150 ACTION OF SOIL ON FOOD OF PLANTS IN MANUEE. 



plied by the manure. As the manured plot gave dou- 

 ble the produce of the unmanured, the effect of the 

 phosphoric acid supplied by the manure is apparently 

 twelve times greater than that of the acid originally 

 contained in the soil. 



The quantity of phosphoric acid supplied (241*4: kilo- 



frammes) amounted to T V th of the total quantity in the 

 eld (2376 kilogrammes). If the action of both had been 

 alike, the surplus crop should have corresponded to the 

 additional supply, but instead of being y^th greater, it 

 was double the crop obtained from the unmanured plot. 



This fact is explained by the absorptive number of 

 the Schleissheim soil for phosphoric acid or phosphate 

 of lime. 



If the store of phosphoric acid in the field had been 

 uniformly distributed in the form of phosphate of lime 

 (5170 kilogrammes) to a depth of 25 centimetres (9-8 

 inches), each cubic decimetre (61 cubic inches) would 

 contain 2070 milligrammes (32 grains), each cubic centi- 

 metre about 2 milligrammes of phosphate of lime. 



The field was manured with 657*4 kilogrammes of 

 phosphorite in a soluble state, corresponding to 525 

 million milligrammes (525 kilogrammes) of pure phos- 

 phate of lime. 



As determined by direct experiments, 1 cubic deci- 

 metre of Schleissheim soil absorbs 976 milligrammes of 

 phosphate of lime. Each square decimetre received in 

 the manure 525 milligrammes, which, dissolved by rain 

 water in its descent through the soil, would be sufficient 

 to saturate the earth fully, with phosphate of lime, to a 

 depth of 5*4 centimetres (rather more than 2 inches), or 

 to half-saturate it to a depth of 10*8 centimetres. Hence 

 the manuring served to enrich the upper layer of the 

 soil with phosphate of lime, not to the extent of T Vth, 

 but to 50 per cent., and the greater part of this in a 

 state available for the nutrition of plants. The absorp- 

 tive power of the soil explains, therefore, why the crops 

 obtained from manured fields are rather in proportion to 

 the nutritive substances supplied in the manure, than to 

 the store of these elements originally present in the soil. 



