Evaluation of Short‐Term Efficiency of Diammonium Phosphate versus Urea plus Single Superphosphate on a Calcareous Soil1

Abstract

AbstractAlthough research has been done on the fertilizer efficiency of diammonium phosphate (DAP) as a source of N or P, little information has been reported on its effectiveness as a dual source of N and P to plants. The objective of this study was to compare DAP with urea plus single superphosphate (SSP) as sources of fertilizer N and P on a calcareous clay soil (Typic Ustochrept). The influence of methods of fertilizer placement (surface broadcast, incorporation, and deep placement) on crop growth and nutrient uptake were investigated in a short‐term (6‐week) greenhouse evaluation using maize (Zea mays L.) as a test crop. Ammonia volatilization losses from both sources, when surface‐applied to the soil followed by daily water additions, were small, less than 6% of the applied N. Olsen P in the soil treated with urea + SSP was higher than the soil treated with DAP regardless of the method of fertilizer placement. Surface broadcasting apparently reduced the accessibility of P to the plant roots and resulted in a lower P uptake and plant yield than incorporation. Nitrogen uptake was as high with DAP as with urea + SSP when the fertilizers were either incorporated or deep‐placed. Surface application, however, resulted in lower N uptake from DAP than from urea + SSP. Both DAP and urea + SSP showed the same relationship in terms of P uptake as a function of Olsen P in the soil for a given method of fertilizer placement. The plant yields obtained with urea + SSP were higher than those obtained with DAP, regardless of the method of fertilizer placement.