Application of Urea Phosphate and Urea Sulfate to Drip-irrigated Tomatoes Grown in Calcareous Soil1

Abstract

The potential benefit of acid applied through drip irrigation on soil nutrient availability, plant nutrition, and yield was studied. Tomatoes (Lycopersicon esculentum Mill., cv. Better Boy) were grown in a P-deficient calcareous loam soil in 114-L plastic-lined cans. Phosphorus was added weekly through drip irrigation as urea phosphate (UP) (17-19-0) at four concentrations (0, 20, 40, 80 kg P ha−1). Two other treatments entailed 40 kg P ha−1 soil-banded triple superphosphate (TSP) (0-20-0) with or without the addition of drip-applied urea sulfate (US) (15-0-0-16). Urea sulfate was added at the rate equivalent to the titratable acidity of the 40 kg UP-P ha−1 treatment. Urea was added to all treatments to provide the equivalent of 100 kg N ha−1. The plants were grown for 73 d after transplanting prior to harvesting, weighing, and analysis. Soil samples were taken in 5-cm depth increments at 0-, 10-, and 20-cm distances from the emitter and analyzed for pH, P, Fe, Mn, and Zn. Yields of fruit and vegetative matter were higher in the 20 kg UP-P ha−1 treatment than in any other treatment. Phosphorus moved in the soil to a depth of 30 cm at the 80 kg UP-P ha−1 application rate. Leaf Zn concentration decreased with increasing rates of P fertilization. Application of acid solubilized native soil P, Fe, and Mn, resulting in highest tissue concentrations of Fe and Mn in the plants receiving US. Urea sulfate was more effective in soil acidification and Fe and Mn solubilization than the equivalent titratable acidity derived from UP. Urea sulfate may be beneficial where Fe and Mn deficiencies occur. Urea phosphate appears to be an effective P fertilizer for application through drip irrigation systems in field soil.