TREATMENT OF ALKALI LAND 229 



carbonate there is however a special kind of pan, which 

 forms at the depth to which the alkali salts are annually 

 brought by the winter rains. In the natural unirrigated 

 soil mentioned in Table XXXVIII such a pan occurs at about 

 32 inches below the surface. This pan is due to an accumula- 

 tion of the finest clay washed down by rain, and hardened 

 by the action of the sodium carbonate. Under the influence 

 of water and gypsum such a pan is effectually disintegrated. 

 To accomplish such a task the gypsum must of course be 

 applied in excess. 



The remedial measures of the most general application 

 have for their object the diminution of surface evaporation 

 during summer, and consequently the prevention of the rise 

 of the band of alkali. As already mentioned, if the alkali 

 can only be kept in the moist subsoil it is comparatively 

 harmless ; it is when concentrated by evaporation at the 

 surface that it becomes so fatal to plants. 



To reclaim alkali land, the soil should be deeply cultivated 

 as soon as possible after the wet season is over, and a layer 

 of 8 inches or more of loose soil should be maintained at 

 the surface all through the summer. Under these circum- 

 stances the amount of water evaporated by the soil is much 

 diminished ; the alkali will also fail to reach the surface, 

 its progress being stopped by the loose dry soil. The rains 

 of the next wet season will now carry the salts to a lower 

 level than before. This treatment may be repeated, and 

 a further lowering of the salt band obtained, till the full 

 effect possible from the winter rains is reached. The land 

 is now cured, if afterwards properly cultivated. Any other 

 plan which diminishes the evaporation at the surface will act 

 in a beneficial manner, as for instance mulching the surface 



