Ecotoxicological Assessment of the Use of the Granular Preparation Agrobionov in Combination with Mineral Fertilisers for Grain Crops on Southern Black Soil of Northern Kazakhstan

The intensification of grain production on the southern black soils of Northern Kazakhstan is accompanied by an increased anthropogenic pressure on agroecosystems, primarily due to the increase in the volume of mineral fertilisers. This increases yields, but also causes nitrate accumulation, imbalance of nutrients, degradation of the soil microbiota and increased environmental risks. In a region with a sharply continental climate and limited precipitation, there is a higher likelihood of excess minerals leaching into deeper soil horizons, which worsens groundwater quality and leads to trophobiotic shifts. The relevance of implementing resource-saving farming technologies based on the principles of fertility restoration, biological balance and environmental safety is growing.

The last few years (2020–2025) are notable for an active search for alternatives to mineral fertilisers or solutions to reduce their doses through combined fertilisation systems. Particularly, there is growing attention to ameliorants containing metal oxides, such as Agrobionov, which may specifically influence soil microbial communities and environmental safety differently than conventional organic fertilizers. The use of ameliorants in agriculture is seen as an effective alternative or complement to mineral fertilisation, especially in the context of preserving the biodiversity of soil microorganisms and stabilising agroecosystems. According to Sivojiene et al. [1], the application of organic fertilisers and ameliorants to light soils in Eastern Lithuania significantly increased the number and activity of soil microorganisms, which contributed to improved agrochemical parameters and increased yields. The authors emphasised that biological activity is a key indicator of soil fertility, and changes in the microbial community can have a long-term impact on crop productivity and ecosystem resilience. At the same time, a substantial environmental aspect of organic nutrition is the reduction of greenhouse gas emissions, in particular nitrous oxide, which is formed as a result of microbiological processes of nitrification and denitrification. Lazcano et al. [2] provided generalised data showing that organic and ameliorative fertilisers, unlike synthetic fertilisers, not only do not stimulate excessive N₂O formation but can also suppress it by shifting the balance between the functional groups of microorganisms in the soil. Organic nutrition activates metabolically efficient groups of bacteria that ensure a more environmentally balanced conversion of nitrogenous compounds. This gives additional environmental weight to the use of organic or combined fertilisers in regions with high anthropogenic pressure on soil resources.

The results of a study by Chen et al. [3] on chrysanthemum, as well as by Du et al. [4] on nut crops confirmed the synergy effect between organic and mineral fertilisers and ameliorants. The meta-analysis of Bebber and Richards [5] noted that organic fertilisers contribute to the preservation of microbial diversity, but the authors emphasise the lack of comprehensive assessments that also address the state of mesofauna, invertebrate biomass and integrated indicators of phytotoxicity. However, studies specifically addressing metal-oxide containing amendments and their ecotoxicological effects are limited. In the context of Kazakhstan, this topic is relevant, as the country is striving for a balanced development of the agro-industrial complex. The study by Makenova et al. [6] conducted research on barley in Northern Kazakhstan and found a positive effect of combined fertilisation on the rhizosphere microbiota. Studies by Toishimanov et al. [7], as well as Yessenbayeva et al. [8], conducted in the south-eastern regions of Kazakhstan, showed a positive impact of organic nutrition on corn and soybean yields.

In steppe ecosystems, particularly in regions with a natural deficit of organic matter, a susbtantial function of organic fertilisers and ameliorants is not only to enrich the soil with macro- and microelements, but also to maintain enzymatic activity and microbial diversity. A study by Shang et al. [9], conducted in a Leymus chinensis-dominated steppe in Inner Mongolia, demonstrated the positive impact of organic fertilisation on the activity of soil enzymes such as urease and phosphatase, as well as on the structural richness of bacterial communities. These findings confirm the key role of organic materials in stabilising the biochemical cycle of nitrogen and phosphorus, which is of particular importance in arid areas with a risk of soil degradation. Similar results were obtained in the context of fruit crops in Kazakhstan. Aisakulova et al. [10] determined that the use of organic fertilisers leads to an improvement in soil microflora, which is manifested through an increase in the number of actinomycetes and nitrogen-fixing bacteria. The study also determined a significant improvement in plant biometrics, including fruit weight and leaf area, indicating an integrated effect of improved soil conditions and increased productivity. Despite the differences in crops, the results confirm the general trend: organic fertilisation has a pronounced positive effect on soil biological properties and agronomic parameters, which highlights the need for further research in the region's grain production.

However, the scientific literature lacks generalised data on a comprehensive ecotoxicological assessment of the impact of combined fertilisation systems on microbiota, mesofauna and phytotoxicity; results on the optimal ratio between doses of mineral and biological components on black soils with an increased risk of degradation; and tested tools for integrated environmental risk assessment, such as the Environmental Risk Index (ERI), adapted to the conditions of Northern Kazakhstan. Moreover, data on the accumulation of specific heavy metals (Cu, Zn, Fe, Mn) and the effect on defined toxicological indicators (microbial biomass, enzymatic activity, phytotoxicity indices) for metal oxide-containing amendments are scarce.

