NITROUS-OXIDE EMISSION IN 3 YEARS AS AFFECTED BY TILLAGE, CORN-SOYBEAN-ALFALFA ROTATIONS, AND NITROGEN-FERTILIZATION

Nitrous oxide (N2O) produced from agricultural activities must be dete rmined if management procedures to reduce emissions are to be establis hed. From 1994 to 1996, N2O emissions were determined using a closed c hamber technique. Continuous corn (Zea mays L.) at four N rates of 0, 170, 285, and 400 kg of N ha(-1) mns used on a Ste. Rosalie heavy clay (a very-fine-silty, mixed, nonacid, frigid Typic Humaquept) and a Chi cot sandy loam (a fine-loamy, frigid, Typic Hapludalf). On two additio nal sites, a Ste. Rosalie clay and an Ormstown silty clay loam (a fine -sift, mixed, nonacid, frigid Humaquept) no-till (NT) and conventional tillage (CT); monocultural corn (CCC), monocultural soybean (Glycine max L.) (SSS); corn-soybean (SSC, CCS); and soybean-corn-alfalfa (Medi cago sativa L.) phased rotations (SAC, CSA, and ACS) were used. Nitrog en rates of 0, 90, and 180 ks of N ha(-1) for corn and 0, 20, and 40 k g of N ha(-1) for SSS mere used. Rates of N2O emission were measured f rom April to November in 1994 and 1995, and from mid-March to mid-Nove mber in 1996. Maximum N2O emissions reached from 120 to 450 ng of N m( -2) s(-1) at the Ormstown site to 50 to 240 ng of N m(-2) s(-1) at the Ste. Rosalie soil. Generally, N2O emissions were higher in the NT sys tems, with corn, and increased linearly with increasing N rates, and a mounted to 1.0 to 1.6% of fertilizer N applied. The N2O emission rates were significantly related to soil denitrification rates, water-tille d pore space, and soil NH4 and NO3 concentrations. A corn system using conventional tillage, legumes in rotation, and reduced N fertilizer m ould decrease N2O emission from agricultural fields.