Crop ontology: integration of standard variables - Valette, L.; Pietragalla, J.; Laporte, Marie-Angélique; Afolabi, A.; Boukar, O.; Cannon, Steven B.; Diers, D.W.; Dreher, K.A.; Gaur, Pooran M.; Guerrero, Alberto F.; Hash, C.T.; Hualla, V.; et al. (2016)