An overview of cover crop impacts on soil organic matter.1

a worm in plant roots

Download this fact sheet (PDF). This fact sheet is part of the Ecosystem Services from Cover Crops fact sheet series.

What is Soil Organic Matter?

  • Soil organic matter is decomposed organic material (leaves, roots, microorganisms) that exists in the soil and acts as a reservoir of water and nutrients.
  • Many analogies have been drawn likening organic matter in the soil to a sponge, a medium in which water and nutrients are stored.
  • Soil organic matter is often a measure of a soil’s fertility, and even a soil’s resilience.

Cover Crops Increase Soil Organic Matter

  • Cover crops are able to increase soil organic matter by protecting the soil surface from erosion, adding biomass to the soil (especially below the soil surface), and creating a habitat for microorganisms like fungi that contribute to the soil biology and provide more pathways for nutrient management in the soil ecosystem.
  • Legume crops were found to increase levels of soil organic matter by 8% to 114%.
  • Non-legume cover crops, including grasses and brassicas, were found to increase soil organic matter levels by 4% to 62%.

Soil Organic Matter is a Boon for Water Quality

  • By providing these services, cover crops contribute to enhanced water quality because soil organic matter enhances soil processes and properties, including soil structure, and alleviates soil compaction.
  • Additions of organic matter also increase water retention capacity, stabilize the soil during extreme weather events like drought or rainfall, and absorb and filter pollutants in runoff.
  • Research into the composition of soil organic matter has shown that it’s comprised of about 58% carbon.2 Attempts have even been made to put a dollar value on soil carbon, asserting that restoring soil carbon levels could result in savings of about $25 billion per year.

Summary

Cover crops are a good management strategy for increasing soil organic matter levels, a benefit that also has positive water quality, air quality and soil health implications. Cover crop management decisions are very important in maximizing their benefits, especially the decision to use no-till practices in conjunction with cover crops.

About Cover Crops

Rye growing in a field with corn stubble

Cover crops are tools to keep the soil in place, bolster soil health, improve water quality and reduce pollution from agricultural activities.

  • They include cereals, brassicas, legumes and other broadleaf species, and can be annual or perennial plants. Cover crops can be adapted to fit almost any production system.
  • Popular cover crops include cereal rye, crimson clover and oilseed radish. Familiar small grain crops, like winter wheat and barley, can also be adapted for use as cover crops.

1 Unless otherwise cited, all data comes from a bibliography compiled by SARE and the University of Missouri.

2 Pribyl, D.W. 2010. A critical review of the conventional SOC to SOM conversion factor. Geoderma. 156(3-4):75:83.