Novel glauconite compounds improve soil properties and sugar beet (Beta vulgaris L.) yields in saline soils

Introduction

Sugar beet (Beta vulgaris L.) is a second major global crop for sugar production, contributing significantly to the world’s sugar supply alongside sugarcane. It serves as a major source of sucrose, accounting for approximately 20% of the world’s sugar supply, with sugarcane contributing the remainder (Hoffmann, Koch & Märländer, 2021). As global demand for sugar rises, sugar beet cultivation has expanded into diverse and challenging environments, including arid and semi-arid regions where saline soils hinder crop productivity (Tayyab et al., 2023; Wang et al., 2024). Egypt, where agriculture is constrained by limited arable land and increasing soil salinity and water scarcity, has considered sugar beet as a valuable crop for both sugar production and crop diversification (El-Mouhamady, Al-Kordy & Elewa, 2021). The Egyptian government encourages sugar beet cultivation to reduce dependence on sugar imports, which helps strengthen food security and supports local sugar industries. Sugar beet has become one of Egypt’s most valuable crops, particularly in the Nile Delta region, where it is cultivated on over 600,000 feddans (approximately 252,000 hectares), contributing significantly to the country’s sugar production (El-Zayat, 2021).

In Egypt, saline soils are widespread, particularly in the northern Nile Delta, where irrigation and intensive farming practices contribute to high levels of soluble salts and exchangeable sodium (Aboelsoud et al., 2022). These conditions result from a combination of natural soil properties, irrigation practices, improper fertilization managements, and climate factors. Potassium (K) is an essential nutrient that enhances plant tolerance to salinity, improving water-use efficiency and physiological processes like photosynthesis and sugar accumulation (Mostofa et al., 2022). In addition to conventional potassium fertilizers, alternative sources such as glauconite “a potassium-bearing mineral abundant in Egypt” have gained interest for their potential to provide a slow-release K source that may enhance soil properties and plant growth under adverse conditions (Oze et al., 2019).

Glauconite, locally sourced in the Western Desert of Egypt, presents a promising alternative as a potassium fertilizer. Its content of potassium, iron, and other micronutrients can help alleviate the nutrient limitations of saline soils by gradually releasing K and other elements (Dasi, Rudmin & Banerjee, 2024). However, the nutrient availability in the solid form of glauconite may be limited due to its low solubility. To increase its effectiveness as a K-source, we hypothesize that various extraction techniques to release potassium from glauconite could enhance its impact on plant growth. Extraction methods involving sulfuric acid, humic acid, and hot water have been studied for other minerals in laboratory scales but have not been extensively investigated for glauconite in the context of Egyptian agriculture. Sulfuric acid extraction has been extensively studied for releasing potassium from silicate minerals, demonstrating high efficiency in increasing K availability (Krupskaya et al., 2015). Humic acid, a natural organic chelator and chemical reactive agent, has shown potential in improving nutrient solubility and availability, especially in saline and sodic soils, making it a promising eco-friendly alternative (Dasi, Rudmin & Banerjee, 2024). Hot water extraction, though simpler and cost-effective, is hypothesized to release water-soluble potassium fractions while preserving the mineral’s structural integrity. The application of extracted glauconite using these methods represents a novel approach to enhance its efficacy as a potassium source in saline soils, and its impact on sugar beet yield and quality has yet to be investigated. This study aims to investigate the effects of various potassium sources, including conventional potassium sulfate, raw glauconite, and different glauconite extracts (sulfuric acid, humic acid, and hot water), on soil fertility, sugar beet yield, and sugar quality under saline conditions. Despite glauconite’s abundance as a potassium-rich silicate mineral, its agronomic application has been limited by the slow release of potassium in its raw form. Novel extraction techniques using sulfuric acid, humic acid, and hot water have been explored to enhance glauconite’s potassium availability. However, a comprehensive evaluation of these methods under field conditions, particularly in saline-affected soils, remains scarce. This research bridges this gap by comparing these innovative extraction techniques and assessing their impact on soil health, nutrient dynamics, and sugar beet productivity. Furthermore, it aims to identify the most effective and sustainable glauconite extraction method, offering a cost-effective and environmentally friendly alternative for improving crop productivity and managing saline soils in Egypt and similar regions.

