224 Fertilisers [pt. hi 



because the special harmful factor the acidity was 

 overcome. 



Qiiantity required. Where a harmful factor has to be 

 thrown out of action the dressing of lime or chalk must 

 be sufficient for this purpose. Where no special function 

 is to be served much less is needed. Certain analytical 

 methods have proved helpful in indicating the quantity 

 needed to counteract acidity^ and there are data for 

 showing how much is needed for maintaining fertility 

 generally. Since lime and chalk are both converted into 

 soluble calcium bicarbonate in the soil they are liable 

 to be washed out. There are sources of production in 

 the soil, but the general tendency is for losses to pre- 

 ponderate, and at Rothamsted they amount to some 

 800 lbs. of lime (CaO) per acre per annum on arable 

 land but less on grass land; very similar results were 

 obtained by Hopkins in Illinois. This amount would be 

 returned to the soil in 8 cwts. of good burnt lime (85 

 per cent. CaO) or 15 cwts. of limestone or chalk and if 

 this dressing were annually given per acre there would 

 be no diminution in the stock. Lime and limestone can 

 readily be had in a finely divided state, and can be put 

 on with a distributor as a regular proceeding: 1 ton of 

 lime or 2 tons of limestone are suitable quantities. Cob 

 lime may be used instead of ground lime and is cheaper, 

 but on the other hand it is more costly to spread. Chalk 

 is not easy to grind and is usually applied in lumps, less 

 than 20 or 30 tons per acre cannot conveniently be 

 added so that regular dressings are not common, and it 

 is only put on at long intervals when other work allows, 

 which means in practice that chalking is commonly 



^ E.g. those of Veitch {Journ. Amer. Chem. Soc, 1902, xxiv. 1120), and 

 of Hutchinson and MacLennan {Journ. Agric. Science, 1915, vu. 75-105). 



