242 Bi-LLF;ri.\ 89 



Altho alkali spots do occur, the tarnished sands which make 

 up the greater portion of the Mesa soil are free from injurious 

 amounts of water soluble salts as shown by the analyses in 

 Table IX. 



table: IX ALKALI IN TARNISHED SANDS ON YUMA MESA 



6917 



6917a 



6918 . 



6919 



6920 



6922 



6923 



6924 



6925 



The results indicate the absence of injurious amounts of sol- 

 uble salts and the entire absence of sodium carbonate or black 

 alkali in the sands. Some apprehension has been expressed that 

 black alkali would develop from the action of irrigating water on 

 the calcium carbonate which occurs so abundantly on all parts of 

 the Mesa. The fact that almost without exception the soils tested 

 had the capacity to neutralize considerable black alkali, and that 

 the Colorado River water has a high permanent hardness thruout 

 the year, should remove any danger from this source. Sodium 

 chloride is also much in excess of sodium sulphate in the river 

 water and this has been shown to inhibit largely the reverse re- 

 action between sodium sulphate and calcium carbonate which gives 

 rise to black alkali. Some white alkali may rise from frequent 

 shallow irrigation, but can be leached back easily into the deeper 

 subsoil. Analyses show the alkali found in the valley to carry 1 

 part of potassium to 4.3 parts of sodium and the year's average of 

 the river flow to be 1 part of potassium to 9 parts of sodium, with 

 a much higher ratio of potassium during flood periods. White 

 alkali then becomes an important source of readily available potash 

 in these soils. 



PHYSICAL CHARACTERS OF THE YUMA MESA SAND 



The soil of the Yuma Mesa when dry is for the most part 

 loose easily shifted sand, but when wet it resembles a sandy loam. 

 The dry appearance and the mechanical analysis are both some- 

 what misleading, due to the calcareous incrustations on the soil 



