The use of the orange I method for determining soil nitrates and a comparison with the phenol‐sulphonic acid method for certain soils of Northern Nigeria

A new method for rapid and precise determination of soil nitrates is described, based on quantitative reduction of nitrate to nitrite, followed by colorimetric estimation of an azo dye (Orange I). The method is sensitive to 0.006 p.p.m. of nitrate nitrogen in solution and with a dilution technique the accuracy has been tested over a range of 0.05–40 p.p.m. in soil. A means of correcting for interference from soil extracts is also discussed. For certain soils of Northern Nigeria, the method is more rapid, and for very small amounts of nitrate considerably more accurate than the phenolsulphonic acid method. Statistical examination of the data shows that the two methods yield results of closely similar agronomic significance, but the Orange I method gives values with greater precision.