Saturday, 15 July 2006
136-8

Subsoil Compaction and Preferential Flow Paths Formation.

Aminat Umarova and Evgeny Shein. Moscow State Univ, Leninskie Gory, Leninskie Gory, Moscow, 119992, Russia

Special attention of the researchers is given to specific, inherent in the basic soil objects, features of soil water and matter movement, - formation separate "of water channels", lines of a primary flow, "fingers”, “preferential flows”. Formation "of water channels" was marked, as a rule, in layered soils. The researchers emphasized, that the existence of layers in soil profile is one of the reasons of non-uniformity of front of humidifying, occurrence "fingers structures" movements of moisture: the instability of flows of water arises in two-layer (hydrophilic/hydrophobic, moisture/dry, high/bad filtration) soils. The majority of the similar phenomena were marked in sandy soils, in which layers were homogeneous, but appreciably differed on hydrological properties. The purpose of the given work is the study of laws of interrelation of the basic ways of migration with spatial (horizontal and vertical) distribution of soil density in field conditions in scale of a soil individual. Thus the following tasks were put: (1) to study migration of a moisture in conditions close to saturation; (2) to find out laws of formation of spatial distribution of the basic ways of migration depending on horizontal and vertical distribution of soil density. As the basic method of research the method of soluble starch label was used. On a surface of ground established a frame, water was filtrated within 6-8 hours. Then, at once after a filtration of water, marked by soluble starch (concentration of starch - 2 %) was used. The ways of a filtration of water were marked in day after on horizontal platforms (through 10 cm steps) on humidifying surface bromide water. Morphology and the preferential ways of water filtration were registries by photo, video or pantograph. After a sketch of ways of movement of a water labeled soil moisture, density, penetration resistance were determined on platforms the size not less than 1 m2 with a step 10 cm on a grid. Total of dates on one platform made about 100-180. The accumulation of moisture above the condensed subsoil layer is rather characteristic, the formation of the separate “water ways” inside the condensed layer on depth 35-55 cm also attract considerable attention. This “water ways”, “fingers” are kept up to sufficient depth. Even these qualitative supervision over movement of water with the help of a label allow to speak about a significant role of subsoil compacted layer in change of movement of substances in a soil structure, about the formation of “the preferential flow paths” just in this layer. Moreover, generated flows have the strictly vertical form, this form and space positions vary only slightly with depth. In this case we come nearer to a "classical" case of formation the preferential flow paths connected with hydrophobic soil layers. But in our case the subsoil compacted layer was the origin of this “fingers”, and this “fingers” were formed in filtration experiments, without hydrophobic layers, but in common agricultural soils with subsoil compacted layer. To our mind this phenomenon is not the same as the "classical" preferential flows: this phenomenon makes itself evident in filtration experiments, in natural clay-loam soils, and the origin of this phenomenon is the spatial (vertical and horizontal) distribution of soil structure (soil density above all). It allows to assume, that the preferential flow paths, generated in a compacted layer keep the orientation and form in process of a filtration in deep layers. Water moves through naturally compacted sites in the bottom part of a soil profile, in spite of the fact that there is an area with much more friable soil structure. It specifies strict orientation of flows, preservation of their form in process of a filtration in deep layers and, therefore, matter penetration in deepest layers. This phenomenon has shares a number of traits with classical preferential flow effects, but is another in origin and a prerequisite to the formation: spatial distribution of soil porosity (different density categories and there orientation in vertical and horizontal directions) and in saturated water conditions. So, in scale of a soil individual (area of research about 1 m2), in conditions of movement of a moisture close to a filtration, the following regularities of spatial distribution of density and preferential ways of water migration in Grey clay-loam soils are observed: 1) The filtration of water is carried out not to all soil pore space, and not only on the most friable sites of a structure. Main volume of water is filtered on those categories of density, which occupy the greatest share within the limits of horizontal platforms and best keep a vertical arrangement in a structure of ground (are least twisting in a vertical direction). 2) An essential role in formation of the specified two characteristics determining the spatial form of the preferential ways of migration, is played subsoil compacted layer, where there is a change of categories of density and the vertical position of a spatial arrangement of these categories is formed.

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