10 DRY LAND FARMING 



any cultivation after they are planted. In dry areas 

 it is the exception to grow these without some cultiva- 

 tion. It is usually given in the form of harrowing. Har- 

 rowing the crop after it appears may make the differ- 

 ence between securing a fair crop and virtually no crop 

 at all. The management of cultivated crops is not great- 

 ly different in humid and in dry areas, save in the degree 

 of the same called for. The cultivation called for in the 

 latter is considerably greater in degree than in the 

 former. It may also be profitably extended to the alfalfa 

 crop. 



In all areas a certain order of succession in the crops 

 is helpful. In those that are humid the succession is 

 much wider than in those that are arid. The rotations 

 in the former may be varied, and yet each may prove 

 satisfactory. In dry areas it is very different. The ro- 

 tations peculiar to and also suitable to each are restrict- 

 ed. This arises from the limited amount of the moisture 

 that is available. In some dry areas but one cereal crop 

 can be grown in two years. In others two crops may be 

 grown in three years, and in yet other instances three 

 crops may be grown in four years (see p. 397). But in 

 all these instances, special methods of cultivation are 

 called for. 



How climates may be classified. With reference to 

 precipitation and production, climates may be classified: 

 (1) as arid; (2) semi-arid; (3) sub-humid, and (4) humid. 

 It is not possible to state in figures, other than in an ap- 

 proximate way, the amount of the precipitation that 

 properly belongs to one or the other of these classifica- 

 tions, since precipitation is by no means the only factor 

 that influences production. It is greatly influenced by 

 soil conditions and by the dryness or the humidity of 

 the atmosphere, in other words by the degree of the 

 evaporation. 



An arid country is one in which .paying crops cannot 



