Soil greenhouse gas emissions, yield, and water-use efficiency affected by maize-soybean intercropping under long-term nitrogen fertilization

Context

Intercropping is widely practiced in many parts of the world due to its high resource-use efficiency, increased productivity, and numerous other agronomic benefits compared to monoculture. However, the interactions between intercropping and varied nitrogen (N) levels under long-term fertilization, particularly concerning soil greenhouse gas (GHG) emissions and water-use efficiency (WUE), are not well understood in the semi-arid North China Plain region.

Objective

This study aimed to quantify the effects of maize-soybean intercropping and varying N levels under long-term N fertilization on soil GHG emissions, crop productivity, and WUE.

Methods

A two-year field experiment was conducted using three cropping systems: maize monocrop, soybean monocrop, and maize-soybean intercrop, combined with four N levels: 0 (control, N0), 100 (N100), 150 (N150), and 200 (N200) kg N ha⁻¹ per growing season. All crops were managed using recommended practices.

Results

Maize monocropping consistently emitted higher levels of N₂O and CO₂ than soybean monocropping and maize-soybean intercropping systems. Intercropping reduced cumulative N₂O and CO₂ emissions by 28 % and 15 %, respectively, compared to maize monocropping. Increasing N rates led to higher GHG emissions, with N200 treatment emitting 127 % and 71 % more N₂O and 10.7 % and 4.1 % more CO₂ than N100 and N150, respectively. Intercropped maize increased grain yield and above-ground biomass by 42 % and 21 % than monoculture maize in 2018 and by 39 % and 22 % in 2019, respectively. Although intercropped soybean yielded less biomass and grain, the total LER ranged from 1.11 to 1.37, suggesting that the overall productivity in intercropping was consistently higher than in monocropping. While nitrogen application significantly boosted biomass and grain yield, no difference was found between N150 and N200 treatments, suggesting that a higher N dose beyond N150 offered no additional benefit. Intercropping increased grain WUE by 47 % than maize monocropping. The water equivalent ratio (WER) ranged from 1.13 to 1.41, and the relative water-saving index ranged from −16.5 % to −28.8 %, suggesting that intercropping used water more efficiently, particularly at N150, where the highest WER for grain yield (1.41) and water savings (-28.8 %) were observed among the N rate treatments.

Conclusion

Maize-soybean intercropping, combined with moderate N rate (150 kg N ha⁻¹), offers a sustainable approach to reducing GHG emissions, enhancing crop productivity, and improving water use efficiency in the semi-arid region of northern China.