Nitrous oxide emission from an irrigated cotton field under semiarid subtropical conditions

摘要

In a 1-year study, quantification of nitrous oxide (NO) emission was made from a flood-irrigated cotton field fertilized with urea at 100kg N hap# ap#. Measurements were made during the cotton-growing season (May-November) and the fallow period (December-April). Of the total 95 sampling dates, 77 showed positive NO fluxes (range, 0.1 to 33.3g N hap# dp#), whereas negative fluxes (i.e., NO sink activity) were recorded on 18 occasions (range, -0.1 to -2.2g N hap# dp#). Nitrous oxide sink activity was more frequently observed during the growing season (15 out of 57 sampling dates) as compared to the fallow period (3 out of 38 sampling dates). During the growing season, contribution of NO to the denitrification gaseous N products was much less (average, 4%) as compared to that during the fallow period (average, 21%). Nitrous oxide emission integrated over the 6-month growing period amounted 324g N hap#, whereas the corresponding figure for the 6-month fallow period was 648g N hap#. Subtracting the NO sink activity (30.3g N hap# and 3.8g N hap# during the growing season and fallow period, respectively), the net NO emission amounted 938g N hap# ap#. Results suggested that high soil moisture and temperature prevailing under flood-irrigated cotton in the Central Punjab region of Pakistan though favor high denitrification rates, but are also conducive to NO reduction thus leading to relatively low NO emission.