Plant Phosphorus Availability in Latosols and Luvisols from Northeastern Semi-arid Brazil

Abstract

Phosphorus (P) availability to plants in samples of soil horizons of up-, mid-, and downslope positions of three toposequences of Latosols and three of Luvisols from Northeastern semi-arid Brazil was evaluated cultivating brachiaria grass, in pots, during 4 months. Plant uptake was compared to changes in soil P fractions, determined before and after cropping, by a modified Hedley sequential extraction in the following order: resin-P, NaHCO₃–P (inorganic and organic), NaOH–P (inorganic and organic), H₂SO₄–P, and H₂SO₄/H₂O₂ digestion (residual P). In general, different horizons and slope positions of the same soil classes had similar P fraction decreases with cultivation. Readily available inorganic P fractions (resin and NaHCO₃) were the most depleted ones (40–90% and 43–76% of the original P, respectively). Luvisol samples had significantly larger readily available inorganic P decreases than Latosol ones but differences in total P decreases were not significant. Inorganic fractions losses were higher at the surface, whereas losses of organic fractions were higher at subsurface horizons. In both soil classes, dry matter production and plant P uptake were highly correlated to the decreases in readily available inorganic P fractions.

Acknowledgments