The Transition from Conventional to Low-input or Organic Farming Systems: Soil Biology, Soil Chemistry, Soil Physics, Energy Utilization, Economics and Risk

1994 Annual Report for SW94-017

Project Type: Research and Education
Funds awarded in 1994: $186,666.00
Projected End Date: 12/31/1996
Matching Non-Federal Funds: $513,844.00
Region: Western
State: California
Principal Investigator:
Steven Temple
University of California

The Transition from Conventional to Low-input or Organic Farming Systems: Soil Biology, Soil Chemistry, Soil Physics, Energy Utilization, Economics and Risk


1.Compare four farming systems, with differing levels of dependence on external resources over a twelve year period, with respect to a) abundance and diversity of weed, pathogen, arthropod and nematode populations; b) changes in soil biology, physics, chemistry and water relations; c) crop growth, yield and quality as influenced by different pest management, agronomic and rotational schemes; and d) economic viability.
2.Evaluate existing and/or novel sustainable and organic farming tactics.
3.Distribute and facilitate adoption of information generated by this project to all interested parties as it becomes available.

The Sustainable Agriculture Farming Systems (SAFS) project was established to evaluate the biological, agronomic, and economic performance of conventional and alternative farming systems in California’s Sacramento Valley. The study consists of four treatment systems which differ primarily in crop rotation and dependence on non-renewable resources. These include a conventional two-year rotation (conv-2) and three different four-year rotations: conventional (conv-4), low-input, and organic. The main crops are tomato, corn, wheat, beans, and safflower. All systems have used best farmer management practices, determined with the assistance of growers who cooperate on the project. Nitrogen in the organic system is derived from winter legume cover crops and animal manure while that in the low-input system comes from cover crops and supplemental inorganic fertilizer.

Crop yields in the organic system have been comparable to somewhat less than those of the conventional systems. Nitrogen has commonly been the limiting factor in the organic corn and tomato crops due to unpredictable mineralization from cover crops and animal manure. Nitrogen availability in the low-input system has been less problematic because of the limited use of mineral fertilizer. Developing cover crop management strategies to optimize nitrogen availability is an ongoing focus of the project but has been complicated by the influence that cover crops have on insect pest and weed abundance, soil water maintenance, and ultimately, farm operating expenses and profits. Disease, insect, and pathogen pressures have usually not been a significant limitation in any of the systems although there are differences in pest abundance across the treatments. Among these pest classes, weeds have been the most difficult to manage in the organic system because of the absence of herbicides.

Current research efforts are underway in the companion area of the SAFS project to improve the cover crop management practices of the low-input and organic systems for improved nitrogen availability for the following cash crop and more effective weed control. An additional experiment is being used to test the effect of late-summer/fall cultural and cropping practices on levels of bacterial-feeding nematodes in the spring, and to determine the effect of those practices on nitrogen availability to transplanted tomatoes. Research findings from the project are being disseminated through a quarterly newsletter, workshops, and a video, as well as through scientific meetings and publications.

Site Information
The research plots are located on 28 acres of the Agronomy Farm at UC Davis, Yolo County. Prior to the experiment, the acreage had been managed with conventional practices including the use of synthetic pesticides and fertilizers. Because different sections were cropped to alfalfa, vetch and beans, replicates were blocked. The plots are 60 by 220 feet (1/3 of an acre) in order to allow for use of large scale farm machinery for all operations, including planting, disking and harvesting.

Economic Analysis
In 1996 total costs for the four farming systems ranged from $694 to $903 per acre. The low-input system was the lowest cost system at $694 per acre. It was followed by conv-4 at $726, conv-2 at $807 and organic at $903 per acre. Surprisingly, the low-input system was also the most profitable among the systems this year returning $196 per acre. Its profits were closely followed by the organic receiving premium prices at $193, conv-4 with $186, and $171 for conv-2 per acre. The organic receiving conventional prices had a net loss of $109 per acre. Replanting conventional tomatoes led to higher costs in both of those systems. The other major sources of cost differences were weed control practices, use of cover crops in the organic and low-input systems, and the addition of manure in the organic tomatoes and corn.

Potential Contributions
Cover Crop Management: Specific data has been collected for production of cover crops for green manure, green chop, and seed harvest. Two winter, companion-area experiments have shown a number of species, grown individually or in mixtures, to be successful in the Sacramento Valley. Oat/vetch, barley/vetch and faba/pea were all economically viable and showed only slight yield reductions under reduced tillage. If implemented, reduced tillage management could increase energy savings and increase profit. Results from these cover crop studies could be very useful and practical for growers needing information about specific cover crops under a various climatic and management conditions. Current research in the companion area is being conducted to evaluate other cover crops for use in this area.

Low Input Management: The low input system is emerging as a very strong alternative to conventionally managed systems. Yields are consistently competitive in the corn and tomatoes. The success of this management system clearly shows that a combination of cover crop and mineral supplement not only provides sufficient N, but that the cover crop has tangible values beyond fertilizer N. The economic success of the low input corn makes it a strong contender for widespread application. Four years of results indicate that mineral fertilizer in corn can be reduced by 50 percent when adequate nitrogen is supplied from a cover crop. Furthermore pesticide use (herbicides and insecticides) in the low-input corn system over the eight years of this study has been only 25 percent of that in the conventional system.

Benefits of Tissue Tests in Corn: Tissue tests at key growth stages in corn have been very useful in identifying N deficiency in the organic corn system and alerting us to a production and N efficiency problem in the conventional system.

Disease Suppression: Corky root and knobby root have been more severe under conventional management, particularly in the two-year rotation. This indicates that the four-year rotation has contributes to disease suppression and that the organic amendments added to the organic and low-input systems through cover cropping and manure applications may suppress soil-borne pathogens.

Soil Physical Characteristics: Although most traditional agronomic experiments are much shorter than the SAFS project, we believe that even eight years is a very short time for certain differences to emerge. It has taken seven years to see negative impacts of the two year rotation as well as the positive effects on soil tilth in the low-input and organic system. Long-term positive benefits such as substantial increases in organic matter contributing to improved soil aggregation or water infiltration are becoming clearer with each season and warrant further exploration. We expect that new benefits will be continually identified as time passes.

Farmer Adoption
Changes observed and reported through verbal communication include greater interest in cover crops, legumes and crop rotations; increased organic acreage in field crops; increased monitoring by growers of water use/efficiency, pest thresholds and soil and crop nitrogen requirements; and heightened interest in a more holistic view of soil health. Agricultural equipment dealers have also begun demonstrating more of an interest in specialized equipment, specifically for tillage and non-chemical weed management. As the project has matured, there is widespread consensus that we have been able to demonstrate to the tomato industry that organic production is biologically possible and economically viable at premium market prices.
Because farmers are such a heterogeneous group and manage their farms in their own unique styles, it would be difficult to assess how many growers have actually used specific project results for their own operations. However, as interest in sustainable agriculture grows, the project has come to serve as an information base for growers and farm advisors in the area looking for either specific or theoretical information.
Reported in 1997