How Do Moisture Patterns in Subsurface Drip Irrigation Impact Soil Microbial Communities and Nutrient Transformations in Organic Systems?.

Over the last decade, subsurface drip irrigation (SDI) has been widely adopted in processing tomato systems in California’s Central Valley. In conventional systems, precise placement of water and fertilizer into the root zone has potential to increase tomato yields while also increasing efficiency of these resources. In organic systems, however, nutrient availability to the plants is largely reliant on mineralization of organic forms in compost and cover crop residues, a process driven by microbial activity. In SDI systems, only a portion of the soil is wetted while the majority of the soil volume remains dry during the growing season, including the surface soil where microbial biomass and activity is usually highest. We wondered whether this prolonged lack of moisture could negatively impact microbial communities, limiting the release of nutrients and transformation of carbon (C). Our study explores how the soil moisture patterns created by SDI affect C and nitrogen (N) pools, soil aggregation, microbial biomass, and plant nutrient uptake. This experiment is being conducted at the Russell Ranch Sustainable Agriculture Facility in Davis, CA, and compares SDI and furrow irrigation in organically managed tomato systems, as well as SDI in conventionally managed tomatoes. Microbial biomass C, permanganate-oxidizable C (POX-C), aggregate stability, inorganic N, plant N uptake, and gravimetric water content were measured throughout the growing season from transplanting until harvest.