CHANGES IN SOIL CHEMICAL PROPERTIES DURING SHORT-TERM REDUCING CONDITIONS FOLLOWED BY NITROGEN FERTILIZER APPLICATION

Historically, denitrification of nitrate (NO₃^-) has been linked to the carbon cycle. Recent studies indicate that Fe(II) oxidation is closely coupled to denitrification as well in a process called nitrate-dependent, Fe(II) oxidation. No-tillage management is a practice where crop residues are returned to the soil, thus, soil organic carbon levels accumulate when compared with plowed (conventionally-tilled) soils. No-till soil has been shown to undergo denitrification more readily than plowed soil, however, the involvement of nitrate-dependent, Fe(II) oxidation has been overlooked. No-till (NT) and conventionally-tilled (CT) soil samples from a Maury silt loam were incubated (100 g/L) in an anoxic glove box to achieve Fe(III)-reducing conditions and relevant redox species were monitored. The redox potential of NT soil dropped more rapidly than CT soil, presumably because of the greater soil organic carbon levels in NT. In addition, there was greater Fe(II) production in NT. After 30 d, fertilizer NO₃^- was added at a concentration of 0.001 mol/L. Addition of NO₃^-resulted in immediate NO₃^- reduction coupled to Fe(II) oxidation. This process was more important in NT soil than CT samples. Where NO₃^--reduction and Fe(II)-oxidation occurred, dissolved Fe(III) increased significantly for 48 hrs. Comparatively little oxidation of Fe(II) was observed in CT soils. We speculate that this research has important implication in biogeochemical cycling of nutrients, global warming, and contaminant transport. Future experiments will evaluate N₂O production and tease out the biotic contribution from abiotic process before and after the application NO₃^- under simulated Fe-reducing conditions in CT and NT soils.