164 ACTION OF SOIL ON FOOD OF PLANTS IN MANURE. 



ought to have done, the conclusion is inevitable, that they 

 had no accurate notion of the nature of their task. 



ISTow, the want of a proper insight into the nature of a 

 phenomenon which is to be investigated is surely the 

 greatest of all difficulties in the way of attaining a practical 

 result. If the unproductiveness of a field for clover and 

 peas depends upon a want of nitrogenous food in the 

 deeper layers of the soil, and upon no other cause, the 

 absorptive power of the various soils for ammonia renders 

 it extremely difficult to enrich the subsoil with tliis ele- 

 ment of food. But the case is quite different with the 

 niti-ates, which penetrate to any depth, as the nitric acid 

 is not absorbed by the soil ; probably, nitrate of soda may 

 afford a means of making a field productive for clover or 

 peas, in cases where there is a deficiency of nitrogenous 

 food. 



As manuring with burnt lime is often found beneficial 

 for clover and also for peas, and a calcareous soil tends, 

 in a special degree, to promote the formation of nitric 

 acid, it is not improbable that it is owing to this property 

 that lime promotes the growth of deep-rooting plants by 

 converting ammonia into nitric acid, and causing nitro- 

 genous food to find its way to the deeper layers of the 

 soil. 



