P RETENTION IN TROPICAL PRE-MONTANE SOILS ACROSS FOREST-PASTURE INTERFACES

Abstract

Changes in soil properties caused by forest-to-pasture conversion and subsequent livestock grazing may contribute to the observed slow rates of tropical forest regeneration in abandoned pastures. As part of a larger study of forest regeneration in abandoned premontane tropical pastures in southern Costa Rica, we studied soil phosphorus characteristics and other soil chemical properties in pastures and adjacent forests to determine if conversion to pasture had measurable effects. We sampled soil at 30 points across five sites in ridge and slope topographic positions and at 25 m into the forest, the forest-pasture edge, and 50 m into the pasture. We quantified plant-available phosphorus, soil phosphorus retention capacity, P fixation rates, water pH, NaF pH, organic carbon, organic nitrogen, and effective cation exchange capacity (ECEC). Although anion resin strips were used to determine plant-available phosphorus, P levels extracted from the resins were below instrumental detection limits. There was a trend of increasing pH and P retention capacity with change from forest to pasture cover, but there were no significant differences between topographic positions or between forest and pasture for any measured soil properties. No differences in soil chemical characteristics across forest-pasture interfaces indicate that fundamental soil properties in the upper 15 cm of pasture soils have not changed since conversion from forest and, therefore, that the soil chemical properties we measured do not hinder recruitment and survival of forest species in abandoned pastures.