Moisture Retention Characteristics in the Vertisols of the Stip, Probistip and Sv. Nikole Region

This paper has studied the moisture retention in the vertisols of the Stip, Probistip and Sv. Nikole region at eight different tensions (0.1; 0.33; 0.75; 1; 2; 6.25; 11; 15 bars) using Bar extractor and Pressure membrane extractor. The moisture retention curves from these data were drawn for each of the soil samples separately. Results showed that the moisture retention is enormously high throughout the soil profiles depth and depends primarily on the richness of the parent material in clay and montmorillonite, and to some extent on pedogenesis (organic matter accumulation, pedoturbation). Hydropedological constants (field water capacity, wilting point) are in positive correlation with the clay content, but, in case of equal clay content between some profiles, every change of the montmorillonite (MLM) content affects the moisture retention intensiveness. Field water capacity (0.33 bars) varies from 22.47 to 40.47 mass %, or in average 32.40 mass %. But, in spite of the high water preservation, plants in these soils are not provided with enough water because the wilting point (15 bars) has also high values, from 13.55 to 24.68 mass % (average 20.09 mass %). For that reason, available water capacity is 12.32 mass %, or only 38 mass % of the whole moisture, which is retained in the soil, is available to plants. The retention curves are relatively close one to another and do not show big differences between them in the profiles (same mechanical and clay mineralogical composition, profiles homogeneity). They are almost horizontal at 2-15 bars in all cases. The greatest decline of the curves occurs at lower pressures (to 2 bars).