Influence of Some Microbial Groups on Stablizing Soil Structure Against Falling Water Drops

S aggregation has been found to be increased by microbial activity in the soil (i, 2, 3, 7, 8, 9). Likewise, microorganisms and their decomposition products increased the stability of the soil structure against the action of falling water drops (5, 6). Fungi were especially effective in stabilizing the soil structure (4), and in addition, Pseudomonas -was found to be an effective stabilizer of soil structure * in native grassland '(8): However, the collective action of fungi and bacteria in soil stabilization was less than that of fungi alone. The presence of the bacteria competing for food reduced the growth and consequently the effectiveness of the fungi in structure stabilization. In influencing the growth of different microbial groups, land management plays an important role. For example, in a forest the leaves and other organic detritus are returned to the surface of the soil to decay. The aerobic conditions more often predominating at the surface of the soil promote the growth of fungi as the primary organisms of decomposition. In plowed fields residues are turned under. Under these conditions the soil'may be less aerated at lower depths than at the surface and this may tend to promote the growth of bacteria or similar organisms requiring less oxygen than fungi. In a system of stubble mulching the residues are left on the surface. Such conditions encourage the growth of aerobic organisms in the decomposition of crop residues. This causes the growth of the organisms and the stabilizing action of the decomposition products to occur largely in the immediate surface of the soil. The purpose of this investigation was to determine the influence of different taxonomic and physiological microbial groups and associations in stabilizing Peorian loess against .falling water drops.