Variable Levels of Biological Activity in Sanborn Field after Fifty Years of Treatment1
From these various observations of the organic matter in the soils under different treatments on Sanborn Field it is evident that there are wide differences in the biological activities now after fifty years. Where the organic matter remains at a relatively high level it has failed to be consumed by the microorganisms very probably because of its deficiencies as a bacterial ration. Some of the deficiencies suggested are (a) nitrogen, (b) calcium, (c) phosphates, and possibly (d) potassium in the mobile forms to serve in the nutrition of the microorganisms. Where these have been added as soil treatments, the total supply of organic matter has been reduced. The increased crop returns, running parallel with organic matter reduction in the soil, suggest strongly that where the organic matter fraction of the soil is not breaking down, it is being retained at modest levels because these mineral elements are too deficient in the soil for the microbiological processes. They are then consequently deficient in the soil for the plants' activity on a high level. Such conditions suggest that when these deficient nutrient items are delivered by the soil to the plant, they may come in the main from the more slow decay of the more stable organic matter.
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