Effects of Soil Sodicity and Application of Gypsum on Dynamic Behavior of Nutrient Elements in Soils Under Simulated Irrigation

Effective utilization of nutrient elements in irrigation effluent water by plants may decrease cost of agricultural production and adverse influence on water environment. Effects of soil sodicity and gypsum applied on dynamical behavior of nutrient elements under irrigation were studied by soil column leaching method in laboratory. Three treatments were designed: 1) effluent leaching of the soil that was equilibrated with solutions at sodium adsorption ratio (SAR) 0; 2) effluent leaching of the soil equilibrated with solutions at SAR=30; and 3) effluent leaching of the soil that was equilibrated with solutions at SAR 30 and mixed with desulfurized gypsum at a rate of 0.5% of soil weight. The experimental data indicated that gypsum application decreased leachate pH of sodic soil to that similar to pH of nonsodic soil. Effects of application of gypsum on soil salinity almost disappeared after leaching of 15 pore volumes (PV) of effluent. Gypsum applied in order to reclaim sodic soil could not be sufficiently utilized under effluent irrigation because of high Ca concentration in effluent. Sodium ion in sodic soil adversely affected utilization of nutrient elements in soil by plants. Magnesium, K and P accumulated in soils under effluent irrigation. About 53.1%~78.7% of Mg, 33.4%~58.1% of K, and 32.7%~95.5% of P that were added into soils from irrigated effluent water were respectively held by soils, and irrigated effluent water is an important additional source of nutrients for plant growth. However, the increased percentages of Mg and P in sodic soil obviously were greater than those in nonsodic soil. Gypsum application obviously decreased accumulation percentages of K and P but increased that of Mg in sodic soil. Boron was slightly leached in nonsodic soil but accumulated in sodic soils no matter whether gypsum was applied or not. After 19~23 PV leaching of effluent water, B content in sodic soil increased about 14 times and to 3.19 mg·kg-1 from initial content of 0.212 mg·kg-1. Although B concentration in effluent water was lower than the National Criteria for Irrigation Water Quality in China, but this content in sodic soil would harm plant growth. However, B content in the sodic soil after gypsum application only increased 68.4%, gypsum application greatly reduced disadvantage of B accumulation in sodic soil. Boron accumulation in sodic soil is the key factor for irrigation application of studied effluent water.