REACTIONS OF UREA PHOSPHATE IN CALCAREOUS AND ALKALINE SOILS .1. AMMONIA VOLATILIZATION

Nitrogen (N) loss in the form of volatilized ammonia (NH3) is a considerable problem when ammonium (NH4+) forming fertilizers are applied to calcareous or alkaline soils. The volatilization of NH3 from urea phosphate (UP) and urea (U) was studied on three selected soils (Hayhook SL, Laveen L, and Latene L) with the use of a laboratory aeration system. Urea phosphate and U were each applied at rates of 0, 50, 100, and 200 mg N kg-1 soil, either to the surface dry or in solution or mixed with the soil. The volatilized NH3 was trapped in sulfuric acid, sampled periodically, and analyzed for N with the semi microkjeldahl distillation apparatus. The highest N loss in the form of NH3 occurred when U was applied to Hayhook soil (neutral to acidic, coarse textured, and low CaCO3 content). However, UP applied to Hayhook soil resulted in the lowest NH3-N loss. Less NH3-N loss was found from U application to Laveen and Latene soils (fine textured with higher CaCO3 content) than with Hayhook soil. The general trend was higher N loss when a surface application was made, either dry or in solution, than when the fertilizer was mixed with the soil. This trend showed an increase in the amount of volatilized NH3 with increasing N application rates. Generally, UP is a potential fertilizer for supplying N and phosphorus (P) as plant nutrients with a low potential for losses due to NH3 volatilization.