Unlike organic polymers, geopolymers have distinct ways of interacting with soil minerals because of their inorganic Si-Al backbone frameworks. Geopolymer is known as alkali-activated cement, geo-cement, alkali-bonded ceramic, inorganic polymer concrete, and hydroceramic, it is an inorganic polymeric material synthesized like thermosetting organic polymers (Abdullah et al., 2015). Geopolymerization includes three stages (i) dissolution of source Al and Si, (ii) gelation, and (iii) reorientation of Si- and Al-complexes, and polycondensation are the primary mechanisms of geo-polymer stabilization (Huang et al., 2021) (Figure 4). The soil’s structure and mineralogy are changed by the cementitious elements produced by this process, which bind soil particles together. After dissolution, aluminosilicate minerals create aluminosilicate oligomers, which finally form an aluminosilicate gel (Huang et al., 2021). At ambient temperature, the geopolymer solidifies and takes on an amorphous to semi-crystalline form. The more complex (N, C)-A-S-H (sodium/calcium aluminum hydrated) gel model is presented in the context of calcium-based geopolymer systems. This type, which is less well-known than the N-A-S-H gel, is divided into two phases: the C-S-H gel and the N-A-S-H gel. Calcium may come from a variety of sources, including calcium silicate activators, slag, Class C fly ash, and additions like Portland cement. The coexistence of N-A-S-H and C-S-H gels contributes to the development of strength in geopolymers. Research indicates that higher curing temperatures (60°C–80°C) may lead to greater early strength but inferior long-term strength compared to lower curing temperatures (10°C–40°C). Furthermore, it has been observed that geopolymerization can take place at temperatures below 100°C (Huang et al., 2021). Applying geopolymers to stabilize soil has shown potential for strengthening soil via the production of cementitious geopolymerization products (Pourakbar et al., 2016). Complexity arises when applying geopolymers to soil because of variables that affect the process of geopolymerization, such as moisture level, alkaline concentration, and sources of silica and alumina. In the geopolymer-soil system, quality monitoring becomes difficult, especially when the geopolymer fraction is low. Changes in soil characteristics, such as cation exchange, may result from the interaction of soil and geopolymers, particularly when calcium-rich precursors or a KOH activator are used (Huang et al., 2021). This increases the complexity since the same geopolymer may have various effects on soils with different mineralogies. Even though this part of geopolymer stabilization has received little research attention, addressing these problems is essential to a thorough comprehension of the underlying processes.

Similarly, chemical reaction, enwrapping, and pore filling are all components of the reinforcing technique used for an organic polymer in clayey soil, as elucidated in several studies (Almajed et al., 2022). However, compared to interactions with sand, the chemical reaction between polymer and clay particles shows some significant differences. Soltani et al. (2018) described how adding a polymer to clay causes changes in the microstructural fabrics that result in the creation of nanocomposites. The adsorption process of polymer in soil has been illustrated in Figure 5. Specifically, electrostatic forces draw cationic polymers, also referred to as polycations, towards the negatively charged clay surface. On the other hand, because of the initial charge repulsion between the polymer and the negatively charged clay surface, anionic polymers, also known as polyanions, undergo less adsorption. However, the adsorption of polyanions can be improved by the presence of polyvalent cations. Furthermore, electrostatic attraction to the positively charged edges of clay surfaces may be the dominant mechanism governing the interaction between anionic polymers and clay (Ghasemzadeh et al., 2021). According to the literature currently under publication (Soltani et al., 2018), non-ionic polymers cling to clay particles via hydrogen bonding or van der Waals (dispersion) forces. Physicochemical bonds, including ionic, electrostatic, cation bridge, ion-dipole, hydrogen bonding, or Van der Waals bonds, are formed as a result of this contact (Soltani-Jigheh et al., 2019). For example, Kang and Bate (2016) observed that kaolinite soil treated with polyethylene oxide (PEO) led to significant face-to-face aggregations. Deng et al. (2006) identified ion-dipole interactions between exchangeable cations and carbonyl (C=O) oxygens of amide groups (CONH₂) as a predominant mechanism for smectite about clay-polymer interactions with particular clay minerals, especially in the context of transition-metal cation exchanged smectite. It was also shown that in the hydration shells of exchangeable cations, amide groups, and water molecules form hydrogen bonds. Additionally, it was shown that montmorillonite significantly and irreversibly adsorbed partly acetylated polyvinyl acetate (PVAC), mostly due to hydrogen interactions formed between the polymer’s hydroxyl groups and the oxygen on the clay surface (Greenland, 1963).

