Fator de reflectância espectral do feijão submetido à adubação orgânica e mineral

Abstract

Bean cultivation has greate conomicand social importance in Brazil, as it is part of the population's basic diet and a source of income for small and large farmers. Aiming at higher productivity and, consequently, higherprofit, techniques are used to increase the productive potential of the crop, and it is possible to highlight the use of fertilization and remote sensing, ensuring better soil conditions and plant nutrition and a rapid nutritional diagnosis of the plant. The objective was to evaluate the spectral reflectance factor of cowpea fertilized with organic compound doses and to generate a model that allows the estimation of nutrient concentration in theleaves. The experiment wa scarried out atthe Federal Universityof Ceará, Campus do Pici (Fortaleza, Stateof Ceará, Brazil). The evaluated culture was cowpea (Vignaunguiculata (L.) Walp) cv. Pitiúba, under localized irrigation by drip irrigation. A randomized complete block design wasused in five treatments with five blocks and five replications. A randomized complete block design was used in five treatments with five blocks and fivereplications. The beans were fertilized with the following doses of organic compound: 100, 200 and 300%, the 100% dose being defined on the basis of equivalence of the nitrogen treatment. For the acquisition of radiometric data, the Field Spec 3 Hi-Res spectroradiometer was used. Leaf analysis was done by means of nitro-perchloric wet digestion, at the Soil, Water and Plant Laboratory of Embrapa Agroindústria Tropical. The analysis of variance between the contents of foliar nutrients in each treatment of thephenological phases evaluated was performed. A correlation analysis between the spectral data and the nutrient contents obtained from the leaf analysis was also performed, adjusting regression models. The results show that in all the phases evaluated, spectral behavior similar to that expected for healthy green vegetation was obtained and that wavelengths 725, 684 and 720 nm were the best to estimate P, K and Ca concentrations, respectively. It was possible to estimate nutrient concentrations of cowpea using spectral data and regression model.