Nitrous Oxide Emissions from Vegetable Cropping Systems

Abstract

Agricultural manipulation of the soil nitrogen (N) cycle has caused a significant increase in nitrous oxide (N2O) emissions during the past five decades. Nitrous oxide is one of the major greenhouse gases with potent and long-lasting global warming effects [298 times higher than carbon dioxide (CO2) over a time period of 100 years]. The major biogenic processes responsible for N2O production in agricultural soils are identified as nitrification which is the oxidation of ammonium (NH4+) to nitrite (NO2-) and nitrate (NO3-) and denitrification that is the anaerobic reduction of NO2- and NO3- to gaseous nitric oxide (NO), N2O or N2. Although the current concentration of N2O in the atmosphere is relatively lower than other greenhouse gases, it is annually increasing at a rate of 0.25%. Vegetable cropping systems, a major agricultural activity worldwide, generally comprise intensive cultivation and high rates of N application. However, the N recovery from intensively cultivated vegetable fields is reported to be only 20 - 50% of the applied N fertiliser, suggesting large amounts of N loss from these fields. In Australia, horticulture represents less than 1% of land used for agriculture, but accounts for 6-12% of N fertiliser use in agriculture and its contribution to national N2O emissions is significant.