Fracionamento do fósforo no solo em função dos sistemas de manejo

Abstract

The choice of the system of soil management is one of the main contributing factors on patterns of production and sustainability of agricultural areas, once that systems such as no-tillage (SPD) are based on long-term contributions that trigger changes in the chemical attributes and distribution of nutrients in the soil. Among the nutrients, P stands especially in highly weathered soils, where its attachment the minerals may limit their availability to plants. Therefore, the objective of this study was to evaluate the fractionation of P in function of the system of management in soils from Cerrado Mineiro. The experimental design was completely randomized with five replications. The treatments consisted in four areas: 1) 5 years ago SPD (SPD5); 2) 17 years ago SPD (SPD17); 3) Conventional Tillage System for 20 years (SPC20) and 4) Native Cerrado (CN) characterized by Cerrado vegetation, from which four composite samples were collected in each area. It was evaluated the available phosphorus (P-dis) the remaining phosphorus (P-rem) in addition to the fractioning of organic and inorganic forms of P from sequential extractions with sodium bicarbonate (labile fraction of P), sulfuric acid (H2SO4) (P moderately labile) and with sodium hydroxide (NaOH) (P moderately resistant), at depths of 0-0.05 and 0.05-0.10 m. Initially, the management systems, although overcome CN in P-rem, not promoted significant effects on this form of P when compared between then selves in the layer 0-0.05 cm, different from P-dis, which showed higher levels in SPC20. The SPC20 showed highest content of total P, which was influenced especially by the content of inorganic P in the system as a result of fertilizations, mostly in the form of accumulated P moderately labile. In SPD5, SPD17 and CN the P h was accumulated manly in the fraction of moderately resistant, demonstrating that both the highest content about the forms of greater lability of P were obtained at SPC20. However, the content of P product of sequences, the surface (0-0.05 m), it was superior in its organic form in SPD17, a situation that has been repeated only in CN, demonstrating the contribution of the system in the conversion of booking of P. The highest proportion of organic P was evident in the more labile fraction.