1. Professor, Univ. of Zaragoza, Carretera de Cuarte s/n, 22071 Huesca, Spain; EPS Carretera de Cuarte s/n, 22197 Huesca, Spain (corresponding author).
2. Agronomical Engineer, Spanish Research Council, EEAD Avda Montañana 1005, 50059 Zaragoza, Spain.
3. Agronomical Engineer, Univ. of Zaragoza, Carretera de Cuarte s/n, 22071 Huesca, Spain.