The Effects of Ammonium Phosphate with Different Sulfur Additions on Crop Yield and Nutrient Uptake in Calcareous Soil

Sulfur (S) deficiency is becoming increasingly prevalent, posing a serious threat to crop yield and quality. The incorporation of S fertilizers into macronutrient fertilizers such as ammonium phosphate represents a straightforward and economically efficient approach to alleviating S deficiency, strengthening S supply, and improving crop yield. However, limited research has been conducted to assess the effect of monoammonium phosphate (MAP) and diammonium phosphate (DAP) with different S additions on agronomic outcomes. In this study, ammonium sulfate and elemental S with S set at 3%, 6%, 9%, and 12% (ensuring a 1:1 ratio of SO4−S to elemental S) were granulated with MAP and DAP, respectively. Maize was used as the test crop to evaluate its yield, nutrient uptake, and apparent sulfur recovery. The results showed that S-fortified MAP treatment increased crop yield and S uptake by an average of 9.3% and 10.6%, respectively. A significant difference in crop yield and S uptake was observed when the S addition in MAP exceeded 9% S. Nevertheless, no statistical difference was found among the DAP-based treatments in calcareous soil. There was a strong relationship between S applied in fertilizers and S uptake by crops for MAP-based treatments. However, the apparent sulfur recovery drastically dropped from 44.2% to 7.19% with the increased addition level of S for MAP-based fertilizers. The results of this study indicate that the addition of S to MAP could be a simple, low-cost, and effective approach with great potential to promote S fertilizer application, minimize soil S deficiency, and improve crop yield in calcareous soil.