THE CULTIVATION OF FARM CROPS. 531 



weeds ; it (4) promotes good drainage by rendering tenacious soils more 

 friable and porous ; and it (5) not only effects a considerable diminution 

 in the number of horses,but,by relieving them of their heaviest work, en- 

 ables you to keep those which are still necessary at less expense. 



Of the two main systems of cultivating by steam, "the double-engine 



in necessarily involves the largest outlay to begin with; but where 



the farm is large enough to afford a reasonable amount of work for the 



tackle, it will cultivate at a less cost per acre than the single engine 



"m. 

 BARE FALLOW. A bare fallow is one of the oldest modes of preparing 



ft >r wheat. The soil is ploughed, and exposed a whole year to atmos- 

 pheric influences, and finally sown with wheat. Intfhe case of a clay soil, 

 this treatment would probably lead to the following results : 1. An im- 

 provement 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 remains in 

 the soil, nitric acid being produced. 



The production of nitric acid is probably the most important result of a 

 bare fallow. In soils at Rothamsted left as bare fallow, there has been 

 found at the end of the summer 34 55 Ib. of nitrogen per acre in form of 

 nitric acid in the first 20 inches from the surface. Supposing the season 



tllow is a fairly dry one, the increase in the available nitrogenous food 

 will probably enable the soil to produce twice as much wheat as it could 

 do without this treatment. If, however, the soil is exposed to heavy rain 



nitrates produced will be more or less wash.-d out, and the benefit of 



y diminished. Bare fallow can be used systematically 



\ -anta^f only on clay soils having a considerable absorptive power 



for ammonia, and in a tolerably dry climate ; under other c-i remittances a 



continuance of the practice mu^t issue in a serious loss of s.il n 



GEAIN CROPS. 



WHKAT. The soil best a-lapte'l to the growth of \vh--ai is a deep loam 



iiK. with. i lry sul^oil heavy land, m >rc >r less compact. 



tically, h\\ irly every kind of Ian 1, wln-t 'IT elay, loam, chalk, 



M.I, \\ill jn-.xlucc- fair crops of wheat if in good con-lit inn, un_ 



the climate Ll really unfavomaM . It is not 



