88 



THE ROTHAMSTED EXPERIMENTS. 



Potash, 

 phosphoric 

 acid, and 

 quality of 

 grain. 



Recapitu- 

 lation. 



Good 



seasons and 

 soda in 

 crop. 



Silica in 

 straw. 



Mineral 

 manures 

 and min- 

 eral com- 

 position of 

 crop. 



of potash, but lower percentages of phosphoric acid, both in 

 the ash and in the dry substance, the higher the quality of 

 the grain. 



In wheat, however, there is lower not higher percentage of 

 ash in the dry substance of the grain the higher its quality. 

 But in wheat, as in barley, there is higher percentage of 

 potash, and lower percentage of phosphoric acid, in the ash, 

 the higher the quality. On the other hand, there is not in 

 the case of wheat, as there is in that of barley, a much higher 

 percentage of potash in the dry substance the higher the 

 quality. This difference may be partly due to the larger 

 proportion of starch to nitrogenous substance in the barley ; 

 but it is probably in part also due to the palece (or chaff) of 

 the barley, but not of the wheat, being adherent, and retain- 

 ing the surplus potash brought up for grain-formation. 



In both descriptions of grain there is very uniformly a 

 lower proportion of phosphoric acid in the dry matter the 

 higher the quality of the grain. 



In the straw there is high percentage of ash in the dry 

 matter, high percentage of potash, and low percentage of 

 phosphoric acid, in the ash, and in the dry matter, the higher 

 the quality of the grain. In the straw, however, the varia- 

 tions show a much wider range, indicating much less definite- 

 ness, and greater irregularity in condition. 



Thus, then, the higher the quality of the barley-grain — 

 that is, the higher its proportion of starch — the higher is the 

 proportion of potash and the lower is that of phosphoric acid. 

 Though not shown in the table, it may be mentioned that 

 with a higher proportion of potash there is generally a lower 

 proportion of both lime and magnesia, and with a lower pro- 

 portion of phosphoric acid there is a somewhat higher propor- 

 tion of sulphuric acid. 



Another point of interest is, although it is true the amounts 

 are small, that there is a tendency to a higher proportion of 

 soda in the grain-ash, and in the dry matter of the grain, in 

 the better seasons, even when there is no deficiency of potash. 

 This, again, is probably due to the ash of the barley-grain 

 containing that of the adherent palece. 



In relation to the composition of the straw, the most 

 striking result is (though not shown in the table) that there 

 is little more than two-thirds as high a percentage of silica 

 in the ash of the produce of the better as in that of the 

 worse seasons. 



The results in the next Table (29) illustrate the influence 

 of exhaustion and of full supply, of mineral or ash constituents, 

 on the mineral composition of the produce, both grain and 

 straw. 



