.2 8.3 Aggregation. An aggregate analysis of soil samples fifty days after planting the roses revealed an increase soil aggregation resulting from the presence of surface mulches of ground corncobs (Table 3). 28 Table 3 SOIL AGGREGATION AS INFLUENCED BY VARIOUS DEPTHS OF CORNCOB MULCHES (Average of Three 25 Gram Samples of Air Dry Soil) Sieve Soil 1“ mulch mm gm gm gm gm 4.00 0.00 0.03 0.04 0.54 2.00 0.05 0.39 0.41 3.4? 1.00 0.63 0.94 1.07 2.85 0.50 1.06 1.91 1.67 2.53 0.25 4.54 6.95 6.42 4.62 0.11 1.11 2.04 1.84 4.12 Total 7.38 12.26 11.45 18.13 Zi" mulch 4“ mulch Water penetration. Water penetration of the soil was more rapid in the mulch and mixture treatments than the control treatment. The number of minutes required for one-half gallon of water to penetrate the soil of the various treat­ ments is shown in Table A.. 29 Table A WATER PENETRATION AS EFE’ECTED BY VARIOUS COMBINATIONS OF SOIL AND CORNCOBS (Average of 12 plants) Treatment Sept. 2A, 1950 July 30, 1951 Minutes Minutes 108 A20 I1* mulch A9 A5 2§w mulch 38 30 A'1 mulch 32 2? 16$ mixture 1A 31 33$ mixture 6 12 66$ mixture 2 3 Corncobs 0 0 Soil Quantity of flowers. The total number of flowers produced during a nine month period from December 15, 1950 through August 1A, 1951 as well as the total linear growth and weight increase from August 2A, 1950 through August 1A, 1951 are shown in Table 5« 30 Table 5 TOTAL NUMBER OF FLOWERS, AMOUNT OF LINEAR GROWTH AND FRESH WEIGHT, AS INFLUENCED BY MULCHES AND MIXTURES OF GROUND CORNCOBS Treatment Flowers Linear Growth Fresh Weight (m) (Kg) Soil 286 127 ^.91 1M mulch 338 170 7.10 315 151 6.1^ 418 mulch 36^ 180 7.38 16% mixture 283 132 5.29 33$ mixture 193 91 3.72 66$ mixture 77 39 1.5^ Corncobs 32 10 .38 mulch Experiment Two Nitrogen level. A reduction in the nitrate level re­ sulted Immediately after incorporating ground corncobs with the soil, but tests of the mixture treatments revealed that nitrate applications had eliminated this deficiency within 10 days. A slight increase in the soil pH developed one week after mixing corncobs with the soil. The pH of the control treatment was 6.8, the 10$ mixture treatment 7.3 and the 20$ mixture treatment 7.7; within one week a reduction In pH value occurred where no additions of acidifying materials were made. Yet no reduction in the amount of linear growth of the plants resulted during this period. In the ground corncob mulch treatments, applied six weeks after planting when the plants were actively growing, the nitrate level of the soil decreased from 40-48 to 9-14 ppm. nitrate over a two week period. This increase occurred al­ though a total of four grams of ammonium nitrate containing 33$ nitrogen had been added to each plant during the same period. Three weeks after applying the mulches, the nitrate level had increased to at least 25 ppm. for all mulch plots. The reduction in the amount of linear groxrth shown in Table 6 was related to the reduction in nitrogen content of the soil. 32 Table 6 THE DELAYED EFFECT OF CORNCOBS ON LINEAR GROWTH (Control Treatment AO Plants, Others 80 Plants) Time in Relation to Application of Corncobs Treatment One Week Before Three Weeks After Seven Weeks After cm cm cm One Year After cm Soil 2,535 6.192 15,631 81,560 2M mulch 5,010 12,079 29,478 181,028 mulch 5,171 10,964 29,229 190,647 10$ mix. 6,28A 14,39** 35,068 179,022 20$ mix. 5,^83 14,693 35,644 184,354 Moisture. surface mulches. Moisture retention was greatest beneath the The soil treatment maintained the least moisture retention, the poorest drainage, and the shortest time Interval in the high moisture range (Fig. IV). Only slightly more moisture was retained by incorporating the corncobs into the soil. The soil moisture readings corresponding to the time in­ tervals at which the aeration determinations were made have been included in the averages of the moisture retention data (Fig. XV). PERCENTAGE OF AVAILABLE MOISTURE o O o H* (Averages RETENTION SATURATION Figure IV AFTER SATURATION WITH WATER WITH WATER mulch, 10 and 20$ mixtures; six replications) IN HOURS AFTER MOISTURE 2 and TIME cc O CD Gn O ro o o 3^ Aeration. The soil atmosphere of the mixture and con­ trol treatments contained more oxygen than those of the mulch treatments. Cracking of the soil in the non-mulch treatments resulted when the soil moisture was reduced below ^5% mois­ ture. The oxygen content of the soil during a A8 hour period after soil saturation is shown in Table 7. The soil aeration study was repeated one month later, but, additional corncobs were applied a week earlier to the mulch treatments to maintain the prescribed depths. Approx­ imately a half inch layer of freshly ground corncobs was ap­ plied to the plots of the two inch mulch treatment and ^ to 3/k. of an inch of mulch was added to the plots of the A inch mulch treatment. Soil aeration readings revealed that the oxygen content of the soil atmosphere beneath the mulches had been reduced below that of the previous month. The aeration of the mixture and the soil treatments was similar to that found earlier, Table 8. 