FORAGE CROPS. 351 



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 inde- 

 fatigable 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 nowise 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 toammoniacal 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-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 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 3I tons of clover- 

 hay from the unmanured portion of the experimental field ; and 

 where sulphates of potash, soda, and magnesia, or sulphate of pot- 

 ash and superphosphate of lime were employed, 17 to 18 tons 

 (equal to from about 4^ to nearly 5 tons of hay) were obtained. 

 When salts of ammonia were added to the mineral manures, the 

 produce of clover-hay was, upon the whole, less than where the 

 mineral manures were used alone. The wheat grown after the 

 clover on the unmanured plot, gave, however, 29^- bushels of corn, 

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