82 ARID AGRICULTURE. 



potatoes if he uses $40.00 expense per acre to 

 raise the crops, over the man who gets 50 sacks 

 by an expense of $15.00 per acre. One man nets 

 $185.00 per acre and the other makes $22.50 

 per acre. The man with the large yield proba- 

 bly works only a forty-acre farm, and from 

 twenty acres of it in potatoes banks $3,700.00 

 for that crop. The second man is probably try- 

 ing to farm eighty acres, and from forty acres in 

 potatoes he banks $900.00. The little farm well 

 tilled has brought its owner ov*r four hundred 

 per cent, the largest net income. The point 

 made is that good tillage for irrigation means 

 thorough tillage and special systems of soil and 

 crop management to produce the best returns. 



IRRIGATION Fertility is measured bv the power of soil to 



AND SOIL , . , . , 



FERTILITY produce crops. As we have shown, moisture is 

 an essential element of fertility. Other ele- 

 ments are nitrogen and minerals which are direct 

 plant foods. In much of the irrigated region 

 the waters used contain large amounts of dis- 

 solved fertilizing elements. It has been shown 

 that waters which contain much silt carry with 

 them large amounts of dissolved plant foods. 

 Studies of the waters used in irrigation from the 

 Hio Grande River showed that where water was 

 used to the depth of one foot it deposited 955 

 pounds of potassium, 58 pounds of phosphoric 

 acid, and 53 pounds of nitrogen to each acre. 

 This would be a sufficient supply of nitrogen for 



