250 



Poisoning of the Soil by Metallic Sulfur. 



In considering factors injurious to plant growth ferric sulfid as pyrites 

 (and rhomboidally crystallized as markasit) must be noticed primarily since 

 it is one oi the most widespread precipitates produced in the formation of 

 moors. Ferric sulfid is found less in moors themselves than in the under- 

 lying sand and on the Une between the organic deposits and the subsoil. If 

 pyrites weathers, there is produced by oxidation and absorption of water sul- 

 furic ferrous oxid,^ferrous sulfate, copperas, and free sulfuric acid (FeS.+ 

 70+HoO=FeSo,+H2SO,) . 



The ferrous sulfate oxidizes with the formation of basic salts to ferric 

 oxid. In the presence of sufficient amounts of calcium carbonate, calcium 

 sulfate (gypsum) is produced. If ferrous carbonate occurs, it passes over 

 into ferric oxid or ferric hydrate with the loss of carbon dioxid and the 

 taking up of oxygen. As is well known, the ferric hydrates cause the yellow 

 to brown color of the soils and are able to absorb gases (carbon dioxid, nit- 

 rogen, etc.) to a very marked degree. Among them is the brown clay iron 

 ore (limonite Fe2[OH]c) which cements together the surrounding sand^ In 

 moor regions, however, the layers containing pyrites are often not oxidized 

 at all ; because of the presence of water and the strongly reducing action of 

 the moor substance they cannot obtain any oxygen. 



The most disasterous effect of the iron sulfid is its inhibition of the com- 

 bining of the bases present in the soil and the free sulfuric acid formed by 

 weathering. As a rule, calcium carbonate is present in the soil, so that gy'p- 

 sum can be formed, often alum or magnesium sulfate are also produced. An 

 excess of the last can act injuriously. When experimenting with an exces- 

 sive supply of alum, I found spotted necrosis appearing in barley. However, 

 if the bases are absent, the free sulfuric acid will act directly as a plant 

 poison. 



If, in improving the soil, the layer containing the pyrites is brought to 

 the surface, the soil will at first remain infertile. 



Minssen- shows that at times the upper layers of the moor also contain 

 iron sulfid. In a sample from Silesia he found 7.286 per cent, of the dry 

 substance of the surface soil to be sulfuric acid, soluble in water, 3.940 per 

 cent, ferrous sulfate and 3.346 per cent, free sulfuric acid and approximately 

 twice as much in the deeper layers, aside from great masses of still un- 

 weathered iron bisulfid. The top of the sulfate here analyzed was later re- 

 moved 62 cm. deep, so that the lower layers richly impregnated with iron sul- 

 fid were laid bare. The oxidation of the pyrites gave such large amounts of 

 compounds injurious to vegetation that any agricultural use of the moor 

 within a conceivable time seemed impossible. Such a case shows the neces- 

 sity for the use of foresight in opening up lowland moors. 



1 Ramann, Bodenkunde, 1905, p. 87. 



- Mitteilungen d. Ver. z. Forderung" der Moorkultur im Deutsch. Reich, 1904. 

 No. 1. 



