MODELING NUTRIENT-UPTAKE - A POSSIBLE INDICATOR OF PHOSPHORUS DEFICIENCY

An understanding of the processes controlling soil nutrient supply and plant uptake has led to process-based models that can predict nutrien t uptake and the concentration gradient that develops at the root surf ace. By using this information, it may be possible to develop an indic ator of soil phosphorus status based on the predicted uptake and/or co ncentration of phosphorus (P) at the root surface. To identify the pot ential for such a test, the relationships between model output and obs erved plant growth were examined using data from a published experimen t. The experiment was initially designed to investigate the relationsh ip between common indices of soil-available P and the growth of maize (Zea mays) in 26 surface soils from Queensland. There was a high corre lation between observed and predicted P uptake, and between relative d ry matter yield and predicted P uptake. The predicted concentration of P at the root surface was alsb highly correlated with P uptake and dr y weight increase. It is hypothesised that the short growth period (25 days) was responsible for the high correlation between P uptake and m easured soil solution P. The hypothesis that a predicted concentration of P at the root surface or predicted P uptake may be valuable indica tors of P deficiency in the longer term still remains to be tested.