Davis, CA | cbrsmith@ucdavis.edu

Cole Smith is a Ph.D. Candidate in the Soil Science and Biogeochemistry Graduate Group at UC Davis working under Dr. William Horwath. Cole’s primary research focus is on the use and application of organic amendments within California agroecosystems. Cole holds a B.S. in Environmental Studies from Michigan State University and a M.S. from UC Davis in Soil Science & Biogeochemistry. He has worked for UC Cooperative Extension for 7 years, focusing broadly on implementing extension-based outreach and education programs aimed at increasing organic waste diversion from landfills, improving soil health, and promoting the adoption of sustainable agricultural practices.

Session Code: A1

Track: Current Research (hosted by CREF)

Session Name: Impact of Soil Carbon and Water Dynamics

Session Time: Wednesday, Jan 25, 8:15 to 9:45 AM

Presentation Title: Compost Application Can Improve Water Quality, Enhance Soil Health, and Increase Climate Resiliency in Coastal California’s Cool-Season Vegetable Agroecosystems.

Presentation Description: As a major source of cool-season vegetables for the U.S. throughout much of the year, California’s Central Coast region is under multiple threats posed by climate change and groundwater nitrate contamination. Practical solutions that reduce negative environmental outcomes while maintaining crop performance in this region are urgently needed. Substituting N fertilizer with compost has the potential to provide many co-benefits, such as improving soil health, reducing fertilizer N loss to the environment, and improving fertilizer N use efficiency, while reducing emissions of the greenhouse gas, nitrous oxide (N_2O). In partnership with a large-scale commercial producer in Salinas, CA, we implemented a split-plot designed field experiment with treatments receiving N applications at grower’s standard (GS) rate (290 lbs N ac^-1), NRCS Nutrient Management Conservation Practice Standard (CPS) 590 rate (232 lbs N ac^-1), and no N (control). In split fertilizer plots, compost was applied at a rate of 5 d.w.t/acre or no compost was applied. Soil, crop, and greenhouse gas data were collected over a period of 12 months. Results showed that crop N uptake was only significantly different (p=0.03) between the GS rate and the no N treatments, while no difference was found between GS and CPS N rates. Regardless of N application rates, the addition of compost did not significantly increase crop N uptake. Cumulative N_2O emissions were highest in the GS treatment (36.3 mg N_2O-N m^-2) and lowest in the no N with compost treatment (9.9 mg N_2O-N m^-2). All the treatments that received compost had lower N_2O emissions compared to those without compost (N application alone). Field data will be used to calibrate and validate the DayCent biogeochemical model for prediction of long-term outcomes associated with N fertilizer substitution with compost.