Investigation of hydrogel properties for enhancing moisture retention in soils of arid regions in Southern Kazakhstan

Investigação das propriedades de hidrogéis para melhorar a retenção de umidade em solos de regiões áridas no sul do Cazaquistão

Abstract

This study compared the effects of two superabsorbent hydrogels (polyacrylamide (PAH) and a starch-acrylamide-kaolin composite (SAKH)) with those of conventional water-saving practices (mulching and drip irrigation) on the soil's hydraulic properties, the growth of plants, and the yield of grains and seeds of rice, wheat, and safflower under arid conditions in southern Kazakhstan. A field experiment was conducted in 2024 using a randomised complete block design with five treatments. Treatment effects were highly significant across all measured variables (p < 0.001). PAH (0.5%) produced the most significant improvements in soil hydraulic performance, increasing water retention by 23.6-23.8% and infiltration depth by 27%, compared to the control. It also resulted in the highest available water content (up to 18.13 mm) and significantly outperformed both mulching and drip irrigation. SAKH and drip irrigation showed intermediate effects, whereas mulching did not differ significantly from the control for most hydraulic parameters. Plant growth and yield responses were crop-specific, but the ranking of treatments remained consistent. Across all crops, PAH produced the largest yield increase (+10.25 units), followed by SAKH (+5.23), drip irrigation (+4.13) and mulching (+2.79). A multiple linear regression model incorporating soil water retention and infiltration depth explained 92% of the variation in yield (R² = 0.92, p < 0.001), demonstrating that soil hydraulic properties strongly predict crop productivity. Overall, hydrogels, particularly PAH proved to be more effective than conventional water-saving practices at improving soil water availability and crop performance. This indicates their high potential for enhancing water use efficiency in arid agroecosystems.

Keywords:
superabsorbent polymers; water-saving technologies; soil water-holding capacity; drip irrigation; straw mulching; grain yield; semi-arid agriculture

Resumo

Este estudo comparou os efeitos de dois hidrogéis superabsorventes (poliacrilamida (PAH) e um compósito de amido-acrilamida-caulim (SAKH)) com os de práticas convencionais de economia de água (cobertura morta e irrigação por gotejamento) nas propriedades hidráulicas do solo, no crescimento das plantas e na produtividade de grãos e sementes de arroz, trigo e cártamo em condições áridas no sul do Cazaquistão. Uma experiência de campo foi conduzida em 2024, utilizando um delineamento em blocos casualizados com cinco tratamentos. Os efeitos dos tratamentos foram altamente significativos em todas as variáveis ​​medidas (p < 0,001). A PAH (0,5%) produziu as melhorias mais significativas no desempenho hidráulico do solo, aumentando a retenção de água em 23,6-23,8% e a profundidade de infiltração em 27%, em comparação com o controle. Esse tratamento resultou também no maior teor de água disponível (até 18,13 mm) e apresentou um desempenho significativamente superior tanto à cobertura morta como à irrigação por gotejamento. O SAKH e a irrigação por gotejamento apresentaram efeitos intermediários, enquanto a cobertura morta não diferiu significativamente do controle para a maioria dos parâmetros hidráulicos. O crescimento das plantas e as respostas de produtividade foram específicos para cada cultura, mas a classificação dos tratamentos manteve-se consistente. Em todas as culturas, a PAH produziu o maior aumento de produtividade (+10,25 unidades), seguida pelo SAKH (+5,23), pela irrigação por gotejamento (+4,13) e pela cobertura morta (+2,79). Um modelo de regressão linear múltipla, incorporando a retenção de água no solo e a profundidade de infiltração, explicou 92% da variação da produtividade (R² = 0,92, p < 0,001), demonstrando que as propriedades hidráulicas do solo predizem fortemente a produtividade da cultura. No geral, os hidrogéis, particularmente a PAH, revelaram-se mais eficazes do que as práticas convencionais de economia de água na melhoria da disponibilidade de água no solo e no desempenho da cultura. Isso indica o seu elevado potencial para aumentar a eficiência do uso da água em agroecossistemas áridos.

