Clover as a Preparalory Crop for Wheat. 
403 
witliout the intercalation of clover. What, it may be asked, is 
the explanation of this apparent anomaly ? 
In taking up this inquiry 1 was led to pass in review the 
celebrated and highly important experiments, undertaken by Mr. 
Lawes and Dr. Gilbert, on the continued growth of wheat on the 
same soil lor a long succession of years, and to examine likewise 
carefully many points, to which attention is drawn by the same 
authors in their memoirs on the growth of red clover by different 
manures, and on the Lois Weedon plan of growing wheat. 
Abundant and most convincing evidence is supplied by these 
indefatigable experimenters that the wheat-producing powers of 
a soil are not increased in any sensible degree by the liberal 
supply of all the mineral matters which enter into the composition 
of the ash of wheat, and that the abstraction of these mineral 
matters from the soil, in any much larger proportions than 
possibly can take place under ordinary cultivation, in no wise 
affects the yield of wheat, provided there be at the same time a 
liberal supply of available nitrogen within the soil itself. The 
amount of the latter, therefore, is regarded by Messrs. Lawes and 
Gilbert as the measure of the increased produce of grain which 
a soil furnishes. 
In conformity with these views the farmer, when he wishes to 
increase the yield of his wheat, finds it to his advantage to have 
recourse to ammoniacal or other nitrogenous manures, and depends 
more or less entirely upon the soil for the supply of the necessary 
mineral or ash-constituents of wheat, having found such a supply 
to be amply sufficient for his requirements. As far, therefore, 
as the removal from the soil of a large amount of mineral soil- 
constituents by the clover-crop is concerned, the fact viewed in 
the light of the Rothamsted experiments, becomes at once intel- 
ligible ; for notwithstanding the abstraction of over 600 lbs. of 
mineral matter by a crop of clover, the succeeding wheat-crop 
does not suffer. Inasmuch, however, as we have seen that not 
only much mineral matter is carried off the land in a crop of 
clover, but also much nitrogen, we might, in the absence of direct 
evidence to the contrary, be led to suspect that wheat after clover 
would not be a good crop ; whereas the result is exactly the 
reverse. 
It is worthy of notice that nitrogenous manures which have 
such a marked and beneficial effect upon wheat do no good, but 
in certain combinations, in some seasons, do positive harm to 
clover. Thus Messrs. Lawes and Gilbert, in a series of experi- 
ments on the growth of red clover by different manures, obtained 
14 tons of fresh green produce, equal to about 3f tons of clover- 
hay from the unmanured portion of the experimental field ; and 
where sulphates of potash, soda, and magnesia, or sulphate of 
