318 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION 



of the more highly saline waters have been applied. The data show, 

 however, that the alkali content of the soil may ultimately reach a 

 harmful concentration where irrigation water is applied that contains 

 only a relatively low concentration of alkali salts. 



It should not be inferred that the application of water similar to 

 sample No. 150 will always produce the same degree of injury; certain 

 other lemon groves of approximately the same age have been irrigated 

 with the same supply as grove (L), which do not, as yet, show any 

 apparent injury. Samples of soil from these groves have not been 

 analyzed. 



Taken in their entirety, the above investigations show a remarkably 

 close relationship between the composition of the irrigation water, on 

 the one hand, and the accumulation of alkali salts and the condition 

 of the orange and the lemon trees, on the other. In every case we have 

 studied, where saline irrigation water has been applied for a period 

 of years, alkali salts have accumulated in the soil and the citrus trees 

 have been injured in consequence. The rates at which salts have 

 actually accumulated vary, however, in different soils, depending on 

 (1) the composition of the water, (2) the amounts applied, and (3) 

 the freedom with which it penetrated into the subsoil. 



It must be apparent from the above discussion that, although the 

 content of alkali in an irrigation water may not be directly injurious, 

 the time may come after it has been applied for a period of years, 

 when exceedingly harmful amounts of salts will accumulate as a result 

 of evaporation and that sooner or later injurious concentrations may 

 even result from the use of only slightly saline water. The more 

 freely the water penetrates into the subsoil, the greater will be the 

 tendency for the salts to be leached down below the roots of plants, 

 but it must not be concluded that saline water can be applied with 

 impunity to a porous soil, for such is not always the case. Even here 

 injurious concentrations may accumulate. As will be shown elsewhere, 

 injury may be produced by lesser amounts of alkali in a light sandy 

 soil than in heavy soil. It should be understood that sufficient amounts 

 of water to leach the soil effectively are rarely applied in any section 

 of California and especially is this true in the citrus groves where the 

 furrow system of irrigation is used and the supply of water is limited. 



THE GROWTH OF CITRUS TREES ON ALKALI SOILS 



It is quite immaterial, so far as the well-being of citrus trees is 

 concerned, or of other crops for that matter, whether alkali be intro- 

 duced into the soil as a constituent of the irrigation water, or whether 



