Irrigation-Initiated Changes in Physicochemical Properties of the Calcisols of the Northern Part of Fergana Valley

Abstract

Agriculture in Central Asia and in the Fergana Valley in general strongly depends on irrigation and drainage of agricultural lands. The Fergana Valley includes about 45% of the irrigated area in the Syr Darya River basin. Active use of irrigation in agriculture can lead to changes in the soil’s natural composition, as well as pollution and changes in the soil’s physical and chemical properties. Soil degradation in the process of irrigation can lead to a decrease in crop yields and, as a consequence, to a decrease in food security in the region. In this study, a comparative analysis of three main types of Calcisols (Dark, Light, and Typical) before (uncultivated soil) and after agricultural use (surface-irrigated agricultural soil) was carried out. Irrigation leads to increment of SOC stocks in Typical (from 113.8 to 126.3 t/ha) and Light (from 62.8 to 100.1 t/ha) Calcisols and to decreasing of SOC stocks in Dark Calcisols (from 160.1 to 175.3 t/ha). In general, the content of biophilic elements (SOC and TN) is lower in irrigated soils, and their distribution in the soil profile is close to the functional relationship (r² 0.98 to 0.99). In uncultivated Calcisols, the profile distribution of SOC and TN is more heterogeneous (r² 0.67 to 0.97). Changes in the humification processes of soil organic matter are also identified; in soils after irrigation the carbon ratio of humic/fulvic acids (CHA/CFA) is lower (<1) compared to their uncultivated counterparts (~1). The alteration of the soil water regime also resulted in transformation of the individual compositions of amino acids. All studied types of Calcisols are characterized by changes in particle-size distribution of soils especially in the number of the silt fraction (0.01–0.05 mm) and the difference between uncultivated and irrigated soils, 10–20%, which is associated with the processes of colmatage by accumulation of a fine fraction and replacement of sub-fractions in the fraction of sand. The highest concentrations of nutrients are characteristic of the upper soil horizons (P up to 231, K up to 2350 mg/kg), which indicate their pedogenic and agrogenic origins rather than inheritance from the parent material. Soil P and K availability is rather high, with non-labile forms prevailing, although of near reserve. The surface irrigation results in apparent accumulation of water-soluble Mg²⁺ (1.6–2.1 meq/100 g) and K⁺ (0.6–0.9 meq/100 g), but the cation of Ca²⁺ predominates in the base cations’ composition, which is the most favorable in terms of soil agrogenic property formation. Data obtained will be useful for development of strategies for effective land use in arid, subtropical, overpopulated regions of Central Asia that have deficient water sources and intensive soil degradation.

1. Introduction

According to FAO data, approximately 1.5 billion hectares of soil worldwide are suitable for agriculture [1]. Neutral and slightly alkaline soils in subtropical zones with dry climates comprise 8177.1 thousand hectares or 5.46% of the total land area globally. Additionally, 14.5 million square kilometers, or 11% of the world’s land area, is suitable for agricultural production. Over the last 50 years, the area of irrigated land has increased by nearly 12%, resulting in a 2.5- to 3-fold increase in agricultural production [1,2]. Consequently, the study of theoretical bases for improving soil-ecological and energy states and increasing the fertility of neutral and weakly alkaline soils, considering the agrogenic and post-agrogenic evolution of virgin and irrigated lands, as well as the development of theoretical and practical aspects of their enhancement, is of significant importance [3,4].

Food security issues are prominent both globally and in Central Asia, where population growth and diminishing agro-productive resources are critical concerns. This is further aggravated by irrigation water scarcity and challenges in water management. In this context, the Fergana Valley serves as a highly informative site for soil and agroecological research. Transboundary and geopolitical risks to food security are pronounced here, as the valley spans parts of Uzbekistan, Tajikistan, and Kyrgyzstan. The Fergana Valley and the Zeravshan oasis are pivotal Central Asian regions within the post-Soviet space responsible for food security. In contrast, Uzbekistan’s vast desert and semi-desert areas are underutilized due to moisture deficits. In the Fergana Valley, more readily available water resources have led to the expansion of farming into the adyr zone, previously deemed unsuitable for agriculture, and even into the Yazvan sand massif, where unique landscapes and fauna are being compromised for rice cultivation [3,4,5].

