56 



THE EOTHAMSTED EXPERIMENTS. 



Nitrogen 

 supplied 

 and recov- 

 ered in 

 crop. 



solid matter in the root as in the leaf. Again, notwith- 

 standing the much higher percentage of nitrogen in the dry- 

 substance of the leaf than in that of the root, there was, 

 owing to the small proportion of leaf, generally less than 

 one- third as much nitrogen remaining in the leaf (only for 

 manure again) as was accumulated in the edible root. Of 

 total mineral matter there was also much less remaining in 

 the leaf than was stored up in the root. Lastly, there was 

 very much less of the potash of the crop, and very much 

 less of the phosphoric acid also, in the leaf than in the root. 



The next point to consider is, What proportion of the 

 nitrogen of the manure, which is seen to be so effective, is 

 recovered in the increase of the crop ? Table 17 shows in 

 the column headings the amounts of nitrogen supplied per 

 acre per annum by manure in the case of each of the Series 2, 

 3, 4, and 5 ; and below are given the amounts of nitrogen 

 recovered in the increased produce of roots (the leaves being 

 returned to the land) for 100 supplied in manure. Eesults 

 are given for plot 5 with superphosphate alone as the 

 mineral manure ; for plot 6 with superphosphate and potash ; 

 and for plot 4 with superphosphate, potash, soda, and 

 magnesia, as the mineral manure. The results are the 

 averages for six years, 1878-83. They are calculated by 

 deducting the amounts of nitrogen in the crops grown by 

 the mineral manure alone from those obtained where nitro- 

 genous manures were used in addition, the difference showing 

 the increased amount of nitrogen in the crop due to nitro- 

 genous supply ; and the figures show the increased amount 

 of nitrogen in the roots for 100 supplied in the manure. 



TABLE 17. — Mangel-Wurzel. Nitrogen recovered in increase of 

 roots for 100 in manure. Average for 6 years, 1878-83. 



