JOURNAL 



OF THE 



ROYAL HORTICULTURAL SOCIETY. 



Vol. XLIV. 1919. 



SOIL MAKING. 



By Dr. E. J. Russell, M.A., F.R.S., C.B.E. 



[Read July 2, 191 8 ; Mr. E. A. Bowles, M.A., V.M.H,, in the Chair.] 



One of the earlier lecturers on soil, Evelyn the famous diarist, intro- 

 duced his subject by a quotation from a philosopher who argued 

 that there were " one hundred and seventy-nine millions, one thousand 

 and sixty, different sorts of earths." Present-day audiences do not 

 favour such minute subdivisions, and I shall therefore adopt a much 

 broader basis of classification. For our purpose it is sufficient to 

 divide the constituents of the soil into two great classes — mineral 

 matter derived from the rocks, and organic matter derived from 

 plants. Generally there is a great disproportion in amount between 

 these : in an ordinary field soil the mineral matter forms about 95 

 per cent, of the whole and the organic matter only 5 per cent., or 

 sometimes less. In a garden soil there may be up to 10 per cent, of 

 organic matter and 90 per cent, of mineral matter. Only in fen and 

 peat soils does the organic matter rise much higher in amount, and 

 there it may constitute 60 or even 70 per cent, of the whole. Trans- 

 lating these figures into tons to the acre we find that to a depth of 

 9 inches the mineral matter constitutes about 950 tons and the organic 

 matter about 50 tons of the dry matter. 



The processes by which the mineral matter has been formed 

 belong to the study of geology ; we are concerned only with the broad 

 results of the changes. The solid rocks have been ground down to 

 particles varying in fineness from an impalpable powder upwards to 

 gravel and stones. There is considerable difference in chemical 



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