Palavras-chave:
polímeros superabsorventes; tecnologias de economia de água; capacidade de retenção de água no solo; irrigação por gotejamento; cobertura morta com palha; produtividade de grãos; agricultura semiárida

1. Introduction

Climate change and progressive desertification pose severe threats to agriculture in arid and semi-arid regions, where water scarcity is the main factor limiting crop productivity (Al-Omran et al., 2004; Yu et al., 2019). In southern Kazakhstan, for example, low and irregular precipitation, high evaporative demand and intensive irrigation practices have accelerated soil degradation and salinisation, resulting in projected cereal yield declines of 20-30% by 2050 (Liu et al., 2017). Conventional water-saving practices, such as straw mulching and drip irrigation, frequently fail to stabilise soil moisture during critical growth stages and often provide only limited yield gains under extreme aridity (Herrick et al., 2006).

The present study is novel in three ways that have not been addressed together in previous research: 1) the simultaneous field evaluation of PAH and a locally synthesised, low-cost SAKH hydrogel against two widely recommended conventional technologies (mulching and drip irrigation) on the same experimental site; 2) the quantification of the effects of the hydrogel on the soil moisture characteristic curves and available water capacity determined in the laboratory in a typical calcareous loamy soil in southern Kazakhstan; 3) the development and validation of a multiple linear regression model linking measured soil hydraulic parameters directly to the grain/seed yield of three major crops (rice, wheat and safflower) grown under full irrigation compensation.

This study aimed to evaluate the effectiveness of superabsorbent hydrogels (PAH and SAKH) compared with conventional moisture-conserving practices (such as mulching and drip irrigation) in improving soil hydraulic properties, plant growth and crop yield in arid conditions.

The specific objectives were:

• To quantify the effects of hydrogel application on key soil hydraulic properties, including soil water retention, the water retention coefficient, infiltration depth and available water;

• The second objective was to compare plant growth parameters and grain/seed yield across hydrogel treatments and conventional water-saving practices (e.g. mulching and drip irrigation);

• The third objective was to evaluate the relative performance of PAH and SAKH against traditional practices under the same field conditions;

• The fourth objective was to develop and validate a multiple linear regression model linking soil hydraulic properties to crop productivity;

• The final objective was to identify the most effective treatment for improving water use efficiency in arid agricultural systems.

It was hypothesised that the application of hydrogels, particularly PAH, would result in greater improvements in soil water retention, available water and crop yield than the control and conventional moisture-conserving practices (such as mulching and drip irrigation) due to enhanced water storage and gradual release within the soil profile.

2. Methods and Materials

2.1. Study site

The field component of the study was carried out during the 2024 growing season at an experimental site located in the foothill zone near the village of Zholdasbekova, South Kazakhstan Region (42.260° N, 69.735° E; elevation 540 m a.s.l.). The site is characterized by a gentle slope and alluvial-deluvial loam deposits. The sharply continental climate, marked by limited summer precipitation and high evapotranspiration, is typical of the arid agrolandscapes of the region.

2.2. Soil characteristics

Standard physico-chemical soil analyses were performed for the 0-30 cm layer; key properties are summarized in Table 1.

Table 1
Agro-physical and chemical properties of the soil (0-30 cm).

Parameter	Value	Method / Notes
Soil texture	Loam	Pipette method (hydrometer)
Sand / Silt / Clay (%)	35 / 45 / 20	Hydrometer
Soil structure	Stable granular	Visual assessment
Organic matter (%)	1.2	Walkley-Black method
CaCO3 (%)	4.2	Acid neutralization
Soil pH (1:2.5 in water)	8.1	Potentiometric
Electrical conductivity (ECe, dS/m)	1.3	Saturation extract
Cation exchange capacity (CEC, cmol+/kg)	14.7	Ammonium acetate method
Bulk density (g/cm3)	1.3	Ring method

2.3. Irrigation water quality

Irrigation was carried out using water supplied from an open canal. The water, with an electrical conductivity of 0.6 dS/m, a pH of 7.3, and a sodium adsorption ratio of 2.1, was suitable for irrigation. Surface furrow irrigation was employed, as this method is standard practice in regional agricultural production. An application efficiency coefficient of 0.75 was used. In calculating water demand, a leaching requirement of 10% of the total irrigation volume was incorporated to prevent salt accumulation in the root zone. Irrigation requirements were calculated using the FAO Penman-Monteith approach. Effective precipitation was estimated using a standard USDA method for semi-arid conditions.

