da Silva, P.R.F. and Rizzardi, M.A. (1993) “Response of sunflower cultivars to plant density in two planting dates. II. Characteristics associated with harvesting”, Pesquisa Agropecuaria Brasileira, 28(6), pp. 689–700. doi:10.1590/S1678-3921.pab1993.v28.3927.