142 CALIFORNIA FRUITS: HOW TO GROW THEM 



the capillary condition still exists, and evaporation proceeds in 

 the same way, though in a somewhat less degree, as if there had 

 been no cultivation. It becomes evident, then, that the pulver- 

 ization of the disturbed layer must be so complete that the particles 

 are separated and capillarity destroyed, and, farther, 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 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 as fast as they use it 

 the supply is replaced through the firm soil below, which evapora- 

 tion being stopped, remains moist and permeable by roots which 

 extent 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, more- 

 over, 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 recently been secured 

 as the result of many moisture determinations in cultivated and 

 uncultivated soil by the University of California Agricultural 

 Experiment Station.* Very striking exhibition of the condition 

 of trees with and without cultivation is found in the engravings 

 which are reproduced herewith. Upon the demonstration, the 

 practice in the uncultivated orchard was radically changed. The 

 exact determination of moisture present at various depths of the 

 soil beneath these contrasted orchards in the month of July is as 

 follows : 



Cultivated. Uncultivated. 



Depth in soil. Per cent. Tons per acre. Per cent. Tons per acre. 



Totals, six feet 6.3 756 512 



* Bulletin 121. 



