MANURE FOR BARLEY. 251 



gen in the soil. In other words, the turnips leave less available 

 nitrogen in the soil than grain crops. 



After alluding to the facts given in the foregoing table, Messrs. 

 Lawes and Gilbert say : 



" There is evidence of another kind that may be cited as show- 

 ing that it was of available nitrogen that the turnips had rendered 

 the soil so deficient for the after-growth of barley. It may be as- 

 sumed that, on the average, between 25 and 30 Ibs. of nitrogen 

 would be annually removed from the Rothamsted soil by wheat 

 or barley grown year after year without nitrogenous manure. But 

 it is estimated that from the mineral-manured turnip-plots there 

 were, over the 10 years, more than 50 Ibs. of nitrogen per acre per 

 annum removed. As, however, on some of the plots, small quan- 

 tities of ammonia-salts or rape-cake were applied in the first two 

 years of the ten of turnips, it is, perhaps, more to the purpose to 

 take the average over the last 8 years of turnips only ; and this 

 would show about 45 Ibs. of nitrogen removed per acre per annum. 

 An immaterial proportion of this might be due to the small 

 amounts of nitrogenous manures applied in the first two years. 

 Still, it may be assumed that about 1|- time as much nitrogen was 

 removed from the land for 8, if not for 10 years, in succession, as 

 would have been taken in an equal number of crops of wheat or 

 barley grown without nitrogenous manure. No wonder, then, 

 that considerably less barley has been grown in 3 years after a 

 series of mineral-manured turnip-crops, than was obtained in an- 

 other field after a less number of corn-crops. 



"The results obtained in Barn-field afford a striking illustration 

 of the dependence of the turnip-plant on a supply of available ni- 

 trogen within the soil, and of its comparatively great power of 

 exhausting it. They are also perfectly consistent with those in 

 Hoos-field, in showing that mineral manures will not yield fair 

 crops of barley, unless there be, within the soil, a liberal supply of 

 available nitrogen. The results obtained under such very different 

 conditions in the two fields are, in fact, strikingly mutually con- 

 firmatory." 