Biodegradation is a process in which microbes are involved in breaking down complex material into simpler forms. The biodegradation process is influenced by environmental factors, microorganisms and their enzymes, and the properties of the polymer itself. The biodegradation process is influenced by environmental factors, microorganisms and their enzymes, and the properties of the polymer itself. Microbial degradation in this process occurs through enzymatic action. Microorganisms, such as bacteria and fungi, play an active role in biodegradation (Bher et al., 2022). These microorganisms have specific optimal growth conditions, making biotic degradation a complex process influenced by various factors related to the polymer, microorganisms, and the environment (Devi et al., 2016). The biodegradation characteristics of bio-polymers can vary depending on the soil environment, which is the least studied. Because biodegradation in soil happens slowly under natural conditions, it allows for a detailed investigation of the initial stage, known as biodeterioration. Research into soil biodegradation is particularly important for farmers, as it can encourage the transition from traditional polyethylene (PE) mulch films to bio-based plastics (Hayes et al., 2017; Slezak et al., 2023).

The most intriguing application of polymers is to modify the surface properties of soil particles (Figure 6). The effective, individual component of the soil, known as the particle, might take the form of a sheet, crystal, or aggregate. Very strong primary valence bonds keep atoms together in sheets; strong or weak secondary valence bonds hold sheets together in crystals, as in the cases of kaolinite and montmorillonite; and weak secondary valence bonds hold crystals together in aggregates. It is only the intra-aggregate forces that can be disrupted by chemical additions or pressures provided by engineering, or the intra crystal forces in the case of expanding clays. Chemicals can change the direction and even the amount of intra-aggregate forces. The methods by which additives might generate repulsive forces between particles and subsequently scatter the soil or attract forces between particles and aggregate the soil have been explained by Michaels (1952). It has been observed that the addition of polymers in specific quantities can change the characteristics of soil.

SAPs (super absorbents polymers) otherwise known as “miniature water reservoirs” are made up of lightly cross-linked networks of hydrophilic polymer chains and are capable of swelling in water, absorbing, storing, and releasing water upon root demand based on the principle of osmotic pressure (Huettermann et al., 2009). Thus, SAPs reduce evaporation and percolation loss of water and ultimately improve the water holding capacity of the soils (Malik et al., 2022). Such polymers hold practical relevance for growing crops, especially in sandy and drought-prone soils.

Polymer/clay superabsorbent composites are also great water absorbers and are more cost-efficient. On the other hand, gel-forming polymers made up of three-dimensional cross-linked polymeric networks can absorb water up to 1,000 times their weight, form gels, and absorb large amounts of water along with soil nutrients in a similar fashion to sponges (Jnanesha et al., 2021). Overall, these polymers prevent water loss, store water efficiently and release it as per crop demand, thereby largely reducing the irrigation frequency (Kujur et al., 2022). Thus, SAPs and hydrogels are promising technologies for effectively dealing with agricultural drought, especially in rainfed areas (Feng et al., 2020).

While synthetic polymers are more efficient in storing water than natural polymers, the latter ones are more biocompatible, biodegradable, and cost-effective (Krasnopeeva et al., 2022). However, the effectiveness of hydrogels reduces with increased salinity and ions such as Mg²⁺, Ca²⁺, and Fe²⁺ as they can break the polymeric structures and release the stored water molecules (Reddy et al., 2015). Nevertheless, the effectiveness of the SAPs would also depend on the initial soil status i.e., soil pH, clay content, soil organic matter status, bulk density, total nitrogen status, nitrogen fertilization, and water supply (El-Asmar et al., 2017). Agri polymers are supposed to work better at a higher initial pH than at a lower initial pH (Zheng et al., 2023). SAP polymers are reported to be more effective under water deficit and rainfed conditions rather than in well-irrigated situations (Zheng et al., 2023). Moreover, SAP application under irrigated conditions may even reduce crop yields (Wang et al., 2012).

These cross-linked polymers also help in reduced nutrient loss, their greater absorption, and subsequent slow release to crop root zones meeting timely crop demand for nutrients. Polymers can reduce nitrogen leaching by 45% (Mikkelsen, 1994). Mazloom et al. (2020) reported higher phosphorus uptake in maize by application of lignin hydrogel. Chen et al. (2016) noted that polymers containing both acrylamide and acrylate side chains exhibited a greater capacity to retain Ca²⁺ ions, thereby promoting the flocculation state of the soils. Eneji et al. (2013) documented reduced nitrate leaching and improved nitrogen uptake by maize crops when superabsorbent polymers (SAP) were applied under deficit irrigation conditions. Yang et al. (2022) reported that SAP application enhanced soil organic carbon status, enzymatic activity, and microbial biomass carbon in a long-term experiment in wheat crops. Recently, Al-Amiri and Al-Baraka (2023) observed that the application of agricultural polymers resulted in increased availability of nitrogen, phosphorus, and potassium in wheat crops. Enhanced availability of nutrients by application of agricultural polymers can be attributed to (i) improved soil physicochemical properties ensuring conservation of soil nutrients, (ii) improved soil moisture status, (iii) nutrient retention in the soluble state for enhanced periods, (iv) preserving of nutrients in soluble form, (v) minimizing nutrient loss for soil ecosystems, and (vi) improved cation exchange capacities (Al-Amiri and Al-Baraka, 2023). Zheng et al. (2023) observed that SAPs act best in soils with low fertility, low total nitrogen, low fertilizer inputs, and low soil organic carbon status.

