Managing Soil Food Webs for Enriched and Suppressive Soils: Effects of Cover Crop Diversity and Quality

Project Overview

Project Type: Graduate Student
Funds awarded in 2007: $19,235.00
Projected End Date: 12/31/2009
Region: Western
State: California
Graduate Student:

Annual Reports


  • Agronomic: oats, wheat
  • Vegetables: tomatoes
  • Additional Plants: native plants


  • Crop Production: conservation tillage
  • Education and Training: extension
  • Natural Resources/Environment: biodiversity, indicators
  • Pest Management: competition, integrated pest management, mulches - killed
  • Production Systems: agroecosystems, holistic management
  • Soil Management: green manures, organic matter, nutrient mineralization, soil quality/health

    Proposal abstract:

    Agricultural landscapes are often deficient in soil food web diversity due to frequent disturbance from tillage and chemical inputs (Wardle, 1995). Yet soil organisms perform important ecosystem services such as nutrient cycling (Ferris et al., 2004; Yeates and Wardle, 1996) and pathogen and pest suppression. As natural systems have evolved over millennia to effectively regulate disease and nutrient availability, it is logical to study and imitate their successful traits, which include: high plant species richness, perennial species and minimal disturbance. Nematodes are indicators of soil health. They are represented at all trophic levels in the soil and regulate many soil functions, thus nematode abundance and diversity indices reflect overall composition and functioning of the soil food web (Ferris et al., 2001). To establish management systems based on our knowledge of productive natural systems, we will study the nematode community and the soil food web of natural systems to assess the capacity of various management practices to return agricultural soil to a more naturally productive and disease suppressive state. Natural systems to be evaluated include the California Jepson Prairie and Kansas undisturbed bottomland prairie. It is important to provide farmers with practical management practices based on natural systems concepts. Comparison of management practices that include plant species diversity and perennial vs annual plants will be evaluated in field and mesocosm trials at UC Davis and Land Institute field sites in Kansas. Management practices tested include cover crops of varying carbon to nitrogen ratios combined with strip tillage and mulching.

    Project objectives from proposal:

    We will use nematodes as an indicator of soil food web structure and function. Nematodes are the most abundant metazoan in soil ecosystems, have high functional diversity, and participate at both resource entry and upper levels of the soil food web (Bongers, 1998). They affect and respond to bacterial and fungal populations, organic matter decomposition, and nitrogen mineralization (Ferris et al., 1997; Yeates et al., 1996; Postma-Blaaw et al., 2005). Bacteria quickly increase in response to nitrogen-rich inputs, and bacterial-feeding nematodes respond quickly to this increased resource. The Enrichment Index (EI), based on the weighted abundances of bacterial and fungal feeding nematodes, quantifies this response and indicates soil productivity (Ferris et al., 2004). The Structure Index (SI), based on weighted abundances of predator and omnivore nematodes, indicates the complexity and maturity of the soil food web (Nagy, 2004; Berkelmans, 2003). We believe that the SI also indicates the ability of the soil food web to regulate disease and parasites (Sánchez-Moreno and Ferris, submitted). Our primary aim is to provide farmers with management strategies that optimize soil food web services, specifically nutrient cycling and disease suppression. Objective 1: Understand the effects of cover crop quality on the soil food web. Do cover crop carbon-to-nitrogen ratios influence the nutrient cycling and suppressive capacity of soils as indicated by the Structure Index (SI) and Enrichment Index (EI)? We hypothesize that high C/N inputs increase soil food web structure, low C/N inputs increase nutrient cycling capacity, and balanced C/N ratios maintain both soil food web structure and enrichment indices. Objective 2: Quantify the effects of increased cover crop diversity on the soil food web. Can complex cover crop mixtures increase disease suppressive and nutrient cycling capacity of soil food webs as indicated by the SI and EI? We hypothesize that higher cover crop diversity will increase suppressive and enrichment capacity of soils as indicated by the SI and EI.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.