Ammonium Sulfate Improves Nutrient Status and Photosynthetic Activity in Sorghum (Sorghum bicolor L.) Grown in Alkaline-Saline-Sodic Soils

This study investigated whether fertilization with urea or ammonium sulfate could mitigate the growth limitations of sorghum imposed by alkaline-saline-sodic (ASS) soils. We hypothesized that the application of these nitrogen sources would improve the plant’s mineral status and photosynthetic activity. Experiments were conducted using three sorghum hybrids under both field and greenhouse conditions, comparing ASS soil to a non-ASS control. The treatments included fertilization with ammonium sulfate, urea, and a non-fertilized control. At the end of both experiments, soil and plant samples were analyzed to assess soil pH, nutrient content, and chlorophyll fluorescence. Our results demonstrate that ammonium sulfate, but not urea, significantly improved plant mineral status by inducing acidification in the ASS soil. This improved status led to increased photosynthetic rates and biomass production compared to unfertilized controls. These findings position ammonium sulfate as an effective tool for improving sorghum growth and productivity in challenging marginal soils. Highlights: Ammonium sulfate (AS) fertilization reduced alkaline-saline-sodic (ASS) soil pH by approximately 1 unit under field conditions, whereas urea (U) shows no significant effect on soil pH. Unlike U, fertilization with AS improves the mineral status of sorghum by increasing the uptake of essential macro- and micronutrients, including N, P, K, and Ca, which are limited in AAS soils. The damage to the photosystem II electron transport chain was mitigated by AS treatment, demonstrating protection of the photosynthetic machinery from ASS stress. Hybrid-specific responses revealed that moderately tolerant genotypes (163 and SIP) achieved biomass production comparable to control soil conditions when treated with AS, highlighting the importance of combining appropriate genotypes with fertilization strategies.