EFFECT OF ENCAPSULATED CALCIUM CARBIDE ON DINITROGEN, NITROUS-OXIDE, METHANE, AND CARBON-DIOXIDE EMISSIONS FROM FLOODED RICE

The efficiency of N use in flooded rice is usually low, chiefly due to gaseous losses. Emission of CH4, a gas implicated in global warming, can also be substantial in flooded rice. In a greenhouse study, the nitrification inhibitor encapsulated calcium carbide (a slow-release source of acetylene) was added with 75, 150, and 225 mg of 75 atom % N-15 urea-N to flooded pots containing 18-day-old rice (Oryza sativa L.) plants. Urea treatments without calcium carbide were included as controls. After the application of encapsulated calcium carbide, 3.6-mu-g N2, 12.4-mu-g N2O-N, and 3.6 mg CH4 were emitted per pot in 30 days. Without calcium carbide, 3.0 mg N2, 22.8-mu-g N2O-N, and 39.0 mg CH4 per pot were emitted during the same period. The rate of N added had a positive effect on N2 and N2O emissions, but the effect on CH4 emissions varied with time. Carbon dioxide emissions were lower with encapsulated calcium carbide than without. The use of encapsulated calcium carbide appears effective in eliminating N2 losses, and in minimizing emissions of the "greenhouse gases" N2O and CH4 in flooded rice.