Effect of different barrier hedges, trees, and grasses on runoff and soil loss.
Agroforestry an established practice for centuries is the deliberate combination of perennials with food crops and/or livestock either simultaneously or sequentially. Agroforestry systems are bio-diverse and are associated in numerous ways for combating desertification and mitigating climate change. Agroforestry practice is a possible way of reducing deforestation and forest degradation and can alleviate resource-use pressure on natural conservation areas. Among many other reasons responsible for climate change, our traditional approaches towards forest management have failed thereby giving way to a drastic climate change, which slowly but has indeed harbingered the cataclysmic future that awaits us if we do not act now. This paper thus acquaints the readers with the role of agroforestry in mitigating the soil erosion, rehabilitation of degraded lands, improving water conservation and replenishment of soil fertility. Besides, the role of agroforestry in improving the soil health and overall ecosystem has also been discussed. This paper furthermore, attempts to recognize the role that agroforestry can play in mitigating the repercussions of climate change apart from improving natural resource sustainability and future food security issues.
- climate change mitigation
- ecosystem services
Population explosion worldwide is putting huge pressure on natural resources, which is creating our planet a precarious place to live. It is expected that by the end of the 21st century the world population will reach 8 billion and food required to feed the entire population will be about 120 M tons. It is estimated that by the year 2050 food demand will increase by 60% globally and 100% for the developing countries. Therefore, there is a pressing need to conserve natural resources like soil, water, and vegetation for future demands to accommodate the ever-increasing population growth. Climate change is threatening our very existence and is accepted as a vital issue in the 21st century. Increased emissions of greenhouse gasses due to anthropogenic factors are responsible for average increase in earth temperature and global climate change. Agroforestry has immense potential in mitigating climate change concerns by lessening global warming since vegetation assimilates the CO2 gas in the process of photosynthesis which is one of the main contributors to greenhouse gases.
Agroforestry is a farming system that integrates crops and or livestock with trees and shrubs . Agroforestry provides many benefits that includes favorable microclimate, reduction in erosion, enhanced biodiversity, increased water quality, more infiltration leading to effective groundwater recharge, enhanced and elongated dry flow, improvement in habitat, soil fertility, etc. Agroforestry is promising for a sustainable solution in response to soil conservation, land degradation, and also can bridge the gaps between climate change and mitigation strategies. Agroforestry has the immense capacity to provide sustainable agricultural benefits and approximately 1.2 billion people of the world is practicing agroforestry one way or the other way . It has high potential to balance between the demands and requirements of population growth and natural degradation. The present review investigated the potential and opportunities of agroforestry in combating soil and water degradation and the role of agroforestry in climate change mitigation.
2. Mitigation of soil erosion through agroforestry
Topsoil on earth is the most productive, as essential macronutrients (N, P, K, Ca, Mg and S) and micronutrients (B, Cl, Fe, Cu, Zn, etc.) for plants are mostly found in topmost layers of the soil. These essential nutrients are required for completing the life cycle of plants. Soil erosion is a process in which topsoil is displaced from its location by different agents mainly water and wind. Globally, about 24 billion tonnes of fertile soil is lost annually through water erosion . The soil pool loses 1100 Mt. C into the atmosphere as a result of soil erosion and another 300–800 Mt. C annually to the ocean through erosion-induced transportation .
It is expected that rainfall pattern will vary greatly due to global climate change and the effect of climate change will increase soil erosion. In India, the annual rainfall amount along with the frequency of high-intensity storm events will increase by 2030 compared to the baseline i.e. 1970 which will accelerate erosion and runoff. Nearing et al.  reported that an increase of soil erosion and rainfall amount is of the order of 1.70. Lee et al.  reported 2°C increase in annual temperature which will increase wind erosion by 15–18%. Therefore, without some improved practices like agroforestry, wind erosion is expected to accelerate in arid and semiarid regions. Windbreaks, alley cropping, and riparian buffers are especially designed to reduce wind erosion . Thus, agroforestry will give more flexibility in socio-economic and environmental service perspective in changing climatic situations. Vegetation with its canopy cover reduces the kinetic energy of the rainfall. The energy left with the falling raindrops depends on the height of canopy cover from the ground surface. It is reported that 4-meter canopy height decreases the kinetic energy by 80% . Plant litter absorbs the rest of the energy of the falling rainfall which reduces the soil erosion to a certain level. The plant litter reduces the runoff by improving the infiltration and water holding capacity of the soils. The decomposition of plant litter, root decay, and exudation from the rhizosphere increases the organic matter content in soil and enhances the soil structure which is less prone to erosion.
