Phosphorus fractionation in oxisols under agroforestry and conventional coffee systems in Brazil

Abstract

Phosphorus is a primary limiting nutrient for crop production in highly weathered tropical soils. We hypothesised that the distribution of P among the various pools is influenced by land use and soil management. The objective of this paper is to compare the soil P pools at different depths in agroforestry and conventional coffee cultivation systems. The study was carried out in Brazil with Oxisols as the dominant soil type. Soils were collected from four coffee (~Coffea arabica~) fields, two with an agroforestry system and two with a conventional system. Per field three profiles were sampled at depths of 2–3, 10–15 and 40–60 cm. A simplified sequential P fractionation was carried out, using resin, NaHCO3, NaOH and HC1 as extractants. P contents were higher in the conventional systems than in the agroforestry systems, but the ratio of organic P to total P was at all depths higher in the agroforestry fields than in the conventional fields. It may indicate that the influence of agroforestry systems on the dynamics of soil phosphorus lies in the conversion of inorganic P into organic P and may increase in this way the amount of P that is within the reach of agricultural crops.