Materials & Methods

Results

Sugar quality

The sugar quality parameters including alkalinity and sugar impurites (K, α-NH₄, and Na) are presented in Fig. 3. Regarding the sugar impurities, all treatments affected significantly (p < 0.01) in K, α-NH₄, and Na contents. It was noteworthy that all treatments increased the K and α-NH₄ impurities compared to control with GH2 increasing both K, α-NH₄ in both seasons recording average increments of 44.64% and 123.23% in the first and second seasons respectively. Regardless, the GW1 recorded the lowest levels of both K, α-NH₄, but it was recorded the highest levels of Na with values of 5.41 and 3.55 Meq 100 g⁻¹ beet in the first and second seasons respectively. As for the alkalinity of sugar, the application of different treatments resulted in reducing the values compared to control with GH1 listed the lowest record (2.79) in the first season, and G (3.05) in the second season. The alkalinity of extracted sugar followed the same pattern in both seasons with GH2 recording the lowest values (2.79 and 3.41) and GW1 recorded the highest addition treatment with values 6.26 and 6.61 in the first and second seasons, respectively.

Discussion

Considering that foliar application is primarily designed for direct plant uptake, it can still indirectly impact soil properties, especially with substances like humic acid, sulfur, and glauconite extracts. While foliar application mainly targets plant tissues, excess nutrients or compounds applied to the leaves can leach or wash off into the soil, influencing its physical and chemical characteristics. The findings showed that different potassium (K) sources and glauconite extracts did not significantly affect soil pH over both seasons. This is consistent with previous studies indicating that soil pH is generally buffered and may remain stable with K or glauconite treatments due to their neutral to slightly alkaline properties (Yang et al., 2020; Leon-Chang et al., 2022). The organic matter (OM) was significantly enhanced by the application of glauconite, with values doubling compared to the control, as glauconite is known for its slow release of nutrients and its impact in improving soil structure (Rudmin et al., 2019), which also might explain its minimal impact on pH levels. The data also revealed that EC and ESP were significantly affected by the treatments (p < 0.01), highlighting their role in mitigating soil salinity. The foliar application with GH2 resulted in significant reductions of salinity in both seasons which could be explained by the role of humic substances as a chelating agent that can bind with sodium ions and other salts, making them less mobile and more likely to be leached out of the soil profile (Huang, 2022). Additionally, humic acid improves soil structure, increasing its porosity and permeability, which is evidenced by the enhancement occurred in water infiltration rate (IR) and facilitates the leaching of excess salts (Sarlaki et al., 2024) which in turn resulted in the enhancement of soil ESP. When humic acid enters the soil, it stimulates the formation of soil aggregates, which improve pore space for water movement (Yang, Tang & Antonietti, 2021). In contrast, the SPR showed fluctuations, with the lowest resistance recorded in the G and K treatments. This reduction in SPR suggests an improvement in soil fragmentation and reduction of soil compaction confirmed by the improvement configured in IR in both seasons, which is consistent with the findings of Rudmin, Banerjee & Makarov (2020) and Chen, Banin & Borochovitch (1983), who reported that the application of potassium sources can enhance soil structure and reduce compaction. The hot water extraction method may inadequately release structural components of glauconite, resulting in limited improvements to soil physical properties (Hamed & Abdelhafez, 2020), which reduces the chemical capability to significantly alter glauconite’s matrix, thereby restricting its potential to enhance soil structure and porosity.

