Past Research in Farming Systems and Agroecological Science
Analysis of Cabbage Aphid Interactions with Organic Broccoli Crops and Non-Crop Vegetation
Broccoli plants infested with the cabbage aphid (Brevicoryne brassicae) may be damaged to the point that they are unharvestable. In a study initiated in the spring of 2001, Center researchers are examined factors that affect the degree of aphid infestation, including the plant’s location in the field, the impact of wind direction, the growth stage of the broccoli when the aphids arrive (arrival time), and the location of the aphid colony on the plant itself. They also examined the effect of planting a “good bug blend” of over a dozen species, mostly clovers, cornflowers, and poppies, adjacent to the broccoli crop to see whether the blend can attract sufficient beneficial insects to help control aphid infestations. The project was located at the former Ft. Ord military base, where UC Santa Cruz leases land to Pure Pacific Farms for organic vegetable production, and at the Center’s on-campus farm; it continued through the 2004 cropping season.
CASFS participants: Diego Nieto, Bill Settle. Cooperators: John Savage, Pure Pacific Farms. Jeff Honda, San Jose State University. Funding: US Department of Agriculture Related publication – Nieto, D. J., C. Shennan, W. H. Settle, R. O'Malley, S. Bros, and J. Y. Honda. 2006. How natural enemies and cabbage aphid (Brevicoryne brassicae L.) population dynamics affect organic broccoli harvest. Environ. Entomol. 35(1): 94-101.
The Effect of Hedgerows on Beneficial Insects and Pest Control on Central Coast Farms
Hedgerows began to appear on Central Coast farm edges in 2000, due largely to the efforts of the non-profit Community Alliance with Family Farmers (CAFF). On the Central Coast, hedgerows consist of linear assemblages of trees, shrubs, herbs and grasses, many of them native species, which provide multiple services to farms.
The objectives of this study, conducted from 2005 to 2007, were (1) to assess the habitat quality of different hedgerow plants for insect natural enemies and pests, (2) to track the movement of insects from hedgerows into adjacent crop fields and (3) to test the effect of hedgerows on parasitism rates of an economically important pest, the cabbage looper (Trichoplusia ni).
The question of whether or not hedgerows can enhance biological control services in Central Coast farm systems is best addressed with on-farm studies. Thus we assessed the hedgerows that growers planted in their fields, rather than manipulate hedgerow and crop field plantings. While this approach can add more variability or “noise” to results, detected patterns also better reflect the ecological reality of hedgerows planted in Central Coast farms.
CASFS/UCSC participants: Tara Pisani Gareau, Carol Shennan. Funding: US Department of Agriculture, Earthbound Farm, UCSC Environmental Studies Department, CASFS. Related publications: Pisani Gareau, T., Farmscaping with hedgerows in the central coast of California: Examining the potential for biological control. Poster session 24: Agro-ecology, Wednesday, August 10. 2005 Annual Ecological Society of America Annual Meeting, Montreal, Canada. Pisani Gareau, T. and C. Shennan. 2010. Can hedgerows attract beneficial insects and improve pest control? Center Research Brief #13, Center for Agroecology and Sustainable Food Systems.
Maintaining Agroecosystem Health in the Organic Management of a Strawberry/Vegetable Rotation System
Organic strawberry and vegetable growers on California’s Central Coast face two major production challenges: managing soil-borne diseases without the use of chemical fumigants, and providing crops with optimum fertility while protecting water quality in sensitive habitats.
UCSC researcher Joji Muramoto, Center faculty affiliate Steve Gliessman, and Steve Koike of UC Cooperative Extension, are working with landowner Robert Stephens and strawberry grower Daniel Schmida to study a five-year organic strawberry/vegetable rotation at Stephens’ Elkhorn Ranch. This work followed three years during which the research team characterized the soil and monitored soil health indicators (levels of V. dahliae, nitrogen, and phosphorus) while the land was undergoing conversion to organic management.
Goals of the strawberry/vegetable crop rotation study include finding ways to shorten the period between strawberry crops while maintaining disease-free soil, and optimizing the use of fertility inputs to ensure that crops receive enough nutrients to produce well while minimizing leaching and nutrient runoff. See the Organic Research Network Workshop Series website for results from this study and other research conducted by members of the Organic Research Network.
