Modelling seasonal nitrogen, carbon, water and heat dynamics of the Solling spruce stand

Abstract

Daily flows of water, heat, carbon and nitrogen from 1976 until 1991 were simulated with the one-dimensional models soil —soiln for a 105-year-old spruce stand on an acid brown forest soil at Solling (central Germany). Nitrogen deposition in the area exceeded 40 kg N ha −1 yr −1. Comparisons were made with measured soil water tensions, chloride and mineral nitrogen concentrations in soil water, and tree biomass components. Down to 60-cm depth, the simulated soil water tensions agreed well with measured data when a summer surface resistance of 125 s m −1 was used to calculate potential transpiration. Modelling efficiency (an indicator of agreement between simulations and measurements) for pF-values of soil water tensions ranged from 0.55 to 0.87. At 100-cm depth, the modelling efficiency was only 0.15. The mean value of the chloride concentrations were, at the same time, underestimated. The average deep percolation was 38% of the precipitation. A lower summer surface resistance of 80 s m −1 was necessary to increase the agreement between simulated and measured chloride concentrations, which decreased the deep percolation to 31% of the precipitation. On average, simulation resulted in an accumulation of N in trees (21 kg N ha −1 yr −1 but a decrease of N in soil (7 kg N ha −1 yr −1). Simulated leaching was high (27 kg N ha −1 yr −1) and probably overestimated due to overestimated soil nitrate concentrations below the root zone. To evaluate the carbon and nitrogen model, too few detailed measurements were available on, especially, plant N uptake and amounts of soil mineral N.