Soil bacterial biodiversity is driven by long-term pasture management, poultry litter, and cattle manure inputs

Soil microorganisms are important for maintaining soil health, decomposing organic matter, and recycling nutrients in pasture systems. However, the impact of long-term conservation pasture management on soil microbial communities remains unclear. Therefore, understanding soil microbiome responses and the impact of conservation pasture management, is an important component of maintaining soil health, fertility, and potentially increasing forage yield on the largest agricultural land-use in the US. The aim of this study was to identify soil microbiota and evaluate soil microbiome community differences based on 13-years of pasture management [hayed, continuously grazed, and rotationally grazed with a fenced, un-grazed and unfertilized buffer strip (control)]. Since 2004, all pastures received broiler litter at an annual rate of 5.6 Mg ha-1. Soil samples were collected at a 0-15 cm depth from 2016-2017 and bacterial communities characterized using Illumina high-throughput 16S rRNA gene amplicon sequencing. Overall, pasture management influenced soil microbial community structure, as well as year effects on it (P<0.05). Soils receiving no poultry litter or cattle manure had the lowest microbial abundance, which corresponded to lower soil fertility. Continuously grazed systems had the highest (P<0.05) soil community richness. Consequently, increased grazing pressure may increase soil diversity, owing to continuous manure deposition, which is rich in microflora and nutrients. Another possibility is that the stressed plants excrete compounds in the rhizosphere that provide substrates that encourage the growth of different types of bacteria. These results suggest conservation pasture management (e.g. rotationally grazed systems) may not result in improved microbial diversity, albeit, filter strips were effective at reducing nutrients and bacterial movement as evident by low diversity and fertility in these areas. Overall, animal inputs (litter or manure) may directly drive phylogenetic community structure and be a source of increased diversity in soil microbiome communities.