CHAPTER IX 



MATERIALS OF INDIRECT FERTILISING VALUE 



Lime — Early Use of Lime — White and Grey Limes — Lime 

 Ashes — Marl — Chalk — Ground Limestone — Indications of the 

 Lack of Lime in the Soil — Action of Lime upon the Soil — 

 Improvement of Texture — Promotion of the Oxidation of 

 Nitrogenous Residues in the Soil — Increase in the Availability 

 of Phosphoric Acid and Potash — General Action of Soluble 

 Salts on the Soil — Gas Lime — Gypsum — Salt — Sulphate and 

 Carbonate of Magnesia — Sulphate of Iron ; Supposed Connec- 

 tion of Iron in the Soil with the Colour of Fruit and Flowers 

 — Manganese Salts — Silicates — Green Manuring — Folding 

 Catch Crops on the Land. 



There are several substances commonly used by 

 farmers as manures, which produce desirable effects 

 upon the crops, although they are not themselves plant 

 foods and only act indirectly on the soil, either by 

 making it more amenable to cultivation or by bringing 

 into action the stored-up reserves in the soil. 



Such substances are lime, gypsum, salt, all of which 

 contain elements present in the plant, though they also 

 exist in the soil in quantities sufficient for the nutrition 

 of the crop ; they are valuable as soluble salts for their 

 indirect effect in making soluble other more important 

 plant foods in the soil. 



Lime. — When the value of lime became known it 

 is impossible to ascertain, but we find that the use of 

 both lime and marl was recognised among the Romans. 



