Composting plant materials and manure offers a practical way to recycle crop residue and animal waste. The process of decomposition of these materials is sped up to provide a nutrient rich soil conditioner that provides a host of agroecosystem benefits including improvements in:
- Soil tilth
- Porosity, water infiltration, and water storage
- Fertility and cation exchange capacity
- Soil borne disease suppression
- Soil organic matter and carbon
What Does the Research Say?
In recent years there has been an increase in the awareness of the multiple benefits compost and organic amendments can offer, in both conventional and organic systems. Compared to synthetic amendments which provide specific nutrients in a relatively quick burst, compost can provide all fourteen of the plant essential nutrients in a slow release form while increasing soil organic matter (SOM) and feeding beneficial soil microbes (6)(10). Increasing soil life has a myriad of benefits such as reduced soil borne diseases (9), weed emergence, and herbicide use (4).
Amendments made with organic materials like compost can significantly increase soil organic matter and sequester soil carbon in California agroecosystems (3)(7). The use of compost can significantly reduce potent nitrous oxide emissions relative to urea-based fertilizer (1). In Mediterranean cropping systems, compost application combined with cover crops or used alone has led to increased soil organic carbon more than any other practice studied including slurry application, cover cropping alone, no-till, and conventional tillage (2). Other benefits related to applying compost to improve soil structure in California cropping systems have also been observed, including: better aggregation and increased porosity, improved water holding capacity, alleviation of compaction (bulk density), and reduced nitrate leaching, surface crusting, and erosion, as well as reduced weed and disease pressure (6)(5)(2)(8).
While the quality of any compost and its nutrient content can vary widely according to feedstock and composting method, with care compost can provide a variety of system-wide benefits to the farm. It’s recommended to test any compost to determine application rates, ensure proper availability of nutrients to plants, and avoid overapplication, runoff, and nutrient loss. Particular care should be taken to prevent overapplication of phosphorus and nitrogen which can lead to eutrophication in waterways.
CAFF’s Policy Work on Compost (on page)
By advocating in the capital, meeting with regulatory bodies, testifying at hearings, and collaborating with other agricultural groups, CAFF advocates for on-farm composting regulations that are both feasible for farmers and encourage responsible practices.
‘What Does the Research Say?’ References:
- Alluvione, F., Bertora, C., Zavattaro, L., & Grignani, C. (2010). Nitrous oxide and carbon dioxide emissions following green manure and compost fertilization in corn. Soil Science Society of America Journal, 74(2), 384-395.
- Brown, S., & Cotton, M. (2011). Changes in soil properties and carbon content following compost application: results of on-farm sampling. Compost Science & Utilization, 19(2), 87-96.
- Drinkwater, L. E., Wagoner, P., & Sarrantonio, M. (1998). Legume-based cropping systems have reduced carbon and nitrogen losses. Nature, 396(6708), 262.
- Fennimore, S. A., & Jackson, L. E. (2003). Organic amendment and tillage effects on vegetable field weed emergence and seedbanks. Weed Technology, 17(1), 42-50.
- Hargreaves, J. C., Adl, M. S., & Warman, P. R. (2008). A review of the use of composted municipal solid waste in agriculture. Agriculture, ecosystems & environment, 123(1-3), 1-14. Horwath et al. 2002
- Jackson, L., Ramirez, I., Yokota, R., Fennimore, S., Koike, S., Henderson, D., … & Klonsky, K. (2003). Scientists, growers assess trade-offs in use of tillage, cover crops and compost. California Agriculture, 57(2), 48-54.
- Kong, A. Y., Six, J., Bryant, D. C., Denison, R. F., & Van Kessel, C. (2005). The relationship between carbon input, aggregation, and soil organic carbon stabilization in sustainable cropping systems. Soil science society of America journal, 69(4), 1078-1085.
- Martínez-Blanco, J., Lazcano, C., Christensen, T. H., Muñoz, P., Rieradevall, J., Møller, J., … & Boldrin, A. (2013). Compost benefits for agriculture evaluated by life cycle assessment. A review. Agronomy for sustainable development, 33(4), 721-732.
- Noble, R., & Coventry, E. (2005). Suppression of soil-borne plant diseases with composts: a review. Biocontrol Science and Technology, 15(1), 3-20.
- Wolf, K. M., Torbert, E. E., Bryant, D., Burger, M., Denison, R. F., Herrera, I., Hopmans, J., Horwath, W., Kaffka, S., Kong, A.Y.Y., Norris, R. F., Six, J., Tomich, T.P., and Scow, K.M. (2018). The century experiment: the first twenty years of UC Davis’ Mediterranean agroecological experiment. Ecology, 99, 503-503.