30 BULLETIN 190, U. S. DEPAKTMENT OF AGRICULTUEE. 



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 wiU 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 desirabihty of using large checks and hberal 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 flrst 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 J 

 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 



