In 1979 I was lucky enough to discover a school in Georgia practicing natural farming. We grew vegetables and an orchard in white clover living mulches. We raised a succession of wheat/rice and corn/rye within clover and vetch ground covers. All vegetation from each crop, except the actual grain, went back to the soil. There was a regular addition of high carbon straw and mowed green residue from the legume ground cover. Hence the important plant nutrients (such as nitrogen and phosphorus) were balanced with carbon in the soil as the dry straw and green, succulent legume residues merged and decomposed. These residues piled up and entangled beneath
the growing crops. It was a completely closed soil fertility system with great diversity at a microcosm level. It was a very structurally diverse place for an earthworm or a dung beetle, with many holes and crevices to hide in within straw tunnels and growing vetch roots, beneath spreading corn leaves. It was a good imitation of a natural grassland ecosystem.
Insect and disease problems were rare in the grain and vegetable fields or the orchard. We did not till to prepare the fields for planting, instead we mulched with the straw from the previous crop. Tillage diminishes the habitat of many organisms beneficial to soil and crop health, including earthworms, spiders, insects, and soil microorganisms. Undisturbed, perennial grass and legume habitats provide stable microclimates for beetles and spiders.
Beneificial parasitic wasps and flies also increase with soil cover, diversity, and reduced tillage. These wasps and flies lay eggs inside crop pests. Their young feed on the pest after they hatch, a little like invasion of the body-snatchers. Populations of parasitic flys and wasps increase in more diverse habitats, that provide season-long pollen and nectar sources. The availability of season-long wasp and fly food plants translates into higher parasitism rates. The proximity of pollen and nectar plants to crops and their pests also affects parasitism rates. In general, as for predators, the closer the pollen and nectar plants, the better.
Permanent soil cover and reduced tillage have also been associated with enhanced disease suppression. In several studies, undisturbed leguminous under-story cover crops resulted in lower levels of Phytophthora root rot and fusarium wilt. Bacterial Spot of radish was significantly reduced in no-till compared to cultivated plots. Pythium root rot suppression was compared in undisturbed and cultivated soils. Undisturbed soils were 82 percent Pythium suppressive. Newly cultivated soils were only 31 percent suppressive. In soils that had been intensely cultivated for annual cropping over an extended period, Pythium suppression dropped to only 7 percent. However, in some non-organic no-till grain production systems, increased disease has been reported. These no-till grain systems utilize large amounts of only one kind of plant residue addition, wheat straw. They do not balance green and succulent legume residue additions with dry straw additions. Diversity in all things.
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