“Mineral Nutrition of Cacao (Theobroma Cacao L. ) IV-Effects of Nitrate and Urea Nitrogen on Deficiency Symptoms of Phosphorus, Potassium, Calcium and Magnesium in Sand Culture”. Tropical Agriculture, vol. 42, no. 1, Jan. 1965, https://journals.sta.uwi.edu/ojs/index.php/ta/article/view/3780.