Analyzing the mobility in granular forms of P fertilizer in Brazilians soils under laboratory conditions

Phosphorus is an essential nutrient for plant growth. Million of tones of P are applied to the soils annually. However, only a small fraction of the P applied with fertilizers is taken up by crops in the year of application, and the effectiveness of any residual P fertilizer declines with time. To improve our understanding of the mechanisms underlying this response to P in the field, we have studied the mobility of P from 3 different fertilizes: monoammonium phosphate (MAP), polymer coated monoammonium phosphate (MAPp) and Organomineral phosphate (OMP) applied on high weathered soil samples in a Petri dish experiment. Total Reflection X-Ray Fluorescence (TXRF) was used to determine the P diffusive flux at different distances (0 - 7.5, 7.5 – 13.5, 13.5 – 25.5 and 25.5 – 43 mm) from granular fertilizer. TXRF analyses were performed at the X-Ray Fluorescence Beamline D09B at Brazilian National Synchrotron Light Laboratory (LNLS), in Campinas, Sao Paulo, using a polychromatic beam with maximum energy of 20 keV for the excitation and an Ultra-LEGe detector with resolution of 148 eV at 5.9 keV. Besides that, the detections were performed in a high vacuum chamber (2.5 x 10-5 mbar) to avoid air absorption. After a period of five weeks, the total P concentration increased in the soil sampled 7.5 to 13.5 mm from the fertilizer showing a diffusive flux of P. About 20% (considering MAP and MAPp) of the total P applied diffused out of the central soil ring. Different sources showed differences in diffusive flux of P. Soil pH also influenced diffusive flux of P showing higher flux on lower pH soils. (author)