ARTICLES 



THE PHYSICAL INVESTIGATION 



OF SOIL 



By B. a. keen, B.Sc, F.Inst.P. 



Goldsmiths' Company's Soil Physicist, Rothamsted Experimental Station, 



Harpenden 



Now that the methods and principles of many branches of 

 science are being applied to agriculture, a worker engaged on 

 a problem apparently lying in one of these divisions frequently 

 finds that the investigation extends into other divisions as 

 well. There are no definite boundaries within agricultural 

 science, although, for convenience in organisation, certain 

 broad lines of research can be marked off and attacked in 

 separate institutions and laboratories. It must, therefore, be 

 borne in mind that the physical problems presented by soil 

 cannot always be clearly defined without reference to other 

 branches of science. For instance, some of these properties 

 depend very much on the type of soil, for information on which 

 recourse must be had to geology and physical geography. The 

 moisture conditions in the soil are largely controlled by the 

 climate, and hence meteorology must be considered in this 

 respect. Again, those soluble nutrient salts in the soil mois- 

 ture which are taken up by the plant roots have to be investi- 

 gated by chemical and physico-chemical, as well as physical 

 methods. 



In general, the physical study of soil may be expected to 

 give results which are capable of application in two directions : 

 firstly, to elucidate the reasons for the comparative advantages 

 of the many forms of cultivation operations employed in farming 

 practice ; and, secondly, to supply information to the biologist 

 on the physical environment in which the plant roots, insects, 

 and micro-organisms exist in the soil. 



Historically, soil physics has grown up in two definite 

 periods. When the scientist first turned his attention seriously 

 to agricultural problems there were many obvious phenomena, 

 the investigation of which promised definite information about 

 the various factors controlling plant growth. There were, 

 for instance, questions of water supply, of the amount of 



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