In oxidic soils, phosphorus is considered the most limiting nutrient for crop productivity because the phenomenon of adsorption occurs, due to its limited availability by adsorption reactions that immobilize the P in the fertilizer. Thus, the soil behaves as a drain of P, being adsorbed or complexed, giving rise to labile phosphorus (available to plants) and non-labile phosphorus (unavailable to plants). With time, the efficiency of phosphate fertilization decreases, requiring the application of much larger amounts of phosphorus than the plants need. Ways to recover the P have been studied and one of them is the rotation of species with high capacity to extract and use the nutrient, such as brachiaria, which contribute to reducing the adsorption of P in the soil, its movement in depth, favoring the retention of phosphorus and its use by plants. Thus, to understand the availability of P, it is intended to evaluate the forms of P in the soil in a long-term experiment, comparing situations of normal fertilization, residual fertilization and no fertilization for a long time, in the presence and absence of brachiaria as a cover crop.
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