DENITRIFICATION AS A PATHWAY FOR NITRATE REMOVAL FROM ORGANIC SOILS

Abstract

Potential denitrification rates of a cultivated, drained Everglades Histosol, Pahokee muck (a Lithic medisaprist), were examined to determine their variation with crop and position in the soil profile. The average rates, as measured with a flooded-soil technique in soil samples collected at monthly intervals between July 1977 and August 1978 from a fallow (bare) field at two depths, 0 to 10 cm and 60 to 70 cm, were 2.02 and 0.99 micrograms of nitrogen per cubic centimeter per day, respectively. As a comparison, the mean rates in soils cropped to sugarcane (Saccharum spp. L.) and St. Augustinegrass (Stenotaphrum secundatum (Walt.) Kuntz), similarly collected and assayed, were 7.21 and 7.27 micrograms of nitrogen per cubic centimeter per day, respectively. Although the relationship among the rates measured from the different soils remained the same, higher values were obtained if nitrous oxide production in nitrate-amended soil in the presence of acetylene was used to estimate denitrification rate. The differences between the two values resulted from variation in the atmosphere of the incubation vessels. The increased denitrification rates of the cropped soil likely reflected the greater availability of organic carbon and increased microbial activity in them. Linear correlation analysis of the data indicated no significant relationship between the initial number of denitrifying bacteria and the denitrification rate. Potential denitrification rates of a cultivated, drained Everglades Histosol, Pahokee muck (a Lithic medisaprist), were examined to determine their variation with crop and position in the soil profile. The average rates, as measured with a flooded-soil technique in soil samples collected at monthly intervals between July 1977 and August 1978 from a fallow (bare) field at two depths, 0 to 10 cm and 60 to 70 cm, were 2.02 and 0.99 micrograms of nitrogen per cubic centimeter per day, respectively. As a comparison, the mean rates in soils cropped to sugarcane (Saccharum spp. L.) and St. Augustinegrass (Stenotaphrum secundatum (Walt.) Kuntz), similarly collected and assayed, were 7.21 and 7.27 micrograms of nitrogen per cubic centimeter per day, respectively. Although the relationship among the rates measured from the different soils remained the same, higher values were obtained if nitrous oxide production in nitrate-amended soil in the presence of acetylene was used to estimate denitrification rate. The differences between the two values resulted from variation in the atmosphere of the incubation vessels. The increased denitrification rates of the cropped soil likely reflected the greater availability of organic carbon and increased microbial activity in them. Linear correlation analysis of the data indicated no significant relationship between the initial number of denitrifying bacteria and the denitrification rate. © Williams & Wilkins 1980. All Rights Reserved.