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Effects of Agricultural Runoff Dispersion on Nitrate Reduction in Forested Filter Zone Soils
Author(s) -
Verchot Louis V.,
Franklin E. Carlyle,
Gilliam J. Wendell
Publication year - 1998
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1998.03615995006200060033x
Subject(s) - denitrification , soil water , surface runoff , environmental science , nitrate , hydrology (agriculture) , soil science , environmental chemistry , nitrogen , chemistry , ecology , geology , biology , geotechnical engineering , organic chemistry
Forested filter zones (FFZ) are being used more frequently for remediation of agricultural non‐point source pollution. The objective of this study was to determine the effects of short‐term dispersal (1–2 yr) of agricultural runoff on the denitrification potential of the soil microbial population and denitrification rates, to a depth of 1 m, in forest soils in two small watersheds (W1 and W2) in the Piedmont of North Carolina. Each watershed consisted of a field and a FFZ. Denitrification potential was measured in a series of soil slurry incubations of soils from inside the FFZ that received agricultural runoff and from soils immediately adjacent to the FFZ that received no runoff (control). Soils were amended with both glucose and nitrate (G + NO 3 ) to ensure adequate supply of substrate and energy source. Denitrification rates were measured at ambient C conditions in a similar incubation with only NO 3 ‐N amendment (NO 3 ). We measured NO 3 ‐N disappearance in both incubations and reported loss as a percentage of initial concentrations. For the FFZ soils, >80% of the added NO 3 ‐N was lost in the G + NO 3 incubation from soils from the upper 50 cm in W1 and from the upper 30 cm in W2. In control soils, high levels of NO 3 ‐N loss were observed in only the upper 20 cm of the profile in W1, and in W2 surface soils had significantly lower denitrification potential than FFZ soils at all depths. Denitrification potential was greatly enhanced ( P = 0.05) throughout the entire first 100 cm in the first FFZ and in the surface 40 cm in the second FFZ. Denitrification rates under ambient C conditions were higher (>40%) in the surface 20 cm of the profile of the FFZ in W1, compared with the unexposed control (∼20%), but no enhancement was observed on W2. Exposure of soil to agricultural runoff had a significant impact on the soil microbial community. Denitrification potential in subsoil was limited by the absence of denitrifiers in unexposed soils, but subsoils exposed to agricultural runoff had a significant denitrifier population. The fact that higher denitrification potential did not translate to higher denitrification rates in these incubations indicates that C availability limited the denitrification process at all depths in these Piedmont forest soils.