EXPERIMENTS ON CLOVEK. 141 



Under ordinary cultivation, in no wise affects the yield of wiicat, 

 provided there be at the same time a liberal supply of available 

 nitrogen within the soil itself. The amount of the latter, there- 

 fore, is regarded by Messrs. Lawes and Gilbert, as the measure of 

 the increased produce of grain which a soil furnishes. 



" In confornut3" with these views, the farmer, when he wishes to 

 increase the yield of his wheat, finds it to bis advantage to have 

 recourse to ammoiiiacal, or other nitrogenous manures, and depends 

 more or less entirely upon the soil, for the supply of the ncccessary 

 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-constitu- 

 ents, 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 docs not suflfer. 

 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 con- 

 trary, be led to suspect that wheat, after clover, would not be a 

 good crop; whereas, the fact 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 three and three- 

 fourths tons of clover hay, from the unmanured portion of the 

 experimental field ; and where sulphates of potash, soda, and mag- 

 nesia, or sulphate of potash and superpliosphate of lime were em- 

 ployed, 17 to 18 tons, (equal to from about four and one-half to 

 nearly five 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, whilst in the adjoining field, 

 where wheat was grown after wheat, without manure, only 15| 

 bushels of corn per acre were obtained. Messrs. Lawes and Gilbert 

 notice especially, that in the clover-crop of the preceding year, 

 very much larger quantities, both of mineral matters and of 

 nitrogen, w^ere taken from the land, than were removed in the 

 unmanured wheat-crop in the same year, in the adjoining field. 

 Notwithstanding this, the soil from which the clover had been 