The observed variations in soil nutrient content across treatments are indicative of the unique contributions of glauconite, potassium sulfates, and glauconite extracts to nutrient availability and soil fertility. The divergences in nutrient availability can be attributed to the unique chemical characteristics of the extractors used, particularly the acidic nature of sulfuric and humic acids, which influence nutrient solubility and mobility in the soil. Foliar applications, though intended for plant uptake, often result in nutrient deposition onto soil surfaces, finding their way to the soil profile through irrigation, and influencing soil nutrient dynamics, especially when high-nutrient extracts like glauconite are used. The foliar applications with glauconite, especially in treatments GS2, G and GH2, demonstrated a significant influence on soil NH₄⁺ and NO₃⁻ levels in both seasons. The poor performance of GW treatments could be attributed to the limited efficacy of hot water extraction in releasing potassium and other nutrients from glauconite, which primarily relies on physical solubilization (Rudmin et al., 2019). This may result in insufficient release of key nutrients, such as potassium, reducing its effectiveness in improving soil fertility. This could be explained by the ability of sulfuric acid to break down soil organic matter partially and mineral structures in glauconite, thereby enhancing the release or replacement of bound nitrogen forms (Hassan & Baioumy, 2006). As well as the integration impacts between humic acid and glauconite facilitates the efficiency of glauconite-derived nutrients through the binding forces with elements (Costa Júnior et al., 2024) and increase the microbial population with its degradation capabilities of soil organic matter resulting in boosting the soil nitrogen dynamics in both NH₄⁺ and NO₃⁻ forms. Potassium levels exhibited substantial increases in response to GH2, possibly due to the ability of humic acid to enhance the availability of potassium by chelating K⁺ ions as presented in the GH compositions in Table 3 exhibiting the highest K content of 95 Meq L⁻¹ producing potassium humates, preventing them from leaching, and making them more accessible to plants (Ampong, Thilakaranthna & Gorim, 2022). Humic acids increase the cation exchange capacity (CEC) of soils, thus holding more K⁺ in an available form (Ali & Mindari, 2016). This mechanism also explains why humic acid-extracted glauconite showed better performance in enhancing soil K⁺ levels compared to water-extracted glauconite (GW1), which had the lowest K⁺ enhancement. The hot water extraction method is less aggressive in breaking down the mineral matrix of glauconite recording the lowest K level in GW with value 4.8 Meq L⁻¹, limiting the release of potassium.

The results regarding micronutrient availability (Fe, Mn, Zn, and Cu) reveal significant variations depending on the type of extraction. The increase in Fe and Zn levels observed with GS2 treatment can be attributed to the strong leaching effects of sulfuric acid. Subsequently, sulfuric acid creates a highly acidic environment with more H⁺ ions that are replaced in the reaction with a glauconite matrix with several elements including K, Fe, Zn, Mn, and Mg making them more available in the soil (Costa Júnior et al., 2024). This is particularly important for Fe, as its availability is highly pH-dependent resulting from the high concentrations in GS composition, and at the same time, the acidification induced by sulfuric acid can solubilize iron oxides in the soil, thus increasing Fe concentrations (Chen & Grassian, 2013). In contrast, The GH composition recorded the highest Mn and Cu than other extraction methods pointing to the role of humic acids in mobilizing these micronutrients. Humic acids are known to form stable complexes with metal ions, particularly Mn and Cu, and prevent their precipitation or fixation in the soil, thus enhancing their bioavailability (Dinu & Shkinev, 2020). These chelating properties of humic acids not only increase the solubility of Mn and Cu but also protect them from being adsorbed onto soil particles, which explains the observed increases in their concentrations with GH2 applications. This is consistent with findings that humic substances can significantly influence the mobility and availability of trace metals in soils (Hattab et al., 2014). The overall lower performance of hot water (GW) extraction in enhancing nutrient availability compared to GS and GH treatments can be attributed to the less effective nature of water as an extractant. Water extraction primarily releases physically adsorbed ions without significantly breaking down the glauconite structure or chelating nutrients, which limits its ability to enhance soil nutrient levels. This is evident in the lower levels of Fe, Mn, and Cu observed in GW treatments, as compared to GS and GH treatments.

