Dissolution and Plant uptake of P from Ca phosphates with varying particle size in two soils. II. Plant uptake by alfalfa and rye grass

P uptake by rye grass and alfalfa from smaller particle size of DCPD (≦ .18 mm) was larger than that from larger granules (0.4–0.5, 1.0–1.25, and 1.5–1.75 mm). Differences, however, became smaller with increasing time of contact. However powdered MCP was superior to all DCPD particles size fraction in an alluvial clay and a calcareous sandy clay loam indicating that under such alkaline reaction, the rate of dissolution is more limiting than the rate of immobilization. Results also indicate that the phosphate mobility in the highly calcareous was much lower than in the clay soil due to high pH and carbonate content.