By 2050, India wants to have 53 M ha under agroforestry, which will be accomplished by reclaiming fallows, cultivable fallows, pastures, groves, and problematic soils (Dhyani and Handa, 2013). In India, agroforestry practices are an important component in the various river rejuvenation programs like Namami Gange, Green India Mission, National Highway Mission, Pradhan Mantri Krishi Sinchayee Yojana (PMKSY), and Mahatma Gandhi National Rural Employment Guarantee Act (MNREGA). Several research Institutes like the Indian Council of Agricultural Research (ICAR), Forest Research Institute (FRI), Council of Scientific and Industrial Research (CSIR), State Agricultural Universities (SAUs), and Krishi Vigyan Kendra (KVKs) have developed cost-effective agroforestry technologies for the rehabilitation of degraded lands. ICAR-CAFRI and AICRPAF published a summary on Agroforestry technologies for different agroclimatic zones of Country, whereas it consists of 84 grassroots levels farmers adopted technologies developed by 26 AICRPAF centers from five different agroclimatic regions of the country (Chaturvedi et al., 2016). FRI has also come up with various river rejuvenation technologies for the rehabilitation of basin areas. The different agroforestry technologies for lands affected by soil erosion (water and wind), physical (mining and industrial waste and waterlogged lands), chemical (saline, sodic, and acidic soils), and biologically degraded lands due to depletion of SOM, reduction in soil fauna, and emission of green house gases (GHGs) are discussed below:

One of the main reasons for the degradation of the land is water-induced soil erosion. A moderate (>10 Mg ha⁻¹ year⁻¹) to extremely severe (>80 Mg ha⁻¹ year⁻¹) intensity of water erosion affects ~68.4% (83 M ha) of the total degraded land (120.7 M ha) in India. The main danger to soil quality posed by runoff water is water erosion. Loss of organic carbon, nitrogen imbalance, compaction, a decrease in soil biodiversity, and pesticide and heavy metal contamination are the results. The lands affected by water erosion can be categorized into three categories: (a) degraded sloping lands, (b) gully and ravine lands, and (c) shifting cultivation lands.

The importance of trees in controlling soil erosion is widely accepted. In agroforestry, tree canopy checks soil erosion mainly by intercepting rainfall, thereby reducing the impact of raindrops and decreasing their erosive capacity (Kaushal et al., 2017). Litter helps in producing water-stable aggregates, thereby reducing the surface runoff volume. Roots and stems restrict sediments from moving down the slope and help water infiltrate. Shallow landslides are prevented by deep tree roots that stabilize slopes. Vegetation affects water and sediment fluxes over the long run by boosting soil water infiltration and soil aggregate stability and cohesiveness (Zuazo and Pleguezuelo, 2008). The most widely utilized agroforestry techniques for erosion management include windbreaks and shelterbelts, hedgerow (alley) cropping, multilayer tree gardens, home gardens, plantation crop combinations, and multilayer tree gardens (Young, 1997). According to McDonald et al. (2002), agroforestry reduced soil erosion by 21 times and surface runoff by seven times compared to control soils. The retention, infiltration, and storage of rainfall-induced overland flow are improved by adding tree leaf litter, its subsequent decomposition in the soil, and the activities of trees’ roots (Dass et al., 2011). The different agroforestry models/technologies developed for lands affected by soil erosion are as below.

In addition, mudslides, landslides, and other gravity erosion processes are more likely to occur in steeper terrain. Longer, steeper slopes are more prone to erosion during heavy rains than shorter, less steep slopes because they lack sufficient plant cover. Various agroforestry models have been developed and evaluated for water-eroded lands in the northwestern and northeastern Himalayan regions (Kaushal et al., 2021a). The best filter strips to stop erosion and boost agricultural output in marginal lands are vegetative barriers made of hedgerows of trees such as Leucaena and Gliricidia and grasses. In various land-use regimes, hedgerows are very helpful in preventing the loss of nutrients and organic carbon during the erosion processes. Hedgerows’ blockage caused soil and nutrients to accumulate close to the biological barrier system. According to Lenka et al. (2012), grass filter strips and hedgerows (Indigofera) have a great capacity to conserve soil organic carbon (SOC) (43%), as well as accessible nitrogen (56%), phosphorus (54%), and potassium (48%) in the soil. According to Hombegowda et al. (2020), under Gliricidia and Leucaena-based hedgerows, respectively, the configuration of the land slope reduced by 0.41 and 0.27 degrees year⁻¹, showing the deposition of eroded soils on the lower slope side and the consequent decrease in the land slope.

