The YrMA Mksa 



239 



the P'Jorida soil occurs in a region of abundant rainfall, and the 

 easily available jihosphorus would be leached out. The potash 

 content of the Yuma sand is several times that of the Florida sand. 



FERTILITY OF THE YUxMA SAND 



The average plant food content of citrus fruits is nitrogen .118 

 percent, phosphoric acid .054 percent, and potash .293 percent. If 

 we take 400 boxes of about 70 pounds each as a large yield per acre, 

 there will be required for the annual crop 33 pounds of nitrogen, 

 6.7 pounds of phosphorus and 68.1 pounds of potassium. A report 

 by G. Harold Powell, Secretary of the Citrus Protective League 

 of California, based on the practice of 271 ranches containing 8095.9 

 acres, showed the expenditure of $44.20 per acre annually for 

 chemical fertilizers and barnyard manure. Florida growers also 

 find heavy fertilization profitable. The waters of the Colorado will 

 in large part furnish the fertilizers which prove so expensive in 

 other citrus districts. 



Table VI, showing the plant food carried in the waters of the 

 Colorado during 1900, has been compiled from Bulletin 44 of the 

 Arizona Agricultural Experiment Station, The River-Irrigating 

 Water of Arizona, by R. H. Forbes. 



TABLE VI — COMPOSITION OF THE WATER OE THE COLORADO RIVEJR 



Parts per Pounds per 



100,000 acre-foot 



Nitrogen in silt and water Average .274 



Nitrogen as nitrates Average .079 



Potassium soluble Average 1.51 



Phosphorus in sediment 



7.45 



2.15 



41.07 



5.56 



Since not less than Zy^ acre-feet of water would be applied 

 annually, the minimum amount of plant food added from this 

 source would be : Total nitrogen 18.6 pounds, of which 5.4 pounds 

 would be nitrate nitrogen ; potassium 102.7 pounds, phosphorus 

 12.9 pounds. A comparison of the crop composition with the plant 

 food content of the irrigating water shows the potassium require- 

 ment to be supplied in excess. The nitrogen requirement is about 

 one-half covered, but it should be mentioned in this connection that 

 much nitrogen would be supplied by leguminous cover crops which 

 should be grown to raise the humus content of the soil and im- 

 prove its physical condition. The phosphorus requirement ap- 

 |)ears to be more than covered by that carried in the silt but this 

 figure is somewhat uncertain for these reasons. The analysis 



