loOcT.. 1912.' 'L'hc Fracticc oj Uni'mg. 609 



2. AciioN OF Lime on the Soil. 



The object of applying lime to the soil is not the same as that involved 

 in the application of ordinarv fertilizers. Fertilizers, such as super- 

 phosphate, Thiiinas' phosphate, guano. &c., supply the soil with elements 

 of plant food in which the .soil is actually deficient, and they are applied 

 in relativelv small amounts, i.e., from \ cwt. to i cwt. per acre under 

 ordinarv farming conditions. I.ime. however, is applied becau.se of its 

 indirect effect upon the soil. i.e.. because of the effect it produces upon 

 the chemical composition and i)hysical and biological condition of the 

 soil, and not because it is actually wanted to supply the plants' immediate 

 requirements. It is not in itself a plant food, as phosphoric acid is, 

 except to a very limited extent, but nevertheless, the application of lime 

 in suitable quantities has a most marked effect on soils wanting in lime. 



Lime corrects soil acidity. — Perhaps the most important effect is that 

 lime being alkaline neutralizes the acidity of the soil, and thus 

 promotes vegetation. Most of our agricultural crops cannot thrive 

 in a soil that is sour or acid, but must have a .soil that is 

 neutral or basic in character. Soils tend to become sour from 

 various cau.ses. In regions of heavy rainfall, lime is being constantly 

 washed out of the surface layers. At Rothamstead this loss amounts to 

 800 lbs. of lime per acre per annum. Carbonic acid gas, which is 

 present in all soil water, has the power of dissolving lime and carrying 

 it off in the drainage waters. It is the presence of lime in solution that 

 causes the " hardness " of certain waters, and it is owing to the power 

 of the .soil waters to dissolve lime that the formation of limestone caves 

 is brought about. 



Again, the organic matter or the humus of the soil is constantly under- 

 going decomposition, and, as a result, various organic acids are formed 

 in much the same wa\, as ensilage becomes acid and sour on exposure. 

 Now. lime is the natural base by means of which these acid substances in 

 the soil are neutralized. Hence, if for any reason the soil has become 

 acid, then a dressing of lime is an indispensable preliminarv for satis- 

 factory crops. This is more particularly true of such leguminous crops 

 as clover and lucerne, for these will not thrive on soils that are sour and 

 acid in character. 



Lime liberates flant fi'od. — Lime is a very powerful soil stimulant, 

 and is very effective in liberating plant food. Most of the phosphoric 

 acid and potash present in the .soil is present in insoluble combinations that 

 cannot be used by the plant. 



The application of liberal dressings of lime renders such insoluble 

 compounds as iron and aluminium phosphates more susceptible to the 

 solvent action of the soil water bv con\erting them into phosphate of lime,* 

 and thus making them immediately available to the crop. 



Lime also replaces potash in its insoluble combinations in the soil, and 

 this probablv accounts for the beneficial action of lime, particularly when 

 applied in the form of gvpsum, on those crops which require relatively 

 large amounts of potash, e.g., lucerne, clover, and other legumes. The 

 action of lime on the organic portion of the soil is extremely important. 

 It hastens the decay and decomposition of the organic matter, and greatly 

 promotes the process of nitrification. 



Lime imfroves the mechanical condition of the soil. — The effect of 

 lime on the physical constitution of the soil is verv marked. Stiff clay 

 soils are rendered more friable, far less adhesive, more open and porous 



