J. A. T. do Amaral, A. T. Cordeiro, and A. B. Rena, “Effects of aluminum, nitrate and ammonium on the metabolic nitrogened composition and of carboidrates in <i>Stylosanthes guianensis</i> and <i>S. macrocephala</i>”;, PAB, vol. 35, no. 2, pp. 313–320, Feb. 2000.