152 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XV, 



highlytrained experts have set themselves to deal systematically -with the 

 problem* arising out of drought ; experimental farms and laboratories have 

 been at their disposal ; and the rich harvest of facts and experience reaped 

 by them contrasts painfully with the meagre results obtained in India by the 

 inadequate machinery provided for similar investigations. The conclusions 

 arrived at, so far as they bear on the subject of this Note, may be briefly 

 summarised under two headings : (A) Chemical analysis ; and (B) Botani- 

 cal research. 



6. (A") Chemical Analysis. By this branch of inquiry it is shown that the 

 salts existing in alkali lands are made up partly of salts that are noxious to 

 plant life, viz., carbonate of soda, sodium chlorid (table salt ), and sulphate 

 of soda (Glauber's salt), and partly of salts which are valuable fertilisers, 

 viz., sulphate of potash, phosphate of potash, and nitrate of potash: that 

 these salts are originally distributed in solution throughout the soil ; and 

 that by means of capillary attraction and evaporation they are accumulated 

 on the surface, forming a crust destructive to most forms of vegetable life. 

 (B) Botanical Research. On the other hand, by the experiments in this de- 

 partment, it is proved that certain fodder plants, notably the Australian salt- 

 bushes, can live and thrive upon such alkali lanis, absorbing large quantities 

 of the noxious salts, while appropriating only a small proportion of the 

 fertilisers. They also possess the valuable property of sharing with the 

 hygroscopic salts the 10 per cent, additional moisture held in suspense in these 

 alkali soils. Among these salt-bushes experience points to Atriplest semihaccata 

 as most suitable for hot dry climates, being drought-resisting, prolific-, and 

 capable of producing abundant supplies of good fodder ; and it is found 

 that by continuous cropping with this salt-bush the excess of injurious salts 

 is eliminated ; so that the alkali lauds may, by this simple process, become 

 "profusely and lastingly " fertile for the growth of ordinary crops. 



7. With reference to the origin of the alkali trouble. Professor Hilgard 

 points out (Bulletin No. 128, p. 13) that the soluble salts in alkali soil have, 

 like the soil itself, been formed by the progressive weathering of the con- 

 tiguous rocks ; that the salts in the upper 4 or 5 feet of soil are usually limited 

 in amount ; and that they are not ordinarily replenished in indefinite quanti- 

 ties from the lower strata. The salts move up and down wiiliin the upper 4 

 or 5 feet of the soil or subsoil, following the movement of the moisture 

 descending in the rainy season, or when irrigated, to the limit of the annual 

 moistening as a maximum, and then re-ascending or not according as surface 

 evaporation may demand. At the end of the dry season, in untdled irrigated 

 land, practically the entire mass of salts may be within 6 or 8 inches of the 

 surface. The injury to vegetation is caused mainly within a few inches of 

 the surface, by the carbonate of soda, which corrodes the bark near the root- 

 crown, and by the sodium chlorid, which acts as an antiseptic, and arrests 

 development. Carbonate of socJa may however be neutralised by treating it 

 with gypsum, which converts it into the sulphate, or Glauber's salt, which 



