Acetylene inhibition technique
Carbon: nitrate ratio
Reliability of AIT
Springer Online Journal Archives 1860-2000
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Summary In model experiments with a silty loam soil the effect of different C : NO inf3 sup- -N ratios on the reliability of C2H2 (1% v/v) in blocking N2O-reductase activity was examined. The soil was carefully mixed with different amounts of powdered lime leaves (Tilia vulgaris) to obtain organic C contents of about 1.8, 2.3, and 2.8%, and of NO inf3 sup- solution to give C : NO inf3 sup- -N ratios of 84, 107, 130, 156, 200, and 243. The soil samples were incubated in specially modified anaerobic jars (22 days, 25°C, 80% water-holding capacity, He atmosphere) and the atmosphere was analysed for N2, N2O, CO2, and C2H2 by gas chromatography at regular intervals. Destruction jars were used to analyse soil NO inf3 sup- , NH 4 + and C. The results clearly showed that N2O-reductase activity was completely blocked by 1% (v/v) C2H2 only as long as NO inf3 sup- was present. In the presence of C2H2, NO inf3 sup- was apparently entirely converted into N2O. The C2H2 blockage of N2O-reductase activity ceased earlier in soils with a wide C : NO inf3 sup- -N ratio (156, 200, and 243) than in those with closer C : NO inf3 sup- -N ratios (84, 107, and 130). As soon as NO inf3 sup- was exhausted, N2O was reduced to N2 in spite of C2H2. The wider the C : NO inf3 sup- -N ratio, the earlier the production of N2 and the less the reliability of the C2H2 blockage. In the untreated control complete inhibition of N2O-reductase activity by C2H2 lasted for 7–12 days. In the field, estimates of total denitrification losses by the C2H2 inhibition technique should be considered reliable only as long as NO inf3 sup- is present. Consequently, NO inf3 sup- monitoring in the field is essential, particularly in soils supplied with easily decomposable organic matter.
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