30 BULLETIN 190, U. S. DEPARTMENT OF AGRICULTURE. 
land into checks and ponding the water as deeply as possible; each 
check should have as large an area as the slope of the ground and the 
amount of available water will permit. In no case should an attempt 
be made to flush the salts from the surface. They must be leached 
out and carried in solution downward to the underground reservoir. 
The desirability of using large checks and liberal quantities of water 
is due to the fact that capillary attraction is equally effective in all 
directions, and it is necessary to offset the tendency of the salts to 
move laterally in the soil and reappear on a higher or drier portion of 
the tract. For this reason it is required in flooding to make sure 
that all the surface is covered, even if knolls and ridges must first be 
leveled. It is generally advisable to thoroughly cultivate a field 
before the leaching process, but in some cases it has been found to be 
more satisfactory to flood first and then to cultivate as soon after- 
ward as possible. If the subsoil be so impervious that the leaching 
water does not percolate readily, it may be necessary to resort to sub- 
soiling or blasting. 
The quantity of salts removed by the leaching process is surprisingly 
large when considered as a total. It is not unusual to find a soil con- 
taining an average of 1 per cent of its dry weight in salts. Taking 
the average dry weight of the soil at 100 pounds per cubic foot and 
the depth of drainage at 6 feet, each cubic foot of the soil contains 
1 pound of salts, and each 6-foot column of soil, 1 foot square, contains 
6 pounds of salts. This amounts to 261,360 pounds, or over 130 tons 
of salts per acre, in a depth of 6 feet. For a 160-acre farm, this would 
amount to nearly 21,000 tons of salts. 
Analyses show that the quantity of salts in the upper 6 feet of soil 
may be reduced 50 per cent by one flooding. But the discharge of I 
cubic foot per second of water containing 1 per cent of salts, which 
is much higher than the average, would represent only 2,470 tons of 
salts per annum, and this takes no account of salts contributed to 
the tract by the irrigation water. From this it is evident that 
only a small portion of the salts is carried away by the drains and 
that by far the larger portion is leached into the underdrainage 
and redistributed below the drainage depth. This is a desirable con- 
dition, for it means that the mineral plant foods, which are also 
soluble in water, are not removed from the tract and wasted, but are 
left within reach of plant roots. It also means that the drainage 
water is sufficiently free from harmful salts to be useful for irrigation 
purposes. Indeed, conservation of the irrigation supply is being 
effected by applying to one tract water that has been drained from 
another, and in a few cases the drainage water is pumped back for the 
irrigation of the reclaimed tract itself. 
The land should be cropped as soon as possible after reclamation; 
some crop which will shade the ground is preferable. If possible the 
