SCIENTIFIC FARMING AT RO TEAMS TED. 89 



a decline from an average of twenty-two pounds over the first twelve 

 years to an average of 14-6 pounds over the next twelve years. Min- 

 eral manures, containing no nitrogen, applied to barley and wheat did 

 not materially increase the yield of nitrogen in the crop. 



A succession of root-crops (with three years of barley intervening 

 after the first eight years), dressed with a complex mineral manure, 

 yielded an average of 26*8 pounds of nitrogen per acre, per annum, 

 over a period of thirty-one years ; with a decline from an average of 

 forty-two pounds over the first eight years to 13*1 (in sugar-beets) 

 over the last five years. Afterward, with the change of crop to man- 

 golds, the yield of nitrogen was somewhat increased. 



Beans, for a period of twenty-four years, yielded an average of 31 3 

 pounds of nitrogen without manure ; and, with a complex mineral 

 manure, an average of 45'5 pounds of nitrogen per acre. The decline 

 in yield of nitrogen was, however, from an average of 48*1 pounds 

 over the first twelve years to only 14 - 6 pounds over the last twelve 

 years, when unmanured, and from an average of 61*5 pounds over the 

 first twelve years to but 29*5 pounds over the last twelve years, when 

 mineral manures were applied. 



An annual average yield of nearly two hundred pounds of nitrogen 

 per acre was obtained in the clover grown for twenty-seven years in 

 succession on a plot of old garden-soil that was exceptionally rich in 

 nitrogen at the beginning of the experiment. As in the case of other 

 crops, there was a marked decline in the average yield of nitrogen in 

 the last half of the period, and there was also a great reduction in the 

 stores of nitrogen contained in the soil. 



The leguminous crops, beans and clover, it will be seen, contain a 

 larger amount of nitrogen per acre than the gramineous crops, wheat 

 and barley. In the Rothamsted experiments it was, however, found 

 that manures containing nitrogen benefited the gramineous crops, 

 while they had but little, if any, influence upon the growth of legu- 

 minous crops. The chemical composition of the crop was not, there- 

 fore, an index of the mauurial constituents required to promote its 

 growth. 



When turnips, barley, clover, or beans, and wheat were grown in 

 rotation for twenty-eight years, the average annual yield of nitrogen 

 per acre was 36'8 pounds, and in the mixed herbage of permanent 

 grass-land, when unmanured, the annual yield of nitrogen averaged 

 thirty-three pounds per acre. 



The larger average yield of nitrogen per acre in the crops in rota- 

 tion and in the mixed herbage of the permanent grass-land, as com- 

 pared with the yield of nitrogen in gramineous crops when grown sep- 

 arately, is not entirely due to the larger amount of nitrogen in the 

 leguminous species themselves, but also to their influence upon the 

 gramineous species which are able to take up and assimilate more nitro- 

 gen when the highly nitrogenous leguminous crops have been appro- 



