326 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



It is also a matter of practical importance, that the repeated appli- 

 cation of any sodium salt to soils, followed by leaching with irrigation 

 water, or rains, tends to reduce the porosity of the soil and thereby 

 restricts the movement of the water through it. Sodium carbonate 

 and sodium bicarbonate probably produce this effect to a greater 

 extent than the other common sodium salts, but all of them produce 

 this effect to an undesirable extent. The experimental plot to which 

 nitrate of soda has been applied, has become badly puddled, and the 

 poor physical condition of the subsoil in a number of the groves where 

 saline waters have been applied, form one of their striking character- 

 istics. The surface soil in some of these groves has become exceedingly 

 baked, so much so as to be readily detectable by merely walking over 

 it. Hence, the effects of alkali are not wholly determined by the con- 

 centration of salts in the soil. The adverse physical conditions must 

 also be considered. 



Therefore, wherever nitrate of soda or saline irrigation water 

 be used in regions of light rainfall, especially if applied for any con- 

 siderable length of time, it is important for farmers to understand 

 that the soil must be kept open and porous. This can probably best 

 be accomplished by growing deep-rooted cover crops and plowing 

 under organic materials, such as manure or bean straw. 



While ordinary irrigation and rains tend to leach more or less 

 alkali down below the reach of citrus roots and probably accomplish 

 this end quite effectively in some soils, our investigations show that 

 the application of saline water has resulted in material!}' increasing 

 the amounts of alkali within reaeli of the roots of the citrus trees. The 

 soil types and climatic conditions of these groves vary widely. Some 

 of them, not reported above, occur in the districts of comparatively 

 heavy rainfall and on soils ordinarily considered to be naturally well 

 drained. 



As suggested above, the irrigation supplies rarely contain enough 

 alkali to harm citrus trees directly. So far as we have been able to 

 learn, no detrimental effects occurred in any of the groves until after 

 the saline waters had been applied for a period of years. The injury 

 came about rather through the concentration resulting from the 

 accumulated residue, left by the evaporation of repeated applications 

 of water, as was pointed out by Dr. llilgard many years ago. 



An excess of chlorides causes the tips and margins of citrus leaves 

 to become yellow or brown, followed by defoliation. Sometimes a large 

 portion of the leaves fall and the young, tender shoots may be killed. 

 An excess of sulfates and bicarbonates, on the other hand, is more 

 likelv to stunt the growth of the trees and cause the leaves to become 