Crosslinked polymers are utilized as carriers for various biocides, including herbicides, molluscicides, fungicides, insecticides, algicides, and bactericides. Polymers are reported to be beneficial for the controlled delivery of formulations/biologically active agents (Milani et al., 2017). Major benefits of applying these agricultural inputs by polymers include (i) the need for less quantity of biocide, (ii) slow and precise release of active ingredient over a long period, (iii) reduced mobility of biocides ensuring targeted application, (iv) protecting the non-persistent biocides from environmental degradation, (v) increase the use efficiency of pesticides and herbicides, (vi) minimizing the need for repeated application, and (vii) health benefits for farm workers. However, the requirement of a large amount of inert material as carriers and disposal of the herbicide residuals are the major limitations of polymers as carrier materials (Ekebafe et al., 2011). Seed additives and some growth regulators can also be applied through SAPs (Krasnopeeva et al., 2022).

Improved crop yield by application of polymers has been reported for many crops e.g., corn (Al-Amiri and Al-Baraka, 2023), peanut (Islam et al., 2011), senna (Jnanesha et al., 2021), potato (Hou et al., 2018). In a study conducted by Reddy et al. (2015), the impact of a cross-linked polymer composed of polyacrylamide and potassium acrylate (PAM) on the yield and water productivity of tomato crops cultivated in sandy loam soil was examined. The research indicated that applying the aforementioned polymer at a rate of 25 kg per hectare, coupled with irrigation on alternate weeks, led to increased yield, improved water retention, and reduced irrigation needs. The enhancement in crop yield due to the utilization of SAPs can largely be credited to the improvement in soil physicochemical properties, increased soil nutrient availability, enhanced water retention, and augmented microbial activity. Furthermore, the application of SAPs can also elevate soil temperature, leaf area temperature, and photosynthetic rate, ultimately leading to higher yields (Yang et al., 2018).

A recent comprehensive review by Zheng et al. (2023) summarizing the results of 310 studies across the world has reported that by application of SAPs, there is an average improvement in yield and water productivity by 13% and 17%, respectively. Tuber crops and vegetables have been reported to be best benefited by the application of SAPs in terms of yield and economics, respectively Zheng et al. (2023). Thus, considering the ever-declining water availability for irrigation, the use of polymers is a potential option for managing water stress and safeguarding food security.

Major limitations of the use of polymers in agriculture include high costs, especially for synthetic ones (Figure 7). Moreover, there exists a knowledge gap regarding the time required for complete biodegradation of different types of polymeric compounds in different environmental conditions. The environmental impacts of the residues and the impact of the residues on subsequent crops/cropping systems are still not fully explored. Thus, identification and mitigation of any potential environmental threat of the agricultural polymers is required. Future research also needs to be conducted considering the impact of different tillage practices on the effectiveness of agricultural polymers. Standardizations also need to be established concerning effective and suitable doses and methods of application of agricultural polymers in different crops. Despite that controlled release of agrochemicals may fail to supply an adequate amount of desired chemicals/nutrients during high crop demand also causes unwanted residue in the soil, which affects soil acidity. Non-biodegradable polymers cause soil pollution destroy soil biodiversity and enter into the human food chain.

To minimize the lingering impacts of herbicide carriers, there have been advancements in dual-application products designed for both herbicide and fertilizer use. In this system, the residual products resulting from polymer degradation serve as beneficial agents for plant growth and soil enrichment, acting as fertilizers (Bourzac, 2020). Such products need to be adopted more. The use of more and more natural polymers/bio-based materials, e.g., polysaccharides and polypeptides/natural-based SAPs should be encouraged to reduce cost and environmental impacts. In the future, there is an opportunity to explore the potential of semi-synthetic, hybrid polymeric materials, and polymeric nanocarrier systems (Sikder et al., 2021). More field trials across a wide range of crop species and with different water management approaches are the need of the hour to establish concrete facts regarding the practical applicability of polymeric substances at a larger scale.