A STELLA model to estimate water and nitrogen dynamics in a short-rotation woody crop plantation
Although short-rotation woody crop biomass production technology has demonstrated a promising potential to supply feedstocks for bioenergy production, the water and nutrient processes in the woody crop planation ecosystem are poorly understood. In this study, a computer model was developed to estimate the dynamics of water and nitrogen (N) species (e.g., NH4–N, NO3–N, particulate organic N, and soluble organic N [SON]) in a woody crop plantation using STELLA (Structural Thinking and Experiential Learning Laboratory with Animation) software. A scenario was performed to estimate diurnal and monthly water and N variations of a 1-ha mature cottonwood plantation over a 1-yr simulation period. A typical monthly variation pattern was found for soil water evaporation, leaf water transpiration, and root water uptake, with an increase from winter to summer and a decrease from summer to the following winter. Simulations further revealed that the rate of soil water evaporation was one order of magnitude lower than that of leaf water transpiration. In most cases, the relative monthly water loss rates could be expressed as evapotranspiration > root uptake > percolation > runoff. Leaching of NO3–N and SON depended not only on soil N content but also on rainfall rate and duration. Leaching of NO3–N from the cottonwood plantation was about two times higher than that of SON. The relative monthly rate of N leaching was NO3–N > SON > N4–N. This study suggests that the STELLA model developed is a useful tool for estimating water and N dynamics from a woody crop plantation.