Coupling effects of reduced nitrogen, phosphorus and potassium on drip-irrigated cotton growth and yield formation in Northern Xinjiang

To elucidate the effects of nitrogen (N), phosphorus (P) and potassium (K) on cotton growth and yield, field studies with four N treatments (506, 402.5, 299 and 195.5 kg ha−1 designated as N1, N2, N3 and N4, respectively) and four managements (M) of P and K application, designated as PK-M1 (total P and K applied at squaring stage (SS)), PK-M2 (25%:75% at SS and bloom-bolling stage (BS)), PK-M3 (50%:50% at each stage), PK-M4 (75%:25% at SS and BS) were conducted in 2018 and 2019. Results are shown in reproduction growth, PK-M3 under N treatments had the highest maximum biomass (K') and fastest speed of biomass accumulation (Vmax), and N2PK-M3 obtained higher K' and Vmax than others, followed by N3PK-M3. The average boll number, boll weight and yield in N2 were greater than others, and N3 with a decrease of 3.4–6.1% in average yield over N2. Although the yield in N3PK-M3 reduced by 1.4–1.5% compared to N2PK-M3 (losses about $8–32 per hectare), the fertilizer input decreased about $60–63 per hectare than N2PK-M3. Results suggest that 50% PK application ratio during SS and 50% during BS coapplied with proper reduced N application rate could compensate the yield loss by maintaining a higher level of reproduction biomass accumulation.