Nitrogen fertiliser effects on litter fall, FH layer and mineral soil characteristics in New Zealand Pinus radiata plantations

The effects of nitrogenous fertilisation on litter fall, FH layer and soil characteristics were investigated in replicated trials in six second rotation New Zealand Pinus radiata plantation forests. Four trial sites also incorporated three different post-harvest organic matter removal treatments. All sites were sampled in early 2002 and 2003. Fertilisation significantly increased the nitrogen content and decreased the carbon:nitrogen ratio of the litter fall. Fertilisation significantly increased the mass of the FH layer in the treatment plots, moisture content in the FH layer, the concentration of nitrogen in the FH layer and the pool of carbon and nitrogen stored in the FH layer. Fertilisation significantly increased the nitrogen concentration of the mineral soil, and decreased the mineral soil carbon:nitrogen ratio and pH. Several significant site × fertilisation interaction terms indicated that variations in the fertilisation regimes and site characteristics substantially influenced the effects of fertilisation. Fertilisation did not significantly decrease the relative differences between the organic matter removal treatments. The significant differences in the litter fall, FH layer and mineral soil characteristics strongly suggest that nitrogenous fertilisation has the capacity to significantly alter the forest floor environment, and may be able to increase carbon storage over the life of the rotation.