Report of Experiments on the Growth of Wheat. 483 
of dressed corn, or by about 20 bushels per acre per annum, and 
gave the highest weight per bushel of dressed corn in the series, 
but the proportion of corn to straw was no higher than in the 
unmanured produce. The annual produce was very much higher 
during the latter than during the earlier half of the 20 years, but 
it increased much less rapidly during the last few years. 
The questions arise — In what constituent, or class of con- 
stituents, was the unmanured land deficient? and — to what 
constituent, or class of constituents, supplied by the farmyard 
manure, was its increase of produce due ? 
3. A complex mineral manure (plot 5), supplying annually 
more^of potass, soda, magnesiaj lime, sulphuric acid, and phos- 
phoric acid, than was taken off in the crops (but no silica), even 
though used after several years of accumulation of unexhausted 
residue from previous ammoniacal (and mineral) manuring, gave 
annually only about 3 bushels increase over the unmanured 
produce, and nearly 17 bushels less than the produce by farmyard 
manure. The proportion of corn to straw was, however, higher, 
but the weight per bushel of dressed corn lower, than in the 
produce by the farmyard manure. 
4. Ammonia-salts alone (plot 10a), employed for 19 consecu- 
tive years after an application of mineral manure supplying of 
potass about as much as would be removed in the first 3, and of 
phosphoric acid about as much as would be removed in the 
first 5 of the 20 years, gave a considerable, but gradually diminish- 
ing, average annual increase (over the produce without manure) 
— amounting over the first 9 years to rather more than 9 bushels, 
over the last 10 to 7^ bushels, and over the 12 to which our 
summary more particularly refers, to rather more than 7 bushels. 
5. As ammonia-salts alone increased the produce very much 
more than mineral manure alone, and did so for a long series of 
years, it is obvious that the practically exhausted land con- 
tained a considerable excess of available mineral constituents 
relatively to the available supply of nitrogen from soil and at- 
mosphere. The results further show, that the plants growing 
under the influence of a liberal artificial supply of mineral con- 
stituents appropriated scarcely any more nitrogen from natural 
sources than those growing on the unmanured land. 
6. The same mineral manure which alone gave scarcely 
any increase, and the same amount of ammonia-salts (400 lbs.) 
which alone gave so much less increase than the farmyard 
manure, and in a diminishing rate from year to year, gave 
when employed together an average annual increase of about 
21 bushels of corn and 22f cwts. of straw over the unmanured 
produce, or about 1 bushel of corn and 3 cwts. of straw over that 
by the farmyard manure. Larger additions of ammonia-salts to 
