308 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



tion of certain fertilizers, especially nitrate of soda, may, under certain 

 conditions at least, bear a very important relation to the accumulation 

 of alkali. With this knowledge, it is hoped that practical citrus 

 growers will be able to adjust their irrigation and fertilizer practices 

 in such a way as to retard the further spread of alkali and thus 

 prevent its accumulation in many groves that have, as yet, not been 

 seriously injured. 



SYMPTOMS OF ALKALI INJURY 



Different varieties and species of citrus trees are affected differently 

 by alkali. Lemon trees show the effects by a pronounced yellowing 

 of the margins and burning of the tips of the leaves, followed by 

 unusually heavy shedding of the leaves in the latter part of the winter 

 and spring. The subsequent new growth may appear to be quite 

 normal and vigorous for several months, but later a large portion of 

 the leaves turn yellow in irregularly shaped areas around the margins 

 and fall excessively. In the presence of excessive concentrations of 

 salts, especially chlorides, complete defoliation may take place. Mottle 

 leaf frequently occurs, and sometimes chlorosis. Both the quality and 

 quantity of the fruit are impaired. 



Orange trees also show the effects of alkali in different ways. On 

 certain soils, mottle leaf is one of the first symptoms. In some locali- 

 ties, the older leaves assume a brownish hue and tend to curl slightly. 

 Kather sudden defoliation takes place, especially when excessive 

 amounts of chloride occur, followed later by a profuse growth of new 

 shoots. The leaves of the new growth are likely to be undersized and 

 paler in color than normally. With especially high concentrations of 

 sulfates and bicarbonates in the soil, orange leaves become chlorotic 

 and strikingly similar to that condition referred to by Hilgard 4 as 

 occurring on highly basic soils. The smaller twigs may be killed. 

 Frequently the leaves are abnormally small on one portion of a tree, 

 and full-sized 011 others. 



Premature shedding of the leaves takes place with both oranges 

 and lemons affected by small amounts of alkali, which may be pro- 

 tracted throughout the greater part of the winter months, thus greatly 

 reducing the number of leaves remaining on the trees at the close of 

 the dormant period. Navel oranges are more sensitive than Valencias, 

 and Eureka lemons more sensitive than Lisbons. In general, lemon 

 trees are more sensitive 1 than orange trees. Neither orange nor lemon 



4 Marly subsoils and the Chlorosis or Yellowing of Citrus Trees. Calif. Agr. 

 Exp. Sta.'Cir. Xo. 27 (190(5). 



