The effects of soil physical and chemical properties related to the soil Phosphorus Buffering Capacity (PBC) on soil P critical levels, by Mehlich-1, Mehlich-3, and Bray-1 extractant solutions were studied in six soil samples of the State of Pernambuco and in plant shoot, for the cultivation of Brachiaria brizantha (Hoscht ex A. Rich.) Stapf. cv. Marandu. This research was carried out under greenhouse conditions with surface soil samples with different clay contents, to which P doses, defined by the soil solution equilibrium P (EP), were applied. The treatments were distributed in a factorial scheme (six soils and six P rates), in a complete block design, with three replicates. Clay content did not reflect the PBC, nor relate with the soil P critical level or P the critical levels in the B. brizantha plants. The characteristics which best reflected PBC were soil P maximum adsorption capacity (PMAC) and EP. Therefore, since PMAC is not a laboratory routine analysis, and is more difficult to be conducted, EP is the most adequate analysis for estimating the soil PBC. Soil P critical levels varied according to the extracting solution in use, with values ranging from 15.2 to 138.5 mg dm-3 at the first cut, and from 2.1 to 62.3 mg dm-3 at the second cut. Chemical characteristics such as PMAC and EP influenced the soil P critical levels. P Critical levels are lower in soils and in B. brizantha plants with higher PMAC and lower EP levels. The extractant solutions best correlated to P taken up by plants were Mehlich-1 and Mehlich-3.
Mehlich-1; Mehlich-3; Bray-1; phosphorus buffering capability; equilibrium phosphorus
