Abstract
The method of estimating nitrate nitrogen concentration of the standing corn (Zea mays L.) in yellow-ripe stage was developed using the equation by Harada et al. that is, nitrate nitrogen concentration of the whole plant on the basis of dry matter can be closely estimated by multiplying the concentration factor by the dilution factor. The concentration factor is nitrate nitrogen concentration of the stem on the basis of fresh matter and the dilution factor is dry matter partitioning ratio of stem divided by dry matter rate of stem. Our results showed concentration factor was significantly correlated with nitrate nitrogen concentration in the juice squeezed from cuts of stems of 10mm thickness at a height of 50cm aboveground (correlation coefficient: 0.871, p< 0.001). The regression equation was found as Y = 0.45 X +0.008 (Y: concentration factor, X: nitrate nitrogen concentration in stem juice). On the other hand, it had been reported that dilution factor decreased as milkline depression score increased. Dilution factor could be estimated by the milkline depression score. To use the relationship between dilution factor and milkline depression score easily, in this paper we made a conversion table. Consequently, nitrate nitrogen concentrations of corn which calculated from both factors estimated could be well corresponded to the values analyzed by ion-chromatography (coefficient of determination: 0.774). Rapid determination of nitrate nitrogen in stem juice was also examined by use of a simple reflection photometer (RQflex), which can read color depth of test paper for nitrate within a minute. The results showed that nitrate nitrogen concentrations in stem juice determined by RQflex had a good correlation with those by ionchromatography method. We concluded RQflex could be useful for rapid determination of nitrate nitrogen in stem juice.
