68 DRY LAND FARMING 



especially when they are properly supplied with humus. 

 The moisture-holding power of course increases with the 

 humus supply, other things being equal. The richness 

 which these soils usually possess gives them great wear- 

 ing power. It is also retentive of gases and soluble plant 

 foods. 



Heavy compact clays are undesirable. They are 

 slow to absorb water and quick to lose it by evapora- 

 tion, because of the readiness with which they impact 

 and form openings in the surface which allow moisture 

 to escape. Stiff clays are composed of the finest par- 

 ticles of the soil, in some instances five hundred times 

 finer than sand grains. They are so fine that they do 

 not settle readily when held in solution. If these soils 

 are tilled when wet they become so adhesive as to be 

 almost unworkable on drying. Such a condition will 

 preclude successful production in dry weather. But the 

 mission of clay particles when mixed with coarser soil 

 particles is most beneficent, since it increases their rich- 

 ness and also their moisture-holding power. 



Sandy loam soils. In dry areas sandy loam soils 

 are such as are composed of sand particles intermingled 

 with clay to the extent of 10 to 15 per cent, of clay. The 

 clay content in them is from two to three times as much 

 as the clay content in sandy soils. In some areas 

 sandy soils have come from sand-bearing rocks which, 

 when decomposed, are not capable of furnishing clay, 

 hence the low fertility of these. But this is not usually 

 true of sandy soils in dry areas, as in arid regions ex- 

 perience has shown that these soils are as productive 

 as other good soils when sufficiently supplied with wa- 

 ter. This holds good even with arid soils that are desert 

 in the absence of irrigating waters. The sand and silt 

 particles in these are capable on further reduction of 

 yielding clay. The clay particles are greatly helpful in 

 lessening the spaces between the soil grains. Many of 



