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

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 (REN) and N fertilizer physiological efficiency (PEN)) 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), REN, and PEN. 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), REN, and PEN 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.