Salvador, João Odemir, et al. “Nutritional Deficiency on Young Guava Plants Due to the Simultaneous Omission of Two Macronutrients”. Pesquisa Agropecuaria Brasileira, vol. 33, no. 10, Oct. 1998, pp. 1623-31, doi:10.1590/S1678-3921.pab1998.v33.5000.