ON THE USE OF LIME, MARL, AND SHELL-SAND. 29 



The different quantities of lime which are removed by those 

 crops partly, no doubt, explain why lime favours the growth of 

 some crops more than others, and partly also why it is necessary 

 to renew the process of liming from time to time. 



3. Lime exercises a beneficial effect upon the organic matters in 

 the soil. 



Organic matters are present in all soils in larger or smaller 

 quantities : and under good cultivation their proportion increases 

 in ordinary circumstances every year. Now although organic 

 substances on the whole are beneficial to vegetation, they will 

 cease to be so when they have accumulated in too large a pro- 

 portion. Lime, on account of its caustic properties, greatly 

 facilitates the destruction of organic matters, and thus prevents 

 their accumulation to an injurious extent. Hence lime is fre- 

 quently added to compost heaps with a view to hasten the de- 

 composition of both vegetable and animal matters, and it has 

 been found to answer that purpose exceedingly well. Lime no 

 doubt exercises an analogous effect upon the organic matters in 

 the soil. During the decomposition of the organic substances, 

 carbonic acid is produced in abundance, and also a small quan- 

 tity of nitric acid. Both carbonic and nitric acid are highly 

 conducive to the luxuriant growth of plants ; and their produc- 

 tion, under the influence of lime, consequently accounts in some 

 degree for the beneficial effects of liming. 



The roots, leaves, and other vegetable remains of former crops, 

 in a comparatively fresh or undecomposed state, it is well known, 

 scarcely produce any fertilizing effect upon vegetation, but they 

 become excellent fertilizers when their organic tissue has been 

 more or less destroyed by the process of decay or putrefaction. 

 They then become converted from an inert to an active state, and 

 in this state exercise a beneficial effect upon vegetation. Now 

 lime possesses the power of hastening the change of inert 

 vegetable matter into active fertilizing substances, and will there- 

 fore prove especially useful on soils abounding in organic matter. 



Its alkaline properties moreover render lime peculiarly ap- 

 plicable for neutralizing any free acid existent in the soil. The 

 prejudicial effects of sour humus on vegetation, as exhibited in 

 the produce of boggy or peaty land, are well known to practical 

 men, and also the benefit which results from an abundant supply 

 of caustic lime to such land. Lime not only combines with the 

 organic acids constituting the sour humus and thus sweetens the 

 soil, but it also hastens the decomposition of the organic matters 

 which give rise to the formation of sour humus, and thus removes 

 also the cause of its injurious effects. 



Whilst speaking of the action of lime on organic matters, we 

 would not forget to mention that all organic substances contain 



