Evaluating spectral vegetation indices for a practical estimation of nitrogen concentration in dual-purpose (forage and grain) triticale

Abstract

There is an ample literature on spectral indices as estimators of the crop’s chlorophyll concentration, and, by extension, of the nitrogen concentration. In this line, the suitability of 21 of these indices was evaluated as nitrogen concentration indicators for the dual-purpose (fodder and grain) triticale (X Triticosecale Wittmack). The interval of interest was the one in that it would be possible to intervene to correct the deficiency of nitrogen (defined according to practical criteria); one peculiarity of this study is that it only develops a model for that period; more developments complicate the profitability, because the annual stability is not guaranteed and calibration studies are expensive. The results showed that, although there are significant correlations between the greenness indices and the crop’s nitrogen concentration, for none of the spectral indices the relationship can reach acceptable values that encourage their use in the new techniques of precision agriculture of low cost. One solution for improving the effectiveness and reduce costs could be to use the information contained in the spectral signature beyond what is easily explicable by biochemistry and biophysics, in other words, using data mining in the search for new spectral indices directly related to the concentration of nitrogen in plant and stable throughout crop development. At present, the squared correlation coefficient (R2) of the best fits reach 0.5 for the later phenological stages, this mark is reduced to 0.3 with an approach of low cost