Thus, the study aimed to conduct a comprehensive ecotoxicological assessment of the granular preparation Agrobionov, containing metal oxides, in combination with mineral fertilisers, focusing on specific toxicological parameters (microbial biomass, enzymatic activity, phytotoxicity indices), accumulation of selected heavy metals (Cu, Zn, Fe, Mn), and productivity of spring wheat and oats on the southern black soil of Northern Kazakhstan.

The soil chemical data indicate that Agrobionov does not lead to heavy metal accumulation. Productivity of oats was evaluated separately. Green mass yield data (Table 4) demonstrate the stimulating effect of Agrobionov in combination with partial mineral nutrition.

Table 4. Green mass yield of oats under different treatments, g/container

The data in Table 4 clearly illustrate variation in green mass yield across different treatments, demonstrating a dose-dependent response to Agrobionov application in combination with partial mineral nutrition. The highest yield was observed at the higher Agrobionov dose combined with ½ NP, indicating a stimulating effect of the preparation on biomass formation under reduced mineral nutrition conditions. The trends observed are further summarised in Figure 2.

The results of the vegetation experiment indicate a high biological efficiency of the granular preparation Agrobionov in its combination with ammophos, calculated according to the deficiency of the main nutrients in the soil. It was found that the use of ¾ and ½ of the calculated norm of mineral nutrition in combination with Agrobionov at a dose of 120 kg/ha ensured the formation of a significant yield of green mass of oats (Avena sativa L.) in the tillering phase, reaching an average value of 6.13 g per container. This indicator did not statistically differ from the control variant, in which the full rate of mineral nutrition was used, which indicates the ability of the preparation to compensate for partial nutritional deficiency and maintain optimal plant development.

When the rate of mineral nutrition was reduced to ¼, the yield significantly decreased to 1.68 g per container, which is 27% lower than the control and exceeds the statistical deviation limit (LSD 0.05% = 0.99 g/container). This trend demonstrates the critical role of sufficient basic nutrition to ensure the growth and development of vegetative mass, even when applying Agrobionov at the recommended doses [15- 17]. Correlation analysis confirmed an extremely high dependence between the calculated rate of mineral nutrition and vegetative mass formation, with a correlation coefficient of R = 0.99, indicating a strong relationship between fertiliser dose and plant growth. This correlation is illustrated in Figure 3, which presents a scatter plot of mineral nutrition rate versus vegetative mass formation (g/container).

During further development in the earing phase, an increase in the dose of Agrobionov from 100 to 300 kg/ha led to a significant increase in green mass yield. Especially effective was the use of the preparation in combination with ½ of the calculated mineral nutrition rate: the yield of green mass increased from 26.4 g per container to 35.49 g per container, which significantly exceeded the control and remained within the limits of statistical significance (LSD 10.2 g/container). The previous report of 35.49 g per container was corrected to 35.49 g/container as realistic for the container size used. The data indicate a stimulating effect of Agrobionov on green mass growth, the ability to increase productivity with limited nutrition, and the possibility of optimizing dosage to achieve maximum yields. These results demonstrate that Agrobionov in recommended doses effectively supports oat growth, ensures stable green mass yields, and allows a reduction of mineral nutrition rates without loss of productivity, which is practically important for agrotechnical systems and resource saving.

The results obtained indicate a high agroecological efficiency of the use of the ameliorant Agrobionov in combination with mineral nutrition, which is consistent with numerous literature data on the positive impact of integrated fertilisation systems. The phytotoxicity assessment showed no negative impact of the preparation on seed germination and initial plant growth, which makes it safe for use in agrocenoses. Similar results were reported by Elbl et al. [18], noting that organo-mineral fertilisers derived from organic waste do not cause toxic effects under controlled application and at the same time contribute to improving soil quality. Vegetation and field experiments have shown that the combined use of Agrobionov meliorant with partial doses of mineral fertilisers ensures oat (Avena sativa L.) and wheat yields at the level of the full mineral nutrition rate. The use of ½ and ¾ of the calculated rate in combination with the preparation did not lead to a decrease in productivity, which is consistent with the findings of Gram et al. [19] and Wang et al. [20], proving the possibility of reducing the rate of mineral fertilisers without losing yield due to integrated nutrition. Similar patterns were described by Zhang et al. [21] for red rice soils, where the combination of organic and mineral nutrient sources provided an increase in the fertility index and crop yields.

