Nitrogen Relations in a Forest Plantation--Soil Organic Matter Ecosystem Model

Two previously published models, after minor modification, areamalgamated to give a model that describes the major carbonand nitrogen pools and fluxes in a plantation forest soil system.The first model is a transport-resistance model of forest growthand dry-matter partitioning. The second is a soil organic mattermodel that was constructed for temperate grasslands. The combinedmodel is used to examine the relations between plantation growth,soil organic matter content, nitrogen deposition rate from theatmosphere, mineralization flux, nitrogen uptake by the plantation,dry matter partitioning between foliage and root, litter productionand the timing and quantity of fertilizer application. The highdemand for N by even-aged plantations during the period of canopybuilding is highlighted. The marked ontogenetic shifts in thegrowth pattern during plantation development is emphasized,indicating several phases of forest development. The resultsindicate that the potential growth of even-aged plantationsmay be greater than that realized in poor soils with commonlevels of atmospheric N deposition and normal fertilizer regimes.The simulations show how the concentrations of soil mineralN change during the development of a plantation, and point towardsthe importance of atmospheric N deposition. They also show thatfertilizer application must be accurately matched to growthstage if fertilizer is to be used efficiently. The nitrogencycle (N-uptake by plant