Grass-Legume Seeding: A Sustainable Approach Towards Reclamation of Coalmine Degraded Lands in India

*Sneha Kumari and Subodh Kumar Maiti*

## **Abstract**

Most of the ecosystem services undergo significant degradation during coal mining activities with negative impacts on ecology, biodiversity and local people's livelihoods. The cumulative effect of such large scale environmental changes is reflected in rising pollution load, earth's temperatures and deforestation. There is no eloquence to it that coal is and will continue to be the primary fossil fuel in global energy production, there is a need to embrace sustainability as a key aspect throughout all phases of mining. The cheapest, easiest and eco-friendly approach to accelerate the trajectory of ecological restoration towards a reference state is the introduction of versatile and pioneering plant life forms like grasses and legumes. These species works on basic scientific principles based on ecological theories and incorporating them in post-mined landscapes provides multitudinous environmental benefits coupled with economic and social development. Keeping this in mind the chapter aims to emphasize the importance of grass-legume seeding during ecological restoration of mine degraded lands concerned with the concepts of sustainability.

**Keywords:** Coal mining, Ecological restoration, Grass-legume seeding, Sustainable development

## **1. Introduction**

In coal powered India, a paradigm shift towards mining sector for energy needs has tremendous negative repercussions in environmental and socio-economic arenas. The idea of '*more hole more coal'* without any conservative measures leaves atrocious footprints on the landscapes like abandoned quarries and discarded dumps devoid of vegetation, including plant stocks and seeds capable to regerminate. Mining is linked to all the Sustainable Development Goals (SDGs) in many ways. A multi-objective approach towards ecological restoration of mining areas keeping with the principles of sustainable development is the need of the hour [1]. "Pioneer" plant species like grasses and legumes are cost-effective and use basic scientific principles based on ecological theories therefore, incorporating them in post-mined landscapes (**Figure 1**) has shown multitudinous environmental benefits coupled with economic and social development [2]. There is no eloquence to it that coal is and will continue to be the primary fossil fuel in global energy production,

#### **Figure 1.**

*Ecologically restored coal mine dumps under Bharat Coking Coal Limited (BCCL), India showing (A) growth of grasses on the overburden dump slope near Bhowra area (B) closer view of grass (Pennisetum pedicellatum) and tree growth in the Gokul Park dump of Lodna area, (C & D) distant view of dense and diverse vegetation cover and closer view of legume (Stylosanthes hamata) growth on the Chandan opencast project dump.*

there is a need to embrace sustainability as a key aspect throughout all phases of mining (**Figure 2**). Keeping this in mind the chapter aims to emphasize the importance of grass-legume seeding during ecological restoration of mine degraded lands concerned with the concepts of sustainability.

**Figure 2.** *Criterias for sustainable mining practices.*

*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*

## **1.1 Current scenario of coal mining in India**

The 'Coal Vision 2025' brought out by the Ministry of Coal, Government of India (GOI), has flagged coal as an essential commodity. It reports an increase in coal production from 777.7 million tonnes (MT) in 2020 to 1.2 billion tonnes (BT) in 2025. In addition data suggests that 67% of India's energy demands depend on fossil fuel, out of which coal makes up to approximately 59%. The major outcomes of the vision are:


As per the vision outcomes and past records, the demand of coal will increase (**Table 1**) and also predicted land degradation escalating environmental complications. There is no data available on how much post-mined lands has been reclaimed in India, however the MONGABAY 2020 article on land reclamation for the year (2018–2019) states that the 52 open-cast coal mines projects of Coal India Limited (CIL) constitutes a total excavated area of 255 square kilometers (sq km) out of which 61 sq. km has been biologically reclaimed, 100 sq. km is under technical reclamation and 95 sq. km is under active mining. The National Mineral Policy (2019) which regulates mining activities in India has therefore stressed about the importance of land reclamation to bring back mined out landscapes to the pre-mining state.


