Agrochemistry and microbial activities under halophytes grown under different salt affected soils

抄録

Management of innovative strategies for marginal low-quality soil and plant resources utilization is crucial in the Aral Sea Basin saline environments. This article is focused on the development of technology of cultivation of wild halophytes and non-conventional crops on saline farmlands in the Delta of Amudarya (Aral Sea Basin) and their phytoindicative role in improving the agrochemistry of saline soils properties. Changes in physical and chemical soil properties along an evident salinity gradient were interrelated with botanic diversity and seasonal activities of soil microbial communities under different halophyte ecological groups and non-conventional crops (NCC). A multi-step approach was used to mobilize appropriate halophytic plant resources in pure stands or in mixed plantations to support salt affected lands restoration and to improve crops-livestock-feeding farming and to secure income for rural communities. Experiments were conducted in the Muynak region (43°46’ N 59°02’ E) under different categories of marginal lands, characterized by different soil chemistry and level of salinity in the topsoil profile.

Significant variation in physical and chemical parameters of soils under wild and cultivated crops were revealed. Differences were in the aggregate composition, structure coefficient, number of salts in the soil at slight change in pH value. According to the content of humus and mobile ions (NPK), these soils are characterized as low-income: total nitrogen 0.022-0.042%; total phosphorus 0.076-0.088%; total potassium 0.7%. The humus content ranges from 0.42-0.56%; the level of N-NH₄ is 2.18-3.41 mg/kg of soil; N-NO₃ is 0.26-3.5 mg/kg, P₂O₅ is 1.22-2.30 mg/kg, while there is an essential difference between soils chemistry of different farmlands categories (e.g., abandoned by farmers paddy rice fields, fields margins, wet marches etc.)

The activity and number of soil microorganisms depends on the total impact of biotic and (or) abiotic factors, as well as the degree of anthropogenic pressure on the agricultural lands. There were differences in numbers and diversity of microorganisms of the soils in cultivated farmer lands. Co-existing of various ecological and trophic groups of microorganisms, such as oligonitrophilic, oligocarbophilic, ammonifying, amylolytic, free-living nitrogen-fixing bacteria, as well as active hydrolytics, bacilli, actinomycetes and micromyceteswere detected. Availability of appropriate proportion of nutrients in salt affected soils is considered the main limiting factor of microbial communities’ diversity and activities. Obviously, this is a reason why oligotrophic microorganisms (oligocarbophilic and oligonitrophilic) dominated in all categories of marginal saline lands, i.e. those microorganisms that are not competing under low soil nutrient compounds (C, N. and P). There is a wide variety of representatives of microorganisms of other ecological and trophic groups. We have also revealed variation in the level of enzymatic activity (ureases and phosphatases), which indicates high metabolic adaptive potential of soil microbial communities and capacity of arid soils to resist negative factors.