Transition to Organic Vegetable Production by Large-Scale Conventional Farmers

Transition to Organic Vegetable Production by Large-Scale Conventional Farmers

Summary

Many changes in soil and pest management, and the diversity and scale of crop production have occurred during transition to organic production of cool-season vegetables in the Salinas Valley of California. On two ranches in the Salinas Valley, 27 transects have been designated, where sampling of crops, pests and soil takes place nearly every time a crop is harvested. Over 50 transects have been sampled in the grant period so far, and the database that has been created will to provide a time course of changes during the 3-year organic transition period. Other experiments are underway to optimize soil management.

Objectives/Performance Targets

In the Salinas Valley of California, we are conducting on-farm research to describe changes and solve problems during the transition from highly-intensive conventional vegetable production to organic production. Our 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.

Our interdisciplinary group is documenting the transition from conventional to organic vegetable production on two ranches in the Salinas Valley. Our objectives are to: 1) Monitor changes in crop species and yield, soil organic matter and soil microbiology, diseases, insects, and weeds during the three-year organic transition. 2) Design experiments to target specific management and pest problems as they arise. 3) Track changes in agronomic management, economic issues and decision-making. And, 4) disseminate findings via field days, public meetings, workshops, and publications.

Our experimental design has two phases: 1) describe the farm system with its deliberate inclusion of diversity and complex rotations, and 2) troubleshoot specific problems with specific experiments. The first phase involves monitoring permanent points on two T&A ranches throughout the 3-year transition for numerous attributes to provide a time course of changes in many variables. This phase began in June, 2000, when organic practices were instated on the two ranches. The SARE grant will allow us to follow this monitoring through the whole transition. These data will allow us to answer questions about specific changes and problems through time, and interrelationships between parameters (e.g., soil characteristics, soil microbial activity, and soilborne diseases) using various statistical approaches, including multiple regression and multivariate statistics.

Accomplishments/Milestones

In June, 2000, when certified organic practices were instated on the T&A ranches, we set up permanent sampling points for frequent monitoring during the 3-year transition. On each of the 9 lots, we set up three transects. Each transect is a 2-bed strip across the entire field. There are 3 equidistant permanent sampling points (±5 m) along each transect. Thus, 81 sampling points exist. A set of measurements was taken in June, 2000. We will statistically test the assumption that the 9 lots initially have similar means and variance for these characteristics. Since then, these permanent points have been re-sampled at least twice for soil (e.g., potentially mineralizable N, soil microbial biomass, nitrate, and ammonium) and plant characteristics (e.g., biomass, nutrient content, and mycorrhizal colonization), diseases and insect pests, and weeds. The transects are sampled 0-4 days before harvest by the grower. The grower has provided us with all information on management practices, irrigation, fertilizer, compost and other inputs used for each of the transect locations for each sampled crop. Since June, 2000, 140 transects have been sampled (422 individual plots) on 46 sampling days. (Over 50 of these transects were done during the SARE grant period.) A total of 25 different crop species have been sampled.

We are still processing samples and continuing to build a database of the 2000-02 data at present. Transect data can be analyzed by several statistical approaches. Changes in individual variables (e.g., a soil characteristic, a crop or weed species, or a disease symptom) 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. These analyses will begin to be pursued in the winter of 2003-04, as organic certification will occur in June, 2003.

At this point, very few problems are evident during the first two years of the transition process. 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.

Nutrient availability is a major concern of conventional growers who are making the transition to organic production. High-grade and commercial-grade compost have been compared for their effect on soils, yield, plant nutrients, and pest problems on a 20-acre field on one of the ranches described above, the Storm Ranch. Each treatment plot is 0.6 acres. The composts are applied at 7 yards/acre. The high-grade compost contains 30% municipal yard waste, and other inputs are manure, clay, finished compost, and baled straw. The commercial-grade compost contains 75% municipal yard waste, along with manure and lime. Use of the commercial-grade compost applications is 25% less expensive than the high-grade compost. A cover crop mixture of legumes and non-legumes was used in every treatment in 2000-01, and Merced rye was used in 2001-02. The field is divided into two separate 10-acre experiments, each with four blocks per treatment. At the onset of the study in May, 2000 and again in Sept., 2002, we sampled soil at two depths (0-15 cm and 15-30 cm) at two locations per plot for NH4+ and NO3-, potential N mineralization, soil microbial biomass carbon (MBC), organic C and N, and EC. Sampling is repeated at harvest of all subsequent crops. Aboveground biomass, fresh weight yield, plant N, P and K content, and density, identity, and biomass of weeds in 1m2 quadrats are also measured. Damage from pathogens and insects is noted. There have been 14 sampling dates since the experiment began.