On degraded slopes, silvipasture systems have proven effective (Chaturvedi et al., 2014). In the Shiwalik foothills, Eucalyptus tereticornis and Eulaliopsis binata (@ 2,500 trees ha⁻¹) were grown in paired rows with understorey grass planted at 50-cm × 50-cm spacing. This method prevented soil loss and produced an annual return of approximately Rs. 4,000 (50 USD) ha⁻¹ year⁻¹ from commercial grass alone, in addition to returns from the Eucalyptus, which made the crop more profitable (Sharda and Venkateswarlu, 2007). When combined with Chrysopogon fulvus (gorda) and Eulaliopsis binate (bhabar) in the Doon Valley, the plant’s Albizia lebbek (siris), Grewia optiva (bhimal), Bauhinia purpurea (kachnar), and Leucaena leucocephala (subabul) were found to be promising. The average yearly production of savanna pasture systems is 8–10 Mg ha⁻¹, consisting of 4.5–5.0 Mg ha⁻¹ of grass-based fodder, 1.5–2.0 Mg ha⁻¹ of leaf fodder from tree loppings, and 2.0–2.5 Mg ha⁻¹ of fuelwood from the lopped branches (Raizada and Singh, 2010).

On degraded sloping lands, the plantation of trees, along with trenching, is useful for improving the survival and growth of plantations. The trenches effectively stop soil erosion and improve the soil moisture regime by breaking the slope and lowering the surface runoff velocity. According to Kaushal et al. (2021a), semicircular ditches and Dendrocalamus. hamiltonii species can be a successful land restoration approach on degraded sloping soils in the Himalayan foothills. Comparing the semicircular trenches to the control treatment, the soil moisture was 16% greater (without trenches). Runoff and soil loss were drastically reduced with bamboo + trenching treatment. After the 5th year of the plantation, no runoff or soil loss was seen, demonstrating the effectiveness of bamboo and in situ water-conserving techniques in preventing soil erosion. In the Eastern Ghats, the Gliricidia + Trench and Leucaena + Trench planting systems, respectively, boosted the efficiency of SOC and accessible NPK by 44%, 63%, 56%, and 33%, 46%, 44%, 42% (Hombegowda et al., 2020). According to Satapathy (2005), mixed land-use schemes that included bench terraces and contour trenches effectively retained 90%–100% of the yearly rainfall and mimicked the impacts of a natural forest in the northeastern region. Base flow accounted for 70%–90% of the water yields in watersheds with continuous stream flow characteristics. The watershed that had been subjected to jhum (shifting) cultivation produced the greatest peak runoff, whereas the watershed that had been left to its natural vegetation produced the least peak runoff.

In the Himalayan area, agri-horticulture is the most significant system in terms of productivity, financial rewards to farmers, and preferences on sloping slopes. As an economically feasible strategy for rehabilitating marginal lands in the Shiwalik region, intercropping of guar, cowpea, or pearl millet with peach, turmeric with papaya, Chrysopogon fulvus or Pennisetum purpureum (Napier grass) with aonla or ber, has been discovered. With pigeon peas, Aonla produced the largest production of 86-kg fruits tree⁻¹; however, the output was decreased by 17% and 23% with Chrysopogon and Napier grass, respectively (Sharda and Venkateswarlu, 2007). Runoff was 8.0%, 13.1%, and 18.6% for aonla + Chrysopogon fulvus, aonla + hybrid Napier, and aonla + perennial pigeon pea, respectively, over control during a period of 10 years (pure aonla). Chrysopogon, Napier, and pigeon pea were the most successful intercrops at reducing soil loss, with reductions of 81, 56, and 25% over sole aonla. By contrast to runoff, less sediment was lost during the post-bearing phases (Yadav et al., 2005). The cowpea-toria sequence was shown to be very profitable, with a gross revenue of Rs. 16,850 ha⁻¹ (210 USD), and successful in preserving soil and water, according to an analysis of mango-based agri-horticulture systems (Rathore et al., 2012).

In dry and semi-arid locations, erosion by water is a serious issue that results in gullies and ravines. The use of gullies by land capacity classes, soil and water conservation measures, and permanent plant cover through afforestation or agroforestry systems are all necessary for the revival of ravine lands (Chaturvedi et al., 2014). The newly planted trees reduce soil and nutrient loss from these lands while providing risk protection against the uncertainties of agricultural production in the tough circumstances of ravine regions (Soni et al., 2018). In the ravine region, the silvi-pastoral system has been proven to be quite successful. Several significant grass species are useful for enhancing the fodder availability in the ravine regions, including Pennisetum purpureum, Brachiaria mutica, Cenchrus ciliaris, Cenchrus setigerus, Panicum antidotale, and Panicum maximum (Chaturvedi et al., 2011). Plantations of Acacia nilotica and Acacia tortilis with Cenchrus ciliaris produced 28.7 Mg ha⁻¹ and 27 Mg ha⁻¹ of fuel wood, respectively, at a spacing of 3 m × 3 m on the top, slopes, and bottom of ravines. Under Acacia nilotica and Acacia tortilis, the mean annual pasturage yield varied from 1.52 Mg ha⁻¹ year⁻¹ to 2.06 Mg ha⁻¹ year⁻¹, respectively (Kurothe et al., 2018).

