Exhaustion of Soil. 



when (after clover) three white straw crops had been grown 

 in succession namely, wheat without manure, barley with 

 sulphate of ammonia, and barley without manure ? An 

 examination of the manuring and the results in experiments 

 2, 3, 4, as shown in the table, can leave no doubt that the 

 increased produce was due to an increased supply of avail- 

 able nitrogen within the soil where it had been applied in the 

 manures for the turnips. Still, in neither case is the pro- 

 duce so great as without manure in Hoos Field, where the 

 barley was grown after several previous corn crops. Experi- 

 ments 5 and 6, however, afford conclusive evidence that it 

 was of available nitrogen for the barley that the soil had. 

 become so exhausted by the growth of ten successive crops of 

 turnips. It may be seen in the table that, in the year 1854, 

 these two plots, by the simple addition of nitrogen in the 

 manures, increased the total produce three to three and a half 

 times. 



Evidence of yet another kind indicates that it was of avail- 

 able nitrogen that the turnips had rendered the soil so 

 deficient for the after- growth of barley. It may be assumed 

 that an average of from 251b. to 301b. of nitrogen would be 

 annually removed from the Rothamsted soil by wheat or 

 barley griown year after year without nitrogenous manure. 

 But it is estimated that from the mineral-manured turnip 

 plots there were, over the ten years, more than 501b. of 

 nitrogen per acre per annum removed, After making every 

 allowance, it may fairly be asstimed that about one and a 

 half times as much nitrogen was removed from the land for 

 eight, if not for ten 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 con- 

 siderably less barley was grown in three years, after a series 

 of mineral-manured turnip crops, than was obtained in 

 another field after a less number of corn crops. The results 

 in Barn Field, moreover, afford a striking illustration of the 

 dependence of the turnip plant on a supply of available 



