Impacts of cacao agroforestry systems on climate change, soil conservation, and water resources: a review

Agroforestry is practiced around the world and can deliver several environmental benefits (for instance, climate change mitigation and climate adaptation), soil conservation (e.g., erosion control, enhanced soil fertility) and ways of dealing with the problems posed by MAPs, such as loss of water quality caused by the overuse of chemical fertilizers (e.g., N and P) and pesticides. MAPs are a type of agricultural practice that are based on maximizing grain yields without respect to quality, the environment, or soil conservation. Fertilizers are broadly used in MAPs to improve the soil fertility (Kadigi et al., 2020). Agroforestry is one of the most effective methods used to reduce a range of forms of abiotic stress, including drought, metal, and salinity resulting from a combination of climate change and the overuse of pesticides and chemical fertilizers, which have negative impacts on plant yields (Kumari et al., 2022). Pesticides in forests and pastures contribute to soil degradation and are widely used by citizens, agroalimentary enterprises and cooperatives. In 2019, the global consumption of pesticides was estimated at 4.2 million tons (Foong et al., 2022). Consequently, the severe impact of pesticide usage in agricultural activities has contributed to more than 50% and approximately 70% of freshwater eco-toxicity and human toxicity, respectively (Foong et al., 2022). The chemical elements in soils cause eutrophication and thus the death of some aquatic organisms (Wear & Greis, 2002), as well as compromising the health and life of human beings. It was estimated that 1 out of 8, 1 out of 6, and 1 out of 4 people are at high risk from biochemical oxygen demand, N, and P pollution, respectively (International Food Policy Research Institute & Veolia, 2015). The Institute for Health Metrics and Evaluation (IHME) reported that 3.4% (80 million disability-adjusted life years (DALYs)) of the world's diseases are associated with inadequate water supply and sanitation (Weidema & Fantke, 2018). Drinking contaminated water is responsible for several diseases, including diarrhea, cholera, and hepatitis A. The Global Burden of Disease (GBD) estimated that 1,800,000 people died from diseases associated with water pollution in 2015 (GBD, 2015). Drinking contaminated water causes a total of 485,000 deaths each year as a result of diarrheal diseases (WHO, 2017). Researchers' attention has come to focus on effective ways to deal with these challenges, taking into account the different roles of agroforestry associated with ecosystem services (ES), including groundwater quality.

Different to MAPs, agroforestry is a sustainable alternative that protects soils against erosion and enhances water quality (Neto et al., 2007). However, there is uncertainty about the impact of cacao (Theobromacacao L.) trees on water quality. Cacao is generally grown in the shade of a thinned forest (Lobão et al., 2007) and is mainly grown in tropical areas of Central and South America, Asia, and Africa (Marita et al., 2001). Cacao is one of the most important perennial crops in the world. Cacao production worldwide was estimated at approximately 3.5 million tons in 2006 (ICCO, 2007). In 1970, the production of cacao represented approximately 0.6% of Brazil's Gross National Product (Fonseca et al., 2020). In 2015, the production of cacao in the southeastern region of the state of Bahia, Brazil, represented 87% of the agricultural land (Sanches, 2019). Integrated cacao agroforestry is a sustainable solution, combining forests and agricultural activities to reduce runoff and soil erosion, mitigate climate change through the storage of carbon, provide goods to human beings, and promote conservation and biodiversity. As compared to the preserved forest, CO₂ emissions in cacao-AFS are variable and depend on soil characteristics attributed to the type of vegetation cover (Costa et al., 2018). Likewise, agri-silvi-based AFS had higher soil moisture than sole crop fields (Bhatt et al., 2016). Other researchers have argued that AFS have a great influence on the supply of regulating ES and enhancing landscape structure (Kay et al., 2018). The adoption of agroforestry can present benefits that significantly differ from other land use. For example, hedgerow-based AFS is more efficient than other land uses regarding its role in reducing surface runoff (Bhatt et al., 2016). AFS soil quality does not differ from that of the forest (Rousseau et al., 2012), and can therefore contribute to the regulation of the water cycle and modify soil water availability.

