The NPK rating (usually written as N–P2O5–K2O) of fertilizers is normally assessed using spectrophotometry [1] or Kjeldahl analysis [2] for N, spectrophotometry [3] or gravimetry [4] for P, and atomic emission spectrometry for K [5].
TheNPK rating (usually written as N–P2O5–K2O) of fertilizers is normallyassessed using spectrophotometry [1] or Kjeldahl analysis [2] for N,spectrophotometry [3] or gravimetry [4] for P, and atomic emissionspectrometry for K [5].