Prediction of nitrogen fertilization for 'Kyoho' grapevine using simplified nitrate coloring indicator

With high N absorption from soil and rapid translocation of N to shoots and fruit, 'Kyoho' grapevines (Vitis labruscana) are apt to grow vigorously and to fail floral bud differentiation as well as have poor berry set. A nitrate coloring indicator (NCI) comprised of 14g sulfanilic acid, 2g α- naphthylamine, 10g MnSO₄ •H₂O, 100g BaSO₄, 7.5g citric acid and deionized water (mixed reagents 1 : water 5, w/v) was prepared by absorption of the reagent solution on to Toyo filter paper #6, and then freeze-dried. The NCI was available to test the nitrate levels of leaf petioles and vineyard soil extracts. The NCI was sensitive over the 1 to 250ppm nitrate-N range in concentration within 1 to 2 minutes after reaction. A leaf petiole extract diluted with 10 times the volume of deionized water had optimal nitrate-N at 50 to 70ppm (500 to 700ppm as actual concentration) and changed the NCI paper from white to pink color : Nitrate deficiency resulted in a colorless response as less than 5ppm, while a dark red color indicated excessive nitrate such as more than 200ppm (2,000ppm as actual concentration) in petioles. In a test of a soil extract diluted with 5 times the volume of deionized water, optimal nitrate-N ranges occured at pale pink color which indicated 10 to 20ppm of nitrate (50 to 100ppm as actual concentration). It was possible to predict how much N fertilizers should be supplied to vineyard by using this test at full bloom.