Predicted Soil Phosphorus Uptake as Affected by Banding Potassium Chloride with Phosphorus

Soil reactions of P may be affected by the ionic strength of the soil solution. Thus, P supply to plant roots may vary due to other nutrients banded with P or added in the same granule. The objective of this research was to quantify the effect of banding KCl with applied P on predicted P uptake. Zero and 1000 mg K kg −1 (a rate comparable to band application) were applied to 13 soils after addition of Ca(H 2 PO 4 ) 2 at rates that varied with soil from 50 to 400 mg P kg −1 . Thirty days later P, Ca, Al, and pH were determined in displaced soil solution and on the solid phase. Some soils were leached with deionized water after the displacement of the soil solution, and 3 d later a new soil solution was displaced. The soil P supply parameters, buffer power ( b ), effective diffusion coefficient ( D e ) and solution P ( C li ), were used in the Barber‐Cushman mechanistic nutrient uptake model to calculate predicted P uptake. Adding KCl decreased predicted P uptake in almost all less weathered soils; for the more highly weathered soils, adding KCl increased predicted P uptake in those with low pH and decreased it in those with moderate and high pH. After adding KCl, C li increased up to three‐fold in the most weathered soils with low pH and decreased up to 0.55 of the value without KCl in the less weathered soils; adding KCl slightly decreased resin‐exchangeable P ( C si ) only in soils with appreciable exchangeable Al. Addition of KCl increased Ca and Al in solution, decreased exchangeable Ca, and decreased pH in the soil solution and of the soil.