1. Brady, N.C., and R.R. Weil. 1999. The Nature and Property of Soils. 12th ed. Prentice Hall, Upper Saddle River, N.J.
2. Cambardella, C.A., T.S. Colvin, D.L. Karlen, S.D. Logsdon, E.C. Berry, J.K. Radke, T.C. Kaspar, T.B. Parkin, and D.B. Jaynes. 1996. Soil property contributions to yield variation patterns.In: Robert, P.C., et al. (ed), Proc. 3rd Intl. Conf. on Precision Agric, Minneapolis, MN. 23–26 June 1996. ASA-CSSA-SSSA, Madison, WI. pp. 188–195.
3. Cox, M.S., and M.C. Wardlaw. 1999. Grid soil sampling to determine manageable physical and chemical properties affecting soybean production.In: Robert, P.C., et al. (ed),. Proc. 4th Intl. Conf. on Precision Agric., St. Paul, MN. 19–22 July 1998. ASA-CSSA-SSSA, Madison, WI. pp. 327–333.
4. Davenport, J.R. and E.M. Bentley. 2001. Does potassium fertilizer form, source, and time of application influence potato yield and quality in the Columbia Basin? Am J Potato Res 78:311–318.
5. De la Rosa, D., F. Cardona, and J. Almorza. 1981. Crop yield predictions based on properties of soils in Sevilla, Spain. Geoderma 25:267–274.