UTILIZATION AND RECLAMATION OF ALKALI LANDS. 457 



portion of a very bad alkali spot was trenched to the depth of 

 two feet, throwing the surface soil to the bottom. The spot 

 thus treated produced excellent wheat crops for two years the 

 time it took the alkali salts to reascend to the surface. 



It should therefore be kept in mind that whatever else is 

 done toward reclamation, deep preparation and thorough culti- 

 vation must be regarded as prime factors for the maintenance 

 of production on alkali lands. 



The Efficacy of Shading, already referred to, is strikingly 

 illustrated in the case of some field crops which, when once 

 established, will thrive on fairly strong alkali soil, provided 

 that a good thick " stand " has once been obtained. This is 

 notably true of the great forage crop of the arid region, alfalfa 

 or lucern. Its seed is extremely sensitive to " black " alkali, 

 and will decay in the ground unless protected against it by the 

 use of gypsum in sowing. But when once a full stand has been 

 obtained, the field may endure for many years without a sign 

 of injury. Here two effects combine, viz., the shading, and the 

 evaporation through the deep roots and abundant foliage, 

 which alone prevents, in a large measure, the ascent of the 

 moisture and salts to the surface. The case is then precisely 

 parallel to that of the natural soil (see p. 432, chapter 22), ex- 

 cept that, as irrigation is practiced in order to stimulate produc- 

 tion, the sheet of alkali hardpan will be dissolved and its salts 

 spread through the soil more evenly. The result is that so soon 

 as the alfalfa is taken off the ground and the cultivation of 

 other crops is attempted, an altogether unexpectedly large 

 amount of alkali comes to the surface and greatly impedes, if 

 it docs not altogether prevent, the immediate planting of other 

 crops. Shallow-rooted annual crops that give but little shade, 

 like the cereals, while measurably impeding the rise of the 

 salts during their growth (see fig. 70. page 452) frequently 

 allow of enough rise after harvest to prevent reseeding the 

 following season. 



" Neutralizing " Black Alkali. Since so little carbonate of 

 soda as one-tenth of one per cent, may suffice to render some 

 soils uncultivable, it frequently happens that its mere trans- 

 formation into the sulfatc is sufficient to remove all stress from 

 alkali. Gypsum (land plaster) is the cheap and effective agent 

 to bring about this transformation, provided water be also 



