1. Baldwin E (1952) Dynamic aspects of biochemistry, 2nd edn. Cambridge University Press
2. Ball PR and Ryden JC (1984) Nitrogen relationships in intensively managed temperate grasslands. Plant and Soil 76, 23?33
3. Bremner JM (1965) Inorganic forms of nitrogen. In Black CA ed Methods of soil analysis Part 2. pp 1179?1237. Madison, Wisc. American Society of Agronomy
4. Burg PFJ van, Dilz K and Prins W (1982) Agricultural value of various nitrogen fertilizers. Results of research in the Netherlands and elsewhere in Europe. Netherlands Nitrogen Technical Bulletin 13, Agricultural Bureau of the Netherlands Fertilizer Industry
5. Colwell JD (1979) National Soil Fertility Project Vol. 2. Soil Fertility Relationships, CSIRO Division of Soils in collaboration with State Departments of Agriculture and the Fertilizer Industry Australia