130 



CALIFORNIA FRUITS: HOW TO GROW THEM 



and capillarity destroyed, and, further, that the free access of air to 

 the lower point, where capillarity exists, must be prevented. This 

 is accomplished by the fine loose earth which acts as a mulch. When 

 this is attained, only that moisture in the upper surface which comes 

 in immediate contact with the air is evaporated, and the balance is 

 largely retained for the use of the plant. Plants growing, then, in a 

 well-cultivated soil, have the water in the lower soil held for their 

 use, and their supply is replaced from the firm soil below, which re- 

 mains moist and permeable by roots which extend freely, seeking the 

 nourishment they need. 



Such is a brief outline of the theory which explains the results 

 gained by thorough cultivation of the soil, so far, at least, as reten- 

 tion of moisture is concerned. The practical demonstration is easy. 

 Go into a well-cultivated orchard or vineyard, push aside the soil 

 with the foot, and moisture will be found two or three inches from 

 the surface, or even less in some soils, while on uncultivated land 

 adjacent, digging to the depth of several feet will show nothing but 

 hard earth, baked and arid. In such hard-baked earth, moreover, 

 the sun heat is conveyed or conducted downward very rapidly during 

 a hot day, so that in some cases the roots are seriously injured. 

 When the surface is well tilled, it will act like a blanket, preventing 

 a too rapid conveyance of heat downward, and thus also diminishing 

 the intensity of evaporation. 



Accurate demonstration of these facts has been secured as the 

 result of many moisture determinations in cultivated and unculti- 

 vated soil by the University of California Agricultrual Experiment 

 Station.* The exact determination of moisture present at various 

 depths of the soil beneath these contrasted orchards in the month of 

 July is as follows : 



Totals, six feet .. 6.3 756 4.2 512 



This shows a gain of nearly fifty per cent of soil moisture by 

 cultivation. 



Rise of Water from Greater Depths. The foregoing facts apply 

 to the movement of moisture from the stratum which the roots of 

 fruit trees chiefly occupy estimated to be to a depth of about four 

 feet from the surface when the soil is hospitable to them to that 

 depth. Formerly it was generally argued that moisture would rise 

 by capillarity from moist subsoils below that depth to replace the 

 exhaustion of moisture from the upper layer and therefore surface 

 cultivation would render all the lower water ultimately available for 



Bulletin 121. 