For ravine areas, fruit plants that can endure moisture stress are appropriate. In humps and gully beds, fruit trees, including lemon, mango, ber, and aonla are planted alongside agricultural products. Agroforestry and soil water conservation practices, according to Kumar et al. (2019), boosted the carbon storage and sequestration capacity in semi-arid, climate change-vulnerable ravine landscapes while also increasing agro-ecosystem resilience to harsh weather. According to Kumar et al. (2020), a sapota-based agri-horticulture system with bench terraces and trenches reduced runoff by 16%–34% and soil loss by 15%–25% when compared to sapota on the slope. In a similar vein, Jinger et al. (2022a) found that using an agroforestry system with cowpea, castor, and sapota reduced soil loss and runoff overall by 37.7% and 19.1%, respectively, when compared to using only one crop. The agroforestry system, which boosted system production by 162% and 81.9%, respectively, above the sole crop and sole tree plantation, yielded the highest system productivity.

Dendrocalamus strictus, a bamboo species, holds great promise for preserving soil and maximizing the use of gullies and ravine areas for agricultural purposes (Rao et al., 2012). Bamboo roots effectively increase infiltration, decrease runoff, and safeguard soil from additional gully bed expansion (Singh et al., 2015; Kaushal et al., 2020, 2021b). A silvopasture system based on Anjan (Cenchrus ciliaris) and bamboo (D. strictus) grass has been created to increase the productivity of ravines. More than 80% of rainwater can be absorbed by this system, which also reduces soil and nutrient losses by 90% and 70%, respectively. These interventions gave an average annual net return varying from USD 814 to Rs. 1,130 ha⁻¹ and a cost–benefit ratio varying from 1.96 to 2.09. Melia dubia + dragon fruit and Melia dubia + lemon grass cultivation along with soil moisture conservation practices has resulted in better fruit yield of dragon fruit and biomass yield of Melia dubia and lemon grass compared to control besides conservation of soil and water in Mahi ravines of Central Gujarat (Jinger et al., 2020, 2021; Kakade et al., 2020).

Approximately 7.60 M ha of shifting agriculture, or jhum cultivation, is performed in India’s eastern and northeastern areas (Bhat et al., 2022). Because of the diminished jhum cycle brought on by strain from a growing human population, significant soil erosion, low productivity, and loss of soil fertility, shifting farming has become unsustainable (Markose and Jayappa, 2016). Agroforestry systems with many stories and improved fallows are essential for rehabilitating regions damaged by shifting farming. Fast-growing, nitrogen-fixing trees are cultivated during the fallow period in an upgraded fallows system. Improved fallows improve soil qualities such as organic matter, greater aggregates stabilizing soil, higher infiltration rate, and carbon sequestration in addition to increasing crop productivity (Chirwa et al., 2004). According to reports, soil in planted fallows contains larger pores and more macropores due to better aggregation and channels formed by dead and decomposing roots (Nyamadzawo et al., 2008). With the aid of the region’s natural resources, suitable alternative land-use systems for agriculture, horticulture, forestry, and agroforestry have been developed with almost equivalent hydrological behavior under the natural system. For the general development of these places, an integrated farming system strategy comprising fruit and forest trees, arable crops, livestock, fisheries, and poultry with sufficient conservation measures for natural resources has been determined to be suitable. In addition to preserving and safeguarding the hill soils, agri-horticultural systems that combine the production of ginger with fruit trees like mandarin and guava be successful. Pineapple is commonly connected with multi-use trees that are arranged in paired rows on a hillside. According to Saha et al. (2012), agri-horti-silvi-pastoral farming systems and bench terrace farming may successfully control runoff and soil losses. In mixed land-use systems with soil water conservation features like bench terraces and contour trenches kept because these systems resemble natural forests, 90%–100% of the yearly rainfall has reportedly been found to be retained. According to some reports, contour hedgerow technology (bio-terracing) is more cost-effective than bench terraces built using the cut-and-fill method across slopes. Saha et al. (2005) found that multi-storied agroforestry systems (3.06) and silvi-horti-pastoral (3.07) had low erosion ratio values, indicating that these systems were best suited for conserving soil and water in the hilly habitat. When compared to traditional farmers’ practices of growing finger millet, a mixed plantation of Moringa oleifera, Gliricidia sepium, Zingiber officinale, and Cajanus cajan in East India reduced runoff and soil loss by 8.26% and 3.45 Mg ha⁻¹, respectively, while increasing SOC, P, and K by 74%, 64%, and 66%, respectively. Drumstick pod output increased 24%–27% as a result of the multipurpose Gliricidia hedgerow approach (Jakhar et al., 2017). Table 5 lists the agroforestry systems for various degraded soils. To check runoff and soil losses, alley cropping (hedgerow intercropping) has also been recommended as an alternative to shifting cultivation. The hedge serves as a barrier for checking the movement of soil and water along the slope and contributes to soil conservation (Sharda and Mandal, 2018). Continuously soil deposition near hedges leads to the formation of biological terrace-like structures in the long term. Leucaena leucocephala and Cassia siamea are the most recommended species for alley-cropping systems in the northeastern region of India (Kaushal et al., 2021a). Improved animal-based and horticulture-based integrated farming system (IFS) models were found to reduce soil erosion (34%–48%) and loss of SOM (26%–51%), N (33%–45%), P (19%–54%), and K (27%–51%) compared to the traditional shifting cultivation system in Nagaland, India (Chatterjee et al., 2021).

