Abstract <p>A method for the determination of nitrate in soil with digital image colorimetry is proposed. This approach is based on photometric methods for the determination of nitrates after extraction with potassium chloride from soil samples. The original method for determining nitrate as an azo dye (a product of the azo coupling reaction of 1-naphthylamine and sulfanilamide) is modified to achieve higher sensitivity and accuracy of colorimetric determination. This approach provides the metrological characteristics of the digital image colorimetric method that are similar to spectrophotometric ones. The adequacy of the proposed method is confirmed by analyzing standard samples and soil samples collected in the Moscow oblast.</p>