42 THE CHEMISTRY OF THE FARM. 



The perennial character of grass, and the abundance of 

 humus in a pasture soil, present favourable conditions for 

 the collection of nitrogen from the atmosphere ; this takes 

 place to a greater extent on pasture land than with most 

 other crops. 



Leguminous Crops. — 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 le- 

 guminous 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 preponderate in the 

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

 in the leaf. Silica is nearly absent in leguminous crops. 



The nutrition of leguminous crops is not at present 

 perfectly understood. A good crop of red clover, when 

 cut for hay, removes a large quantity of nitrogen from the 

 land, but it nevertheless leaves the surface 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 atmosphere. 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 the fact that nitrogenous manures 

 generally produce but little effect upon leguminous crops. 

 It seems pretty certain that leguminous crops possess to 

 some extent a distinct source of nitrogen ; they are pro- 



