1. Annon. 1925. Report of Committee on Soils and Cultural Research. pp. 15–16. Proc. 12th Annual Meeting of Potato Assoc Amer.
2. Beaufils, E.R. 1973. Diagnosis and recommendation integrated system (DRIS). A general scheme for experimentation and calibration based on principles developed from research in plant nutrition. Soil Sci Bul 1, University of Natal, Pietermaritzburg, South Africa.
3. Buchholz, D.U. and N.C. Wallenhaupt. 1990. Varying fertilizer applications within a field. Better Crops with Plant Food 74:12–13. PPI, Atlanta, GA.
4. Carter, J.N., D.T. Westermann and M.E. Jensen. 1976. Sugar beet yield and quality as affected by nitrogen level. Agron J 68:931–936.
5. Cole, C.V., J. Williams, M. Shaffer and J. Hanson. 1987. Nutrient and organic matter dynamics as components of agricultural production systems models. p. 147–166.In: R.F. Follet,et al., (Eds.) Soil Fertility and Organic Matter as Critical Components of Production Systems. SSSA Special Pub No 19, Madison, WI.