lO 
Colorado Experiment Station 
to secure so that sub-irrigated fields are usually either too dry or too 
wet. The rise of the sub-soil water following sub-irrigation has 
carried up alkali which has accumulated at the surface— in fact, 
sub-irrigation has produced more pernicious results in this respect 
than any other method of irrigation practiced. While sub-irriga¬ 
tion is very easy on the irrigator and enables one man to irrigate 
a large acreage at a cheap labor cost, it is very hard on the land and 
may be very hard on the crop. Practically all of the land which 
has been subjected to one system or another of drainage was for¬ 
merly watered by sub-irrigation, but is now being surface irrigated. 
To change from sub-irrigation to surface irrigation, it is only 
necessary to enlarge the supply ditches and build the field laterals 
closer together. For surface irrigation, especially on the lighter 
soils which slope, all water should be run across narrow strips of 
land—that is, the field laterals should be close together. In porous 
sandy soils the water should be run across the gentlest slope so as 
to reduce washing to the lowest possible limit. A change from sub¬ 
irrigation to checks or borders could be made with equal ease, the 
only difficulty being the expense of constructing levees. Rectangu¬ 
lar and border checks are now being used in several sections of the 
Valley in alkali reclamation work. 
Irrigation, especially on the sandier lands, which dO' not have 
a high water-holding capacity, must be rather frequent to give best 
results. Lands which tend to form a crust should be irrigated 
prior to the seeding, where it is necessary to “irrigate up” the crop. 
If this is done cultivation can be given before seeding and the seed¬ 
ing operation itself effects some cultivation which will produce a 
surface mulch and effectually break up the crust. On lighter soils 
where a crust is not formed there is a tendency for the formation 
of a natural mulch. On such soils to “irrigate up” the crop it is 
best to plant the crop and irrigate after seeding, because the soils 
will not hold moisture in contact with the seed long enough if they 
are irrigated first and seeded afterwards. 
Until recently very little land has been leveled for irrigation. 
What leveling was done consisted in running a field float over the 
surface after plowing. Now, however, considerable land is fairly 
well leveled with slips and fresnos after plowing. Usually such 
work pays well because it permits putting all of the land into grow¬ 
ing crop. 
Clearing land for irrigation was formerly done by burning off 
the sagebrush or hacking it out with grub hoes. Now the land is 
usually broken with heavy plows pulled by tractors, and the brush is 
raked off. Preliminary leveling done and a crop or two planted, the 
ground will be settled enough for final leveling. 
