ROOT-CROPS. 



21 



season, it being nearly twice as great in the third year as in 

 the first. 



Now, the farmyard manure employed would contain much 

 more of nitrogen, and also of most of the mineral constituents, 

 than the crops grown. 



The fact is that, independently of the great advantage Advan- 

 accruing from the opportunity for cleaning the land, the {^JJ^fJj 

 value of the root-crop in rotation is mainly to be attributed a rotation. 

 to the large amount of farmyard manure generally applied 

 for its growth ; to the large proportion of the constituents of 

 the manure which remain, and become slowly available to 

 succeeding crops ; to the large amount of the nitrogen and 

 other constituents remaining in the leaf, which serve directly 

 as manure again. Then they are gross feeders, so to speak, 

 converting a large amount of manure into vegetable produce ; 

 whilst, when the edible portion — the root — is consumed by 

 store or fattening stock, a very small proportion of the 

 nitrogen, and of other constituents valuable as manure, is 

 retained by the animal ; the remainder, perhaps more than 

 90 per cent, of the nitrogen, being voided, becoming manure 

 again. When, however, roots are consumed for the produc- 

 tion of milk, a much larger proportion is lost to the manure. 



The next table (3) shows which constituent, or class of Table 3 ex- 

 constituents, of the complex material farmyard manure, has P iained - 

 the most characteristic influence on the growth of the root- 



TABLE 3. — Norfolk White Turnips grown year after year 

 on the same Land. Results showing the effects of exhaustion 

 and manures, four seasons, 1845-48. Manures and produce per 

 acre per annum. 



WITHOUT MINERAL MANURE (THREE YEARS ONLY, 1846-4S). 



WITH VARIOU3 MINERAL MANURES. 



Roots 

 Leaves 



Total 



8 4 

 2 14 



10 18 



9 18 

 4 6 



14 4 



10 

 6 



16 8 



11 

 4 12 



15 12 



