NUTRITION OF PLANTS 



from mineral matter, but usually contains a small percentage 

 of ammonia which it obtains from the atmosphere ; it also contains 

 carbon dioxide, so that it is able to dissolve carbonate of lime in 

 the soil. Rain-water is thus said to be "soft," and is preferred for 

 watering plants or crops. Spring or well-water usually contains 

 varying quantities of carbonate of lime and other mineral matter, 

 when it is said to be "hard" ; in some cases it also contains large 

 quantities of iron oxides, and these form encrustations on bodies 

 placed in the water ; this is often characteristic of well-water in 

 the northern part of Ceylon, which consequently is injurious in 

 that condition to plant or animal life. Such water should always 

 be exposed for some time to the sun before use. Running- water 

 also contains in the form of sediment different mineral substances 

 varying in quantity according to the source of the water and the 

 course through which it runs. Irrigation waters in their passage 

 through the soil remove large quantities of nitrogen (in the form 

 of nitrates) and other valuable ingredients from the soil. It has 

 been established by experts that the quantity so removed is in some 

 cases so great that if the water could be supplied to crops in 

 sufficient quantity it would supply the place of manure. 



