Transition to Organic Production by Conventional Farmers
Nutrient availability is a major concern of conventional growers who are making the transition to organic production. In the Salinas Valley of California, on-farm research was conducted to document changes and solve problems during the transition from highly-intensive conventional vegetable production to organic production. The main focus was on changes in soil biology and nutrient availability, but many other variables were measured.
On two ranches in the Salinas Valley, 27 transects with a total of 81 sampling points were designated, where sampling of soil, crops, and pests took place nearly every time a crop was harvested. The farmer-cooperator was Tanimura and Antle, Inc. (T&A), a large vegetable production company that made the decision to allocate some of their acreage for organic production. Compost was applied and cover crops were used at least once per year. Chicken manure and organic soluble fertilizers were also applied.
Sampling began when the ranches began the transition to organic practices. The following variables were sampled repeatedly during the subsequent three years, until farms were in certified organic production:
- Soil microbial biomass C
- Net mineralizable N
- Inorganic N
- Total soil C and N (at beginning and end of 3-year period)
- PFLA (at beginning and end of 3-year period)
- Crop biomass and nutrient content
- Arbuscular mycorrhizal colonization
- Weed biomass and density by species
- Pest and disease damage and identity
- All management inputs from the grower
In addition to the monitoring of transects, a field experiment compared composts largely based on manure vs. municipal yard waste (CIWMB report ). Results show that:
- Compost derived largely from municipal yard waste increased lettuce yields after one year, compared to a compost made from manure and a lower percentage of yard waste.
- A small rather than large amount of cover crop biomass in the previous season tended to increase difference in lettuce yield between the two compost types.
- No effects of the composts on assays for soil carbon and nitrogen availability were found, although soil microbial biomass and potentially mineralizable N increased across all treatments throughout the 1.5 year period.
Very few problems were evident during the first 2.5 years of the organic transition process. Relative yields increased with time. Plant nutrition was adequate. Only a few incidences of diseases were recorded. Leafminer and aphid outbreaks occurred, but were typical of surrounding fields. The farming capabilities of this company promoted a smooth transition to large-scale organic farming.
Smukler, S.M., L.E. Jackson, L. Murphree, R. Yokota, S.T. Koike, and R.F. Smith. 2008. Transition to large-scale organic vegetable production in the Salinas Valley, California. Agriculture, Ecosystems and Environment 126:168-188. groups.ucanr.org/jacksonlab/files/52509.pdf