53G Abstract, Report of Agricultural Discussions. 
required for the growth of plants, and require only to bo thoroughly 
penetrated by the air in order to furnish an unlimited quantity of food. 
The atmosphere really exercises a most beneficial effect both on the 
inorganic aud organic constituents of the soil. I have alluded to 
the large quantity of carbonic acid present in the air which exists in 
the interstices of the soil, but this supply cannot be produced unless 
the air finds its way into the soil. An excess of organic matter in 
the shape of decaying roots or leaves is so injurious, that where it 
exists in soils which are not easily penetrated by air it would 'be much 
better for it to be burnt altogether away. At first sight this may 
appear to involve a great waste of useful material in clay-soils ; but 
if the beneficial effect bo greater than the sacrifice, it can scarcely 
be called a waste ; for although serious doubt has been entertained 
respecting the utility of burning, some soils arc with so much difficulty 
penetrated by air that burning is the only way of destroying the 
organic matter, which when present in an imperfectly aerated con- 
dition is rank poison to most cidtivated plants. It is certain that the 
destruction of sour humus, as it has been called — though in a chemical 
point of view all humus is acid- — has been attended with most bene- 
ficial effects, and when recourse cannot be had to proper means of 
aeration, this destruction has been practised with very great advan- 
tage to the succeeding crop, even if, as in the case of turnips, it 
would bo otherwise benefited by the presence of carbonaceous matters 
in the soil. When, however, we can effect the destruction of organic 
matters by the atmospheric oxygen, the practical result, I have no 
doubt, will be greater ; for not only does the air, and more especially 
the atmospheric oxygen, act upon the organic matters in producing 
carbonic acid, but it also has an important effect upon them in pro- 
ducing nitrates in the soil. 
The quantity of organic nitrogen in the soil is very large. Some 
years ago I made an experiment with the view of ascertaining how 
much nitrogen was present after the clover crop had been removed, 
and I ascertained that, taking an acre as the experimental area, it 
was equivalent to rather more than the amount of nitrogen present in 
8 cwt. of Peruvian guano. It has been found that the clover crop is 
the most excellent preparation for the succeeding wheat, and it is 
known now as a fact, that after growing a good crop of clover a very 
large amount of root is left in the soil. It cannot be maintained that 
the nitrogen, to the whole extent I have stated, will be available in 
the shape of nitric acid ; yet, if only one half becomes so available, 
the reason will at once bo seen why a good crop of clover is almost 
invariably followed up by an abundant crop of corn. But in order 
that the beneficial effect should take place, it is most essential that 
the soil should be penetrated by the air, and that after growing a 
good crop of clover immediate steps should be taken to work the soil, 
for the better the soil is worked by proper machinery the sooner the 
clover-ley is broken up, the sooner atmospheric air enters the soil, the 
more rapidly the nitrogenous constituents of the root are destroyed, 
and the more abundantly arc nitrates formed in the soil. I never 