2.4. Experimental design

The experiment was conducted using a randomised complete block design (RCBD) and comprised five irrigation treatments: a control treatment involving no moisture-conserving practice; mulching; drip irrigation; and two hydrogel treatments involving 0.3% and 0.5% SAKH and PAH, respectively. Each treatment was replicated across four blocks (n = 4). The plot size was 10 m² with 1 m buffer zones. The control treatment involved conventional surface irrigation, with no mulch, drip irrigation or hydrogel amendments applied.

Sowing was carried out on 15 April 2024, and hydrogel application took place on 10 April. Soil moisture was monitored weekly, and plant growth was measured at 30, 60, and 90 days after sowing. Harvesting was completed on 20 September.

2.5. Hydrogel source and application

Two types of hydrogels were used in the study. The SAKH hydrogel (starch-acrylamide-kaolin) was synthesized under laboratory conditions by radical polymerization at 60 °C using 1% potassium persulfate and 0.8% MBA as initiator and crosslinker, respectively. The PAH hydrogel (polyacrylamide-based) was obtained from Sigma-Aldrich. Both materials were applied in particle-size fractions of 0.3-1.0 mm. Hydrogels were incorporated into the topsoil layer (0-15 cm) and mixed manually to ensure uniform distribution. Hydrogels were applied at a rate of 250 g m⁻².

2.6. Measurements and observations

Soil moisture was measured using KET FPM-220 sensors for the 0-10 cm layer and Hydrosense II sensors for the 10-30 cm layer. To obtain an integrated soil-moisture value for the 0-30 cm profile, measurements were averaged across the vertical gradient. All measurements were taken at the center of each plot to avoid edge effects.

Laboratory assessments of water-rention capacity were conducted on soil mixtures containing hydrogels at the same concentrations used under field conditions, as the objective was to evaluate the actual influence of the amendment on soil properties. Accordingly, moisture characteristics—including water-retention curves at 0.3 and 1.5 bar, as well as measurements at –33 kPa for determining field capacity—were derived exclusively for the soil-hydrogel mixtures.

Available soil moisture was calculated as the difference between field capacity and the permanent wilting point, the latter measured using a Richards plate at 1.5 bar. For each treatment, complete soil water-retention curves were constructed and subsequently used to interpret field-based moisture dynamics. In situ hydraulic conductivity was determined using the Guelph permeameter method. Effective wetting depth was calculated from the soil-moisture profile 48 hours after irrigation.

Plant observations included recording phenological stages using the BBCH scale. Crop yield was expressed in tonnes per hectare. The measured variables included soil water retention, water retention coefficient, infiltration depth, and available water, which were subsequently used in statistical and regression analyses.

2.7. Statistical analysis

Hypothesis testing for factor effects was conducted using two-way analysis of variance. Distributional normality was assessed with the Shapiro-Wilk and Kolmogorov-Smirnov tests. When normality assumptions were violated, the Kruskal-Wallis test was applied. Tukey’s post hoc comparisons followed significant effects. Yield was modelled using multiple linear regression, with soil water retention and infiltration depth as predictor variables. The model was specified as Equation 1:

$$\begin{array}{c}\text{Y =}\beta \text{0 +}\beta \text{1·SoilWaterRetention +}\\ \beta ₂\text{·InfiltrationDepth}\end{array}$$ (1)

where X represents a water-related parameter derived from the soil water-retention curve (i.e., water-holding capacity or infiltration depth). This model was selected to account for the nonlinearity of the relationship between yield and water availability. All computations were performed in RStudio, and differences were considered statistically significant at p ≤ 0.05.

3. Results

3.1. Experimental design and statistical analysis

Treatment effects were highly significant across all measured variables, whereas crop and crop × treatment interactions were generally negligible for soil hydraulic properties, but significant for plant growth and yield parameters (see Table S1 in the Supplementary Material for ANOVA results).

3.2. Physical properties of soil moisture and available water

Soil water retention, the water retention coefficient, infiltration depth and available water were all strongly affected by the treatment (Table 2, all p < 0.001).

Table 2
Soil water physical properties and irrigation efficiency across treatments (mean ± SE).

