90 THE EOTHAMSTED EXPERIMENTS. 



They relate to the mineral composition of the produce 

 grown for forty years in succession : 



1. By ammonium-salts and superphosphate. 



2. By ammonium -salts, superphosphate, and potassium, 



sodium, and magnesium, salts, in addition. 



There are given results obtained by complete analyses of 

 the ash of samples mixed in proportion to the amount of the 

 produce (grain and straw separately) each year — for the four 

 ten-year periods, 1852-61, 1862-71, 1872-81, and 1882-91. 



The upper division of the table gives for the potash, the 

 second for the soda, the third for the phosphoric acid, and 

 the fourth for the silica — 



1. The percentage in the ash (pure) of the grain, and of the 



straw. 



2. The amounts per 1000 dry matter of grain, and of straw. 



3. The amounts per acre per annum, lb., in the grain, in 



the straw, and in the total produce (grain and straw 



together). 

 Potash. First referring to the potash : its percentage, even in the 



grain-ash, is seen somewhat to diminish from period to 

 period where none was supplied in manure, and somewhat to 

 increase where there was an annual supply of it by manure. 

 In the straw-ash, however, the percentage of potash went 

 down from 18.44 over the first period to only 7.36, or less 

 than half, over the fourth, where none was supplied; but it 

 increased from 27.85 per cent over the first, to 33.64 over 

 the third, but to only 29.72 over the fourth period, where it 

 was annually supplied. Thus the influence of exhaustion, or 

 of full supply, of potash, has been comparatively small on 

 the mineral composition of the grain, but very great on that 

 of the straw. 



The point is further illustrated in the next results, which 

 show the amounts of potash per 1000 dry matter of grain 

 and of straw respectively. There is, again, comparatively 

 little variation in the relation of the potash to the organic 

 matter in the case of the grain, but very great variation in 

 that of the straw, accordingly as there is exhaustion or full 

 supply. When it is borne in mind that the ash of barley- 

 grain contains that of the adherent palece as well as that of 

 the grain proper, the conclusion is that the variation in the 

 proportion of potash to the fixed organic substance of the 

 grain itself, is much less than the figures would indicate. It 

 is probable that the variation, such as it is, is associated with 

 a different relative proportion of the organic compounds 

 themselves — of the fully -matured non- nitrogenous to the 

 nitrogenous bodies. In fact, the evidence, duly considered, 