#### **Table 1.**

*Total coal demand in India for the last 10 years (in million tons).*

## **1.2 Multi dimensional impact of coal mining**

Coal can be mined through open-cast and underground extraction methods based on the site specific geological condition [3]. An open-cast mining operation affects the ecosystem services as a whole (**Figure 3**). It involves generation of huge mass waste (overburden materials) due to mining activities like blasting, drilling etc. [4]. Coal mining is usually associated with land degradation and the excavated toxic waste materials create serious environmental and socio-economic problems in the adjoining areas. The most severe post-mining impact on the ecosystem are environmental damage such as deforestation, air and water pollution, detoriation of topsoil quality, loss of biodiversity and landscape destruction by invasive species [5–8]. Coal mining activities in Nokrek Biosphere Reserve, India adversely affected the native vegetation and greatly reduced the density of trees and shrubs [9]. The phenomenon of spontaneous heating through interconnected oxidative and thermal process affects various coal mines in the country leading to mine fires. Data estimates report that 10% of total national coal resources are in the fire affected regions. Mine fires give rise to several ecological problems besides safety hazards and economic losses [10]. Coal mining activities puts tremendous pressure on economic–socio-cultural aspects of the people residing around mine areas. Mining induced displacement and rehabilitation is accompanied by loss of social assets including income earning resources, networking, cultural identity, homes and productive land etc. [11, 12]. Coal combustion releases dangerous levels of toxic gaseous pollutants including coal bed methane and dust particles adversely affecting human health, local and global environment as well [13]. The negative effects of mining over large stretch of lands persist for years and can get the better of by relevant planning and policy making ensuring sustainable development. An ongoing challenge for the coal mining industries is sustainable development owing to rising demand for coal in the energy sector. Overcoming these challenges will require ecological resolution pertaining to technical, economic, environmental and social performances.

**Figure 3.**

*Multi-dimensional impact of coal mining activities.*

*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*

## **2. Ecological restoration**

Abrupt changes in natural environment have become an indispensable part of mining activities, still mining cannot be ignored nor can environmental protection be sidelined. Therefore, a balance has to be worked out between mining and environment for sustainable development. Ecological restoration ultimately aims to attain a self-sustainable ecosystem by reconstructing ecosystem functions and structures and may be regarded as identical to secondary succession after the site recovers sustainably on its own [3]. Furthermore, following coal excavation, besides the environmental detoriation, result in a series of social and economic issues. Thus the ecological restoration in mined out lands not only means ecosystem reconstruction but should also include enhancement of environment as well as social and economic development [14]. Ecological restoration provides a solution for sustainable resource management and environmental protection in mining industry through ecological interventions [15–17]. Primary steps involved in ecological restoration are shown in **Figure 4**.

## **2.1 Reclamation approaches during ecological restoration**

Reforestation/revegetation of barren mined out lands over time can bring it to a more or less pre-mining state. The main challenges faced during re-establishment of vegetation on hostile mine lands that has lost their upper soil horizon is finding plant species that will grow under harsh conditions. The success of reclamation depends on the adaptive potential of plant species to the highly variable and newly formed reclaimed mine soils. Surface Mining Control and Reclamation Act (SMCRA) of 1977 have recommended the use of native grass and legume species in mine degraded areas. Forage mixtures containing legumes plays an expanded role

**Figure 4.** *Primary steps involved in ecological restoration process towards a reference state.*

in the nitrogen (N) economy, lowers carbon (C) footprints and out-yield monocultures [18]. Native trees and a more species/genetic diversity accelerate the recovery to a self-sustaining ecosystem (forest) [19, 20]. The development of forest and the trajectory with which it develops on mine degraded sites depends upon geo-climatic conditions and reclamation practices. Successful and sustainable reclamation practices must focus on bringing the disturbed ecosystem back to normalcy leading to restored ecological, aesthetical, and socioeconomic functioning of the postmining area [21]. Different reclamation approaches have been proposed for various disciplines like forestry, archeology, mining, landscape architecture etc. [22]. The reclamation approaches for mining sector has been discussed below

## *2.1.1 Forestry reclamation approach*

The forestry approach (FRA) has been promoted as a desirable method to reclaim productive forest in coal mined land under the SMCRA act of 1977 [23]. The main features of the approach are:


## *2.1.2 Holistic reclamation approach*

Holistic approach has been promoted by Dan Dagget in mining areas. Local environmental microclimatic conditions sometimes prevent forest succession, therefore in such areas establishment of rangelands may be a better option. A holistic approach requires necessary knowledge of ecological (biotic and abiotic) components along with good drainage patterns. The main features of the approach are:


