THE RELATION OP SOILS TO IRRIGATION. 33 



which are flooded by the annual overflow, leaving a 

 large deposit of sediment. 



If the soil is of such texture that it will bake when 

 water is applied to the surface, or the slope should be 

 too great, furrows are made with a roller or furrower 

 at such an angle to the slope of the land as to give the 

 water the proper fall to prevent erosion of the surface 

 soil and to facilitate the deposition of the sediment. 

 By these methods the soil is enriched annually with 

 little or no additional expense, and the crops are in- 

 creased accordingly. Care should be taken, however, 

 lest the crop be irrigated too freely in the early spring 

 while the water is cold. The soil is thus likely to 

 become chilled, which at least retards the growth of 

 crops. Under such circumstances a farmer may think 

 the soil is thiii and poor, but this dedud;ion results 

 merely from lack of experience. 



I^arge amounts of fertilizing material thus natur- 

 ally find their way to the soil in the water used, tending 

 to countera(5l the drain on the land due to the removal 

 of crops. As a result of a five- month study of the 

 water of the Rio Grande, a stream which carries exces- 

 sive quantities of silt, it was estimated that in using 

 one acre-foot of the muddy water in irrigating, 955 

 pounds of potassium sulphate, fifty-eight pounds of 

 phosphoric acid, and fifty-three pounds of nitrogen 

 were added to each acre. A thirty-bushel crop of 

 wheat usually removes twenty-eight pounds of potash, 

 twenty-three pounds of phosphoric acid, and forty-five 

 pounds of nitrogen. It is also true that considerably 

 more than one foot of water is generally applied to the 

 land each year in irrigating. It would seem to be 



