2017 ASHS Annual Conference

The soil microbial community regulates many key agroecosystem services including nutrient cycling and biological control of pathogen and insect pests. The composition and activity of the soil microbial community is affected by site-specific soil and environmental conditions, as well as agricultural management practices. The objectives of this project were to: 1) determine how composition of organic fertility amendments interact with resident soil microbial communities to affect nitrogen (N) availability and pest incidence and severity on organic vegetable farms, 2) identify amendments that can improve soil biological quality, provide plant available N during periods of critical N uptake, and reduce pest outbreaks, and 3) demonstrate and increase the practice of on-farm research. Experiments were conducted during 2013-2015 on three farms that varied given soil type and length of time under organic production. Growers participated in development of the study design, data collection, and outreach events. Repeated applications of four amendments were applied to experimental plots annually and plots were planted with cabbage, squash, and tomato in years 1-3 respectively. Plots were monitored regularly for N availability, soil chemical and biological properties, pest incidence and severity, and crop yield. Nitrogen availability, severity of black rot, root rot and white fly, and crop yield varied given amendment composition as well as initial soil quality characteristics. Some variability in soil quality improvement due to amendment composition was observed within each farm, though all amendments increased labile soil carbon, soil microbial activity, and pathogen suppressiveness over time. Results of this study demonstrate that soil biological quality is intimately tied to N availability, pest severity and yield on organic vegetable farms. On-farm research is a valuable tool that can provide new insights into soil microbial ecology, and identify organic fertility amendments that improve soil quality, provide sufficient plant available N, and optimize vegetable crop productivity.