NITROUS-OXIDE EMISSION AS AFFECTED BY TILLAGE, CORN-SOYBEAN-ALFALFA ROTATIONS AND NITROGEN-FERTILIZATION

Nitrous oxide (N2O) produced from agricultural activities represents a threat to the ozone layer and economic losses. Rates and magnitudes o f N2O emissions of cropping systems must be determined to establish co rrective management procedures. In 1994, N2O emissions were determined with corn (Zea Mays L.) and corn-legume rotations. Continuous corn wa s studied on four soils, two from a long-term experiment, a Ste. Rosal ie heavy clay (Humic Gleysol) and a Chicot sandy loam (Grey-Brown Podz ol), at 0, 170, 285 or 400 kg N ha(-1), and two from a corn rotation s tudy, a Ste. Rosalie clay (Humic Gleysol) and an Ormstown silty clay l oam (Humic Gleysol). Treatments included no-till (NT) and conventional tillage (CT), monoculture corn (CCCC), monoculture soybean; corn-soyb ean; and soybean-corn-alfalfa phased rotations. Nitrogen rates of 0, 9 0, or 180 kg N ha(-1) for corn and 0, 20, or 40 kg N ha(-1) for contin uous soybean were used, and soybean/alfalfa following corn no fertiliz er N. Rates of N2O emission were measured from closed chambers through the growing season. About 0.99 to 2.1% of N added was lost as N2O. Ni trous oxide emission increased with increased soil water content, NO3 Concentration and fertilizer N rates. Emission of N2O was higher with NT than with CT, and with corn than with soybean or alfalfa. A corn sy stem using CT, legumes in rotation and moderate fertilizer N would red uce N2O emission.