for Twenty Years in succession on the same Land. 303 
the experiments, in that of the wheat 8 experimental crops had 
aheady been taken. During that period, however, large quantities 
of superphosphate of lime, and potass, soda, and magnesia-salts 
had been applied, as well as liberal dressings of ammonia- 
salts. It would hardly be concluded, therefore, that the plot had 
suffered in wheat-growing condition by its previous treatment. 
Still, though the quantity of wheat-grain averages nearly the 
same over the two periods, that of the straw and total produce 
falls off considerably during the latter half of the 20 years. On 
the other hand, with the barley the quantity of corn is slightly 
higher, that of straw slightly lower, and that of total produce 
almost identical, over the two halves of the total period. 
It is possible, therefore, that the previous history of the plots 
may be somewhat to the detriment of the results with wheat ; but 
it is not probable that it has had much adverse influence. 
Taking the results as they stand, the barley gives, with exactly 
the same manure over 20 years, an average annual produce of 
more than one-half more corn, more than one-sixth more straw, 
and about 1400 lbs. more total produce (corn and straw together) 
than the wheat. If, instead of the acreage produce, the increase 
over that by the same mineral manures without ammonia be taken, 
the general result is the same ; namely, a great deficiency of corn, 
of straw, and of total produce, of wheat compared with barley, by 
the same manuring. How is this to be explained ? 
In reference to this point attention may here be recalled to the 
facts — that whilst the wheat is autumn-sown and autumn-manured, 
the barley is both spring-sown and spring-manured ; and that 
when ammonia-salts are sown in the autumn, the winter drainage 
carries with it large amounts of the nitrogen of the ammonia-salts 
in the form of nitrates. The probable extent of the loss that may 
thus arise, will be consideied in Section IV. It must suffice here, 
therefore, to state in general terms that existing evidence leads 
to the conclusion that it may be very considerable. 
The difference of result obtained with wheat and with barley 
is again illustrated, under somewhat different conditions, in Table 
XXXVII. (see next page). The comparison is between the 
effects of the " mixed mineral manure" and 400 lbs. of ammonia- 
salts, annually applied to the two crops. For wheat the produce 
is averaged over 20 years (1852-'71) of the treatment, and also 
over the first 6 years only, those being the seasons in which the 
same experiment was made with the barley. 
In all previous comparisons between wheat and barley the 
quantity of produce per acre has been taken, and not the increase 
of produce over that without manure, or, as the case may be, the 
increase by mineral manure and ammonia-salts over that by 
mineral manure without ammonia. It has, however, been re- 
