Estimation and correlation of chlorophyll and nitrogen contents in Psidium guajava L. with destructive and non-destructive methods by Güiza-Castillo, Luisa-Liliana, Pinzón-Sandoval, Elberth-Hernando, Serrano-Cely, Pablo-Antonio, Cely-Reyes, German-Eduardo, Serrano-Agudelo, Pablo-Cesar