Cover Crop Impacts on Soil Microbial Activity and Nitrogen Cycling in Rainfed Cotton.

Cover crops in no-till agriculture has been used to increase soil health under environments with low precipitation. This study was conducted to determine the impact of cover crop treatments on soil microbial activity and their influence on nitrogen (N) mineralization. Evaluated treatments in a continuous rainfed cotton system included: 1) conventional tillage; 2) no-till; and no-till with the following cover crops 3) wheat; 4) Austrian winter field pea; 5) crimson clover; 6) hairy vetch; and 7) mixed species. The soil sampling times chosen surrounded the chemical termination of cover crops and planting of cotton. Soil incubation studies from flush of CO₂ following rewetting of dried soil under standard laboratory conditions was used as a method to estimate soil biological activity. We hypothesize that an increased CO₂ flush will be strongly correlated to microbial activity and an increase in N mineralization. Quantitative polymerase chain reaction (qPCR) will be used to quantify the ammonia-oxidizing archaea (AOA) and bacteria (AOB) community composition, which could affect the rate of nitrification, and further improve the relationships between the flush of CO₂ and active, passive, and total carbon and nitrogen pools. Results from total organic carbon, inorganic nitrogen, phospholipid fatty acid (PLFA) data, and depth were compared to the mentioned treatments. Trends indicated higher total microbial biomass for cover crop treatments, particularly legumes, compared to conventional tillage. Microbial activity declined over time as moisture became scarce. Austrian winter field pea and hairy vetch had higher soil nitrate concentrations in the surface compared to other treatments. Mixed cover, wheat, and Austrian winter field pea had the highest concentrations of soil organic carbon.