JAMAICA. 



BULLETIN 



OF THE 



BOTANICAL DEPARTMENT. 



New Series.] APRIL, 1901. ■ ' 



J Part 4. 



THE CONSERVATION OF SOIL MOISTURE AND 

 ECONOMY IN THE USE OF IRRIGATION 

 WATER.* 



By E. W. Hilgard and R. H. Loughridge. 



Amount of icater required by crops. — It is not very generally under- 

 stood how large an amount of water is required for the production even 

 of fair crops ; for the maximum of possible product is rarely obtained 

 on the large scale, because it is not often that alt conditions are at 

 their best at any one time and locality. But from numerous observa- 

 tions, made both in Europe and in the Eastern United States, it has 

 been found that from 300 to over 500 tons of water are on the average 

 required to produce one ton of dry vegetable matter. . . 



These data should enable us to estimate the adequacy of the mois- 

 ture contained in the soil at the beginning of the dry season to mature 

 the crop, provided we make due allowance for any growth already made 

 at the time, and provided also that the estimates as to the water 

 requirements derived from the experience of the countries of summer 

 rains (the humid regions) hold good for the arid region also. The 

 /surprisingly successful growth and bearing especially of deciduous 

 trees, without irrigation, despite a drought of five or six montht in the 

 (i Franciscan climate/'f has led to an impression that a less amount of 

 water may suffice under arid conditions For in the East, as many 

 weeks of drought and intense heat would frequently suffice to destroy 

 the crop. 



Probable causes of this endurance of drought, — Doubtless the main 

 cause of this remarkable endurance is to be found in the much deeper 



* Bulletin 121, Agricultural Experiment Station, University of California. 



f This name has been felicitously applied by Powell to the climate of middle 

 and Southern California, which is characterized by the concentration of rains 

 within a winter which is mild enough to constitute a growing season, while the 

 summer is practically raiDless. 



