70 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



THE NEW SOIL SCIENCE. 

 By R. Hedger Wallace. 



■Lecture delivered March 11, 1902.] 



Many may recollect that in 1879 the Marquis of Salisbury, in a memo- 

 rable speech, told English farmers to "manure their land with brains ; " 

 and although since then much has been done in respect to land 

 manuring, and our knowledge of soil contents and plant action has 

 increased, yet the inception of the science that now occupies such a pro- 

 minent position in respect to soil cultivation goes back to a period more 

 remote than that in which the Prime Minister spoke, a period when agri- 

 cultural depression in this country was becoming very acute. 



Yet the "new soil science," as the name indicates, is of recent growth, 

 and is a happy term coined by a Scotch agricultural journalist to denote 

 the biological, and more especially the bacteriological, point of view in 

 manuring which to a great extent is to-day supplanting the purely 

 chemical views that have for nearly sixty years held the field. 



It is not my intention to trouble you with any historical data, for 

 I take it that it is a matter of supreme indifference to the practical man 

 whether it was Brown, Jones, or Robinson that first discovered or applied 

 certain facts. He wants to know what the facts are, what common- 

 sense conclusions can be drawn from them, and how he can utilise them 

 to his personal advantage. The "new soil science," so far as it has 

 already developed, has given rise to much controversy, and there are many 

 claimants with their own theories in the field. I therefore limit myself 

 in this paper to views that meet with general acceptance ; for it must be 

 borne in mind that our knowledge of soil bacteria as yet is very imperfect 

 and limited. 



Cultivators, be they termed agriculturists or horticulturists, have to 

 deal with two factors — i.e. soils and plants. What is a soil ? The usual 

 reply to such a question is that it is disintegrated rock broken down 

 by physical and chemical processes called weathering. It used to be 

 regarded as a mass of dead inert matter containing plant-food material 

 which by a chemical action was made available for plant growth. A 

 plant obtains its food material through its leaves and its roots. This food 

 material is of three kinds : (1) water, (2) chemical substances, and 

 (8) gas. Water is an actual necessity to the plant, not only as a food, 

 but as food solvent and food-material carrier. The chief chemical 

 substances that affect plant life are potassium, magnesium, calcium, iron, 

 phosphorus, and sulphur. These inorganic substances do not enter the 

 plant as such, but combined with other substances and dissolved in 

 water. The gases essential to plants are carbonic acid, hydrogen, 

 oxygen, and nitrogen. By the aid of the green chlorophyll leaves absorb 

 carbonic acid from the atmosphere. The hydrogen is obtained from the 

 decomposition of water ; and the oxygen is obtained from the same source 



