NITROGEN RELATIONS IN A FOREST PLANTATION - SOIL ORGANIC-MATTER ECOSYSTEM MODEL

Two previously published models, after minor modification, are amalgamated to give a model that describes the major carbon and nitrogen pools and fluxes in a plantation forest soil system. The first model is a transport-resistance model of forest growth and dry-matter partitioning. The second is a soil organic matter model that was constructed for temperate grasslands. The combined model is used to examine the relations between plantation growth, soil organic matter content, nitrogen deposition rate from the atmosphere, mineralization flux, nitrogen uptake by the plantation, dry matter partitioning between fohage and root, htter production and the timing and quantity of fertilizer application. The high demand for N by even-aged plantations during the period of canopy building is highlighted.The marked ontogenetic shifts in the growth pattern during plantation development is emphasized, indicating several phases of forest development. The results indicate that the potential growth of even-aged plantations may be greater than that realized in poor soils with common levels of atmospheric N deposition and normal fertilizer regimes. The simulations show how the concentrations of soil mineral N change during the development of a plantation, and point towards the importance of atmospheric N deposition. They also show that fertilizer application must be accurately matched to growth stage if fertilizer is to be used efficiently. The nitrogen cycle (N-uptake by plant -* plant dry matter-»-litter-»-soil organic matter-»-mineral N pools N-uptake by plant) generates damped oscillations in response to a single application of fertilizer. © 1992 Annals of Botany Company.