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 availability in calcareous soils with a high phosphorus fixation capacity was studied. Tests were run with commercial fertilizers, differing in the ionic species provided (urea phosphate, triple superphosphate, simple superphosphate, and diammonium phosphate), and experimental controlled-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 soils) with a plant (glasshouse test) and with no plant (incubation test). Phosphate availability and, therefore, plant phosphorus absorption increased in such soils when fertilizing with urea phosphate (UP) or with lignin-coated triple superphosphate (TSPL-11). Other fertilizers such as uncoated superphosphates or diammonium phosphate (DAP) did not significantly increase P availability compared to the unfertilized soil. The electroultrafiltration (EUF) technique was also used for predicting the P absorbed by a crop in calcareous soils after applying a phosphate fertilizer.