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Title: OVERWINTER SOIL DENITRIFICATION ACTIVITY AND MINERAL NITROGEN POOLS AS AFFECTED BY MANAGEMENT PRACTICES

Author
item JACINTHE, P - OSU-OARDC, WOOSTER, OH
item DICK, W - OSU-OARDC, WOOSTER, OH
item Owens, Lloyd

Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2001
Publication Date: 4/9/2002
Citation: JACINTHE, P.A., DICK, W.A., OWENS, L.B. OVERWINTER SOIL DENITRIFICATION ACTIVITY AND MINERAL NITROGEN POOLS AS AFFECTED BY MANAGEMENT PRACTICES. BIOLOGY AND FERTILITY OF SOILS. 2002. v. 36. p. 1-9.

Interpretive Summary: A current environmental concern is water becoming contaminated from agricultural nutrients. Agriculture can be a major contributor of excess nitrogen in some areas. Research has shown that much of this nitrogen leaves the soil and enters water during the late winter and early spring when plant uptake of nitrogen is very minimal. Some forms of nitrogen move emore readily than others, and the transformations from one form to another usually result from microbial activity. Sometimes nitrogen is in the nitrate form, which leaches very readily, and sometimes nitrogen can be transformed (denitrified) into elemental nitrogen, which returns to the atmosphere. This study indicated that the freeze-thaw conditions of overwintering temporarily reduced the populations of denitrifying bacteria in the surface soil layer. This allowed for other forms of nitrogen, such as nitrate, to increase by several-fold (2 to 10 times) from late autumn to ospring thaw. Such an accumulation of nitrate in soils during the winter months represents a potential source of nitrogen that could impact surface and groundwater quality. With this information, management plans can include options to reduce the production of nitrate during the winter months. This information will be useful to producers, management planners, and consultants as well as other scientists.

Technical Abstract: During freeze-thaw events, numerous biophysical changes occur in soils and these can affect processes such as mineralization, nitrification and denitrification which control inorganic N balances. To evaluate these effects, a study was conducted comparing soil denitrification activity, dissolved organic C (DOC), and inorganic N concentrations before and after the winter season. Soil cores, collected in late autumn and in early spring (immediately after thaw), were sliced into 0.5, 5-10, 10-15 and 15-30 cm depth increments, sieved and bulked into composite samples by depth. A significant loss of denitrification activity was measured in the 0-5 cm soil layer following freeze-thaw and this loss was significantly greater in soils which had been plowed during the previous growing season. No significant change in denitrification activity was noted in the 5-30 cm samples. At all the soil depths sampled, concentrations of DOC, NH4-N and NO3-N were several-fold (2 to 10 times) greater following spring thaw than in late autumn. Accumulation of NO3-N in soils during the winter months represents a potential source of N that could impact surface and ground water quality. Implementation of strategies to reduce NO3-N production and transport during the winter months could prove beneficial to farmers and the environment.