Evaluation of wheat nitrogen status by colorimetric characteristics of crop canopy presented in digital images

Abstract

The main factor responsible for non-uniform density of planting is the inequality of soil fertility in different parts of the field and above all the inequality of the content of available nutrients. The aim of our work is to study, in field conditions, the relationship between the nitrogen status of crops and colorimetric characteristics of their digital images and to develop a method of selecting uniform management zones for spatially differentiated fertilization. The field was photographed using a small radio-controlled aircraft equipped with a digital high resolution camera at the flight altitude of 500-700 m. The colour of crop images was characterized by parameters L, A and B of the CIELAB colour system. Changes in these parameters (?L, ?A and ?B), hue (?C) and saturation (?H) were calculated relative to their values at reference plots with different content of nitrogen in the soil. Dissimilarities in the colour of the crop canopy between reference plots and various sections of the field were determined from the value ?E that summarizes changes in the parameters L, A and B. To quantify nitrogen status of plants for spatially differentiated fertilization, regression relationships between colour characteristics of the canopy and the dose of nitrogen at test plots were used. The experiment performed has shown that the method we used to analyze colorimetric characteristics of crop canopy by its digital image, test plots with known nitrogen content in the soil including, is of considerable promise for quantitative evaluation of plant needs in nitrogen nutrients, management zones selection and spatially differentiated fertilization.