Enhancing cotton field productivity in arid northwest China through improved farm-level nitrogen balance and reduced nitrogen footprint

Contexts

Cotton is the most important economic crop in Xinjiang of China. However, due to the excessive application of nitrogen fertilizers, the region is experiencing considerable environmental stress. Optimizing water and nitrogen management practices presents an effective approach to mitigating nitrogen losses and minimizing the risk of environmental pollution.

Objectives

This study aims to evaluate the effects of various nitrogen (N) and irrigation strategies on N uptake by cotton plants, and compare the effectiveness of different management approaches on field-level N balance and overall N footprint.

Methods

A two-year field experiment was conducted to investigate the effects of drip irrigation under various soil matric potential (SMP) thresholds (-30, −20, and −10 kPa, as W1, W2 and W3) and three N rates (200, 300, and 400 kg ha⁻¹, as F1, F2 and F3) on N uptake and translocation in various parts of the cotton plant, nitrate N accumulation in the soil, and N inputs and outputs. This comprehensive analysis evaluated the N balance and footprint for each system.

Results

The results showed that excessive irrigation and fertilization intensified N accumulation in the roots, stems, and leaves of cotton plants but did not significantly enhance N accumulation in cotton bolls. The N transport efficiency (NTE) decreased by 25.1 % and 26.1 %, and N reproductive efficiency (NRE) contributions to seeds decreased by 25.2 % and 17.8 %, respectively. Higher N application rates reduced the proportion of nitrogen allocated to cotton bolls. Higher fertilizer and irrigation levels led to a deeper and wider distribution of nitrate N, increasing the risk of deep percolation and horizontal volatilization. The NH₃ emerged as the primary form of reactive N loss in cotton fields, ranging 7.8–24.8 kg N ha⁻¹. The N balance indicated decreased surplus with intensified irrigation, N deficiency was observed at rates below 250 kg N ha⁻¹, and excess N was noted above 350 kg N ha⁻¹.

Conclusions

An irrigation lower limit of −20 kPa promoted increased N accumulation in cotton bolls and ensuring production. Based on the system's N balance, 275–307 kg N ha⁻¹ was recommended to avoid N deficiency or excess. This approach balanced N environmental friendliness with production, achieving an N footprint of 7.7–8.4 kg N t⁻¹ in this system.

Significance

This study provides critical insights for achieving N balance and minimizing N footprint, and holds substantial promise for the development of cotton cultivation in arid regions.