Effects of long-term sugarcane-soybean intercropping coupled with varying levels of nitrogen input on soil legacies: A field experimental study

Abstract

Long-term agricultural management practices alter the biochemical properties of soil, leading to the formation of distinct soil legacies. Sugarcane-soybean intercropping is recognized as a sustainable and stable agricultural practice, while the application of nitrogen (N) fertilizer is essential for enhancing crop yields. However, research on the effects of long-term sugarcane-soybean intercropping coupled with varying N levels on soil legacies remains limited. Therefore, we selected four treatments in a long-term field experiment: sugarcane monoculture with reduced N application (MSN1), sugarcane monoculture with conventional N application (MSN2), sugarcane-soybean intercropping with reduced N application (SB2N1), and sugarcane-soybean intercropping with conventional N application (SB2N2). The study aims to investigate the effects of soybean intercropping coupled with varying N application levels on soil abiotic (chemical properties) and biotic (microbial communities) legacies. The results showed that under conventional N application (525 kg ha⁻¹), intercropping, compared to monoculture, significantly increased the contents of total potassium (TK), nitrate nitrogen (NO₃⁻), available zinc (AZn) and the network complexity of the arbuscular mycorrhizal fungi (AMF) community. Under intercropping conditions, reduced N application (300 kg ha⁻¹), compared to conventional N application, significantly increased the content of exchangeable calcium (ECa), pH, as well as the alpha diversity and network complexity of the bacterial community. Under monocropping conditions, conventional N application significantly increased the complexity of the bacterial community network. Stochastic processes dominated the assembly of bacterial and AMF communities, but under the same cropping pattern, deterministic processes in fungal communities increased with N application. Soil pH, N nutrients, and trace metal elements are key factors affecting the diversity and composition of soil microbial communities. These findings highlight the significant impact of intercropped soybean on soil legacies, whereas the N level of application plays a key role in regulating the effectiveness of biotic and abiotic soil legacies. This study provides valuable insights into managing soil legacies and provides a theoretical basis for the development of sustainable agriculture.