Part 1, Section 10: Cover Crops
Cover Crops
COVER CROPS AND GOOD STEWARDSHIP
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, their roots create biopores in dense soil, and organic molecules are released and fungal networks are produced when the cover crop is decomposed.
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 controversial findings regarding the benefit of plant species with thick (tap)roots to penetrate compacted soil. In several studies, root growth of species with or without taproots were equally inhibited by soil compaction. However, species with taproots often produce a lower amount of root biomass than those with a fibrous root system. Present knowledge indicates that plant species that produce more root biomass in good soil also produce more root biomass in compacted soil. That is probably why crops such as corn, sorghum, sudangrass, pearl millet, ryegrass, and rye have been observed to relieve the effects of compaction. Perennial cover crops that grow during the winter are well-suited to break up 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). Through careful management, cover crops can improve soil structure at certain times of the year.
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 at 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).