Fertility Amendments Alter Soil Health and Affect Susceptibility to Rhizoctonia Solani in Intensively Managed High Tunnel Production Systems.

High tunnels are increasingly being used in vegetable systems to extend the growing season and protect crops from weather extremes. We previously determined that these structures can increase pepper yield relative to production under open-field conditions, and fertility needs can be met using either inorganic or organic fertility amendments without affecting pepper yield. However, labile soil organic matter and microbial activity decreased over the course of the three year study in plots receiving inorganic fertility amendments in the high tunnel system, whereas these soil properties increased over time in plots receiving organic fertility amendments derived from plant residues. In this study, soil collected from these trials was inoculated with Rhizoctonia solani and planted with snap bean to determine how differences in soil properties could affect disease severity in a susceptible crop. Plants grown in soil collected from the high tunnel system were generally more susceptible to R. solani than plants grown in soil collected from the open field, but there was no difference between the two systems in plots that received the organic fertility amendment derived from plant residues. When soils were pasteurized prior to R. solani inoculation, there was no difference in disease severity between systems or treatments indicating that biological factors likely played a role in the differences observed. Consequently, rhizosphere soil was subject to a metatranscriptomic analyses to identify the active microbial community associated with snap bean plants, and determine their potential functional role in the suppressive activity observed. Preliminary results indicate that Actinobacteria were enriched in soils that received the organic amendment derived from plant residues, whereas Enterobacteria were enriched in soils that received the inorganic fertility amendment. Results of this study indicate that while high tunnels can increase crop productivity, soil health can be degraded over time making crops more susceptible to soil-borne and human pathogens, unless plant residues are applied to improve or maintain soil health.