## *2.1.3 Integrated reclamation approach (three-tier plantation)*

Several countries have opted for plantation of fast-growing exotic tree species during reclamation of post-mined areas. Such single-tier plantation is successful to provide green canopy cover but remains unsuccessful in controlling erosion, groundwater recharge and re-establishing biodiversity. Moreover, the selections of exotic species are not considered to meet socio-economic requirement of the local community. In view of all such drawbacks an integrated approach was proposed which favored plantation by three-tier method [24]. The objective is to replicate natural forest with native species and biodiversity revival as existed prior to mining. The main features of the approach are:


## **3. Sustainability aspects of grass and legume species**

Both grasses in woody bamboo forms while legumes as shrubs and trees have their origin from the tropical forests. The grasses belong to the Gramineae family of monocotyledons with around 780 genera and 12,000 species [25]. The fifth largest flowering plant family currently appears to be most widespread throughout the world and adapted to conditions from rain forest to dry deserts and seashores to cold mountain tops. Grasses are the most versatile and pioneering plant life forms. Grasses have greater digestible fiber compared to legumes. Their adaptability to a diverse ecosystem is due to the fact that they grow very close to soil surface therefore safe from environmental damage including grazing and fire. Grass species recommended for reclamation of coal mine degraded lands are listed in **Table 2**.

Legumes belong to the Fabaceae family that comprises almost 770 genera and more than 19,500 species. It is the third largest family of flowering plants that comprises economically important trees and shrubs adapted to a wide variety of ecological and climatic regime [27]. Research on legume nodulation started in the mid 1960 [28]. Legumes are rich in nutrient composition including crude protein, energy and micronutrients compared to grasses. Legumes contain symbiotic N-fixing bacteria (*Rhizobia*) within root nodules structures hence, a key component in crop rotation. Legumes are often referred to as "green manure" and alternating between legumes and grasses during rotational cropping produces good results by providing ample amount of N compounds [29, 30]. Legume species recommended for reclamation of coal mine degraded lands are listed in **Table 3**.

#### **3.1 Forage production**

A grass and legume mixture represents prime example of diversification and adaptation in plant community. Incorporating grasses and legumes as a forage in mine degraded lands started from the early 70's [31]. The main aim of grass-legume mixed seeding in any system is to produce higher yields and improve natural resource use efficiency than monoculture. Legumes (*Stylosanthes hamata*) and grass (*Cenchrus ciliaris*) seeding offer great potential to cope with the prominent challenge of mine reclamation to produce adequate biomass cover where no commercial N-fertilizer is applied [2]. It is generally accepted in studies that the grass species have a competitive advantage over legumes and therefore can dominate pastures. A balance between grasses and legumes is advisable to maintain high biomass productivity [33]. Grass (*Miscanthus sinensis)* and legumes (as a functional group) enhance diverse plant communities, greater biomass and less toxic forage for rapid reclamation of mine degraded lands [34]. This is because legumes improve the functioning of soil systems through bacterial symbiosis [29]. Irreversible changes due to coal mining activities threaten the economy and sustainability of local livelihood such as agriculture and livestock production [35]. Improved animal productivity is associated with the lower fiber contents and higher ruminal rates of passage which are characteristic feature of legume forages compared to grass forages [36]. Forage legumes can overcome the insufficient dietary problem that limits animal production. Grass-legume mixtures produce more forage biomass and feed with less resources therefore improving resource use efficiency in animal production. The high proportion of protein and soluble carbohydrates in legume foliage enables digestion by ruminants (herbivorous mammals). These nutritional benefits of legumes will be most evident with young and lactating ruminants, because their requirements for crude protein are higher than mature ruminants [37]. The quantity of milk produced was significantly higher in livestock's feeding on forage legume (*Stylosanthes)* supplements compared to natural pasture. Experimental results suggested that 3 kg of *Stylosanthes* dry matter (DM) was the optimal level of supplement for the milk production of 1.8 L day−1 [38]. Multipurpose forage legumes like *Stylo* spp. is a potential environment-friendly feed strategy to supply crude protein to grazing livestock's during drought conditions when availability of protein rich


*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*


#### **Table 2.**

*Grass species recommended for reclamation of coal mine degraded lands.*

forages is scarce. Several forage legumes also possess tannins and polyphenoloxidase (plant secondary metabolites) [39]. Tannins protect proteins degradation in the rumen, and subsequently ruminants excrete less urinary N and greater fecal N.