After water erosion and vegetation degradation, wind erosion is the third most contributing factor for land degradation in India, covering 18.19 M ha, i.e., ~6% of the total geographical area. The causes, impact, and control of wind erosion are summarized in Figure 2. In dry and semi-arid areas, such as the states of Rajasthan, Haryana, Gujarat, and Punjab, wind erosion can range from mild to severe. In addition, it is common in coastal locations with sandy soils predominating and in the chilly desert regions of Leh (Jammu & Kashmir), which are both in the far northwestern part of India (Singh D. V. et al., 2017; Singh C. et al., 2017). In drylands, erosion by wind is one of the principal processes associated with land degradation covering 33%–37% of the continental areas of the planet (Sivakumar et al., 1998) and is of major concern for policymakers and land managers (Duniway et al., 2019).

The most widely used agroforestry technologies to restore wind-eroded lands are stabilizing dunes, windbreaks, shelterbelts, alley-cropping, and silvopastoral systems (Figure 2). According to CAZRI (2015), covering the space beneath trees, providing a surface cover of grasses, and protecting them from biotic intervention are the most crucial steps in stabilizing sand dunes. On the windward side of the dune, small windbreaks are built in strips or chessboard patterns of 5 m each. Locally accessible brushwood species such as Leptadenia pyrotechnica (Khimp), Aerua tomentosa, Ziziphus nummularia (Pala), Crotalaria burhia (Sania), and Calligonum polygonides (Phog) are constructed upside down for the purpose of producing micro-wind barriers (Singh D. V. et al., 2017; Singh C. et al., 2017). Mulching is done in April and May to slow down the speed of the wind and stop sand from moving. To build the plants in the trench and create a dry hedge, sand is removed to a depth of 25 cm along the mulching line. Before the start of the rain, trees, bushes, and grasses are planted (Luna, 2006). After the rains have started, 1 × 1 m of grass is sown. During the monsoon, seeds of grasses and leguminous plants are sown on the side that receives micro-wind breaks and is mixed with clay and sodium arsenate. Many different types of grasses are employed, including Lasiurus sindicus, Panicum turgidum, P. antidotale, Saccharum munja, Cenchrus ciliaris, C. setigerus, Dichanthium annulatum, and Sachharum bengalense. The vegetation used to stabilize sand dunes is extremely drought resistant and has deep roots that may draw rainwater from shallower soil layers. The most effective combination of trees for stabilizing sand dunes has been determined to be Acacia tortilis, Acacia jacquimontii, Acacia leucophloea, Acacia senegal, Azadirachta indica, Balanites roxburghii, Prosopis cineraria, P. juliflora, and Holoptelia integrifolia (Singh D. V. et al., 2017; Singh C. et al., 2017). Sand dune stabilization technology helped in fixing up 0.4 M ha of sand dunes with the help of the Rajasthan state forest department (Harsh and Tewari, 1993).

Raising shelterbelts around the agricultural fields also minimizes wind hazards and increases farm productivity through the moderation of micro-climate (Prasad et al., 2009). The technology involves raising strips of vegetation composed of trees and local shrub wood material against the prevailing wind direction. Shelterbelt plantation helps fix the movement of sand from dunes and provides multiple products to farmers. It was reported that almost 84% of farmers have received the benefits of better groundwater availability and improved soil texture for the production of crops by raising shelterbelts (The Energy and Resources Institute, 2016). In the IGNP (Indira Gandhi Nahar Pariyojna) area of Jaisalmer (W. Rajasthan), the assessment of efficiency of single- and double-row shelterbelts of Dalbergia sissoo revealed that the double-row shelterbelt of 15–20 years of age having 8–10 m height hold great promise for moderating micro-climate and providing effective shelter to crops against wind-borne hazards in arid areas. Shelterbelts have improved soil characteristics and modified air temperature (Prasad et al., 2009). Another study reported that the shelterbelts increased net returns from agricultural production by 430.8% in the net returns due to shelterbelt plantation, in which shelterbelt technology has contributed ~399% (Gajja et al., 2008).

