Phosphorus Mobility and Behavior in Soils Treated with Calcium, Ammonium and Magnesium Phosphates.

Over the last several decades innumerous types of phosphorus (P) containing fertilizer have been developed, with the goal of improving P use efficiency. However, little is known about the behavior of P from many of the new fertilizer formulations in soils. This research was developed to study the P mobility from various fertilizer formulations and also to investigate the effects of the different formulations on the different P pools in the soil. Three Mollisols from the USA and one Ultisol from Brazil, and six fertilizer sources, monoammonium phosphate (MAP); sulfur coated MAP; humic acid coated MAP; calcium phosphate as triple superphosphate; polyphosohate as ammonium potassium polyphosphate; and a magnesium ammonium phosphate commonly known as struvite, were used in this study. The results of this study showed differences between fertilizers with respect to lability and mobility of P in soil. The rate at which P moved from the granule towards the soil was closely related to clay content, as the higher the clay content the lower the distance traveled by phosphate ions. In terms P of mobility as a function of P source, the greatest P mobility was found for the monoammonium phosphate sources. In contrast, struvite granules remained intact and showed the least lability and mobility. A sequential fractionation study was used to investigate the behavior of the fertilizer P after it moved from the granule into the soil. Overall, more than 50% of the fertilizer P was recovered as labile P in the first 13.5 mm from the fertilizer placement.