At present, many scientific studies are devoted to the problems of sustainable development of the Fergana Valley. Some studies are focused on the problems of water resources and changes in their quality in the process of agro-industrial development of the region [3,4]. The influence of irrigation on soil quality under cultivation of different crops (cotton, wheat, barley, etc.) was studied [5]. The relationship between irrigation and drainage water composition and their influence on chemical properties of soils in the Fergana Valley were studied with the example of hydromorphic and other soils [6,7,8]. Earlier, it was also shown that long-term irrigation leads to overconsolidation of soils and formation of pedolitic (petrocalcic) soil layers, which leads to changes in biochemical properties of soils in the context of crop cultivation [9,10]. The parent materials of the Fergana Valley include loess rocks, alluvial layered rocks, proluvial pebble deposits, and sands of various origins. Despite sands occupying a smaller area, overgrazing has led to significant wind erosion problems [11]. Historically, the Andijan district had over-moistered soils typical of swampy conditions before intensive drainage efforts in the 20th century [12]. Under the direct influence of anthropogenic factors, the soils of the central Fergana desert zone, which began to be intensively developed from the 1930s to the 1950s, have undergone significant changes. Notable transformations have occurred in their morphology, agrochemical parameters, and salt composition. Calcisols, a crucial component of the soil cover in the Fergana Valley, have particularly been affected. Following their cultivation and incorporation into agricultural practices, several issues emerged, especially concerning the impact of irrigation on farming and the quality of agricultural products [6,9,10]. Therefore, the study of modern agrochemical, agrophysical, and in particular biogeochemical energy states of soils and their fertility (of uncultivated and irrigated Calcisols) of the northern Fergana Valley faces numerous difficulties.

Consequently, the main purpose of the present study is a comprehensive study of different types of Calcisols in the Fergana Valley in the process of surface irrigation. The particular aims of the study included: (1) conducting a morphogenetic analysis of the soils, (2) determining their basic chemical parameters and properties of uncultivated and irrigated Calcisols, and (3) assessing the humus state and amino acid composition of soil organic matter.

2. Materials and Methods

2.1. Field Survey

The field plots are located in the northern part of Fergana Valley (Figure 1), composed of various types of late Pleistocene and current Holocene sediments and parent materials. During the 20th century, the relief and environment of the Fergana Valley were intensively transformed as a result of land reclamation, soil transfer, soil drainage, and further irrigation and reclamation. However, in the same place one can find places with uncultivated (reference) soils, also used in this research in comparison with the same types of soils, transformed by agricultural impact (surface-irrigated agricultural soil). Uncultivated and irrigated agricultural soils were sampled in the areas indicated in Figure 1. Soil sections were plotted in irrigated and uncultivated plots. Soil samples were collected in triplicate from each genetic soil horizon. After air-drying, the samples were prepared as a mean sample for further analysis.

The climate is dry, with an average precipitation rate of about 200 mm and average annual temperature of about 14.3 °C. The valley belongs to a dry subtropical climate. Water deficit makes agriculture completely impossible without irrigation, which completely depends on the supply region with waters of natural sources—rivers and artificial irrigation channels. Currently, more that 95% of the region’s area is completely occupied by anthropogenic soils, mainly of agrogenic origin.

The soils investigated are natural and irrigated Calcisols (Serozems) of the northern Fergana Valley. The “Calcisols” are more close term in the WRB soil taxonomy system [13] to “Serozems” in USSR (Soviet) soil taxonomy [14]. Serozems are absent in current Russian classification, because it concerns only the Russian lands, where there are no Serozems. Nevertheless, in our collaboration we use the terminology of current Russian soil taxonomy [15] and its designation of soil horizons. A schematic description of soil profiles and photos of selected soil profiles is provided of Figure 2.

