545 



shown signs of diminution of produce. The yield of the legumi- 

 nous crops had fallen considerably. Turnips, again, appeared greatly 

 to have exhausted the immediately available nitrogen in the soil. The 

 amount of nitrogen harvested in the leguminous and root crops was 

 considerably increased by the use of " mineral manures," whilst that 

 in the graminaceous crops was so in a very limited degree. 



Direct experiments further showed that pretty nearly the same 

 amount of nitrogen was taken from a given area of land in wheat 

 in 8 years, whether 8 crops were grown consecutively, 4 in alterna- 

 tion with fallow, or 4 in alternation with beans. 



Taking the results of 6 separate courses of rotation, Boussingault 

 obtained an average of between one-third and one-half more nitrogen 

 in the produce than had been supplied in manure. His largest 

 yields of nitrogen were in the leguminous crops ; and the cereal 

 crops were larger, when they next succeeded the removal of the 

 highly nitrogenous leguminous crops. In their own experiments 

 upon an actual course of rotation, without manure, the Authors 

 had obtained, over 8 years, an average annual yield of 57' 7 Ibs. of 

 nitrogen per acre ; about twice as much as was obtained in either 

 wheat or barley, when they were, respectively, grown year after year 

 on the same land. The greatest yield of nitrogen had been in a clover 

 crop, grown once during the 8 years ; and the wheat crops grown 

 after this clover in the first course of 4 years, and after beans in the 

 second course, were about double those obtained when wheat suc- 

 ceeded wheat. 



Thus, cereal crops grown year after year on the same land, 

 gave an average of about 30 Ibs. of nitrogen, per acre, per annum ; 

 and leguminous crops much more. Nevertheless the cereal crop 

 was nearly doubled when preceded by a leguminous one. It was 

 also about doubled when preceded by fallow. Lastly, an entirely 

 unmanured rotation had yielded nearly twice as much nitrogen as 

 the continuously grown cereals. 



Leguminous crops were, however, little benefited, indeed fre- 

 quently injured, by the use of the ordinary direct nitrogenous ma- 

 nures. Cereal crops, on the other hand, though their yield of ni- 

 trogen was comparatively small, were very much increased by direct 

 nitrogenous manures, as well as when they succeeded a highly nitro- 

 genous leguminous crop, or fallow. But when nitrogenous manures 



