Some relationships between denitrification potential and fractions of organic carbon in air-dried and field-moist soils

Abstract

Denitnfication potential (DNP). with nitrate non-limiting, was examined in relation to total organic carbon (TC) and fractions of organic carbon in a number of soils, both field-moist and air-dried. The fractions of organic carbon were water-soluble carbon (WSC) and carbon mineralized under both aerobic (AMC) and anaerobic conditions (AnMC). The soils, all sampled to 5cm depth, were in three groups, from grassland in Berkshire, from grassland in Devon and from arable fields in Berkshire. Thirty-two soils were examined in field-moist condition, of which 21 were also air-dried. Contents of organic carbon ranged from 0.89 to 6.73% dry soil. With the 21 air-dried soils, the highest correlations between DNP and organic carbon were with WSC ( r = 0.96∗∗) and AMC ( r = 0.95∗∗). When the groups of soils were considered individually, AMC generally showed rather closer correlations than did WSC with DNP. Correlations between DNP and TC ( r = 0.91∗∗) or AnMC ( r = 0.92∗∗) were lower than with WSC or AMC but, as with these fractions, were higher when all samples were considered together than when the groups were considered individually. With the field-moist soils, the closest correlation with DNP was given by AnMC, both when the soils were considered together ( r = 0.96∗∗) and when considered in individual groups. The second closest correlation was given by AMC. The results suggest that, in the field, denitrification may often be limited by the amount of C susceptible to mineralization under anaerobic conditions.