CLOVER AS A PREPARATORY CROP FOR WHEAT. 455 



was, upon the wliolc, 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 

 15J 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 minei'al matters and of 

 nitrogen, were 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 

 taken was in a condition to jacld 14 bushels more wheat per acre 

 than that upon which wheat had been previously grown ; the yield 

 of wheat after clover, in these expoi-iments, being fully equal to 

 that in another field, where very large quantities of manure were 

 used. 



Taking all these circumstances into account, is there not pre- 

 sumptive evidence that notwithstanding the removal of a large 

 amount of nitrogen in the clover hay, an abundant store of avail- 

 able nitrogen is leit in the soil, and also that in its relations towards 

 nitrogen in the soil clover difiers essentially from wheat ? The 

 results of our experience in the growth of the two crops appear to 

 indicate that whereas the growth of the wheat rapidly exhausts 

 the land of its available uiti'ogen, that of clover, on the contrary, 

 tends somehow or other to accumulate nitrogen within the soil 

 itself. If this can be shown to be the case, an intelligible explan- 

 ation of the fact that clover is so useful as a preparatory crop for 

 wheat will be found in the circumstance that during the growth of 

 clover, nitrogenous food, for which wheat is particularly grateful, 

 is either stored up or rendered available in the soil. 



An explanation, however plausible, can hardly be acceiDted as 

 correct, if based mainly on data which, although highly probable, 

 are not proved to be based on fact. In chemical inquiries espe- 

 cially, nothing must be taken for granted that has not been proved 

 by direct experiment. The following questions naturally suggest 

 themselves in reference to this subject : What is the amount of 

 nitrogen in soils of different characters ? What is the amount, 

 more particularly after "^ good and after an indifferent crop of 

 clover ? Why is the amount of nitrogen in soils larger after clover 

 than after wheat and other crops ? Is the nitrogen present in a 

 condition in which it is available and useful to wheat ? and lastly, 

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