AgriEngineering AgriEngineering Assessment of RGB vegetation indices to estimate chlorophyll content in sugar beet leaves in the final cultivation stage Sánchez-Sastre Luis Fernando Alte da Veiga Nuno M.S. Ruiz-Potosme Norlan Miguel Carrión-Prieto Paula Marcos-Robles José Luis Navas-Gracia Luis Manuel Martín-Ramos Pablo Universidad de Zaragoza 2020 research-article