Soil phosphorus stocks and distribution in chemical fractions for long-term sugarcane, pasture, turfgrass, and forest systems in Florida

Phosphorus distribution and stability in soils of the Everglades Agricultural Area (EAA) of south Florida is important because of changing land uses. We investigated the effects of land use on P distribution in the soil profile and between chemical fractions for a histosol of the Florida Everglades. Labile, Fe-Al bound, Ca-bound, humic-fulvic acid, and residual P pools in 0-15, 15-30, and 30-45 cm depths were determined for drained soils planted to sugarcane (Saccharum sp.) for 50 yr, pasture for 100 yr, turfgrass for 60 yr, and forest for 20 yr. The P concentrations of all chemical fractions decreased with depth in the profile, indicating accumulation in surface soil resulting from oxidation and fertilization. Trends in P distribution between chemical fractions were similar between land uses. Labile P comprised less than 1% of total P. Fe-Al bound P averaged 2.9% of the total P for turfgrass and forest, but 11.4 and 9.6% for sugarcane and pasture. Increasing soil disturbance and long-term fertilization increased P allocation to inorganic fractions, as Ca-bound P contained 49% of total P for sugarcane but 28% for other land uses. Total P stocks in the soil profile (0-45 cm) averaged 1,323, 2,005, 2,294, and 2,317 kg P ha(-1) for pasture, sugarcane, turfgrass, and forest, respectively. Under current land uses P in organic fractions represents an unstable pool since the soil is prone to oxidation under drained conditions. In contrast, P sequestered in inorganic fractions is more stable under current land uses, thus sugarcane cultivation and incorporation of bedrock CaCO3 into surface soil by tillage will enhance long-term P sequestration.