Phosphate Balance Studies in Irrigated Cotton

A field experiment was conducted to study the phosphate balance in irrigated cotton NHH-44 on a calcareous Vertisol of Parbhani. The treatments consisted of three P sources, viz. superphosphate. diammonium phosphate and Sulpala (20:20:0) + superphosphate @ 25. 50 and 75 kg P₂O₅ ha⁻¹ along with control. Superphosphate produced significantly higher seed cotton yield (16.27 q ha⁻¹) and dry matter yield (49.29 q ha⁻¹) followed by diammoniumphosphate. Seed cotton and dry matter yield increased with increasing levels of P up to 50 kg P₂O₅ ha⁻¹. Uptake of P ranged from 27.18 to 32.95 kg ha⁻¹ with different P sources. There was gradual increase in P uptake with increasing levels of P up to 75 kg PzOs ha⁻¹. In general, there was positive balance of available P in soil when cotton crop was fertilized with different P sources. superphosphate showed highest build up of phosphorus (+ 6.47 kg ha⁻¹) at the harvest of cotton. The P balance at 25 kg P₂O₅ ha⁻¹ rate was negative. However, 50 and 75 kg P₂O₅ ha⁻¹ resulted in build-up of available P in soil.