Forests can act as water filters depending on the forest extensions and forest types. For instance, riparian forests contribute to clean water owing to their positive influence on pesticide removal in water-saturated zones (Aguiar et al., 2015). The researchers argued that wood > shrubs > grass in terms of forest performance for removal of pesticides in the riparian zones. As such, riparian vegetation has a fundamental role in the ES associated with water quality. In other words, agroforestry can play a crucial role in restoring riparian habitats and solving river problems. In addition, agroforestry can be seen as encouraging environmental protection and biodiversity conservation (Nair, 2011). For example, vegetative filter strips (VFS) can be planted in an area with the purpose of removing sediments, nutrients, and pesticides from both surface and subsurface waters (Dillaha et al., 1989; Nair & Graetz, 2004; Nair, 2011). The VFS play an impressive role in controlling erosion rate and maintaining soils in the field (Grismer et al., 2006). Also, AFS are suitable strategies for soil conservation and infiltration recovery. Soil water content (SWC) can be increased in the agroforestry areas depending on the type of tree, slow-growing or fast-growing trees, and soil composition. Taking into account the importance of AFS for environmental challenge mitigations, and their importance for ES, this state-of-the-art review investigated the influence of AFS on climate change, soil conservation, and groundwater quality. We hypothesize that: (i) agroforestry can control erosion and improve water quality; and (ii) agroforestry can be used for pollution abatement in soils and groundwater. This review proceeds as follows: the introduction, importance of AFS for soil conservation, the role of AFS in enhancing water infiltration, the importance of AFS on soil chemical properties, role of AFS in reducing climate change, influence of AFS on water quality, future challenges and ways forward, and finally conclusions.

Among numerous alternatives that can be used for natural resources management, agroforestry is one of the most sustainable and environmentally friendly. Agroforestry enhances ES via improved soil structure and increases water retention and carbon sequestration (Mukhlis et al., 2022), which can be possible thanks to the decomposition of fine roots of trees (Siegwart et al., 2022). As such, the carbon sequestration rate might depend on soil depth. For example, topsoils, upper soil, and lower subsoils can potentially influence carbon sequestration in AFS in the following order: topsoils (0.92 Mg ha⁻¹ yr⁻¹) > upper subsoils (0.72 Mg ha⁻¹ yr⁻¹) > lower subsoils (0.52 Mg ha⁻¹ yr⁻¹) (Hübner et al., 2021). Moreover, research carried out in the West African Sahel has concluded that agroforestry can promote landscape resilience in the greater region (Ellison & Ifejika Speranza, 2020). For example, AFS have reduced soil loss from 1.22 to 0.17 t/ha over a 6-year period (Panwar et al., 2018). This reduction might be possible due to the capacity of cacao trees to maintain and improve soil structure. These findings explain that agroforestry has great importance for soil conservation. As such, AFS promote sustainable development (i.e., functional ecosystems, livelihoods, and human security) through the accomplishment of goals including providing water, energy, and food security, among others (Elagib & Al-Saidi, 2020). Importantly, AFS also protect land use and maintain good physical, chemical, and biological properties in tropical soils (Arévalo-Gardini et al., 2015, 2020; Matos et al., 2020), and contribute to the restoration of a local landscape scale (Martin et al., 2021). However, these properties can be improved if cover crops and trees are included in the system (Alegre & Cassel, 1996).

Similarly, scholars underscored that the biological, chemical, and physical characteristics of forest soils contributed to high quality water in streams, and moderated stream hydrology (Neary et al., 2009). Research conducted in Ejido, Mexico, has demonstrated that cacao agroforests have lower land change as compared to other types of land tenure (Oporto-Peregrino et al., 2020). Cacao agroforestry, it is worth noting, is characterized by a large accumulation of the amount of soil organic carbon (SOC) (Monroe et al., 2016), and it can be used to reduce deforestation and forest degradation (Batsi et al., 2020), improve soil fertility, maintain soil ecological functions, and restore soil quality to degraded pasturelands (Suárez et al., 2021).

