Using a nitrate specific ion electrode to determine stalk nitrate-nitrogen concentration

The end-of-season stalk NO3 test has been used to determine N sufficiency in corn (Zea mays L.). Nitrate concentration is commonly determined with flow-injection analysis (FIA), which is accurate but uses hazardous chemicals and is time-consuming. Use of a simpler method of NO3 determination, such as the NO3 specific ion electrode (SIE), may save time and rests, and reduce hazards. The objective of this study was to compare estimates of stalk NO3 concentration by FIA and NO3 SIE. For FIA, NO3 was extracted with 2 M KCl, and the extract was filtered before analysis. For SIE, NO3 was extracted with 0.04 M (NH4)(2)SO4, and the extract was analyzed without filtration. The slope of the linear regression between concentrations estimated by SIE and FIA did not differ from 1.0. Use of the NO3 SIE, compared with FIA, reduces costs, sample processing, and use of hazardous chemicals.