As for sugar beet (Beta vulgaris L.) productivity and sugar quality, the results demonstrate the positive impact of GH2 on yield components and extracted sugar, while indicating varied effects on sugar losses to molasses (SLM) and sucrose content across treatments. The increased root, shoot, and sugar yields observed with the GH2 treatment can be attributed to the role of humic acid as an organic enhancer, which improves nutrient availability, water retention, and overall soil health (Ampong, Thilakaranthna & Gorim, 2022), and the glauconite as inorganic enhancer rich in potassium rates with slow releasing functions. Both humic acid and potassium contents increase root development and nutrient uptake efficiency by enhancing the cation exchange capacity (CEC) and stimulating microbial activity, which aids in the release of nutrients that are essential for growth (Selladurai & Purakayastha, 2016). Enhanced root systems, in turn, allow the plants to access nutrients more effectively, thereby promoting greater shoot and sugar yields. Besides the role of both humic acid and K in sustaining the environmental stresses such as salinity. Conversely, the poor performance of GW treatments in enhancing plant productivity, particularly shoot and root yields, may be linked to insufficient nutrient release. Limited nutrient availability directly impacts plant growth, as key nutrients like K and Fe are critical for metabolic processes such as photosynthesis and enzyme activation (Pandey, 2018). The improvement in extracted sugar percentages, particularly with the G treatment in the first season and GH2 in the second season, suggests that the mineral and organic composition of glauconite treatments plays a crucial role in sugar quality with long residual effects with GH treatments. Glauconite, being a natural source of potassium and other minerals, is known to improve sugar content in sugar beet and other crops by enhancing osmotic balance and carbohydrate transport within the plant (Shabana et al., 2024). The presence of potassium is vital for sugar translocation and is directly linked to sugar accumulation in roots, which may explain the notable increase in extracted sugar with the G treatment in the first season (Xie et al., 2022). Although the GH treatments recorded the highest sucrose and extracted sugar content, it recorded the highest SLM percentage in both seasons. Humic substances are known to mobilize micronutrients, including Fe, Mn, and Zn, which may play a role in the biochemical pathways involved in sucrose metabolism and molasses formation (Makhlouf, Khalil & Saudy, 2022). However, the magnitude of GH2 and GH1 treatments to increase SLM is consistent with the higher level of impurities (α-NH₄ and K) that occurred in both seasons. These impurities, which might be resulted from the improvement of nutrient availability and uptake facilitated by the treatments, likely contributed to an increase in non-sucrose impurities. Such impurities can interfere with sucrose crystallization and increase molasses formation, thereby elevating SLM. This relationship aligns with previous findings that highlight the role of α-amino nitrogen (α-NH4), potassium (K), and sodium (Na) as key contributors to molasses formation due to their ability to disrupt sucrose recovery (Muir, 2022; Shabana et al., 2024; Zhao et al., 2024). While GH treatments recorded the lowest alkalinity levels in both seasons indicating a better magnitude for achieving high-quality sugar that meets industry standards (Jaśkiewicz et al., 2024). The ideal alkalinity level for high-quality sugar extraction is generally below 4.5 Meq/L (Henke, Hinkova & Gillarova, 2019). Lower alkalinity ensures that a greater proportion of sucrose crystallizes effectively and enhances the extractable sugar yield, while High alkalinity levels indicate the presence of non-sugar impurities, which can interfere with sugar crystallization and reduce overall sugar quality (Velásquez et al., 2019). Another factor that should be considered in the sucrose content with a significant increase in the first season but no effects in the second, is the seasonal variations. The enhanced sucrose content observed with GH2, G, and GH1 treatments indicates that humic acids and potassium-rich treatments can improve sugar accumulation by facilitating carbohydrate metabolism and sucrose translocation in sugar beet roots (Shabana et al., 2024). The lowest sugar beet yield and sucrose content observed with GW treatment, beside the remarkable high sodium impurity levels in extracted sugar, could be explained as the low nutritional content in this extraction method. Consequently, the GW-treated plants receive fewer nutrients, particularly potassium, which is crucial for plant productivity. The potassium deficiency may limit the ability of sugar beet to accumulate and transport sugars, reducing sucrose content and yield. In this circumstances if low potassium availability, plants often absorb more sodium to maintain osmotic balance and cellular functions (Xie et al., 2022), leading to an increase in sodium impurities in the roots, which detracts from sugar quality.