*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*

**Table 3.**

*Leguminous species recommended for reclamation of coal mine degraded lands.*

This is environmentally beneficial because it reduces the conversion of urinary N to ammonia and nitrous oxide, a potential greenhouse gas (GHGs). In addition, several studies have reported that high quality forage can also reduce enteric methane emissions, other powerful GHGs [39, 40]. Livestock grazing legume (*Medicago sativa)-*grass mixture reported 25% reduced enteric methane emissions compared to only grass pastures [41]. Adopting strategic use of grass-legume mixtures in ruminant's diet can be beneficial for health of livestock, sustainable use of resources and environment by mitigating GHGs in addition to benefits like enhanced productivity and reducing shift towards N fertilizer. The linkage between mining and engagement of local communities in mining activities is not only complex but also contentious. However, legume inclusive mining systems can turn in line with sustainability principles at food, animal, human and environmental level.

## **3.2 Soil fertility**

Grass-legume mixture is widely accepted for restoration of coal mine dumps (**Table 4**). Grass-legume mulch residues act as soil conditioner to enhance soil physical properties via moisture conservation, reducing soil erosion and moderating soil temperature. The branching fibrous roots of grasses lowers the bulk density of compacted mine soil which accelerates the recovery of soils physical conditions at surface 10 cm depth [48]. Under drought stress conditions, root length and root area of grasses are more than legumes at the 30–60 cm depth of soil, therefore grass-legume mixture having different water use strategies can be opted for restoration of fragile areas [49]. The aggressive taproot system of legume species penetrates to a depth of 6–8 feet into soil. The N rich high protein legume residues stimulates earthworm burrows which in turn increases soil porosity, movement of air and water to deeper soil depths. Furthermore, legumes have extended value because they are naturally high quality forage that could enhance the quality and productivity of associating species specially grasses by biologically fixing atmospheric N [50]. Legumes can furnish up to 90% of their own N therefore when associated with grasses legume can regulate soil nutrient balance. When legumes are grown with grasses, the amount of atmospheric N fixed depends on three factors (1) available soil N, (2) legume proportion in mixture, and (3) the rate of biological N fixation (BNF). Soils that are N-deficient, legumes will out-compete grasses to grow and produce greater biomass/forage due to their N-fixing ability. Moreover in such situations BNF may be very similar to monoculture. In contrary if the soil contains adequate amount of available N to support grasses they will usually out-compete legumes for available soil N (**Figure 5**). In such situation the leguminous species will be stimulated and BNF will be greater compared to monoculture however, the total atmospheric N fixed will be lower in mixture because of lower legume biomass accumulation and competition with grass species. Adding grasses as an intercrop can increase the competitive aspects between grass and legume plant species but will continue to retain and recycle more total N than their pure strands (**Figure 6**). Non-competitive interferences may be the direct stimulation between species, for example the N fixed by a legume species becoming available to nonlegumes. Grass-legume mixtures can yield more N than legumes monocultures due to mutual stimulation of N uptake via symbiotic and non-symbiotic rhizospheric micro-organisms and endophytic association as illustrated in (**Figure 7**) to sustainably improve the soil processes [51, 52]. Soil N management is necessary to reduce negative environmental impacts. The unused or excess N can lead to eutrophication in surrounding water bodies and nitrate poisoning in livestock. The concept of using mixture of N scavenging grasses with N addition legume will maintain the N balance under proper management strategies.


*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*

#### **Table 4.**

*Various field experiments in India using grass-legume mixture and the positively affected mine soil parameters post- reclamation.*

A grass-legume association potentially accumulates high quality organic substrates in soil with soil organic carbon (SOC) and N pool accretion and promoting beneficial soil micro-organisms [53–55]. The difference in the chemical composition of grass-legume mixture incorporated in soil shifts the nutrient cycling via mineralization which stimulated the soil microbial activities [56]. Soil microorganisms are a necessary link between plant–soil interaction for productivity, nutrient availability and cycling thus, legumes are one of the necessary components to increase soil microbial activity accelerating the process of ecological restoration in mined areas [29]. Legumes add high quality of soil organic matter (SOM) because of their low biomass C:N ratio that can be readily decomposed by soil microbes improving soil biodiversity, deep taproot system and high water infiltration [57]. Also, legumes provide additional benefits to strengthen ecosystem services like (1) protection from pests

#### **Figure 5.**

*Competitive aspects of grass-legume mixture under varying soil nitrogen (N) concentration.*

#### **Figure 6.**

*Potential benefits of diverse species mixture in comparison to monoculture under varying soil nitrogen (N) concentration in binary nitrogen fixation (BNF), nitrous oxide emission (N2O), carbon sequestration and soil fertility.*

