WHY TREES NEED CULTIVATION 13 \ 



the use of the tree. It has recently been shown, however, that the 

 rise of moisture from a deep moist layer to a drier layer above is 

 slow and limited, and the practical lesson is that even with a deep 

 soil and the best of cultivation, irrigation if often desirable for trees 

 which for any reason are not inclined to root very deeply and help 

 themselves to deep-lying moisture. 



Necessity of Adequate Cultivation. It has been very fully dem- 

 onstrated by California experience that adequate depth of tilth must 

 be attained. The depth of cultivation, or the thickness of the dust- 

 mulch, as some like to call it, must be sufficient to prevent the access 

 of the dry air to the firm soil below. At the East, where they have a 

 moister air, a thin mulch may answer, but in California, with a 

 thirsty air for such a protracted period, there must be deeper tilth. 

 Two or three inches of dust spread over a hardpan layer formed in 

 some soils by cultivation, will not retain moisture well in California. 

 The cultivator should go twice that depth, ordinarily, and then the 

 result will be accomplished if it is done frequently enough to prevent 

 the re-firming of the surface by atmospheric moisture or by the rise 

 of moisture from below. 



Loss of Moisture by Weed Growth. One of the most active 

 agencies for the exhaustion of moisture from the subsoil is the 

 growth of weeds. To cultivate the soil in winter and spring, and 

 then to allow a summer growth of weeds to "shade the soil" is a 

 great error. Although under cover of rank weeds moisture may 

 appear even at the surface and convey the impression of moisture- 

 saving, the fact is, as fully demonstrated by experience and actual 

 experiment, the moisture in the lower layers of the soil is reduced 

 and trees are thus robbed of their supply. Weed growth must be 

 resolutely suppressed during the dry season, if one has to operate 

 by rainfall or desires to make best use of irrigation water. 



Moisture Storage in the Soil. Conservation of moisture in the 

 soil is not only the surety of the current season's growth and fruit- 

 fulness, but is the safeguard against injury from the years of de- 

 ficient rainfall which occur now and then in California. The mois- 

 ture supply is equalized by this storage of the soil, and a surplus 

 from the liberal rainfall of one year is held over to supply the lack 

 of the next. Of course, the well-cultivated surface is also well calcu- 

 lated to catch water. While from a hard surface much of a heavy 

 rainfall flows off quickly to a lower level before it can penetrate, a 

 loose soil, if sufficiently deep, retains all that falls upon it, except 

 the excess, which disappears by drainage. 



It has sometimes been held by California orchardists that plant- 

 ing some tall-growing crop, like corn, so as to shade the young tree 

 and the ground around it, is an advantage. This is a great mistake. 

 Though some rich, moist soils may afford moisture enough to grow 

 both the tree and the corn, it is a fact that in most cases the growth 

 of the corn is made at the expense of the tree, and sometimes almost 

 costs its life and thrift. It has been amply shown by investigation 

 that though shading ground by a leafy growth may make the sur- 



