Fig. 2. Laboratory microplate nitrate reductase kit (M-NaR, •), ion specific electrode card (ISE-card), test strip reflectometry (TSR, ), and field nitrate reductase kit (spectrophotometer detection; F-NaR abs, ) determinations of nitrate using fresh tissue extracts compared with measurements obtained by flow injection analysis (FIA) using fresh tissue extracts. Winter wheat samples were collected at Feekes growth stage 7 and nitrate concentrations are expressed on a dry weight basis. Diagonal dashed line corresponds to nitrate measurements by alternate methods that would be equivalent with the FIA method (y = x).