Crop	Treatment	Soil Water Retention	Water Retention Coeff.	Infiltration Depth (cm)	Available Water (mm)	Irrigation Efficiency (%)	Tukey group
Rice	Control	18.20 ± 0.05	0.29 ± 0.01	16.08 ± 0.15	15.08 ± 0.33	91 ± 2	c
Rice	Mulching	18.20 ± 0.05	0.30 ± 0.00	16.03 ± 0.05	14.72 ± 0.12	90 ± 3	c
Rice	Drip	21.05 ± 0.06	0.37 ± 0.00	18.85 ± 0.05	16.68 ± 0.17	84 ± 2	b
Rice	SAKH 0.3%	20.15 ± 0.06	0.36 ± 0.00	17.78 ± 0.05	16.15 ± 0.14	85 ± 3	b
Rice	PAH 0.5%	22.53 ± 0.06	0.41 ± 0.00	20.35 ± 0.06	17.87 ± 0.09	86 ± 3	a
Wheat	Control	18.20 ± 0.05	0.29 ± 0.01	16.05 ± 0.05	14.43 ± 0.28	90 ± 3	c
Wheat	Mulching	18.18 ± 0.03	0.30 ± 0.00	16.00 ± 0.00	14.71 ± 0.08	88 ± 4	c
Wheat	Drip	21.00 ± 0.00	0.37 ± 0.00	18.90 ± 0.06	16.80 ± 0.15	85 ± 4	b
Wheat	SAKH 0.3%	20.13 ± 0.03	0.36 ± 0.00	17.83 ± 0.05	15.94 ± 0.18	89 ± 3	b
Wheat	PAH 0.5%	22.50 ± 0.00	0.41 ± 0.00	20.30 ± 0.00	18.13 ± 0.19	88 ± 4	a
Safflower	Control	18.20 ± 0.00	0.29 ± 0.00	16.00 ± 0.00	14.63 ± 0.28	90 ± 4	c
Safflower	Mulching	18.20 ± 0.00	0.30 ± 0.00	16.00 ± 0.00	14.29 ± 0.14	89 ± 4	c
Safflower	Drip	21.00 ± 0.00	0.37 ± 0.00	18.90 ± 0.00	16.75 ± 0.19	86 ± 4	b
Safflower	SAKH 0.3%	20.10 ± 0.00	0.36 ± 0.00	17.80 ± 0.00	16.62 ± 0.14	85 ± 3	b
Safflower	PAH 0.5%	22.50 ± 0.00	0.41 ± 0.00	20.30 ± 0.00	18.10 ± 0.12	89 ± 3	a

• Different letters within the same crop and column = significant difference (Tukey HSD, p < 0.05).

All soil hydraulic variables in Table 2 are accompanied by full ANOVA statistics and Tukey HSD post-hoc groupings, and their significance is further supported by Supplementary Table S2, where treatment effects are reported as F-values and exact p-values. Separate ANOVA models were fitted for each soil hydraulic variable independently, and the corresponding statistical outputs are reported individually in Supplementary Table S2, ensuring parameter-specific inference rather than a single aggregated test.

However, crop effects and crop × treatment interactions were not significant for most hydraulic variables (see Supplementary Table S2). The strongest effects were consistently observed for PAH 0.5%, which significantly outperformed all other treatments across all crops.

Treatment explained the majority of the variance in soil water retention (F = 9551.80, p < 2 × 10⁻¹⁶), while crop (F = 0.81, p = 0.451) and interaction (F = 0.33, p = 0.951) effects were not significant (see Supplementary Table S2). Tukey post-hoc comparisons confirmed that PAH 0.5% significantly increased soil water retention by 4.29 units relative to the control (p < 0.001), followed by SAKH (Δ = 1.92, p < 0.001) and drip irrigation (Δ = 2.81, p < 0.001); mulching did not differ significantly from the control (p = 0.998).

Similar patterns were observed for the water retention coefficient (F = 2325.65, p < 2 × 10⁻¹⁶) and the infiltration depth (F = 9283.94, p < 2 × 10⁻¹⁶). PAH increased the infiltration depth by 4.29 cm relative to the control group (p < 0.001), while SAKH produced intermediate but consistently significant effects (see Supplementary Table S2). Mulching again showed no statistical difference from the control group for any hydraulic parameter.

Figure 1 visually summarises these results, illustrating consistent improvements in soil hydraulic performance under PAH across all crops. Supplementary Figure S1 further confirms PAH's superior water retention capacity across the full matric potential range.