Protecting the topsoil from erosion is of high priority for ensuring sustainable food production and food security. Agroforestry systems are widely accepted and agreed around the globe due to its influence on soil erosion control. Studies reported in the past concluded that developing countries have well-adopted agroforestry systems for controlling soil erosion from the steep slopes [9, 10, 11, 12, 13, 14]. Alley cropping reduces soil loss to a great extent mainly due to its dense canopy cover which reduces the kinetic energy of falling rain. Alley cropping system is very effective in absorbing almost the entire energy of rain as the trees used in this system are mostly of short stature or shrubby. The shrubs form a barrier to runoff and take more time to infiltrate into the soil and thus less runoff. Soil loss is proportional to the square root of runoff volume, the less the volume of the runoff, the less is the transportation power of the runoff .
In Nigeria in an alley cropping system consisting of maize with Leucaena hedge results in soil loss only 76 kg ha−1 in comparison to No-till condition without Leucaena where soil loss was 10737 kg ha−1 . In an experiment in north-western Himalaya at Dehradun, India (rainfall 1740 mm), the effectiveness of different barrier hedges, trees, and grasses on runoff and soil loss at 4% slope was studied (Table 1). Grasses were very effective in reducing soil loss despite with higher runoff (Table 1). Tree alleys are also effective in reducing the soil loss and runoff. Soil deposited in front of Leucaena based agroforestry system and Eucalyptus based system is represented in Figure 1, which represents that average deposition ranged from 15.77–28.5 t ha−1 in front of Leuceana hedges . In Rwanda and Burundi in ferrallitic soils (Ultisol) with rainfall, erosivity ranges from 250 to 700 on 20 to 60% slopes, soil loss ranges from 300 to 700 t ha−1 yr.−1 in the form of sheet and rill erosion. However, surprisingly the runoff rate was only 10 to 30% of the rainfall. In these circumstances, agroforestry practices have been found suitable in reducing soil loss and produced enough biomass to mulch the surface as well as to increase soil fertility.
|Treatment||Runoff (%)||Soil loss (t ha−1 yr.−1)|
|Corn on contour||40||21|
|Panicum (0.75 m wide)||36.7||7.0|
|Eulaliopsis (0.75 m wide)||42.7||10.0|
|Veteveria (0.75 m wide)||39.6||8.1|
|Leucaena trees (6–8 years)||20.4||8.4|
|Eucalyptus trees (6–8 years)||16.3||5.8|
Numerous studies on soil loss and runoff for different agroforestry models have been carried out in Shivalik Himalayas in India. The soil loss and runoff of the agroforestry models i.e. Eucalyptus + bhabar grass,
Windbreaks/shelterbelts are very effective in arid and semi-arid regions specifically for wind erosion-prone areas. They comprised of single/multi rows/belt of trees which are planted in orientation perpendicular to the direction of wind. The belts of trees are very effective in ameliorating the microclimate and improving growth and yield of associated annual crops. Shelterbelt comprising of castor on the windward and shorter tree in leeward direction increased the yield of lady’s finger and cowpea by 41% and 21% respectively than the control . From different studies, it has been reported that shelterbelts reduce soil erosion by 50% .
Home gardens are also very effective in reducing soil erosion. Study conducted in Kerala (India) revealed that cardamom, pepper and mixed home gardens with coconut trees remarkably reduces the soil loss to 0.65, 3.55 and 1.45 t ha−1 respectively in comparison to soil loss 130 t ha−1 from land after removing forest canopy . In an experiment in Nilgiris in India, runoff and soil loss was measured for 5 years (1959 to 1963) on 16% sloping land under five different vegetation cover viz., blue gum, black-wattle plantation, slola, broom, and indigenous grass. The runoff and soil loss data showed that blue gum cover produced the highest (1.08%) and grassland produced almost nil (0.018%) runoff.
3. Rehabilitation of degraded lands through agroforestry
Land degradation means the gradual deterioration of land quality in terms of agricultural productivity. An assessment by United Nations Development Programme (UNDP) showed that globally 40% of the land area comes under dryland out of which 29.7%, 44.3%, and rest falls in arid, semiarid, and dry sub-humid region respectively. The Food and Agricultural Organization (FAO) estimated that 43% of rangelands and 20% of cropping lands are degraded while Sub-Saharan Africa has the highest rate of land degradation. About 46% of land in Africa is affected by land degradation which suggests productivity loss of 20% over the last 40 years. About 68% of the land in Australia is under degradation while as in Asia about 25% of the land is vulnerable to degradation and will likely increase due to climate change issues. About 19.65 Mkm2of the land worldwide is degraded out of which 10.94 Mkm2 was caused by water. Many studies pertaining to agroforestry have been carried out in to tackle land degradation.
