240 On the Manuring of Grass Land. 



Wheat 25 bushels of 60 lbs., and straw 1| ton = 48 J cwt. 

 Barley, 40 bushels of 63 lbs., and straw 1 ton = 42 J cwt. 

 Hay, first crop, 1^ ton ; second, 1 ton . . . . = 50 cwt. 



Throughout the preparation of the grass manures, a mixing with 

 earth of some kuid (preferahly clay, which has been dried and 

 pulverized) has been recommended, and it may be well to give the 

 reason of this. Grass is covered with a coating of silica, which 

 forms a shiny varnish, just like that seen on the straw of wheat. 

 This silica must be taken up in solution and deposited where it 

 is found, and yet it is quite insoluble itself, and the natural com- 

 pounds existing in the soil are almost insoluble likewise. It is 

 required in large quantity, as an inspection of the above table 

 Avill show, where the number which represents the silica in grass 

 is larger than that which represents any other constituent, l^he 

 same is seen in the analyses of Boussingault, page 222, and re- 

 markably in that of rye-grass by Thompson, on the same page. 

 In order to grow grass, therefore, a due supply of soluble silica at 

 the roots of the plants throughout the season of growth is as requi- 

 site as a supply of ammonia, or potash, or phosphorus, or any other 

 constituent found bv analysis. The natural supply of this element 

 in a soluble state is probably always deficient, and one of the 

 problems of successful agriculture is the supply of a due quantity 

 in a suitable form at the right time. Mixing earth with manurial 

 substances during their decomposition tends to liberate a quantity 

 of silica in soluble combinations ready for use as soon as applied. 

 When decomposition of organic substances takes place, their ele- 

 ments become oxidized and form new compounds. Chlorine 

 unites with hydrogen, and forms hydrochloric acid ; sulphur with 

 oxygen, and forms sulphuric acid : carbon with oxygen, and forms 

 carbonic acid, &c. ; and these unite with alkalies and form salts. 

 How these set free silica in the earth, with which they are in 

 contact, is described by Liebig : — 



" The effect of ammoniacal salts is not the same as that of free ammonia. 

 These salts contain an acid which exerts an action on the constituents of the 

 soil — an action not exerted by pure ammonia. The acids of the aannoniacal 

 salts render the earthy phosphates more soluble in water than they would 

 otherwise be. These acids also render available the silicates, that is, they 

 ])roduce such a decomposition of the natural silicates, that the constituents of 

 these minerals acquire a degree of solubility in solvents, which, while in the 

 form of natural silicates, they either do not possess, or possess in a far lower 

 degree. While the silicates are thus acted on, their silica or silicic acid (ichich 

 is indispensably necessary to the yrarninea/) is brought into a state in which 

 it is soluble in water, so that all the rain-water which comes in contact with 

 it finds and dissolves a certain quantity of silicic acid beyond that quantity 

 which the same amount of rain-wat^r would have found available without the 

 ammoniacal salts. By means of the atmospheric constituents accumulated in 

 the soil, — by means, for example, of annnonia, — the action of tlie mineral con- 

 stituents, which are present in available or soluble forms, is accelerated, that is, 

 increased in a given time. 



