The use of gypsum to ameliorate soil sodicity in irrigated cotton production on the Southern High Plains of Texas

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.