Organic Manuring and Soil Amendments

In some instances, adding large amounts of organic materials to soil results in reduced populations of plant-parasitic nematodes and higher crop yields. The reduction in nematodes is thought to be caused, at least in part, by an increase in natural enemies of nematodes. In addition, the presence of decomposing organic materials in the soil apparently provides host plants with some tolerance to nematode attack. Decomposition products of organic matter and plant residues may also be detrimental, directly or indirectly, to plant-parasitic nematodes, as demonstrated by the butyric acid released by the decomposition of cover crops such as rye and timothy. Other examples of green manure crops and soil amendments reportedly effective for reducing plant-parasitic nematodes include ground sesame stalks and crabmeal. Some research suggests that ammonia released by decomposition of these soil amendments might be the active killing agent. This theory has been supported by reduced nematode populations after incorporation of agricultural-grade urea in the soil.