Silvi-pastoral systems are other important agroforestry systems in wind-eroded areas. In addition, providing nutritional fodder to livestock protects them from hot and warm winds, improving overall animal health and productivity (Atangana et al., 2014). There are several examples where different agroforestry systems have contributed to minimizing erosion and enhancing farm productivity, soil fertility, and ameliorated micro-climate (Table 6). With all these efforts sand dune area has reduced by 12% between 1980 and till date. The portion of western Rajasthan that is impacted by wind erosion has shrunk by 3%. The region has seen a rise in the net sown area, a decrease in culturable wastelands, and an increase in total crop area. This impact has come from using different agroforestry techniques for combating wind erosion in the area (Moharana et al., 2018).

The mining sector, which plays an essential role in national economic growth, involves more than 20,000 known mineral deposits and provides the bulk of employment and job creation of ~5,60,000 individuals daily in India. India’s mining sector is large, with 9,200 mines spread across 11 states producing 84 different minerals, comprising four fuel, 11 metallic, 49 non-metallic industrial, and 20 minor minerals (Ministry of Mines, 2018), according to Das et al. (2018), ~3,100 mines operating in India. It is estimated that ~12,000 stone crusher units are operating in India (Patil, 2001). Although it contributes 10%–12% of GDP to India’s entire industrial sector, it is also harmful to the environment. Unscientific mineral mining is a severe environmental issue, resulting in forest loss, widespread soil erosion, and pollution of air, water, and land (Pal and Mandal, 2017). Mining produces vast amounts of tailings and trash containing heavy metals, posing a serious hazard to water sources, agricultural soils, and food. Increased heavy metal concentrations in soils can induce phytotoxicity, a direct threat to human health, as well as indirect impacts such as pollution of water bodies (Pulford et al., 2002). Unplanned mining activities, as well as a lack of care for land reclamation or mining’s environmental effects, have resulted in the formation of vast swaths of industrial wastelands (Ghosh, 1991).

Trees can penetrate the stony layer with their roots, causing fissures and allowing surface water to percolate, or holding any quantity of dirt by their roots to protect against erosion and percolation. Ghosh (1991) reported successful species survival after 1 year of reclamation of wastelands of Jharia coalfield, India, by mixed plantation of Azadirachta indica, Ricinus communis, Phoenix dactylifera, Psidium guajava, Butea frandosa, Leucaena leucocephala, and Artocarpus integrifolia. Species selected for rehabilitation should be N-fixing, fast-growing, well adopted to arid-zone climatic circumstances (i.e., extreme heat and sunlight), and have drought-tolerant root architectural adoption with significant socioeconomic utility. It also helps increase soil microbial activity leading to nutrient mineralization, increased below-ground biodiversity, increased nutrient cycling, and soil matrix stabilization (Datar et al., 2011). Due to the long rotation age of trees to obtain an economic return, combining trees with crops or grasses is a good land-use option for land-use choice for the restoration of mined areas. Seedlings of Ceiba pentandra have shown 100% survival when transplanted to ex-tin mining land. Although Acacia mangium has thrived in the ex-tin mining land, Paraserianthes falcataria does not appear to be adopted to these conditions. Other species such as Casuarina equisetiolia, Terminalia catappa, and Acacia auriculiformis, also perform well. Datar et al. (2011) reviewed the rehabilitation of post-mined in India and found that four species Pongamia sp., Dalbergia sp., Albizia sp., and Azadirachta sp. species have the highest potential for recovering agro-ecosystem function within the context of Indian post-mined landscapes.

Dadhwal et al. (1991) reported that 20 Mg ha⁻¹ of mulch was the optimal dose for Eulaliopsis binata, resulting in superior results. Grevillea pteridifolia and Eucalyptus camaldulensis showed excellent survival and growth in 5-year-old plantations in the bauxite mine of Amarkantak. Planting nitrogen-rich leguminous species such as Leucaena leucocephala and Peuraria hirsuta in mine debris offered fodder, organic manure, mulch, and other benefits. Under geotextiles, Thysonoleana maximum, Saccharum munja, Pennisetum purpureum, Eulaliopsis binata, Ipomoea carnea, and Vitex negundo performed well (Juyal et al., 2007). Approximately 80% survival and good establishment were obtained when two-thirds of the pit was filled with a mixture of red soil, FYM, and sand after leveling for Eucalyptus citridora, Dalbergia sissoo, Albizia lebbeck, Casuarina equisetifolia, Acacia auriculaeformis, Leuceana leucocephala, and A. nilotica and in Neyveli (Narayana, 1987). Norem et al. (1982) found that Acchariss arothroides and Nicotiana glauca were shown prolific growth on the north aspect, while only one shrub, Dodonea viscosa, survived on the east aspect. This study suggested the chemical makeup of mine waste material, slope exposure, and species compatibility to the dry climate all have a role in the restoration of mined areas. Successful techniques adopted for the planting of trees in mined areas have been summarized in Table 7.

