Optimizing plant density and nitrogen fertilization in jujube/cotton intercropping systems for sustainable yield and reduced greenhouse gas emissions

Abstract

Context

Jujube (Zizyphus jujube Mill.) and cotton (Gossypium hirsutum L.), renowned for their drought and salt tolerance, form a resilient intercropping system in arid northwest China. While optimizing planting density and nitrogen (N) fertilization can enhance system productivity, their combined effects on greenhouse gas (GHG) emissions, carbon (C) sequestration and yield in such systems remain understudied. We hypothesize that strategic adjustments to plant density and N management could achieve sustainable yield while mitigating GHG emissions in the intercropping system.

Methods

A two-year field experiment evaluated three planting densities (D1: 14 × 10⁴, D2: 18 × 10⁴, D3: 22 × 10⁴ plants ha⁻¹) and three N application rates (N1: 140, N2: 280, N3: 420 kg N ha⁻¹) to quantify impacts on yield, GHG emissions (CO₂, N₂O, CH₄), soil C storage, and N use efficiency (NUE) in a jujube/cotton intercropping system.

Results

Increasing plant density and N rates elevated CO₂ and N₂O emissions by 37.8–69.4 % and 18.6–70.3 %, respectively, while diminishing CH₄ uptake under higher N inputs. The D2N2 treatment (18 ×10⁴ plants ha⁻¹, 280 kg N ha⁻¹) achieved the highest seedcotton yield, surpassing D3N2 (22 × 10⁴ plants ha⁻¹, 280 kg N ha⁻¹) and D3N3 (22 × 10⁴ plants ha⁻¹, 420 kg N ha⁻¹) by 9.7 % and 11.2 %, respectively. This combination (D2N2) also minimized greenhouse gas intensity (GHGI) by 55.8–120.1 % and enhanced NUE by 48.3 % compared to D2N3. Soil organic C (SOC) storage increased by 13.5–23.8 % under D2N2, whereas excessive N application (N3) reduced soil inorganic C (SIC) by 9.6–17.7 %.

Conclusions

Optimizing plant density (18 × 10⁴ plants ha⁻¹) and N fertilization (280 kg N ha⁻¹) synergistically balances productivity, GHG mitigation, and soil C sequestration. These findings highlight the viability of tailored agronomic practices to achieve environmentally sustainable intercropping systems in arid regions, aligning with global climate resilience goals.