The development of a portable chlorophyll meter, which allows instantaneous measurement without leaf destruction, has been used as a new tool to assess plant N status. The reading in the equipment indicates a relationship with leaf chlorophyll and they are calculated based on the emission of light quantity through of the leaf in two wavelengths with different chlorophyll absorbance. Some researchers have established association between SPAD reading and chlorophyll content and between chlorophyll content and plant N content. In rice, wheat, oat and maize there were determined good associations between SPAD reading and grain yield. The critical level of a portable chlorophyll meter, correspondent with adequated N level, determined in rice (panicle differentiation), wheat (leaf flag) and maize (silking) are of, respectively, 40-42, 41-42 and 58-62. However, since it is a new tool, this equipment presents some limitations such as: little variation between readings, the readings are influenced by other factors besides N and, especifically for maize, to present low correlation with grain yield in the initial stages of plant development. These limitations were be to solve or minimize through the utilization of correction factores such as the use of strip reference, specific leaf weight, leaf area and plant dry matter. Despite of the limitations presented, the use of the leaf chlorophyll content shows high potential as an indicator for nitrogen fertilization recommendation in cereals, especially if associate as soil indicators.
Zea mays; Triticum aestivum; Oryza sativa; Avena sp.; nitrogen fertilizer; chorophyll meter