REACTIONS AND TRANSFORMATIONS OF FERTILIZER-DERIVED NITROGEN AND PHOSPHORUS IN IRRIGATED SOILS (NITRIFICATION INHIBITOR, DRIP, UREA PHOSPHATE, ACIDIFICATION, TERRAZOLE)

In arid regions of the world, the application of irrigation water and fertilizer to agricultural land can greatly increase crop production. These studies were undertaken to determine the fate of applied fertilizers in irrigated soils in achieving high crop yields while conserving resources and minimizing environmental pollution.; The first experiment dealt with growing tomatoes (Lycopersicon esculentum Mill.) in soil columns in the greenhouse with drip irrigation for 60 days. Nitrogen was added with every irrigation at four concentrations (0, 50, 100, 200 mg N/L) as urea-ammonium nitrate. The drip emitters were placed either on the soil surface or 2.5 cm below the surface. Ammonia volatilization was less than 0.1% of the total N applied. Soil nitrate concentrations were highest near the soil surface while NH(,4)('+) was localized near the emitter. Soil pH values as low as 5.0 were measured 5 to 7 cm beneath the emitter but approached the initial value (6.8) at increased distance from the emitter.; In the second experiment, tomatoes were grown in a P-deficient calcareous soil in 114 L cans. Phosphorus was added weekly through drip irrigation as urea phosphate (UP) (17-44-0) at four concentrations (0, 20, 40, 80 kg P/ha). Two other treatments entailed 40 kg P/ha soil banded triple superphosphate (0-45-0) with or without the addition of drip-applied urea sulfate (15-0-0-49). The plants were grown for 73 days prior to harvesting and analysis. Soil samples were taken at selected distances from the emitter. Whole plant and fruit yields were highest in the 20 kg UP-P/ha treatment. Phosphorus moved to a depth of 30 cm with the addition of 80 kg UP-P. Leaf Zn concentrations decreased with increasing rates of P fertilization. Application of acid solubilized native P, Fe, and Mn, resulting in higher tissue concentrations of Fe and Mn in the plants receiving urea sulfate. Urea sulfate was more effective in soil acidification and Fe and Mn solubilization than the equivalent titratable acidity derived from UP. Urea phosphate appears to be an effective P fertilizer for application through drip irrigation systems in field soil.; The third study was conducted in the field on two sandy loam soils to determine the effect of Terrazole nitrification inhibitor (5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole) on N movement and transformations. Terrazole addition significantly slowed nitrification and decreased N movement, while higher irrigation additions increased movement. However, there was no significant increase in tissue N concentrations or yields due to Terrazole additions. (Abstract shortened with permission of author.)...