35 Table 7 PART I: OXYGEN CONTENT OF SOIL SOLUTION (Averages of 10 Electrode Readings at 2" Depth, September 1-3, 1952) Time 2U mulch mulch Treatments Control 10$ mix. 20$ mix After 12 hrs. ^8 2k hrs. 35 25 58 2k ^3 36 hrs. Ik 17 62 36 28 ^8 hrs. 33 37 5k 50 k? PART II: Headings in Microamperes 38 30 3k 52 0XZG-EN DIFFUSION RATE ~ READING-S AFTER FIVE MINUTES (Averages of 10 Electrode Readings at 2W Depth) Time 2W mulch kn mulch Treatments Control 10$ mix. 20$ mix Readings in Microamperes After 12 hrs. 3.6 3-3 2.0 5.3 6.k 2k hrs. 2.5 2.8 6.1 3.1 5.8 36 hrs. l.k 1.7 Q.k k.2 2.6 kQ hrs. 3.8 k.2 8.9 6.2 k.9 36 Table 8 PART I: OXYGEN CONTENT OF SOIL SOLUTION (Averages of 10 Electrode Readings at 2n Depth, October 3-5, 1952) Time 2'*'mulch A®1 mulch Treatments Control 10$ mix. Readings in Microamperes A0 32 37 20$ mix. After 0 hrs. 35 12 hrs. 15 12 A5 77 5A 2A hrs. 7 7 82 79 70 36 hrs. 11 8 79 82 75 A 8 hrs. 16 8 80 67 73 60 hrs. AA 31 PART IX; 55 OXYGEN DIFFUSION RATE ~ READINGS AFTER FIVE MINUTES (Averages of 10 Electrode Readings at 2W Depth) Time 2* mulch AM mulch Treatments Control i mix. 20$ mix. 2.5 Readings in Microamperes 2.6 2.9 2.5 3.5 12 hrs. 1.3 1.1 2.9 7.1 A .6 2A hrs. .7 .6 6.7 8.1 ^.3 36 hrs. .9 .A 9.5 9.5 11.7 A8 hrs. 1.2 .6 10.1 9.1 10.2 60 hrs. 3.1 2. A After 0 hrs. 37 Soil temperature. A lower dally maximum soli tempera­ ture as well as a more uniform soil temperature were main­ tained during the summer months beneath the mulches. The soil temperature readings for an 18 hour period obtained from thermometers inserted in the soil in a central location of each plot are listed in Table 9 . Table 9 DAILY SOIL TEMPERATURES IN VARIOUS COMBINATIONS OF SOIL AND CORNCOBS {Average of 3 Thermometer Readings) Time 2*® mulch ^®® mulch deg. F. 10 A.M. deg. F. 72 Treatments Soil 10$ mix. 73 deg. F. 70 deg. F. 70 20$ mix. deg. 69 1 P.M. 76 7^ 85 8^ 82 k P.M. 78 76 82 82 81 7 P.M. 81 79 79 79 79 10 P.M. 79 77 7^ 75 75 1 A.M. 75 76 73 73 73 k A.M. 74 75 70 71 71 38 The soil temperatures in the southern one-fourth of the bench during an eighteen hour period are shown graphically in Figure V. The presence of the mulches reduced temperature fluctu­ ations in the soil along the southern edge of the bench# The dally soil temperature variations over an 18 hour period for the non-mulch treatments was 80° £10°F. compared with daily soil temperature fluctuations of 75° £5°F. for the mulch treatments# The soil temperatures of the various treatments were,uniform after saturation of the soil with water. Soil temperature of the check treatment had Increased 19°F. com­ pared to a soil temperature rise of only 2°F. beneath a Ut inch mulch when temperatures were recorded three hours after the application of the water. The soil temperature of the con­ trol treatment remained higher than the soil temperature be­ neath the mulch until 8:30 P.M. in the evening (Fig. V). Fewer flowers and less linear growth were produced by those treatments where soil temperatures became excessively high# This relationship is shown in Table 10. Soil Temperature - Deg. F. o v_r\ 00 o oo Vj\ vO o H O H* I-1 CD O tn o 3 ca ct rr o Q M H* o SB c+ H* O 3 m 6C ROW OF BENCH CD H O SOUTHERN P H O tr ALONG K> S» 3 P' -P SOIL TEMPERATURE $ 4 P> m H 40 Table 10 YIELD OF FLOWERS AND LINEAR GROWTH (Average of 20 Plants; July, August and September, 1952) Flowers Linear Growth Soil 13-5 cm 631 10$ corncobs 90$ soil 12.4 618 20$ corncobs 80$ soil 13.6 551 2™ mulch on soil 15.4 735 4W mulch on soil 16.2 709 Treatment During the winter months saturation of the soil with water having a temperature of 43°F. resulted in cooler soil temperatures beneath the mulches than in the other treatments. The data in Table 11 indicated that there was no appar­ ent difference in either flower production or In the amount of linear growth made by plants in any treatment during the fall and winter periods. ki o o o vo A ’33CI 3HftXVH3