Using a mechanistic model to evaluate the effect of soil pH on phosphorus uptake

Abstract

The objective of this research was to show how a mechanistic uptake model that accurately predicts phosphorus (P) uptake by maize (Zea mays L.) in a pot experiment may be used to evaluate the reasons for the differences in P availability observed when soil pH is varied. The model predicts P uptake by integrating soil P supply by mass flow and diffusion; size, shape and growth rate of roots; and P uptake kinetics of the root. The P supply parameters of the model that may be affected by soil pH are P_li, initial P concentration in the soil solution; b, the buffer power of P in the soil, P_si, for P_li, and D_e, effective diffusion coefficient. The effect of these changes on P uptake was predicted with the model by using measured values of the three soil supply parameters and of size, shape, and growth rate of roots and keeping the other parameters at values characteristic of maize. Values for three soil supply parameters can be calculated from measurements of P_li, P_si, and θ, volumetric water content. The predictions of the model closely agreed with observed uptake when form of P present at the higher pH's was accounted for. There was a significant positive correlation (r=0.94) between P_li and observed P uptake and a significant negative correlation (-0.93) between P_si and observed P uptake. The use of the model demonstrated the significance of P form and the importance of P_li in P uptake. It also showed importance of root growth rate.