In recent years, studies have been carried out to search for sustainable routes to maintain the soil's physicochemical properties, which are essential for its conservation and productivity. Research conducted in Nepal showed that there were significant differences in soil pH, Al content, base saturation, electrical conductivity, organic matter and N content, and cation exchange capacity between AFS and conventional system (CS) (Schwab et al., 2015). This finding was consistent with the finding of research conducted by Tornquist et al. (1999) in Costa Rica, which concluded that soil exchangeable bases and pH were lower in agroforestry treatments as compared with pastures. This indicates that AFS have higher soil quality and are more fertile than CS. AFS have more ability to ensure plant and animal health, and to preserve environmental quality, as compared to CS. This finding is supported by another study carried out in the central mid-hills of Nepal by Schwab et al. (2015). AFS reduce surface runoff, SOC, and associated nutrient losses by an average of 58, 65, 9, and 50%, respectively (Zhu et al., 2020). The reduction of runoff by the AFS is a part of soil conservation and therefore maintains the chemical and physical properties of soil (Figure 1). Tree roots in AFS reduce N and P residues in soils by 20–100% (Pavlidis & Tsihrintzis, 2018). Findings of other research have also reported that AFS can reduce pesticide leaching and runoff by up to 90% (Pavlidis & Tsihrintzis, 2018). This is possible due to soil and water management in this system (Wang et al., 2017), which can potentially reduce non-essential trace metals in soil. For example, cacao trees enable the reduction of non-essential trace metals such as Cd and thus transfer it from roots to the shoot (Oliveira et al., 2022) (Figure 2). Another study conducted in the province of Bagua in Amazonas, Peru, indicated that the amount of Cd concentrated in the roots of cacao trees is five times higher than the Cd level in the soils (Oliva et al., 2020). In the same line of reasoning, another study conducted in Brazil highlighted that AFS improved soil chemical indicators based on pH increase, soil nutrient content (Ca, Mg, and K), reduced Al saturation (Silva et al., 2020), and Hg (Béliveau et al., 2017) (Figures 1 and 2). Notably, AFS contribute to the maintenance of soil integrity (Béliveau et al., 2017). These findings indicate that cacao-AFS is effective at reducing trace metals in soils that are often caused by MAPs. Accordingly, AFS are an effective technique to be used as pollution abatement for soil and water decontamination (Figure 1). For instance, trees or woody plants with developed root systems and large biomasses are attractive for vegetation and phytoremediation in metal-polluted sites (Lee et al., 2009; Capuana, 2013).

AFS play a crucial role in reducing the need to drain, soil evaporation, runoff, erosion, and silting up of rivers (Figure 2). The reduction in runoff can be attributed to ground cover plants in AFS, and the slope of the landscape. For example, research carried out in the Philippines reported that the risk of soil erosion on slopes was 8% higher with non-agroforestry use than with agroforestry use (Delgado & Canters, 2012). Other researchers underlined that AFS increased aggregate soil stability, and decreased runoff and soil erosion (Roose & Ndayizigiye, 1997; Marwah, 2012), due to enhanced infiltration (Mwangi et al., 2016), which resulted in increasing soil water storage (Zhao et al., 2022). Scholars have pointed out that agroforestry can increase evapotranspiration (ET) in the watershed (Wang et al., 2017) and thus reduce water availability owing to water uptake by tree roots (Mwangi et al., 2016), which is strongly related to root-length densities and root surface areas (Bayala & Prieto, 2020). Similarly, findings of another study highlight that apple fine roots decrease the SWC (Shen et al., 2022). Importantly, the ability of trees to reduce the SWC depends on tree and soil types. For example, a previous study demonstrated that the SWC decreased rapidly during the summer in Putnam silt loam dominated by agroforestry buffers (Sahin et al., 2016). In contrast, the walnut-wheat alley cropping system (JTACS) increased water infiltration in the shallow soil layer during the rainfall season (Wang et al., 2015). Water availability through soils and air moisture is one of the main drivers of AFS (Pérez-Girón, 2022). In the case of cacao trees, the density of lateral roots exponentially decreases with depth, and 20% of these roots can uptake water (Mommer, 1999). Research carried out in a coastal area of northern Iran has indicated that the combined scenarios of agroforestry, no-tillage, and rice straw mulch are an effective way to increase groundwater recharge in the region (Mohseni et al., 2022). Thus, AFS has among its functions the regulation of rainwater, support of the microclimate (crop production), and ecosystem stability (Theresia Sri Budiastuti et al., 2021).

The effectiveness of agroforestry to increase or reduce the SWC may depend on the type of vegetation cover, and soil properties. Vegetation density and type of vegetation are correlated with soil hydraulic properties (Reddy et al., 2016). Similarly, organic matter produced by AFS enhances the effective rewetting and water retention capacity (Lestari & Mukhlis, 2021).

Agroforestry reduces excessive evaporation and maintains groundwater availability during the dry season (Lestari & Mukhlis, 2021). It also helps improve soil quality by cooperating with water stress and improving hydraulic conductivity and infiltration, owing, perhaps, to grass and cover crops. Therefore, agroforestry is a strategy to be used to control runoff and erosion. Infiltration has a major impact on controlling soil erosion and runoff, soil moisture content, and groundwater recharge (Lozano-Baez et al., 2019; Figure 2). Depending on the precipitation regime, runoff carries chemical substances from an agricultural field into the watershed (Figure 2). Consequently, syntropic agroforestry systems, which are a type of agroforestry involving very large amounts of organic matter, can be used to improve soil water infiltration (Murta et al., 2021). In addition, there are other solutions such as covering the soil, rather than leaving the bare soil. Recent research has highlighted that AFS reduce the total soil loss and runoff by 37.7 and 19.1%, respectively (Jinger et al., 2022).

