

ROTATION OF CROPS. 237 



— indeed, on the average, about three-fourths as much in the 

 continuous as in the rotation crops. 



Lastly, the figures show that by far the larger proportion of Phosphoric 

 the total phosphoric acid in the wheat crops is stored up in the ^inand 

 grain, which is assumed to be sold off the farm. Thus, without straw of 

 manure more than four-fifths, and with superphospate nearly wheaL 

 four-fifths, of the total phosphoric acid of the crops was in the 

 grain. With the mixed manure, however, with rather larger 

 total amounts taken up than with superphosphate alone, there 

 was comparatively little more stored up in the grain, the ex- 

 cess for the most part remaining in the straw. The larger 

 amount of total phosphoric acid taken up with the mixed 

 manure than with superphosphate, the amount supplied by 

 manure being the same in the two cases, is to be attributed 

 to the coincident supply of other constituents in the mixed 

 manure, inducing greater luxuriance, and with it greater 

 activity of collection. 



The Amounts of Potash in the Rotation, and in the 

 Continuous Crops. 



The results relating to the amount and distribution of 

 potash in the rotation and in the continuous crops are re- 

 corded in Table 64 (p. 239). 



The Potash in the Root-crops. — Before referring to the de- Sugar in 

 tails on this point, attention should be recalled to the facts root - cro P s ' 

 fully illustrated in other papers — that root-crops are essen- 

 tially sugar crops ; that the very characteristic effect which 

 nitrogenous manures exert on their increased growth is mainly 

 represented by a greatly increased production of the non- 

 nitrogenous substance — sugar; that, however the action is to 

 be explained, it is certain that the presence of potash is an 

 important condition of the formation in plants of carbohy- 

 drates generally ; and that, in the case of root-crops, the pro- 

 duction of the carbohydrate — sugar — is greatly dependent 

 on a liberal available supply of potash. 



Eeferring to the upper division of the table, and for the Potash in 

 purpose of the first illustrations to the rotation results, it is r ? oot v s s a ^f 

 seen that, without manure and very abnormally small crops, turnips. 

 there were only three, four, or five times as much potash in 

 the roots as in the leaves ; with superphosphate, on the other 

 hand, and greatly increased root development, there were 

 eight or nine times as much potash in the roots as in the 

 leaves ; and with the mixed manure (including potash), there 

 were, with the further greatly increased actual amount of 

 roots and of potash in them, seven or eight times as much in 

 the roots as in the leaves. That is, there was the greatest 



