1. Black CA (1992) Soil Fertility Evaluation and Control. CRC Press, Inc., Boca Raton, Florida, USA
2. Colwell JD (1994) Estimating fertilizer requirements: A quantitative approach. CAB International, Oxon, UK
3. Pesek J & Heady EO (1956) A two nutrient-response function with determination of economic optima for the rate and grade of fertilizer for alfalfa. Proc Soil Sci Soc Am 20: 240?246
4. SAS Institute Inc. (1989) SAS/STATrUser's Guide, Version 6, Fourth Edition, Volume 2. SAS Institute Inc. Cary NC
5. Sinclair AG, Risk WH, Smith LC, Morrison JD & Dodds KG (1994) Sulphur and phosphorus in balanced pasture nutrition. Proc N Z Grass Assoc 56: 13?16