Agrogenic soils are characterized by the same type of profiles, but the topsoil horizon is changed to an arable version of the P horizon in the Russian soil taxonomy—P [15] which means ploughed, tilled, or arable horizon. Thus, if the initial layer was AU, ploughed will be PU. Thus, the dark humus horizon became a dark humus arable one. The same applies to the light humus layer AJ, which became a light humus arable horizon. Designated as lithogenic carbonate, inherited from parent materials, they are described as Cca in the parent material in the Russian soil taxonomy [15] and as Cα in WRB [13]. The accumulation of secondary carbonate in the middle part of the solum is a diagnostic feature of Calcisols; they are designated as “CA” in capital letters in addition to a designation of soil genetic horizon, e.g., B + CA = BCA. If secondary carbonate is presented by dense noodles, it should be indexed as “na”. Gleyification is designated by symbol “g”.

The soils are formed on parent material of different genesis. They are all carbonate containing and have features of gleyification caused by the presence of ground water at the depths of 80–100 cm. The humus horizon is more pronounced and dark-colored in Dark and Typical Calcisols than in Light Calcisol. In the horizon of the secondary accumulation of carbonates, BCAnc, “nc” means accumulation nodules of cemented carbonates. This horizon is more expressed in Dark and Typical Calcisols. Gleyic features are more expressed in Light Calcisols.

2.2. Laboratory Analyses

Soil samples were air-dried, ground, and passed through a 2 mm sieve. Soil organic carbon (SOC) was determined by a standard Tuyrin dichromate oxidation method [16], and total nitrogen (TN) was determined by the standard Kjeldahl procedure [17]. To determine the pH values, we used the traditional method of analysis of aqueous extract at a ratio of soil:water of 1:5 (pH/ORP/Temp tester Milwaukee Mi106 (Milwaukee Electronics (USA)) The particle-size distribution of the soils was measured by the sedimentation (pipette) method [18]. Also, the classical [18] methods of soil bulk density, porosity rate, and internal surface were used for a soil physic survey. Soil carbonates were determined gravimetrically [17] after treatment of the sample with hydrochloric acid. Potassium content was determined by flame photometry. The phosphorous content was determined with use of photometry. Exchangeable forms of Ca and Mg were determined by titration trilonometry [17]. Exchangeable phosphorous and potassium within the Olsen extract were detected with the use of molybdenum ammonium and flame photometry, correspondingly. Carbon of humic acids (CHA) and carbon of fulvic acids (CFA) were determined by the Tuyrin dichromate oxidation method [16] in extracts, prepared according to [19].

Determination of amino acids composition is described as follows. From the averaged crushed homogeneous sample of soil fine earth and dry extract for analysis, an accurate sample was weighed into test tubes with an error of no more than 0.1%. Next, free amino acids were isolated [20]. Precipitation of proteins and peptides from the aqueous extract (1:10) of the samples was carried out in centrifuge beakers. To do this, 1 mL (exact volume) of 20% trichloroacetic acid was added to the test samples (1:1). After 10 min, the precipitate was separated by centrifugation at 8000 rpm for 15 min. After separating, 0.1 mL of the supernatant fluid was lyophilically dried. Phenylthiocarbamyl (PTC) derivatives of amino acids were obtained by reaction with phenylthioisocyanate according to the method of Steven A., Cohen Daviel [21]. Identification of PTC amino acids was carried out on an Agilent Technologies 1200 (California, USA) chromatograph using a Discovery HS C18 column, 75 × 4.6 mm with a diode-array detector. Solution A: a mixture of 0.14 M sodium acetate and 0.05% triethylamine, pH 6.4. Solution B: acetonitrile. The flow rate was 1.2 mL/min; absorption was 269 nm. Gradient %B/min: 1–6%/0–2.5 min; 6–30%/2.51–40 min; 30–60%/40.1–45 min; 60–60%/45.1–50 min; 60–0%/50.1–55 min. Qualitative analysis and quantitative calculation of the concentration of the studied free amino acids were carried out by comparing the retention time and peak areas of the standard and studied PTC derivatives of amino acids [20].

