RELATIONSHIPS BETWEEN DENITRIFICATION RATE AND DETERMINANT SOIL PROPERTIES UNDER BARLEY

To better understand environmental regulation of denitrification, we e xamined relationships between denitrification rate and six determinant soil properties: moisture content, air-filled porosity, NO3- content, respiration rate, mineralizable-C concentration and denitrifying enzy me activity (DEA). Soil cores were collected on 27 sampling dates over a growing season at a site seeded to barley (Hordeum vulgare). Denitr ification rate was measured using a static core technique and acetylen e blockage. Moisture content and air-filled porosity and, to a lesser extent, mineralizable-C concentration and respiration rate were more s trongly related to denitrification rate than was DEA. Denitrification rate was unrelated to NO- content. On most sampling dates, mean denitr ification rate increased substantially only below an air-filled porosi ty of 0.3. Moreover, the distribution of individual measurements of de nitrification rate was less skewed at lower air-filled porosities. App roximately 60% of variation in mean values of denitrification rate for each sampling date could be accounted for by measurements of bulk soi l properties, of which moisture and air-filled porosity were most impo rtant. Measurements of bulk soil properties did not account for nil va lues of denitrification rate at low air-filled porosities or for small -scale spatial variability. Such measurements were better indicators o f temporal variation - that is, when denitrification occurred - than o f actual rates.