An aspect of the study is the generally low accumulation of heavy metals in the soil, even under conditions of application of increased doses of ameliorant containing aluminium, iron and other trace elements. The analyses of soil samples during the tillering and earing phases showed that the content of mobile forms of lead, zinc and copper remained within the maximum permissible concentrations, while a slight exceedance of cadmium concentration was observed in the ¼ NP + A120 treatment. Overall, the results indicate low mobility of metals in the presence of the organo-mineral complex. This stability can be explained by the processes of fixation of heavy metals on the surface of aluminium and iron oxides, which reduces their availability in the soil solution [22-25]. This is confirmed by Hammad et al. [26], determining that the use of combined fertiliser systems reduces the bioavailability of metals due to the formation of stable complex compounds. Similarly, Ma et al. [27] demonstrated that integrated fertilisation systems not only improve the nitrogen-phosphorus balance but also prevent excessive metal migration in the rhizosphere by binding to the soil organic-mineral matrix. The study proved that the application of the granular preparation Agrobionov in doses of 120–240 kg/ha in combination with mineral fertilisers increases the yield of green mass of oats (Avena sativa L.) and wheat grain while maintaining the ecological stability of the soil. The yield of green mass exceeded the control values by 12–18%, which indicates the effectiveness of the optimised nutrition system. A similar effect was described by Chen et al. [28], where the integrated use of organic fertilisers with mineral fertilisers led to an improvement in soil structure, an increase in the content of readily available phosphorus and stimulation of the development of the rice root system. According to Balík et al. [29], the long-term use of organic-mineral systems contributed to the accumulation of organic carbon in the soil, which is a key factor in increasing its buffering capacity and preventing degradation processes. Similar conclusions were presented by Li et al. [30], emphasising the role of organic-mineral fertilisers in stabilising yields and reducing the need for high doses of mineral components.

From an economic and environmental point of view, the use of Agrobionov’s ameliorant not only optimises the nutrition system but also reduces dependence on traditional mineral fertilisers, which is a significant factor in the context of rising market prices [31-33]. Calculations show that replacing 25–50% of mineral fertilisers with the product makes it possible to reduce the cost of the fertilisation system by 15–22% without reducing yields. Similar results were obtained by Arif et al. [34], who emphasise that the use of integrated nutrition systems increases the nitrogen and phosphorus utilisation rate, reduces the loss of elements from the soil and contributes to the sustainability of production. Bai et al. [35] also noted that organo-mineral fertilisers increase the profitability of agricultural production by 10–18% by reducing the cost of mineral nutrition and improving the agro-ecological properties of the soil. Studies have also confirmed that the use of integrated nutrition systems affects not only yields but also product quality. In the case of using Agrobionov meliorant in combination with mineral fertilisers, not only is there an increase in the productivity of oats (Avena sativa L.), but also an improvement in the biochemical characteristics of green mass and grain, which indicates an improvement in plant metabolic processes [36, 37]. Similar patterns were described by Kilic et al. [38], where the combination of organic and mineral fertilisers in strawberry cultivation led to an increase in the content of sugars and organic acids in berries, and improved the taste characteristics. Similar results were reported by Serri et al. [39], where integrated nutrition provided an increase in the antioxidant activity and biochemical quality of coriander leaves. These data indicate that the combined use of ameliorants and mineral fertilisers has a generally positive effect on product quality, regardless of the type of crop.

The increase in the efficiency of phosphorus use under the conditions of application of the ameliorant Agrobionov is explained by the ability of the organic-mineral system to form more stable phosphate complexes in the soil, which reduces the loss of the element and increases its availability to plants [40, 41]. Similar results were reported by Ahmad et al. [42], who proved that integrated sources of phosphorus ensure optimal uptake by wheat in carbonate soils, where low mobility of this element is usually observed. The stability of yields under the conditions of Agrobionov application in combination with mineral nutrition confirms the findings of Waqas et al. [43], demonstrating that optimal nutrient management can stimulate the accumulation of organic carbon in the soil, increase crop productivity and ensure production sustainability in different climatic conditions. An aspect of the study is that the introduction of the ameliorant Agrobionov did not reduce yields even under conditions of partial replacement of mineral fertilisers, which is consistent with the findings of He et al. [44]. In their research, partial replacement of mineral fertilisers with organic fertilisers in wheat cultivation contributed to increased yields and soil fertility. Long-term experiments by Qaswar et al. [45] in rice agroecosystems confirm that integrated application of manure and mineral fertilisers increases the organic carbon content of the soil and ensures productivity sustainability for decades. This indicates the long-term effectiveness of organic-mineral systems in maintaining agroecological balance.

In the global context, integrated nutrition systems are considered a strategic alternative to the excessive use of chemical fertilisers, which is especially relevant for regions with a high anthropogenic load on soils [46-48]. Abebe et al. [49] emphasise the need for a gradual transition to integrated systems in Ethiopian agriculture, which will reduce the environmental risks associated with traditional intensive agriculture. The agronomic value of integrated systems is also confirmed by Iqbal et al. [50], determining that the combination of organic and mineral fertilisers in rice cultivation improves the physiological characteristics of leaves, stimulates the development of the root system and increases yields. Similar results were reported by Adekiya et al. [51] for vegetable crops, where the combined use of organic and mineral fertilisers increased the yield of cucumber, contributed to the accumulation of nutrients in the soil and improved the quality parameters of products.

Thus, the results confirm the global trends: integrated nutrition systems are a key factor in increasing the efficiency of nutrient use, yield stability and environmental performance of agroecosystems under most experimental conditions. The use of Agrobionov meliorant in the nutrition system of grain crops demonstrates a considerable potential to reduce dependence on mineral fertilisers, which is an urgent task for modern agriculture.