Abstract
Growers of tropical maize (Zea mays L.) are often reluctant to invest in seeds and fertilizers because they are seeking to minimize risks. A chlorophyll meter measures leaf greenness, which non-destructively indicates the leaf N concentration. This may be an alternative to sampling N in the soil and to analyzing N in plant tissue, both of which are costly methods for estimating the N status of a crop at a certain growth stage. Thus, at earlier growth stages, the N status of a crop could be related to the final yield. At early growth stages of maize, the chlorophyll meter has been used successfully to predict the yield in many regions. In this study, a Minolta chlorophyll meter (type SPAD 502) was calibrated to distinguish between two maize varieties [Local Variety and HB-83 (a white hybrid)] and three fertilizer treatments [zero, recommended (89:13:24 N:P:K kg ha-1), and supra optimum (151:37:76)]. The meter was more useful at lower than at higher levels of fertilization, where SPAD readings as estimates of chlorophyll content appeared to reach a plateau. Both linear and quadratic relationships were observed between SPAD readings and maize grain yields. Central American farmers often apply low levels of fertilizers. If chlorophyll meter readings were to diagnose N deficiency accurately and inexpensively, fertilizers could be applied late in the season to counteract N deficiency. The chlorophyll meter should be calibrated for each variety in order to predict the yield with sufficient precision.