The heatmap presented in Fig. 4 reveals the important relationships between soil physico-chemical properties and sugar beet yield characteristics under various potassium sources and glauconite extracts over two seasons. A strong negative correlation of soil pH with root yield (−0.9109), sugar yield (−0.9013), and shoot yield (−0.7962), while EC showed a negative relationship with sugar yield (−0.721) and root yield (−0.6837). This suggests that slightly acidic to neutral levels improve sugar beet productivity by enhancing soil nutrient solubility and uptake (Draycott & Christenson, 2003; Zi et al., 2024). The adverse impact of EC emphasizes the need for treatments that reduce salinity levels, such as humic acid amendments, which help in maintaining nutrient balance and supporting healthier root development. Similarly, weak but consistent negative correlations with yield occurred with ESP, BD, and SPR. High BD indicates compacted soils, which restrict root expansion linked with poor soil structure and increasing soil SPR and ESP (Vasu, Tiwary & Chandran, 2024). On the contrary, OM and IR explored strong correlations with sugar beet yield particularly with root yield and sugar yield. The presence of organic matter improves soil structure, nutrient retention, and water-holding capacity, creating favorable conditions for improving the infiltration rate (IF) in soil and consequently enhancing plat yield (Bashir et al., 2021). This positive relationship highlights the role of soil conditioners, such as humic acid and glauconite, in enhancing soil permeability.

To delve into more outstandings of the correlations between more soil parameters and sugar beet productivity and sugar quality parameters, the use of a self-organizing map (SOM) in Fig. 5 as a kind of unsupervised machine learning used to cluster the data based on the optimum similarity, providing an in-depth understanding of the measured variables concerning the input parameters (Klaine et al., 2017; Zi et al., 2024). The SOM analysis, in the upper left map, clustered the dataset into four distinct groups, with cluster (2) revealed the higher significance and correlations, indicating potential differences in treatment effects or soil conditions within each group. Higher OM levels were observed in clusters associated with humic acid (GH) treatments, which improved soil structure, water retention, and nutrient (Fageria, 2012). Higher OM levels in clusters indicate the positive impact of organic amendments, such as humic acid, on soil health and crop productivity. Increased OM is closely associated with improved soil fertility, which is essential for sustaining crop yields, particularly in degraded soils. Maps with lower electrical conductivity (EC), pH, and ESP values were linked to maps with higher root, shoot, and sugar yields, underscoring the role of soil amendments in mitigating salinity and enhancing soil conditions. This indicates that soil properties directly influence yield, with soil conditions favoring lower salinity, moderate pH, and higher organic content promoting better yields (Nelson & Ham, 2000). Conversely, the clusters’ maps of soil rich in nutrients availability of K, NH₄, NO₃, Zn, and Fe are typically correlated with increased yield and quality in sugar beets, as these elements are crucial for various physiological functions, including photosynthesis, enzyme activation, and sugar metabolism (Tariq et al., 2023). Additionally, the maps emphasize that the reduction of SLM and increment of sucrose content and purity of extracted sugar are correlated with the reduction of sugar NH₄, sugar NO₃, Sugar Na, alkalinity, and the enhancement uptake of Fe, and Mn elements. This suggests that the treatments impact the uptake of macro and micro-nutrients which play critical roles in crop growth and sugar formation. These findings highlight the potential of organic and mineral amendments, such as humic acid and glauconite, to optimize soil conditions, mitigate salinity issues, and enhance nutrient availability, leading to higher and better-quality sugar beet yields.

