Nitrogen Release and Disease Suppressive Activity of Four Compost Amendments on Three Vegetable Farms

Plant and animal byproducts can replenish soil organic matter, supply nutrients, and influence disease incidence on vegetable farms. However, amendment composition and site-specific soil and climatic factors that are not well understood affect these processes, making management challenging. In this project, repeated applications of four amendments are being evaluated on three organic vegetable farms in Indiana and Ohio. Preliminary results indicate that both farm and amendment type alter nitrogen availability and pest incidence in cabbage and winter squash. Ongoing analyses will determine how resident soil microbial communities are influencing these processes, improving our understanding of the role of soil microbes and amendments in crop productivity. Results are expected to increase the practice of on-farm research and help organic farmers improve nutrient and disease management on their farms. Background Healthy soil is the foundation of sustainable crop production. Characteristics of a healthy soil include: good structure to facilitate water infiltration and plant root growth, a storehouse of nutrients released throughout the growing season, and a diverse and active soil microbial community that cycle nutrients and help plants withstand biotic and abiotic stress. To maintain soil health on intensively managed vegetable farms, growers must continuously replenish soil organic matter. Animal and plant byproducts are well known for their potential to contribute soil organic matter as well as supply nutrients on organic farms. In some cases, amending soil with these byproducts has also been found to suppress soilborne (Hoitink et al., 1997) and foliar diseases (Rotenberg et al., 2005). However, effectively meeting crop fertility needs with these amendments is challenging, and their application does not always result in pathogen suppression. Animal and plant byproducts must mineralize before nutrients are available for crop uptake, but the rate at which nutrients are released can vary substantially. The carbon to nitrogen (C:N) ratio is one factor that influences nutrient release, though site-specific factors such as moisture and tillage also have an effect. Consequently, timing nutrient release with critical periods of crop nutrient uptake can be difficult. The amount and rate of nutrient release, particularly N, could also influence disease severity in vegetable crops and may be one factor contributing to variation in the disease suppressive activity of these amendments. Changes in the composition and activity of resident soil microbes and induction of latent resistance mechanisms in plants are other factors that could contribute to the disease-suppressive activity of these amendments. Carefully designed on-farm experiments that track nutrient release from these amendments will help organic vegetable growers improve nutrient management on their farms. Such studies will also help Midwest Vegetable Trial Report for 2014