Source and formulation matter: New insights into phosphorus fertilizer fate and transport in mildly calcareous soils
2020
Weeks, Joseph J. Jr | Hettiarachchi, Ganga M.
Phosphorus fertilizer use efficiency can be poor in calcareous soils as a result of calcium phosphate precipitation reactions. To avoid crop P deficiency, growers may apply more fertilizer than is agronomically necessary, creating a surplus of P in soil that can erode or leach into nearby waterbodies and promote eutrophication. This study investigated the effects of liquid P fertilizer source, application volume, and co‐application of a gelling agent on P partitioning in two mildly calcareous soils from Kansas. Treatments included phosphoric acid, monoammonium phosphate (MAP), diammonium phosphate, ammonium polyphosphate (APP), and an 80% MAP/20% APP mixture applied at one total P rate over two concentrations or co‐applied with sodium alginate (AG). Soils were incubated for 4 wk in Petri dishes and then sectioned in concentric rings from the point of application. Anion exchange resin (AER) extractability assessed plant availability and total P determination evaluated diffusion. Sequential extraction and synchrotron‐based X‐ray absorption near‐edge structure spectroscopy were implemented to probe reaction products and pathways. Incorporation of polyphosphates, co‐application of AG, and dilution with water improved the proportion of P that was AER extractable in the case of monoammonium phosphate from ∼36 to 66, 58, and 65%, respectively. Increased plant availability may be accomplished through a combination of at least two mechanisms: retarded ripening of calcium phosphate minerals into sparingly soluble forms and altered partitioning of P to soil colloids. Understanding the conditions under which these concepts scale to the field could result in increased farm profitability and nutrient use efficiency.
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