In-season estimation of rice grain yield using critical nitrogen dilution curve

•Critical nitrogen dilution curve is an effective and simple tool for in-season estimation of crop grain yield.•Estimating in-season grain yield potential is essential for precision nitrogen management.•In-season estimation of grain yield is essential for ensuring global food security.•Crop growth stages can play an essential role in predicting grain yield.•This study will offer a useful approach for in-season estimation of rice grain yield.

Crop nitrogen (N) status during vegetative growth is an essential indicator of crop vigor and predictor of subsequent grain yield. The concept of the critical nitrogen (Nc) dilution curve has been used for in-season assessment of crop N status, yet it remains to be determined that how plant N status during vegetative growth can be related to grain yield at maturity in rice. The present study was endeavored to establish the relationships of relative grain yield (RY) to N nutrition index (NNI), accumulated N deficit (AND), and N requirement (NR) at different growth stages of Japonica and Indica rice on the basis Nc dilution curve of the rice plant. Four multi-N rate field experiments were conducted in Jiangsu province of east China using five rice hybrids. Growth analysis was carried out to determine the Nc dilution curve and related N parameters during vegetative growth period. The relationships between RY and NNI, AND, NR at different growth stages were highly significant with R2 values all greater than 0.74 for both Japonica and Indica rice, with the strongest R2 ranging from 0.94 to 0.99 for the relationships at panicle initiation (PI) and booting (BT) stages. Validation of the regression models with independent datasets exhibited a solid model performance at PI and BT stages with R2 values greater than 0.92 and RMSE values lower than 10%, confirming the robustness of the relationships at PI and BT stages. The k coefficients at PI and BT stages for the observed and predicted RY were close to 1. Overall, the robust relationships of RY to NNI, AND and NR at PI and BT stages well explained the variation in RY under limiting and non-limiting N growth conditions, and gave a reliable estimation of rice grain yield in east China.