I genuinely don't think citric acid would do that for large amount of soil. Yet, there are some microbial processes to remove nitrates from soil though (Ref.1):
Abstract: The microbial processes of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are two important nitrate reducing mechanisms in soil, which are responsible for the loss of nitrate ($\ce{NO3-}$) and production of the potent greenhouse gas, nitrous oxide ($\ce{N2O}$). A number of factors are known to control these processes, including $\ce{O2}$ concentrations and moisture content, $\ce{N, C,}$ pH, and the size and community structure of nitrate reducing organisms responsible for the processes. There is an increasing understanding associated with many of these controls on flux through the nitrogen cycle in soil systems. However, there remains uncertainty about how the nitrate reducing communities are linked to environmental variables and the flux of products from these processes. The high spatial variability of environmental controls and microbial communities across small sub centimeter areas of soil may prove to be critical in determining why an understanding of the links between biotic and abiotic controls has proved elusive. This spatial effect is often overlooked as a driver of nitrate reducing processes. An increased knowledge of the effects of spatial heterogeneity in soil on nitrate reduction processes will be fundamental in understanding the drivers, location, and potential for $\ce{N2O}$ production from soils.
Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are two of several important processes that are responsible for nitrogen cycling in soil. Other key nitrogen transforming processes in soil include anaerobic ammonium oxidation (Anammox), which oxidizes ammonium to nitrogen gas ($\ce{N2}$) gas using nitrite ($\ce{NO2-}$) as the electron acceptor. Nitrification, denitrification, and DNRA are all capable of producing $\ce{N2O}$ (See Figure). Both denitrification and DNRA are processes that reduce nitrate ($\ce{NO3-}$) through various intermediate steps to N2 and ammonium ($\ce{NH4+}$), respectively, and are the only soil microbial processes capable of both removing soil $\ce{NO3-}$ and producing $\ce{N2O}$. Denitrification produces $\ce{N2O}$ when abiotic conditions or gene complement prevent its reduction to $\ce{N2}$ and DNRA releases $\ce{N2O}$ as a by-product of the reduction process.

References:
- M. Giles, N. Morley, E. M. Baggs, T. J. Daniell, “Soil nitrate reducing processes – drivers, mechanisms for spatial variation, and significance for nitrous oxide production,” Frontiers in Microbiology 2012, 3, 407 (Rewiew with 16 pp.) (doi: 10.3389/fmicb.2012.00407).