Gi uwtk iij Red Clover by different Manures. 
l'J7 
'inoro where Rape-cake, or Salts of Ammonia ]uul been applied in 
lS4il, than wliere mineral manures only had been employed. 
Exhaustion of the Soil. — Some of the plots in the experimental 
(Jlover-field liave doubtless been subjected to great exhaustion of 
certain constituents, bv the removal of the whole of the produce, 
Avithout adequate restoration by manure. On others, however, 
tliere has been considerable accumulation of constituents. Cal- 
<ni];iti()n shows, indeed, that, on many of the plots, there have 
been much larger quantities of every " mineral "' constituent 
supplied in the manures, than have been removed in the total 
produce, during the entire period of the experiments. Of 
■certain organic constituents, however, including nitrogen, moi'e 
has been taken off in the crops than has been supplied in the 
manures. But if, in the cases in question, the produce grown 
without manure, be deducted from that grown with it, it then 
appears, that the manures have provided very much more, not 
onlv of the mineral constituents, but of nitrogen also, than was 
contained in the "increase due to the manures. It cannot be 
supposed, therefore, that, in the instances here referred to, any of 
the ultimate elements of the crop could be wanting. 
It should be remembered, too, that in some of the experi- 
ments mineral manures alone were employed, in others mineral 
manures and ammonia salts, and in others large quantities of 
farmyard dung, mineral manures, and ammonia -salts, and so on ; 
so that the proportions, and conditions of combination, in which 
the different constituents were supplied, were very variable. 
How then are we to account for the fact, that Avhilst, under 
the conditions described, the Clover-plant would not grow 
healthily in the experimental field, we have been able to cut 
fourteen crops from seed sown six years ago in a garden only 
a few hundred yards distant? Are we to suppose, simply, that 
the ultimate constituents required by the Clover, were more 
abundantly available to the plant in the garden soil ? or is it 
that they there existed in different states of combination ? It Avill 
not be out of place to make a few observations bearing upon the 
Jatter supposition. 
According to Mulder, who has investigated the organic com- 
pounds of the soil, the vegetable matters, rich in carbon, decom- 
posing in the soil, go through a gradationary series of changes 
before being finally converted into carbonic acid. He supposes 
the intermediate compounds to constitute a series of acids, which 
■combine with ammonia, and with fixed bases, in the soil, forming 
so many organic-acid salts. Now, if we were to suppose that 
some plants (Clover for example) required for healthy growth a 
certain proportion of their food to be presented to them in the 
form of such carbon-compounds, more complex than carbonic 
^icid, and perhaps combined with ammonia, we should then the 
