Assessment of nitrogen status in maize-soybean intercropping system by establishing a novel critical nitrogen dilution curve under different irrigation amounts

Abstract

Context

The critical nitrogen dilution curve, an established diagnostic tool for assessing crop nitrogen status, faces challenges in intercropping systems due to species-specific resource utilization patterns.

Objective or research question

This study aimed to develop a novel critical nitrogen dilution curve for maize-soybean intercropping systems and propose nitrogen management strategies to optimize crops productivity under varying irrigation levels.

Methods

A two-year maize-soybean intercropping experiment was conducted in northwest China, employing three irrigation levels (W60: 60 %, W80: 80 %, W100: 100 % of crop evapotranspiration) and five nitrogen application levels (N0–0: 0–0, N120–60: 120–60, N180–60: 180–60, N240–60: 240–60, N300–60: 300–60 kg ha^–1 for maize-soybean).

Results

Results indicated that optimal irrigation (W80 and W100) combined with moderate-to-high nitrogen inputs (N180–60, N240–60, and N300–60) significantly enhanced system productivity, particularly maize yield and aboveground biomass. The highest nitrogen use efficiency occurred under W80 with N180–60 or N240–60 treatments. By integrating biomass proportion dynamics, a novel critical nitrogen dilution curve for maize-soybean intercropping was developed under different irrigation levels. This model effectively accounts for interspecific biomass allocation, differential nitrogen uptake efficiencies, and irrigation-mediated nitrogen availability.

Conclusions

Based on nitrogen nutrition index dynamics, we recommend a uniform base fertilizer application of 60 kg N ha^–1 for both crops in maize-soybean intercropping systems. Then, under limited irrigation (W60), maize topdressing should be maintained at approximately 60 kg N ha^–1, while under sufficient irrigation (W80-W100), a moderate increase to approximately 120 kg N ha^–1.

Implications

These findings offer a theoretical basis for nitrogen diagnosis and management in intercropping systems, though further validation across diverse environments is needed to enhance model generalization.