Twenty forage samples were collected and selected for variation in nit
rate content. Each forage sample was analyzed 4 times by 4 different m
ethods: diphenylamine spot plate, spectrophotometric, nitrate-selectiv
e electrode, and high-performance liquid chromatographic. Five feed ex
tracts were spiked with 2 different amounts of nitrate and analyzed by
each method. The spectrophotometric and nitrate-selective electrode h
ad similar percent recoveries, which were close to 100%. The nitrate-s
elective electrode method had the least variation of the 4 methods. Th
e diphenylamine spot plate method had the poorest average recovery, gr
eatest variation, and was the least accurate. The average coefficients
of variation for all samples within a method were 15%, 12%, 6.4%, and
16% for the diphenylamine spot plate, spectrophotometric, nitrate-sel
ective electrode, and high-performance liquid chromatographic methods,
respectively. The variation in the nitrate-selective electrode method
was lower (P < 0.05) than the other methods. The results from this st
udy suggest that the nitrate-selective electrode method is more accura
te and precise than the other methods of analysis tested.