1. S. Bailey, 1986 . The analysis of agricultural materials . Third Edition . London: HMSO.248 pp.
2. R. J. Bailey, E. I. Lord, and D. J. Williams, 1992 . Effect of rate, timing and source on the uptake of nitrogen and yield of irrigated potatoes .Aspects of Applied Biology 33, Production and protection of potatoes, pp.9 -14 .
3. B. Bastiman, A. J. Bevis, and L. W. Wellings, 1985 . Methods for measuring potato crops .Aspects of Applied Biology 10, Field trials methods and data handling, pp.199 -212 .
4. J. Benton Jones, B. Wolf, and H. A. Mills, 1991 . Plant analysis handbook: a practical sampling, preparation, analysis and interpretation guide . Georgia, USA: Micro-Macro publishing.213 pp.