Soil P Fractions in Farmed and Unfarmed Organic Soils.
Miguel Castillo1, Xing Wang2, and Alan Wright2. (1) Zamorano Univ, 9300 Lee Hwy, Suite G130, Fairfax, VA 22131, (2) Everglades Research & Education Center, Univ of Florida, 3200 E Palm Beach Rd, Belle Glade, FL 33430
Tillage and agricultural practices for calcareous organic soils may alter the distribution of P among labile and recalcitrant pools. The objectives of the study were to determine the long-term impacts of tillage and cropping on P distribution in organic muck soils. Soil samples were taken from soils cropped to sugarcane and vegetables for 80 yr and from adjacent unfarmed soil. Soil P was fractionated into labile, Fe-Al bound, Ca bound, humic-fulvic acid bound, and residue P pools. Phosphorus contents of all fractions except humic-fulvic acid P were greater for farmed than unfarmed soil due to P fertilizer inputs. The P levels decreased with depth for all fractions except for Ca-bound P for unfarmed soils, which were highest for soil depths (30-45 cm) directly above bedrock limestone. Incorporation of limestone into 0-15 cm soil by tillage significantly altered P dynamics, increasing P levels in the Ca-bound fraction 72% compared to unfarmed soil. Added fertilizer (0 to 150 kg P ha-1) to farmed and unfarmed soils increased P in the labile and Fe-Al fractions of both soils, but only the Ca-P fraction of farmed soils, suggesting that incorporation of limestone into surface soils increases fertilizer-P incorporation into non-labile pools, possibly necessitating increases in fertilization rates for crops.