On the Valuation of Unexhausted Manures. 
5 
Barley has now been grown in one field at Rothamsted for 23 
years in succession. On one portion there has been applied, 
every year, a mineral manure, consisting of salts of potass, soda, 
and magnesia, and superphosphate of lime ; and the average 
produce over the 23 years has been 26^ bushels of dressed corn 
per statute acre. On other portions there were used, every year^ 
the same mineral manures, with the addition of ammonia-salts 
or nitrate of soda, and the average produce then reached very 
nearly 49 bushels per acre per annum ; or nearly double that 
by the mineral manures used alone. Indeed, the produce ob- 
tained by using this mixture of mineral and nitrogenous manure 
was even rather higher than that yielded by the use, for 23 years in 
succession on the same land, of 14 tons of farmyard-manure per 
acre per annum. 
In an immediately adjoining field wheat has been grown, 
without manure, and by different descriptions of manure, for 31 
years in succession, and with very similar results. Mineral 
manures alone have given very little increase of produce ; nitro- 
genous manures alone, in the form of ammonia-salts or nitrate 
of soda, have given considerably more produce than mineral 
manure alone ; and the mixture of mineral and nitrogenous 
manures has yielded much more still, and more, of both corn 
and straw, than the annual application of farmyard-manure. 
Thus, then, not only are those manures which are rich in 
nitrogen the highest priced, but direct experiments, extending 
over a long series of years, have shown that nitrogen has in 
reality a higher money-value for the purposes of manure than 
any of the other substances used. 
It will be seen further on, how much the settlement of all 
questions of compensation for unexhausted manures must depend 
upon the estimate formed of the amount, and of the condition, 
of the nitrogen of the manure remaining in the soil ; and how 
much this, in its turn, must depend on the description of the 
manure employed, the character of the soil to which it has 
been applied, the characters of the climate or of particular 
seasons, and the kinds of crop which have been grown since the 
application. 
Unexhausted Manukes. 
When a manure is applied to the soil, what happens? This 
point may be illustrated very usefully for our present purpose 
by reference to direct results obtained at Rothamsted. 
To certain plots given quantities of salts of potass, soda, and 
magnesia, superphosphate of lime, and salts of ammonia (or 
nitrate of soda), have been applied every year ; and for between 
