THE CHEMISTRY OF THE FARM. 417 



phosphate ; but a continuance of such treatment promotes a coarse herb- 

 age. 



The natural clovers of a meadow are destroyed by the continued 

 application of highly nitrogenous manures, a hay consisting almost exclu- 

 ly of grass being produced. The clovers are developed by the appli- 

 cation of manures supplying potash and lime, and by pasturing instead of 

 mowing. 



The perennial character of grass, and the abundance of humus in a 

 soil, present favourable conditions for the collection of nitrogen 

 from the atmosphere ; this takes place to a greater extent on pasture Ian 1 

 than with most other crops. 



LEGUMINOUS CHOPS. Some of these are grain crops, as beans and peas; 

 others are fodder crops, as red clover, sainfoin and lucerne. A striking 

 characteristic of all these crops is the large amount of nitrogen which 

 they contain, the quantity being about twice as great as that found in 

 cereal crops. The quantity of potash and lime in leguminous crops is also 

 very large. The relative proportion of these two bases varies much in 

 crops grown on different soils ; upon a calcareous soil lime will prepon- 

 ite in the crop, but on a clay soil potash. The lime is found chiefly in 

 the leaf. Silica is nearly absent in leguminous crops. 



Tlie nutrition of leguminous crops is not at present perfectly under- 

 stood. A good crop of red clover, when cut for hay, removes a large 

 quantity of nitrogen from the land, but it nevertheless leaves the surf 

 soil actually richer in nitrogen than it was before from the residue of 

 roots and stubble left in the soil. From whence is this large quantity of 

 nitrogen obtained ? It must be procured either from the subsoil, or the 

 ,osphere. The former seems the more probable, as experiments have 

 hitherto failed to prove that leguminous plants have any special power of 

 obtaining nitrogen from the air. The question is further complicated by 

 tact that nitrogenous munuivs generally produce but little effect upon 

 nninous crops. It seems pretty certain that leguminous crops pos- 

 nt a distinct source of nitrog.-n ; they are probably cap.i 

 of feeding on soim- compounds of nitrogen and carlx.n which are com; 



to nt her crops, ami hence the facility with which th.-y acquire 

 nitrogen from the soil. A deeply rooted crop like red clover col! 



'oinpoiimU from tin- sul.soil, and accumulates nitrogen at the 

 surface in tin- form of a crop. 



The particular food supply of a leguminous crop becomes exhausted by 

 i cropping, an. 1 the land is said to be " clover " or "bean Mck ;" 



AA 



