SOILS AND THEIR PROPERTIES 67 



the temperature is practically constant. At Greenwich 

 Observatory at a depth of 25*6 feet the seasons are reversed, 

 with a difference of 3 between summer and winter. 



A very great deal of attention has been paid to what has 

 been called mechanical or physical analysis of soils. In a 

 district where one is dealing with geological strata which 

 have never been seriously interfered with for many years 

 past there is little doubt that these methods have considerable 

 value, but where much farmyard manure and lime have been 

 applied in the past, and the surf ace of the soil has beenmodified 

 by road sweepings, then little value can be attached to any 

 of these methods. The books in the bibliography should 

 be consulted on this highly technical subject. The fertility 

 of a soil is dependent upon an almost innumerable number 

 of factors, and which one happens to be of most importance 

 at the moment will depend upon an almost innumerable 

 number of circumstances. For example, many square 

 miles of the Punjab had for thousands of years borne few 

 crops, but the introduction of irrigation has converted these 

 areas into very fertile soils, growing large crops of wheat of 

 first-class quality. Here the determining factor happens 

 to be water, but the physical and chemical properties of the 

 soil are the same. The problem is an engineering one. 

 There are large areas of very poor pasture in the British 

 Isles, such as occur in Northumberland in the north, and 

 Sussex in the south. The application of basic slag has 

 revolutionized the whole character of such soils. Here the 

 determining factor appears to be phosphorus, and possibly 

 lime as well. In this latter case chemical analysis would have 

 been of great value for information, but no single test, or 

 group of tests, can possibly solve the problem of the fertility 

 of a soil. All any such methods can do is to point out useful 

 lines of investigation. It must then be left to the cultivator 

 to experiment upon the land, and find out for himself what 

 treatment is most satisfactory. The great value of both 

 physical and chemical analysis lies in suggesting possible 

 systems of improvement. 



Capillarity. As is well known, water will wet the surface 



