352 HANDY-BOOK OF HUSBANDRY. 



while 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 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 yield 14 bushels more 

 wheat per acre than that upon which wheat had been previously 

 grown ; the yield of wheat after clover, in these experiments, 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 availa- 

 ble nitrogen is left in the soil, and, also, that in its relations 

 toward nitrogen in the soil, clover differs 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 nitrogen, 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 

 explanation 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 accepted 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 a 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. Are there any other circumstances, apart from the supply 

 of nitrogenous matter in the soil, which help to account for the 

 beneficial effects of clover as a preparatory crop for wheat ? 



" In order to throw some light on these questions, and, if possi- 

 ble, to give distinct answers to at least some of them, I, years 

 ago, when residing at Cirencester, began a series of experiments. 



