SOIL CONDITIONS AFFECTING PLANT GRO WTH 83 



Table XXVI. — Effect of Acid Rain-water on the Growth of Timothy 



Grass. Crowther and Ruston (71). 



Wdfrht of dry matter obtained when plants were regularly watered with : — 



Metallic Salts. — Complaints are sometimes made by 

 farmers in mining districts that their crops suffer damage from 

 the waste products — generally metallic salts — turned into the 

 streams from the works, especially where the water is wanted 

 for irrigation, or where, as in Japan, rice is grown in the 

 marshes. The damage done to pastures by the lead mines of 

 Cardiganshire has been investigated by J. J. Griffith (115) at 

 Aberystwyth, Clovefr is particularly susceptible. A heavy 

 dressing of lime proved a useful remedy. 



Zinc also causes injury in parts of Wales. ^ 



Traces of zinc are regarded as essential by Maze (197). 

 Working with larger quantities Dr. Brenchley (53^) was un- 

 able to find definite indications of stimulating action in water 

 culture, although Javillier (143) claimed to obtain increases 

 in soil. Ehrenberg {g^a) concludes that zinc salts are always 

 toxic when the action is simply on the plant, but they may 

 lead to increased growth through some indirect action on the 

 soil itself (see p. 281). 



A vast number of experiments have shown that copper 

 salts are extraordinarily toxic in water cultures or where they 

 actually come into contact with the plant, even the minute 

 trace sometimes present in distilled water being harmful. 

 This property finds useful application in removing algae from 

 water and in killing weeds. For example, a 3 per cent, solu- 

 tion of copper sulphate is sprayed over cornfields in early 



^ The soil of an Anglesey garden examined at Rothamsted contained 078 

 per cent, of zinc. It proved, as might be expected, highly infertile. 



6* 



