Soil-borne diseases result from the reduction of the biodiversity of soil organisms. Restoring beneficial organisms that attack, repel, or antagonize disease-causing pathogens will render a soil diseasesuppressive. Plants growing in disease-suppressive soil resist diseases much better than in soils low in biological diversity. Beneficial organisms can be added directly, or the soil environment can be made more favorable for them through use of compost and other organic amendments. Compost quality determines its effectiveness at suppressing soil-borne plant diseases. Compost quality can be determined through laboratory testing. Although crop rotation reduces the risk of many row crop and cereal diseases, it does not eliminate them. Small amounts of the disease organism may persist in the soil or crop refuse over extended periods. In addition, crop rotation does not affect disease organisms that survive on or in the seed, such as the cereal smuts. Crop rotation also does not affect disease organisms that blow in from the south, such as the cereal rusts.
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