Effect of wax-coated calcium carbide and nitrapyrin on nitrogen loss and methane emission from dry-seeded flooded rice

Summary The effectiveness of wax-coated calcium carbide (as a slow-release source of acetylene) and nitrapyrin in inhibiting nitrification and emission of the greenhouse gases N₂O and CH₄ was evaluated in a microplot study with dry-seeded flooded rice grown on a grey clay near Griffith, NSW, Australia. The treatments consisted of factorial combinations of N levels with nitrification inhibitors (control, wax-coated calcium carbide, and nitrapyrin). The rate of nitrification was slowed considerably by the addition of wax-coated calcium carbide, but it was inhibited only slightly by the addition of nitrapyrin. As a result, the emission of N₂O was markedly reduced by the application of wax-coated calcium carbide, whereas there was no significant difference in rates of N₂O emission between the control and nitrapyrin treatments. Both nitrification inhibitors significantly reduced CH₄ emission, but the lowest emission rates were observed in the wax-coated calcium carbide treatment. At the end of the experiment 84% of the applied N was recovered from the wax-coated calcium carbide treatment compared with 43% for the nitrapyrin and control treatments.