*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*

**Figure 7.**

*Pathways of soil nitrogen (N) and other nutrients transfer between associating grass and legume species.*

and diseases (2) *Rhizobium*-legume symbiosis accelerates the removal of soil pollutants. *Rhizobium* is a burgeoning component of the degrading microcosm in polluted soil and controlling tool for hazardous metal bioremediation reclaiming soil fertility [58, 59]. Some of the promising leguminous species used to remediate soil pollution are *Dalbergia sisso, Acacia auriculiformis, Albizia lebbeck,* and *Pongamia pinnata* while grasses are *Vetiveria zizanoides* and *Cymbopogon flexuosus* [44].

### **3.3 Carbon sequestration**

Carbon sequestration is the natural process of capturing atmospheric CO2 into the soil C pool through conversion of biomass residues into stable humus forms. It is one of the most important determinative biological factors of soil quality, productivity, and fertility [60]. Nearly 80% of total terrestrial C accounting to 2500 gigatons (GT) is found in soil out of which 1550 GT is organic C and 950 GT is inorganic C. The amount of C found in living plants and animals is relatively very small (560 GT) compared to soil C [61]. Plant biomass residues increase C sequestration through decomposition of their residues which links soil C sequestration to elevated biomass production and hence to soil fertility. Increasing soil fertility is the most effective way of rapidly accelerating SOC storage and can be accomplished through addition of soil N fertilizers. In contrast the role of legumes in supplying ecofriendly N through fixation is being favored more because of co-benefits like GHGs stability by reducing emissions. Grass-legume based vegetation system contributes to accelerate biomass production which improves the SOC stock and maintains a high amount of sequestered soil C [19, 29, 62]. The potential of C sequestration varies between different species depending on rate of decomposition and rate of conversion of soil liable C to recalcitrant C [57]. Perennial legumes like *Medicago sativa, Lespedeza davurica* and *Astragalus adsurgens* growing on arable lands increased the

soil C sequestration by 79, 68 and 74% respectively [63]. Several practices have been reported to increase forage biomass yields, including better pasture management, fertilization, organic amendments, improved irrigation, grass-legume mixture, reduced tillage and crop rotations. All these techniques are associated with reduced C loss and increased C input however, the rates of C sequestration vary with different management practices and inclusion of legumes or N sources. Land degradation due to coal mining disturbs the ecological processes of photosynthesis, decomposition and soil respiration and consequently to depletion of SOC pool. These anthropogenic activities negatively affect the global climate by rapid inputs of CO2 and other GHGs to the atmosphere [64]. The French "4 per mile" initiative signed by more than 100 countries at Conference of parties (COP21) states that increase in soil C by 4% (0.4%) a year we can halt the annual CO2 increase in the atmosphere. A Grass-legume mixture management strategy provides an opportunity for sequestering C back into soil reducing exacerbation of GHGs and climate change.

## **3.4 N fertilizer and N2O emission**

Legumes owing to their N fixation capabilities have little exogenous fertilizer requirement except the starter dose of application depending on site-specific conditions. The effect of previous legume in rotational cropping also reduces the need for fertilization in succeeding plant cover. Without fertilization legumes like *Trifolium* spp. have reported N fertilizer savings of (160–310 kg ha−1) through BNF [65]. At current times when the chemical inputs like fertilizer application is not a viable option for environment along with increased cost of natural gas-based N fertilizers we need to consider legume as an eco-friendly option to sustain fertility and yields over longer time periods compared to fertilizer [29]. Nitrous oxide (N2O), powerful GHG is 300 times more potent compared to CO2 in relation to global warming potential. Nutrient poor or degraded soil requires greater amount of N fertilization to sustain biomass cover and increase yields. The emission of soil N2O increases linearly with the quantity of N fertilizer applied to soil thus, BNF via legumes will become an essential aspect in all systems. Diverse mixture with legume addition improves biomass yield, in some cases equivalent to mineral N fertilization at the rate of 33–150 kg ha−1 and reduce soil N2O emissions by 30–40% [66]. The study of [67] also showed consistent lower N2O emissions in binary grass-legume mixtures compared to only grass with N fertilization. The reduced emission rate is associated with species complementarities between grasses and legumes which creates a synchrony in the timing of N mineralization and N demand. Soil systems including grass-legume mixture significantly lower the annual N2O emissions saving N fertilizers and thus GHGs and a considerable potential for climate change mitigation [50].

