148 ACTION OF SOIL ON FOOD OF PLANTS IN MANURE. 



with the available nutritive substances which it contains ; 

 a lower crop corresponds to a smaller store of these mat- 

 ters. In any one of the cases stated, if we compare the 

 amount of nutritive substances in the unmanured por- 

 tion of a field with the crop which it produces, and then 

 compare the additional nutritive substances or the 

 quantity of dung with the increased crop, the increase 

 appears to be beyond all proportion much greater than 

 the additional supply. Hence we are led to suppose 

 that the phosphoric acid, potash, and ammonia given 

 in the manure must be much more efficacious than the 

 substances present in the soil, or that the greater por- 

 tion of them in the soil was ineffective, and that its 

 power of production had depended chiefly upon the 

 supply of manure. Thus it arises, that while some 

 farmers believe that all manure can be dispensed with 

 because tillage is enough to render a field productive, 

 others suppose that the field can be kept fruitful only 

 by manuring. All these views are based upon indi- 

 vidual cases and have no general application ; for 

 neither one nor the other of the contending parties 

 have any clear knowledge of the true causes upon 

 which the power of production of this kind is founded. 

 In the experiments made in the year 1857, by order 

 of the General Committee of the Bavarian Agricultural 

 Union, on the action of phosphorite upon certain fields 

 at Schleissheim deficient in phosphoric acid, the follow- 

 ing crops of summer wheat were reaped from two plots 

 of ground, one unmanured the other dressed, per hec- 

 tare ( = 2J acres), with 241 '4 kilogrammes ( = 530 

 Ibs.) of phosphoric acid, 657*4 kilogrammes ( = 13 cwt.) 

 of phosphorite decomposed by sulphuric acid : 



