The Effect of Cover Crops on the Rate of Decomposition and Nitrogen Mineralization

Cover crops are key for improving soil properties for subsequent crops. Leguminous and nonleguminous cover crops each have their own specific effects on soil quality. Mixtures of these cover crops may provide the benefits of both simultaneously; legumes fix nitrogen into the soil and decompose quickly while nonlegumes tend to retain nitrogen and water. To model the optimal ratio of legume to grass cover crops for decomposition, 150 samples were prepared with set amounts of sand, organic farm soil, and water; these were divided into 6 treatments of 25 replicates each with the addition of different ratios of dried clover (legume) powder to dried rye (nonlegume) powder. Five replicates from each treatment were placed in mason jars and routinely monitored for CO2 output; CO2 is produced as plant tissues decompose. The remaining samples were harvested, mixed with KCl, shaken, and centrifuged. Liquid extracts of these samples’ supernatants were used to analyze ammonium and nitrate production. A 3:1 ratio of clover to rye produced the most CO2, followed by 100% clover. Samples containing more rye produced less CO2. T1 (100% clover) and T6 (control) samples returned much higher nitrate concentrations than samples containing rye (suggesting nitrogen immobilization among samples containing rye); ammonium concentrations increased as the amount of clover increased. These data show that a higher ratio of clover to rye in a mixture is best for decomposition, and the presence of rye in said mixture may be sufficient to prevent NO3 leaching and retain atmospheric nitrogen in the soil