Farias, Iderval, et al. “Harvest Managing and Plant Spacing of Spinelles Fodder Cactus, under Grain Sorghum Intercropping at the Semi-Arid Region of Pernambuco State, Brazil”. Pesquisa Agropecuaria Brasileira, vol. 35, no. 2, Feb. 2000, pp. 341-7, doi:10.1590/S1678-3921.pab2000.v35.5759.