Ecology Action
submit search

March 27-29, 2000 GROW BIOINTENSIVE conference on the U.C. Davis campus
Home | Intro | Presentations | Breakout Sessions | Friends: Old & New | Sponsors

Soil: Its Context in Sustainable Agriculture
Louise Jackson | Jeff Mitchell

Louise Jackson is an associate professor and Cooperative Extension specialist in the Department of Vegetable Crops at U.C. Davis. For over 10 years she has conducted a research and teaching program in agricultural ecology at Davis.

Her goal is to use her research to improve water and nitrogen management in vegetable crop systems, so that fertilizer and irrigation inputs are reduced, and nitrogen losses to the environment are minimized.

Jackson stated that as a biologist, she is interested in the life of the soil, and how it changes with more organic matter input and less pesticide and fertilizer. She is addressing how soil ecology relates to sustainable agriculture. She said that interactions in the soil are complex and hard to separate. It is necessary for researchers to separate soil ecologies into their component parts.

In studying the partitioning and flow of nutrients among soil, soil biota, atmosphere and ground water, the question to ask is whether nutrients are retained or lost within the whole system. In her research, it has been shown that cover crops are instrumental in keeping nitrates from leaching to the subsoil during winter rains and that lettuce is particularly efficient in absorbing nitrogen from a cover crop.

Jackson said:

  • they also study the ecology of the soil community, the composition and interaction of all organisms in the soil, including plants and how this affects nitrogen cycling,
  • this is a very complex system and a difficult area to research,
  • markers for soil organism identification are now starting to be used and that these may eventually serve as fingerprints of community soil organism composition
  • a third area of study used is individual soil organisms and how they change under various circumstances is a key area being studied.


Jeff Mitchell is a Cooperative Extension vegetable crops specialist at U.C. Davis' Kearney Agricultural Center.

His work emphasizes soil quality assessment and improvement as well as reduced tillage production systems.

Mitchell said that he has had the opportunity in the past 4 or 5 years to work directly with farmers in a team effort that includes the USDA and other organizations. He stated that:

  • the quality of the soil is the business of everyone at the conference,
  • the ability of the soil to sustain its multitude of functions has come under question, particularly in the last 2 decades, and
  • defining soil quality has been a very difficult task.

Mitchell mentioned that on the west side of California's San Joaquin Valley there was once a wide variety of crops grown, which returned a great deal of organic matter to the soil. Today that area is mainly monocropped, leading to serious concerns among its producers about soil quality. He has been working with 15 farmers in the area to provide answers about how the regular use of manure, compost and cover crops affects the soil's organic matter, microbial activity and fertility. After 3 years, the farmers were using these inputs 70% of the time.

Mitchell also explained how difficult it is to break down the mass of data collected into component parts. They were testing the soil for its physical, chemical and biological properties, which he said had never been done before. At a different test site, near Davis, they are also experimenting with reduced tillage methods, trying to discover the optimal tillage to preserve the greatest amount of carbon in the soil.


Ecology Action has been a small 501(c)(3) nonprofit organization since 1971.

©2006 Ecology Action.

Memberships/Contributions | Site Map