Effects of reduced nitrogen application rate on drip-irrigated cotton dry matter accumulation and yield under different phosphorus and potassium managements

To elucidate effects of reduced N application rate on dry matter accumulation and yield of drip-irrigated cotton (Gossypium hirsutum L.) under different phosphorus and potassium managements (PK-Ms), field studies with four reduced N application rates and four PK-Ms were conducted in 2018 and 2019. Results show that after early peak boll-forming (PB) stage, the leaf area (LA) in N3PK-M3 was the highest among all treatments. The net assimilation rate (NAR), crop growth rate (CGR), boll dry weight (BDW), and boll growth rate (BGR) were highest in N2, followed by N3 with insignificant differences, and those parameters in PK-M3 were the highest. The reproductive/vegetative biomass ratio (RVR) for N3PK-M3 was the highest. The CGR, BDW, BGR, and NAR for N3PK-M3 were insignificantly lower than those for N2PK-M3, which increased yield in N2PK-M3 and N3PK-M3 treatments. Correlation analysis showed that BGR was positively related with CGR and NAR from peak flowering (PF) stage to boll opening (BO) stage, and CGR was significantly correlated with NAR and LA from PF to BO stage, and BO stage, respectively. Moreover, the yield was positively correlated with boll weight (BW) and boll number (BN), and BGR was significantly correlated with BN and BW from peak squaring stage to late PB stage. Therefore, high yield in N3PK-M3 due to higher value in LA after boll-forming stage, with higher NAR, CGR, RVR, and BGR, suggesting that early boll formation and successive partitioning of dry matter in boll growth were important factors for yield formation.