EFFECT OF APPLYING SOLUBLE AND COATED PHOSPHATE FERTILIZERS ON PHOSPHATE AVAILABILITY IN CALCAREOUS SOILS AND ON P-ABSORPTION BY A RYE-GRASS CROP

The effect of using several phosphoric fertilizers on phosphate availa bility in calcareous soils with a high phosphorus fixation capacity wa s studied. Tests were run with commercial fertilizers, differing in th e ionic species provided (urea phosphate, triple superphosphate, simpl e superphosphate, and diammonium phosphate), and experimental controll ed-release fertilizers (lignin-coated triple superphosphate and rosin- coated diammonium phosphate), each providing phosphate to the soil at a different rate. Simultaneous experiments were run (in calcareous soi ls) with a plant (glasshouse test) and with no plant (incubation test) . Phosphate availability and, therefore, plant phosphorus absorption i ncreased in such soils when fertilizing with urea phosphate (UP) or wi th lignin-coated triple superphosphate (TSPL-11). Other fertilizers su ch as uncoated superphosphates or diammonium phosphate (DAP) did not s ignificantly increase P availability compared to the unfertilized soil . The electroultrafiltration (EUF) technique was also used for predict ing the P absorbed by a crop in calcareous soils after applying a phos phate fertilizer.