A. E. JOHNSTON, P. R. POULTON and J. McEWEN (1981) The Soils of Rothamsted Farm. The Carbon and Nitrogen of the Soils and the Effect of Changes in Crop Rotation and Manuring on Soil pH, P, K and Mg in : Rothamsted Experimental Station Report for 1980 Part 2 - pp 5 - 20