322 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



per annum. Previously, and especially during the first few years of 

 the experiment, lesser amounts were applied. The total amount that 

 has been applied as an aggregate for the twelve years is 7944 pounds 

 per acre. While the amounts applied have undoubtedly been exces- 

 sive during the past five years, as is shown by the soil analysis, the 

 amounts of nitrogen applied are not in excess of that sometimes 

 applied by practical citrus growers, who occasionally apply as much 

 as 1000 pounds of sodium nitrate per acre during a single season. 



The control plots (H) and (M) lie adjacent to the sodium nitrate 

 plot. Each plot contains six Navel and six Valencia orange trees, and 

 six Eureka and six Lisbon lemon trees. All of them have been irrigated 

 and cultivated as nearly alike as possible. During the first five or six 

 years of the experiment, the growth of the young trees of each variety 

 was markedly stimulated by nitrate of soda. The soil is notably 

 deficient in organic matter and nitrogen and the successful culture of 

 non-leguminous crops requires the addition of considerable nitrogen. 



While the growth of the trees was notably stimulated by sodium 

 nitrate during the first few years of the experiment, and healthy, 

 normally appearing trees were produced, since that time excessive 

 mottle leaf has appeared on every tree in this plot. The mottling here 

 became so severe during the past two or three years as to render the 

 trees wholly unprofitable. No marketable fruit whatever is now 

 produced by these trees. 



Soil samples from the control and sodium nitrate plots, taken to 

 a depth of six feet in June, 1919, show the effects that have been 

 produced (table 15). The composition of the soluble matter in the 

 soil has been greatly changed as a result of applying nitrate of soda. 

 The total soluble matter has been increased more than twofold in every 

 foot section down to and including the sixth foot. Among the indi- 

 vidual constituents, the sodium and nitrate have been most markedly 

 increased. The bicarbonate has also been increased to a limited extent, 

 although not greatly, but the soil of this plot has not accumulated 

 any soluble normal carbonate. 



This soil has now accumulated a considerable amount of alkali 

 merely as a result of applying sodium nitrate as a fertilizer for a 

 period of twelve years. Its suitability for the growth of citrus trees 

 has been destroyed, or at least seriously impaired. The alkali in this 

 case is largely sodium nitrate, a substance of unquestionable value as 

 a fertilizer in humid climates and possibly so under certain soil and 

 climatic conditions in the semi-arid west. 



