286 ANNUAL OF SCIENTIFIC DISCOVERT. 



introduction to the record of the results would obviously be, to illustrate, by 

 reference to direct experiment, that which had been before only assumed, 

 regarding the yield of nitrogen in our different crops. To this end had been 

 determined the annual produce of nitrogen per acre, in the case of various 

 crops, which were respectively grown, for many years consecutively, on the 

 same land; namely, wheat, fourteen years ; barley, six years ; meadow hay, 

 three years; clover hay, three years out of four; beans, eleven years; and 

 turnips, eight years. In the majority of the instances referred to, the yield 

 of nitrogen had been estimated, both for the crop grown without manure of 

 any kind, and for that with purely mineral manure, that is, excluding any 

 artificial supply of nitrogen. It was the object of the present communica- 

 tion to give a summary view of some of the facts thus brought to light. 

 Beans and clover were shown to yield several times as much nitrogen per acre 

 as wheat or barley. Yet the growth of the leguminous crops, carrying off so 

 much nitrogen as they did, was still one of the best preparations for the growth 

 of wheat; whilst fallow (an important effect of which was the accumulation 

 within the soil of the available nitrogen of two years into one), and adding 

 nitrogenous manures, had each much the same effect in increasing the pro- 

 duce of the cereal crops. Other experimental results were adduced, which 

 illustrated the fact, that four years of wheat, alternated with fallow, had 

 given as much nitrogen in eight years as eight crops of wheat grown con- 

 secutively. Again, four crops of wheat, grown in alternation with beans, 

 had given nearly the same amount of nitrogen per acre as the four crops 

 grown in alternation with fallow ; consequently, also much about the same 

 as the eight crops of wheat grown consecutively. In the case of the alterna- 

 tion with beans, therefore, the whole of the nitrogen obtained in the beans 

 themselves was over and above that which was obtained, during the same 

 series of years, in wheat alone, whether it was grown consecutively, 

 or in alternation with fallow. Interesting questions arose, therefore, as to 

 the varying sources, or powers of accumulation, of nitrogen, in the case of 

 crops so characteristically differing from one another as those above referred 

 to. It had been found that the leguminous crops, which yielded in their 

 produce such a comparatively large amount of nitrogen over a given area 

 of land, were not specially benefited by the direct application of the more 

 purely nitrogenous manures. The cereal crops, on the other hand, whose 

 average yield of nitrogen, under the same circumstances, was comparatively 

 so small, were very much increased by the use of direct nitrogenous ma- 

 nures. But it was found that, over a series of years, only about four-tenths 

 of the nitrogen annually supplied in manure for wheat or barley (in the 

 form of ammonia salts or nitrates), were recovered in the immediate increase 

 of crop. Was any considerable proportion of the unrecovered amount 

 drained away and lost? Was the supplied nitrogenous compound trans- 

 formed in the soil, and nitrogen, in some form, evaporated? Did a portion 

 remain in some fixed and unavailable state of combination in the soil? 

 Was ammonia, or free nitrogen, given off during the growth of the plant? 

 Or, how far was there an unfavorable distribution, and state of combination, 

 within the soil, of the nitrogenous matters applied directly for the cereal 

 crops, those, such as the leguminous crops, which assimilated so much 

 more, gathering with greater facility, and from a different area of soil, and 

 leaving a sufficient available nitrogenous residue within the range of collec- 

 tion of a succeeding cereal crop? These questions, among others, which 

 their solution more or less involved, required further elucidation before some 



