122 Some Causes of iinprodiictiveness in Soils. 



Composition of Soils deficient in Phosphoric Acid. 



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I have selected for illustration one sandy and two clay soils, in 

 order to show that the same defect may exist in soils of dia- 

 metrically opposite physical characters. 



Those who pretend to form a just estimate of the agricultural 

 capabilities of soils by mere classification and examination of 

 their mechanical condition make as great a mistake as men who 

 hastily form an opinion of the quality of a sample of guano or 

 superphosphate by handling and smelling it. 



Experience, indeed, shows that there are poor clays as well as 

 poor sands, and on the other hand rich clay soils and very fertile 

 sands. If we examine carefully these differences in the only way 

 in which they can be examined with certainty, that is, by 

 chemical analysis, we often find the relative productiveness of 

 different soils to be intimately connected either with an abund- 

 ance or a deficiency of phosphoric acid. 



Another substance which sometimes only exhibits traces, and 

 often occurs in too small a proportion, is lime. The practice of 

 liming and marling which prevails in many districts of England 

 is a proof of the want of lime in many light as well as heavy 

 soils. In the following Table I have incorporated the analyses 

 of various kinds of soils which are all benefited by the direct 

 application of lime or chalk : — 



Composition of Soils deficient in Lime. 



No. 1. Xo. 2. Xo. 3. No. 4. 



Sandy soil 

 from Kent. 



Moisture 



Organic matter 3-62 



Oxides of iron and alumina 7-50 



Phosphoric acid -13 



Sulphuric acid 



Lime -43 



Magnesia '49 



Potash and soda -48 



Insoluble siliceous matter .. 87-35 



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