Bacterial-mediated nutrient cycling and yield recovery in high-density cassava–maize intercropping systems enhanced by maize straw return

Background

High-Density Cassava-Maize Intercropping (HDCMI) has been proven effective in improving land-use efficiency. However, interspecific competition arising during the symbiotic period often reduces cassava or maize yields compared with monocropping.

Objective

This study explored the potential of the HDCMI system with maize straw return to address these challenges. The approach emphasized possible improvements in soil nutrient cycling and beneficial microbial communities.

Methods

Field experiments involved four treatments: cassava monoculture (C), maize monoculture (M), cassava-maize intercropping without straw incorporation (CM), and cassava-maize intercropping with maize straw return (CMr). The assessments covered crop growth, yield, soil chemical properties, and microbial diversity in rhizosphere, non-rhizosphere, and inter-row soils. Advanced techniques, including co-occurrence network analysis, Mantel tests, partial least squares path modeling (PLS-PM), clarified the relationships among soil nutrients, bacterial network modules, and cassava yield.

Results

Intercropping resulted in an 10.13 % reduction (P = 0.03) in maize yield and caused a temporary suppression of cassava growth during the symbiotic period; however, cassava recovered following maize harvest. Although the HDCMI system achieved a land equivalent ratio (LER) of 1.86, cassava yield declined by 6.62 % (P = 0.02) compared with the monoculture treatment. In comparison with CM, the CMr treatment boosted cassava yield (P = 0.024) and nitrogen accumulation in storage roots (P = 0.018) by 6.5 % and 24.22 %, respectively, which restored yield to levels observed in the monoculture. CMr also increased soil organic matter, improved nutrient cycling, and raised nitrogen/potassium accumulation in cassava tissues; nitrogen effects were the most pronounced. Bacterial analysis revealed that CMr promoted soil microbial α-diversity and enriched beneficial genera such as Mycobacterium, Bradyrhizobium, IMCC26256, WPS-2, and Bacillus. Furthermore, network analysis demonstrated that maize straw return facilitated nitrogen-related taxa (e.g., Candidatus Solibacter, IMCC26256) by suppressing Modules 2 (P > 0.05) and 4 (P = 0.024). These adjustments promoted nitrogen transfer and utilization in the cassava rhizosphere.

Conclusions

The HDCMI system with maize straw return enhances soil nitrogen availability through modifications in bacterial networks, ultimately supporting cassava nutrient absorption and yield formation.

Significance

This study advances the understanding of nitrogen-efficient strategies in cassava intercropping systems with maize straw return, providing a basis for nutrient-efficient agroecosystem management.