Evaluation of the Minolta SPAD-502 chlorophyll meter for nitrogen management in corn

The field study investigated the relationship of Minolta SPAD 502 (SPAD) readings to applied nitrogen (N) fertilizer rate, corn (Zea mays L.) yield, and leafy concentration. The experiment was conducted on a total of six sites in Illinois during 1991 and 1992. Ten different open pedigree corn hybrids were grown at a final population of 65,000 plants ha(-4)). Nitrogen was applied at four rates (0, 90, 180, and 270 kg N ha(-1) as 28% liquid N solution. Significant main effects of environment (E), and hybrid (H), and E x H interaction were detected for all measured parameters. SPAD readings and leafy concentration at all sampling times (V7, R1, and R4) as well as grain N concentration were affected by N fertilizer rate. Maximum mean grain yield and maximum grain N concentration were obtained at 110 and 195 kg N ha(-1), respectively. At all sampling times the correlation of SPAD readings to N fertilizer rate were low but significant (R=0.22 at V7 and R1, R=0.11 at R4). SPAD correlation to corresponding leaf N concentration improved over time. The Pearson correlation was R=0.33 at V7 and increased to R=0.78 at R4. The SPAD meter did a good job at providing a measure of the relative greenness of living leaves at a specific point in time. Chlorophyll, readings can therefore be useful in detecting N deficiencies in growing crops. But, the SPAD meter cannot be used to make accurate predictions of how much fertilizer N will be needed by a crop during the future growing season. We conclude then that the SPAD meter will be most useful as a diagnostic aid rather than a tool for N management in corn.