There is a complex relationship between soil water infiltration and tree roots. For example, trees with deep roots increase macropores vertically and modify both micro and mesopores laterally (Wang et al., 2017) as well as being more suitable to improve soil moisture content as they are able to lift up or redistribute water to the topsoil via a process known as hydraulic lift (Bayala & Prieto, 2020). Both hydraulic lifting processes and deep roots allow trees to uptake the groundwater from the deeper layer and make it available to understory vegetation with shallow roots (Pérez-Girón, 2022). In addition, deep-root trees improve soil physical conditions and higher soil microbiological activities under AFS (Nair et al., 2008). Thus, the infiltration depends on the land use history prior to the application of agroforestry in an area (Lozano-Baez et al., 2019). For instance, mechanical clearing reduces infiltration rates because the infiltration can depend on the woody vegetation roots. As such, the infiltration rate of soil increase is positively linked with the enhancement of soil mechanical stability (Schnug & Haneklaus, 2002). Furthermore, the greater the infiltration capacity of buffer soils, the more agroforestry species are able to remove pesticides from overland runoff (Dollinger et al., 2019). Infiltration may vary with agroforestry practices and plants used and may be affected by plant age, which could reduce baseflow and water yield in the soil or watershed due to a possible increase in ET of some agroforestry species.

Soil moisture may depend on a range of factors, including the type of land cover and soil characteristics. The uppermost soil layer in the AFS has higher soil moisture as compared to monoculture (Niether et al., 2017). On the other hand, Sarto et al. (2022) highlight that AFS reduce water availability in the superficial soil layer, particularly during the rainy seasons. These findings indicate that the capacity of trees to recharge the groundwater depends on several factors, including the climate, soil types (e.g., sand, silt, clay, etc.), and soil characteristics, including fracture depth, soil texture, and fractured rock. Water in the soil can be influenced by pedotransfer functions (Reichert et al., 2009), which have a great influence on infiltration and water quality. For example, research reported that loamy sites could have a water availability greater than clay loam or sandy (Dodd & Lauenroth, 1997). Similarly, another study indicated that infiltration can be lower in sandy soils than in clayey soils (Lozano-Baez et al., 2019). Therefore, these findings indicate that a high infiltration rate depends on soil characteristics, including high soil aggregation. The quality and quantity of coastal waters result from a complex interaction of anthropogenic activities with soil and climate (Daly et al., 2018). In other words, coastal and groundwater quality depend on soil properties and land use. The soil in a constructed wetland is an optimal substrate and has great performance in the adsorption and passivation of pollutants, including N, P, and heavy metals in water (Cheng et al., 2021). Another study has outlined that a decrease in soil pH and salinity accompanied by a decrease in Cl and Na concentrations is registered in an area irrigated with treated wastewater combined with the plantation of agroforestry species (Zouari et al., 2019).

A study conducted in Spain indicated an agroforestry catchment feeds a water reservoir with a sedimentation rate estimated at 3.5 tons/ha per year (Palazón et al., 2016). This amount of sediments depends on agricultural practices, particularly the types of chemical substances used in the AFS. Pesticides can threaten groundwater quality if they are used in the root-affected zone (Dollinger et al., 2019). Moreover, other factors (for instance, precipitation, slope, soil porosity, and buffer localization) can also play an important role in water pollution. According to Canencia et al. (2011), N, P, and potassium levels in watersheds dominated by AFS are moderately high and suitable for crop production. This demonstrates that agroforestry has great potential to remove these chemical elements.

