Prediction of phosphorus uptake by a mechanistic model in a low phosphorus highly weathered soil as affected by mycorrhizae inoculation

Abstract

Mechanistic models need to be validated before being widely used. The Barber‐Cushman mechanistic nutrient uptake model has successfully predicted phosphorus (P) uptake in high‐P soils, but it has not been tested in soils with low available P. Some assumptions of this model (no influence of mycor‐rhizae and root hairs on nutrient uptake) may have different implications according to the soil P level. The objective of this study was to test the ability of the Barber‐Cushman model to predict P uptake for corn in an Oxisol with low P values as influenced by mycorrhizae inoculation. The experiment was carried out in a greenhouse, in a factorial with two levels of P (25 and 100 mg/kg), of limestone (pH 4.7 and 5.5), and of mycorrhizae inoculation (with and without). Observed P uptake was determined in the roots and in the shoots of 46‐day‐old corn plants. The predicted P uptake by the model was calculated using a computer program. There was a good agreement between observed and predicted P uptake (r² = 0.97). The model, however, underpredicted the amount of P taken up by corn plants, probably due to the contribution of root hairs. Inoculation with mycorrhizae did not affect corn yield and had a small influence on both observed and predicted P uptake. The model predicted, respectively, 31% and 41% of the P taken up by plants for treatments with and without mycorrhizae inoculation. Sensitivity analysis demonstrated that P in the soil solution and the rate of root growth were the parameters that most influenced predicted P uptake, and that plant uptake kinetics had a small contribution.