THE USE OF GYPSUM TO AMELIORATE SOIL SODICITY IN IRRIGATED COTTON PRODUCTION ON THE SOUTHERN HIGH PLAINS OF TEXAS by QUINT CHEMNITZ, B.S. A THESIS IN SOIL SCIENCE Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Dr. Wayne Hudnall Committee Chairperson Dr. Richard Zartman Dr. Stephen Maas Dr. David Wester Fred Hartmeister Dean of the Graduate School December, 2007 Texas Tech University, Quint Chemnitz, December 2007 Acknowledgments This project was made possible by the United States Department of Agriculture, Texas Natural Resources Conservation Services (Project number: 68‐7442‐5‐464/TXCIG‐ 05‐10 CFDA 10.912). I would also like to thank Texas Tech University for the opportunity and facilities to carry out this project, along with the professors and staff who helped with all aspects of the work. I would like to thank Dr. Wayne Hundnall in particular for his guidance and support for the duration of the project. Without his help and the help of several of my fellow graduate students and research assistants, I would not have been able to complete this project. I would also like to thank my parents for their support and guidance throughout the years. Lastly, I would like to thank my wife, Betty for her patience, understanding, and love. ii Texas Tech University, Quint Chemnitz, December 2007 Table of Contents ACKNOWLEDGMENTS ...................................................................................... ii ABSTRACT ............................................................................................................. v LIST OF TABLES ................................................................................................. vi LIST OF FIGURES .............................................................................................. vii I. INTRODUCTION .............................................................................................. 1 II. BACKGROUND ................................................................................................ 3 GYPSUM SOLUBILITY AND MOVEMENT ................................................................................... 5 OVER‐ABUNDANCE OF GYPSUM ............................................................................................ 6 THE CHEMICAL PROPERTIES OF GYPSUM ................................................................................ 7 HUMIC ACID ....................................................................................................................... 7 SITE LOCATION ................................................................................................................... 9 III. OBJECTIVES ................................................................................................. 12 IV. EXPERIMENTAL DESIGN ......................................................................... 14 V. METHODS ...................................................................................................... 16 FIELD METHODS................................................................................................................. 16 Field Variability ............................................................................................................ 16 Pre-Planting Methods .................................................................................................... 17 Post-Planting Methods ................................................................................................... 18 LABORATORY METHODS ..................................................................................................... 19 Sample Preparation ....................................................................................................... 19 Particle Size Analysis ..................................................................................................... 19 Saturated Paste ............................................................................................................. 21 Electrical Conductivity and pH ........................................................................................ 21 Atomic Absorption Spectrophotometer .............................................................................. 21 VI. RESULTS ....................................................................................................... 23 2006 RESULTS .................................................................................................................. 23 Field Variability ............................................................................................................ 23 Particle Size Analysis ..................................................................................................... 26 Electrical conductivity and pH ......................................................................................... 26 iii Texas Tech University, Quint Chemnitz, December 2007 Atomic Absorption Spectrophotometer .............................................................................. 27 Emergence .................................................................................................................... 29 Yield ............................................................................................................................ 30 2007 RESULTS .................................................................................................................. 32 Field Variability ............................................................................................................ 32 Particle Size Analysis ..................................................................................................... 35 Electrical conductivity and pH ......................................................................................... 35 Atomic Absorption Spectrophotometer .............................................................................. 37 Emergence .................................................................................................................... 40 Yield ............................................................................................................................ 42 VII. ECONOMIC IMPACT ................................................................................. 47 VIII. DISCUSSION .............................................................................................. 48 IX. CONCLUSION ............................................................................................... 53 BIBLIOGRAPHY ................................................................................................ 54 iv Texas Tech University, Quint Chemnitz, December 2007 Abstract The purpose of this project is to reduce the exchangeable sodium within the soil by the addition of gypsum. Even though the addition of gypsum is the standard reclamation technique for sodic soils, its effectiveness has not been shown for cotton production on the Southern High Plains of Texas. Exchangeable sodium disperses the soil, which increases the potential for wind erosion as well as the formation of a salt‐ based crust. The addition of gypsum to sodic soils improves aggregation of soil particles. The addition of calcium improves particle‐to‐particle association which increases water infiltration and percolation. A flocculated soil allows water to move more easily through the profile which increases the probability of leaching sodium out of the rooting zone and decreases crusting. The accepted rate of gypsum for this study to reduce the sodium adsorption ratio and soil electrical conductivity is approximately 4.5 mt ha‐1 (2 tons acre‐1). Rates half and twice the recommended rate were applied in a completely randomized design. The application of gypsum to the soil was broadcast and in‐row. Plant emergence was counted for 15 consecutive days after planting and the yield was used to measure the effectiveness of the gypsum application. Results indicate that there is no significant difference in yield between the treated and untreated plots. With no increase in yield, there is no reason to spend money on either a gypsum or humic acid treatment. The cost of gypsum is currently $31.81 for one metric ton. The farmer could potentially spend anywhere between $144,167.25 and $572,842.75 on gypsum to cover a field of 2023 hectares (5,000 acres) depending on the rate. Without sufficient water to move the Na from the rooting zone once it is in solution, the gypsum applied will be of no benefit. v Texas Tech University, Quint Chemnitz, December 2007 List of Tables 1. AVERAGE PARTICLE SIZE DISTRIBUTION OF THE 36 SAMPLES TAKEN FROM 17 SITES IN 2006. ................................................................................................................. 26 2. AVERAGE PH AND EC COMPARISON OF PRE‐GYPSUM APPLICATION AND POST‐GYPSUM APPLICATION. POST‐APPLICATION AVERAGE IS TAKEN FROM ALL THE PLOTS COMBINED, WHEREAS THE PRE‐APPLICATION AVERAGE IS TAKEN FROM THE ENTIRE HALF PIVOT. ............. 27 3. STATISTICAL ANALYSIS OF 2006 LINT YIELD SHOWING NO SIGNIFICANT DIFFERENCE BETWEEN RATES AND METHODS OF APPLICATION. MEAN COMPARISON OF LINT YIELD ‐1 ‐1 REPORTED IN KG HA . TREATMENT RATES REPORTED IN MT HA . ................................... 31 4. AVERAGE PARTICLE SIZE DISTRIBUTION PERCENTAGE FOR STUDY SITE IN 2007. ................... 35 5. COMPARISON OF AVERAGE PH BY TREATMENT FOR 2007. TREATMENT APPLICATIONS ‐1 ‐1 REPORTED AS MT HA FOR GYPSUM AND KG HA FOR HUMIC