400 On Maiden, or Virgin, Soil. 



been produced from rotten pieces of turf or decayed straw mixed 

 with the soil, or from having chanced to get what is called a 

 good tid in the working, having been pulverised dry, and, con- 

 sequently, keeping more open in the pores. This is one of the 

 principal benefits, also, of farm manure, and is one reason why 

 we may always expect this sort of manure to be more lasting in 

 its effects than any of the very concentrated manures. The 

 undecayed portions of the stable manure not only yield food 

 as they decay, but, being intimately mixed with the soil, leave 

 it full of pores by the void which their decay occasions ; and 

 by this means admit and retain heat, so necessary in promoting 

 the chemical action of the various ingredients in the soil, and 

 reducing them to soluble substances fit for absorption by the 

 roots. By being full of pores, the rain is admitted ; and by the 

 pores being small, the water is retained by capillary attraction, 

 excessive evaporation prevented, and the soil kept in a proper 

 state as to moisture, a certain quantity of which only is needed 

 to assist the decomposition and absorption of the food ; too much 

 or too little, an excess on either side, being both injurious. The 

 carbonic acid, ammonia, nitric acid, and other substances con- 

 tained in the air and brought down by every shower of rain, are 

 also thus admitted into the soil, and also the oxygen and nitrogen 

 of the air itself. 



It has been denied that this last substance, namely, the 

 nitrogen of the air, is at all useful to plants, and that the whole 

 of the nitrogen of plants is derived by the roots, not the leaves, 

 from ammonia alone, or, at farthest, ammonia and nitric acid. 

 This theory of the French and German chemists, however, has 

 not yet been confirmed by practice. It has been stated that 

 ammonia is the sole substance of any value in manure, and tables 

 have been furnished by which the relative value of manures is set 

 down according to the quantity of ammonia they contain. It will 

 follow, of course, that crops will exhaust ground according to the 

 quantity of ammonia they extract from it. Ammonia is so 

 mixed up with the other ingredients in manure, that it will take 

 some time before we can decidedly talk as to the truth of the 

 first proposition. Manures containing much ammonia do, in- 

 deed, seem most valuable, but whether altogether from the 

 ammonia they contain, or the way it is mixed up with the other 

 ingredients, is not so easily decided. To the last proposition, 

 namely, that crops exhaust according to the quantity of am- 

 monia they extract from the soil, or according to the quantity of 

 nitrogen they contain, there seem also many corroborations. 

 Wheat, and other crops containing much nitrogen, are very 

 scourging exhausting crops ; and a period of rest and dressings 

 of manure are needed before any other crop will succeed well. 

 If we follow out the theory, however, and apply it to another very 



