Major Procedural Discrepancies in Soil Extracted Nitrate Levels and Nitrogen Isotopic Values

Preliminary vadose zone nitrate extraction experiments have revealed the extractant (2N KCl) volume affects the determination of nitrate and its nitrogen isotope ratio. In five cores, extractable NO 3 ‐N concentrations increased an average of 1.7 times after the soil‐to‐extractant ratio was increased from 1:1 to 1:10. An increased extractant volume resulted in a large positive shift of stable nitrogen values (δ 15 N), which averaged +6.2%. An underestimation of available NO 3 ‐N for leaching and transport through the vadose zone and a biased source interpretation from the δ 15 N values probably would occur if a procedure which leads to incomplete extraction of nitrate is used.