Chlorophyll meter can help in the management of topdressing nitrogen fertilization, however, there isn't a critical reading value with a satisfactory relationship with grain yield. The objective of this study was to monitor the nitrogen (N) level in flooded rice plants, cultivars IRGA 422CL and IRGA 424, using the chlorophyll meter and associating the readings with green/dry matter production and grain yield. Two experiments were carried out in the crop years 2007/08 and 2008/09 with N rates for the 1st and 2nd topdressing fertilizations, followed by SPAD (Soil Plant Analysis Development) readings and determination of green/dry mater, N content in plant tissue, accumulated N and grain yield. It was found effect of the 1st and 2nd N applications on chlorophyll meter readings along the cycle, however, the SPAD readings became similar with time for all treatments. Green/dry matter production and accumulated N responded linearly to the N rates. There was no effect of interaction for N rates and grain yield, but the response of grain yield as a function of N rates was described by a quadratic equation in both experiments. SPAD readings evaluated the nutritional status of flooded rice plants but did not show accurate information about N needs with reflexes in the yield. Therefore, chlorophyll meter readings could be associated to other parameters, such as green/dry mater to help interpretation and adjustment of N topdressing fertilization.
Oryza sativa; green/dry matter; grain vield; management of nitrogen; lowland soils
