Tillage and Irrigation 79 



How often to irrigate. 



The effective and economical use of water is an art 

 learned only by experience ; book directions are of little 

 value. The amount of water to use depends primarily on 

 the annual rainfall of the locality and its distribution dur- 

 ing the year; also, to a considerable extent, on the na- 

 ture of the soil. At Watsonville, California, the annual 

 rainfall is thirty inches, yet so little of this falls during 

 the growing season that strawberries are irrigated every 

 ten to fourteen days. Near San Diego, California, which 

 is cloudless most of the year, strawberries are irrigated 

 every three or four days throughout the protracted pick- 

 ing season of six to eight months. There are few localities 

 where it is necessary to irrigate more often than once in 

 two weeks, except while the fruit is ripening, when it is 

 customary to irrigate as soon as possible after each pick- 

 ing, so that the soil will be dry for the next picking. 

 Usually, irrigation is discontinued in the fall, about the 

 time that strawberry-growers in humid regions lay by 

 their fields. Where plants suffer from winter injury, an 

 irrigation of two or three inches in late fall, just before 

 the ground freezes, may be an advantage, as winter in- 

 jury is most serious when the ground is dry. 



Irrigation does not make tillage unnecessary. The 

 ditches frequently get foul with weeds, and weed seeds 

 are carried to the land in the irrigation water. More- 

 over, the soil needs to be stirred to prevent it from crust- 

 ing, to promote aeration and to check evaporation. 

 Except during the picking season, the middles should 

 be cultivated after each irrigation. The most successful 

 growers maintain soil moisture as far as possible with 

 tillage and irrigate only enough to supplement this 

 natural supply. 



