214 Bulletin 88 



is much larger on heavy loams and adobe soil than on sandy soil. 

 It is greatest, of course, during and just after each irrigation and 

 decreases gradually until the next irrigation. In the case of alfalfa 

 it is comparatively high after each cutting and decreases as the 

 plants grow again and shade the ground. It is greater on an open 

 wind-swept area than on one protected by w^indbreaks. 



Many methods for reducing the evaporation loss are available 

 to the farmer. They are : 



1. Deep plowing. A shallow seed bed underlain by packed 

 soil tends to cause a high evaporation loss. From seven to nine 

 inches of soil should be turned over by the plow. 



2. Cultivation. In the case of crops planted in rows, such as 

 corn, the ground between the rows should be cultivated as soon as 

 possible after each irrigation. In the case of orchards, the ground 

 should be furrowed just before irrigating and cultivated just after- 

 ward. If the furrows are 6 inches in depth, one may expect to save 

 60 percent or more of the loss which would occur without the 

 mulch. Even alfalfa needs cultivation at least twice a year, and 

 particularly after the soil has been packed by winter pasturing. 



3. Increase in soil fertility. It is difficult to make a mulch 

 when humus is lacking. A fertile soil takes water readily and, if 

 cultivated, retains it with comparatively little loss by evaporation. 

 Straw should be spread on the ground and plowed in. Weeds, 

 "trash, and perhaps a green manure crop can be utilized to improve 

 the fertility. All stable manure should be spread and plowed into 

 the soil. 



4. More thoro and less frequent irrigation. This practice, be- 

 sides saving water, tends to establish deep root feeding, while 

 frequent light irrigations encourage shallow roots. For alfalfa one 

 irrigation per cutting is ample except for sandy soils, where two 

 lighter irrigations are preferable. 



5. Irrigation at the right time. Irrigate heavily before plant- 

 ing, and withhold water after the planting for a considerable time. 

 In the case of alfalfa, irrigate about a week before cutting. This 

 will supply the water when it is most demanded for plant growth, 

 and after cutting, the ground being still moist, the new crop will 

 spring up quickly and shade the ground. Wheat should be planted 

 in thoroly irrigated ground, and, with the aid of good winter rains,, 

 no irrigation is needed until the boot or flower stage. Cotton 

 should be irrigated sparingly in the early stages of growth. 



6. Irrigation at night. Evaporation is much restricted in the 



