Part 1, Section 10: Cover Crops
Cover Crops
PURPOSES OF COVER CROPS
Soil Structure Improvement
Cover crops can help to maintain or improve soil structure because they protect soil from rainfall impact and extreme temperature fluctuations, their roots hold soil particles together and create biopores in soil, and organic molecules are released and fungal networks are produced when the cover crop grows and when it decomposes.
Overall, the best cover crops for soil structure improvement are those that produce a fibrous, extensive root system such as gramineous (grassy) species. The roots of these species hold soil together and also find ways to penetrate dense soil. There are indications that tap-rooted species that penetrate sub-soil layers create gateways for the roots of the succeeding crop. This way, a soybean crop following a cover crop such as ‘Daikon’ radish extracted moisture from deeper depths than if the soybeans did not follow a cover crop. Plant species that produce large amounts of root bio-mass can also also help to alleviate soil compaction. That is probably why crops such as corn, sorghum, sudangrass, pearl millet, ryegrass, and rye have been observed to relieve the effects of compaction. Cover crops that grow during the winter are well-suited to loosen hard layers in the soil because they can grow into those layers when they are softened by plentiful water (this is less likely in the summer).
Cover crops with a low C:N ratio will, when decomposing, release large quantities of organic molecules such as polysaccharides that improve soil structure. This is the reason why soil is mellow in the spring following a soybean crop. This effect is expected to last only as long as there is decomposable residue. Cover crops with a high C:N ratio will have a slower release of polysaccharides, which improves soil structure more slowly but for a longer time than cover crops with a low C:N ratio (Figure 1.10-3).