16 Irrigation and Drainage 



much larger returns in grass than do river, lake or 

 well waters. The writer learned, while visiting the 

 celebrated Craigentinny meadows near Edinburgh, that 

 the purchasers of the grass from those lands are very 

 particular to specify, as a condition of their purchase, 

 that their grass shall be watered with the day sewage, 

 which contains a higher per cent of soluble and sus- 

 pended organic matter than that of the night ; and 

 they are also particular to stipulate that they shall 

 have the first rather than the second or third use of 

 the water, knowing that water which has passed over 

 a cultivated field or meadow has lost something of its 

 fertilizing value. 



It is asserted, also, by the owners and renters of 

 water meadows in the south of England, where the 

 irrigation is directly from the streams, that that land 

 which receives the water first is most benefited by it. 

 It is true that there are those who contend that on their 

 lands the second and third waters are as good as the 

 first, but this is quite likely to be due to the presence 

 in those particular soils of an abundance of the sub- 

 stances carried by the waters. 



It is, however, impossible to overestimate the im- 

 portance of water as a plant-food. It is indispensable 

 and is used more than any other substance. It must 

 be borne in mind, however, that irrigation waters are 

 seldom, if ever, a complete plant-food. 



THE AMOUNT OF WATER USED BY PLANTS 



The amount of water which is required to mature crops of 

 various kinds under field conditions varies between wide limits ; 



