GROWING BY IRRIGATION. 289 



to the amount of water available. A yield of 6 tons 

 per acre actually needs 30 inches of water an^l cer- 

 tainly there will be some loss by evaporation from 

 the surface of the soil and by percolation through 

 into the subsoil. The Utah Agricultural Experi- 

 ment Station in co-operation with the United States 

 Department of Agriculture made numerous tests of 

 water used, with varying amounts and varying fre- 

 quency of application. Briefly, it was learned that 

 frequent applications gave much larger returns than 

 infrequent, and that the yield was somewhat directly 

 in proportion to the amount used. 



RESULTS OF EXPERIMENTS IN IRRIGATING ALFALFA IN UTAH. 



Inches of water Number of Yield per acre, 



applied. irrigations. in tons. 

 17.058 3 3.125 



17.33 4 3.468 



24.97 4 5.017 



25.002 2 1.55 



61.465 12 6.243 



Penetration of Roots in Irrigated Soils. Soils in 

 the arid regions are quite unlike those of humid 

 regions. There is often little difference in physical 

 texture or fertility between the surface soil and sub- 

 soil. Furthermore they are usually more permeable 

 than soils in humid regions ; both water and air can 

 enter them readily. Thus alfalfa roots penetrate to 

 great depths in such soils. Boots have been traced 

 to a depth of 30' and even farther. And all down 

 in that soil will be found air, nodules, bacteria; it 

 is a vast factory of nitrogen-gathering, wonderwork- 

 ing plant life. No wonder the " deserts blossom as 

 the rose" when water is applied to them. 



Grassing the Ditch Banks. It is a convenience to 



