A test of CoupModel for assessing the nitrogen leaching in grassland systems with two different fertilization levels

Abstract

Land-use and crop-biomass development influence water and nutrient dynamics in soils. Nitrate-N leaching rises with increasing mineral-N input during seepage periods in sandy soils. Leaching of N was simulated for two grassland treatments (N0: unfertilized; N300: highly fertilized: 300 kg mineral N ha -1 y -1 ) using CoupModel. Parameter uncertainty was considered by an automated calibration based on the General Likelihood Uncertainty Estimation (GLUE) approach. The results of this optimization approach showed a realistic reproduction of abiotic and biotic patterns of the system. Modeled abiotic parameters, i.e., soil temperatures and water contents in different soil depths, led to plausible results with minor differences between fertilization levels and some respect for discrepancies due to heterogeneous soil conditions. Groundwater levels were slightly underestimated by CoupModel with a smoother dynamic than measured in both treatments. CoupModel provided plausible results for nitrate-N concentrations below the rooting zone at 60 cm depth with higher uncertainty ranges than standard deviations of the measurements. Simulated nitrate-N concentrations of the unfertilized grassland confirmed the measurements, and no potential environmental risk for water bodies existed according to the standards of the European Drinking Water Directive. The model reproduced satisfactorily the observations for the N300 system with a slightly overestimation in 40% of the simulated seepage periods. Higher uncertainties were found for the simulated N300 than for the N0 plot. Modeled N flows below the rooting zone of 11 kg nitrate-N ha -1 per seepage period were comparable to calculations of the model "Büchter" with a mean of 10 kg nitrate-N ha -1 . For the N300 plot, a more than twice as high N-leaching amount of 74 kg nitrate-N ha -1 was modeled compared to a calculated average of 30 kg nitrate-N ha -1 . Finally, small-scale modeling can provide plausible results for nitrate-N leaching on plot-scale when uncertainties in soil water, N flows, and biomass growth are considered.

Modelling temperature, moisture and surface heat balance in bare soil under seasonal frost conditions in China

“…Hence, the performance indices used in this study were R 2 , the determination coefficient of the linear regression between simulated and measured, ME, the mean error of the model, and RMSE, the root mean square error of the model. These measures have been commonly adopted in other uncertainty analyses (Conrad & Fohrer, 2009; Dean et al , 2009; Juston et al , 2010).…”

“…The generalized likelihood uncertainty estimation (GLUE) technique (Beven & Binley, 1992) is a commonly used uncertainty analysis method. It has been applied to many different environmental models to estimate the error in model outputs and to assess the uncertainty in model structures, parameters and input data (Dean et al , 2009; Conrad & Fohrer, 2009).…”

Application of the Bayesian calibration methodology for the parameter estimation in CoupModel

“…Measurements were taken with puncture tensiometers with a rubber septum at the top during summer 1998 and 1999. Further information about data acquisition can be derived from Conrad and Fohrer (2009b). Observed soil solution concentrations can vary considerably, and measurement uncertainty is affected most likely by the spatial variability within the plot (Reinds et al, 2008).…”