VALUE OF FARMYARD MANURE. 45 



necessity to add in a manure an} 7 more than the 

 three ingredients, nitrogen, phosphoric acid, and potash. 

 Its value, then, as a direct manure must depend on 

 the quantity and proportion in which these three in- 

 gredients are present. These substances, as we have 

 already seen, it contains only in very small quantities. 

 It is, judged from this point of view, a comparatively 

 poor manure. Furthermore, only a certain percentage 

 of these substances are in a soluble or immediately 

 available condition, in this respect the rotten manure 

 being very much more valuable than the fresh manure. 

 Again, a point of great importance in a universal 

 manure is the proportion in which the necessary plant- 

 foods are present. If it be asked, Are the nitrogen, 

 phosphoric acid, and potash in farmyard manure pres- 

 ent in the proportion in which crops require these 

 constituents ? the answer must be in the negative. 

 Heiden l has very strikingly illustrated this point, in 

 so far as the relations between the two ash ingredients 

 are concerned, by some computations as to the amount 

 which would be removed from the soil in the course of 

 different rotations. 2 In the case of five different rota- 

 tions, it was found that the ratio between the potash 

 and phosphoric acid removed was as follows : 3 (1) 

 2.96 to 1 ; (2) 2.76 to 1 ; (3) 2.95 to 1 ; (4) 4.13 to 1; 



1 See Heiden's Diingerlehre, vol. ii. p. 171. 



2 For full details see Appendix, Note XVI., p. 64. 



3 Storer reproduces these results in his ' Agricultural Chemistry,' 

 vol. ii. p. 21. 



