ARID AGRICULTURE. 83 



more than thirty bushels of wheat per acre, 

 enough phosphoric acid for thirty bushels per 

 acre, and enough potassium to last for thirty 

 years, if as much wheat was raised on the land 

 each year. Such large amounts of soil fertility 

 are unusual, however, but even our clear waters 

 from mountain streams carry with them a con- 

 -iderable amount of silt and plant food in the 

 late spring and early summer. Under irrigation 

 such large annual crops are taken off the soil that 

 the subject of available plant food becomes an 

 important one. Our soils will wear out unless 

 a good farm practice is inaugurated which will 

 keep them productive. With a proper system of 

 rotation and cropping, adding plant food to the 

 soil in the form of barnyard manure, the waste 

 of feed pens, gr een manure and growing of legu- 

 minous crops will keep the soils always richly 

 productive. Only in special locations or with 

 special crops will the use of any artificial fertil- 

 izer be found advisable. 



IRRIGATION There has been much useless alarm about al- 



kali. Our soils are very rich in soluble salts 

 and in places these accumulate to such an extent 

 that they destroy productiveness. The alkali 

 salts are dissolved by water, and where there is 

 not good drainage below, this water evaporating 

 again from the surface, leaves the alkali behind 

 as a white incrustation where it is most detri- 

 mental to plants. In nearly all cases the alkali 



