Accurate prediction of nutrient status of plants during the growing period is necessary for the efficient use of fertilizers, low yields and high quality products. The cheap and affordable methods of image analysis are promising techniques for monitoring crops for decision making to optimize the production process. Colorimetric method is based on an analysis of the optical characteristics of plants by digital images. To improve the colorimetric method we developed the module for the automatic construction of calibration curves for quantifying nitrogen status of plants. Refs 11. Figs 2.