In Search of a Solution to Pollution: Improving Phosphorus Fertilizer Use Efficiency through Simple Formulation Alterations.

Phosphorus (P) fertilizer use efficiency can be poor in acid and calcareous soils as a result of fixation reactions between the orthophosphate anion and various forms of calcium, iron or aluminum that limit the nutrient’s availability to plants. To prevent P deficiency, growers with access to fertilizers tend to apply more than the crop will remove creating a surplus of P in soil that is not highly labile but can still erode or leach into nearby waterbodies compromising drinking water quality, recreational activities, and aquatic wildlife. Where fertilizer access is limited by economic/political forces, getting the most benefit out of what can be applied will assist in lifting poor farmers out of poverty. This study utilized liquid fertilizers to investigate the effects of application volume and ortho-/polyphosphate blends on phosphorus fate and transport in a calcareous soil from Kansas and a Brazilian oxisol. Monoammonium phosphate, diammonium phosphate, ammonium polyphosphate, and an 80/20 MAP/APP mixture were applied at two P rates over a range of total solution volumes. Soils were incubated for four weeks in Petri dishes and sectioned in concentric rings from the point of application. Anion exchange resin extractability as a percent of total P assessed potential plant availability, and synchrotron based X-ray absorption near-edge structure (XANES) spectroscopy was implemented to probe reaction products and pathways. Blending polyphosphates into orthophosphate fertilizers and increasing application volumes by diluting with water reduced fixation in the calcareous soil whereas these approaches were less effective under highly weathered conditions. The results suggest that further investigation into the partitioning of P fertilizers in acid soils is necessary to find ways to mitigate P fixation and highlights that soil specific approaches to P management could allow for greater use efficiency in the future.