118 Some Causes of Unjirodtictiveness in Soils. 



This soil abounds in all the mineral elements which enter into 

 the composition of the ashes of plants, and is especially rich in 

 phosphoric acid ; it moreover contains a considerable proportion 

 of organic matter capable of yielding on decomposition rather 

 more than ^ per cent of ammonia, but unfortunately it is impreg- 

 nated with sulphate of iron, which neutralises all its useful pro- 

 perties, rendering it unproductive. 



An interesting circumstance may be mentioned in connection 

 with the field from which this soil was taken. Before it came 

 into the hands of its present proprietor, the land was only slightly 

 scratched on the surface as a preparation for the next crop, and 

 then produced scanty but still remunerative crops. Not satisfied 

 with that yield, Mr. Wilson, an enterprising Englishman, the 

 present owner of th(> land, ploughed deep, and, to his astonish- 

 ment, found this attempt to improve its productiveness result in 

 a complete failure of his corn-crop. A heavy dressing of farm- 

 yard-manure proved e(|ually unsuccessful, or rather aggravated 

 the evil ; for after the application of the dung even the deeper- 

 rooting weeds were affected, and nothing but surface weeds would 

 grow. This curious circumstance led to a chemical examina- 

 tion, which was committed to me. 



The preliminary examination showed at once that there was 

 present some injurious substance, for the wetted soil strongly 

 discoloured the blue litmus-paper. The acid reaction I found 

 was caused by sulphate of iron, and I also succeeded in detecting 

 sulphide of iron, or iron pyrites. As long as the land was 

 left unploughed, the latter constituent was not brought to the 

 surface, and most of the iron existing there originally was no 

 doubt gradually removed into the subsoil by the rain, which 

 accounts for the better crops when the subsoil was unstirred. By 

 deep cultivation the sulphide of iron was turned up, and air 

 admitted into the soil more freely, which had the effect of 

 oxydizing the iron pyrites, and changing it into green vitriol. As 

 the available mineral elements and soluble salts in the land were 

 already rather in excess of the amount which is beneficial, the 

 dressing of farmyard-manure, containing a good deal of soluble 

 matter, could only aggravate the evil. 



The proper remedy for such a state of things is a heavy dressing 

 of lime, marl, or chalk ; for quicklime, or the lime in marl or 

 chalk, decomposes sulphate of iron, and uniting with the liberated 

 sulphuric acid, gives rise to gypsum — a useful fertiliser — and to 

 oxide of iron, which occurs in all fertile soils. In the case 

 before us, my recommendation to apply a heavy dressing of lime 

 was adopted with complete success. 



Since green vitriol, as well as iron pyrites, sometimes occur in 

 subsoils, care should be taken to test the subsoil, before the opera- 



