Effect of Nitrogen Fertilizer and Nitrification Inhibitors on Methane and Nitrous Oxide Fluxes in Irrigated Corn

Abstract

Agricultural systems contribute a large proportion of the global emissions of methane (CH4) and nitrous oxide (N20) to the atmosphere. Nitrogen (N) fertilizer influences the flux rates of these gases in agroecosystems. Methane and nitrous oxide fluxes were measured periodically in an irrigated corn (Zea mays L.) field from time of fertilization to harvest. Fertilizer treatments included 0 and 218 kg urea-N ha-\, as well as applications of the nitrification inhibitors (Nls), nitrapyrin [2-chloro-6-(trichloromethyl)-pyridine], and encapsulated calcium carbide (ECC). Brief periods of CH4 emissions were observed after irrigations , with no effect of N or Nls. Methane consumption was not affected by urea fertilization, but was reduced 43% by the addition of ECC. The contribution , however, of changes in the consumption of CH4 as a result of ECC addition to the net greenhouse effect was negligible «0.1%) compared to the reduction in N20 emissions. Nitrous oxide emissions were 16 times greater in urea-fertilized plots than in unfertilized soils. The application of Nls with urea decreased N 2 0 emissions 43-71%. Methane consumption or oxidation in soils is carried out by a diverse group of methanotrophic bacteria. 40 Consumption of atmospheric CH 4 has been reported by several workers. 19 ,27,35,39 Changes in the sink activity of soils for CH 4 , in addition to sources such as rice paddies, cattle, landfills, and biomass-burning, might explain the 1 % per year increase in atmospheric CH 4 • Methane is 15 times more effective than CO 2 (mass basis) in absorbing infrared radiation. 29 Nitrous oxide (N 2 0) is emitted during nitrification of ammonium (NH 4 +), and as a product of denitrification of nitrate (N0 3-).10 Applications of N fertilizer to soil result in increases in N 2 0 emissions. 26 ,3o Nitrous oxide is 300 times (mass basis) more radiatively active than CO 2 ,29 and nitrogen oxides (NO and N0 2) from N 2 0 oxidation may catalytically destroy ozone (0 3) in the stratosphere.1 2 The proportion of applied fertilizer N that is emitted as N 2 0 in corn-cropped systems ranges from 1.3% (Ref. 25) to 2% (Ref. 14). Global emissions of N 2 0 emitted from fertilized soils is estimated to be 1.5 Tg N 2 0-N/yr-1 • 34 278 R. S. Oremland (ed.), Biogeochemistry of Global Change