128 



SOIL CONDITIONS AND PLANT GRO WTH 



been made in this country and on the Continent throw some 

 light on the composition of the soil solution. As might be 

 expected from the known absorptive properties of clay and of 

 humus, drainage water contains mere traces of NH 4 and PO 4 , 

 and only little K ; it contains chiefly carbonic acid, SiO 4 , Cl, 

 SO 4 , NO 3 , Ca with some Fe, Mg, and Na. Typical analyses. 

 are given in Table XXXVII. 



TABLE XXXVII. ANALYSIS OF DRAINAGE WATERS FROM CULTIVATED FIELDS r 

 PARTS PER MILLION OF SOLUTION. 



It will be observed that the total concentration of the 

 Rothamsted drainage water varies from -02 to "05 per cent. 



Organic Matter. 



The distinguishing characteristic of soil is that it contains 

 part of the complex material synthesised by plants. This 

 material affords energy to numerous micro-organisms, and is 

 gradually converted by them into simple substances appro- 



1 A. Voelcker's analyses of five samples collected between 1866 and 1869 

 (289^); 



2 Von Seelhorst's analyses of samples collected weekly, or fortnightly, from 

 a field between August, 1899, and August, 1900 (258) 



