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XXV. — Report of Experiments on the Growth of IVhcat for 20 Years 
in succession on the same Land. By J. B. Lawes, F.R.S., 
F.C.S., and J. H. Gilbert, Ph. D., F.B.S., F.C.S. 
[Continued from Page 145.] 
II. Effects of the unexhausted residue from previous 
MANURING UPON SUCCEEDING CROPS. 
W hen the same crop has been grown for many years in suc- 
cession on the same land, in some cases with a change of 
manures, and in others with the same manure year after year, it 
is obviously essential to a right interpretation of the results 
obtained, carefully to consider the effects of the unexhausted 
residue from previous manuring upon the succeeding crops. 
The questions of the permanency of effect of different manures, 
and of the tendency to exhaustion which partial manuring may 
induce, are, moreover, of great practical importance, and are 
frecpiently discussed by practical men. 
These questions cannot, however, be satisfactorily dealt with 
without such evidence as the accurate record of the amounts of 
produce obtained year after year, on the application of manures 
of known description and amount, can alone afford. The results 
ot the experiments which form the subject of this Report 
obviously provide data well fitted to aid the elucidation of some 
of the important points involved. The subject is necessarily 
one of detail, requiring analytical as well as field results for its 
full consideration ; but it will be here treated of by reference 
to the field results alone, and only so far as may be necessary to 
aid the proper interpretation of the results themselves, and to 
give some indication of their bearings upon the important prac- 
tical questions — on the one hand of accumulation, and on the 
other of exhaustion. 
The results first adduced will illustrate more particularly the 
effects upon succeeding crops of an accumulated residue from 
previous nitrogenous manuring. 
In the first year of the 20 of the experiments, plot 4 was 
manured with the ashes of farmyard-dung, and gave no increase 
of produce whatever ; during the next 7 years it was manured 
with superphosphate of lime and sulphate of ammonia, the latter 
in amount averaging about 277 lbs. per acre per annum; and 
throughout the subsequent 12 years it received no manure what- 
ever. Table XXIII. shows the produce and increase obtained 
during the 7 years of the application of the artificial manures, 
and also during the succeeding 12 years under the influence of 
the previous heavy cropping, and of the unexhausted residue of 
the previous mineral and ammoniacal manuring : — 