Watershed contamination is a worldwide problem that can become hypertrophic and thus cause the extinction of some species of aquatic organisms when these chemical elements are in high concentrations. These challenges have compelled researchers to search for facile and sustainable solutions, such as agroforestry. Kim & Cho (2014) found in their study that agroforestry crop fields and open crop fields had similar runoff loadings of total N, total P, and total suspended solids. Notably, AFS can reduce nonpoint source pollution due to tree growth and tree roots taking more space in the soil, reducing the amount of fertilizer in the watershed (Udawatta et al., 2010) and generating cleaner water (Brown et al., 2018) (Figure 3). As compared with other existing reviews, this study shows that, in an agroforestry area, trees with deep root systems have a great influence on the effectiveness of removing contaminants in soil and improving groundwater quality through trapping of nutrients, and metals deposited in the surface and topsoil (Kumar et al., 2020; Pavlidis et al., 2021). Therefore, agroforestry acts as a technique for the remediation of polluted soils owing to tree roots that can uptake the excess agrochemicals that would otherwise pollute groundwater via leaching and surface water via runoff (Pavlidis et al., 2018, 2020, 2021). In other words, AFS can act as a technique to improve water quality, which is an objective of ES (Keeler et al., 2012).

The challenges of managing climate change are increasingly drawing researchers' attention to the need to find sustainable solutions. AFS can be an effective tool for mitigating climate change (De Zoysa & Inoue, 2014; Murthy et al., 2016) and carbon and environmental footprints, by reducing greenhouse gas emissions into the atmosphere (Tefera et al., 2019), regulating rainwater (soil and water conservation), and supporting the microclimate (Budiastuti et al., 2021), due to the shade provided by this system (Lestari & Mukhlis, 2021). AFS are suitable for climate mitigation, particularly as they have a high density and diversity of shade trees (Boreux et al., 2016). The adoption of AFS with 50% shade cover can reduce the mean temperature (Gomes et al., 2020). AFS are climate-resilient agricultural practices (Jhariya et al., 2019). Other researchers have pointed out that AFS can contribute to climate adaptation (Verchot et al., 2007). Shade has an important role to play in the reduction of temperature and enhances rainfall (Panozzo et al., 2022). The effect of trees on soil water conservation increases with the intensity of shading. Thus, the density and composition of the species have a great influence on climate mitigation. For example, coffee systems reduce the effect of extreme temperature and precipitation (Lin et al., 2008), findings have shown that the shaded coffee AFS improve microclimate conditions and deep-water drainage as compared to unshaded coffee systems (de Carvalho et al., 2021).

People around the world are currently facing food and water insecurity owing to the depletion of natural resources, such as water and crops. This challenge has increasingly spurred scientists to seek out a simple and environmentally friendly solution. Scholars report that AFS maintain high levels of biodiversity and biomass (Sistla et al., 2016), which are necessary for the integrity and conservation of the soil. Similarly, other researchers argue that AFS combine production and conservation (Vallejo-Ramos et al., 2016) and are the best option to deal with the erosion, and degradation of biodiversity (Saha et al., 2010) usually caused by the MAPs. Scientists have reported that farmers are used to felling trees to enlarge their gardens and producing furniture (Pauleus & Aide, 2020; François et al., 2022). Importantly, AFS can reduce deforestation and cultivable land extension (François et al., 2022), protect environmental areas (Laudares et al., 2017), recycle nutrients lost in MPAs (Izac & Sanchez, 2001) via their root systems (Raj, 2020), lift people out of poverty and stem the decline of agricultural productivity (Jama et al., 2006). In the other words, AFS is a promising and sustainable option for natural resources management and this can contribute to human well-being and environmental protection.

Cacao agroforests are described as being sensitive to climate change and water deficit (Lahive et al., 2019), do not cause undesirable environmental change (Gama-Rodrigues et al., 2021), and have a crucial role in drought-tolerant land use (Gateau-Rey et al., 2018), particularly in tropical regions (Schwendenmann et al., 2010). Wang et al. (2017) have underscored that AFS increase vertical preferential flow and retard the subsurface lateral flow and thus enhance water retention capacity. Another study highlighted that cacao is tolerant to shade, and the maximum photosynthetic rate occurs at an irradiance of around 400 μmol m⁻² s⁻¹ (Arévalo-Gardini et al., 2021). Admittedly, unshaded cacao monocultures are vulnerable to climate change (Heming et al., 2022). In contrast, shade trees reduce water loss from top soil via ET of the cocoa (Niether et al., 2017). Therefore, canopy structure has a great influence on the ET in AFS (Wang et al., 2021). The age of trees may have a great influence on the capacity of AFS to enhance the advantages and ecological services.