Industries such as plastics, electronics, electrical, mineral-based dyes, fabrics, chemicals, and other materials, produce industrial wastewater of 50 million liter daily containing a high concentration of heavy metals, chemicals, and dyes (Singh, 2018). With an installed sewage treatment capacity of 21.9 billion liters per day, India produces ~0.5 billion liters of industrial wastewater and 61.7 billion liters of sewage per day (Roy, 2020). Increasingly, industrial effluents and municipal wastes are making their way into freshwater bodies, posing major health and environmental risks (Ranjan, 2021). Many industrial facilities release untreated effluents into water streams due to capacity constraints and poor pricing processes. Oil has been illegally spilled into the Hindon river by industries operating along its banks in the past (Rajput, 2019).

Agroforestry-based wastewater reclamation contributes to the solution to agriculture’s growing water scarcity (Ranjan, 2021). Large amounts of industrial wastewater are used as irrigation water. They are regarded as a reliable source of vital nutrients, primarily N, P, K, and organic matter, which are beneficial to soil fertility, plant growth, and production (Libutti et al., 2018). Rasheed et al. (2020) reported an increase of 30% in growth parameters and biomass production, 34% in net CO₂ assimilation rate, and 42% in water use efficiency under wastewater treatment compared to control in Conocarpus lancifolius seedlings. Plant species that will be employed for phytoextraction must be able to tolerate heavy metals (HMs). In some plants, HMs are accumulated in the roots, while in others, HMs are transferred to the leaves (Kafil et al., 2019). In response to wastewater irrigation, Zn, Pb, and Cd accumulation increased dramatically in roots, followed by leaves and shoots in C. lancifolius. The high translocation of Zn and Cd from the root to the aerial portions of C. lancifolius suggests that it has significant phytoextraction capability. Conocarpus lancifolius may thus be employed to rehabilitate soils polluted with Zn, Pb, and Cd, because of its improved biomass production, water usage efficiency, metals accumulation, tolerance, and translocation factor (Rasheed et al., 2020). The largest biomass distribution to stem in A. indica, twigs in P. cineraria, and roots in other species demonstrated the adoption mechanisms by different species when comparing the average contributions of various components in total dry biomass (Singh et al., 2021). The species include Acacia nilotica, Azadirachta indica, Cupressus spp., Casuarina spp., Eucalyptus spp., Khaya senegalensis, Morus spp., Swietenia mahogany, and Tamarix spp. were evaluated successfully under afforestation using untreated and secondary treated wastewater (Singh et al., 2021). Both Acacia ampliceps and Azadirachta indica demonstrated high biomass increment, high Pb concentrations, and an excellent antioxidative defence mechanism, indicating that they may be utilized for planting in industrial water irrigated soils in Pakistan (Hussain et al., 2021). Wastewater can be an alternative source of water in dryland afforestation if proper species are selected. Several studies highlighted the importance of treated wastewater in urban greening and reducing land degradation along with the usage of freshwater in arid areas. Eucalyptus camaldulensis, S. persica, S. oleoides, and T. undulata responded better in terms of survival, adaptation, and growth to wastewater for enhanced productivity in Indian deserts condition (Singh et al., 2021). It was found that plant growth-promoting rhizobacteria can effectively accelerate the phytoremediation process through a variety of mechanisms, including methylation, altering soil pH, encouraging redox processes, and secreting siderophores, bio-surfactants, and a variety of organic acids (Khan et al., 2009). Plant selection, as well as physicochemical soil factors and the research of plant–microbe interactions, could aid in the development of cost-effective remediation solutions.

Heavy or prolonged rainfall, over-irrigation, flooding, or high water table leads to waterlogging. In recent years, more intense and unpredictable rainfalls associated with climate change have raised waterlogging incidents worldwide and become one of hazardous abiotic stress (IPCC, 2014). Waterlogging affects various chemical, biological, and physical properties of soil, which in turn affects the ability of soils to support vegetation growth (Kozlowski, 1997). Highly adapted species survive waterlogging periods without any injuries up to a specific period. By contrast, sensitive or less tolerant species can suffer damage within a short period under the oxygen deprivation stage (Kreuzwieser and Rennenberg, 2014). Season, height and duration of flooding, water movement (moving or stagnant), environmental conditions, and various plant-specific characteristics determine the damage’s extent (Vreugdenhil et al., 2006). Within the same species, adult trees were more tolerant than younger ones. As an aerobic organism, trees depend on a constant oxygen supply to all living cells of the body and disturbance in metabolism. This leads to disruption in normal functioning at the cellular level based on their tolerance toward the depletion of soil oxygen and damage becomes visible later. Some of the negative impacts of the waterlogging stress in fruit crops include a decrease in net photosynthetic rate, stomatal conductance and root hydraulic conductivity, and hormonal changes (increase in ABA and ethylene), which ultimately result in reduced leaf size, leaf abscission, restriction of vegetative and root growth, etc. (Schaffer et al., 2006). The activity of several metabolic pathways (mineral, carbohydrate, organic acid, protein, lipid metabolism, and hormone relations) reduces under anaerobic circumstances (Kennedy et al., 1991). Waterlogging hampers root growth, root formation, branching, and mycorrhizae formation and causes root decay (Kozlowski and Pallardy, 1997). Ultimately it causes a reduction in flowering, yield, and in severe cases, death of plants through wilting, root necrosis, root rot, etc.

