LAND AND OTHER AGENTS OF PRODUCTION 141 



The prospects of sustained productivity. The use of irrigation 

 water as an aid in crop production is as old as history, but the history 

 of irrigation is, with some exceptions, a story of rise and decline. 



Our modern irrigation development in this country is still too new 

 to give very definite indications as to what may be expected in the 

 future. Some disturbing symptoms have appeared in recent years 

 on our older irrigated lands, but as a people we are going deeper into 

 agricultural science than our predecessors, and it remains to be deter- 

 mined whether or not we can meet and overcome the difficulties that 

 have caused failures in the past. Most people have only a casual 

 interest in the welfare of posterity. But there are certain phases of 

 this matter that are of acute interest to the irrigation farmer. What 

 is known as the rise of alkali is a matter that may become serious in 

 months as well as in centuries, and is a problem that is likely to 

 become acute on nearly every tract of irrigated land. 



The so-called rise of alkali may be defined as the accumulation in 

 the soil of soluble salts which are the products of soil weathering and 

 disintegration. Whenever this accumulation becomes excessive these 

 salts hinder or prevent the growth of crop plants. These salts seldom 

 accumulate in harmful quantities where the rainfall is adequate, 

 because they are usually leached out of the soil as fast as they become 

 soluble. If it were possible to apply irrigation water in such a manner 

 and in such quantities as to provide the crop plants with what they 

 need and in addition to insure some percolation of water through the 

 soil into the underground drainage, it seems probable that one of the 

 most acute difficulties of irrigation would be overcome. But this is 

 not easy to accomplish. In the great majority of cases the land is 

 irrigated too little or too much. When irrigated too little the salts 

 remain and accumulate in the soil, and when irrigated too much they 

 are transported from one place only to come to the surface in another 

 where the ground-water collects. Thus the use of irrigation water 

 under the ordinary conditions of farming results in serious disturb- 

 ances in the normal equilibrium between the soluble and the insoluble 

 constituents of the soil. And these disturbances are soon manifested 

 by consequent derangement in the nutrition of the crop plants. 

 Methods of control involve, among other things, the maintenance of 

 a supply of organic matter in the soil and at least the occasional per- 

 colation of water through it. 



Aside from cases where alkali or seepage water is the obvious 

 cause of a decline in the productivity of irrigated land, there are other 



