Maize-soybean intercropping reduces greenhouse gas emissions from the fertilized soil in the North China Plain

Continuous monocropping with high nitrogen (N) fertilizer input substantially increases greenhouse gas (GHG) emissions in maize-based agroecosystems in the North China Plain (NCP). Introducing soybeans as an intercrop with maize and partially substituting urea with manure might effectively decrease GHG emissions. The aim of this study was to quantify the synergistic effect of maize-soybean intercropping and manure on soil GHG emissions.

A two-year field experiment with three cropping systems (maize monocrop, soybean monocrop, and maize-soybean intercrop) and four N treatments (control, urea, manure, and manure + urea) was carried out at Luancheng Agro-Ecosystem Experimental Station in the NCP. All N treatments, except the control, received 150 kg N ha⁻¹season⁻¹, either full dose as a basal application or two equal split applications.

Results showed that all treatments contributed as a net source of N₂O and CO₂ fluxes but acted as a net sink of CH₄ fluxes. In both cropping seasons, intercrops had significantly lower N₂O emissions compared to monocropping systems, with 38% and 14% less emissions than maize monocrops in 2018 and 2019, respectively. Additionally, maize monocrops had significantly higher soil CO₂ emissions than other systems, while maize-soybean intercropping had 12% and 13% less CO₂ emissions than maize monocrops in 2018 and 2019, respectively. Among fertilized treatments, manure-treated soils emit notably lower N₂O fluxes compared to sole urea treatments. In this study, N₂O and CO₂ fluxes had a strong positive correlation with soil mineral N concentrations, soil temperature, and moisture content. Possibly due to more efficient N utilization, intercrop soils exhibited significantly lower NH₄⁺ and NO₃⁻ concentrations, leading to reduced nitrification and denitrification in the system, resulting in lower N₂O emissions from maize-soybean intercrops.

Our findings indicate that intercropping maize and soybean reduces soil NH₄⁺ and NO₃^– concentrations, as well as significantly decreasing soil N₂O and CO₂ emissions when compared to traditional maize monoculture. Therefore, due to its potential for reducing soil GHG emissions, maize-soybean intercropping can be regarded as an effective alternative cropping system to the prevailing maize-dominant monoculture to develop a sustainable agroecosystem in the NCP region.