Biological denitrification in a clay soil was measured under the annual crop black gram ( Vigna mango) and the perennial pasture grass green panic ( Panicum maximum var trichoglume). The soil treatments were: water, water plus C 2H 2, or water plus C 2H 2 plus glucose applied down brass tubes to depths of 7.5, 22.5, 52.5 and 112.5 cm. Soil gas samples were taken just before and 24 h after treatments were applied. Treatments and samplings were repeated every 3 months for 2 years. In untreated soil, the amounts of N 2O from crop and pasture were highest in spring and summer with approximately 75% of the total amount being measured. For black gram, this represented equal amounts in spring and summer (approx. 34g N 2O-N ha −1) whereas for green panic, 25.9g N 2O-N ha −1 was found in spring and 9.2g N 2O-N ha −1 in summer. Soil water was correlated with N 2O concentration beneath black gram ( r = 0.87, d.f. = 6, P < 0.01) and CO 2 concentration under green panic ( r = 0.69, d.f. = 6, P < 0.05). Multiple regression analysis showed that 87.8% of the variation in N 2O concentration from beneath black gram was associated with monthly rainfall and NO 3 −concentration. Gas samples collected 24 h after the application of the treatments showed that N 2O and CO 2 concentration did not vary between treatments. However, treatment application did increase the N 2O found beneath black gram. A mean increase of 29 g N 2O-N ha −1 was observed in January, 1986. Concentration of N 2O changed little after the application of the treatments to green panic. N 2O due to microsite activity represented 11% of the measured loss of nitrate from the subsoil in the field.