CHAPTER VIII 



THE CHEMICAL COMPOSITION OF THE SOIL 



Plant Food found in Normal Soils. Dormant and Available 

 Plant Food. Rotations and Plant Food in the Soil. Systems 

 of Farming — Wasteful and Conservative. Requirements of 

 Different Crops for Fertilisers. Types of Soil — Characteristic 

 Weeds and Crops. 



It has already been stated that while the greater part 

 of the soil consists of sand and clay, materials that are 

 of no service as food for the plants, there are also 

 present much smaller quantities of the elementary 

 substances — nitrogen, phosphoric acid, potash, lime, mag- 

 nesia, etc. — elements which we have found in plants and 

 learnt to be necessary to their nutrition. In Table XII. 

 a series of chemical analyses of characteristic English 

 soils are set out, and though the number of soils repre- 

 sented is not great, the examples show almost as wide 

 variations in composition as may be expected anywhere 

 in the United Kingdom. The first things that may be 

 noticed in these analyses is that the range of variation 

 in composition is not great, in few of the soils does the 

 nitrogen fall below o-i per cent, in very few arable soils, 

 on the other hand, does it rise above 0-3 per cent. ; 

 phosphoric acid may be as low as o-o6 per cent in 

 exceptional cases, but very rarely will it be higher than 

 0-2 per cent. ; potash perhaps shows the greatest varia- 

 tions, ranging between o-i per cent to i-o per cent. 

 These comparatively small variations hardly seem to 



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