Applications of Gypsum and Ammonium Sulfate Change Soil Chemical Properties of a Salt-Affected Agricultural Soil

Irrigation water with high electrical conductivity (EC) compromises the sustainability of agricultural soils. Calcium sulfate (CS) or gypsum is commonly used on removal of soluble ions such as sodium (Na), however, large applications of CS can affect soil pH, EC, and nutrient availability to plants. The objective of this study was to investigate the effects of CS and ammonium sulfate (AS) rates on the soil pH, EC, and exchangeable cations in a salt-affected agricultural soil. Samples from the 0-20 cm soil depth layer were collected from an agricultural soil reported to have low potato yield due to high EC irrigation water. Soil was incubated with rates ranging from 0 to 4000 kg ha-1 of CS and 0 to 600 kg ha-1 of nitrogen (N) using AS. The treated soil was incubated for 60 d at 25 ºC and moisture was maintained at 60% of soil field capacity. After incubation, the soil was analyzed for pH, EC, Na, manganese (Mn), and zinc (Zn). Increasing rates of CS resulted in a small decrease in soil pH and a significant linear increase in soil EC, while the application of AS linearly reduced the soil pH and quadratically increased soil EC. The application rate of 200 kg ha-1 of N as AS resulted in a decrease of soil pH from 5.9 to 5.2, while the EC increased from 1.3 to 3.0 dS m-1. Extractable Na increased linearly with the application of AS due to its effect on the soil pH. The soil extractable Mn and Zn were not affected by the application of CS. Applications of AS resulted in a linear increase in soil extractable Mn and Zn concentrations, respectively. Results from this incubation study suggest that the use of large rates of CS for consecutive years may further impair soil conditions for cropping in areas with high EC in the irrigation water.