CHOAPT ER .ALU, 
CULTIVATION. 
It was demonstrated very early in California experience in 
fruit growing, that “clean culture” is the proper treatment for 
trees and vines. Though the frequent stirring of the soil and 
the complete eradication of grass and weeds have been advocated 
by certain horticulturists for generations as the true practise, it 
has nowhere secured such wide adherence as in California. It 
may even be held to be an essential to successful growth of tree 
and vine in most soils and situations in California, and the ad- 
vantages of clean culture, which have been urged elsewhere, are 
intensified under our conditions. 
Chief of these advantages is the maintenance of the soil in 
a condition favoring root growth, and the main feature of this 
condition is the retention of the moisture, though regulation of 
summer temperature in the soil is also involved. Where mois- 
ture-retention is not the chief concern, because of ample irriga- 
tion facilities, and the moderation of soil temperature is of 
greater moment, a summer-growing cover crop may be of bene- 
fit to the trees. In irrigated districts of excessive heat and dry 
air this policy may prevail, but it will be only the exception to 
the rule of clean culture. 
Retaining Moisture by Cultivaiion.—lt is a familiar fact that 
water will rise in a tube of exceeding small diameter very much 
higher than the surface of the body of water in which the tube is 
held upright. The water rises by capillary attraction. A com- 
pact soil has extending through it minute spaces, formed by the 
partial contact of its particles, which facilitate the rise of water 
from moist layers below, in accordance with the same principle 
which causes the water to rise in the capillary tube. This move- 
ment is constantly going on in a firm soil, and as fast as the top 
layer is robbed of its moisture by evaporation, the water rises 
from below and it too is evaporated. During a long, dry sum- 
mer, the water rises and is evaporated from a depth of several 
feet in some soils, and the earth, beneath the baking sun heat, 
becomes “‘dry as a brick.” 
When a soil is broken up by cultivation, its capillarity is 
temporarily destroyed through the disturbed layer, because the 
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