A comparative assessment of the biological activity of soils in the Selenga river upper delta according to the content of enzymes

Soils of the Selenga river upper delta main tributary of the freshwater Lake Baikal experience arid conditions, as well as the influence of uncontrolled pasture use by cattle in the areas of the central floodplain (hereinafter "floodplain"). The aim of the study was to compare the biological activity (hereinafter "activity") of soils of hard-to-reach islands and floodplains according to the degree of enrichment with catalase, protease and urease. In August 2005, soil samples from the upper horizons of 8 soil profiles were selected for the study in the same period. Three soil profiles (prof. 1-05-3-05) were laid on two islands upstream from the village of Murzino, Kabansky district of the Republic of Buryatia. Two were on the island "Residence", opposite Murzino, on the other side of the river (prof. 4-05 and prof. 5-05). In the floodplain near Murzino 3 incisions were laid. Profile 6-05 was on the edge of the Selenga river bed, regulated by a dam, and now a small pond. Profile 7-05 was 200 m from an artificial dam east of Murzino. Profile 8-05 was on the elevated terrain, about 500 m from the river bed. The geographic coordinates of biotopes are given in the paper. The enzymatic activity of soils was investigated according to the standard methods described in the practical guide of KSh Kazeeva et al. (2003). Other methods of soil investigation were used from the classic manual "Agrochemical Methods of Soil Research" (1975). The most pronounced activity of soils is the degree of enrichment with protease, a very high degree. The activity was high according to the content of catalase. According to urease, the activity was weak in all soils (See Table 1). In arid conditions in biotopes with an increasing terrain, the activation of soil enzymes was influenced by the arrival of fresh plant litter, and in the floodplain, in addition, the supply of cow's waste products from the livelihoods. The soils of the lowlands of the floodplain are more moistened than the soil of the islands, they have better parameters for the content of humus and physical clay (See Table 2), therefore, the activity of enzymes is higher than that of island soils (differences are statistically significant, P_U<0.05). Correlation analysis was performed comparing the series of values of the enzyme content, water-soluble ammonia, nitrates in the day horizons of delta soils with a series of values of physical and agrochemical parameters (See Table 3). A complete direct correlation was found between the soil moisture content and the protease content (r= +1.00). With these parameters and the contents of water-soluble ammonia, there is a strong correlation (r = +0.81). With the same soil indices and catalase (r= + 0.18), urease (r= + 0.20) there is a weak degree of correlation. The inverse of the average degree of correlation is also with the moisture values and the series of values of the nitrate content (r= -0.55). Positive correlation between pH values of water and values of all enzymes: with catalase (r= +0.43), with protease (r= +0.54), and with urease (r= +0.4). Positive correlation is determined between the values of cations Mg²+, Na² + and mobile phosphorus (P₂O₅), on the one hand, and the contents of enzymes and CO₂ emission values, on the other hand (See Table 3). In general, the biological activity of soils in the floodplain is higher than that of soils of less humidified islands.

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