Physicochemical variability of agricultural soils in the bulb onion (Allium Cepa L.) crop of the irrigation and drainage district Usochicamocha in Boyacá, Colombia Tekijä Forero-Pineda, Nicolás, Serrano-Cely, Pablo-Antonio, Forero-Ulloa, Fabio-Emilio, Gómez-Palacio, Andrés Mauricio, Acero-Cristancho, José Luis