Experimental Plots at Rothamsted, from 1864 to 1883. 443 
nitrogen each year, a quantity much less than that supplied in 
the dung — gives, over a period of 32 years, a total produce in 
straw and corn of 6982 lbs. per acre, or 1200 lbs. more than that 
obtained on plot 2. 
It is quite evident from these results, that the amount of 
organic matter in the crop bears no relation to that supplied in 
the manure ; and that the atmosphere, and not the soil, is the 
source of this supply. 
The farmyard-manure not only furnished a large amount of 
organic matter to the soil, but it also furnished a larger amount 
of nitrogen than the artificial manures on plot 7. To produce 
a crop equal to that grown by artificial manures on plot 7, we 
estimate that the farmyard-manure furnished the soil with more 
than twice the amount of nitrogen supplied by the artificial 
manures. 
In the two years of 1863 and 1864, on plot 2 — which was 
estimated to supply 400 lbs. of nitrogen — the total produce 
amounted to 13,653 lbs. ; while that of plot 16 — which furnished 
144 lbs. of nitrogen in salts of ammonia — was 20,043 lbs., or 
in other words, more than 6000 lbs. excess of crop in two 
years ! 
As so much less growth can be obtained from the nitrogen in 
dung, than from that in salts of ammonia, or nitrate of soda, 
it is evident that the nitrogen in these substances must be in 
different chemical combinations. 
In the soil, the nitrogen, which constitutes one of the most 
important elements in what we aescribe as permanent fertility, 
is always in combination with carbon. In this form it is both 
insoluble and inactive, and it only becomes an active food for 
vegetation when, by the process of nitrification, it ceases to be 
in combination with carbon. 
In dung, by far the greater part of the nitrogen is in combi- 
nation with carbon ; and, when we consider the various sub- 
stances which make up a mass of manure, we recognise at once 
that the individual periods of their decay, or nitrification, must 
vary greatly. The carbon may be separated from the nitrogen 
in urine in the course of a few weeks or months, while it may 
take many years to nitrify portions of the woody matter of 
straw, especially on heavy land. 
We have mentioned that in consequence of the inactive condi- 
tion of much of the nitrogen in dung, it requires a considerably 
larger application of that substance, to grow the same amount of 
crop as that produced by a much smaller application of nitrogen, 
in the more active form of ammonia and nitrates. This being 
the case, it is evident that in the soil where dung has been 
employed, we ought to find a larger amount both of carbon and 
