High-Density Planting of Panicum virgatum Enhances Soil Carbon Sequestration, Whereas Cultivar Selection and Temporal Dynamics Drive Root and Soil Microbiomes

Understanding how agricultural conservation practices influence soil and rhizosphere microbiomes is critical for advancing sustainable crop production and soil health. While Panicum virgatum L. (switchgrass) is widely used in conservation agriculture for its potential to enhance soil carbon storage, limited research has explored how planting density and cultivar selection affect microbial communities and soil properties. This study aimed to evaluate the effects of four switchgrass cultivars planted at two densities on soil and root microbiomes, as well as key edaphic parameters, over a growing season in a common garden experiment in southeast Mississippi. High planting density resulted in higher soil carbon and organic matter, and marginally higher soil nitrogen, but had negligible effects on the microbiomes. In contrast, switchgrass cultivars minimally affected soil properties, but differed in their microbiomes. Both microbiomes and soil properties varied temporally, likely due to plant nutrient uptake and microbial activity. These findings demonstrate that while planting density can enhance soil carbon sequestration, microbiomes are strongly shaped by cultivar selection and temporal dynamics. This study contributes to optimizing conservation agriculture practices to promote soil health and long-term ecosystem sustainability.