EOOT-CROPS. , 57 



It should be stated that on the plots of Series 1 with the 

 mineral manures alone, there was obtained in the mangel- 

 roots an average of only about 13 lb. of nitrogen per acre per 

 annum. But it is to be remembered that the plots yielding 

 these very small amounts, even in the powerfully-rooted 

 mangel, had been under experiment with roots for nearly 40 

 years, during which time they had not received any nitrogen 

 by manure. During the earlier years, however, the common 

 and Swedish turnips yielded much more ; but in recent years 

 neither sugar-beet nor mangel-wurzel, even with their greater 

 powers of collection and growth than turnips, has removed 

 so much nitrogen without nitrogenous manure as wheat or 

 barley grown for more than 30 years in succession without 

 artificial nitrogenous supply. 



In the first place, the figures show that under each of the Influence 

 conditions of nitrogenous manuring there was more, and with ^^^ 

 the ammonium-salts or rape-cake very much more, of the the recovery 

 supplied nitrogen recovered in the roots where potash as well %^^ ,en 

 as superphosphate was used than where superphosphate 

 alone was employed as the mineral manure. 



Comparing the average results of the two plots (6 and 4), 

 where both potash and superphosphate were supplied, it is 

 seen that the amounts of nitrogen recovered as increase in 

 the roots for 100 supplied in manure were — 



With nitrate of soda . .59.9 



With ammonium-salts . . .42.3 



With rape-cake .... 49.3 



With rape-cake and ammonium-salts . 45.9 



Thus, even under the most favourable conditions as to 50 or 60 

 mineral supply, in three out of the four cases less than 50 ^w^ ^ 

 per cent of the nitrogen supplied by manure was recovered supplied in 

 in the increased produce of roots obtained by its use ; and 7 r ^^^ ot 

 even with the most effective of the nitrogenous manures, the in crop. 

 nitrate of soda, scarcely 60 per cent was so recovered. It is 

 true that the nitrogen in the roots alone by no means repre- 

 sents the total quantity assimilated per acre, but as the 

 leaves are annually returned to the land as manure, it is 

 clear that, taking the average over a number of years, it is 

 only the amount in the roots that can be credited as im- 

 mediate return from the manure employed. Where, how- 

 ever, large amounts of organic matter are returned to the 

 soil, more or less of the at first unrecovered constituents of 

 the manure will remain for future crops. 



Then as to the less return in the roots from a given amount Rape-cake 

 of nitrogen supplied as rape-cake than as nitrate of soda, it a 3 s ^ ate 

 should be borne in mind that although the nitrogen of such 



