8o RELATIONS OF SOIL TO WATER 



The amount of water retained by a soil after rain is one 

 of the factors which, more than any other, determines its 

 suitability for different kinds of agricultural crops. The 

 typical American soils described on p. 20 owe their suitability 

 for their respective cultures chiefly to the varying percentages 

 of water which they retain. The requirements of a plant for 

 water vary a good deal in the various stages of its life. In 

 the earlier stage of leafy growth, when the production of veget- 

 able tissue is proceeding with the greatest vigour, the demand 

 for water is greatest, and luxuriant growth at this period is 

 largely determined by the quantity of water supplied. But 

 in the later stage of seed production, when the transference of 

 matter rather than its new formation is the great business 

 of the plant, the presence of an excess of water is for many 

 plants highly injurious, and greatly diminishes the proportion 

 of seed yielded by the plant. For seed production, therefore, 

 dry conditions are desirable. 



The general idea of the relation of water supply to plant 

 function we have just presented serves to explain why different 

 crops, or different styles of culture, require different proportions 

 of water in the soil. Wheat land must be drier than grass land, 

 if both crops are to develop to the best advantage. A soil for 

 the production of a fine sample of malting barley must be 

 drier than one yielding maximum wheat crops. A soil that 

 is to supply early market-garden crops must be a dry one, 

 for the object is to obtain early and not heavy crops ; and to 

 obtain early maturity the crop must be hastened through 

 its preliminary stage of tissue formation and brought as 

 quickly as possible to the completion of its career. 



Little information exists as to the proportion of water 

 actually held by the soils most suitable for the production 



