THE NEW SOIL SCIENCE. 



79 



former, plants of the same species could not be grown continuously in 

 the same soil, as plants left a residue or ejecta in the soil which could 

 be utilised by other types of plants, but not by the same species. 

 Liebig's views were that the fertility of a soil depended chiefly on the 

 solubility of its chemical constituents and also on the presence of all the 

 constituents required by the plant, in the quantities or amount demanded 

 and requisite for growth. The value we place on the germ life in the 

 soil will depend a good deal on our conception of what is the life of a 

 plant. If the plant be a living thing, then five points are summed up in 

 the word " living," and the plant must therefore be held to eat, drink, 

 breathe, grow, and multiply. It is with the roots of plants that culti- 

 vators of the soil are most concerned. The duties of roots are, first, to 

 anchor the plant in the soil, and secondly, to drink rain water mixed 

 with food- making stuffs ; while the leaves are present for making food, 

 and the flowers &c. consume the food made. The difference between 

 Man and a Cabbage is that the former has no organ or machine to make 

 food out of simple organic and inorganic constituents, while the plant 

 has. Again, it would not be wrong to say that the breathing of a plant 

 is the same as the breathing of an animal, and a soil should therefore 

 have fresh air just as if man lived in it. The air in the soil must there- 

 fore be pure, and it follows that a well-aerated soil is a healthy one. 

 This air goes into the root dissolved in water, but too much water in the 

 soil will, of course, prevent pure air getting into the roots. 



A soil may be said to contain sand, clay, organic matter, water, gas, 

 bacteria, and we may add lime ; in fact, no soil in which plants will grow 

 is without carbonate of lime. Water, as already indicated, is of great 

 importance to plant life : it envelops the particles of sand, fills up the 

 interstices of clay, and is held by the organic matter as in a sponge. Sand 

 holds the stuff the plant will absorb, and clay provides the plant with 

 certain food-making stuffs ; but neither sand nor clay can dissolve in water, 

 and so enter the roots. It is, perhaps, with the organic matter in soils 

 that the "new soil science" is most concerned, for it feeds the bacteria 

 in the soil. Bacteria are also " living " organs or bodies, like plants, and 

 it is held by many that it is really the voidings and excrements of bacteria, 

 which must necessarily permeate the soil, that enter into the plant. Others, 

 again, state that humus is not simply the organic matter in the soil, but is 

 the vegetable matter which has been digested by soil germs ; in other words, 

 that humus is the excrements of bacteria ; and it is added that roots do 

 not feed on humus. The last view is probably correct, for after the growth 

 of plants there is more humus in the soil than before, and cultivation 

 of plants, it is acknowledged, increases the humic contents of the soil. 

 The roots of plants use the soil, first, for space or room ; secondly, for 

 stability ; thirdly, for obtaining raw material ; and fourthly, for obtaining 

 . air to breathe. But if there is air in the soil there must also be, as the 

 result of germ life, carbonic acid gas, and this must be a detrimental 

 factor. How is it removed or overcome ? That it has an influence we 

 can conclude from the general observation that bacterial results are better 

 and greater in fresh soil than in any other. 



The main point, I take it, which has to be recognised is that the 

 soil is not a chemical laboratory, and is not made up of a number of 