CASFS participants: Joji Muramoto, Steve Gliessman (faculty affiliate), Carol Shennan. Cooperators: Steve Koike, Daniel Schmida, Robert Stephens. Funding: U.S. Department of Agriculture Related publications – Brown, M. 2003. Organic strawberry/vegetable rotation study monitors agroecosystem health. The Cultivar, 21:2, 5-6. Muramoto, J. et al. 2005. Maintaining agroecosystem health in an organic strawberry/vegetable rotation system: the first 4 years. Poster presented at the Annual Meeting of the ASA-CSSA-SSSA, Salt Lake City, Utah, Nov. 6-10, 2005. Muramoto et al. 2006. Maintaining agroecosystem health in an organic strawberry/vegetable rotation system (part 5): Final results. Poster presented at the Annual Meetings of the ASA-CSSA-SSSA, Indianapolis, Indiana, Nov 13-16, 2006. Brown, M. 2009. Organic research network members present findings at central coast workshops. The Cultivar 27 (1): 10-12.
Monitoring Water Quality in the Monterey Bay Watershed
Maintaining water quality is an ongoing challenge in the Monterey Bay watershed, where industry, urban development, and farming all affect sensitive waterways. Center researchers are collaborating with researchers and growers in the Pajaro River and Elkhorn Slough watersheds to monitor and identify the impacts of various land uses on water quality, and advise growers on ways to minimize soil erosion and runoff from their farms. Both watersheds drain into the Monterey Bay National Marine Sanctuary, the largest such sanctuary in the U.S. Initiated in fall of 2000, the Center’s water quality monitoring efforts focus on nitrate and phosphorous levels in rivers, creeks, and agricultural drainages, as well as algae "blooms" and their effects on aquatic systems. Results of this monitoring work were used to help landowners and resource managers understand the relationship between land use activities and local water quality, and to help growers reduce nutrient runoff from their fields.
CASFS Participants: Marc Los Huertos, Gerhard Epke, Kristy Morris, Carol Shennan. Cooperators: Community Alliance with Family Farmers, Monterey Bay National Marine Sanctuary, Natural Resources Conservation Service, Santa Cruz County Farm Bureau, UC Cooperative Extension, USDA-Agricultural Research Service, Watershed Institute at CSU Monterey Bay.
Funding: US Department of Agriculture, State Water Quality Control Board Related publications – Brown, M. Study examines agriculture’s impact on central coast water quality. The Cultivar 19:2, Fall/Winter 2001. Los Huertos, M., L. Gentry, and C. Shennan. 2003. Land use and water quality on California’s central coast: Nutrient Levels in Coastal Waterways.Center Research Brief #2, Center for Agroecology & Sustainable Food Systems.
Los Huertos, M., C. Phillips, and C. Shennan. 2006. Land use and phosphorus levels in the Pajaro River and Elkhorn Slough watersheds. Center Research Brief #8. Santa Cruz, CA: Center for Agroecology and Sustainable Food Systems. Los Huertos, M., C. Phillips, A. Fields, and C. Shennan. 2004. Pajaro River nutrient loading assessment. Central Coast Water Quality Control Board. SWRCB No. 02-056-130-0. Los Huertos, M., L. E. Gentry, and C. Shennan. 2001. Land use and instream nitrogen concentration in coastal agricultural watersheds. In Optimizing Nitrogen Management in Food and Energy Production and Environmental Protection: Proceedings of the 2nd International Nitrogen Conference on Science and Policy. Ruehl, C. R., A. T. Fisher, M. Los Huertos, S. D. Wankel, C. G. Wheat, C. Kendall, C. E. Hatch, and C. Shennan. 2007. Nitrate dynamics within the Pajaro River, a nutrient-rich, losing stream. Journal of the North American Benthological Society, 26(2):191–206. Ruehl C., A. T. Fisher, C. Hatch, M. Los Huertos, G. Stemler, and C. Shennan. 2006. Differential gauging and tracer tests resolve seepage fluxes in a strongly-losing stream. Journal of Hydrology 30 : 235-248. Ruehl, C. R., A. T. Fisher, M. Los Huertos, S. D. Wankel, C. G. Wheat, C. Kendall, C. E. Hatch, and C. Shennan. 2007. Nitrate dynamics within the Pajaro River, a nutrient-rich, losing stream. Journal of the North American Benthological Society, 26(2): 191–206.
Optimizing Water Use in Organic Tomato Production
In 2008, Center farm manager Jim Leap and UC Cooperative Extension farm advisor Aziz Baameur established a study of water use in organic tomato plantings to test the effects of various irrigation treatments, with the goal of finding an optimum water-use strategy that would result in improved flavor while minimizing potential yield losses.
