In oxidic soils phosphorous is considered the most limiting factor for agricultural production because of P adsorption. So, this nutrient is applied larger quantities than needed by plants and the P ends up accumulating in the soil, which it is known as phosphorus legacy. One tool to recover available P would be the use of cover crops able of recycle the nutrient in the period between cash crops. In this way, the recycled P becomes bio available to crops grown afterwards, and can be used throughout the crop cycle. Brachiarias, for example, can reduce phosphorous fixation through the exudation of low molecular weight organic acids, besides an increase in acid phosphatase activity in the rhizosphere. Several microorganisms are capable of solubilizing unusable forms of P to plants by organic acid excretion. Therefore, crop rotations with brachiarias can result in better conditions for microorganism development and can be an important tool to increase the use of P efficiency in the system. Since cultivated grasses in the period between crops can result in better soil biological quality, it is possible to establish the hypothesis that the diversity and quantity of microorganisms involved in the P cycle are also affected, improving the recovering of accumulated P in the system and improving its use efficiency. The objective of this study is to evaluate the effect of soybean-brachiaria-maize in the diversity and quantity of microorganisms involved in the P cycle in the soil.
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