EFFECTS OF SURFACE RESIDUE LEVELS ON PLANT AVAILABLE SOIL MOISTURE IN MONOCULTURE WHEAT PRODUCTION IN OKLAHOMA By Alan Jeffrey Corr II Bachelor of Sc1ence Un1versity of Nebraska L1ncoln, Nebraska 1978 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE December, 1986 \t:19~ c:;a.,~jQ C!~, ........,. cAZf'e- d... ... EFFECTS OF SURFACE RESIDUE LEVELS ON PLANT AVAILABLE SOIL MOISTURE IN MONOCULTURE WHEAT PRODUCTION IN OKLAHOMA Thesis Approved: Dean of the Graduate College 1263951 i i PREFACE I wish to express my sincere gratitude to all persons who have assisted me in the development of this thesis, and to all who helped me through my graduate program at Oklahoma State University. In particular, I wish to thank my thesis advisor, Dr. Eugene G. Krenzer, for his guidance and help. Also, I wish to thank the other committee members, Dr. James H. Stiegler, Dr. David L. Weeks, and Dr. John F. Stone for their ass1stance 1n the preparation of this thesis. The aid of Mr. Mark Hodges, project Senior Agriculturist, in all field work is deeply appreciated. I am also indebted to. Senior Agricultur1sts Mr. Harold R. Gray, and Mr. Joseph R. Williams for the1r time and assistance given in the laboratory work for th1s project. A special thanks, and my deepest appreciation go to my wife Gwen, and daughter Casy for their understanding and support of my continued education. I would also like to thank both mine, and my wife's parents for their financ1al and moral support of my educat1onal program. 1 i 1 TABLE OF CONTENTS Chapter Page I • INTRODUCTION 1 II. PREVIOUS WORK AND LITERATURE REVIEW 3 III. MATERIALS AND METHODS 9 IV. RESULTS AND DISCUSSION . 14 SELECTED BIBLIOGRAPHY . 22 APPENDIXES • • 25 I APPENDIX A - TILLAGE DATES, FIELD CONDITIONS, AND RESULTS • • • • • • • • •• 25 APPENDIX B - SOIL WATER CONTENT DATA . 37 lV LIST OF TABLES Table Page I • Summary of Herbic1de Applied, Date of Application, and Rate of Appllcation • 26 II. Summary of In1tial T1llage Dates, Planting Dates, Seed1ng Rates, and Harvest Dates . • 27 I I I. Effect of Tillage Treatment on Soil Bulk Density for 75-225 mm Depth . • 27 IV. Water Held in So1l at a Tension of 1.5 MPa for Various 'Soll Classes in the Study . 28 v. Percent Ground Cover after Plant1ng as Affected by Tillage . • 28 VI. Ranking of Treatments in Total Water by Depth over Time. 1982 . • 29 VI I. Ranking of Treatments in Total Water by Depth over Time. 1983 . • 30 VI I I. Ranking of Treatments 1n Total Water by Depth over Time. 1984 . 31 IX. Ranking of Treatments in Total Water by Depth over Time. 1985 . • 32 x. Rank1ng of Treatments in Plant Available So1l Water by Depth over T1me. 1982 . 33 XI. Ranking of Treatments in Plant Available So1l Water by Depth over T1me. 1983 . 34 XII. Ranking of Treatments in Plant Available So1l Water by Depth over Time. 1984 • 35 XIII • Ranking of Treatments in Plant Ava1lable Soil Water by Depth over Time. 1985 • 36 v LIST OF FIGURES Figure Page 1. Plant Available Water Content of the 1.6 m Soi 1 Profile. 1982 . 38 2. Plant Available Water Content of the 1.6 m Soil Profile. 1983 . 39 3. Plant Available Water Content of the 1.6 m Soil Profile. 1984 . 40 4. Plant Ava1lable Water Content of the 1.6 m So1l Profile. 1985 . 41 5. Total Water Content of the 1.6 m Soi 1 Profile. 1982 . 42 6. Total Water Content of the 1.6 m Soil Profile. 1983 . 43 7. Total Water Content of the 1.6 m So1l Profile. 1984 . 44 B. Total Water Content of the 1.6 m So1l Profile. 1985 . 45 9. Changes in Plant Available Water by Depth ·over Time. 1982 . ' . 46 10. Changes in Plant Available Water by Depth over Time·. 1983 . 47 11. Total Water Content of the 1.0 m So1l Prof1le. 1982 . 48 12. Total Water Content of the 1.0 m Soi 1 Profi~e. 1983 . 49 13. Total Water Content of the 1. 0 m Soil Profile. 1984 . 50 14. Total Water Content of the 1. 0 m Soil Prof1le. 1985 . 51 Vl Figure Page 15. Plant Available Water- Content of the 1.0 m So1l Pr-ofile. 1982 . 52 16. Plant Available Water- Content of the 1.0 m Soil Pr-ofile. 1983 . 53 17. Plant Available Water- Content of the 1.0 m Soil Pr-ofile. 1984 . 54 18. Plant Ava1lable Water- Content of the 1.0 m Soil Pr-ofile. 1985 . 