GREENHOUSE GAS EMISSIONS FROM SUGARCANE SOILS AND NITROGEN FERTILISER MANAGEMENT: Ⅱ

摘要

Emissions of the greenhouse gases carbon dioxide (CO_2), nitrous oxide (N_2O) and methane (CH_4) from a sugarcane crop have been measured for the whole of the 2005-2006 growing season of 342 days. The investigation employed chambers and micrometeorological techniques. The ratoon crop, grown on an acid sulfate soil (ASS) at Murwillumbah NSW, received 160 kg urea-N/ha. Rainfall for the period was 1879 mm so that the soil was frequently wet. Soil respiration over the season was 29.8 t/ha of CO_2 and the CO_2 sequestered from the atmosphere was 51.4 t/ha. Soil respiration thus amounted to 37% of the net assimilation by the crop. Soil moisture conditions were near optimal for N_2O production through both nitrification and denitrification and emissions were large and prolonged, totalling 45.9 kgN/ha over the 342 days and persisting at substantial rates for 5 months. Emissions from unfertilised plots totalled 11.3 kgN/ha. The corresponding emission factor for N_2O was thus 22% of the fertliliser N applied. The N_2O several times higher than those measured for other sugarcane soils. Also in contrast to other sugarcane soils, ASS appear to be sources of CH_4, not sinks. The average emission rate over the season was 0.154 kg/ha/d, which is 2 to 10% of rates for rice and wetlands. For the growing season, the net sequestering of CO_2 by the crop from the atmosphere of 51.4 t/ha was offset by the emission to the atmosphere of 23 t/ha CO_2-e through N_2O and CH_4.