202 



Analyses of Ashes of Plants. 



proportion of the samples analyzed. It is not supposed that the 

 produce of beans and peas should be the same on the same soil, 

 but these numbers will serve for the foundation of a calculation. 

 The following would then be their relative composition : — 



Table 26. — Comparison of Mineral Matter in Beans and Peas — both 



on Clay Soil. 





One Ton 



One Ton 



2989 lbs. 



2270 lbs. 



Entire 



Entire 





of 



of 



of 



of 



Crop 



Crop 





Peas. 



Beans. 



Pea-Straw. 



Bean-Straw 



Peas. 



Beans. 





0-42 



0-22 



4-62 



2-95 



5-04 



3-17 



Phasphoric Acid , 



14-43 



15-23 



2-93 



0-55 



17-36 



15-78 



Sulphuric Acid 



2-93 



1-62 



5-38 



1-58 



8-31 



3-20 





2-2S 



2-75 



86-80 



22-25 



89-08 



25-00 



Magnesia .... 



3-48 



3-66 



13-62 



2-85 



17-10 



6-51 



Peroxide of Iron . 







1-74 



0-69 



1-74 



0-69 





20-75 



27-40 



30-18 



36-96 



50-93 



64-36 





2-51 



0-2S 



0.57 



3-13 



3-08 



3-41 



Chloride of Sodium . 



2-15 





23-00 



13-88 



25-15 



13-88 



Total . . 



53-15 



51-16 



16S-84 



84-84 



207-79 



136-00 



The difference between the beans and peas^ so far as the 

 grain is concerned, is very trifling. Nor are the numbers for 

 the entire crop very dissimilar. A crop of peas will require 

 more lime and magnesia, but less alkali, than beans. Peas there- 

 fore should flourish on a light calcareous loam^ — beans on stiff 

 clay. The trifling quantity of silica removed in these crops is the 

 all-important point. It will be seen by reference to our last 

 paper {Journal, vol. vii. p. 674), that a crop of wheat is in no 

 other way more exhausting to the soil than in requiring a great 

 quantity of silica, which beans and peas do not want. Beans, 

 indeed, are known to be a good preparation for wheat, and they 

 seem to follow it with equal advantage. It appears to us that 

 this may be in great measure due to the alkali contained in beans. 

 In explaining the benefits of rotations on chemical principles, it 

 is usual to say that one crop may follow another with advantage 

 because it requires a different kind of mineral food. A plant, 

 that is, which contains but little alkali would best precede or 

 follow one that drew largely upon the soil for potash. This, no 

 doubt, is true, but something more may be added to it. One 

 crop may really not only dispense with mineral nourishment re- 

 quired by another, and therefore leave it for the benefit of its suc- 

 cessor^ but it may be active in the preparation of such food for 

 the following crop. This, we believe, is the case with beans in 

 reference to wheat or barley. A crop of beans or peas requires 

 nearly as much phosphoric acid, and a great deal more potash. 



