AGRICULTURE AND RURAL ECONOMY. 359 



periments it is noticeable that the " root crops " turnips 

 and sugar-beets fell away more in their yield, and exhaust- 

 ed the nitrogen of at least the superficial layers of the soil, 

 more than the gramineous crops wheat and barley, and, in- 

 deed, more than any other crop. 



Leguminous Crops and Soil Nitrogen. 



Referring to the fact that leguminous crops contain much 

 more nitrogen than gramineous crops, Dr. Gilbert says that 

 "we have no evidence leading to the conclusion that this 

 increased assimilation [of nitrogen] is done at the expense 

 of the nitrogen of the soil." On the other hand, after taking 

 away so much more nitrogen than other crops, they leave a 

 o-ood deal more behind. In discussing the well-known fact 

 that leguminous crops receive less benefit than others from 

 nitrogenous manures, he cites the results of a number of com- 

 parative soil-analyses after clover and after barley. These 

 "all concurred in showing an appreciably higher percentage 

 of nitrogen, especially in the surface soil (nine inches deep) 

 of the land from which the clover had been removed than 

 that from which the barley had been taken ; and this was 

 so, although in every case all visible vegetable debris had 

 been carefully picked out. Here, then, the surface soil, at 

 any rate, was positively enriched in nitrogen by the removal 

 of a very highly nitrogenous crop.' 



55 



Assimilation of Nitrogen by Leguminous Crops Aided by Potassic 



Fertilizers. 



In experiments on the mixed herbage of grass land con- 

 tinuing through twenty years, " complex mineral manure " 

 without potash increased the yield over unmanured plots 41 

 per cent.; the same with potash" increased it 67 per cent. 

 The extra increase with potash was due almost entirely to 

 leguminous plants which the potash brought in. The aver- 

 age annual yield of nitrogen per acre without potash was 

 38.1 pounds, with potash 56 pounds. Dr. Gilbert concludes 

 that "mineral manures, and especially potassic manures, in- 

 crease in a striking degree the growth of crops of the le- 

 guminous family grown separately, and coincidently the 

 amount of nitrogen they assimilate over a given area." 



We may add that this observation, which is well substan- 



