Phosphorus Fertilizer Source and Rate Effect on Irrigated Alfalfa in Arizona.

Abstract

 

Many sources of phosphorus fertilizer are used for high-yield and high-quality alfalfa production in Arizona. Questions are often asked about the effectiveness and plant availability of various P fertilizer sources. The objective of this study was to compare the effect of sources of P fertilizer: monoammonium phosphate, MAP (11-52-0), phosphoric acid, PA (0-52-0) and superphos, SP (0-50-0) at equivalent application rates (0.71, 1.42, 2.13 g P₂O₅ m^-2) plus two higher rates for MAP (5.60 and 11.2 g P₂O₅ m^-2) with untreated check (0.0 g P₂O₅ m^-2) on alfalfa yield, soil test and plant P levels. The experiment was laid out in a randomized complete block design with four replications at the University of Arizona, Maricopa Agricultural Center (MAC) in March 2015. Hay yield data was obtained for five consecutive cuttings. Soil and plant tissue samples were collected two times during the research period. Our findings revealed that alfalfa yields were similar when fertilized with MAP, PA or SP at equivalent application rates. When averaged over the three application rates, we found relatively higher cumulative yield of 2463 g m^-2 for SP as compared to 2387 g m^-2 for PA and 2310 g m^-2 for MAP. Generally, yield increased with increased rate within the same source of P fertilizer but only the highest rate of MAP gave significantly higher cumulative yield (2765 g m^-2) than the untreated check (2214 g m^-2). P fertilizer source and application rate had little effect on soil P and plant P. This research demonstrates that the three sources of P fertilizer were equally effective at equivalent rate of application on irrigated alfalfa in low desert Arizona. Considerations other than agronomic performance such as cost per unit of nutrient, ease of application and availability must be taken into account in selection of specific P fertilizer.