Increase in vegetation coverage is the fundamental approach to control land degradation. UNCCD (2004) revealed that forests and tree cover have potential combat land degradation and desertification by stabilizing soils, reducing water and wind erosion and maintaining nutrient cycling in soils. Different agroforestry systems have been designed after years of research for different categories of degraded lands. These agroforestry systems not only provide higher productivity but are also capable of conserving the resources efficiently. Silvipasture systems have been found to be very successful on degraded lands. Eucalyptus trees in combination with
|Air dry grass yield (t ha−1)||1.2||8.6||1.5||5.1||4.1|
|Mean Eucalyptus height (m)||1.5||4.7||6.7||8.4||10.5|
|Mean Eucalyptus DBH (cm)||1.2||4.3||5.5||6.6||7.4|
|Soil loss (t ha−1)||—||—||—||0.17||—|
|Monsoon rainfall (mm)||686||905||313||1586||934|
Natural causes like forest fire, avalanches, landslides, flooding, and anthropogenic activities such as deforestation, overgrazing, construction works, unscientific farming in hills resulted in excess soil erosion and land degradation [25, 26]. A 4 ha landslide-prone area at Nalotanala on Dehradun-Mussoorie road in India, agroforestry plantation of
4. Soil moisture conservation and water quality improvement by agroforestry practices
Trees in the agroforestry system can increase the crop yield by conserving soil moisture through mulching. Soil moisture availability is higher under trees than open areas and the agroforestry system increases the infiltration characteristics of the soil and thus, it traps more water and increases the soil water content. In the arid region, Kumar et al.  observed the effect of soil water availability on
Seobi et al.  studied the effect of agroforestry and grass-legume buffers on soil hydraulic retention and soil physical properties for Putnam soil (fine, smectitic, mesic Vertic) in corn (
The land is being cleared in arid and semi-arid regions of Australia to meet agricultural development by clearing the native forests. However, gradual salinization is being a problem of those lands due to rising groundwater level. In a study in two different experiment sites in Western Australia, the reclamation of those lands is carried out by using pinus (
5. Agroforestry promising for soil fertility replenishment
The role of the agroforestry system in enhancing and maintaining soil fertility and productivity and sustainability has been well documented . Even those trees which do not fix N, enhance soil physical properties which helps in crop growth. Maintenance and enhancement of soil fertility levels are necessary for regional and global food security purposes. Several studies are reported and proved that from agroforestry system nutrient loss is less as compared to the agriculture farming. Grewal et al.  have reported that leucaena-napier grass allowed less nutrient loss compared to the traditional agricultural system. There was net gain of 38 kg N, 10 kg P, and 20 kg K as compared to the net loss of 15 kg N, 2 kg P and 14 kg K ha−1 in the traditional agricultural system. In a study with
|Treatments||Grain yield(t ha−1)||Straw yield(t ha−1)||Organic carbon (%)||N (kg ha−1)||P (kg ha−1)||K (kg ha−1)|
In an alley cropping system red alder (
In semi-arid region of India for neem-based agroforestry system, the annual litterfall was estimated as 6059 kg ha−1 from 400 neem trees which returned 98, 2.25, 3.2, and 131 kg ha−1 of available nitrogen, phosphorous, potassium, and calcium to soil . Kang et al.  reported the comparative efficiency of pruning of
6. Interference of agroforestry in soil health management
The agroforestry system increases the soil infiltration capacity. In an experiment, it was reported that the infiltration capacity of soils which were mostly clay to silt clay in texture and acidic in nature were in the order of Eucalyptus, Bhabar, Eucalyptus + Bhabar, and agricultural plot. The infiltration rate was about 3 times in Eucalyptus + Bhabar than the agricultural plot . The effects of five agroforestry systems on soil physical properties have been investigated in the ICAR complex for the north-east region in India. The name of the agroforestry systems are Khasi mandarin (
An increase in porosity was reported by Udawatta et al.  in the Midwest Region of the United States in maize-soybean field in conjunction with using agroforestry buffers. In grass and agroforestry buffer strips pore path was observed three and five times higher than in soil of maize-soybean field which may be a reason for increased infiltration rate. Pandey et al.  reported that the sand particles declined by 10% and 9%; clay particle increased by 14% and 10% under mid-canopy and canopy edge respectively compared to under canopy gap position. Silt particles quantity was not influenced by canopy position. Soil organic carbon, total N, total P were more under mid-canopy and canopy edge compared to the canopy gap. Seobi et al.  observed improved soil physical properties in agroforestry and grass buffer system in comparison to the row crop system.
