Ecological-Geochemical Assessment of Soil Salinization and Humus Degradation in the Irrigated Lands of Kashkadarya Province, Uzbekistan
Author: Oʻktamova Sabrina Mahmud qizi
1st-year Student of Ecology, Faculty of Geography and Agronomy, Karshi State University, Uzbekistan
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Abstract
Anthropogenic land degradation in the arid zones of Central Asia poses a severe threat to agricultural security. This study presents a comprehensive ecological-geochemical assessment of irrigated soils in the Karshi Steppe of the Kashkadarya Province, focusing on Kasbi and Nishan districts. Soil samples collected from the 0–20 cm and 20–40 cm depths were systematically analyzed for pH, electrical conductivity (EC_1:5), dry residue (TDR), individual toxic ions (Cl^-, SO_4^2-), and soil organic matter (SOM/Humus). The geochemical analysis revealed a predominant sulfate-chloride type of secondary salinization, with dry residue values exceeding $1.1\%$ in heavily impacted zones of the Kasbi district. Concurrently, a critical decline in soil organic matter was observed, with average humus levels dropping to $0.65\%–0.88\%$. This paper establishes the direct correlation between high saline groundwater tables and topsoil degradation, proposing integrated ecological mitigation measures such as gypsum application, biological drainage, and conservation agriculture to halt further desertification in southern Uzbekistan.
Keywords: Karshi Steppe, Kashkadarya, Soil Salinization, Sulfate-Chloride Chemistry, Humus Depletion, Arid Geochemistry.
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1. Introduction
The transformation of the Karshi Steppe in the southern part of Uzbekistan during the 1970s via the construction of the Karshi Cascade of Canals stands as one of the largest hydrological engineering feats in Central Asia. It brought over a million hectares of virgin grey-brown (bo’z-qo’ng’ir) and desert soils under intensive irrigation, primarily for cotton and wheat monoculture. However, this massive anthropogenic intervention lacked sufficient closed horizontal and vertical drainage networks, leading to a long-term ecological imbalance (Gafurova et al., 2020).
Under the influence of a sharply continental, arid climate—where potential evapotranspiration exceeds precipitation by almost tenfold—the water-salt balance of the region’s soils has shifted dramatically. The saline groundwater table has risen from a depth of 10–15 meters to a critical level of 1.5–2.0 meters from the surface (Kuziev & Sektimenko, 2009).Capillary forces continuously pull this brackish water upward, depositing high concentrations of toxic sodium chloride and magnesium sulfate in the root zone upon evaporation.
In addition to salinization, the ecological status of these soils is highly threatened by organic carbon depletion. Humus (soil organic matter) is the core indicator of soil biological activity and physical structure. Intensive tillage, burning of crop residues, and lack of organic manure application have accelerated the mineralization of organic carbon, leading to a structural collapse of the soil. This study aims to provide a precise geochemical and ecological evaluation of these dual degradation processes in the Kasbi and Nishan districts of Kashkadarya.
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2. Materials and Methods
2.1. Study Area and Environmental Settings
The research focused on the irrigated agricultural zones of Kasbi district (characterized by clayey-loam meadow alluvial soils) and Nishan district (characterized by sandy-loam grey-brown soils). The regional climate is characterized by an average annual temperature of 16.2°C and an annual rainfall of only 180–210 mm, concentrated mainly between November and April.
2.2. Sampling and Analytical Geochemical Methods
A total of 20 representative soil profiles were dug, and composite samples were collected at depths of 0–20 cm (rhizosphere/plow layer) and 20–40 cm (subsoil). The samples were air-dried, crushed, and passed through a 2-mm sieve.
• Water Extract Analysis (1:5 ratio): Used to determine total soluble salts (Dry Residue), chloride anions (Cl^-) via Argentometric titration, and sulfate anions (SO_4^2-) via precipitation with barium chloride.
• Electrical Conductivity (EC_1:5): Measured using a calibrated digital EC meter.
• Soil Organic Matter (SOM): Determined using the Tyurin method (wet combustion with K_2Cr_2O_7 and H_2SO_4), followed by titration with Mohr’s salt.
• Soil pH: Evaluated in a 1:2.5 soil-water suspension using a glass electrode pH-meter.
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3. Results and Discussion
The laboratory geochemical data presents a clear picture of severe soil degradation and secondary salinization profiles in the studied districts (Table 1).
Table 1: Geochemical and Chemical Profile of Irrigated Soils in Kashkadarya Province
3.1. Chemical Typing of Salinization
The ratio of anions (Cl^- / SO_4^2-) is the primary geochemical index used to classify the type of soil salinity.
• In the Kasbi district, the ratio is approximately $0.54$, which firmly categorizes the soils under the Sulfate-Chloride type of salinization. This indicates a highly toxic environment, as high chlorine ions inhibit the enzymatic activity of the soil and restrict the uptake of essential nutrients like nitrogen and phosphorus by crops.
