Transformations of nitrate N-15 under different forest harvest residue regimes in a hoop pine plantation in Australia

摘要

A study was conducted to quantify the effects of harvest residue management on denitrification, leaching and immobilization of N-15-labelled nitrate applied at 20 kg N ha(-1) to 1-year-old hoop pine (Araucaria cunninghamii) in subtropical Australia. The experiment was undertaken in PVC microplots of 235 mm diameter and 300 mm long, driven into the soil (Lithosol) to a depth of 250 mm. Three replications were undertaken for each of the seven treatments: control without any residue, ground and unground foliage at 20 Mg dry matter (DM) ha(-1), ground foliage at 40 Mg DM ha(-1), ground and unground branches at 40 Mg DM ha(-1), and ground branches at 80 Mg DM ha(-1). In 15 days after simulated daily rainfall of 100, 50 and 25 mm respectively in the first three days, 6-26% of applied N-15 was lost via denitrification, 14-35% was immobilized and 32-53% was leached. The treatment incorporating foliage materials lost more N-15 (21-26%) via denitrification than other treatments. Measurement of N-15 gases (N-15(2)+(N2O)-N-15) showed higher N-15 gas emission on day 1, followed by low gas emissions thereafter. This study showed that significant amounts of mineral N could be lost through leaching and denitrification during plantation establishment.