Estimation of the total gaseous nitrogen losses from clay soils under laboratory and field conditions

SUMMARY Acetylene blockage was evaluated as a method for measuring losses of N 2 O + N 2 from two Denchworth series clay soils. The denitrification potential in anaerobic, dark incubations at 20°C with nitrate (equivalent to 100 kg N ha −1 0–20 cm depth), maximum water holding capacity, and acetylene (1%), was equivalent to 32 ± 11 and 39 ± 6 kg N ha −1 per day for the two 0–20 cm soils and was positively correlated with carbon content ( r = 0.98). After 4 days N 2 O was reduced to N 2 in the presence of C 2 H 2 . In April 1980 following irrigation (24 mm) and applications of ammonium nitrate (70 kg N ha −1 ) and acetylene, the mean nitrous oxide flux from soil under permanent grass was 0.05 ± 0.01 kg N 2 O‐N ha −1 per day for 8 days. In June 1980, the losses of nitrogen from cultivated soils under winter wheat after irrigation (36 mm) and acetylene treatment were 0.006 ± 0.002 and 0.04–0.07 ± 0.01 kg N ha −1 per day respectively before and after fertilizer application (70 kg N ha −1 ). The nitrous oxide flux in the presence of acetylene decreased briefly, indicating that nitrification was rate determining in drying soil.