Mm. Roper et al., NITROGENASE ACTIVITY (C2H2 REDUCTION) BY FREE-LIVING BACTERIA IN SOILIN A LONG-TERM TILLAGE AND STUBBLE MANAGEMENT EXPERIMENT ON A VERTISOL, Soil biology & biochemistry, 26(8), 1994, pp. 1087-1091
The effects on nitrogenase activity (C2H2 reduction) of cereal stubble
management, tillage and N fertilizer practices were studied in a long
-term experiment on a vertisol at the Hermitage Research Station in so
uthern Queensland, Australia. The experiment compared 8 treatments com
prising 3 factors (1) tillage (zero, mechanical cultivation), (2) stub
ble (burnt, retained) and (3) N fertilizer applied at sowing (0, 69 kg
N ha-1 yr-1 as urea) in four randomised blocks. Measurements of nitro
genase activity, using in situ C2H2 reduction assays, began on 1 March
1991 following stubble treatment and continued for 4.5 weeks. Followi
ng the application of water to wet the soil to field capacity, nitroge
nase activity was observed in all treatments. Nitrogenase activity was
greater in the stubble-retained treatments than in the stubble-burnt
treatments although this was significant at only 5 of the 8 sampling t
imes. The results suggested that the application of N fertilizer depre
ssed nitrogenase activity and that cultivation encouraged activity com
pared with the zero-tillage treatments, but these effects were only si
gnificant at one each of the 8 sampling times. By using an appropriate
mix of management practices it may be possible to promote N2 fixation
by free-living bacteria using cereal stubble for energy.