92 ARID AGRICULTURE. 



In the arid region systems of irrigation and 



* OP null 

 PLANTS 



cultivation which induce plants to send their 



roots deep into the soil are important. Deeply 

 rooted plants are not so subject to drouth and 

 find a comparatively large soil pasture from 

 which to gather moisture and plant food. Deep 

 and continuous cultivation from the time the 

 plant is started until the crop has become thor- 

 oughly established, will do much to secure deep 

 rooting. This is important in orchards and tree 

 plantations. The cultivation must be continu- 

 ous, however, for if left for a long enough season 

 of growth most of the plant roots will be thrown 

 into the surface soil, after which cultivation 

 would so severely prune the roots as to set back 

 the growth and injure the plants. Light or su- 

 perficial irrigation which simply puts enough 

 moisture into the soil to wet the surface induces 

 plants to throw out surface roots instead 

 of those which should go deeper into the sub-soil. 

 It also starts evaporation from the surface which 

 causes loss of water. Deep and thorough irriga- 

 tion causes deep rooting. 



