Managing Organic Matter

Fred Magdoff

Organic matter is the foundation of healthy soils. It consists of three main types of materials: living organisms, relatively fresh residues, and well decomposed, or humified, materials. We want to promote good levels of all three kinds of organic matter. A diverse population of soil organisms is one of the best ways to prevent soil-borne diseases and nematode infestations. A good supply of fresh residues supplies food to soil organisms and in the decomposition process provides nutrients to plants and sticky materials that helps develop stable soil aggregates. Well decomposed humus holds water and is a major source of soil cation exchange capacity. Good organic matter management promotes better conditions for plants, including improved soil tilth, water storage, aeration, and plant nutrition, as well as fewer pest problems.

Organic Matter Management Strategies:

1) Enhance additions of organic materials to soils. One of the primary management strategies is to encourage practices that increase the amount of organic residues added to soils annually. This encourages build-up of soil organic matter levels.
2) Reduce losses of organic matter from soils. Losses of organic matter occur by the decomposition activities of soil organisms and through erosion of topsoil. So practices that reduce erosion and that reduce the rate of decomposition work to maintain organic matter. 3) Use diverse sources of organic materials. It is through the use of diverse sources of organic materials that a diverse population of soil organisms is developed and maintained. The diverse population functions as a system of checks and balances, keeping many potential pests from developing populations high enough to cause significant crop damage.

Organic Matter Management Practices:

Enhance additions

• Better use of crop residues
• Seek out local sources of organic materials (manures, leaves, grass clippings, etc.)
• Rotations that include crops that leave large amounts of residues as well as sod-forming grasses and legumes (hay crops)
• Extensive use of cover crops

Reduce losses

• Reduce tillage intensity (use no-till or zone-till, if possible)
• Maintain surface residue cover
• Use of cover crops
• Other erosion control practices

Use diverse sources of organic materials

• Good rotations are important
• Cover crops add to the diversity of materials
• Adding animal manures and composts
• Other sources, such as leaves from towns

No individual practice is sufficient by itself. Each farmer needs to figure out what grouping of practices makes sense given the soils, labor availability, equipment availability, off-farm residue availability, and economic realities of the farm. You might start improving organic matter management by using cover crops. Other practices such as reduced tillage can be added in the following years. The more practices that can be combined, the more potential benefit to your crops. For example, a New Jersey producer of high value vegetables, Bob Muth, grows only one year of vegetables out of four. He uses cover crops, leaves from nearby towns, and rotates his vegetables with a two-year hay crop. Steve Groff grows no-till vegetables in Pennsylvania, using cover crops, a good rotation that includes hay crops, and uses animal manure. It is combinations of practices such as those farmers use that produce the best quality soils.

Managing organic matter to build high quality soils takes considerable thought and action. However, the returns can be substantial – less water runoff (more infiltrates into the soil), better soil water-holding properties, enhanced nutrient availability, better soil biological health, a soil that is more resistant to negative changes and more resilient following such a change. The payoff for the farmer is high yields of healthy crops. The payoff for society is a healthier environment.

Fred Magdoff
Department of Plant & Soil Science, Hills Building
University of Vermont
Burlington, VT 05405
Tel: (802) 656-0472
fmagdoff@zoo.uvm.edu

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