The aforementioned relationships were specifically to describe the linkages between soil dynamics and sugar beet attributes. To deepen into the specific relationships between sugar beet plants conditions and the output sugar status, the non-metrical multidimensional scaling (NMDS) has been accomplished and presented in Fig. 6. The NMDS plots provide further insight into the relationships between the sugar beet plants as independent variables (e.g., shoot yield, root yield, sugar yield, shoot Mn, shoot Fe, root Fe, and root Mn) and the extracted sugar as dependent variables (e.g., % extractable sugar, SLM, sucrose, purity, sugar K, sugar Na, sugar NH₄, and alkalinity) under the influence of different potassium sources and glauconite extracts over two seasons of sugar beet cultivation. The Figure 6A shows distinct groupings with overlapping clusters, indicating that certain treatments have a pronounced effect on variables such as shoot and root yield, along with micronutrient accumulation in plant tissues. The clustering patterns here imply that specific potassium sources and glauconite treatments are enhancing the uptake of Mn and Fe in both shoot and root tissues, intunrs influencing plant growth and yield (El-Mageed et al., 2022). Notably, the grouping of root yield and shoot yield in proximity within specific clusters (as shown in purple groups) suggests that treatments might enhance both biomass and nutrient allocation in sugar beet plants. Additionally, Fig. 6B further emphasizes the effect of these treatments on sugar-related attributes such as extractable sugar, SLM, and sucrose. Clusters with high sucrose and extractable sugar content (shown in green grouping line) reflect optimal growing conditions where nutrient availability and soil amendments, like glauconite extracts, positively affect sugar quality metrics. Treatments that enhance potassium (K) availability are crucial since potassium regulates osmotic balance and sugar translocation within the plant, which are critical for increasing both sucrose content and purity (Kaur et al., 2021). Additionally, the clustering patterns in variables like sugar Na and alkalinity (shown in red grouping line) provide insights into how different treatments impact the ion balance, which directly affects SLM and the overall extractable sugar yield. The presence of distinct clusters for sugar NH₄ andsugar K (shown in purple grouping line) suggests that certain treatments are particularly effective in influencing these variables. For example, enhanced levels of potassium in sugar tissues are linked to increased sugar quality and lower sugar losses, indicating that specific K-sources contribute to better ion regulation within the plant (Shabana et al., 2024). These findings underscore the potential benefits of combining K-sources with glauconite to enhance both the yield and quality of sugar beet crops, especially in challenging soil environments.

Conclusions

A two seasons field experiment was conducted to investigate the effects of different potassium (K) sources and glauconite extracts on sugar beet yield and quality grown in saline soils. Potassium sources include traditional potassium sulfate (K), glauconite (G) and different glauconite extracted using sulfuric acid (GS), humic acid (GH), or hot water (GH) in two foliar concentrations (20- and 40-mL L⁻¹). The findings revealed that GH and G treatments improved soil properties by reducing the EC, ESP, and BD, while increased OM and IR levels. The findings investigated that despite glauconite rock is a cheap waste, when extracted with humic acid, a highly concentrated extract of trace elements is obtained, which could be used as a foliar fertilizer alternatively to manufactured trace element fertilizers, as they are more concentrated, easier to absorb, and less expensive compared to the mineral elements available in the markets. The GH2 also improved sugar beet yield attributes recording average enhancements of root yield (94.84%), shoot yield (100.45%), and total sugar yield (137.22%) compared to control, while GW recorded the lowest improvement. Additionally, although the GH2 recorded the highest SLM with highest sugar impurities of K and α-NH₄, it recorded the lowest alkalinity levels which is preferable for sugar industries. The NMDS plots emphasized the high impacts of different treatments particularly GH treatments in both sugar beet plants productivity, sugar yield and sugar quality progress. These findings underscore the potential for integrating natural resources like glauconite with eco-friendly extractants such as humic acid into sustainable agricultural practices. Future research should focus on long-term studies across various agro-ecological zones to validate these results under different climatic and soil conditions. Investigations into alternative eco-friendly extraction methods, such as microbial or enzymatic processes, are necessary to enhance glauconite’s nutrient availability while minimizing environmental impacts.

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