1997 Annual Report for SW97-045
Decomposition and Nutrient Release Dynamics of Cover Crop Materials
Summary
Objectives
The objectives of this research are:
1. To compare potential cover crops or cover crop mixtures in terms of dry matter production and total nutrient content.
2. To monitor the loss of weight and the percentage of nutrients remaining as indicators of cover crop decomposition.
3. To compare the estimated amount of nutrients released from cover crops by the bag method vs soil sampling.
4. To showcase this work by holding periodic field data update meetings for interested people including local participating farmers in the West Side On-Farm Demonstration Project.
Abstract
The West Side of the San Joaquin Valley is one of the most productive agricultural regions of the world. The leading crops of this region include processing tomatoes, cotton, onions, garlic, cantaloupe and lettuce that are grown on over 570,000 acres annually. During the last 30 years, land use patterns on the West Side have changed considerably. Over 60 percent of the acreage in this area was typically planted to wheat, barley and safflower in 1965, whereas in 1994, these crops were grown on less than 7 percent of the area. The intensification in the production of high-value crops has led to fewer additions of organic matter to the soil, more aggressive tillage operations and a reported decline in soil quality.
In the fall of 1995, a group of 12 West Side farmers in conjunction with a team of University of California extension advisors, specialists and researchers, as well as other public and private agency consultants, initiated an extensive on-farm demonstration project of soil building practices and pest management options in this intensive row crop region. This project, extending biologically integrated farming practices within the San Joaquin Valley’s West Side, is evaluating sixteen on-farm demonstration comparisons of biologically soil building/pest management systems with conventionally managed systems.
In each of the biologically integrated parcels, cover crops and composted organic materials are integrated into rotations wherever appropriate, whereas in the conventionally managed parcels mineral fertilizer applications are made. Key soil physical, chemical and biological attributes are currently being monitored at each site. Where there is considerable dogma about the difficulty of increasing organic matter and humus contents of soils such as those of the irrigated, arid and hot Central Valley, very little is actually known about basic mechanisms and rates of organic matter decomposition and nutrient release under customary crop management conditions of this region. If farmers are to invest wisely in organic soil inputs, as a possible means of conditioning their soils and efficiently cycling nutrients, they will need much more information than is currently available on these aspects of organic amendments.
This research project is comparing three cover crops, barley, lana woolypod vetch, Phacelia and a barley/vetch mix in terms of biomass production, nitrogen content, decomposition and nutrient release dynamics. The study is being conducted at the University of California West Side Research and Education Center which serves as the organizational and educational activities hub of our local on-farm demonstration project. In August and September 1998 this field was planted with a sorghum/sudan hybrid crop so as to create more uniform water and fertility initial conditions for the start of the cover crop work. The sorghum/sudan was mowed, baled and removed in late September. The field was then leveled and 40” beds were prepared. On October 26, 1998, the four cover crops were planted in 0.09 acre (14 ft x 280 ft) plots replicated six times. Plant biomass determinations have started and will be continued every two weeks during the winter. Neutron probe access tubes have been installed for routine determinations of soil water content under the cover crops and in fallow plots.
Due to quite severe irregularities in the experimental field that was assigned to us in 1997 when we had expected to initiate this field, we requested and received from WRSARE a no-cost extension which has enabled us to begin the experimental work in the fall of 1998.
Potential Benefits
Winter cover cropping is an alternative agricultural practice that has received much attention as a means of ameliorating soil physical properties and for contributing to pollution reduction. It has been shown to increase soil water retention and infiltration and to decrease soil surface strength. Keisling et al. (1994) showed that hydraulic conductivity and bulk density were significantly improved as a result of winter cover-cropping. The use of winter cover crops also has been shown to be effective in stabilizing soil aggregates and improving porosity. Surface water quality is improved as sediment and nutrient-bearing runoff decreases.
However, benefits of improved soil physical properties and water quality must be evaluated in light of the economic costs of additional management, water demands and potential impacts on crop quality and yield. Over the last several decades, cover crops have not been widely used in Central Valley row crop production systems because of the many uncertainties associated with their management. It is hoped that this project will provided needed information on several aspects of possible benefits of cover crops in this region.
Farmer Adoption and Direct Impact
A recent survey of participating farmers in the West Side On-Farm Demonstration Project revealed that 60 percent of them intend to use cover crops more during the next five years. Because this WRSARE-sponsored work was only started in October of this year, it has not yet had direct impact on farmer adoption.
Producer Involvement
A group of 12 West Side farmers are currently involved with the West Side On-Farm Demonstration Project. This WRSARE project will provide opportunities for these farmers to become more familiar with cover crop management in the West Side region by the discussions that will be generated once data are available from the project and through possible on-farm studies that may be initiated pending project results.
This summary was prepared by the project coordinator for the 1999 reporting cycle.