AFS have an evident ecological advantage over monoculture, particularly for young apple trees in the semi-arid region (Zhao et al., 2022). As compared to older cacao trees, shade is more necessary for young cacao tree plantations (Tscharntke et al., 2011). In addition, AFS can both contribute to capturing soil carbon and play an important role in mitigating atmospheric CO₂ (Verchot et al., 2007; Rita et al., 2011). The total carbon (aboveground and root biomass) stored in an AFS, including cacao and shade trees, was 2.5 times higher than in a monoculture (Niether et al., 2020). Shade trees have great importance in cacao-AFS because of their role to influence radiation, wind regimes, nutrients, and hydrological cycling (Tiralla et al., 2013). Notably, shade trees within AFS protect the understory cacao against extreme climate (Niether et al., 2018). Cacao agroforestry can make an important contribution to mitigating climate change and contribute to the national economy of a country. AFS can also be a promising solution for improving low soil fertility in tropical zones (Rangel Mendoza & Silva Parra, 2020) and contribute to the achievement of Sustainable Development Goal 2, which aims to end global hunger.

It is crucial to find a sustainable and environmentally friendly alternative to deal with the problems of soil loss, nutrient loss, soil contamination, climate change, and water contamination. These challenges are drawing scientists' attention to focus more on AFS. Herein, this present review revised the influence of AFS on soil conservation, climate change, and groundwater quality. This study revealed that AFS offer a sustainable approach for dealing with climate change, groundwater contamination, and nutrient loss, among other environmental challenges. The strengths of this study encompass a range of evidence about the relationship between AFS and water quality and how environmental and geologic factors, as well as human activities, can be associated with agroforestry to contaminate the waterbody. Insufficient evidence about how woody plants can influence the intercept and/or reduction of heavy metals in soil is a limitation of this review. Another limitation is that it does not take into account the effects of fast-growing and low-growing trees on soil water availability. This lack of evidence could be filled via an experiment carried out using fast-growing and low-fruit trees planted in arid, semi-arid, and/or humid sites where the SWC is measured before and after the observations. Such an observation requires consideration of the soil type and the different phases of the trees’ growth as important factors. Researchers report that fast-growing trees are not suitable for forestation in areas with medium precipitation and brackish groundwater (Sudmeyer & Simons, 2008), and their photosynthetic rates and stomatal conductance are higher than slow-growing trees (Liu et al., 2021). Moreover, the interaction between shape of tree roots, the type soil and trees' physiology should be studied to enlarge knowledge concerning trees' behavior towards infiltration or soil water availability. In conclusion, further studies are required to identify other factors that may influence the ability of AFS to improve water quality and to examine how agroforestry age and agroforestry density can influence soil water infiltration.

There is an urgent need to find a sustainable option for reducing soil loss, recharging groundwater, and improving water quality altered by industrial activities and MAPs. This review investigated the effects of AFS on soil conservation, climate change, and groundwater quality. It was found that AFS can enable soil water infiltration and ET. We also found that agroforestry is a promising and sustainable alternative for improving water and soil quality and controlling erosion. This review showed that AFS improve soil structure through the vegetal material of tree components. Also, AFS support soil biological, chemical, and physical properties. Therefore, AFS are crucial for soil conservation and the enhancement of water quality. In addition, AFS are a promising alternative to be used to remove trace metals (e.g., Cd, Al, Hg) in contaminated sites. However, several factors, including surficial geologic controls, slope gradient, soil types, and topographical conditions can combine with the AFS to deteriorate water quality in the watersheds. These factors can be accentuated by land use/anthropic activities. The deep-root trees play an important role in reducing pollutants in the soil and enhancing humidity. Our hypotheses were verified because we have found that AFS control erosion and improve water quality, and can be used as a phytoremediation technique to remove trace metals in the soils. The novelties of this review, compared to existing ones, are that AFS can contribute to reducing non-essential trace metals in soils caused by MAPs and improve soil quality by increasing infiltration, soil organic matter, macropores, aggregate stability, and aeration by decreasing erosion, runoff, and soil bulk density, and reducing nutrient loss. Conclusively, the adoption of AFS can be a promising alternative to improve upstream water quality, soil conservation, agricultural sustainability, mitigate climate change and allow carbon sequestration, and reduce environmental footprints.

This study was financed in part by the Brazilian National Council for Scientific and Technological Development (CNPq Grant 142018/2020-1). Many thanks to the Editor of the journal and all the anonymous reviewers for providing their insight and opinions to improve this manuscript.

M.F.: Conceptualization, methodology, design, material preparation, data curation, writing – original draft, writing – review & editing, validation. E.M.-N.: Supervision, writing – review & editing, validation. M.C.G.P.: Writing – review & editing, validation. A.L.S.: Writing – review & editing, validation.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.