Assessing Soil Microbial Biomass and Communities As an Indicator of Soil Health in Wheat Systems Under Different Nitrogen and Tillage Practices.

Wheat (Triticum aestivum L.) is a major cereal crop around the world, and its monoculture production systems consume almost 30% of all of the N fertilizers globally.  However, the N use efficiency (NUE) in wheat is only around 40-55%. As a result, the nitrogen fertilization is not only a significant economic burden on production, but also a substantial contributor to N leaching, and NOx gas emissions, with undesired consequences on water quality and climate.  Other undesired consequences of intensive monoculture wheat production systems is the decline in soil organic matter status along with the subsequent decline in soil fertility, physical structure, and buffering capacity of soils. This study was originally initiated to evaluate the diversification of wheat production systems for organic N supplementation using a summer legume rotation, and its influence on soil health and soil microbial communities, under different tillage practices. Field experiments were under till and no-till, with either inorganic N fertilization or cowpea green manure rotations. Soil core samples (0-60 cm depth) at several time points were obtained for assessing soil microbial diversity.  Abundance of eukaryotes, prokaryotes, methanogens and methanotrophs was estimated based on molecular marker quantifications using qPCR. Microbial biomass was estimated based on phospholipid fatty acids (PLFA). Soil quality was estimated by comparing the water extractable organic carbon and nitrogen pools in soil profile. Different tillage practices did not significantly affect the soil carbon pools or soil microbial communities in surface soil. However, the overall trends in subsurface soil indicated higher carbon accumulation and microbial biomass in cowpea rotations and tilled plots.