356 INVESTIGATION BY CULTURE EXPERIMENTS 



Even the yield of turnips has been fairly good and practically 

 maintained since 1852 in the legume system, but it should be noted 

 that the yield of Swede turnips fell off nearly 10 tons from 1848 to 

 1852 (see fallow series only for Swedes in 1848). In case of the 

 barley the influence of the legumes grown three years before is 

 less apparent, and the barley yields have decreased during the 

 sixty years by 22 bushels in the legume system and by 31 bushels 

 in the fallow system, if we consider that the averages for the first 

 and third 2O-year periods are 40 years apart. 



(3) Where both minerals and nitrogen have been applied (al- 

 ways to the turnip crop only), the yield of turnips has been appre- 

 ciably increased; and, if allowance be made for the failure of 1868, 

 the increase has been somewhat regular; while the barley crop, 

 which follows the turnips, has apparently suffered approximately 

 in proportion to the increasing drafts upon the soil by the turnips, 

 and with as near approach to regularity. The fact that this marked 

 decrease in yield appears in the barley straw as well as in the grain 

 clearly indicates that the abundant supplies of minerals applied 

 and liberated from the soil make it possible for the enormous 

 turnip crop to appropriate so much of the available nitrogen supply 

 that the quick-growing spring barley is limited in yield by lack of 

 nitrogen. In the case of the legumes the average yields have dis- 

 tinctly decreased where commercial nitrogen has been supplied. 

 This raises the question whether the larger crops of turnips and 

 barley where nitrogen was supplied have not removed such large 

 amounts of the mineral elements that the yield of the legumes 

 (which have power to balance their own nitrogen ration) is thereby 

 limited. In this connection it may be noted that, as an average, the 

 yields of both clover and beans have been better where the full 

 minerals alone are applied (middle section since 1884) than where 

 nitrogen also has been added. The yield of wheat following the 

 legumes has been well maintained, not only where both minerals 

 and nitrogen are applied, but also where minerals alone are 

 used. 



(4) On the unfertilized land the fallow system has given better 

 average yields of turnips, of barley, and of wheat than the legume 

 system, throughout the entire sixty years, except for the wheat 

 in the last twenty. The fallow system also gave better results 



