238 



Bulletin 89 



The remaining samples, which are all tarnished sands varying 

 chiefly in their content of calcium carbonate, compare favorably 

 with the medium and less fertile soils of the United States with 

 regard to phosphorus, but are very deficient in potash — a matter 

 that need give little concern since the Colorado water, as will be 

 shown, carries large amounts of water soluble potash. The aver- 

 age acid soluble phosphorus in 2,000,000 pounds of the Mesa tar- 

 nished sand as shown by nine analyses is 681 pounds, as compared 

 with 875 pounds shown by 262 samples of surface soils of California 

 according to Hilgard (Hopkins' Soil Fertility, p. 102). The aver- 

 age of the Yuma Mesa set is lowered much by a single sample 

 (6917) which contains only 419 pounds. The richest sand from the 

 Mesa contained 908 pounds. While the acid soluble phosphorus 

 content is not high, the citric acid soluble phosphorus shows a 

 large part of it readily available. An average of nearly one-third 

 of the strong hydrochloric acid soluble phosphorus is also soluble 

 in 2 percent citric acid, whereas it has been estimated roughly that 

 in humid regions usually only one percent annually of the total 

 phosphorus could be rendered available by practical cultural means. 

 In a few cases only about one-half of the total phosphorus dissolved 

 m 1.115 sp. gr. hydrochloric acid. The high apparent availability 

 of the phosphorus agrees with the rapid growth made by vege- 

 tation when sufficient water is supplied. This condition would be 

 expected in an almost rainless region where slow weathering has 

 gone on for ages with no leaching. 



For comparison the average composition of the very sandy 

 orange soils of Florida is given in Table V. 



TABLE V. AVERAGE COMPOSITION OF FLORIDA SANDY ORANGE SOILS 



Percent 



Percent of 

 the element 



Elements in 

 2,000,000 lb. soil 



Silica 



Phosphoric acid . 



Potash 



Soda 



Lime 



Magnesia 



Iron and Ahiniina. 



Nitrogen 



Humus , 



Loss on ignition. 



93.82 

 .085 

 .039 

 .107 

 .295 

 .129 

 .760 

 .054 

 .64 

 3.11 



.037 

 .032 



Pounds 



740 

 640 



While the Yuma Mesa sand is quite similar to the Florida 

 sand with regard to phosphorus, it probably has a decided ad- 

 vantage with regard to easy availability of the phosphorus, since 



