In-season assessment of agronomic nitrogen use efficiency and its components in winter wheat using critical nitrogen...

Accurate and timely nitrogen (N) scheduling requires knowledge of in-season crop N deficit. Therefore, understanding the association between crop growth and crop N demand during its growth period is imperative for fine-tuning N scheduling decisions to actual crop N demand and to enhance N use efficiency. The concept of the critical N dilution curve has been employed to assess and quantify the intensity and time of crop N deficit. However, research regarding the association between crop N deficit and N use efficiency in wheat is limited. The present study was carried out to determine whether there are relationships between the accumulated nitrogen deficit (N_and) and agronomic N use efficiency (AE_N) as well as with its components (N fertilizer recovery efficiency (RE_N) and N fertilizer physiological efficiency (PE_N)) of winter wheat and to explore the potential capacity of N_and for predicting AE_N and its components. Data acquired from five variable N rates (0, 75, 150, 225, and 300 kg ha^-1) field experiments using six winter wheat cultivars were used to establish and validate the relationships between N_and and AE_N, RE_N, and PE_N. The results indicated that plant N concentration in winter wheat was significantly affected by N application rates. N_and varied from -65.73 to 104.37 kg ha^-1 after Feekes stage 6 under different N application rates. The AE_N and its components were also affected by cultivars, N levels, seasons, and growth stages. A positive correlation was observed between N_and, AE_N, and its components. Validation using an independent data set showed the robustness of the newly developed empirical models to accurately predict AE_N, RE_N, and PE_N with an RMSE of 3.43 kg kg^-1, 4.22%, and 3.67 kg kg^-1 and RRMSE of 17.53%, 12.46%, and 13.17%, respectively. This indicates that N_and has the potential to predict AE_N and its components during the growth period of winter wheat. The findings will assist in improving in-season N use efficiency by fine-tuning N scheduling decisions in winter wheat cultivation.