KOOT-CROPS. 29 



same comparatively limited and superficial root -range, for so Reduction 

 many years in succession, the surface-soil became less easily in P r °d™ e 

 worked, and the tilth, so important for turnips, was frequently continuous 

 unsatisfactory ; whilst for want of variety and depth of root- J??*** 

 range of the crop a somewhat impervious pan was formed 

 below. 



The fact is, however, of itself of considerable interest, as 

 indicating one important and very beneficial influence of a 

 rotation of crops. Indeed, we shall presently see that even 

 the change to another description of root-crop, with a totally 

 different and much more extended root-range, is accompanied 

 with a much increased production over a given area by the 

 use of the same manures. 



Looking to the Table (7), it is seen that there are now five Nitrate of 

 series of plots instead of only four, nitrate of soda being soda and 



i« t « a • . i-,i • ammon- 



applied on Series 2, in amount supplying the same quantity ium-saits 

 of nitrogen as in the ammonium-salts on Series 3. The co mp ared - 

 result is a greater produce of both root and leaf than with 

 the ammonium-salts. 



The superphosphate alone (see lower division of column 1) Superphos- 

 gives much less produce than the mineral manures in the series phate ' 

 of four years before considered, doubtless to a great extent 

 owing to the still further exhaustion of the available nitrogen 

 of the surface-soil. In fact the surface-soils in question 

 showed, on analysis, lower percentages of nitrogen than those 

 of any other experimental field at Eothamsted — a result 

 which is quite consistent with the fact of the large amount 

 of root distributed through the surface-soil by the growing 

 turnip. 



Again, consistently with this supposition, and with the Nitrogen- 

 results that have gone before, there is still very marked but 

 somewhat reduced effect from all the nitrogenous manures ; 

 and again, the amount of leaf is very small, but it is the 

 greater the higher the nitrogenous manuring, and the greater 

 the luxuriance of growth. 



Table 8 shows the proportion of leaf to 1000 of root ; also Table 8 ex- 

 the percentages of dry matter, and of nitrogen and mineral P lmned - 

 matter in the dry matter ; and, as before, the amounts of each 

 per acre, in the roots and in the leaves. 



With the soil gradually becoming closer, and less favour- Propor- 

 able for root-development, the proportion of leaf to root is ^f^nd 

 somewhat higher. root. 



It should be explained that the percentages given in par- 

 enthesis are not the results of direct determinations in each 

 particular case, but are deduced from comparable results. 

 They are, however, undoubtedly near enough to the truth for 

 the purpose of the present illustrations. 



ous man- 

 ures. 