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, especially in plots that had a small rather than large amount of cover crop biomass in the previous season. There were no effects on assays for soil carbon and nitrogen availability, and no effects of one vs. two applications of compost per year. Soil microbial biomass and potentially mineralizable N increased across all treatments throughout the 1.5 year period. The trial will be continued through 2003, and possibly longer.

The following presentations addressed factors involved in the transition to organic production in vegetable production and in most cases, specifically described this SARE project:

Weeds During the Transition to Organic Vegetable Production. Nov. 12, 2002. Salinas. UC Cooperative Extension Weed Meeting. Speaker: Murphree.

Roots, Microbes and N Cycling: Soil Ecology in Salinas Valley Agriculture. May 23, 2002. Palo Alto. Stanford University Seminar. Speaker: Jackson.

Minimum Tillage and Organic Matter Management. Mar. 12, 2002. Davis. DANR Conservation Tillage Workgroup. Speaker: Jackson.

Cover Crop Field Day. Feb. 21, 2002. Salinas. UCCE Cooperative Extension Monterey County. Speakers: Brennan and Smith.

Cover Crop Field Plot Demonstration. Jan. 16, 2002. Salinas. Irrigation and Nutrient Management Conference 2002. Speakers: Brennan and Smith.

Organic Matter Management, and Soil and Plant Health. Jan. 16, 2002. Salinas. Nutrient Management Conference 2002. Speaker: Jackson.

Nutrients and Irrigation. Jan. 29, 2002. Hollister. Water Quality Short Course. Speaker: Smith.

Minimum Tillage and Organic Matter Management. Mar. 12, 2002. Davis. DANR Conservation Tillage Workgroup. Speaker: Jackson.

Soil Biology and Transition from Conventional to Organic. Jan., 2002. Ag Alert Newsletter. Staff Writer: Bob Johnson.

Soil Aspects of the Transition to Organic. Dec. 5, 2001. Davis. DANR Vegetable Crops Continuing Conference. Speaker: Jackson.

Transition to Organic-A Multidisciplinary Approach. Dec. 4, 2001. Salinas. Annual Entomology Seminar. Speakers: Smith and Chaney.

Weeds in the Community. Nov. 16, 2001. Salinas. WOW Weed Symposium. Speaker: Jessyka Wengren (CSU Monterey Bay intern).

Salinas Valley Organic Strawberries and Vegetables: Research Results and Implications for Production. Nov. 1, 2001. Davis. DANR Organic Farming Workgroup. Speaker: Jackson.

Effects of Organic Amendments and Tillage Practices on Soil Microbial Biomass, N Availability and Crop Yield in Intensive Agriculture. Aug. 9, 2001. Madison, WI. Ecological Society of America National Meeting. Speaker: Jackson.

Ecological Principles: Components of a Sustainable Organic System (What we know and don’t know). July 22, 2001. Sacramento. American Society for Horticultural Science National Meeting. Speaker: Jackson.

Impacts and Contributions/Outcomes

Our research team involves a major vegetable company, farm advisors, extension specialists and faculty, and by the nature of its collaboration, has both direct and indirect impacts on the visibility and success of this organic transition project.

1) On-farm research is an effective way to directly distribute research to farmers and other members of the agricultural industry. Although we started this project on other funds from the California Integrated Waste Management Board and a Workgroup grant from the University of California Division of Agriculture and Natural Resources, the SARE grant provides a way to carry on the project through the full organic transition process, and develop a much more comprehensive research plan than before.

2) The project has been introduced to public audiences and results have been disseminated, as described above.

3) An undergraduate student internship program between our project and California
State University Monterey Bay (CSUMB) has been very effective. Three students were employed all summer, and ten others were involved during the most intensive sampling periods.

4) The results from this long-term trial will provide other growers with information needed to optimize the organic transition process. The information will also be useful to conventional growers who are interested in increasing soil quality and alternative pest management.

Collaborators: