64 THE CHEMISTRY OF THE FARM. 



exposed a whole year to atmospheric influences, and finally 

 sown with wheat. In the case of a clay soil this treat- 

 ment would probably lead to the following results : 1. An 

 improvement in the mechanical texture of the soil. 2. 

 The disintegration of some of the mineral silicates, 

 whereby potash and other necessary ash constituents of 

 plants would be liberated and made available for vegeta- 

 tion. 3. The absorption of ammonia from the atmosphere 

 by the soil. 4. The receipt of both ammonia and nitric 

 acid from the air in the form of rain. 5. The oxidation 

 of ammonia, and of the vegetable and animal remains in 

 the soil, carbonic and nitric acids being produced. 



The production of nitric acid is probably the most 

 important result of a bare fallow. In ordinary farm soils 

 at Rothamsted left as bare fallow, there has been found 

 .at the end of the summer 34 55 Ibs. of nitrogen per acre 

 in the form of nitric acid in the first 20 inches from the 

 surface, the quantity depending on the richness of the soil 

 in nitrogenous matter and the character of the season. 

 The whole amount of nitrates produced during the 15 

 months that the land remains without a crop has been 

 estimated at not less than 80 Ibs. of nitrogen per acre for 

 the fields under ordinary cultivation at Rothamsted. Sup- 

 posing the season of fallow, and the following 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, however, the 

 soil is exposed to heavy rain, the nitrates produced will be 

 more or less washed out, and the benefit of the fallow 

 greatly diminished. Amass of soil at Rothamsted, 5 feet 

 deep, left for 20 years uncultivated, unmanured, and kept 

 free from weeds, has lost by drainage in the last 13 years 



