90 THE CHEMISTRY OF THE FARM 



ploughed, and exposed a whole year to atmospheric 

 influences, and finally sown with wheat. In the case 

 of a clay soil this treatment would probably lead to the 

 following results : (1) An improvement in the mechani- 

 cal texture of the soil. (2) The storing of water in it. 

 (3) The disintegration of some of the mineral silicates, 

 whereby potash and other necessary ash constituents 

 of plants would be liberated and made available for 

 vegetation. (4) The absorption of some ammonia from 

 the atmosphere by the soil. (5) The oxidation of 

 ammonia, and of the vegetable and animal remains in 

 the soil, carbonic acid and nitrates being produced. 



The production of nitric acid is one of the most 

 important results of a bare fallow. In ordinary farm 

 soils at Eothamsted, left as bare fallow, there has been 

 found at the end of the summer 34 — 55 lbs. of nitrogen 

 per acre in the form of nitric acid (equal to 218 — 352 

 lbs. of nitrate of sodium) in the first twenty inches 

 from the surface, the quantity depending on the rich- 

 ness of the soil in nitrogenous matter, and the character 

 of the season. The whole amount of nitrates pro- 

 duced during the fifteen months that the land remains 

 without a crop has been estimated at not less than 80 

 lbs. of nitrogen per acre for the fields under ordinary 

 cultivation at Eothamsted.^ Supposing the season of 

 fallow, and the following autumn and winter, are 

 fairly dry, this increase in the available nitrogenous 

 food will probably enable the soil to produce twice as 

 much wheat as it could do without a fallow. If, how- 

 ever, the soil is exposed to heavy rain, the nitrates 



• A nearly similar quantity of nitrates will often be available to cropg 

 euch as turnips, for which the land receives a sununer tillage. 



