Dinâmica do fósforo em latossolo do cerrado sob sistema de integração lavoura-pecuária

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The integration of crop-livestock systems (ILP) is one of the alternatives to recover the fertility of soils under degraded pastures in the Cerrado region. This system has positive effects on soil fertility and quality, increasing organic carbon contents and soil biological activity, thus requiring a new characterization of soil fertility by identifying soil indicators (physical, chemical, and biological) that are sensitive to changes in P bioavailability perceived by cultivated plants. Within this context, this study aimed to make considerations on the effects of the crop-livestock integration system, on residual effect of phosphate fertilization of pasture on a soybean crop. The study was conducted in an experiment area at Embrapa Cerrados, Planaltina-DF, where the pasture was sown into three subareas of 1,5 ha, which received fertilization levels of 0 (P0), 20 (P1), and 40 (P2) kg ha⁻¹ P2O5, for each subfragement of pasture applied annually in the form of single superphosphate. After the fourth year of grazing the entire area was desiccated and soybean cv. BRS Valiosa RR was sown, at three fertilization levels, 0 (S0), 50 (S1), 100 (S2) kg ha⁻¹ of P2O5 in the form of triple superphosphate applied in the planting furrow, totaling 9 fertilization zones. A soybean crop evaluation (productivity value and P content by plant), available inorganic P contents (P-Resina, P-Mehlich and P-Olsen), and organic P mineralization potential (acid phosphatase) throughout the crop cycle was done collecting samples in three seasons, as follows: the first in the vegetative period (V5.), the second at full bloom (R2.), and the third at the end of maturation (R8.2.). The available P contents on soil, the activity of acid phosphatase, the drying material production and the P content accumulated by soybean plant were analyzed. P-Mehlich, P-Resin and P-Olsen contents produced positive correlations in the three sampling seasons. Differently from the others, the Olsen extractor indicated a tendency of stability with a small increase in P contents with time, especially in the three fertilization zones where only pasture fertilization was performed (P0S0, P1S0, and P2S0). However, all extractors presented positive correlations with MS produced by soybean, where the best coefficient o correlation was obtained with the Resin. P accumulation by the plant in the fertilization zone P2S0 was not different from P0S2, suggesting that early fertilization in the pasture can be as effective as direct fertilization in the soybean crop. This confirms that the residual P available arising from the pasturecontribute to meet the soybean litigation as much as the phosphatase fertilization accomplished exclusively to the aforesaid crop. The high acid phosphatase activity values obtained may have facilitated organic residual P mineralization in the pasture, but its variation between sampling seasons, suggests that this is the main factor of influence. The residual fertilization effect in the pasture can be observed in the fertilization zone P2S0, which reached a productivity value of 3735 kg ha⁻¹ soybean. Conversely, the negative value of P (-5.7 kg ha⁻¹) on P0 pasture, exported by meat production, confirms the reason for increased pasture degradation under systems of an extractivist nature. The fertilization zones that received the highest portions of P during fertilization exported the most P, but approximately 85% of all P applied stayed as residue.

ASSUNTO(S)

fertilizantes fosfatados agricultural systems agroforestry phosphatic fertilizers sistemas agrícolas agrosilvicultura solos - teor de fósforo soils - phosphorus content

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