54 



essential that proper means be employed for retaining it in the land, 

 and especially to prevent evaporation, lhat this is best accomplished 

 by a mulch on the surface, and that the best mulch for the purpose, 

 which need not be hauled on or off and is always ready, is a surface 

 layer of loose, well-tilled soil, is now pretty well understood by all. 

 But the extent to which the presence or absence of such a non-evaporat- 

 ing layer influences plant growth and fruit production in a critical 

 time, is not so fully appreciated. We have seen trees and fruit grown 

 this season on adjacent fields, with only a lane between, the soil and 

 all natural conditions being absolutely identical; the only difference 

 being the presence and absence of cultivation. In the present case the 

 cultivation was emitted on principle by one owner, who considered 

 cultivation superfluous on the loose, generous soil of Alameda creek ; 

 while his neighbour, across the way, held the opposite belief, and had 

 this season cultivated to an extra depth to conserve moisture. The 

 detei ruination of the moisture held by the soil in July to the depth ot 

 six feet gave the following results : — 





Cultivated. 



Uncultivated. 



Depth in Soil. 















Tons per 





Tons per 





Per Cent. 



Acre. 



Per Cent. 



Acre. 



First Foot 



6.4 



128 



4.3 



86 



Second Foot 



5.8 



116 



4.4 



88 



Third Foot 



6 4 



128 



3.9 



78 



Fourth Foot 



6.5 



130 



5.1 



102 



Fifth Foot 



6.7 



134 



3.4 



68 



Sixth Foot 



6.0 



120 



4.5 



90 



Tota I for six feet 



6.3 



756 



4.2 



512 



The difference of 244 tons per acre of ground shown by the analyses is 

 quite sufficient, according to the data given at the beginning of this 

 bulletin, to account for the observed difference in the cultural result. 

 The cause of this difference was that in the uncultivated field there was 

 a compacted surface layer several inches in thickness, which forcibly 

 abstracted the moisture from the substrata and evaporated it from its 

 surface ; while the loose surface soil on the cultivated ground was 

 unable to take any moisture from the denser subsoil. This is well 

 illustrated by the familiar fact that while a dry brick will suck a wet 

 sponge dry, a dry sponge (corresponding to the loose surface soil) is 

 unable to take any water from a wet brick. Besides, the tilled surface 

 soil foims a non-conducting layer protecting the subsoil from the sun's 

 heat and the dryness of the air. 



In the East, where this principle is well understood, it is considered 

 that a surface layer three inches in thickness is sufficient to afford 

 effective protection. But what is adequate in the region of summer 



