188 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



which received no fertilizer averaged only 20 pounds, which difference 

 is the only striking one obtained in the whole experiment. 



The effect of differences in soil is very marked in comparing the 

 crops of the west and east ends of the orchard, on the light and heavier 

 soils respectively. On the ten west rows of the eight-year-old trees, 

 the crop averaged 16.3 pounds per tree, while on the ten east rows of 

 the same block on heavier soil it averaged 30 pounds per tree. These 

 were all trees of approximately uniform appearance and not especially 

 stunted where the smaller yield was obtained. The westernmost row 

 averaged 7.56 pounds per tree, while the easternmost averaged 32.56. 

 Between the two the average production per row graded off fairly regu- 

 larly regardless of the fertilizer used. 



The results of this experiment are typical of all experience in ferti- 

 lizing walnuts. Many attempts have been made to determine the most 

 effective practice in this respect, but all of these have shown no 

 positive effect on account of variation in the trees and an apparent lack 

 of response to fertilizers. In regard to walnut fertilization it is, 

 therefore, impossible to offer definite advice based on actual experi- 

 ments, but the most that can be done is to suggest such practice as 

 may reasonably be expected to give good results with any crop on 

 California soils. We know in general that nitrogen and phosphoric 

 acid are our most needed elements and that the application of these 

 substances, especially on older plantings, is almost certain to result in 

 improved growth and vigor in almost any plant. We also know of the 

 walnut that individual trees produce as a general rule in proportion to 

 their size, and that the larger they become the greater crops they will 

 bear. It is, therefore, our conclusion that in fertilizing walnuts nitro- 

 gen and phosphoric acid should be the elements most largely supplied. 



Along with fertilization there should not be forgotten the importance 

 of keeping the soil in good mechanical condition, especially in order 

 that it may absorb and retain the greatest possible amount of moisture. 

 Indeed, it is evident from the results of the Cudahy experiment, as 

 well as from general observation, that this factor is much more impor- 

 tant, at any rate for several years, than that of fertilization. To keep 

 the soil in good condition applications of stable manure are very effec- 

 tive, likewise the growing and turning in of green manure or cover 

 crops to as great an extent as possible. The latter practice, in southern 

 California at least, is not as feasible with walnuts as with the citrus 

 crop, since it is not practicable to plant the crop until after the walnuts 

 have been gathered, which brings it quite late in the season. For a 

 cover crop in walnut groves Canada field peas have been found one 

 of the best in southern California, as they start quite readily during 



