40 



THE ROTHAMSTED EXPERIMENTS. 



Table 12 

 explained. 



Leaf and 

 root. 



crop-residue. With farmyard manure, so far as there had been 

 larger crops, there will be much crop-residue ; but a very large 

 proportion of the effect on future crops is to be attributed to 

 slowly decomposing manure-residue. 



The next Table (12) shows for the produce of the two years 

 without further application of nitrogenous manures, the same 

 particulars as to composition as Table 10 for the preceding 

 three years — namely, the amount of leaf to 1000 root, and the 

 percentages, and the amounts per acre, of certain constituents 

 in the root and in the leaf. The results need not be con- 

 sidered in much detail. 



Excepting in the case of Series 5, the proportion of leaf to 

 root is considerably less over the two years, with the less 

 supply of nitrogen within the soil, and the consequent much 

 less luxuriance. There is, nevertheless, over the two years 

 a lower percentage of dry substance in the root, doubtless 

 owing to the less formation of sugar with the less nitrogen 

 available to the plant. There is also generally a somewhat 

 lower percentage of dry or solid substance in the leaf over the 

 two years of comparative exhaustion. Again, there is, where 

 nitrogenous manures had previously been applied, generally a 

 lower, and in some cases a considerably lower, percentage of 

 nitrogen in the dry substance of the roots over the two years 

 of only residual supply. The percentage of nitrogen in the 

 dry substance of the roots is indeed very low over both 

 periods, but especially in the second ; and it will be seen 

 further on that it is much lower than in either of the descrip- 

 tions of roots cultivated for feeding purposes. In fact, so 

 much is the sugar-forming habit of the plant developed, and 

 so largely does the amount of the non-nitrogenous substance 

 — sugar — contribute to the percentage of dry matter, that the 

 percentage of the nitrogenous bodies is relatively very low, 

 even though a large amount of nitrogen may have been taken 

 up over a given area. As in the case of the three years with 

 direct nitrogenous manures, so now over the two years with 

 only residual supply of nitrogen, the percentage of nitrogen 

 in the dry substance of the leaf is very much higher than in 

 that of the root. It is, however, in each series somewhat 

 higher over the two years than over the three of direct sup- 

 ply, perhaps owing to somewhat less matured — that is less 

 exhausted — condition of the leaves over the two years. 



Turning now to the percentage of total mineral matter in 

 the dry substance over the two years, it is seen that in the 

 root and leaf respectively it is approximately the same over 

 the two years as over the preceding three ; and it is as was 

 the case over the three years, four or five times as high in 

 the dry substance of the leaf as in that of the root. 



