RELATION OF FERTILISERS TO SOIL FERTILITY. 15 



Of the various problems presented by a study of the physical nature of 

 the soil, the one which is of the greatest importance is the question of the 

 behaviour of water in the soil. This applies with special force to us in 

 Australia, where the problem of conserving the soil-moisture is of even greater 

 importance than that of manuring. The action of fertilisers, especially 

 potash salts, in keeping the surface soil moist, is well known. The applica- 

 tion of fertilisers has been found to have a very considerable effect upon the 

 transpiration ratio of plants, enabling them to make a better use of the 

 available moisture. 



In fact J. W. Leather* in the course of an investigationinto the water require- 

 ments of crops in India, finds that the transpiration ratio (that is the relation 

 between the weight of water transpired by the crop and the weight of the 

 dry crop) is always lower when suitable manures are employed, and 

 concludes that " speaking generally the effect of suitable manure in enabling 

 the plant to economise water is the moot important factor which has been 

 noticed in relation to transpiration." 



It appears possible, however, from more recent researches of the same- 

 author^ that the decrease in the transpiration ratio when suitable manures ara 

 added, is due rather to the more vigorous growth of the plant than to any 

 specific action of the manure on the transpiration ratio. 



Dr. Leather has, at all events, shown this to be the case with super- 

 phosphate, which when supplied to a soil known to have no need for 

 phosphatic manuring did not lower the transpiration ratio. 



This, however, is a case in which it is possible to confuse cause and effect. 

 The soil in question was unusually rich in available phosphoric acid, 

 containing more than three times as much as the richest of the other soils, 

 and it is not impossible that the transpiration ratio was affected by the 

 presence of soluble phosphoric acid in the soil. 



J. W. PatersonJ has published results of experiments to determine the 

 transpiration ratio of oats, which are of interest in this connection, although 

 the question of the effect of manuring does not enter into the investigation. 



He finds the transpiration figure for this crop, grown in pots and partially 

 shaded during the period of their growth, to be about 483, that is to say, 

 483 tons of water are transpired for every ton of dry crop produced. 



He assumes that for plants of moderate development, grown in the open 

 air in Victoria, this figure would be 700, as against 870 in India (Leather, 

 loc. cit.) ; 522 in America (King) ; and 665 (Wollny) to 376 (Helleriegel) in 

 Europe. 



According to Leather a 13-bushel crop of wheat (about 1 ton grain and 

 straw) will transpire 693 tons of water (or 6*8 inches of rain) per acre in 

 India. Dr. Paterson states that local conditions indicate that about 600 

 tons of water (6 inches of rain) per acre would pass through a 13-bushel 

 crop of wheat during its growth under Victorian conditions. 



* " Memoirs," Dept. Agric., India, Cheml. Series, vol. 1, No. 8, p. 170. 

 f " Memoirs" Dept. Ag-'lc, India, Cheml. Series, vol. 1, No. 10, p. 230. 

 % "Jour. Dept. Agric., Victoria, vol. 10, p. 349. 



