Chlorophyll measurements and nitrogen nutrition index for the evaluation of corn nitrogen status

Plant-based diagnostic techniques are used to determine the level of crop N nutrition but there is limited comparative research on the different methods. Our objectives were to establish the relationship between chlorophyll meter (CM) readings and N nutrition index (NNI) during the corn (Zea mays L.) growing season, and to compare both methods as diagnostic tools for predicting grain yield response to N fertilization. The study was established at eight site-years using four to seven N fertilization rates. The CM readings from the youngest collared leaf were taken on five to eight sampling dates in 2004, 2005, and 2006 along with NNI determinations. Generally, CM readings and NNI increased with increasing N rates. Chlorophyll meter readings and relative CM (RCM) readings were related to NNI, but the intercepts and/or slope of the response curves varied with site-year. Because they are site-specific, these relationships may not be reliable indicators of corn N status. The relationship between CM readings and relative grain yield (RY) at stage of development approximate to V12 was also site-specific. Relative CM readings (RY = -0.64 + 1.65 RCM if RCM <= 0.98 and RY = 0.97 if RCM > 0.98; R-2 = 0.60) and NNI (RY = -0-34 + 1.47 NNI if NNI <= 0.88 and RY = 0.96 if NNI > 0.88; R-2 = 0.79) at stage of development approximate to V12 were related to RY. These two relationships were stable across site-years and could be used to detect and quantify N deficiencies of corn.