Cover Crop Impact 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 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; and 5) mixed species. The soil sampling times chosen surrounded the herbicide burn and planting of cotton. Soil incubation studies from flush of CO₂ following rewetting of dried soil under standard laboratory conditions will be used as a method to estimate the active organic matter composition in soil. We hypothesize that an increased CO₂ flush will be strongly correlated to microbial activity and an increase in nitrogen 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 C and N pools. We the expect AOA community composition to be more abundant at depth (nutrient-poor) and AOB to be more abundant closer to the soil surface (nutrient-rich). Results from total organic carbon, inorganic N, phospholipid fatty acid (PLFA) data, and depth were compared to the mentioned treatments.  As moisture became scarce, microbial activity declined. Conventional tillage noted a large spike in biological activity at the time of planting. However, the three leguminous treatments had a higher overall microbial abundance throughout the sampling. The assessment of active soil health indicators could become more modernized with the adoption of the CO₂ flush method as a quick and reliable method for quantifying the soil biological activity and their impact on the nitrogen cycle.