366 
MESSRS. J. B. LAWES AUD J. H. GILBERT OR THE RESULTS OF 
less (though still an excess) of mineral constituents supplied—the description and 
condition of the herbage (on plot 18) were inferior; a somewhat larger proportion of the 
produce was made up of a few of the poorer grasses ; leguminous herbage was greatly 
reduced; and among miscellaneous species Rumex cicetosa was more prominent. 
Again, the results afford a pretty direct test of the validity of the principle ac¬ 
cording to which all, and neither more nor less, of the constituents removed from the 
land in crops, should be returned to it in manure. 
In Ltebig’s earlier writings he did not recognise the fact that a considerable propor¬ 
tion of the constituents removed from the land in crops is, in the actual practice of 
agriculture, periodically returned to it, and that, therefore, the loss to the soil is not 
measured by the amount of constituents in the crops grown, but more nearly by that 
in the produce sold off the farm. Further, his recommendations for the carrying out 
of his principle were confined to the application of the “ mineral” or ash-constituents; 
he maintaining that the atmosphere would supply the necessary nitrogen. It is true 
that subsequently, in the course of controversy, he changed the meaning of his terms, 
and then included ammonia-salts in the category of mineral manures. It is seen, 
however, that even with a supply of the amount of nitrogen, as well as ash-consti¬ 
tuents, contained in 1 ton of hay, not two-thirds of a ton of increase of produce was 
obtained. 
With regard to the applicability of the principle under the actual conditions of 
practical agriculture, attention may be called to the following considerations 
In the first place, there is no conceivable condition of chemical combination, and of 
distribution within the soil, in which the various constituents could be annually sup¬ 
plied so as to be all annually taken up by growing vegetation; and there is conclusive 
evidence that, in some cases, the unrecovered residue is, in greater or less part, lost by 
drainage ; and that, so far as it is not so, it becomes so locked up, or distributed within 
the soil, that it is—at any rate, very slowly, and in some cases, perhaps, never fully— 
recovered in subsequent crops. 
In the second place, the principle ignores the difference in the character and capa¬ 
bilities of different soils. Take, by way of illustration, two extremely opposite cases : 
A light, porous, almost exclusively sandy soil, which itself yields up little or nothing 
to growing plants, but which may, nevertheless, produce good crops under high farming, 
will probably suffer great loss of manurial constituents by natural drainage ; so that, 
if no more were to be supplied than were removed, there must obviously be a decline 
of fertility. Suppose, on the other hand, a rich and deep loam, which would, under 
good mechanical cultivation and drainage, supply annually a considerable amount of 
potass, for example, to say nothing of other constituents, for hundreds and perhaps for 
thousands of years ;—surely, in such a case, it is not necessary to supply as much in 
manure as has been removed in the crops ? 
Further, experience teaches that, in the actual condition of our soils, and of agri¬ 
cultural practice, the exact composition of the crops we remove, or wish to grow, is no 
