SOILS IN DRY AREAS 63 



where much organic matter is buried in the same, a condi- 

 tion that is often seriously detrimental to plant growth 

 in humid climates. In the semi-arid belt the amount of 

 lime present is relatively very large before it proves in- 

 jurious. In many humid climates" the application of lime 

 may in many instances be necessary in order to insure 

 good returns. It is seldom necessary to add lime thus to 

 semi-arid soils. Western soils are comparatively low in 

 humus. For the reasons, see p. 413. 



Because of this it is a matter of prime importance 

 that the humus supply in these shall be increased if 

 maximum production is to be obtained from them. For 

 some of the ways in which this may be brought about 

 see p. 420. The moisture-holding power of much of the 

 soil in the semi-arid country is very marked. This fol- 

 lows from the fact: (1) that while it is sufficiently por- 

 ous it is not unduly loose, a condition arising from the 

 character of the soil grains which compose it; (2) that 

 it is possessed of sufficient firmness, without that undue 

 consolidation which is a barrier to the penetration of 

 moisture; (3) that it is close grained, but not run to- 

 gether and so adhesive that it cannot be readily 

 penetrated by the roots of plants. This moisture-holding 

 power is increased by proper cultivation (see chapter 

 VIII) and increasing the supply of humus in the soft. 



The following are among the essential characteristics 

 of a good dry land soil: (1) It must be easy of tillage. 

 Such will be its condition when the sand and clay con- 

 stituents are properly blended. Western soils have 

 usually enough sand in them to make them easy of 

 tillage when they are sufficiently moist. They also 

 excel in flocculation, that is the looseness or fineness of 

 the particles. (2) It must be easily penetrated by 

 moisture when subjected to the processes of tillage. 

 Many soils that are so firm as to resist the easy penetra- 

 tion of water when not yet broken are easily penetrated 



