Use of a mechanistic model to evaluate phosphate fertilizers and effects of added salts on phosphorus availability

Paulo Roberto Ernani, Purdue University

Abstract

The Barber-Crushman mechanistic nutrient uptake model was used to evaluate P availability as affected by phosphate fertilizer and changes of the concentration of electrolytes. Thirteen soils were used to compare the effectiveness of monocalcium phosphate (MCP) and diammonium phosphate (DAP); the effect of adding salts was evaluated in Rarden subsoil with low pH and predominantly variable charge (Hapludalfs); a pot experiment was conducted in Rarden soil, limed or unlimed, to evaluate rock phosphate, partially acidulated, and soluble P fertilizers to supply P to corn, and the ability of the model to predict P uptake in acid soils. Treatments were applied to soil samples that were incubated for 18 to 30 days depending on the experiment. Predicted P uptake did not differ between MCP and DAP in almost all soils; DAP was, however, the most effective P fertilizer to increase corn dry matter especially on unlimed soil because DAP decreased Al in the soil solution. Addition of salts increased predicted P uptake and P in the soil solution (P$\sb{\rm li}$) in soils with low pH and predominantly variable charge, and decreased them in soils with permanent charge. The increase of P$\sb{\rm li}$ in soils with variable charge and low pH after addition of salts was caused by changes of the surface potential, which was associated with the ability of salts to displace native cations from the exchange sites; for KCl P$\sb{\rm li}$ started to increase at rates equal or above 500 mg K kg$\sp{-1}$. Predicted P uptake was most highly correlated with D$\sb{\rm e}$ when different soils were evaluated, with P$\sb{\rm li}$ for a given soil. The model underpredicted P uptake by corn due to the effect of root hairs on P uptake. Addition of salts also increased Al, Ca, Mg, and K in the soil solution, and decreased soil pH and resin-exchangeable P. All effects caused by salts on P parameters and on the composition of the soil solution disappeared after leaching the soil samples.

Degree

Ph.D.

Advisors

Barber, Purdue University.

Subject Area

Agronomy

COinS