Soon-Ju Chung

The Use of Nitrate Color Paper to Test Nitrate Status of ‘Kyoho’ Grapevines in Korea

Abstract The absorption of high amounts of nitrogen from the soil and rapid translocation of N to shoots and berries in ‘Kyoho’ grapevines (Vitis labruscana)can result in vigorous growth and potentially in reduced floral bud differentiation as well as poor berry set. In order to make the nitrate color paper (NCP), the mixed reagents of 14 g sulfanilic acid, 2 g a-naphthylamine, 10 g MnSO4-H2O, 100 g BaSO4, and 7.5 g citric acid were dissolved with deionized water (mixed reagents 1:water 5, w/v). Five mm strips of Toyo filter paper #6 were allowed to absorb the reagent solution, and then freeze-dried. The NCP test strips were used to test the nitrate levels of leaf petiole extracts. The NCP was sensitive over a 10.2 to 168.5 mg-L−1 nitrate-N concentration range within 2 minutes after reaction. Leaf petiole extracts were diluted 10 Xwith deionized water, had optimal nitrate-N concentration in the range of 50.7 to 82.4 mg-L−1 (507 to 824 mg-L−1 raw sap concentration) and changed the NCP from white to pink in color. A colorless response of NCP showed nitrate deficiency of less than 10.2 mg-L−1, while a dark red color indicated excessive nitrate of more than 168.5 mg-L−1 (1,685 mg-L∼ 1 actual concentration) in petioles. By using this test at full bloom, the ‘Kyoho’ grapevines of NCP-II to-III showed better shoot growth and development, and higher berry qualities as measured by berry set, cluster weight, soluble solid and anthocyanin concentration than those in the NCP-I, -IV and -V categories after harvest. Therefore, it was possible to predict how much N should be supplied to the vineyard by using the NCP at full bloom.