References
- Bremner , J. M. 1965 . Methods of soil analysis , Edited by: Black , C. A. vol. 2 , 1339 – 41 . Madison, Wisc : Am. Soc. Agron. Inc. . Ser. Agron.
- Bærug , R. , Lyngstad , I. , Selmer-Olsen , A. R. and ⊘ien , A. 1973 . Studies on soil nitrogen. I. An evaluation of laboratory methods for available nitrogen in soils from arable and ley-arable rotations . Acta Agr. Scand. , 23 : 173 – 81 .
- Fried , M. and Dean , L. A. 1952 . A concept concerning the measurement of available soil nutrients . Soil Sci. , 73 : 263 – 71 .
- Henriksen , A. and Selmer-Olsen , A. R. 1970 . Automatic methods for determining nitrate and nitrite in water and soil extracts . Analyst , 95 : 514 – 18 .
- Keeney , D. R. and Bremner , J. M. 1966 . Comparison and evaluation of laboratory methods of obtaining an index of soil nitrogen availability . Agron. J. , 58 : 498 – 503 .
- Selmer-Olsen , A. R. 1971 . Determination of ammonium in soil extracts by an automated indophenol method . Analyst , 16 : 565 – 68 .
- Stanford , G. and Legg , J. O. 1968 . Correlation of soil N availability indexes with N uptake by plants . Soil Sci. , 105 : 350 – 76 .
- ⊘ien , A. and Selmer-Olsen , A. R. 1980 . A laboratory method for evaluation of available nitrogen in soil . Acta Agr. Scand. , 30 : 149 – 56 .