334 SOIL CONDITIONS AND PLANT GRO WTH 



rate at which potential food is likely to become available. 

 But as the problem is vague, so the methods are empirical and 

 the interpretation of the results often very difficult. 



The following discussion is confined to English soils and 

 English methods. No claim is made that these methods are 

 superior to those of other countries or that they give absolute 

 information about the amounts of plant nutrients in soils. 

 They are intended only to facilitate comparison of given soils 

 with a standard soil, and they are probably neither better nor 

 worse than other analytical methods which might be pro- 

 posed. 



In the United States chemical analysis is not in much 

 favour with the younger school of investigators, though 

 determinations are made of the components of the water 

 extracts of soils.^ 



For a discussion of the chemical and physical properties 

 of soils formed direct from granite in Aberdeen, or from the 

 paleozoic soils of North Wales, the reader is referred to the 

 papers by Hendrick and Ogg (132)2 and G. W. Robinson 

 (240). 



Organic Matter. — The analyst should note whether the 

 organic matter is fairly well decomposed, whether it still shows 

 definite plant structure, and whether or not it is acid to litmus 

 paper. He can then interpret his observations as shown on 

 pages \2^ et seq. 



Nitrogen. — Unlike the other soil constituents nitrogen 

 and carbonates are determined absolutely. The amount of 

 nitrogen is closely related to the loss on ignition, of which in 

 a large proportion of cases it is about 3 per cent. As a guide 

 to fertility it is therefore subject to the same limitations ; a 

 high nitrogen content may be associated either with a rich 

 soil containing abundance of valuable non-acid organic matter, 



^ See, e.g., J. S. Burd, Journ. Agric. Res., 1918, 12, 297-310, and Soil Set., 

 1918, 5, 405-419, who finds water more useful than citric acid and holds hydro- 

 chloric acid worthless as a means of assessing the crop producing power of a 

 soil (see p. 234). 



* See also Aberdeen Bulls., 1, 3, and 10, where the relationship between soil 

 analysis and manurial results is discussed. 