## **3.5 Weed control**

Weed invasion on post-mined lands negatively affects plant survival and biomass yield and therefore needs to be fully eradicated. Use of herbicides for weed removal can be effective at times but not environmental friendly and induces GHGs emission. Plant diversity (grass-legume mixture) can effectively suppress weed invasion. Sanderson et al., [68] found consistently lower weed abundance in legume-dominated mixtures compared to monocultures. Weed management system should be consistent with the principle of control, prevention and eradication. Organic mulches including grass and legume mulch residues can suppress the invasion of weeds [69] in several ways like (1) blocking germination by intercepting light (2) lowering soil temperature (3) greatly humidified day and night temperature fluctuations (4) thick mulch layer lowers weed seeds to germinate than non-mulched soil (5) organic

*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*

mulches enhances competition of resources, favors plant growth eradicating weeds. Study on weed suppression reported 52% less weed biomass across mixtures varying in species proportions. Weed invasion can be lowered via forage species combination and plant diversity and persistence traits in systems designed to reduce reliance on N fertilizer [70]. Nitrogen is not required for legumes or grass-legume mixture establishment. Application of N in such conditions can deter N fixation by legumes and in turn will accelerate competitive growth of grasses and weeds.

## **4. Case study: a successful case study promoting sustainable mining in India**

**Objective of the study:** To conserve and enhance the biodiversity along with generating natural resources to cater the needs of local community and better esthetic view of the mined area.

## **4.1 Study area description**

Ecological restoration (using 3-tier plantation model) of Tetulmari coal mine dump under Bharat Coking Coal Limited (BCCL), India was carried out to reverse the environmental degradation post-mining. The total area cover was 8–10 hectares located at 23°48′210" N and 86°20'527" E and at an elevation of 704.9 m above mean sea level. Prior to restoration the mined out area was 14 years old and fully invaded by exotic weeds (*Lantana camara, Eupatorium odoratum, Heptis suaveolens*). The area was completely devoid of grass cover and native tree species.

#### **4.2 Restoration approaches**


## **4.3 Results**

**Re-vegetation status:** The ecological restoration approach was successful in establishing dense and diverse vegetation (trees, shrubs, herbs and grasses) cover on the mined dump within three years of restoration. Vegetation analysis during the course of restoration showed that among planted species *Dalbergia sissoo* was the most successful at the site with a maximum density of 514.3 tree ha−1. The total


**Table 5.**

*Species composition under the three-tier plantation method during ecological restoration of Tetulmari coal mine dumps, India.*

*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*

#### **Figure 8.**

*(A) Closer view of dense and diverse vegetation cover of understory biomass and tree growth (B) biomass carbon stock and CO2 sequestered after ecological restoration of Tetulmari coal mine dumps, India.*

shrub and herbs density was 1114 Ind ha−1 and 6.79 Ind m−2. Similarly *Cenchrus ciliaris, Cenchrus setigerus* were found to be the promising grass species whereas *Pennisetum pedicellatum* was the first grass species to colonize the site. Successful horticultural species includes *Emblica officinalis, Mangifera indica Syzygium cumini* and *Psidium guajava.* Horticulture and grasses-legume species besides providing ecological stability were able to cater the needs of local communities and adjoining societies by providing food, fodder, timber resources and livelihood opportunities.

**Nutrients status**: Besides successful vegetation establishment, a notable change is soil physicochemical and biological properties were also observed in the span of three years. The soil pH increased from 6.0 to 7.1. SOC and total N concentration increased by 46% and 180% respectively after ecological restoration. The total biomass (77 t ha−1) accumulated on the dump surface accumulated 39 t ha−1 C stock in soil equal to 141 t ha−1 CO2 sequestered (**Figure 8**). The ecological restoration of mine degraded land considerably increased the ability of biomass and soils to sequester C. The development of terrestrial C sinks reduces ill-effects of polluting gases (GHGs) caused to the climate change.

**Biodiversity status:** The diverse vegetation started attracting different types of faunal species including birds, butterflies, insect, reptiles and naturally re-colonizing animals like foxes, rabbits, jackals etc. The enhanced biodiversity also facilitates to support food chains and better esthetics at the eco-restored area.

