Transition to Organic Production by Conventional Farmers

Louise Jackson, Liese Murphree, Irenee Ramirez, Ron Yokota, Steve Koike, Bill Chaney, Dennis Rolston, Richard Smith

Nutrient availability is a major concern of conventional growers who are making the transition to organic production. In California, research in organic production is increasing to meet the needs of this growing agricultural sector. In the Salinas Valley of California, on-farm research is being conducted to document changes and solve problems during the transition from highly-intensive conventional vegetable production to organic production. The main focus is on changes in soil biology and nutrient availability, but many other variables are also being measured.

On two ranches in the Salinas Valley, 27 transects with a total of 81 sampling points have been designated, where sampling of soil, crops, and pests takes place nearly every time a crop is harvested. The farmer-cooperator is Tanimura and Antle, Inc. (T&A), a large vegetable production company that recently made the decision to allocate some of their acreage for organic production. Compost is applied and cover crops are used at least once per year. Chicken manure and organic soluble fertilizers are also applied.

Sampling began in June, 2002, when the ranches began the transition to organic practices. The following variables have been sampled repeatedly during the subsequent three years, at which time the farms will be 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

The data will be analyzed by changes in individual variables (e.g., a soil characteristic, a crop or weed species, or a disease symptom), which can be compared year-by-year. Multiple regression can assess factors contributing to changes in a particular variable, e.g., relationships between soil moisture, soil microbial biomass, potential N mineralization, and NH4+ and NO3-. Multivariate statistical approaches (e.g., Canonical Correlation Analysis) using all or a subset of variables will also be useful for determining major interrelated changes through time.

In addition to the monitoring of transects, a field experiment has compared composts largely based on manure vs. municipal yard waste (CIWMB report ). Preliminary 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.
  • Current work is examining soil organic matter constituents and soil physical properties as causal factors for higher plant growth in the yard waste compost, which had more recalcitrant organic matter sources as starting materials.

Very few problems are evident during the first 2.5 years of the organic transition process. Plant nutrition appears to be adequate. Only a few incidences of diseases have been recorded. Leafminer and aphid outbreaks have occurred, but are typical of surrounding fields. The excellent farming capabilities of this company have promoted a smooth transition to large-scale organic farming.

References

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

Jackson, L.E., I. Ramirez, R. Yokota, S.A. Fennimore, S.T. Koike, D. Henderson, W.E.
     Chaney, F.J. Calderón, and K. Klonsky. 2004. On-farm assessment of organic
     matter and tillage management on vegetable yield, soil, weeds, pests, and
     economics in California. Agriculture, Ecosystems, and Environment
     103:443-463. ucce.ucdavis.edu/files/filelibrary/5472/21413.pdf