TILLAGE AND FARM MACHINERY ]07 



spring and you will find the soil under it more damp 

 than the ground not covered. The board has kept 

 the moisture from passing off into the air. When 

 we remember how much moisture crops need; we 

 will see how important the dust mulch is. Every 

 time it rains hard it packs this mulch dowm, and the 

 farmer should cultivate his crop again, to loosen the 

 top soil. 



Dry Farming. Perhaps you have read or heard of 

 dry farming. In many places in our great West 

 there is not enough rainfall in a year to raise a crop. 

 But if all that falls in two years could be kept, it 

 would raise one crop. The farmers have learned 

 that if they keep a dry mulch on the ground and 

 save all the rainfall of one year, they have a pretty 

 good chance to raise a crop the second year. It 

 means that they must cultivate or till the ground 

 for two seasons to get one crop, but that is better 

 than raising nothing at all on these wide, dry areas. 

 Where rainfall is less than twenty inches per year, 

 dry farming or irrigation must be practiced. 



Irrigation. Two-fifths of the land of the United 

 States is too dry to produce regular crops without 

 irrigation. By irrigation is meant the storing of 

 water in lakes and reservoirs by means of huge 

 dams. This is done in the rainy season, when there 

 is plenty to be had. This water is then turned on 

 the fields by means of ditches when crops are grow- 

 ing, where it takes the place of rainfall (Fig. 56). 

 Some reservoirs are supplied from rivers that flow 



