394 DRY LAND FARMING 



has been stated, even where it is as high as 15 inches 

 and more per year. It is not absolutely necessary, how- 

 ever, to adhere to such a rotation as a rule, in order to 

 grow good grain crops with a rainfall above 10 inches, 

 providing the climatic conditions will admit of growing 

 cultivated crops. 



The objections that may be urged against this rota- 

 tion are: (1) that it reduces the fertility of the land; (2) 

 that it leads to the depletion of the humus supply, and 

 (3) that it encourages blowing in light soils. That it 

 does lower the supply of plant food in the soil cannot be 

 questioned. It lowers it by the amount that is taken 

 out by the crop grown, for this system gives nothing 

 back in return. That it lowers the amount of available 

 fertility would also seem true, for, as the gross amount 

 of fertility in the soil becomes reduced, it would seem 

 reasonable to conclude that the relative amount re- 

 leased would become less and less from year to year. 

 The store of plant food, however, in some of those west- 

 ern soils is so great that in some instances they have 

 produced crops thus covering a period of not less than 

 40 years, without any diminution in the yields. Because 

 of this some farmers have concluded that so it will be 

 always, but the end will inevitably be reached. The 

 day will come when the yields will wane. 



What has been said about waning fertility will apply 

 equally to the depletion in humus. It will probably apply 

 even in a greater degree, since the supply of humus in 

 these soils was less "bountiful at the first than the supply 

 of. plant food. This system only puts back the humus 

 furnished by the stubbles, and it consumes humus rapid- 

 ly while the fallowing is being done. With decrease in 

 humus comes proportionate decrease in the moisture- 

 holding power of the soil, and this in semi-arid regions 

 will in time work serious harm. 



