142 LANDS OF THE ARID REGION OF THE UNITED STATES. 
cut the straw, which is never returned as mulch; and, as there is but little 
rotation in crops, the result can be easily comprehended. So long as new 
land costs nothing but the labor to clear of the Artemisia or sage brush, 
there is always the tendency to invade it as rapidly as the old lands show 
signs of fatigue. Thus the waters are constantly irrigating every year a 
large proportion of new land, and the consumption of water is correspond- 
ingly great. 
A serious loss of water and fertility is produced by any method of 
irrigation which employs more water than is just sufficient to saturate the 
soil. Whatever water runs off from a field carries with it great quantities 
of mud and fine silt, together with the most precious elements of fertility. 
These elements are the soluble alkaline salts and organic manner which are 
readily taken up by the water, and once removed are not speedily restored. 
A field which is so irrigated that a large surplus of water is continually 
running from the tail ditches during the flow will rapidly deteriorate in 
fertility. But a field which receives water which is allowed to stand until 
it has soaked into the earth, without any surplus passing into the tail 
ditches, will increase in fertility. These irrigating waters bring with them 
a sufficiency of plant food to compensate, and more too, for the drain upon 
the soil caused by the harvest ; but they will carry off more than they bring 
if they are permitted to run over the field and escape from it, instead of 
being caught and held until they are absorbed. It is not always prac- 
ticable to attain this exact distribution of water, and many cases occur 
where great expense and labor might be required to arrange the ditches 
and fields in this manner. Ordinarily, it is cheaper to throw away old land 
and take up new than to improve the system of irrigation, and there are 
many fields in the valley of the Sevier which have been abandoned because 
the fertility of the soil has been washed out by a reckless method of irriga- 
tion. Connected with this is another source of waste, arising from very 
unequal requirements of contiguous areas, in consequence of which many 
lands, especially old ones, are liable to be excessively watered. When a 
community farms a large number of small fields, using water from the same 
canals, it is usually impossible so to regulate the distribution of the privilege 
that each field will receive the exact amount it needs. Some fields can 