Baameur and Leap established four replicates each of five irrigation treatments: 100%, 75%, 50%, 25% and 0% of water requirements based on California Irrigation Management Information (CIMIS) recommendations. Each replicate consisted of a 40-foot row of ‘Early Girl’ variety tomatoes irrigated with drip tape; the water stress treatments began after the plants were established. Soil water moisture sensors (a type of tensiometer) were used to quantify water depletion at the root level.
Results of the 2008 study showed no significant yield differences across the water treatments. According to Baameur, the ‘Early Girl’ variety showed remarkable plasticity to water stress. All treatments produced respectable yields of between 19,000 and 21,000 pounds per acre.Three tasting panels of 44 participants preferred the taste of tomatoes from water-stressed plots compared to those grown with ample water. Similarly, the panels found more appealing fruit aroma in tomatoes receiving the low water treatment.
Related publications - Brown, M. 2008. Study of reduced water inputs on tomatoes underway. The Cultivar 26 (1): 13. Brown, M. 2009. Less irrigation makes for similar yields, tastier tomatoes. The Cultivar 27 (1): 15.
Perennial vs. Annual Cover Crop Trials
Sustainable farming practices include improving soil conditions by planting cover crops. In 2002, Center researchers and affiliated faculty established trials at the Center’s Farm to compare two cover cropping strategies: a one-year fallow treatment cover crop of perennial rye grass, overseeded after a few months’ growth with crimson clover, versus an annual winter cover crop treatment (bell bean, vetch, oat grass mix). The researchers were particularly interested in the levels of organic matter generated by each treatment and the nitrogen available to crops following the cover crops’ incorporation.
Researchers found that available nitrogen in the perennial cover crop treatments was consistently lower through most of the experiment, suggesting that less nitrogen was available for loss from the system, but also less available to the developing crop. Yields of broccoli (a nitrogen-sensitive crop) planted after the cover crops were incorporated were significantly lower in the perennial cover crop treatment. However, yields of a potato crop planted following the cover crops were not affected by the treatments. In addition, soil respiration remained higher in the perennial cover crop treatment, even following the cover crop’s incorporation, suggesting higher levels of microbial populations in the soil.
One reason for the relatively lower available nitrogen from the perennial cover crop was the poor establishment of the overseeded clover due to gopher and slug damage. Nitrogen limitation for subsequent crops would be reduced with a good clover stand or with an addition of compost at the time of the perennial cover crop's incorporation.
Despite the impact on yields, the goals of organic production (e.g., soil building, decreased nitrogen loss) may justify the use of perennial covers and fallow periods to improve soil quality, especially in systems undergoing the transition from conventional to organic management where soil organic matter and microbial activity levels tend to be low. CASFS participants: Jim Leap, Marc Los Huertos, Carol Shennan. Cooperators: Weixin Cheng, Michael Loik, UCSC Environmental Studies Department. Funding: US Department of Agriculture.
Perennial Habitat for Conservation Biological Control in Annual Cropping Systems: An Investigation at Two Spatial Scales
Annual crops receive a substantial proportion of the insecticide used in California agricultural fields. Biological control of agricultural pests, a powerful alternative to insecticides, is difficult to achieve in short-term crops such as vegetables because frequent tillage and harvest of crops as well as the reduction of non-crop vegetation near to crop fields in recent decades, disrupts the natural enemies of crop pests. Improved biological control of pests could reduce reliance on pesticides along with concomitant environmental and public health problems. Although innovative California growers have implemented the use of hedgerows and farmscaping tactics—such as patches of perennial vegetation in lands surrounding vegetable crops—to conserve and enhance natural enemy populations for biological control by providing stable resources and refuges, these practices have not been evaluated.
In research conducted on 34 central coast organic farms, from 2004-2007, we measured natural enemy use of both common hedgerow plant species (farm-scale) and association with vegetation and other landuse factors in the land surrounding each farm (landscape-scale). Additionally, we measured movement distance of both pest and natural enemy species from hedgerows into crop fields and whether presence of hedgerows on farms or vegetation at the landscape-scale was associated with rates of attack on “sentinel” pest species within crop fields.
For images of the research, click here (3.9 mb pdf).
CASFS/UCSC Participants: Deborah Letourneau, Carol Shennan, Sara Bothwell, Tara Pisani Gareau. Cooperators: 25 central coast organic farmers/producers. Funding: U.S. Department of Agriculture NRI, UCSC STEPS Institute, UCSC Department of Environmental Studies, CASFS. Related publication: Pisani Gareau, T. and C. Shennan. 2010. Can hedgerows attract beneficial insects and improve pest control? Center Research Brief #13, Center for Agroecology and Sustainable Food Systems.