Nitrogen mineralization following fall-applied compost to subsurface drip-irrigated processing tomatoes in California

Organic wastes diverted from landfills can reduce greenhouse gas emissions and are used as supplemental nutrient sources for agricultural crops after they are composted. In California, compost should be applied in the fall to processing tomatoes (Solanum lycopersicum L.) to avoid delaying field preparation and transplanting in the spring. The objective of this study was to determine soil nitrogen (N) mineralization following fall application of greenwaste compost (GWC) based on the change of mineral N during a 4 month in-field buried bag soil incubation in 2 prospective subsurface drip-irrigated processing tomato fields (PTF1 and PTF2). GWC rates of 0, 11, 22, and 34 Mg ha(-1) were evaluated in PTF1 and PTF2 in October 2019. Very dry surface soil conditions in fall 2019 and the disruptive procedure used to prepare soil for in-field incubation using the buried bag method led us to calculate net N mineralization after adjusting for the initial mineral N concentration of the unamended (0 Mg ha(-1)) control. The adjusted net N mineralization was significantly less in PTF1 (8.6 mg N kg(-1)) than PTF2 (16.4 mg N kg(-1)) and the estimated net N mineralization rate of the surface 0-15 cm soil depth following GWC application to PTF1 was less than PTF2 (1.6-1.9 vs. 2.3-3.1 kg N ha(-1) week(-1)). In-field incubation requires soil disturbance that likely affected N mineralization and additional research should consider the feasibility of using pretreatments or pre-incubations to account for disruption to antecedent soil conditions.