55 vii CHAPTER I INTRODUCTION In crop production, soil water content is an 1mportant factor relating to yields. Where water stress is a yield limiting factor, conservation of soil water 1s vitally important during both the fallow per1od and the grow1ng season of w1nter wheat <Triticum aestivum L.). We are interested in the effect of tillage practices, or levels of surface residue on soil water, and the effect these tillage systems have on soil characterist1cs such as bulk density and soil structure, which influence the availability of soil water. Soil water can be evaluated on either a total water, or a plant available water bas1s. Since not all water 1n the soil lS available to plants, the use of plant available water or water held in the so1l at a tension of less than 1.5 megapascals is best 1n evaluating the influence of tillage practices, or surface residue levels on soil moisture. Research has shown that tillage practices may affect soil bulk density, which in turn influences the availability of water in the soil profile. Therefore, proper characterization of so1l bulk density is essential 1 2 for an accurate interpretation of exper1mental results dealing with plant ava1lable soil water. Although many studies of tillage effects on gravimetric soil water content have been conducted, whether or not plant available soil water is significantly affected by various tillage practices is still unclear. Therefore the objectives of this research are: A. To evaluate soil bulk dens1ty as influenced by four tillage systems <plow, disk, V-blade, and no-till>. B. To determine the effect of crop residue management treatments <burled, mixed with surface 100 mm, slight mixing but most on surface, and no mixing>, as achieved through tillage, on plant available soil water. CHAPTER II PREVIOUS WORK AND LITERATURE REVIEW Smika et al. (1969), reported that in simiarid conditions, so1l water is a predominant factor that influences grain yields. Numerous stud1es have been conducted concerning water storage and phys1cal aspects of the soil, and how they are influenced by tillage practices. A four year study conducted by Davidson and Santelman <1973>, showed no sign1ficant tillage effect upon bulk density in the top 220 mm of the soil profile. Also, Bhatnagar et al. <1983>, reported that a tillage treatment of disk plow1ng and disk harrowing did not cause significant changes in soil properties. However, several studies have shown resulting bulk density differences between tillage treatments. Tanchandropongs and Davidson <1970>, showed that aggregate stabil1ty, organic matter content, and bulk density were significantly better in the top 300 mm of the soil prof1le after 11 years of stubble mulching in wheat, compared to plow or clean t1ll procedures. Power et al. <1984>, stated that bulk density is often greater with no tillage than with tillage. 3 4 Gantzer and Blake <1978>, found that soil under no-till had signlficantly greater bulk dens1ty both in spring and fall as judged from samples taken from the surface 300 mm 1n comparison to those of conventional tillage. Although reports indicate that differences are apparent only in the surface 300 mm and bulk density differences due to tillage generally converge at depths greater than 300 mm <Gantzer and Blake, 1978>, bulk density readings should be taken to a greater depth to eliminate var1at1ons in bulk density due to d1fferences 1n soil texture when reporting plant ava1lable water content on a volumetric basis <Cassel and Nelson, 1985>. Several researchers have reported significant increases in water storage with increasing amounts of straw on the so1l surface. Greb et al. <1970>, reported a progressive increase in soil water storage with 1ncreased application rates of straw mulch regardless of the quant1ty of precipitation during the fallow per1od. However, Unger <1976> showed that little improvement in water storage could be expected from applying surface residues, even at relatively high rates, when precipitation amounts are small. Cochran et al. ( 1982> reported that surface crop residues significantly improved water storage dur1ng seasons with maJor runoff events, however, had no effect 5 when soil profiles were filled by spring. Also, they reported that considerably more soil water was stored in the no-till treatments than in either the tilled or stubble burned treatments. Water left in the profile after harvest was not s1gnif1cantly different among treatments, wh1ch indicated that the plants were able to extract the additional water. Unger and Parker <1975>, indicated that growing season water storage was greater <about 40-50% as compared with 20%), and that crops utilized more of the growing season precipitation for growth and grain production on residue covered, no-till seeded areas than on bare soil. Also, direct drilling of sorghum into cereal residues increased water storage during a season with lower than normal precipitation. Studies concerning evaporation of stored so1l water have shown a reduct1on in evaporation losses with an increase 1n straw mulch. Good and Smika (1978>, reported that a d1sc t1llage operation reduces res1due by as much as 75 percent per operation, and that water loss in the top 127 mm of the soil was much greater after the d1sc operation than when the stubble was present.