Smart nutrient management Nutrient Expert® enhances rice productivity through adjusting source-sink relationships during grain filling

Smart nutrient management optimises chemical fertiliser application while maintaining crop yields. Nutrient Expert® (NE) is a user-friendly smart nutrient management system designed to improve the productivity of smallholder farmers. However, the physiological mechanisms underlying the effects of nutrient management have yet to be fully understood. We analysed data from field experiments conducted in South and Northeast China to explore the effects of different nitrogen (N) fertiliser inputs and nutrient management systems on panicle weight and post-flowering source-sink relationships in various cropping seasons of rice. Treatments included NE recommendation, local farmers’ practices (FP), soil test based fertiliser recommendation (ST), and four N rate treatments with plus or minus 25 % and plus or minus 50 % of NE. Our analysis indicated that rice panicle weight and N accumulation increased with increasing N application rate up to a recommended rate by NE in most cases, beyond which there was little further increase. Moreover, NE significantly enhanced rice panicle weight and N accumulation compared to FP and ST in the single-season rice in Northeast China. In all experiments, both in South and Northeast China, the post-flowering source-sink difference gradually increased from negative to positive values with an increase in N application rate. Too low N application rate resulted in insufficient source supply, while too high N application rate gave excessive source supply since the sink demand reached its upper limit. Compared with FP and ST, NE achieved higher source supply and sink demand in the single-season rice, and mobilised more N from source organs to sink organs. Our analysis provides evidence for positive impacts of integrated nutrient management strategies on rice source-sink relationships and offers a physiological basis for improved rice productivity of designed NE nutrient management strategies.