Update to neonNTrans R package: implement statistical correction to account for nitrite contamination in soil extractions prior to 2022
February 15, 2024
Prior to 2022, NEON was not purity testing all batches of potassium chloride (KCl) used for soil extractions, and some batches had high nitrite. Because nitrite is turned into a gas in the presence of acidic soil but not in blanks (Homyak et al. 2015), this led to apparent negative nitrate + nitrite N concentrations for some samples when blank-corrected. In order to resolve this, Weintraub-Leff et al (2023) developed a quantile regression approach to quantify and add back the nitrite that was present in blanks but removed in samples, which resolves the apparent negatives. This statistical correction has now been implemented in the neonNTrans R package def.calc.ntrans function. The new function parameter called noxCorrection defaults to T (true), but can be opted out of by selecting F (false) in the function call, and users may handle the apparent negatives in a different way. For more details, consult the Readme for the neonNTrans R package and the help file for the def.calc.ntrans function.
Note that as of 2022 and onward, NEON tests all batches of KCl used for soil extractions, and only utilizes the powder if nitrite concentrations are < 0.02 ppm (preferred) or < 0.05 ppm (if higher purity powder is not possible to source). Now that nitrite contamination is avoided, analyses suggest data from 2022 and onward do not require the noxCorrection. def.calc.ntrans does not apply the correction to data collected in 2022 and later.
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References:
Homyak, P.M., Vasquez, K.T., Sickman, J.O., Parker, D.R. and Schimel, J.P. (2015). Improving Nitrite Analysis in Soils: Drawbacks of the Conventional 2 M KCl Extraction. Soil Science Society of America Journal, 79: 1237‐1242. doi:10.2136/sssaj2015.02.0061n
Weintraub-Leff, S.R., Hall, S.J., Craig, M.E., Sihi, D., Wang, Z. and Hart, S.C. (2023). Standardized data to improve understanding and modeling of soil nitrogen at continental scale. Earth’s Future, 11, e2022EF003224. doi.org/10.1029/2022EF003224
