Soluble phosphorus release from organic soils

Abstract

Soluble P release during soil organic matter decomposition was measured under fluctuating seasonal temperatures in several of Florida's organic soils. Natural soil profiles obtained from seven locations in central and south Florida were used in the study. Soil columns were leached once every 25 days, followed by applying a suction of 100 cm. Soil columns were flooded for 25 days in the months of July and August (between 14 and 21 weeks after initiation of the study for central Florida organic soils and between 11 and 18 weeks for south Florida organic soils) to simulate normal agronomic practice. The amounts of P released into effluent from Florida's organic soils were in the range of 2.9–26.2 μg P/cm 3 of soil per year (16–168 kg P ha −1 year −1). This represents 2.2–20% of the total soil P for central Florida organic soils and 0.75–1.1% of total soil P for south Florida organic soils. Soluble ortho-P accounted for about 70–89% of total effluent P for central Florida organic soils and 54–57% of effluent P for south Florida organic soils. Estimated soil P mineralization during organic matter decomposition was about 38–185 kg P ha −1 year −1 for central Florida organic soils and 16–23 kg P ha −1 year −1 for south Florida organic soils. Seasonal temperature fluctuations had minimal influence on the P release into effluent. Flooding the organic soils, however, increased P release into drainage effluent by about 4–8 times, compared with drained conditions.