USING CALCIUM CARBIDE WITH THE ACETYLENE INHIBITION TECHNIQUE TO MEASURE DENITRIFICATION FROM A SPRINKLER IRRIGATED VEGETABLE CROP

The use of calcium carbide (CaC2) pellets as a source of acetylene (C2 H2) for the C2H2 inhibition technique to measure denitrification in th e field was examined in a sandy loam soil cropped to lettuce. CaC2 was used in combination with vented closed chambers. Three grams of 2-4 m m CaC2 pellets were inserted at 7 and 20 cm for raised beds, and 6 and 15 cm for furrows, in four holes located at right angles, 2.5 cm outs ide a 20 cm dia. chamber pushed 4 cm into the soil. Acetylene concentr ations were determined in the centre of the chamber 1.0 and 4.0 hours after applying CaC2, in beds (two dates) and furrows (one date) at dif ferent depths to 20 and 15 cm, respectively, for beds and furrows. At soil matric potentials of ca. 0.01 and ca. 0.06 MPa, soil C2H2 concent rations were >1.0 % (v/v) for all determinations. Weekly measurements of denitrification were made from a sprinkler irrigated lettuce crop f or 8 weeks. Measurements were made 24 hours after irrigation and on on e occasion 48 hours after. Measured mean rates of denitrification were generally <100 g N ha(-1) d(-1), much less than published data follow ing furrow irrigation of vegetable crops in a nearby region. In anothe r sandy loam soil at ca. 0.08 MPa, soil C2H2 concentrations were great er than or equal to 2.0 % at 5 and 15 cm, 1.0 and 6.0 hours after addi ng CaC2. Using CaC2 to generate C2H2 in soil is a convenient approach for field measurements where the C2H2 inhibition technique is used wit h chambers to determine the nitrous oxide flux. In comparison with C2H 2 supply via probe systems, CaC2 overcomes the requirement for cylinde rs of pressurised C2H2 gas and complex on-site plumbing.