Phosphorus acquisition and cycling in crop and pasture systems in low fertility tropical soils

Soil-plant processes which enhance P acquisition and cycling in low-P Oxisols were investigated in a crop rotations and ley pasture systems experiment on the Colombian eastern plains. Comparison of rooting patterns indicated that, despite low available P at depth, there are important differences in root size and distribution among native savanna, introduced forage and crop species which affect their ability to acquire P from these soils. Differences in crop/forage residue decomposition and P release rates suggest that managing the interaction of residue with soil may help slow P fixation reactions. Despite these differences, soil P fractionation measurements indicate that applied P moves preferentially into labile inorganic P pools, and then only slowly via biomass production and microbes into organic P pools under both pastures and crop rotations.