Statistical processing and data visualization was performed using GraphPad Prizm 9.0.0, Golden Software Grapher 13.0 and Microsoft Office Excel 2016 16.0.

3. Results and Discussion

Data on SOC stocks are provided in the Figure 3. In general, the SOC stocks were higher in irrigated Light and Typical Calcisols than in reference types of this Calcisols. This could be caused by the effect of irrigation on soil biological productivity and additional accumulation of organic matter. The alteration of key soil properties under irrigation has been reported previously [22,23]. In opposition, irrigated Dark Calcisols demonstrate decreasing SOC stocks. This could be caused by leaching of water-soluble fractions of organic matter in conditions of water saturation, while in mature non-irrigated soils there is a lack of water.

Another reason for Dark Calcisol decarbonization is weak slope erosion; these soils are located in transitional zones from adyr to valley on elevated slope positions. The Light and Typical Calcisols are located on flatter territories with less pronounced or completely absent erosion. The gravimetric content of SOC in topsoil humus or the humus arable horizon is provided in Figure 4. These data demonstrate that the highest organic matter and total nitrogen content are typical for Dark Calcisols. If one compares SOC and TN data in pairs of soils investigated, it is evident that there is an essential decrease in both these biogenic elements in irrigated soils. Thus, the SOC stock (volumetric content) does not directly connect with its mass concentration in the fine earth and depends on the alteration of soil density and thickness of the whole solum and SOC-enriched horizons. It is very interesting that there are remarkable changes in C/N ration in all the investigated irrigated soils in comparison with the non-irrigated reference soils. This corresponds well with the data of Karabekov [24] regarding the old, irrigated “tugay” soils of Uzbekistan. The profile distribution of the C/N ratio is completely different in mature and irrigated soils. Thus, topsoils of irrigated soil demonstrate more a narrow ration than the deepest ones. The volumetric content of TN was essentially higher in investigated soils of the Fergana Valley (this research) than in Calcisols and Cinamonic soils of the adjacent Namangan Valley [25], which illustrates the essential role of local climatic factors in the variability of the soils’ chemical properties.

The degree of soil organic matter depends on numerous factors: quality and quantity of the organic precursors, component composition of the fine earth, and climatic conditions [26]. The qualitative index of humification degree is the ratio of carbon of humic acids to carbon of fulvic acids—the CHA/CFA ratio [19]. The highest ratio value indicates the highest humification degree. These indexes, for the soil investigated, are provided in

Table 1. Carbon of humic acids (CHA) and carbon of fulvic (CFA) acids (% to fine earth) and CHA/CFA rations in soils investigated.

Horizon	CHA 1	CFA 2	$\frac{\mathbf{CHA}}{\mathbf{CFA}}$	Horizon	CHA	CFA	$\frac{\mathbf{CHA}}{\mathbf{CFA}}$
Dark Calcisol
Reference				Irrigated
AU	0.51	0.49	1.04	PU	0.40	0.42	0.95
BCA	0.31	0.30	1.03	BCA	0.29	0.34	0.85
Typical Calcisol
Reference				Irrigated
AJ	0.24	0.26	0.92	PJ	0.28	0.35	0.80
BCA	0.09	0.10	0.90	BCA	0.10	0.14	0.71
Light Calcisol
Reference				Irrigated
AJ	0.10	0.13	0.77	PJ	0.12	0.18	0.67
BCA	0.05	0.06	0.83	BCA	0.07	0.11	0.63

¹ Carbon of humic acids; ² carbon of fulvic acids.

. It is evident that irrigation results in a decrease in humification degree. It is quite logical, because the reference non-irrigated soils are drier, and the reactions of polymerization in that state are more pronounced [26]. Moistening of the soil climate under irrigation results in an increase in fulvic acids and, by this, a decreasing CHA/CFA ratio. This tendency was revealed for all three pairs of soils investigated. Thus, we can speak about reorganization of the systems of humic acids under irrigation towards a decreasing humification degree in all irrigated soils. It is remarkable that the gravimetrical content of both groups of humic acids increased in Typical and Light Calcisols and decreased in Dark ones. This in good correspondence with the fact the stocks of humus in irrigated Dark Calcisols decreased and, conversely, showed incremental increase in the cases of Typical and Light Calcisols. Data on the humus state of the soils investigated are more or less similar to results from soils of Azerbaijan [27].

