Compost

The effects of compost on soil health are almost exclusively related to the direct addition of soil organic matter to the soil with several benefits for soil's chemical, physical, and biological properties.

Compost is a great source of plant nutrients that, if used as fertilizers, can contribute to closing the loop of nutrients in agriculture. The C-rich organic compounds in compost are a source of energy for soil microorganisms. 
 
The use of compost is known to improve soil structure, water-holding capacity, and infiltration rates. These changes in soil physical properties, and water cycling and retention capacity, are directly associated with the increases in soil organic matter and biological activity with compost application.  

Compost Connector, Zero FoodPrint's newest program aims to make the best use of California’s rapidly increasing supply of compost by directing it to farms and ranches.

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Compost Application

Factors such as source materials (food waste, yard trimmings, woody material, among others), composting process, or age can affect the physicochemical and biological properties of the finished compost. Compost that has higher carbon and low nitrogen (C to N ratio higher than 20) can result in the slow release and availability of nutrients. The C to N ratio is strongly associated with the predominant feedstock used in the composting process; typically high carbon:nitrogen (C:N) ratio composts, such as those produced from yard trimmings and pruning waste, release up to 5% of the nitrogen within the first three months after application whereas low C:N carbon:nitrogen ratio composts produced from animal manures can release up to 15-30% of the applied nitrogen over the same amount of time (Azim et al. 2017; Bernal et al., 2017). 

The benefits for soil health are largely determined by management decisions such as the rate, timing, frequency and mode of application (broadcasted vs. banded). Application rates should be chosen carefully not to exceed the N and P loading capacity of the system and increase the potential for leaching, emissions of N2O, or changes in crop vigor that would affect quality. 

CDFA Compost Application Rates

Additional Resources

Altieri Lab at UC Berkeley: Vineyards Benefit from Compost and Mulch  
The Grape Community of Practice (GCoP): Compost Use in Vineyards
Cornell Composting: Compost Chemistry