SOIL FERTILITY.

Press, Volume LXVI, Issue 13910, 8 December 1910, Page 5

SOIL FERTILITY.

("Weekly Press and Referee.")

An interesting and instructive address was given by Mr A. i>. __11, director oi tho llothanisted expenuienUil Ration, in his position as president ot mo Bnusn Association, jluch ot the intormauon lie gave is especially x«i«resving and useiul to farmers and gardeners. He dealt with the W ed water in plant growth, . and showea that water and not the soil Bupphw the material oi which planis «c'» He mentioned an experiment made by Van Helmont, who placedl 2001b ot dried earth in a tub, »-§ Pi»nt«J therein a willow weighing olb. Alter twelve years the willow *?<» ™*-* d loyib 3oz, whereas the soil «hen redried had lost but 2oz, though the surface had been carefully, protected with a coyS of tin. A similar experiment made by Boyle with pumpkins and cucumbers cave similar results He dSed the plants and obtained from them various tars and oils, charcoal, and ash, from which lie concluded that a real transmutation had been effected; that salt, spirit, and earth may be produced out or water. There is as every t Itivat.-r knows, an abundance of dissolved material in ordinary X?. Hensl-r Pointed out that the salt which is found in. vegetables and niimlk is but the nitre that is so univetally dispersed through all the elements a little altered from its first complexion. About the beginning of tho nineteenth century Priestly and others arrived at the sound idea of what the air is and does. Gardeners, however, belie „t then, as they do now that the fertility of the soil depended upon the character and quantity ot organic matter it contained. Professor Daubeny, of Oxford, the real founder of the science of agriculture in England, first pointed out in 1854 the enormous difference between the amount or plant food in the soil and that taken out by the crop. It is now an accepted fact that any normal soil contains the material for from 50. to 100 crops, but combined in the soil in some form that kept it from the plant, and only a small portion from time to time became soluble and available for food, water passing • through the soil being the great natural solvent. Mr Hall stated: *I am still of opinion that we shall come back to the water charged with carbon dioxide as the only solvent ot its kind for which any Justification can bf* found." American investigators arr-uo that as the plant feeds upon the soil water, and as that soil water must be equr.llv saturated with, say, phosphoric acid, whether the soil contains IOOOIb or 3COOIb per acre of the comparatively insoluble calcium and iron salts of phosphoric acid wluch occur m the soil, the plant r.ust be under equal conditions as regards phosphoric acid, whatever the soil in which it may fie grown. From this it is inferred that the chief factor in plant production must he the supply of water to the plant, and that soils differ from one another far more in their ability to maintain a good supply of water than in the amount of nlant food they contain. It is also supposed that the fertility of soil is often determined by excretions from the plants themselves, and thereby noison the land for a renewed growth of the same crop, though the toxin may be harmless to a different plant which follows it in the rotation. Gardeners experienced in the cultivation of plants in pots and tubs do not believe that plants excrete poisons such as is here suggested. It is not uncommon for a.plant to occupy the same pot and soil for twenty years or more with a supply of ordinary water to maintain bt-alth and vigour. Nitrate producincr soil bacteria may keep up the supply of food for plants thus grown; certainly tho conditions said to be most conducive to this, viz., good drainage, aeration, and warmth, are provided by pot cultivation. Mr Hall called attention to the importance of recognising that those soil bacteria aro most abundant in the surface soil, the most fertile soil being on top, so that deep trenching and ploughing are often not only a waste of labour, but had for the plants. "Not only is the subsoil deficient in humus, which is the accumulated debris of previous applications of manure, and vegetation, but in the humus is tho whole of the bacteria which have co much to do with fertility." Many gardeners will object to this view, deep trenching being a fundamental principle of good cultivation. The nature of tli3 subsoil does, however, make a great difference. The important part played by leguminous plants in drawing nitrogen from the atmosphere by means of tho bacteria which exist upon 4 rielr roots is now generally recognised, but the discovery that there are also nitro-gen-fixing organisms in the soil itself which are capable of gathering combing ed nitrogen without the assistance o* any host plant, provided they are supplied with carbonaceous material, is a j most interesting one. It accounts xor j those differences, in tho quality of soils which gardeners understand and describe as richness, poorness, etc. Another important factor, the discovery of which has'recently been mado by Drs. Russell and Hutchinson at Rothamsted, is that normal soil contains, in addition to the bacteria that cause nitrification, other organisms of the protozoa class, which feed upon bacteria. These can be removed by the application of fire heat, steam, or treatment by antiseptics, when the bacteria increase to an enormous degree. | the fertility of the soil being thereby improved. Mr Hall mentioned tho practice of gardeners who grow cucumbers, tomatoes, etc., under glass, and who find it impossible to use tho same soil for more than two years; but by giving this used soil a good baking, not only is its fertility restored, but it is sometimes too rich for the plants. Heating the soil to be used for raising choice seedlings is quite a common practice, and a market gardener who purified his soil from cucumber and tomato disease by steaming it, found tho treatment had made the soil richer in plant foods. Mr Hall admits that there is yet no simple solution of the problem as to what is the-cause of the-ier-tility of the soil, and all that can Ik 1 done at present is to ascertain % -Jie factors that limit and determine the growth of a plant and and to bring them successively under control. Though production has been increased in various directions, the various forces at work are, not yet all defined.