Figure 1
Effect of water-saving treatments on key soil hydraulic properties across three crops. (A) Soil volumetric water content at field capacity (–33 kPa); (B) Infiltration depth 48 h after irrigation.

Overall, PAH increased soil water retention by ~23.6-23.8% and infiltration depth by ~27% relative to the control group, confirming its significant impact on soil water dynamics (see Figure 1 and Supplementary Table S2).

Laboratory water-retention curves (see Figure 2) confirmed the superior water-holding capacity of PAH across the full matric potential range. PAH demonstrated consistently higher volumetric water content at equivalent matric potentials than all other treatments.

Figure 2
Volumetric water content as a function of matric potential (soil water retention curves) under different irrigation and hydrogel treatments.

3.3. Plant growth parameters

Both plant height and leaf number were significantly influenced by crop and treatment (Table 3), with a strong interaction between the two factors (height: F = 668.30, p < 2 × 10⁻¹⁶; leaves: F = 121.20, p < 2 × 10⁻¹⁶).

Table 3
Plant growth parameters (mean ± SE).

Crop	Treatment	Height (cm)	Tukey	Leaves (no. plant−1)	Tukey
Rice	Control	78.90 ± 0.42	c	12.0 ± 0.0	c
Rice	Mulching	77.60 ± 0.24	c	12.3 ± 0.3	c
Rice	Drip	70.65 ± 0.15	d	9.3 ± 0.5	d
Rice	SAKH 0.3%	79.33 ± 0.27	b	15.3 ± 0.3	b
Rice	PAH 0.5%	84.48 ± 0.13	a	17.5 ± 0.3	a
Wheat	Control	70.08 ± 0.08	c	10.0 ± 0.0	c
Wheat	Mulching	69.58 ± 0.13	c	10.0 ± 0.0	c
Wheat	Drip	71.03 ± 0.05	b	11.0 ± 0.0	b
Wheat	SAKH 0.3%	69.90 ± 0.04	b	13.0 ± 0.0	b
Wheat	PAH 0.5%	72.53 ± 0.03	a	14.0 ± 0.0	a
Safflower	Control	60.08 ± 0.08	c	10.0 ± 0.0	c
Safflower	Mulching	60.95 ± 0.24	c	10.0 ± 0.0	c
Safflower	Drip	62.08 ± 0.08	b	11.0 ± 0.0	b
Safflower	SAKH 0.3%	63.50 ± 0.00	a	11.0 ± 0.0	b
Safflower	PAH 0.5%	65.90 ± 0.00	a	12.0 ± 0.0	a

This indicates that sensitivity to water-saving treatments varies between species (see Supplementary Table S3). The apparent numerical discrepancy is explained by the fact that statistical significance is not assessed by directly comparing rounded mean values across treatments. Instead, it is assessed using ANOVA followed by Tukey HSD, which is applied to the full underlying dataset (i.e. unrounded, replicated observations). This is reported in Table 3 and Supplementary Table S3. Therefore, the significance of treatment effects reflects the variance structure within groups rather than a simple comparison of rounded, descriptive means. As key mechanistic variables, available water content and soil moisture-related hydraulic indicators are already included in Table 2 (Available Water, mm), and are statistically integrated into yield explanation through the validated regression model linking soil hydraulic properties to crop productivity (Figure 3). Stage-specific physiological measurements were beyond the scope of the present experimental design, and are instead addressed through integrated soil-plant system indicators, rather than phenological-stage sampling.

Figure 3
Observed vs predicted yield (R² model). Note: Figure 3 illustrates this relationship by showing the observed versus predicted yield across all treatments and crops.

PAH 0.5% produced the strongest positive effect on plant height across all crops (F = 1668.59, p < 2 × 10⁻¹⁶), increasing height by 4.62 cm relative to the control group (p < 0.001); SAKH increased height by only 1.23 cm (p < 0.001). In contrast, drip irrigation significantly reduced rice height by 1.77 cm (p < 0.001), while its effect on wheat and safflower was smaller or inconsistent

A similar pattern was observed for leaf number, with PAH increasing it by 3.75 leaves per plant (p < 0.001) and SAKH by 2.42 leaves (p < 0.001). Mulching and drip irrigation showed weak or non-significant effects in most cases (see Supplementary Table S3).