7. Agroforestry in climate change mitigation potential
Agroforestry system acts as an atmospheric carbon sink and in carbon sequestration process, carbon is captured from the atmosphere and stored as carbon sink such as by oceans, vegetation and soils through certain biological and physical processes. Agroforestry system traps more atmospheric carbon compared to crop plants or pastureland [56, 57]. The capacity of agroforestry systems to sequester carbon depends on different factors such as tree species, age of tree, tree density, climate, geographical location, and management practices. In general, tropical humid climate sequestrates more carbon than arid, semi-arid, temperate region. On an average soil organic carbon pool in the soils of arid climate and cold region below 1 m depth is 30 and 800 tons ha−1 respectively. The total worldwide land area under agroforestry system is 1023 Mha which has potential to sequester carbon approximately 1.9 Pg over 50 years . By improving the present management practices involved in agroforestry system, additional 17000 Mg year−1 carbon can be sequestrated by 2040 . In another estimate, the area under agroforestry in world is 8.2% of total reported geographical area (305.6 m ha) and contributes 19.3% of total C stock under different land uses (2755.5 m t C) [60, 61, 62]. If worldwide present area of unproductive cropland and grassland of 630 Mha is converted to agroforestry which can harness additional 586000 Mg year−1 carbon by 2040. Riparian buffer, alley cropping and silvipasture system can sequester 4.7, 60.9, and 474 Tg C year−1, respectively. Additional protection of farmland and cropland with windbreak can sequester additional 8.79 Tg C year−1. Therefore, the agroforestry system in USA has a potential to sequester C as 548.4 Tg year−1. By this way, agroforestry system in USA can trap 34% of greenhouse gas in the form of CO2 . In India, degraded land amounts over 100 Mha where only bushes and grasses grow only in monsoon season . These lands are low in soil carbon and have ample scope to increase the soil carbon by planting proper tree species and grasses with proper management practices. In India, potential of agroforestry system in storing C is estimated 2400 m tons. It is estimated that the total area under agroforestry in India is 8.2% which contributes 19.3% of total carbon under different land uses . Newaj et al.  found that
8. Ecosystem services from agroforestry systems
According to the 2005 Millennium Ecosystem Assessment, human beings are relished by supporting, regulating, provisioning, and cultural services from the ecosystem. They have become the most widely used framework to study the relations between ecosystems (including natural and human-modified ecosystems) and people . Agroforestry has been demonstrated to combine production with multiple ecosystem services and goods  it provides multiple ecosystem services, combining the provision of agricultural, livestock and forestry products with regulating services, cultural services and supporting services. In this context, there is a general need to gain more insight into the overall, total functioning of an agroforestry system i.e., a broad picture of the simultaneous and multiple services provided by such a system.
Agroforestry is a viable land-use option that, in addition to the socio-economic benefits, offers several ecosystem services in the face of different environmental and social challenges [37, 72]. Agroforestry promotes multiple ecosystem services like improvement in soil quality, water conservation by slowing down surface runoff, reducing sediment transportation, soil biodiversity, enhances carbon sequestration, and increases diverse food and cover for wildlife habitat [73, 74]. However, being these services much interlinked so are difficult to measure autonomously but agroforestry has the potential to promote economic, environmental, social vitality, and land stewardship . Sileshi et al.  while working in eastern and southern Africa reported that when agroforestry properly designed and strategically located, and the practices of agroforestry can contribute to ecosystem services by mitigating land degradation, climate change, and desertification while adding structural and functional diversity to the agricultural landscapes in the Miombo eco-region. Trees on farms can prevent environmental degradation and provides healthy system for human welfare . However, agriculture has changed enormously in the second half of the last century, driven by agricultural policy and technological progress. Trees that characterized many agroecosystems across the globe have been lost to a large extent [77, 78]. Although, promoting the concept of ecosystem services, to better understand the diverse ecosystem services provided by agroforestry is very important to know. In Ethiopia, agroforestry was credited as a sustainable farming practice that uses and conserves biodiversity and limits agricultural expansion into natural forests . However, this farm-based conservation of biodiversity was only recently advocated by the Convention on Biological Diversity [80, 81, 82]. If managed properly, agroforestry holds promise for ecosystem services and environmental benefits. The practices of agroforestry can be considered an adaptive strategy in areas with increasing climate variability and can serve as viable carbon sinks as they trap and store carbon.
Agroforestry provides goods and services from trees and reinstates degraded lands. The agroforestry system has the potential for making habitats for edge species conservation of remnant intrinsic species and their gene pools. In the wake of food scarcities and predictable climate change, the practices of agroforestry are gaining attention from the researchers and policymakers as a lucrative approach to develop food security, while at the same time backing to climate change adaptation and mitigation. However, to achieve the target of sustainability, we need to practice agroforestry with improved water management and innovative practices. Climate change will intensify constraints by creating weather more inconstant and will influence the yield by a further decrease in average yields worldwide. Changing food habits with an increase in population and water and land scarcity are also long-term trends that threaten our shared vision of a more prosperous future in which well-fed people everywhere can achieve their full potential without damaging their environment. Agroforestry can improve the resilience of agricultural production to current climate variability as long-term climate through the use of trees for intensification and diversification and buffering of farming systems.
This work was carried out without any funding.
Conflict of interest
No potential conflict of interest was reported by the author(s).