Optimizing nitrogen application rate by establishing a unified critical nitrogen dilution curve for maize under different mulching planting patterns

Nitrogen (N) nutrition is essential for crop production and a critical N dilution curve (CNDC) could provide a novel strategy for diagnosing plant N status. CNDCs for several crops under different scenarios have been established to optimize N management. However, few studies have been conducted to establish a CNDC for maize (Zea mays L.) under ridge-furrow planting with film mulching over ridges, a planting pattern that has been widely adopted in semi-arid regions due to its improvement in soil water status. In addition, the effects of varied planting patterns on CNDC remain unknown. Therefore, a four-year (2018-2021) field experiment was conducted to establish CNDCs and provide a precise diagnosis of maize N status under different mulching planting patterns. Four N levels (0, 90, 180, and 270 kg N ha-1 for the 2018-2020 period; and 100, 150, 200, and 300 kg N ha-1 for 2021) were applied under three mulching planting patterns: fiat planting without film mulching, ridge-furrow planting with transparent plastic film mulching over ridges, and ridge-furrow planting with biodegradable film mulching over ridges. Taking into consideration of the 95 % credibility intervals, no significant differences in CNDCs and its estimated parameters were observed across years and mulching planting patterns. Therefore, we derived a unified CNDC equation defined as NC = 3.10 W-0.40 based on data obtained from the three mulching planting patterns during the four years. Furthermore, no significant differences were observed in critical N nutrition index thresholds. Consequently, the results supported establishing a universal CNDC model to diagnose maize N status in northwest China. The optimal N application rate for maize to obtain great yield and high N use efficiency in the region was 180-200 kg ha-1. Further studies are required to evaluate CNDC for maize grown under various N fertilizer types, planting patterns, rainfall years, and regions, which would lead to a more precise diagnosis of maize N status and a more accurate N management regime.

Automated summary

This study aims to establish critical nitrogen dilution curves (CNDC) for maize and diagnose the nitrogen status under different mulching planting patterns. The results showed no significant differences in CNDC and its estimated parameters across years and mulching planting patterns, suggesting the establishment of a universal CNDC model for maize nitrogen diagnosis.