A rOTATO-CROP AND THE MINERALS IN THE SOIL. 205 



plioric acid is as necessary for the developcinent of tlie 

 potato as it is for cereals ; and the eilective quantity 

 of the transmuted potash and hme is essentially determined 

 by the phosphoric acid and nitrogen absorbed at the same 

 time. Where one of the two latter elements which, as 

 we have remarked, are equally constituents of cereals, 

 is deficient in the soil, the potato crop will be propor- 

 tionate to the available quantity of these two substances, 

 and the greatest excess of potash or lime in the soil will 

 have no influence whatever upon the amoimt of the 

 produce. 



The arable siu-face soil of the field at Oberbobritzsch is 

 much richer in phosphoric acid and nitrogen than that of 

 the Kotitz field ; yet the potato crop yielded by the former 

 was only half that given by the latter. 



Accordingly, nothing can be more certain tlian that the 

 field at Oberbobritzsch contained much less potash or 

 hme in an available state, than the Kotitz field ; and by 

 manuring -with hme alone, or with wood-ashes (potash 

 and hme), it might readily be ascertained in which of the 

 two substances the ground was deficient. 



But from the inferior potato crop given by the field at 

 Cunnersdorf, we cannot infer that it was poorer in potash 

 or lime than the field at Kotitz ; the latter decidedly con- 

 tained, as the preceding corn crop shows, somewhat more 

 phosphoric acid and nitrogen than the field at Cunners- 

 dorf: consequently, the larger potato crop at Kotitz may 

 have been mainly owing to the greater quantity of these 

 two elements contained in it. Even if the field at Cun- 

 nersdorf had been still richer in potash and lime than 

 the Kotitz field, yet after all, under the given conditions, 

 it would have produced a smaller crop of potatoes. 



Oa^s-,1853. — The oat plant derives part of its nutriment 

 from the ara])le smface soil, but sends its roots, wlien the 



