Organic Matters Conference Grounded in Soil Biology

By Brenda Frick, Ph.D.

Life above the ground depends on the life within the soil. Soil organisms are responsible for the decomposition, recycling and nutrient exchange that builds soil fertility. Healthy farming systems must foster the well being of the soil community. This is a major focus of the Organic Matters conference to be held in Brandon November 12th. Keynote speaker, Elaine Ingham, noted soil biologist and President of Soil Food Web Inc. will provide advice on how farmers can improve the health of the soil’s living community.

The soil community is highly diverse. A single gram of soil (about 1 teaspoon) can be home to 10 billion microbes of several thousand species. Microbes can be of several types, including bacteria, fungi and protozoa. Bacteria are crucial in decomposition, and in nitrogen cycling. They increase where carbon and nitrogen levels are balanced to their needs. This is usually near fresh plant materials or close to plant roots. Plant roots release dead cells, proteins and sugars that feed bacteria. Plants may foster the growth of beneficial bacteria that protect the plants from disease. Protozoa are important predators of bacteria. Bacteria concentrate nitrogen from plant sources, and protozoa release it from bacteria, and thus aid in the cycling of nitrogen. Protozoa also prey on bacteria that cause plant disease.

Fungi spread through the soil as long filaments. They are especially important in decomposing leaf litter with a high carbon to nitrogen ratio, because they can bring nitrogen to the leaf litter to balance their needs. They are also able to decompose more complex substances such as wood and fiber. Fungi can bind soil particles together, which gives the soil greater stability and water holding ability. Some fungi partner with plant roots. They are able to search a much larger volume of the soil for water and nutrients, and thus can be important to plant growth. A small proportion of both bacteria and fungi are parasitic, causing disease.

The soil life includes large numbers of bacteria, fungi and protozoa, as well as plant roots, rhizomes, tubers and seeds; and small animals such as nematodes, arthropods, and earthworms. The soil organisms live within a soil matrix that includes mineral particles and the remains of plant and animal litter. The relationship of soil organisms to each other and to the soil matrix is incredibly complex.

Many farm management decisions have an impact on the soil ecosystem. The soil food web is fed and sustained by plant material. Maintaining plant cover, especially with green manures, feeds the soil; bare fallow can starve the soil system. Increasing the number of crops grown in rotation or increasing the number of species grown at a time increases the diversity of soil organisms and the health of the soil system. Increasing the number of species grown at a time, by intercropping or by letting some of the weeds remain, also increases the diversity of plants that feed the soil.

Grassland soils tend to be dominated by bacteria, while forest soils are dominated by fungi. Dr. Ingham suggests that highly productive agricultural soils tend to be balanced in terms of the biomass of bacteria and fungi. The balance of bacteria and fungi is affected by management. Bacteria increase when plant material is mixed with the soil. Larger soil organisms like earthworms, ants and soil insects can mix plant material into the soil. Tillage can also mix plant residues with soil, but excessive tillage breaks up fungi, reduces the number of larger organisms in the soil, and causes other damage to soil structure.

Chemical use also influences the soil system. Dr. Ingham likens the decomposition of soil organic matter to digestion. Overuse of antibiotics can kill beneficial microbes in the digestive tract, resulting in resistant disease organisms and disrupted digestive processes. Similarly overuse of farm chemicals can disrupt the soil ecosystem resulting in less effective nutrient cycling and greater levels of disease.

The benefits of a healthy soil system are profound. Farmers that wish to augment the life of their soils might consider increasing the amount and variety of green cover, reducing the amount of tillage, and reducing the use of chemical fertilizers and pesticides. Farmers interested in finding out more are encouraged to attend the Organic Matters conference this fall.

Brenda Frick, Ph.D., P.Ag., is the Prairie Coordinator for the Organic Agriculture Centre of Canada at the College of Agriculture, University of Saskatchewan. She welcomes your comments at 306-966-4975 or via email at brenda.frick@usask.ca . For more information on the Organic Matters conference see www.organicmatters.ca. For more information on the Soil Food Web and their upcoming courses on the Prairies see www.soilfoodweb.ca .

This article first appeared in The Western Producer, and is published here on the OACC website with permission.

Posted on the OACC website, October 2005