54 RELATIONS OF SOIL TO WATER 



Striking illustrations of the sufficiency of a small supply 

 of water under specially favourable conditions are to be found 

 in the case of some of the soils rich in soluble salts which 

 occur in the semi-arid regions of the western States of North 

 America. Good crops of wheat are here grown with an annual 

 rainfall of 13-18 inches, most of which falls in winter time 

 before the growth of the crop has commenced. The water 

 level in the subsoil is 20-30 feet below the surface. Such a 

 supply of water would prove quite inadequate on the soils 

 of the eastern States. The richness of the saline soils of the 

 western States in soluble plant food will be referred to later 

 (p. 215). The presence of much soluble saline matter in the 

 soil is probably in itself a check to the transpiration of water 

 by the plant. 



A plant may succeed in reaching perfect maturity with 

 a scanty supply of water, and in this case there will be a 

 relatively large produce for the quantity of water consumed, 

 but a maximum crop will not be obtained in this way. A 

 luxuriant growth demands permanent turgidity of the cells, 

 and in an ordinary climate this condition can only be at- 

 tained by a large supply, and a large evaporation of water. 

 The largest crops can thus only be grown with a luxurious 

 or wasteful consumption of water. 



King's experiments at Wisconsin were made in barrels sunk 

 in pits, the surface of the soil in the barrel being on the level 

 of the field. The crop grown in the field was the same as 

 that grown in the barrel, so that the experimental crop was 

 surrounded by a similar growth in the same manner as it 

 would be under ordinary cultivation. The water was supplied 

 through a pipe passing to the bottom of the barrel, and the 

 water level in the barrel was permanently maintained at six 



