| Popis: |
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 C2H2, or water plus C2H2 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 N2O 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 N2O-N ha−1) whereas for green panic, 25.9g N2O-N ha−1 was found in spring and 9.2g N2O-N ha−1 in summer. Soil water was correlated with N2O concentration beneath black gram (r = 0.87, d.f. = 6, P < 0.01) and CO2 concentration under green panic (r = 0.69, d.f. = 6, P < 0.05). Multiple regression analysis showed that 87.8% of the variation in N2O concentration from beneath black gram was associated with monthly rainfall and NO3−concentration. Gas samples collected 24 h after the application of the treatments showed that N2O and CO2 concentration did not vary between treatments. However, treatment application did increase the N2O found beneath black gram. A mean increase of 29 g N2O-N ha−1 was observed in January, 1986. Concentration of N2O changed little after the application of the treatments to green panic. N2O due to microsite activity represented 11% of the measured loss of nitrate from the subsoil in the field. |