#### **5. Conclusions**

The mining process is not only ecological and socially devastating but also extremely demanding on natural resources like water land and energy. The postmined areas are highly susceptible to weed invasion and prone to erosion that can cause mine waste to pollute adjoining soil and water resources. The rising demand of coal is likely to escalate ecosystem damage in several ways. The agronomic benefits' of grass and legume species has lead us to recognition of its environmental and socioeconomic advantages in mined-out landscapes (**Figure 9**). Sustainable mining is essential for the survival of humankind. The review of literature presented here in ascertains that grass-legume based management practices hold a vast potential to advance mine sustainability owing to benefits of BNF, soil

#### **Figure 9.**

*Sustainability aspects of grass-legume mixture in environmental, social and economic arenas.*

regeneration, creating terrestrial C sinks, weed control, reducing GHGs emissions and socioeconomically viable by increasing profit potential. Future perspective ascertains the need of ecological restoration using grass-legume seeding aimed towards sustainable intensification of mine degraded lands besides supporting livelihoods of millions.

## **Acknowledgements**

The first author is grateful to Indian Institute of Technology (Indian School of Mines), Dhanbad, and Ministry of Human Resource Development, Government of India for providing fellowship and other research facilities to support the research work.

*Grass-Legume Seeding: A Sustainable Approach towards Reclamation of Coalmine Degraded… DOI: http://dx.doi.org/10.5772/intechopen.99741*

## **Declaration of competing interest**

The authors do not have any conflict of interest.

## **Author details**

Sneha Kumari and Subodh Kumar Maiti\*

Department of Environmental Science and Engineering, Center of Mining Environment, Indian Institute of Technology (Indian School of Mines), Dhanbad, India

\*Address all correspondence to: subodh@iitism.ac.in

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## **Chapter 14**

## Faba Bean Agronomic and Crop Physiology Research in Ethiopia

*Dereje Dobocha and Debela Bekele*

## **Abstract**

Faba bean is an important pulse crop in terms of protein source, area coverage, and volume of annual production in Ethiopia. The aim of this paper is to assess the agronomic and crop physiology investigations in the past two decades in Ethiopia. The production limiting factors of this crop are low input usage, natural disasters, depletion of macronutrients, and unavailability of essential nutrients. Phosphorus is among the main limiting nutrients in soil systems in Ethiopia. Seed yield and biomass yield of faba bean were increased from 1338 to 1974 kg/ha and from 3124 to 4446 kg/ha when phosphorous was changed from 0 to 52 kg/ha, respectively at Holeta whereas application of 40 kg P ha − <sup>1</sup> resulted in higher grain yield (6323 kg ha−1) and 3303 kg ha−1 at Lemu-Bilbilo and Bore highlands, respectively. The highest grain yield of 32 kg ha−1 was obtained from the application of 92 kg P2O5 ha−1 at Sekela district while application of 46 kg P2O5 ha−1 resulted in a substantial increase in seed yield over unfertilized plots on vertisols of Ambo. On the other hand, the results suggest that using starter nitrogen from 0 to 27 kg/ha has marginally increased faba bean yield but, a farther increase of nitrogen has indicated deteriorate of yield at Arsi zone. Proper plant populations play a crucial role in enhancing faba bean production. Planting faba bean at 30 cm × 15 cm spacing gave the highest grain yield in Duna district while it was 30 × 7.5 cm at vertisols of Ambo University research farm. Significantly higher seed yield (4222 kg/ha) was observed in the 40 cm inter-row spacing as compared to 50 cm inter-row spacing, which gave the lowest seed yield per hectare (3138 kg/ha) on fluvisols of Haramaya University. Intercropping and crop rotation are cropping systems that can increase soil fertility and crop yield. Intercropping of faba bean with barley at Debre Birhan increased land equivalent ratio than both crops when planted as sole. An additional income of 18.5% and 40% was gained than planting sole faba bean and wheat, respectively at Kulumsa. Faba bean can fix about 69 kg/ha nitrogen in Northern Ethiopia. Generally, the current review results showed that only limited studies in organic and bio fertilizer, plant density, and cropping systems were done on faba bean in Ethiopia. Hence, studies regarding soil acidity, organic fertilizer, and secondary plus micronutrient impacts on faba bean production and productivity along soil types and weather conditions need great attention in the future in Ethiopia.

