The impact of long-term irrigation on the degree of aggregation and the mineralogical composition of the clay fraction in dark chestnut soils of the Transvolga region |
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| Authors: | N P Chizhikova V A Baranovskaya N B Khitrov |
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| Institution: | 1.Dokuchaev Soil Science Institute,Moscow,Russia |
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| Abstract: | Dark chestnut soils of the Ershov Experimental Station in the Transvolga region are characterized by the even distribution
and aggregation of clay minerals in the profile. Hydromica, chlorite, kaolinite, and smectitic minerals predominate in the
clay (<1 μm) fraction. The smectitic phase consists of randomly ordered mixed-layered minerals of the following types: mica-smectite
with a low (<50%) content of smectite layers, mica-smectite with a high (>50%) content of smectite layers, and chlorite-smectite.
In some horizons, the smectitic phase occurs in the superdispersed state. The long-term irrigation of these soils with fresh
water of the Volga River has led to certain changes in the composition and properties of the clay particles. The weakening
of bonds between them has taken place. As a result, the content of water-peptizable clay has increased by two times, and the
content of aggregated clay of the first category (AC1) has increased by 1.5 times at the expense of a decrease in the contents
of tightly bound clay (TBC) and aggregated clay of the second category (AC2). Also, the redistribution of organic matter bound
with clay particles has taken place: its content in the AC1 fraction has decreased, whereas its content in the AC2 and TBC
fractions has increased. In the topsoil horizon, the amount of the smectitic phase has lowered, whereas the contents of hydromica,
kaolinite, and fine-dispersed quartz in the clay fraction have increased. In general, some amorphization of the clay material
has occurred. The periodic alkalization of the soil solutions upon irrigation has led to the conversion of the smectitic phase
into the superdispersed state in the entire soil profile. |
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