Construction of critical nitrogen concentration model based on canopy coverage and the accuracy in yield prediction of maize

Objectives The critical nitrogen concentration dilution curve of irrigated maize based on canopy coverage was constructed. Then, the nitrogen in maize was assessed by nitrogen nutrient index and nitrogen accumulation deficit model for predicting maize yield.

Methods Field trials with four nitrogen fertilizer rates (0, 120, 240 and 360 kg/hm²) were conducted in Ningxia Yellow River Irrigation Area of China from 2019 to 2020. Water and fertilizer integration technology of drip irrigation was adopted. Nitrogen top-dressing was divided into eight times with irrigation according to the proportion of 10% at seedling stage, 45% at jointing to flare opening stage, 20% at tasseling to silking stage, and 25% at grain-filling stage. Aboveground biomass, plant nitrogen concentration and yield were measured during the critical growth stages of maize, and the empirical model of maize critical nitrogen concentration based on canopy coverage was established and verified.

Results The R² values of maize critical N concentration, maximum N concentration and minimum N concentration based on canopy coverage were 0.917, 0.843 and 0.873, respectively. RMSE and n-RMSE of critical nitrogen concentration model were 0.242 and 11.753%, respectively. Based on N nutrient index and N accumulation deficit, the optimal N application treatment for maize was 240 kg/hm². The relationships between N nutrient index, N accumulation deficit and relative yield were strongly significant at different growth stages, with R² not less than 0.922, and the R² values were the highest at trumpet and tasseling stages. The independent test results showed that the model performance was stable at the flaring stage and tasseling stage, with R² value greater than 0.944 and n-RMSE less than 9.089%. At the trumpet stage and tasseling stage, the N nutrient index and N accumulation deficit were significantly correlated with the relative yield, which could accurately explain the change of relative yield under the growth conditions of nitrogen restriction and no nitrogen restriction.

Conclusions The critical nitrogen concentration dilution curve constructed based on the canopy coverage can accurately judge and evaluate the N nutrition status from the jointing stage to the silking stage of maize. The relationship model constructed based on the N nutrition index, N accumulation deficit and relative yield can more accurately predict the yield at the large bell-opening and tasseling stages. This study provides a simple and new method for precise management of nitrogen fertilizer and yield prediction during crop growth.