Zagonel, Jeferson, and Cláudio Mário Mundstock. 1991. “Nitrogen Rates and Side-Dress Timing on Two Sunflower Cultivars”. Pesquisa Agropecuaria Brasileira 26 (9):1487-92. https://doi.org/10.1590/S1678-3921.pab1991.v26.3489.