Studies have revealed that fast-growing and short-rotation tree-based systems have bio-drainage potential to prevent waterlogging in areas irrigated by canals. The bio-drainage techniques are eco-friendly and economically attractive. Fast-growing tree species such as Eucalyptus spp. Terminalia arjuna, Casuarina glauca, Syzygium cuminii, and Pongamia pinnata are also suitable species for bio-drainage (Uthappa et al., 2015). The block planting of Eucalyptus tereticornis at the IGNP site in Rajasthan and Dhob-Bhali in Haryana is very successful in lowering the water table. According to reports, the tree plantations built along the canal drained 14 m of water in just 6 years (Kapoor, 2001). In addition, Ram et al. (2011) observed that the 5-year-old E. tereticornis had an average transpiration rate of 30.9 L day⁻¹ tree⁻¹, which was 268 mm per year by 240 trees ha⁻¹ in comparison to the mean annual rainfall of 212 mm. According to Behera et al. (2015), multifunctional woodlots, agri-silviculture, agi-horticulture, and silvi-pasture are popular strategies for addressing saline and waterlogged situations. Rice, wheat, berseem, mustard, cowpea, pigeon pea, sorghum, turmeric, and annual oat crops were effectively produced beneath Salix, Eucalyptus, Acacia, Albizia, Terminalia, Prosopis, and Populus tree species in the instance of an agri-silviculture system (Sarvade et al., 2017). Table 8 provides a selection of plants that are appropriate for bio-drainage therapy in salt-affected, waterlogged regions of India.

Salt-affected soils adversely affect the physiological processes and productivity of plant species across the globe (Singh et al., 2009). These soils modify the soil properties and reduce plant water availability, resulting in the alteration of the structure and function attributes of the exposed plants (Gentili et al., 2018). Salt-affected soils mostly contain Na⁺, K⁺, Ca²⁺, and Mg²⁺ cations, CO₃²⁻, and HCO₃⁻¹ (alkali), and Cl⁻ and SO₄²⁻ (saline) as dominant anions (Zhang et al., 2006). The presence of salts in soils causes alteration of the physiological and biochemical traits of the exposed plant, resulting in low agriculture productivity and deterioration of precious land resources (Parida et al., 2016). Therefore, the reduction in agricultural productivity as a consequence of salinization promotes the interest in growing salt-tolerant tree plantations to increase the sustainability, productivity, and profitability of the salinity-afflicted landscapes (Kumar et al., 2020). Tree species can be characterized as sensitive, moderately tolerant, highly tolerant, or extremely highly tolerant to salt, depending on their level of tolerance (Tomar et al., 2003; Dagar, 2014). Moreover, different salt stress could have a contracting effect on the biomass production and yield of tree species (Banyal et al., 2017). Therefore, agroforestry seems to be the only viable option for obtaining greater ecological and economic benefits for such soils.

Most of the research findings have indicated that tree plantation improves the soil’s physicochemical properties-decrease, the soil pH and EC, and improves the nutrient cycling, organic carbon, and cation exchange capacity of the salt-affected soils (Garg and Jain, 1992; Singh, 1998). In northwest India, salt-tolerant crops such as pearl millet and mustard can be intercropped with Eucalyptus tereticornis and Melia composita in saline soils (Banyal et al., 2017). The various fruit species, such as Bael (Aegel marmelos), Aonla (Emblica officinalis), and Karonda (Carrisa carandas), along with the salt-tolerant annual crops, were observed to be suitable and economically viable under moderate saline irrigation water conditions (Dagar et al., 2008, 2016). The salt-tolerant multipurpose tree species—such as P. juliflora, A. nilotica, Casuarina equisetifolia, Tamarixarjuna, T. articulata, and Pongamia pinnata have grown in association with various grass species such as, Leptochloa fusca, Chloris gayana, Brachiaria mutica, and Sporobolus spp. in the form of the silvopastoral system have been found highly effective for reclaiming high alkali soil as well as for the fodder production (Dagar, 2014). The block plantation of various tree species, such as A. nilotica, Albizia procera, L. leucocephala, Azadirachta indica, and Eucalyptus hybrid, was observed to be the best practice for reclaiming the alkali soils. Furthermore, there is tremendous scope for bio-fuels (Energy plantations) in saline conditions under the prevailing scenario of climate change. In areas having abundant saline water, the saline aquaforestry practice consisting of various salt-tolerant fishes reared in the saline water and trees planted on the pond bund has also indicated immense potential in the saline areas (Banyal et al., 2018). In low-lying areas prone to water logging due to the high water table is a major issue, and the biodrainage technique can be designed, which consists of planting waterlogging tolerant species to transpire excess water into the atmosphere and to lower the high water table. Dagar et al. (2016) evaluated the impact of three planting spacings viz. 1 × 1, 1 × 2, and 1 × 3 m of Eucalyptus tereticornis in waterlogged saline soils. Due to the high transpiration rate of Eucalyptus, the water table was lowered by 43.0 cm in 1 × 1 m, 38.5 cm in 1 × 2 m, and 31.5 cm in 1 × 3 m spacing during the 4th year of the plantation than in adjacent fields without plantation. Therefore, the above evidence indicates that agroforestry and tree plantation is the only ecologically and economically viable option to improve the productivity potential of salt-affected soils. The various agroforestry systems developed for saline and sodic soils of India are summarized in Table 9.

