17 



a 



lot 

 be 

 to 

 to 



its; 



iits. 



of 



On tliis point it may be observed that, in parts of the continent of 

 Europe where some of the very free-growing and deep-rooted Legn- 

 minosaj are cultivated, it is usual to let them grow for several years, 

 after which they cannot be repeated for twenty years or more. We 

 shall recur to the result? above quoted further on. 



Summary of Yield of Nitrogen in Crops. 



The foregoing facts of production, showing the yield of nitrogen 

 in different crops grown without nitrogenous manure, generally for 

 very many years in succession on the same land, may be briefly 

 summed up as follows : 



The average yield of nitrogen per acre per annum, was, with 

 wheat, thirty-two years without manure, 207 pounds, and twenty-four 

 years with a complex mineral manure, 22 "1 pounds ; with barley, 

 twenty-four years without manure, 18"3 pounds, and twenty-four years 

 with a complex mineral manure, 22"4 pounds ; with root-crops, thirty- 

 six years (including three of barley), with a complex mineral manure, 

 25*2 pounds; with beans, twenty-four years without manure, 31*3 

 pounds, and twenty-four years with a complex mineral manure, 45'5 ; 

 with clover, six crops in twenty- two years, with one crop of wheat, three 

 crops barley, and twelve years fallow, without manure, 30'5 pounds ; 

 with complex mineral manure, 39"8 pounds ; with clover, on land which 

 had not grown the crop for very many years, one year, 151*3 pounds ; 

 with a rotation of crops, seven courses, twenty-eight years, without 

 manure, 36'8 pounds, and with superphosphate of lime, 45'2 pounds ; 

 with the mixed herbage of grass land, twenty years without manure, 

 33 pounds, and with complex mineral manure, including potash, 55'6 ; 

 lastly, with Bokhara clover, five years, with mineral manure, between 

 80 and 90 pounds of nitrogen per acre per annum. 



The root-crops yielded more nitrogen than the cereal crops, and 

 the leguminous crops very much more still. 



In all the cases of the experiments on ordinary arable land — 

 whether with cereal crops, root-crops, leguminous crops, or a rota- 

 tion of crops (excepting as yet the Bokhara clover) — the decline in 

 the annual yield of nitrogen, none being supplied by manure, was very 

 great. 



Sources of the Nitrogen of Crops. 



We must next consider whence comes the nitrogen of the crops, 

 and especially whence comes the much larger amount taken up by 

 plants of the leguminous, and some other families, than by the 



h 