3.4. Actual and predicted yield

Grain/seed yield was found to be sensitive to treatment (Table 4), F = 393.60, p < 2 × 10⁻¹⁶), crop (F = 4458.73, p < 2 × 10⁻¹⁶) and the interaction between crop and treatment (F = 38.45, p < 2 × 10⁻¹⁶).

Table 4
Grain/seed yield and treatment effects (summary across crops).

Crop	Treatment	Yield effect (relative to control)	Tukey group
All crops	Control	baseline	c
All crops	Mulching	+2.79	b-c
All crops	Drip	+4.13	b
All crops	SAKH 0.3%	+5.23	b
All crops	PAH 0.5%	+10.25	a

This indicates that there are strong crop-specific responses to water-saving strategies (see Supplementary Table S4). PAH 0.5% produced the greatest yield increase across all crops, exceeding the control by 10.25 units (p < 0.001). This was followed by SAKH (+5.23, p < 0.001), drip irrigation (+4.13, p < 0.001) and mulching (+2.79, p < 0.001) (see Table 4).

A unified multiple linear regression model significantly predicted yield based on soil hydraulic properties (Equation 2):

$$\begin{array}{c}Yield=-42.1+3.84\times \\ SoilWaterRetention+1.12\times \\ InfiltrationDepth\end{array}$$ (2)

This model explained 92% of the variance in yield (R² = 0.92, adjusted R² = 0.91, p < 0.001; see Figure 3), showing that soil water retention and infiltration depth are strong predictors of crop productivity.

Excluding hydrogel treatments substantially reduced model performance (R² = 0.24), highlighting their central role in driving system behaviour.

3.5. Chemical properties of the soil after harvest

Post-harvest soil analysis revealed significant effects of the treatments on pH (Table 5) (F = 1.35 × 10²⁸, p < 2 × 10⁻¹⁶) and organic matter content (F = 3.33 × 10³⁰, p < 2 × 10⁻¹⁶).

Table 5
Soil chemical properties after harvest.

Treatment	pH	Organic Matter (%)	Salinity
Control	6.1	1.5	no change
Mulching	6.3	1.6	no change
Drip	6.1	1.5	no change
SAKH 0.3%	6.5	1.8	no change
PAH 0.5%	6.7	2.0	no change

In contrast, crop effects and interactions were not significant (see Supplementary Table S5). The application of PAH at a concentration of 0.5% increased soil pH from 6.1 to 6.7 and organic matter content from 1.5% to 2.0 (p < 0.01), whereas SAKH produced only moderate increases. Soil salinity was unaffected by any treatment (p > 0.05), indicating that hydrogel application did not induce salt accumulation (see Supplementary Table S5).

4. Discussion

The results of this study support the hypothesis that superabsorbent hydrogels, particularly polyacrylamide (PAH) at a concentration of 0.5%, are more effective than conventional water-saving practices at improving soil hydraulic properties and crop productivity under arid conditions. Across all three crops, PAH produced the most significant effects on soil water retention, infiltration depth, and available water. It demonstrated clear advantages over both the control and mulching and drip irrigation methods.

The observed effects were primarily driven by changes in soil hydraulic behaviour rather than crop-specific responses. The treatment explained most of the variance in soil water retention and infiltration, while the effects of the crop and interaction were negligible for these parameters. This indicates that hydrogel performance is largely governed by soil physical processes. This is further supported by laboratory-derived water-retention curves showing that PAH maintains a higher volumetric water content across the full range of matric potentials, thereby enhancing water availability under near-field-capacity and drier conditions. These improvements in soil water dynamics resulted in consistent increases in plant growth and yield across all treatments. The strong predictive relationship identified by the multiple linear regression model (R² = 0.92) confirms that soil water retention and infiltration depth are key drivers of crop productivity in this system. In this context, PAH's superiority can be attributed to its greater swelling capacity and more effective regulation of water release, which together improve the continuity of the soil's moisture supply.

In contrast, the SAKH exhibited intermediate performance, indicating that the composition and structure of polymers play a critical role in determining functional efficiency. Although SAKH improved soil hydraulic properties compared to conventional methods, its effects were consistently weaker than those of PAH, likely due to its lower swelling capacity and reduced influence on infiltration processes. Similar dependencies between polymer architecture, mineral fillers, and sorption efficiency have been documented for synthetic and composite sorbents, where crosslinking density and matrix heterogeneity govern water uptake and release dynamics (Bakhrushina et al., 2024; Bondarev et al., 2024). These material-level mechanisms provide a plausible explanation for the consistent ranking of treatments observed in the field.

