194 SOILS AND MANUEES 



in need of phosphatic than of nitrogenous or potash 

 manures. From the fact that the graminaceous crops 

 contain less, and mangolds more, phosphoric acid than the 

 others which are all much alike in this respect it may 

 be supposed that the former require less, and the latter 

 more, phosphatic manure than the other crops. The 

 same is true, in part, also of the other constituents. 

 It is also noticeable that in the graminaceous and legu- 

 minous crops the proportion of nitrogen exceeds that 

 of the potash and in the other crops the reverse is the 

 case. In potatoes and mangolds the excess of potash is 

 very conspicuous. The proportion of nitrogen to potash 

 is about the same in the two crops, but the quantities of 

 all the ingredients are much greater in the latter. 



The most important inferences, relating to the manurial 

 requirements of the crops, that can be drawn from their 

 chemical composition, are as follows : 



Graminaceous crops contain smaller quantities of all 

 the fertilising ingredients than any of the other crops ; 

 nitrogen is the largest of the three constituents. 



The leguminous crops contain larger quantities of all 

 the ingredients but especially of nitrogen and potash. 



The root crops not including mangolds contain about 

 the same quantity of nitrogen as the leguminous crops 

 but much more potash. 



Potatoes contain less nitrogen bat nearly as much 

 potash as the turnips and swedes. 



Mangolds contain much the largest quantities of all 

 the fertilising ingredients. 



Assimilative Capacity. The various kinds of crops 

 exhibit great differences in their powers of assimilating 

 the plant foods in the soil. Those which have greater 

 assimilative capacity are less dependent on manures. 

 Of the ordinary crops, cereals and grass have the greatest 

 power of assimilation, and root crops and potatoes 