When studying the content of free amino acids in Light Calcisols, 14 to 20 free amino acids were detected and identified. Data on amino acids content and composition are presented in Figure 5 and Figure 6. Among commonly occurring amino acids, the following were not found in reference soils: cysteine and histidine. In irrigated soils, alanine, asparagic acid, glutamic acid, cysteine, and histidine were not identified. An interesting picture is observed regarding the content of a number of other amino acids, so from the group of aromatic amino acids, both in the reference and irrigated Light Calcisols, there is no histidine in the soil profile, and in irrigated soils, there is no asparagine or glutamic acid from the group of monoamine-dicarboxylic acids. Some decrease in amino acid content in irrigated soils is observed. The content of free amino acids in virgin Light Calcisols as a total mass averages 26.56 mg/kg. In soil horizons, they vary from 5.83 to 64.24 mg/kg. The relative distribution of free amino acids in soils is as follows: monoaminodicarboxylic acids (glycine, alanine, serine, threonine, methionine, valine, leucine, and isoleucine) 35.55–46.11%; monoamindicarboxylic acids (asparagic acid, asparagine, glutamic acid, and glutamine) 35.53–45.04%; diaminmonocarboxylic (lysine and arginine) 3.6–9.65%; aromatic amino acids (phenylalanine, tyrosine, and tryptophan) 4.99–13.07%; and imino acids (proline) 2.62–4.43% of total amino acids.

Some decrease in amino acid content in irrigated soils is observed. The content of free amino acids in virgin Light Calcisols as a total mass averages 26.56 mg/kg. In soil horizons, they vary from 5.83 to 64.24 mg/kg. The relative distribution of free amino acids in soils is as follows: monoaminodicarboxylic acids (glycine, alanine, serine, threonine, methionine, valine, leucine, and isoleucine) 35.55–46.11%; monoamindicarboxylic acids (asparagic acid, asparagine, glutamic acid, and glutamine) 35.53–45.04%; diaminmonocarboxylic (lysine and arginine) 3.6–9.65%; aromatic amino acids (phenylalanine, tyrosine, and tryptophan) 4.99–13.07%; and imino acids (proline) 2.62–4.43% of total amino acids.

Increase in the number of amino acids, in particular arginine, which under the influence of the enzyme arginase in soils increases the synthesis of urea, can be noted as a positive factor. Between 14 and 20 amino acids were found in the Calcisols investigated. In virgin light gray soils, cysteine and histidine dominated. In irrigated soils, alanine, asparagic acid, glutamine, cysteine, and histidine prevailed, as well as dicarboxylic amino acids lysine and histidine, which have a weakly alkaline medium isoelectric point and are contained in practically all studied soils. Thus, the irrigation effect on the component composition of amino acids and humification degree, corresponds well with data from other regions [28]. The regime of irrigation also effects Calcisols of the Chirchik-Keles interfluve (Uzbekistan) [29].

The profile distribution of the particle-size fraction as well as the alteration of the granulomentric composition are given in Figure 7. Alteration of soil texture under irrigation is a well-known fact [30]. Colmatage is the process of filling of soil porous media with suspended particles brought by irrigation water. Irrigated soils demonstrate increasing fine silt and clay. At the same time, there is a replacement of sand fractions—fine sand content decreases, and a coarse sand fraction appears. In general, however, the change in particle-size distribution occurs within the gradation of one particle-size distribution class. Thus, irrigation transformation of the soil solid phase is rather slow, which is confirmed by the data of Sh. Eshpulatov [31]. The soils of the adyr zone are described by N. Vavilov as containing more primary or secondary loess material [32]. Nevertheless, our Dark Calcisols do not demonstrate features of high presence of loess-type material even in deepest part of the solum. Increased content of the silt fraction (0.05–0.01 mm) in the superficial layers of both reference and irrigated soils may have resulted from aeolian accumulation, because this fraction is known as maximally labile under wind erosion [33,34].

