494 Report of Experiments on the Growth of Wheat. 
Avitliout manure, and smaller amounts of increase, especially of 
corn, with the nitrogenous manures. Still, the general character 
of the average results over the four years, is the same as in the 
other cases. There is but a small amount of increase by the 
mixed mineral manure alone, much more by ammonia-salts 
alone, and more still by the mixed mineral manure and ammonia- 
salts together. 
But, independently of the evidence of direct experiment, such 
as is afforded in the results above referred to, we would here 
reiterate the opinion given in substance in former papers, and 
founded on a very extensive acquaintance with the practical 
experience of farmers in the use of artificial manures in every 
district of Great Britain for many years past, that, in 99 cases 
out of 100 in which wheat grown in the ordinary course of 
agriculture requires further manuring, it would be much more 
increased by the application of nitrogenous than of purely mineral 
manures ; in other words, that in the ordinary course of agri- 
culture with rotation, as practised in this country, the supply of 
mineral constituents immediately available for the wheat crop, is 
almost invariably in excess relatively to the immediately avail- 
able supply of nitrogen from the atmosphere, or the accumulated 
stores within the soil itself. Furthermore, with few exceptions, 
the worse the so-called " condition " of the land, that is, the more 
it is in the agricultural sense exhausted, the more striking would 
be the effect of exclusively nitrogenous compared with that of 
exclusively mineral manures. 
What, then, are the common practices of British agriculture 
which lead to this result ? 
Let us take as an example, as we have done before, the practice 
of the so-called four course rotation — of roots, barley, clover (or 
beans), and wheat. Let us further assume, for the sake of argu- 
ment, that on the average 30 bushels of wheat, 35 bushels of 
barley, and the meat from the consumption of 10 tons of swedes, 
and clover equal to 6000 lbs. of clover hay (or 1500 lbs. of bean 
corn), are the products sold from each acre of the farm in the 4 
years, and that the straw of the corn crops, and the excrements 
from the animals feeding on the roots and the clover or beans 
are retained on the farm as manure, and returned periodically 
to the land. Confining attention, for the sake of simplicity of 
illustration, to those mineral constituents which, so far as exist- 
ing knowledge goes, are the most likely to become relatively 
deficient in the majority of soils, it may be estimated that, under 
such a course, the average annual loss per acre by the sale of 
corn and meat, would be of potass from 4£ to 5 lbs., of phos- 
phoric acid from 7 to 8 lbs., and of silica about 3 lbs. 