• In the Nishan district, the salinity is slightly lower but still harmful, displaying a Chloride-Sulfate chemistry with a dry residue of $0.58\%$ in the topsoil.
3.2. Humus Depletion and Ecological Imbalance
The soil organic matter (Humus) content in the plow layer (0–20 cm) of both districts is dangerously low, ranging between $0.68\%$ and $0.85\%$. Historically, the native soils of the Karshi Steppe maintained a humus baseline of $1.5\%–1.8\%$.
This dramatic decline ($>50\%$ loss) is a direct consequence of:
1. Intensive tillage: Conventional deep plowing accelerates the exposure of organic compounds to microbial decomposition, leading to rapid carbon mineralization into CO_2.
2. Absence of Crop Rotation: The continuous rotation of cotton and wheat without alfalfa (bedapoya) or cover crops has depleted the natural nitrogen-carbon cycle.
3. High Salinity Stress: High salt levels restrict the growth of soil microbes, lowering the overall microbial biomass carbon and preventing the natural synthesis of humic substances.
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4. Advanced Ecological Mitigation Strategies
To restore the ecological health of Kashkadarya’s soils, a multi-tiered ecological approach must be implemented:
1. Chemical Amelioration (Gypsum Application): Since these soils exhibit high pH ($>8.3$) and sodium accumulation, applying phosphogypsum (CaSO_4 · 2H_2O) is necessary to replace toxic sodium ions (Na^+) on the soil clay exchange complex with calcium (Ca^2+), thereby improving soil structure and water permeability.
2. Phytoremediation with Halophytes: Cultivating deep-rooting halophytes like Glycyrrhiza glabra (Licorice) and Atriplex nitens helps lower the saline water table through biodrainage and removes toxic salts from the upper horizons.
3. Humus Restoration via Conservation Tillage: Transitioning to Minimum Tillage or No-Till systems, coupled with applying biochar and organic composts (15–20 tons/ha), will sequester carbon and rebuild the degraded humus layer.
5. Conclusion
The agricultural lands of Kasbi and Nishan districts in the Kashkadarya Province are undergoing profound ecological stress. The dual pressure of sulfate-chloride secondary salinization and extreme humus depletion has crippled the soil’s natural productivity. Correcting this ecological trajectory requires an immediate transition from intensive conventional farming to modern, eco-friendly conservation agriculture and biological
References
1. **Gafurova, L. A., & Nabiyeva, G. M.(2020). Degradation of irrigated soils under the influence of anthropogenic factors in the southern regions of Uzbekistan. Journal of Soil Science and Agrochemistry, 74(3), 145-154.
2. Kuziev, R. K., & Sektimenko, V. E. (2009). The Soils of Uzbekistan: Genesis, Classification, and Ecological Status. Tashkent: Fan Publishing House, 256 p.
3. Pankova, E. I., & Konyushkova, M. V. (2013). Assessment of soil salinization in the irrigated lands of Central Asia using remote sensing and ground truth data. Arid Ecosystems, 3(4), 212-221.
4. Shirokova, Y. I., & Morozov, A. N. (2006). Salinization of irrigated lands in Uzbekistan and ways to improve the state of soils. Irrigation and Drainage, 55(s1), 53-62.
5. Ibrakhimov, M., Park, S. J., & Vlek, P. L. G. (2007). Temporal dynamics of groundwater table and salinity in the lower reaches of the Amu Darya River. Agricultural Water Management, 92(3), 115-126
Oʻktamova Sabrina Mahmud qizi is a prominent and highly intellectual young representative of modern Uzbek youth, distinguished by her thirst for knowledge, social activism, and ambitious goals for the future.
Born on March 24, 2007, in Karshi city, Kashkadarya region, into an intellectual family, Sabrina graduated from school with excellent grades. She gained admission to Karshi State University (QarDU) on a state grant, where she is currently pursuing her bachelor’s degree in Ecology.
Despite her young age, Sabrina’s ability to fully capitalize on opportunities and achieve remarkable success is greatly supported by her parents, Islomov Mahmud and Geldiyeva Shahnoza. Her elder sister, Jasmina Makhmudovna, has been a key mentor and a significant source of inspiration in fostering Sabrina’s profound passion for knowledge and excellence.
Sabrina’s current achievements include:
• An active Eco-Volunteer and Social Volunteer.
• Regional winner of the Vociep project.
• Member of the “Children and Youth Support Movement” and a recipient of its special badge.
• An active member of the People’s Democratic Party.
• Recipient of over a hundred certificates from various educational and extracurricular programs.
• Participant in several international forums.
• An active participant and international certificate holder in the recent International Eco-Zakovat competition, recognized as a talented and active student and leader.
• An active member of the Kashkadarya “Golden Wing” Organization and the Youth Golden Wing initiative.
• Recipient of multiple Machine Learning (ML) grants.
Sabrina embodies a dynamic spirit, combining academic excellence with a strong commitment to social and environmental causes, making her a highly promising future leader and expert in the field of ecology.