BULLETIN 231] WALNUT CULTURE IN CALIFORNIA. 185 



During the summer it is ordinarily desirable to irrigate at least once 

 or twice, especially toward the time of maturity of the crop, in order 

 that the nuts may have plenty of moisture for their proper develop- 

 ment. Walnut irrigation therefore resolves itself very largely into, 

 first, guarding against drying out of the soil during the fall with irri- 

 gation at this time if necessary to accomplish such a result; second, 

 copious irrigation during the latter part of the winter, unless the rains 

 have been sufficient to thoroughly saturate the subsoil down to the 

 depth of the lowest roots ; third, at least one irrigation during the sum- 

 mer, usually in August, when the nuts are approaching maturity. 

 When interplanted with other crops greater care must be given to irriga- 

 tion than otherwise, since these other plantings will draw a large amount 

 of the moisture which would otherwise be available for the walnut 

 trees. 



FERTILIZATION. 



Very little of a specific nature can be said upon this subject since 

 no definite data are available in connection with the fertilization of 

 walnut groves. Fertilization has been practiced to some extent by 

 walnut growers and an extensive experiment was arranged and carried 

 on for several years at one time by ourselves. In no case, however, 

 have sufficiently definite results been obtained to justify any specific 

 recommendations in regard to the requirements of the walnut tree in 

 this respect. 



The experiment mentioned may be described at this point. 



Fertilizer Experiment. A cooperative arrangement was made with 

 the Cudahy Ranch, situated just south of the city of Huntington Park, 

 near Los Angeles, to carry on a fertilizer experiment upon walnut trees 

 on a considerable scale. A block of Santa Barbara Soft Shell seedling 

 trees was chosen for this purpose, consisting of 56 rows of 21 trees 

 each, a total of slightly over 1,000 trees, comprising between 50 and 60 

 acres of grove. Each of the various fertilizers or combinations used 

 was applied to two rows of trees, so that there were 42 trees in each 

 plot. At the time of commencing the experiment in 1907 part of the 

 grove was five and part six years old, the different applications being 

 arranged in such a way as to bring about comparative tests on trees of 

 the same age. The soil of the experimental orchard consisted of a 

 sandy loam, being decidedly more sandy on the west end and gradually 

 becoming heavier toward the east. The rows ran north and south so 

 that the westernmost plots were on much lighter, sandier soil and the 

 trees were smaller than those farther east. Except for these smaller 

 trees at one end the grove was as uniform as any seedling grove of 

 this size which could be obtained. This variation was provided for by 

 duplication of plots. The fertilizers were applied for two successive 



