Life above the ground depends on 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 focus of the Organic Matters conference in Brandon Nov. 12.
The keynote speaker will be soil biologist Elaine Ingham, president of Soil Food Web Inc. She 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 one 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, in turn, protect the plants from disease.
Protozoa are important predators of bacteria. Bacteria concentrate nitrogen from plant sources and protozoa release it from bacteria to aid in the cycling of nitrogen. Protozoa also prey on bacteria that cause plant diseases.
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 fibre.
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 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. There are also small animals such as nematodes, arthropods and earthworms. The 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 matrix is complex.
Many farm management decisions affect 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 means a wider diversity of soil organisms and improved health of the soil system. Increasing the number of species grown at the same 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. 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. Ingham likened 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 who 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.
For more information on the Organic Matters conference, check the website www.organicmatters.ca. For more information on the soil food web and upcoming courses, see www.soilfoodweb.ca.
Frick is the Prairie co-ordinator for the Organic Agriculture Centre of Canada located at the University of Saskatchewan. Frick can be reached at 306-966-4975, at firstname.lastname@example.org, or www.organicagcentre.ca.The opinions expressed in this column are not necessarily those of The Western Producer.