ALKALIS 



REH 



Oanal Influence. 



Defective 

 Drainage. 

 Medlicott's 

 Opinions. 



Percentage of 

 Carbonate in 

 Fertile Soils. 



Special Crops. 



Healthy 

 Circulation. 



Permeation of 

 Water. 



Conditions that 

 favour Reh 

 Formation. 



Kankar. 

 Capillary Action. 



Californian 

 Experiments 

 and Results. 



ALKALIS AND ALKALINE EARTHS 



from being in accordance with modern views. It is certainly strange that Royle 

 (Prod. Res. Ind.,* 1840-75) makes no mention of the phenomenon of reh efflor- 

 escence. He remarks that Dr. Helenus Scott had sent from Bombay to England 

 a sample of a "mineral alkali" as a substitute for barilla, and so closes his account. 

 He was for some time resident in Saharanpur, and if the usar tracts existed as they 

 do to-day, it is curious that he should not have mentioned them. In 1804 was 

 published (Select. Rec. Gov. Ind., No. xlii.) a correspondence which deals with the 

 deterioration of village lands lying along the W. Jumna Canal and contends that 

 the canal was not responsible for the existence of injurious salts, but that 

 defective drainage in connection with it had led to the accumulation of salt to 

 such an extent as to render cultivation impossible. The inquiry had no practical 

 result. In 1876, however, a committee was appointed to investigate the matter 

 in consequence of a planter's complaint that his land had been spoilt by the 

 mismanagement of canal irrigation. This was the Reh Committee of 1877, of 

 which Mr. H. B. Medlicott was a member. Medlicott (at one time Director 

 of the Geological Survey) began the study of this subject early in the 'sixties. 

 As a member of the committee, he wrote a masterly report which may be 

 said to contain all we know regarding the formation and movement of the 

 soluble alkali salts within the soil. These, he tells us, are formed from 

 normal soil-materials by the disintegration caused through the growth of plants 

 and tillage. The silicates are broken up by the action of heat, air, water 

 and carbonic acid, etc., with the manifestation of the various alkalis that are 

 formed or reformed during the several changes that ensue. During the pro- 

 duction and maintenance of fertile soils, carbonate of soda, for example, is as a 

 rule a transitional compound and is destroyed with the elaboration of other and 

 more essential constituents, especially in the presence of lime. In most fertile 

 soils the percentage of that carbonate is accordingly remarkably low. In fact 

 the total of soluble soda salts in good soils rarely exceeds O'l, of which ordinarily 

 one-half may be the carbonate. Crops, more especially cereals, may however 

 be grown on soils that contain O'l per cent, of carbonate of soda, and 0'2 per 

 cent, is sufficient to cause serious injury if it be not found fatal, except perhaps 

 to the so-called saltworts or saltbush plants that are actually found to luxuriato 

 on briny soils or littoral swamps. At times, however, as already observed, the 

 surface soil may become encrusted with soluble salts, as much as 2 to 6 per cent, 

 or much more being often present. Normally these soluble alkalis are carried 

 by the rain-water or irrigation to the subsoil, and a certain percentage are de- 

 tained mechanically, the surplus being carried away by the drainage. Where 

 subsoil drainage is defective, as a purely local and temporary measure surface wash 

 may prove beneficial. For this purpose trenches or pits are dug, and the surface 

 water dissolves the salts and carries these to the trenches, thereby leaving the 

 higher ground less charged with alkali. But the evil consequence of even a tem- 

 porary cessation of soil-permeation may be exaggerated under certain conditions 

 such as (1) recurring periods of hot, parching winds ; (2) absence of soil-covering 

 (i.e. wild herbage or crops and trees) ; and (3) defective tillage (i.e. superficial 

 ploughing or puddling during flood). These are the very conditions that produce 

 reh efflorescence, aided by (a) the chemical nature of the original soil-materials ; 

 (b) the physical attributes (or texture, as it has been called) of the soil (i.e. abun- 

 dance of clay and the conditions of the clay; abundance of sand or of lime, etc.) ; 

 and (c) the accidental or irregular distribution of (a) and (b) brought about through 

 countless ages of water action, both during the formation of the alluvial plains and 

 subsequently. For particulars regarding the association of concretionary lime 

 (kankar) with reh, the reader is referred to Lime, p. 711. 



Diffusion and Capillary Action. Dr. Center (then Chemical Examiner to 

 the Panjab Government) wrote in 1880 a most valuable Note on Reh or Alkali 

 Soils and Saline Well Waters, in which he dealt in great detail with the movement 

 of these salts within the soil and their temporary accumulation on the surface. 

 They may be spoken of as first diffused', then carried to the surface by capillary 

 action. Hilgard and Loughbridge, in connection with the Californian Experi- 

 mental Station of Tulare, have carried these investigations to their final issue by 

 tracing, in every detail, the actual movement of the salts in sterile soils, before and 

 after irrigation, and have exhibited their results graphically, in direct corre- 

 spondence with a most critical analysis of practically every inch of soil to a depth 

 of 4 feet. They have also demonstrated beyond dispute that this movement to 

 and from the surface is directlya result of imperfect drainage in conjunction with 

 severe surface evaporation. 



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