The quantitative effect of chemical phosphate mobilization by carboxylate anions on P uptake by a single root. I. The basic concept and determination of soil parameters

Model calculations on the uptake of inorganic nutrients by single roots and root systems do not include chemical nutrient mobilization by root exudates. In this paper, a model description of Nye (1984) was applied to the case of a single root (cylindrical case) and chemical mobilization of phosphate (P) by carboxylates. Experimental results are reported which allow the quantification of soil parameters required for the model calculations. These include the solubilizing effect of carboxylates on P. The experiments showed a strong positive correlation between carboxylate adsorption to the soil solid phase and chemical P mobilization by the carboxylate. Below a concentration of adsorbed citrate and oxalate of 10 μmol g−1 soil no mobilization occurred in the 3 soils which were investigated. Differences in pH did not affect P solubility, but did, however, affect the quantity of adsorbed carboxylate and thereby the mobilization of P. Citrate and oxalate have a greater ability to mobilize soil P as compared with oxaloacetate and malate. Model calculations which are based on these experimental results are presented in a second paper.