The improvement to soil health is one of the more attractive benefits of cover crops. The use of cover crops can lead to greater soil biological activity, greater soil aggregation, and increased organic matter. Increases in these metrics are consistently associated with increased yields
How do cover crops accomplish this? Like their name implies, cover crops keep a constant plant cover on your soil. This helps to stop erosion of the fertile topsoil layer, helps promote microbial colonization, suppress weed growth and increase soil fertility.
Cover crops and soil fertility
Cover crops from the Fabaceae family (vetch and clover, for example) are nitrogen fixers. The amount of nitrogen added to the soil nutrient bank is dependent on plant life stage, health, and density. Typically cover crops for plant fertility are terminated at least 14 days before planting and often earlier. This allows time for soil microorganisms to begin breaking down the material and releasing the nutrients into the soil. Nitrogen tends to be highest in plants right before seed set. This means there is a push-and-shove between when is the peak time to terminate a cover crop and how late can you wait to plant. The longer you wait, the more nitrogen stacks in the plant and ultimately becomes available. The longer you wait, the less vegetative growth for your Cannabis, meaning reduced yield. The balance between maximizing nutrient content and vegetative growth is a decision each grower has to make.
Cover crops and weed suppression
Cover crops can also be good weed suppression tools. By keeping cover on soil, you can inhibit weed seed germination through either the release of germination-suppressing chemicals or blocking the seeds from receiving crucial germination-inducing signals. High biomass cover crops such as rye grass can provide impressive weed suppression. The effectiveness of rye can be extended into the growing season by terminating with a roller crimper. A roller crimper breaks the stalks of rye, leaving a covering of green mulch. The high C:N ratio in rye means it decomposes slower than high nitrogen residues such as vetch and clover, allowing for longer term suppression. The effectiveness of a weed suppression cover crop is directly proportional to the amount of biomass produced. Inconsistent germination, survival, and growth of cover crops can inhibit the weed suppressive abilities of the crop.
Cover crops, like all things in sustainable agriculture, are not a fix-all. Their utility is obvious, but their success is very dependent on germination and survival. Additionally, the benefits of cover crop may be apparent in the short term (weed suppression) or may not be realized for years (soil health).
