CH. vii] Acid Effects 135 



serious for two reasons: the lime is greatly needed for 

 other purposes ; and in its absence ammonium sulphate 

 leaves an acid residue in the soil, the ammonium portion 

 being more completely taken by plants than the rest. 

 Now most agricultural plants will not tolerate this 

 acidity, and in extreme cases completely refuse to grow. 

 This remarkable action was first observed by Dr Wheeler 

 at the Rhode Island Experiment Station in 1890^ and 

 was investigated in an important series of experiments 

 which showed that the trouble could be completely re- 

 medied by dressings of lime. A few years later the same 

 phenomenon appeared at the Woburn Experimental 

 Farm and has been fully described by Dr Voelcker^; 

 there also lime was found to be the proper remedy. 



Thus sulphate of ammonia tends to make the soil 

 acid, and therefore physiologically unsuited for plants, 

 while, as already pointed out, nitrate of soda tends to 

 make it alkaline and therefore physically unsuited to 

 them. A mixture of the two fertilisers produces no such 

 effects, as each neutralises the other. 



Sulphate of ammonia, unlike nitrate of soda, is com- 

 pletely absorbed by the soil and shows no tendency to 

 wash out. This can be demonstrated by packing 50grams 

 of soil (preferably a loam) on to a funnel, moistening with 

 water and then pouring on 100 c.c. of 1 per cent, ammo- 

 nium sulphate solution. Test the filtrate for calcium, for 

 sulphate, and for ammonia. The two former occur in 

 quantity, but the ammonia is reduced in amount. Now 

 repeat the experiment with a fresh lot of soil and a 

 1 per cent, sodium nitrate solution. The nitrate shows 



^ Rhode Island Exp. Station, 3rd Anmial Report, 1891, p. 53; 4Jh 

 Report, et seq. 



- Journ. Roy. Agric. Soc, 1897, p. 287; and subsequent years. 



