Effects of Nitrogen Application and Cropping System on Soil Structure and Nitrogen Fractions

Objective The aims were to clarify the differences in soil structure and soil organic nitrogen (N) components under N application and different cropping patterns (intercropping and rotation), and to explore the effects of N application and cropping patterns on soil structure and N components, in order to provide a scientific basis for optimizing cropping systems and achieving sustainable agricultural production.

Methods Based on a long-term field experiment established in 2013 in the irrigated desert soil area of the Hexi Corridor in Gansu, two N application rates (0 and 300 kg hm⁻²) and three cropping patterns (maize/soybean intercropping; maize-soybean rotation; soybean-maize rotation) were set up. By measuring the distribution of soil water-stable aggregates, soil bulk density, total porosity, total N, and organic N components under rotation and intercropping conditions in 2024, the differences in the above soil indicators between rotation and intercropping conditions were compared and analyzed to clarify the effects of N application and cropping patterns on soil structure, N components, and N storage.

Result N application significantly reduced the proportion of water-stable macroaggregates (> 2 mm) in the maize zone, increased microaggregates (< 0.25 mm), and decreased aggregate stability (MWD, GMD). It also elevated bulk density and reduced total porosity in the soybean zone, with more pronounced effects under intercropping. Intercropping enhanced maize zone total N by 10.56% and N storage by 10.53%, while increasing acid-hydrolyzable N (19.13%) and amino acid N (21.71%). In contrast, N application in rotation significantly improved soybean zone total N and N storage.

Conclusion Intercropping increased soil bulk density compared to rotation. N application show no significant effect on maize zone N pools, whereas intercropping promoted soil N accumulation relative to rotation. However, rotational N application synergistically enhances soybean zone N storage. Overall, intercropping and rotation exhibite complementary advantages in N pool regulation: intercropping facilitated N activation in maize zones, while rotational N application sustainably improved soybean zone N storage. These findings provide differentiated strategies for crop-soil synergy-driven strategies in Northwest China’s irrigated desert soils.