Denitrification in No‐Till and Plowed Soils

Abstract No‐till and plowed soils were compared with regard to denitrifying activity. To assay denitrification with minimal physical disruption of the soil, an important consideration in the study of tillage effects, a procedure was developed employing acetylene (C 2 H 2 ) inhibition of nitrous oxide (N 2 O) reduction in intact soil cores. This approach and a short‐term, anaerobic soil slurry assay were consistent in indicating greater denitrifying activity in no‐till than in plowed Maury silt loam soil. In the intact core assay, ratios of no‐till to plowed soil activity were >1 on all sampling dates, and were as high as 77. Intact cores from a Crider (Typic Paleudalfs) soil showed a similar tillage effect, but tillage had inconsistent effects on both soil water content and denitrifying activity in a Tilsit (Typic Fragiudults) soil. It is suggested that the generally higher soil moisture contents observed in no‐till soils, rather than tillage per se, are primarily responsible for higher denitrifying activity. Enhanced denitrification may account, in part, for the lower soil NO ‐ 3 concentrations and higher N fertilizer requirements sometimes reported for no‐till soils.