In any crop rotation, proper weed control is important since many weeds are suitable pest hosts. There are some green manures that result in remarkably good nematode control when they are incorporated into the soil. Rapeseed, sudangrass, white mustard, and rye not only control nematodes, but they have also been shown to suppress weeds and diseases such as the soilborne fungus Verticillium dahliae, which causes potato early dying. That is, they release a compounds into the soil which are toxic to certain other plants and animals. All green manures have benefits to the soil that extend beyond the chemicals they may release.
Cover crops can reduce erosion from rain or wind, especially in the winter or early spring.
When green manures are incorporated into the soil, they build up the organic matter content, which improves water retention, reduces compaction, and makes the soil a healthy habitat for beneficial organisms. Pests have to compete with the beneficial organisms in the soil, so their populations are unlikely to rise to damaging levels. Legumes are important green manures for any organic farms. They have a symbiotic relationship with bacteria that can fix nitrogen into a form that plants can use. When legumes are incorporated into the soil prior to a potato crop, the nitrogen is made available to the potatoes.