Impact of Sulphur Application Timing and Phosphate Doses on Soluble Phosphorus, Growth, and Yield of corn in Calcareous Soil

This study investigates the effects of sulphur application timing and phosphorus dosage on phosphorus availability, growth, and yield quality of corn in calcareous soils at the Grdarasha field, Agriculture College of Engineering Science, Salahaddin University–Erbil. The experiment was designed as a randomized complete block design (RCBD) with three replications across 12 treatment combinations, incorporating sulphur applications at varying timings (control, 15 days before planting, at planting, and 15 days after planting) at a rate of 300 kg sulphur ha⁻¹ and triple super phosphate (TSP) at doses of (0, 60, and 160) kg ha⁻¹.Results demonstrated that sulphur applied 15 days before planting significantly enhanced key growth, and, yield quality the highest grain yield, straw yield, total dry matter values (14.74, 8.49, 23.23) t/ha respectively, and 1000-seed weight (423 g). In contrast, the control treatment exhibited the lowest values, underscoring sulphur's critical role in nutrient availability during early growth stages. While leaf area did not show significant variation across treatments, the synergy between early sulphur application and higher phosphorus doses markedly improved other presentation, particularly with the St1P2 treatment yielding 17.23 t/ha of grain and 431.67 g for 1000-seed weight.Phosphorus availability was significantly influenced by both sulphur timing and TSP dosage, with the highest phosphorus solubility observed in treatments where sulphur was applied 15 days prior to planting and in combination with 160 kg ha⁻¹ TSP. This study highlights the importance of optimizing sulphur and phosphorus fertilization strategies in calcareous soils, which typically restrict phosphorus solubility due to high pH and calcium content. The findings provide valuable insights for improving fertilizer management practices aimed at enhancing crop productivity in nutrient-deficient soils.