Apply 25 to 200 pounds of compost per 100 square feet of soil. Be aware that high levels of woody material composted will deplete the soil of nitrogen. Add animal manure before application. A soil high in organic matter decreases nematode populations. Nematodes are microscopic eelworms damage plant by forming lesions on the roots.
Some soil microbes are natural enemies of nematodes.
Consider green manuring or planting cover crops prior to planting your main crop. Incorporated the crop into the soil to add organic material, improve soil drainage and microbial activity. Important elements such as nitrogen, phosphorus, potassium, magnesium and iron retained to benefit the intended crop. Legumes have added Rhizobium bacteria in their root systems. Green manuring proves to decrease soil nematode populations.