Nitrous oxide emission from greenhouse fields in Hokkaido and methods to reduce the emissions.

摘要

We monitored nitrous oxide (N2O) emissions from greenhouse fields in Hokkaido, Japan, over four years, and determined the factors influencing the emissions. The effects of some field management practices such as mulching and manure application on N2O emissions were studied to evaluate N2O mitigation efficiencies of these practices while maintaining current yield levels. Mean N2O flux was 28 micro g m-2 h-1 (-8-425 micro g m-2 h-1) from the greenhouse field where spinach was cultivated. N2O flux increased when both its soil temperature and soil moisture were relatively high. Slight N2O was emitted constantly from the greenhouse field even during winter when the soil temperature was approximately in the range between 1 and 3 degrees C. When clear polyethylene mulch covered the soil in early spring, N2O flux was at the same level as that from a non-mulch field, which was attributed to the fact that the mulch did not raise the soil temperature enough. When the clear mulch was used in summer, 30 times as much as N2O was emitted from the non-mulch field, which was attributed to the mulch increasing the soil temperature up to 28 degrees C. On the other hand, white mulch did not increase N2O flux even in summer, since it did not increase the soil temperature. These results suggest that choosing an appropriate mulch colour contributes to regulating the soil temperature and mitigating the N2O flux. When immature manure, made from a mixture of cattle slurry and rice straw, was applied to a field, the mean N2O flux was 608 micro g m-2 h-1 over the two years duration of the experiment. It was 8 times as large as that when a matured one was applied. When manure and nitrogen fertilizer were simultaneously applied to a greenhouse field, the mean N2O flux was 216 micro g m-2 h-1 over the two years duration of the experiment and it was 7 times as large as that when nitrogen fertilizer was solely applied. However, when manure was applied more than a week before the application of nitrogen fertilizer, the flux was as low as that when nitrogen fertilizer was solely applied. Results indicate that proper management practices of a greenhouse field such as the choice of appropriate mulch colour to regulate the soil temperature and application of matured manure more than a week before application of nitrogen fertilizer enable the mitigation of N2O emission from the field.