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By Jodi DeJong-Hughs, Published September 21 2009

Soil organic matter is good for crop production and the environment

ST. PAUL — Soil organic matter is directly related to soil fertility and agricultural productivity potential. There are many advantages to increasing or maintaining a high level of soil organic matter (SOM), including:

- Resistance to soil compaction.

- Enhanced fertility.

- Reduced nutrient leaching.

- Resistance to soil erosion.

- Increased biological activity.

- Reduction of greenhouse gases by soil carbon sequestration.

In most agricultural soils, organic matter is increased by leaving residue on the soil surface, rotating crops with pasture or perennials, incorporating cover crops into the cropping rotation, or by adding organic residues such as animal manure, litter, or sewage sludge.

Tillage results in the loss of organic matter, and is responsible for substantial loss of carbon from the soil. As carbon is released from the soil as a result of tillage, it leaves in the form of carbon dioxide. The deeper and more aggressive the tillage, the more carbon dioxide is released to the atmosphere. But reducing tillage intensity (strip tillage is an example) can maintain or increase the soil organic matter.

Near Jeffers, Minn., the U.S. Department of Agriculture measured the carbon dioxide loss from three tillage systems in a continuous corn system. The moldboard plow, the most aggressive system used, lost the most carbon dioxide in a 24-hour period. Disk-rip was the intermediate tillage system, and it lost 47 percent of what moldboard plowing did.

Strip tillage, a tillage system that tills less than 30 percent of the soil and leaves the rest undisturbed, lost by far the least carbon dioxide. Strip till lost only 18 percent of the carbon dioxide that the moldboard plow system lost.

Crop rotations that include cover crops, perennial grasses and legumes, and reduced tillage are an important factor in SOM management and can be adapted to any cropping system. Crop rotations also affect the biological diversity of an agroecosystem. The biological diversity is important for maintaining a high-functioning, disease-resistant, and stable ecological system. Crop rotations that maximize soil carbon inputs and maintain a high proportion of active carbon are important factors in establishing a sustainable cropping system.

Increasing soil organic matter has a host of benefits from both an agricultural and environmental standpoint.

Jodi DeJong-Hughes is a crops educator with University of Minnesota Extension.