Data on available nutrient content in fine earth are provided in

Table 2. Main nutrient and carbonate contents in different Calcisols.

Horizon	Depth, cm	Bulk, mg/100 g		Labile, mg/100 g		Carbonates, %
		P2O5	K2O	P2O5	K2O	CaCO3	MgCO3
AU1	0–7	220	2450	3.7	40.4	1.7	0.8
AU2	7–17	210	2350	2.1	40.1	1.3	0.7
BCAnc	17–43	170	2100	1.0	39.0	5.6	2.0
BCAg	43–73	170	2100	0.0	28.5	5.7	2.0
Ccag	73–101	161	2050	0.0	22.0	6.1	2.1
Dark Calcisol (irrigated)
AU	0–30	230	2350	4.7	35.5	1.4	1.0
BCAnc	30–42	231	2100	3.2	34.0	1.8	1.0
BCAg	42–70	220	2000	2.0	20.1	3.1	1.0
Ccag	70–100	180	2100	0.0	20.0	3.2	1.3
D	100–135	180	2100	0.0	25.0	6.2	2.1
Typical Calcisol (reference)
AU1	0–6	201	2100	3.0	34.1	3.3	1.2
AU2	6–23	210	2000	2.0	28.6	4.2	1.3
BCAnc	23–70	188	2000	0.6	31.5	6.3	2.3
BCAg	70–101	180	1950	0.0	8.8	7.3	2.4
Ccag	101–131	205	2010	0.0	10.5	7.1	2.2
Typical Calcisol (irrigated)
AU	0–26	220	2200	4.2	33.5	3.6	1.5
BCAnc	26–40	220	2100	3.0	25.0	4.5	1.0
BCAg	40–67	195	2100	1.8	25.0	7.1	2.3
Ccag	67–100	210	1800	0.0	20.0	7.8	2.1
D	101–120	210	2200	0.0	24.0	7.2	2.2
Light Calcisol (reference)
AJ1	0–5	141	1850	2.6	25.5	4.2	2.2
AJ2	5–27	140	1650	1.2	30.3	4.3	1.2
BCAnc	27–43	121	1600	0.5	31.3	6.4	3.7
BCAg	44–89	120	1700	0.0	10.5	7.5	2.4
Ccag	89–114	118	1600	0.0	11.5	8.1	2.2
Light Calcisol (irrigated)
AJ	0–36	181	2000	2.0	25.5	4.3	2.2
BCAnc	36–42	153	2100	2.1	20.0	4.5	1.9
BCca	42–86	131	2000	2.0	24,0	6.3	3.8
Ccag	87–113	121	1800	0.0	0.0	7.6	3.4
D	113–120	123	1800	0.0	0.0	8.4	3.3

. The bulk and labile forms of potassium and phosphorous demonstrate a gradual decline from topsoils to the deeper layers in reference and irrigated soils. It is remarkable that in some parent materials labile forms of nutrients are almost absent. Thus, we can conclude that biogenic nutrients are only in part inherited from parent material and are mostly accumulated in soil due to irrigation and application of fertilizers. Conversely, the content of calcium and magnesium carbonates in soils increases with depth, which indicates the important role of mineralized soil water in the profile distribution of these salts. The prevalence of calcium on magnesium shows the favorable chemical state of the soils. The percentages of carbonates in the soils are comparable with results published by previous researchers for Uzbekistan [34] and are essentially lower than those of the parts of the Fergana Valley that belong to Kyrgyzstan [35].