Acidic soil covers ~800 M ha globally (Behera et al., 2011), accounting for half of the world’s arable land (Tarin et al., 2021); especially in the humid tropics, soil acidity affects nearly one-third of India’s farmed land (Kumar et al., 2012). Acidity affects ~48 M ha of India’s 142 M ha of fertile land (Mandal, 1997). Soil acidification is caused by natural pedological processes such as carbonic acid influx from the atmosphere and internal acidity generation resulting from organic matter and nutrient cycling (Wong et al., 2004). Soil acidity can also be caused by heavy rainfall combined with nutrient leaching, cation mining from high-yielding crops, acidic soil parent material, and the use of acidifying fertilizers, or a combination of these causes (Xu et al., 2019). In high-rainfall regions, nitrate leaching appears to be the primary source of acidification, followed by the removal of harvested materials (Olego et al., 2021). Acidification in arable soils is primarily caused by crop nutrient extraction and losses of basic cations owing to leaching with downward water flow (Xu et al., 2019), particularly of Ca (Litvinovich et al., 2021).

Trees play a great role in the agroforestry system. Tree-based systems reduce nitrate leaching more efficiently than tree-less systems, and deep-rooted trees absorb leached base cation from deep layers and are pumped back to the top layer via litterfall through nutrient pumping. In general, tree-based systems keep the SOM content higher than tree-less systems (Muchane et al., 2020). The key soil acidity management component in tropical habitats is the agroforestry method of management (Fageria and Nascente, 2014). Muchane et al. (2020) reviewed the acidity alleviation potential of agroforestry systems and concluded that overall, agroforestry practices elevated soil pH compared to monoculture, with minor differences depending on soil type. The incorporation of plant materials into acid soils or litterfall has resulted in higher soil pH, decreased Al saturation, and enhanced plant growth conditions in several laboratory trials. These plant materials also provide base cations such as Ca, Mg, and K (Wong et al., 2004). Gliricidia sepium had the greatest effect on improving soil pH and lowering monomeric Al content at the 10th week of incubation by its high base cation content. Application of 15 Mg ha⁻¹ Gliricidia sepium biomass suppresses monomeric Al to the same amount as 90 Mg ha⁻¹ Melastoma biomass or 15 Mg ha⁻¹ Peronema biomass, according to a prior pot experiment (Hairiah et al., 1996). Alkalinity resulting from the deposition of leached base cations in a deep soil and mineral weathering might be exploited by deep-rooted perennial plant species in the agroforestry system (Wong et al., 2004). Senna siamea has been proven to recycle calcium from subsoils and improve pH in the top soil considerably (Vanlauwe et al., 2005). Trees that produce high-calcium litter are frequently linked to soils with higher exchangeable Ca, percent base saturation, and pH and are also associated with greater abundance and activity of soil organisms (Muchane et al., 2020). In charcoal-making areas of Acacia decurrens-based agroforestry landscape in Ethiopia, soil pH improved by one unit, and SOC increased by 10%, which was comparable to applying lime 4–5 t⁻¹ (Amare et al., 2022). Incorporation of pruning’s of immature tree branches of Calliandra calothyrsus, Cassia siamea, Flemingia congesta, Grevillea robusta, Gliricidia sepium, Leucaena diversifolia, and Leucaena leucocephala resulted in a rise in soil pH and a reduction in exchangeable Al concentration due to high base cation content of the pruning 0.94–2.25 mol kg⁻¹ (Wong et al., 2000). The liming impact of adding plant material or perennial components of agroforestry depends on is proportional to the total base cation charge (Wong et al., 2004). Trees with higher amounts of P or base cations such as Gmelina arborea rich in Ca and Mg alleviated soil P and pH (Wong et al., 2004).