A Comparison of Liquid Phosphoric Acid and Dry Phosphorus Fertilizer Sources for Irrigated Alfalfa Production on Calcareous Soils

Abstract Alfalfa production in the Western United States requires large quantities of phosphorus (P) fertilizer. In 1998, phosphoric acid (PA) became available as a fertilizer source. Phosphoric acid was more expensive per kg of P than other fertilizers, but was promoted on the basis of convenience of application when tank mixed with other chemicals, and superior agronomic performance (higher yield per kg P applied) in alkaline soils due to the neutralizing effect of the acid. The objective of this study was to compare the effects of PA, triple superphosphate (TSP, 0-45-0), and monoammonium phosphate (MAP, 11-52-0) on alfalfa yield and soil and plant tissue nutrient levels. Phosphorus was broadcast at rates based on soil test recommendations for two years at two sites having calcareous soils typical of alfalfa production systems in the Western U.S. At one site, potassium chloride (KCl, 0-0-60) and zinc sulfate were also mixed with the PA based on soil test recommendations. Responses to fertilizer ranged f...