The source–sink balance during the grain filling period facilitates rice production under organic fertilizer substitution

Abstract

Partial organic fertilizer substitution for chemical fertilizer has been proven to reduce the synthetic nitrogen (N) fertilizer requirement while maintaining or improving rice yield. However, little is known about the underlying physiological mechanisms of such an effect. Field trials were conducted to investigate the effect of organic fertilizer substitution for chemical fertilizer on rice yield and the source–sink relationship in two growing seasons. The treatments were as follows: no N fertilizer application (CK); farmers’ fertilizer practice (FFP); optimal chemical N management (OPT); and organic fertilizer substitution based on the OPT treatment (OPT-SN). Compared with treatments of chemical N fertilizer alone, rice yield was maintained in the OPT-SN treatment. The value of the sink–source difference in rice was positive during the grain filling period irrespective of the treatments, implying that the grain yield was source-limited. Although the effects on sink growth were similar among the different N addition treatments, organic fertilizer substitution improved source capacity by extending the duration of source activity when compared with treatments only containing chemical N fertilizer. The source–sink relationship was more balanced (lower sink–source difference) in the OPT-SN treatment relative to treatments of chemical N fertilizer alone, and a significant negative relationship between sink–source difference and grain yield was observed. Overall, organic fertilizer substitution could maintain grain yield by establishing a more balanced source–sink relationship during the grain filling period. Our findings clarify the positive effect of organic fertilizer substitution on source–sink balance and provide a basis for fertilization strategies to improve crop productivity.