The effect of the function type for describing the soil buffer power on calculated ion transport to roots and nutrient uptake from the soil

The relationship between amount of a nutrient in soil and its concentration in solution, the buffer curve, is usually non-linear. However. most models that calculate nutrient transport in the soil and nutrient uptake by the plant often assume a linear buffer curve because of simpler programming. In this paper a model is presented that uses the Freundlich function to describe the non-linear buffer curve in the soil. It has been shown that calculated uptake and depletion curves were not influenced by the shape of the buffer curve. In a sensitivity analysis the buffer capacity, soil solution concentration, soil water content, soil impedance factor, maximum influx and the curvature of the Freundlich function were varied and the influence on calculated uptake was studied. The buffer capacity in general had a minor influence and the linearity or non-linearity of the buffer capacity had under no circumstances an influence on calculated uptake. Thus, the use of a linear buffer curve in transport models does not lead to a significant error in the results.