464 BOARD OF AGRICULTURE. 



fully many points to which attention is drawn by the same authors 

 in their memoirs on the growth of red clover by difi'erent manures, 

 and on the Lois Weedon plan of growing wheat. Abundant and 

 most convincing evidence is supplied by these indefatigable experi- 

 menters that the wheat-producing powers 6f a soil are not increased 

 in any sensible degree by the liberal supply of all the mineral mat- 

 ters which enter into the composition of the ash of wheat, and that 

 the abstraction of these mineral matters from the soil, in very much 

 larger proportions than possibly can take place under ordinary 

 cultivation, in no wise aflects 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 pro- 

 duce 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 asli-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 con- 

 stituents by the clover crop is concerned, the fact viewed in the 

 light of the Rothamsted experiments, becomes at once intelligible; 

 for notwithstanding the abstraction of over 600 pounds 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 experiments on the 

 growth of rod clover by different manures, obtained 14 tons of 

 fresh green produce, equal to about 3| tons of clover hay from the 

 unmanured portion of tlie experimental field ; and where sulphates 

 of potash, soda, and magnesia, or sulphate of potash and superphos- 

 phate of lime were employed, 17 to 18 tons (equal to from about 

 4^ to nearly 5 tons of hay) were obtained. When salts of ammo- 

 nia were added to the mineral manures, the produce of clover hay 



