Optimizing nitrogen application rate through critical nitrogen concentration dilution curves for sesame under different water conditions

Sesame (Sesamum indicum L.), a crucial oilseed crop renowned for high oil and protein content of seed, faces yield and quality constraints in southern China's red soil regions due to seasonal drought and low soil fertility. To optimize nitrogen (N) management under varying precipitation regimes, we developed and validated critical nitrogen concentration (N_c) dilution curves using two sesame cultivars, Jinhuangma and Ganzhi 14, in different water conditions and locations. Compared with the wet year, drought stress triggered a 53.3 % yield loss for sesame in dry year. There was no statistical differences in the N_c dilution curve across two varieties in the same precipitation year. Therefore, we derived a unified N_c dynamics of sesame (the dry year: N_c = 3.05 DM^−0.24; the wet year: N_c = 2.60 DM^−0.29). Independent experiments verified that the N_c curves for different precipitation years effectively distinguish between N-limiting and non-N-limiting treatments. The nitrogen nutrition index (NNI) and accumulated nitrogen deficit (N_and) effectively reflected N status, identified that optimal N application rates were 135 kg ha⁻¹ in wet years and 90 kg ha⁻¹ in dry years. The strong correlations between NNI, N_and and yield across precipitation scenarios, indicates the predictive power of them in enhancing yield outcomes. This study underscores the applicability of N_c dilution curves in refining N management strategies, advocating for tailored nitrogen fertilization approaches to bolster sesame productivity and sustainability in drought-prone agricultural regions.