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March 27-29, 2000 GROW BIOINTENSIVE conference on the U.C. Davis campus
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Soil Quality Options
John Doran | William Horwath | Kate Scow

John Doran is a soil scientist and professor of agronomy at the University of Nebraska, Lincoln. For over 25 years, he has conducted research on microbial ecology as it relates to the development of sustainable management systems which enhance soil quality, economic crop production and environmental quality.

Doran mentioned first that it is only when we get together like this at larger venues that we realize how little we as individuals know. He stated that a major challenge of sustainable agriculture is translating science into practice.

He told the story of how, while studying agronomy at the university, he had received "his first lesson in soil microbiology" helping his future father-in-law plant potatoes. Mistakenly tamping the soil after each potato was planted, he was told about the geology, climatic conditions and soil needs of that particular plot of earth, by a man who had only graduated from fourth grade.

Doran gave that as an example of how we, with all of our advanced technology, have gotten away from a basic understanding of the natural world.

Doran stated that though industrial agricultural practices have increased productivity, it has always been at a high cost, and always subsidized by oil. He said when he first came to the University of Nebraska in the mid-70's, many scientists could not believe that our agricultural practices were impairing the environment. But he believes we actually do have the technological capabilities to adversely influence global functioning. Doran believes that one of our greatest challenges at the present is to reduce our dependence on fossil fuels.

He gave a couple of definitions of sustainable agriculture and stated that giving value to soil health is one of the most important avenues towards sustainability. He said "the soil is a primary interface with the global environment."

Doran said that as a first step we need to define what our goals are for sustainable agriculture and the strategies that we will use to achieve those goals. His own priorities are to:

  • conserve soil organic matter,
  • balance production with the environment, and
  • provide better use of renewable resources to get away from the use of fossil fuels and petro-chemicals.

He closed by saying that our children are not going to care if we have defined sustainability, but whether they and others have enough food to eat and a natural world to nurture them.


William Horwath is a soil organic matter specialist in the Department of Land, Air and Water Resources at U.C. Davis. His research emphasizes the role of soil organic matter in controlling soil fertility and the sustainability and productivity of managed and natural ecosystems. He uses stable isotopes to understand the carbon and nitrogen cycling processes that affect soil organic matter and microbial-plant interactions.

Horwath said that "carbon sequestration" is a term used a lot these days that means pulling carbon out of the air and putting it back in the soil to help alleviate the greenhouse effect. They are looking for management practices that will help to do that. But he stated that when carbons are put back in the soil, it changes the way nutrients cycle through the soil.

Horwath's research has been comparing conventional, low-input and organic systems, using crops normally grown in that area (the Sacramento Valley). Inputs in the organic system included compost, manure and leguminous cover crops. The low-input ("hybrid") system relies on the cover crops as well as about half of the amount of inorganic fertilizer as is used in conventional systems.

The conventional treatment uses "the best of Green Revolution treatments," which he feels have done well and have fed the world. After 10 years, the organic plot had an increase of 10 tons of carbon per hectare. The low-input treatment increased carbon by 5 tons. There was no change in the conventional plot.

He said the introduction of a cover crop significantly increased carbon, and when manure was added, the increase was even greater. And he pointed out that this happened in an increased tillage situation. As the carbon increases, so does nitrogen. When organic matter is added, the C:N ratio remains the same. He stated that these experiments have proven that in a hot, irrigated situation, carbon can be put back into the soil.

Horwath said that when using inorganic fertilizer in a conventional method, it is barely possible to get 40% of it into the crop. But the fertilizer also stimulates micro-organisms in the soil to release their nutrients. He stated that these are the types of things we need to know to optimize nutrient management, when manipulating carbon in the soil. Adding inorganic fertilizer or manure to a vetch cover crop will increase the uptake of fertilizer by the following crop by 2-1/2 %, while vetch alone will not affect the uptake. He believes the data show that low-inputÑa hybrid of conventional and organic agricultural systemsÑdoes the best job and that we should look at this without bias.

After 10 years, there are no significant differences in production of tomatoes and corn between any of these treatments, which he looked on as a plus for organic and low-input. They have not yet compared the economics of the different treatments.


Kate Scow is a professor of soil microbial ecology at U.C. Davis. Her research includes the influence of environmental variables and management practices on microbial community structure and function in soils, and the effects of pollutants and fumigants on microbial populations in agricultural and contaminated soils.

Scow first showed a fascinating slide show of greatly magnified microorganisms in various stages of activity, as she said, "to whet the audience's interest." She stressed how important microorganisms are in any kind of system, and particularly in an agricultural ecosystem the drivers of carbon and energy flow. Among other functions, they release the nutrients from pulverized matter in the soil so they can be taken up by plants, help create soil structure, and fulfill symbiotic relationships with plants. Scow said that micro-organism activity and biomass are usually greater in an organic soil.

Scow said there are numerous ways to measure soil microorganisms, but that she has broken them down into three categories:

  • count them,
  • measure their activities (the kind of work they do in their community), or
  • look at their guts, break them down into biomass and measure the resulting nitrogen and carbon.

She said there are new biological methods for fingerprinting the soil to tell, for example, how a fumigant might have affected it, or to assess the kind of research mentioned above by William Horwath.

Scow stated that you can tell the difference between organic and conventional soil communities but that the biggest difference is found in the microbe populations that exist in the soils growing different crops. She said she is now mapping soils all over California to look at the differences in patterns.


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