136 ACTION OF SOIL ON FOOD OF PLANTS IN MANURE. 



which gives the following numbers for the relative diffu- 

 sibility of ammonia : — 



Cuban Schleissheim Garden moiUd Bogenhausen 



1-0 1-24 1-50 2-12 



The absorptive power of arable soils for phosphate of 

 hme, phosphate of magnesia, and phosphate of magnesia 

 and ammonia, may be determined in the same way, and 

 the relative diffusibility of these several constituents in 

 different soils may be expressed numerically. 



By the term ' absorption number,' we designate, in the 

 following pages, the quantity reckoned in milligrammes 

 (= 0-0154 grain) of the several mineral constituents, 

 Avhich one cubic decimetre ( = 61 cubic mches) of earth 

 extracts from their solutions. 



To determine the condition of a field, the action of the 

 manures applied to it, and the depth to wliich the several 

 nutritive substances will penetrate, it is important to 

 estabhsh proportionately the absorptive power of the soil 

 for each of them ; thus, for example, 1 cubic decimetre 

 of Bogenhausen loam absorbs : — 



Accordingly, the second series of these numbers ex- 

 presses that if a certain quantity of ammonia in its passage 

 through the soil penetrates to a depth of 10 centimetres, 

 the same quantity of potash will attain a depth of 11 

 centimetres, and a hke quantity of phosphate of hme will 

 reach 23-6 centimetres. 



In a soil hke the Bogenhausen, which absorbs per cubic 

 decimetre 1098 miUigrammes of dissolved phosphate of 

 hme, let us suppose that granules of phosphate of lime 



