BULLETIN 231] WALNUT CULTURE IN CALIFORNIA. 183 



apparently retains much of the nature of a forest tree in this respect and 

 does better when left to itself with the soil undisturbed than when the 

 soil is cultivated in the above-described irregular manner. This by no 

 means goes to prove, however, that good cultivation is injurious or 

 unnecessary in walnut culture, for experience has shown this to be far 

 from the case. Especially in regions where the rainfall is limited and 

 the dry season long and hot, regular, thorough cultivation is as beneficial 

 and profitable in the walnut orchard as with citrus or other trees. In 

 regions with more abundant rainfall and less severe dry seasons cultiva- 

 tion is not so essential ; the chief consideration in all cases is that of the 

 conservation of soil moisture. The latter must be maintained, but 

 whether by irrigation or cultivation matters little. If the soil is suffi- 

 ciently moist cultivation is not as essential with the walnut as with many 

 other fruit trees. 



In practice it is customary to plow the grove once a year during the 

 spring, followed by harrowing and cultivation to put the soil into good 

 mechanical condition. After this, the ground is usually cultivated 

 occasionally during the summer, at least after each irrigation if this be 

 practiced, in order to keep it from baking, keep down the weeds and 

 hold the moisture. A number of growers in southern California have 

 tried in recent years the experiment of carrying on their walnut groves 

 with no plowing or cultivation whatever, but with abundant irrigation. 

 In some cases permanent irrigation furrows have been made between the 

 trees, while in others the water is simply turned into the orchard and 

 allowed to flood the whole ground as thoroughly as possible. The weeds 

 and grass have been allowed to grow up or pastured off with horses and 

 cattle. Under such treatment an actual improvement has been mani- 

 fest in the condition of some walnut groves. Whether such improve- 

 ment, however, is due to the lack of cultivation we are inclined to doubt, 

 but would rather attribute it to the increased water supply which the 

 trees have received. Such experiments have strengthened the opinion, 

 however, that cultivation is not particularly essential with the walnut so 

 long as it receives plenty of moisture. In cases where walnuts are 

 grown without irrigation there can be no question that thorough^ syste- 

 matic cultivation during the summer season will assist in holding the 

 moisture of the soil. That many trees grow and flourish without such 

 cultivation and without irrigation is again no indication of beneficial 

 effects of non-irrigation, but simply shows that in these particular local- 

 ities sufficient soil moisture is present without any special efforts toward 

 its conservation. 



IRRIGATION. 



The walnut tree, while not dependent upon constant irrigation like the 

 orange and many other more shallow-rooted trees, is at the same time a 

 large consumer of water and needs plenty of moisture for successful 



