A NITROGEN-CYCLE MODEL FOR CALCULATING THE REDUCTION OF N-INPUT NECESSARY TO REDUCE SOIL ACIDIFICATION AND NITRATE LEACHING AND THE CONSEQUENCES OF THIS FOR WOOD PRODUCTION

The biogeochemical cycle of elements has been established in a spruce stand in the French Ardennes on a site with a poor acidic soil and a large inputs of nitrogen and sulphate from the atmosphere. This paper shows the interest of studying the seasonal N cycle instead of the global annual cycle, because part of the N input seems to be immobilized in the soil during the dormant season and is released afterwards and taken up during the growing season, and because of the important participation of N inputs in the N-uptake by trees during the growing season. The very large amount of NO3-N leached towards the water table level should be reduced. Using the seasonal cycles, we discuss the relationship between the desirable reduction in the NO3-N output and the N (NH4-N + NO3-N) input. A fertilization trial, including N and Ca, shows a decrease in the wood production after N fertilization. These models give us the opportunity to calculate the reduction of wood production in relation to the reduction of the N input in the ecosystem.