COATED DIAMMONIUM PHOSPHATE EFFECT ON SOIL-NITROGEN LIXIVIATION AND ITS RELATION WITH PROPERTIES KINETICS

Slow-release fertilizers were prepared by coating diammonium phosphate (DAP) with rosin and tricalcium phosphate. The DAP dissolution kineti cs in water of these products is of the Ist order, leading to the conc lusion that the values of the dissolution rate constants depend on the coating percentage. A glasshouse test with rye grass was carried out in order to evaluate the efficiency of the fertilizers as regards nitr ogen (N) uptake by the plant and N lixiviation in high leaching condit ions. It has been proved that by using coated products the loss of N w as reduced, but the yields of dry matter were still good as was the N uptake by the plant. It has also been proved that losses through lixiv iation are lower when the fertilizers are mixed with the soil. Finally it was possible to establish linear correlations between kinetic indi ces deduced from the solubility of the products in water and indices d educed from the response of the soil-plant system.