Scientific Agrieultwe. 



72 



Hilgard has abundantly demonstrated the great value of gypsum (laud 

 plaster) in renovating "alkali"' soils iu the arid portions of the United States. 

 Wherever too much sodium carbonate (black alkali) is the cause ol the unproductive 

 condition of the soil the gypsum reacts with it, producing sodium sulphate 

 and carbonate of lime, whereby the alkalinity may be sufficiently reduced to 

 render possible the profitable production of crops. In case protosulphate of 

 iron and certain other poisonous compounds are present in soils, liming so 

 changes them as to render them harmless to plants. 



When the remains of plants undergo decay upon soils deficient in carbonates 

 of lime and magnesia, acid or sour humus is liable to be produced, which is 

 supposed to be particularly noxious to most agricultural plants, though appa- 

 rently not detrimental to the growth of the cranberry, watermelon, rhododendron, 

 azalea, and a few other herbaceous plants, trees, and shrubs. Such conditions 

 are liable to occur even in upland aud naturally well-drained soils. Liming is 

 in all such cases an effectual and probably the most economical remedy. 



PHYSICAL EFFECTS OF LIMING. 



Many clay soils when wet by rains are not porous enough to allow the 

 water to pass through them with sufficient rapidity, in consequence of which 

 they become water-logged, and air which is necessary for the healthful deve- 

 lopment of plant roots within the soil is excluded. In times of drought, also, 

 such soils cake readily, thus becoming more difficult to till and less adapted 

 physically to the growth of plants. Liming is an effective preventive or remedy 

 for all of these unfavourable conditions. Upon certain loamy soils containina 

 considerable clay, liming often renders the surface more friable and less liable 

 to form a crust upon drying. The improvement of drainage brought about by 

 liming is one of the most effective means of preventing surface washing. When 

 heavy rains occur on limed soils the water sinks into the soil instead of rush 

 ing over the surface, carrying the fine soil particles with it and thus producing 

 galls and washes. 



Soils which are composed of siliceous sands are frequently benefited by 

 being rendered more compact by liming. On such soils pulverized limestone is 

 preferable to ground burnt lime, hydra ted lime, or even air-slaked lime, 

 owing to the more powerful action of the latter, and the best material to employ 

 where it is obtainable is a clay marl containing a fair amount of carbonate of 

 lime. The clay, as well as the lime, tends to materially improve the physical- 

 condition of the soil. It should also be the aim to increase the amount of 

 organic matter in such soils by the use of muck and stable manures, or by 

 the occasional plowing under of a green crop or of sward. 



EFFECT OF LIME ON THE ACTION OF MICROSCOPIC ORGANISMS IN THE SOIL. 



Many important changes are produced in the soil by organisms so small that 

 they can only be observed by the aid of the most powerful microscopes. Some of 

 the changes of this character in which lime plays an important part are the 

 following :— 



(1) The change of ammonia and of nitrogen in organic matter, such as blood, 

 meat, fish, tankage, plants, etc., into nitrates, the form in which it is chiefly assimi- 

 lated by most cultivated plants. This is known as the process of nitrification 

 and is promoted by the presence of lime in soils. 



(2) The decomposition of organic matter in muck and other soils. In this 

 process the production of carbonic acid is much accelerated by the use of lime 

 This carbonic acid in turn so acts upon inert plant food of the soil as to make 



