Vízügyi Közlemények, 1936 (18. évfolyam)
Kivonatok, mellékletek - Kivonat a 4. számhoz
19 The inorganic substances are minerals (detailed in the Hungarian text). There is a definite difference between the mineral substances of particles larger and those smaller than 0.002 mm. Particles larger than 0.002 mm may consist of very different minerals, while those smaller than 0.002 mm contain, besides a small amount of quarzite, olimmer, feldspar and calcite, chiefly various clayminerals which form the most active part of soils and possess the property of base exchange. The organic matters consist partly of vegetable and animal remainders or their components, but in most cases chiefly of organic compounds called humus substances. Clay minerals and humus form the absorption complex, which is decisive for the chemical and physical properties of soils. The absorbed kations : H, Fe, AI, Ca, Mg, К and Na play the most important part in it. As one or another prevails in the absorption complex, the soil shows acid (11 soils), alkaline (Na soils), neutral or slightly alkaline (Ca soils) properties. These are in close connection with the physical properties, which, in general, are good in calcium soils, mediocre in hydrogen soils, and bad in alkali soils. Soil solution. Its quantity and concentration vary with the water content of the soil, and its composition in most cases indicates the type of soil. The soil air differs from the atmospheric air in having mostly a high content of C0 2. Furthermore there are various living organisms, plants and animals, which play an important part in the transformations proceeding continuously in soils. Physical properties. Coherence or the degree of coherence is one of the most important properties of soils. The more coherent a soil is, the more it is inclined to have a definite structure. The degree of coherence depends to a certain extent on the mechanical composition. Sandy soils have no coherence ; it increases with augmenting quantity of clay particles. Moreover, bases in the absorption complex also play an important part ; heavy clayey soils containing calcium are moderately coherent, while looser loam soils containing sodium may be as coherent as heavy clay soils. Shrinkage and swelling are in close connection with the water-carrying capacity and the coherence of soils. Sandy soils do not shrink and swell, while clayey soils do so very much. Plasticity and liquid limit also belong to this group of properties. The. volume of voids of soils in a natural state is variable. Therefore the minimum volume of voids (related to 100 gramms of dry substances in one cu cm) seems to be a better characteristic of this property (Table IV.). The volume of voids free from tension (after Zunker) plays an important part in the permeability of soils. From the point of view of agricultural engineering, the behaviour of the soil towards water is the most significant. Minimum water capacity indicates a quantity of water that the soil can detain against gravity. It is fairly independent of the settlement and structure of soil. Ilygroscopicity characterises, according to Mitscherlich, the total surface of soil. Recent investigations (references and tables in the Hungarian text) have shown that the quantity of the hygroscopic water is dependent on the bases absorbed. In addition, the quantity of the absorbed water is a hyperbolic function of the vapour pressure or the osmotic pressure of the surrounding solution (fig. (i). The quantity of water available to plants depends upon the suction force of roots and the osmotic pressure of the water and soil solution absorbed. 2*
