54 THE farmers' handbook. 



Sourness. 



This is one of the most common causes of infertility in soils. It is 

 brought about either by the absolute exclusion of air, as in water-logged 

 soils or soils in which the surface has been impacted; or it may also be the 

 result of an excessive amount of organic matter, as in peaty soils. In both 

 cases the result is the formation of organic acids (humic acids, &c), which, 

 in the absence or deficiency of basic substances, such as lime, to neutralise 

 them, act as plant poisons. They not only affect the growth of the plant, 

 but have a solvent action upon the soil constituents, which are liable to be 

 dissolved out and' pass into the subsoil. Soils which are red or chocolate in 

 colour from the presence of oxide or iron, if allowed to become sour, are very 

 frequently bleached in colour. They also exercise a reducing action upon 

 the higher oxides, such as ferric oxide, reducing it to the state of ferrous 

 oxide. It is commonly stated that this latter substance is itself a plant 

 poison, but since this compound would not be present in soils in good tilth, 

 but would be converted into the higher (ferric) oxide, it is probable that 

 the ill effects noted when ferrous oxide is present are in reality due to sour- 

 ness, and that the presence of ferrous oxide is only one of the results of this 

 condition. 



The remedies for sourness are thorough cultivation and turning of the 

 soil and exposing it to the air. In cases where it is the result of accumu- 

 lation of water (in swampy soils) it will be necessary to have recourse to 

 drainage. The addition of lime to neutralise the acids formed is in all 

 cases beneficial ; and by a proper system of drainage, together with thorough 

 cultivation and the addition of lime, it should be possible to reclaim the 

 most sour land. A sour condition of land is usually quite readily recog- 

 nisable by the experienced farmer from its appearance, the peculiar odour 

 when moist, &c. 



As this condition is due to acidity, sour soils have always a strong acid 

 reaction towards litmus; but as this reaction is influenced by other factors, 

 it is not a reliable indication except in experienced hands. It must also be 

 remembered that cultivated soils nearly always possess an acid reaction. 



Protoxide of Iron and Pyrites. 



The presence of these compounds in the soil is generally an accompani- 

 ment of a sour condition of the soil, and is due to the same cause — want of 

 aeration. It is doubtful whether they are themselves active plant poisons, 

 but their presence is always associated with an infertile condition. 



The presence of ferrous oxide is indicated by a bluish or greenish colour- 

 ation in the clay. This colour changes to red or reddish brown when the 

 soil is aerated. 



Pyrites and marcasite (sulphide of iron) are commonly occurring minerals, 

 and their presence unchanged is also a sign of deficient aeration. 



It is also stated that ferrous sulphate, the substance into which the sul- 

 phide is at first converted on oxidation, is itself a plant poison if present in 

 excessive quantities, so that such soils will require very thorough aeration in 

 order to convert the ferrous sulphate into the fully oxidised ferric compound. 

 At the same time it must be remembered that ferrous sulphate is recom- 

 mended by many writers as a manure. A very effective fertiliser was pre- 

 pared locally by mixing boiling-down soup with ferrous sulphate. It is 



