Long-Term Effects of Maize-Soybean Systems on Soil Microbial Diversity and Fusarium verticillioides Inoculum Potential

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Abstract
Crop succession involving soybean and maize is the predominant grain production system in many regions, while crop rotation is often recommended to enhance sustainability. However, the specific effects of these practices on plant disease dynamics and soil microbial diversity remain insufficiently understood. This study evaluated bacterial community diversity and the presence of Fusarium verticillioides fumonisin-producing strains (fum1) under monoculture and rotational systems. Maize stalks were used to assess the influence of land use on pathogen persistence in crop residues. Metagenomic sequencing (16S rRNA, V3–V4 region) was conducted across four growing seasons (2016/2017 to 2019/2020). Results showed that a three-year rotation did not significantly increase soil bacterial diversity compared to continuous maize or soybean cultivation. Precipitation was a major driver of community composition during the first three seasons, with Actinobacteria dominating in the driest year. Both bulk soil and rhizosphere microbial communities were shaped by prior land use, with continuous soybean showing the highest diversity indices. Community composition differed most between continuous soybean and rotational systems. The abundance of fum1 decreased in soils under crop rotation but remained lower in maize stalks under continuous maize. Interestingly, continuous maize cultivation appeared to suppress some diseases, suggesting that not all pathogens respond equally to rotation. While crop rotation generally reduces disease incidence, it may promote others, highlighting the need for integrated management strategies, particularly those targeting pathogen survival in crop residues.

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