Water requirements of cowpea (Vigna unguiculata (L.) Walp.). calculated with the cultivation coefficient using drainage lysimeter ‌ Chavarria Parraga, Jesus Enrique, Ugando Peñate, Mikel, Sabando García, Angel Ramon, Muñoz Parraga, Jean Pierre, Bravo Ferrín, Richard Xavier, Villalón Peñate, Antonio