The content of water-soluble base cations are provided in Figure 8. All the soils demonstrate prevailing calcium in component compositions of salts. Irrigated soil is characterized by an increased concentration of magnesium, but calcium also dominates. Thus, the soil solution composition is favorable for plants in terms of formation of soil structure. The potassium content decreases in irrigated Typical and Light Calcisols, but not in irrigated Dark Calcisols. In general, irrigation does not drastically affect the base cation composition of soil solutions. Nevertheless, it was established that irrigation leads to more pronounced alterations of soil salt composition on the Calcisols adjacent to the Samarkand oasis [36]. Thus, irrigation has regional peculiarities in various regions of Uzbekistan.

On the one hand, the soil cover of Central Asia is quite diverse due to geogenic and climatic conditions [32]; on the other hand, there is a long history of soil development and irrigation, which obviously leads to the convergence of their properties, in particular chemical ones. Therefore, soil profiles accumulate a huge number of results regarding previous stages of soil formation. That is why current irrigation does not always lead to strong shifts in soil formation. Land use, and in particular the utilization of soils in arid zones, faces many challenges, and the question arises whether we can achieve land degradation neutrality [37,38]. Nevertheless, without detailed knowledge of irrigation processes of soil formation, the methodological apparatus of this assessment cannot be formed. In this regard, this study makes it possible to approach the formation of a holistic picture of arid subtropical irrigated soil formation in the densely populated valleys of Central Asia.

4. Conclusions

Uncultivated and surface-irrigated Calcisols have been investigated in the northern part of the Fergana Valley in terms of morphology, chemistry, organic matter content and quality, soil texture, and chemical composition. Dark, Typical, and Light Calcisols showed intensive transformation under the surface irrigation. This study presents a comparative analysis of three primary types of Calcisols (Dark, Light, and Typical), examining their conditions before (uncultivated soil) and after agricultural use (surface-irrigated agricultural soil). Irrigation has been found to increase SOC stocks in Typical Calcisols (from 113.8 to 126.3 t/ha) and Light Calcisols (from 62.8 to 100.1 t/ha), while decreasing SOC stocks in Dark Calcisols (from 175.3 to 160.1 t/ha). Overall, the content of biophilic elements is lower in irrigated soils, with their distribution in the soil profile showing a closer alignment with a functional relationship (r² = 0.98 to 0.99). Conversely, the distribution of SOC and TN in uncultivated Calcisols is more heterogeneous (r² = 0.67 to 0.97) with a wider confidence interval. Uncultivated (reference) Calcisols are characterized by higher C/N ratios in surface horizons compared to post-irrigation soils. For uncultivated Calcisols, the C/N ratios vary from 14 to 25; after irrigation they from 10 to 13.5. Changes in the SOC transformation processes have been identified; in irrigated soils, the carbon ratio CHA/CFA is lower (<1) compared to the uncultivated type (~1). Modifications in the soil water regime due to irrigation have resulted in transformations in the individual compositions of amino acids. All studied types of Calcisols exhibit changes in particle-size distribution, particularly in the silt fraction (0.01–0.05 mm), with a difference of 10–20% between uncultivated and irrigated soils. This variation is associated with the processes of colmatage through the accumulation of fine fractions and the replacement of sub-fractions in the sand fraction. The highest concentrations of nutrients are found in the upper soil horizons (phosphorus up to 231 mg/kg, potassium up to 2350 mg/kg). Increased content of mobile forms of P and K are found in surface horizons of soils subjected to irrigation, indicating their pedogenic and agrogenic origins rather than inheritance from parent materials. Surface irrigation results in the apparent accumulation of water-soluble magnesium (Mg²⁺) (1.6–2.1 meq/100 g) and potassium (K⁺) (0.6–0.9 meq/100 g), while Ca²⁺ remains the predominant cation (more than 50% of base saturation) in the base cation composition. This predominance of calcium is favorable for the formation of soil agrogenic properties. In summary, it was established that Calcisols of different types in the Fergana Valley significantly change their properties in the process of surface irrigation, especially regarding SOC stocks, particle-size distribution, quantity and profile distribution of biophilic elements, and base saturation. Nevertheless, it should be noted that the quality and quantity of irrigation water may have a special influence on soil characteristics, which requires separate specialized studies.