1. Botha , A. D.P. 1963 . 391 – 395 . Utilization of nitrogen by tobacco plants using the nitrogen isotope 15N. Nat. Conf. on Nuclear Energy 1963: Appl. Isotopes Radiation, Pretoria, R.S.A
2. Botha , A. D.P. and Britz , P. J. 1986 . Hydraulic lift with rotating platform for growth room experimentation. 7 SIRI Info. Bull. No. B2/5, Soil and Irrigation Research Institute, Pretoria
3. Plant Uptake and Residual Value of Six Tagged Nitrogen Fertilizers
4. Isotope studies on the comparative efficiency of nitrogenous sources