TREATMENT OF 08AB BOD B 



ALKALIS 



REH 



Tillage. 1 >r. I'.ioun (thru Chemical Kx.uniner t> ill.- I'anjiib) 

 ,| the ii-. '(' lii :> ! emp|o\ IM| in tin- trealn,. 



nd his views were published b) Mr. I'.nl. n Powell (]'/,. J'rud., IM,-.. Id, 



" When t hi- deleterious sulphates ami cai lionatea ore mixed with any 



milulilf suit "I linn , Mich ,i -: 1 In- nit ratoof lime, decomposition occurs ami nitrate of 



iied while carbonate and .Milphateof lime are produced. Carbonate of 

 lime is infill i Me ia pure water and has no power of injuring plants, while nitrate of 

 and sulphate i>f lime are beneficial in supplying tliein with nitrogen, the 

 former l>\ direct decomposit ion of its acid and t ho latter by absorbing ammonia 

 from tin- air. Nitrate of lime U formed whenever organic matter decomposes 

 :itaet with carbonate of lime." Some years later Brown advocated the 

 if farm -yard manure and green manuring with such plants as *//,.<., 

 ,/i./. i n/.-.i on the ground of their supplying the nitrogen which, in combination 

 with the lime (naturally present in all kalr soils;, would tend to reduce the carbonate 

 da to a harmless condition. Center wrote along and highly instructive 

 report on the chemistry of the usar soils, and confirmed in the most striking way 

 Urown's recommendations for limo nitrate. He also gave an account of the 

 operations in the Utah Basin and other parts of America, where heavy nitrating 

 manures were employed as a remedial measure for alkali soils. Later on the 

 sulphate of lime (Gypsum, see pp. 71G-7) gained a well-deserved reputation as a 

 chemical substance that mi^bt be employed with groat advantage in the neutrali- 

 sation of the sodium carbonate in iisar soils whenever that salt predominates. 

 \Vhoro reh consists chiefly of sulphate of soda, gypsum would very possibly do 

 harm rather than good. 



The next most important step, therefore, in the study of the chemical treatment 

 of usar soils maybe said to be Leather's various papers that have appeared in 

 The Agricultural Ledger. These give extensive analyses of soils, waters, etc., 

 from the entire alkali area of India. They contain the results of practical ex- 

 periments to test the amount of soluble alkali salts that may exist in soils before 

 these become poisonous to vegetation. They indicate the plants that first show 

 signs of succumbing to the influence of these salts, and the amount of each salt 

 that proves fatal. By special pot cultures of various plants, Leather proved 

 that sodium carbonate is (as has always been upheld) infinitely more injurious 

 to plant life than are any of the other soda salts. But perhaps the most 

 instructive part of his researches was the demonstration of the physical 

 property (alluded to by Romanis, Wallace and others) possessed by carbonate 

 of soda, which greatly augments its injurious chemical influence on plants. While 

 filtering soils in order to obtain their soluble salts, Leather observed that 

 certain soils could practically not be filtered. A little muddy water percolated 

 tlirough at first, but very soon the surface of the filter-cloth became coated with 

 a perfectly impenetrable layer, and further filtration was then impossible. The 

 soils that manifested this peculiarity were those most highly charged with 

 carbonate of soda. To remedy this defect he experimented with gypsum 

 and soon ascertained that its well-known merit as a chemical manure in the 

 reclamation of usar soils rested as much on the destruction of the impervious 

 deposit as in the reduction of the " white " to the " black alkali." It would thus 

 appear that should climatic and soil conditions exist sufficient to give origin to a 

 reh efflorescence containing carbonate of soda, there must sooner or later bo 

 produced (at a certain position or depth) an impenetrable layer through which 

 surface percolation of water would be impossible. This waterproof layer may 

 not be sufficiently developed to be visible to the naked eye as a " hard pan," but 

 if carried near to the surface it will give origin to a crust of salt. A change in the 

 physical condition of the soil is accordingly quite as urgent a necessity as in its 

 actual chemical composition. It may thus be inferred that subsoil drainage, 

 below an impervious layer, would be next to useless unless the soil be chemically 

 treated with some of the soluble lime salts, or be penetrated for tree cultivation 

 by deep pits filled in with fresh soil. It would indeed seem probable that the 

 surface vegetation that has been reported as accompanying successful tree culti- 

 vation, may be due very largely to the pits dug for trees having acted as openings 

 t hrou^h the impenetrable layer by which the soluble saltsof the surface have been 

 washed into the natural drainage. 



By way of concluding these observations regarding gypsum, it may be 

 suggested that it is not necessary to assume that the exact amount of that salt 

 which would be required chemically to neutralise the ascertained weight of 

 carbonate present need be given as a manure before beneficial results may be 



53 



i ,- .,( 

 - in.,. 



farm-yard 

 Manure. 

 Green Manure. 



American 

 Itecliimatiou 

 Methods. 

 Gypsum. 



( 'lii'miml 



Investigations. 



Sodium 

 Carbonate. 



Physical 

 Property of 

 Soils. 



Value of 

 Gypsum. 



Principled 

 Involved. 



" Jl.irJ pan." 

 Initial Action. 



Tree Cultivation. 



Is Complete 

 Neutralisation 

 Essential ? 



