216 
Experiments on the Growth of Wheat. 
of the others, than is observable in that of the produce of corn 
alone. We now proceed to a study of the results of the individual 
manures; and in the course of it it will be rendered pretty obvious 
what was the nature of the unexhausted matters of previous- 
manuring, which gave this greater produce in the first year of the 
experiment. 
Plot 1, which was unmanured, gave 39^ bushels of dressed 
corn the first year, 15^ the second, 21i the third, and 16| the 
fourth ; the average of the four years being 23j bushels, and that 
of the last three years nearly 18 bushels ; which latter amount is 
nearly 22 bushels less than was obtained on the same plot in the 
first year. This average of 18 bushels per annum yielded after 
the condition of the land derived from recent previous manuring 
had been reduced by the first crop, is very nearly exactly that 
obtained annually on the much heavier soil of Rothamsted. Tiiis. 
is a result which would scarcely have been anticipated ; and it 
shows that, at any rate for the present, the annually available 
supplies of minerals in the soil are fully equal to the not very 
widely differing atmospheric resources of the two localities, as- 
judged both by the results obtained, and by a comparison of the 
meteorological registries of the several seasons. 
Plot 2, which was manured with salts of potash, soda, and mag- 
nesia, and super-phosphate of lime, gave o4t bushels of dressed 
corn in the first year, rather more than 19 in the second, 19f in 
the third, and 18i in the fourth. It is seen, therefore, that there 
is only a variation of about 1 bushel during the last three 
years ; and that the average of these last three years is about 
15 bushels less than was obtained in the first year. It is obvious 
that whatever were the elements of fertility present in the soil 
which were the source of the larger crop of the first year, they 
were in no way restored by the mineral substances supplied in 
the experimental manure. Again, comparing the produce of this, 
mineral mixture with that of the unmanured plot, we find that 
taking the four years together there was actually rather more corn, 
obtained without manure than by the minerals ; the tendency of 
the latter being to increase the growth of straw, of which, taking 
the last three years together, there was about half a ton more 
obtained by means of the minerals. It is obvious therefore that 
mineral manures alone did little to remedy the characteristic 
exhaustion induced by the growth of the first crop of wheat, and 
that the annual mineral supplies of the soil were at any rate equal 
to the natural annual supply of nitrogen available for the growth 
of the crop. 
In the next experiments (Nos. 3 and 4), the manure employed 
in each case consisted of 200 lbs. of sulphate of ammonia and' 
200 lbs. of muriate of ammonia per acre ; but on Plot 3 they were 
sown in the autumn at the same time as the manures of all the 
