REGULATING THE EVAPORATION 163 



summer cultivation is somewhat more difficult, but 

 must be practiced for the greatest certainty of crop 

 yields. Potatoes, corn, and similar crops may be 

 cultivated with comparative ease, by the use of 

 ordinary cultivators. With wheat and the other 

 small grains, generally, the damage done to the crop 

 by harrowing late in the season is too great, and 

 reliance is therefore placed on the shading power of 

 the plants to prevent undue evaporation. However, • 

 until the wheat and other grains are ten to twelve 

 inches high, it is perfectly safe to harrow them. The 

 teeth should be set backward to diminish the tearing 

 up of the plants, and the implement weighted enough 

 to break the soil crust thoroughly. This practice 

 has been fully tried out over the larger part of the 

 dry-farm territory and found satisfactory. 



So vitally important is a permanent soil mulch for 

 the conservation for plant use of the water stored in 

 the soil that many attempts have been made to de- 

 vise means for the effective cultivation of land on 

 which small grains and grasses are growing. In 

 many places plants have been grown in rows so far 

 apart that a man with a hoe could pass between 

 them. Scofield has descril^ed this method as prac- 

 ticed successfully in Tunis. Campbell and others 

 in America have proposed that a drill hole be closed 

 every three feet to form a path wide enough for a 

 horse to travel in and to pull a large spring tooth 

 cultivator, with teeth so spaced as to strike between 