One of the study's most important findings is the multiple linear regression model (R² = 0.92), which demonstrates that water retention at −33 kPa and infiltration depth together account for most of the variability in crop yield across different treatments. The sharp decline in model performance when hydrogel treatments were excluded (R² = 0.24) suggests that yield increases were primarily driven by changes in soil hydrophysical properties induced by hydrogel rather than by irrigation management alone. This finding corroborates earlier studies indicating that enhancements in soil water-holding capacity can have a more significant impact on yield formation than irrigation efficiency alone (Oladosu et al., 2022; Zhao et al., 2020). In the sharply continental climate of southern Kazakhstan, characterised by short irrigation intervals and high evaporative losses, the application of PAH proved to be not only agronomically effective, but also practically advantageous. The enhanced soil-water interactions observed in this study are consistent with broader evidence that polymer-based and composite materials can significantly modify mass transfer processes in heterogeneous systems, including agricultural substrates and food-processing mixtures (Ospanov et al., 2022). Furthermore, analogous effects of polymer structure on retention and controlled release processes have been reported for other biopolymer systems. This suggests that similar physicochemical principles govern water dynamics across different application domains (Lukashou et al., 2025). Overall, these findings demonstrate that polyacrylamide hydrogel is a robust and scalable solution for enhancing water use efficiency and crop productivity in arid agroecosystems. In the conditions studied, PAH clearly outperformed traditional methods such as mulching and drip irrigation, confirming its potential as a practical soil amendment for calcareous soils under increasing climatic water stress (Ali et al., 2024).

5. Conclusions

This study demonstrates that the application of superabsorbent hydrogels, particularly polyacrylamide hydrogel (PAH) at a concentration of 0.5%, significantly improves the soil's hydraulic properties and increases crop productivity in arid regions such as southern Kazakhstan. Across all three crops (rice, wheat and safflower), PAH outperformed the control and conventional moisture-conserving practices (mulching and drip irrigation) by producing the greatest increases in soil water retention, infiltration depth and available water.

The strongest and most consistent effects were observed for soil hydraulic parameters: PAH increased soil water retention by 23.6-23.8% and infiltration depth by ~27%, compared to the control. It also demonstrated clear advantages over mulching and drip irrigation. These improvements translated into enhanced plant growth and yield formation across all crops.

The results also show that crop productivity is strongly influenced by soil hydraulic properties. A multiple linear regression model based on soil water retention and infiltration depth explained 92% of the variation in yield (R² = 0.92), confirming the central role of soil water dynamics as a driver of agronomic performance. By contrast, the starch-acrylamide-kaolin hydrogel (SAKH) produced moderate but consistent results, surpassing traditional methods in some instances, though it remained inferior to PAH.

The findings suggest that hydrogel-based soil amendments, particularly PAH, are a highly effective and scalable approach to improving water use efficiency and stabilising crop production in arid agroecosystems with limited water resources. This offers a robust alternative to conventional moisture-conserving practices.

Supplementary Material

Supplementary material accompanies this paper.

Table S1

Full ANOVA summary for all variables

Table S2

Tukey test – soil hydraulic variables (combined effects of Treatment)

Table S3

Tukey test – plant growth

Table S4

Yield ANOVA and Tukey comparisons

Table S5

Regression model coefficients

This material is available as part of the online article from https://doi.org/10.1590/1519-6984.306624

Acknowledgements

This research was conducted under the framework of program No. 414- PCF-23-25 dated November 15, 2023, BR21882218, titled “Development and implementation of new highly efficient moisture-resource-saving technologies that increase crop yields and modernize the agro-industrial complex” and No. 393- PCF-24-26 dated October 10, 2024, BR24993129 “Development of a biodegradable thermosensitive hydrogel capable of absorbing and storing moisture and regulating moisture release”, funded by the Ministry of Science and Higher Education of the Republic of Kazakhstan.

Data Availability Statement

All data generated or analysed during this study are included in this published article.

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Edited by

• Editor:
  Takako Matsumura Tundisi

Publication Dates

• Publication in this collection
  14 Aug 2026
• Date of issue
  2026

History

• Received
  18 Mar 2026
• Accepted
  14 May 2026