SAVING WATER BY CULTIVATION 59 



that it re-establishes capillary connections between the 

 mulch and the moist soil below, and evaporation is then 

 resumed. Such soils, which are soon recognized, should 

 be cultivated several times between each irrigation. When 

 soils show no such tendency to settle, it may be sufficient 

 to give them one good cultivation after each irrigation. 

 Generally, it is well to cultivate the soil at least once 

 every three weeks throughout the irrigating season and a 

 bi-weekly cultivation is probably better. 



Summer showers also determine the frequency of 

 irrigation. A summer shower, unless it is very light, 

 beats down the the mulch and usually saturates the soil 

 sufficiently to establish vigorous capillary communica- 

 tion with the lower soil layers. This condition may lead 

 in a few hours to large evaporation losses. For that 

 reason, every summer shower should be followed, as soon 

 as the soil is dry enough, with a thorough cultivation. 

 Where the precipitation comes chiefly in the fall, winter 

 or spring, the summers are relatively dry and the few 

 light summer showers may easily be followed by the 

 cultivator; but, where the winter is relatively dry and the 

 precipitation comes chiefly in early or midsummer, the 

 rains are often so frequent and heavy that to follow them 

 with cultivators is difficult, if not practically impossible. 

 True, under such conditions, the water necessary in irri- 

 gation is relatively smaller, so that evaporation losses 

 can better be sustained there than in districts of dry 

 summers, where the annual precipitation is also usually 

 low. Wherever possible, however, cultivation should 

 follow both summer shower or rain and irrigation. 



41. Cultivation and soil fertility. So much has been 

 said concerning the value of cultivation in the conserva- 

 tion of soil moisture that one may be led to believe that 



