1. Broeshart, H., The Application of Foliar Analysis in Oil Palm Cultivation. Thesis, Wageningen (1955).
2. Bull, R. A., Studies on the deficiency diseases of the oil palm: I. Orange Frond Disease caused by magnesium deficiency. J. West African Inst. Oil Palm Research2, 94–129 (1954).
3. Ferwerda, J. D., Fertilising of the African oil palm. Trans. Vth Intern. Congr. Soil Sci.3, 284–287 (1954).
4. Ferwerda, J. D., Boron deficiency in oil palm in the Kasai region of the Belgian Congo. Nature173, 1097 (1954).
5. Ferwerda, J. D., Replanting in Oil Palm Cultivation. Thesis, Wageningen (1955).