. 
DRAINAGE OF IRRIGATED LAND. 31 
plants should be alkali resistant. It must be kept in mind that the 
salts are brought to the surface of the ground, in solution, by the 
capillary action of the soil particles and that they are deposited upon 
the surface when the solution is evaporated ; hence the advisability of 
planting shading crops which reduce the evaporation. Artificial or 
soil mulches accomplish the same thing, and if shading crops are not 
planted, the soil should be kept well stirred. Subsoiling, besides 
assisting the leaching waters to percolate to the drains, breaks 
up the capillary columns and retards the upward movement of salts. 
Alfalfa hay is a staple crop everywhere in the irrigated region. 
The alfalfa plant transpires a great deal of water^ shades the ground 
surface well, gathers nitrogen, which is usually deficient in reclaimed 
alkali soils, and provides a liberal amount of humus when plowed under. 
It has been shown by Thomas H. Kearney 1 that a mature plant 
withstands well the action of salts, but unfortunately the young 
plants are very tender and germination of seed is next to impossible 
if there be much salt present. Sweet clover, also, is resistant to 
alkali and possesses all the good qualities of alfalfa, except as to its 
value as hay. It makes good forage if kept pastured down and should 
be employed at first if the more valuable crops can not be grown. 
Bermuda grass is fairly resistant and makes a good pasture, but its 
use can not be recommended, as it is more difficult to get rid of it than 
to reclaim the land from an alkali condition. 
Mr. Kearney has also shown that the sorghums, Kafir corn, milo 
maize, etc., are adapted to use on reclaimed lands. Field corn is 
fairly resistant in most sections. Of the small grains, barley is the 
most resistant; but it has been found that when newly reclaimed 
tracts are devoted to grain it should be planted in the fall, so that the 
plants may become sturdy before the salts are brought to the surface 
by excessive evaporation in the spring. Grain does not afford much 
shading and is of little benefit in reclamation beyond the value of the 
stubble as a source of humus when plowed under. 
WHAT DRAINAGE ACCOMPLISHES. 
As a result of draining, excess water, whether it be from precipita- 
tion, waste or irrigation water, or seepage, is removed from the soil 
and the ground-water table is permanently lowered. Fluctuations 
of the ground-water table are more injurious to plant life than is a 
permanently high-water table and, within certain limits, drainage 
prevents such fluctuations. 
The removal of the excess water allows air to be drawn into the soil 
spaces and the proper equilibrium between air and moisture is thus 
maintained and the soil is made warmer. As a result of this, bacterial 
activity is increased and more plant food is produced. Moreover, 
'U. S. Dept. Agr., Farmers' Bui. 446. 
