Physical properties of alluvial soils on the fields of perennial grasses and potato
The aim of present work was profound research of changes of soil physical properties in the flood plain of Insara and Sura rivers when cultivating vegetable crops and perennial grasses. The object of study is soils of the flood plain of Insara and Sura rivers occuried by potato and perennial grasses. Fields were located in the central part of flood plain. Depth of humus-accumulated horizon is 45-55 cm. Groundwater is at 1.4-1.8 meters depth. Plot relief is plain. The average content of humus in the researched area soil in plowing layer is 4,4-5,8 %. According to the degree of acidity of the soil is characterized as slightly acidic - neutral. Base saturation is 92-94 %. The content of mobile phosphorus and exchange potassium is very high: phosphorus - 20,6 - 26,0, potassium - 25,2 - 36,2 mg/100 g of soil. One half of the floodplain area was cultivated and has been used for disposal of vegetable crop rotation (vegetables and potatoes) since 1994. Heavy wheeled equipment has been used for cultivated crop tillage, and for harvest - heavy vehicles. The second half of the area has been occupied by perennial grasses since 1994. The researched areas are perpendicular to the direction of Sura and Insar rivers. Observations, tests and calculations on soil samples from 0-120 cm depth were conducted during the research to determine crops impact. We have determined: granulometric composition - pipette method by N. A. Kachinsky, soil preparation was carried out by the processing with 0,05 n. HCl and further boiling; soil density (g/cm<sup>3</sup>) - by volume-weight method; density of matrix soil - by picnometer method; soil porosity and aeration porosity -calculation method by B.A. Dospekhov and co-authors (1987). Conducted research revealed significant differences of alluvial soil physical properties under perennial grasses and potatoes. It was revealed that under the influence of 15 years of tilled crops cultivation, a highly tight soil layer of 20-50 cm has appeared. Cultivation of perennial grasses leads to decompaction of this layer and decrease of soil density by 0,15 cm<sup>3</sup> in comparison with potato cultivation, increase of total porosity by 3-5 % and aeration porosity by 2,8-4,7 %. It is proved that moderate-recovery range is typical for researched soils. Soil layer 0-20 cm in the potato planting has higher redox in comparison with perennial grasses fields. In the layer 50-120 cm, alternatively, redox parametres in perennial grasses seedings are higher by 9, 4-10, 3 %. To improve the physical properties of alluvial soils, it is necessary to organize agricultural land use territories with development and exploration of schemes, projects of land regulation and implementation of vegetable-grass crop rotation instead of already existing vegetable.