J. Michael Kelly

Nutrient uptake estimates for woody species as described by the NST 3.0, SSAND, and PCATS mechanistic nutrient uptake models

Minimalist mechanistic nutrient uptake models based on the fundamentals of nutrient movement in the soil, nutrient uptake kinetics, and root growth and morphology, have become important tools for research. Because different approaches to solution may lead to different simulation results, it would be useful to evaluate the SSAND, and PCATS mechanistic models along with the very successful crop model NST 3.0 using common data sets and by conducting both one dimensional and multiple dimensional sensitivity analyses. The predictions of nutrient uptake by the three models using the same data set were diverse, indicating a need to reexamine model structure. Both types of sensitivity analyses suggested that the effect of soil moisture on simulation can be influential when nutrient concentration in the soil solution is low. One dimensional sensitivity analysis also revealed that Imax negatively influenced estimates of nutrient uptake in the SSAND and PCATS models. Further analysis indicated that this phenomenon was also related to the low nutrient supplying ability typically found in forest soils. The predictions of SSAND under low-nutrient-supply scenarios are generally lower than these of NST 3.0. We suspect that both results are artifacts of the steady state models.