Organic Amendments and Cover Crops in Sustainable Agricultural Systems and Urban Landscapes

NON-TECHNICAL SUMMARY: Sustainability in an agricultural system has environmental, economic, and social components, and is focused on both short-term and long-term viability of natural and human resources. Several key components of sustainability include practices that maintain and improve soil quality in the long term; use of local, renewable resources; reduction of soil disturbance; and protection of human health through safe food production practices. This project will address each of these aspects of sustainability through five field projects focused on 1) how organic amendments and practices affect soil quality and carbon sequestration in the "long term" (10 to 20 years), 2) predicting the fertilizer value of cover crops, based on the type, growth, and maturity of the cover crops, 3) reducing tillage on intensive organic farms by using cover crops as mulches, 4) evaluating the effectiveness wastewater biosolids as a component of rain garden soils to reduce runoff pollution in urban areas, and 5) a comparison of irrigation systems in reducing the risk of food-borne pathogens in intensive vegetable production. We expect this project to lead to implementation of more sustainable soil and water management practices on farms and in urban environments, and inform decision makers about the role of soil amendments in sequestering carbon and maintaining soil quality.

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APPROACH: Objective 1. Long-term effects of soil amendments on soil quality indicators. Soil quality indicators will be measured in three long-term field experiments: 1)biosolids applications to dryland wheat every 4th year since 1994, 2)single compost application surface and incorporated to beds planted to woody landscape plants in 2001, and 3)organic vegetable crop systems experiment established in 2003 comparing cover cropping systems, amendments, and tillage type. Measured indicators will include total C and N, basic nutrients and pH, bulk density, water holding capacity, infiltration (single-ring), compaction (penetrometer), C sequestration, substrate-induced respiration, nematode ecology, soil enzymes (dehydrogenase and b-glucosidase), PLFA profiles, and nitrogen mineralization (150-day incubation). Objective 2. Develop guidelines for nitrogen management from winter cover crops. Data collection from on-going fall cereal rye-hairy vetch blends and timing study will be used with lab incubation data to make biomass and available N estimates based on stand composition, maturity, and growing degree days. Objective 3. Evaluate the effects of a reduced tillage cover crop system on available N and soil quality indicators. After selecting an appropriate cover crop (cereal or cereal-legume blend), a new reduced tillage cover crop treatment will be integrated into the existing Puyallup Organic Systems experiment, and compared with a standard fall-planted rye-hairy vetch blend incorporated with tillage each spring. Soil quality indicators (see Objective 1 above) will be measured along with weed counts and soil available N. Objective 4. Determine the effectiveness of a biosolids-sand based stormwater retention mix on plant growth and stormwater treatment. A biosolids-sand based bioretention mix will be compared with a standard compost-sand mix in 1.5m-diameter planted mesocosms , with and without water treatment residuals for P management. Water inflow and outflow will be measured, and flow-composited samples collected from selected storms. Infiltration rate, compaction, and bulk density will be measured in the soil mixes over time. Objective 5. Determine the effects of drip irrigation and chlorination on food-borne pathogen and indicator presence in vegetable production. We will compare three irrigation systems: traditional overhead sprinkler irrigation, drip irrigation to reduce contact between water and plant tissues, and chlorination + drip irrigation to reduce indicators and pathogens in the irrigation water. Crops (lettuce and broccoli) will be sampled at harvest, and soils and irrigation water throughout the growing season. Analyses include fecal coliforms, generic E coli, and the presence or absence of Salmonella and E coli O157:H7. Evaluation of objectives 2-3 and 5 will be done through surveys at workshops, field days, and farm walks and follow-up surveys of innovative farmers. Evaluation of objective 4 will be 1) if the technology can be successfully developed and if so, 2) an assessment in the City of Tacoma to determine if technology is adopted. Evaluation of all objectives will also be through publication of refereed manuscripts.