Long Term Impact of Tillage and Crop Rotation on Soil Microbial Diversity and Soil Health.

Soil health provides an overall picture of soil functionality that includes chemical, physical and biological features necessary for long-term, sustainable productivity.  Studies have shown that tillage has profound and complex influence on soil physical, chemical and biological properties. However, there is still a knowledge gap regarding the effect of tillage, crop rotation and residue management on soil microbial diversity .A three-year (2013-2015) study was initiated to evaluate the effects of tillage, crop rotation and residue management on soil biodiversity in a corn-soybean production system. Soil samples were collected from ongoing field experiment that studies the effects of tillage and residue on soil quality under soybean-corn rotation scheme located at North Mississippi Research and Extension Center (non-irrigated) and Delta Research and Extension Center (irrigated) in Verona and Stoneville, Mississippi, respectively. Four tillage treatments [No-till, Conservation-till (bed- roller), Conventional till (disc (2X) + Terra Till®) and Terra Till® alone] and two residue treatments [burn and no-burn (corn only)] were applied. Microbial community diversity was characterized by sequencing 16S rRNA gene on the Illumina Mi-Seq platform. The distribution of 200 most abundant OTUs (Operational taxonomic Units- Bacterial species groups) across the treatment plots from Verona and Stoneville showed strong relationship between the bacterial community change and tillage treatment .The bacterial community change at the No-Till (NT) plots was significantly different from other tillage treatments as explained by the axis of maximum variability from Bray-Curtis ordination for year 1 (2013) (Axis 1= 76 %).  Year 2 ( 2014) results showed that the bacterial community change at the No-Till (NT) and Terra till  plots were significantly different from other tillage treatments as explained by the axis of maximum variability from Bray-Curtis ordination  (Axis 2= 46 %,  ). There was no significant difference in the pattern of bacterial OTU distribution between other tillage management practices. However, there was a moderate location effect along the minor axis of variation (Axis 2= 4 %) and bacterial community composition at Verona was moderately different from Stoneville plots. Across all soils, the broad level of phylum classification (> 97% sequence similarity) showed that Proteobacteria were most abundant in conventionally tilled plots. Tillage operations in conventional plots leads to breaking up and incorporation of crop residues that would have accelerated the microbial decomposers (Proteobacteria)activity that act on the readily available carbon.  The results suggest that tillage had a profound effect on biomass and composition of soil microbial communities. Results from subsequent years would help to analyze the impact of crop rotation on soil health attributes under corn-soybean production systems.