Effect of Irrigation Method and Acetylene Exposure on Field Denitrification Measurements

An increased understanding of denitrification in situ may contribute to the development of agricultural practices that minimize denitrification losses from cropland. The objectives of this study were to: (i) observe the effects of sprinkle and flood irrigation on denitrification losses; and (ii) to evaluate the effects of acetylene (C2H2) exposure on inhibition of nitrification and C2H2decomposition. Acetylene was introduced into the soil atmosphere of field plots either by flood irrigation with C2H2‐treated water or by continuous diffusion of C2H2from dispersion tubes placed in the soil to a depth of 25 cm. Some plots received C2H2through dispersion tubes continuously for 42 d, while rotated plots received the gas for 7 d and were then abandoned in favor of fresh plots. Denitrification losses from the fallow, clay loam soil were approximately 16‐kg N when the soil was flood‐irrigated and approximately 3‐kg N when the soil was sprinkle‐irrigated. Soil environmental conditions within the disintegrated structure of the flood‐irrigated soil promoted denitrification losses. Nitrification rates in C2H2‐treated soils were only 30 and 87% of control rates, but nitrification rates recovered within 4 d after removal of the gas. The complications of nitrification inhibition by acetylene in field denitrification studies may be minimized by intermittent exposure of soil to acetylene or by rotation of experimental sites. Soil microorganisms began to metabolize C2H2after 7 d of continuous exposure. The problems of C2H2decomposition and decreased C2H2partial pressures were overcome by rotating field plots every 7 d.