**Keywords:** seed yield, biomass yield, fertilizer, plant population, row spacing, intercropping, crop rotation, soil fertility

## **1. Introduction**

Faba bean (*Vicia faba* L.) is an important legume crop that contains a high protein amounting to 33% and is consumed worldwide as protein source by humans [1]. It is also a crop of considerable importance as a low-cost food rich in carbohydrates [2]. In addition to its great nutrition content, faba bean plays an essential role in crop rotation. It has the ability to fix nitrogen, and provide a significant level of nitrogen from the soil air using a symbiotic relationship with Rhizobium bacteria [3]**.** Depending on the plant density and the field management, this plant is able to fix nitrogen up to 40 kg ha−1 annually [4]. Like the other members of *Fabaceae*, *V. faba* also increases the humus of soil [5].

Faba bean production occupied nearly 2.1 × 106 ha worldwide [6]. Its global production is 4.4 million tons [7]. The main faba bean global producers are China (1.64 Mt), Ethiopia (0.92 Mt), Australia (0.34 Mt), France (0.27 Mt), and Sudan (0.16 Mt) [7].

Faba bean is an important pulse crop in terms of area coverage and volume of annual production in Ethiopia [8]. The crop takes the largest share of the area under pulses production [9]. The annual area coverage of the crop in Ethiopia is 492,271.60 hectares with a total production and productivity of 1.04 million tons and 2.1 tons/ha respectively [9]. It is a major staple food crop among pulses and it is mainly grown in the mid and high altitude areas of the country with an elevation ranging from 1800 to 3000 meters above sea level [10]. Some limiting factors of faba bean production are climatic conditions, edaphic factors, disease problems and agronomic practices [11].

According to Central Statistical Agency [12] report, in Ethiopia about 4.34% of the grain crop area of land was covered by faba bean with annual production of about 3.94% of the total grain production and yield of 1.84 t/ha. Despite the importance, the productivity of the crop is far below the potential and is constrained by several limiting factors [13, 14]. Even though the availability of high-yielding varieties, the productivity of faba bean under smallholder farmers is less than 1.89 t ha−1 [15]. The low yield of faba bean was related to the vulnerability of the crop to biotic and abiotic stresses [16]. Among the abiotic category, declining soil fertility and low pH (acidity) are the most determinants for the low productivity of most crops [17]. Most of the reports revealed significant improvements in the yield of faba bean due to chemical fertilizers applications [18, 19].

#### **1.1 Socio-economic significance of faba bean**

Broad beans are one of the most popular legumes in Ethiopia. It is a crop of manifold merits in the economy of the farming communities in the highlands of Ethiopia. It serves as a source of food and feed and a valuable and cheap source of protein. Faba bean also plays a significant role in soil fertility restoration in crop rotation through the fixation of atmospheric nitrogen [13, 14]. It is tightly coupled with every aspect of Ethiopian life. It is mainly used as an alternative to peas to prepare flour which is used to make a stew used widely in Ethiopian dishes. Its boiled broad bean (*nifro* in Amharic) is also common in Ethiopia. It is also a crop of high economic value [20]. Ethiopia's faba bean export has moved northward since the year 2000 and the major destinations are Sudan, South Africa, Djibouti, Yemen, Russia, and USA, though its share in the countries pulses export is small [21].

#### **1.2 Main constraints for faba bean production or general production constraints**

Despite its importance, the productivity of faba bean is far below the potential and is constrained by several limiting factors [14]. It was also mentioned that the productivity of faba bean is far below the expected potential due to low input usage, natural disasters like a snow storm, depletion of macronutrients from cultivable land, and unavailability of essential nutrients [22]. There are also other limiting factors of faba bean production like climatic conditions, edaphic factors, disease problems, and agronomic practices [11].

## **2. Research achievements**

## **2.1 Fertilizer study**

Soil fertility is an important factor affecting crop productivity in general and faba bean in particular. All plants have their own type and amount of nutrient requirements from the soil. Excess nutrients in the soil cause toxicity to the plant and deficient nutrients cause nutrient deficiency symptom. Nitrogen, phosphorus, and sulfur are among the essential elements determining soil fertility.

## *2.1.1 Phosphorus*

Phosphorous has a great role in the growth and development of crops. It plays a prime role in the growth of roots, nodulation, dry matter production, N fixation, and protein synthesis of leguminous crops [23]. Phosphorous is implicated in speeding up maturity and enhancing the root-shoot growth ratio. It is involved in many metabolism activities [24]. Phosphorous exerts many and varied functions in plant metabolism and hence inadequate phosphate supply to the plant seriously affects numerous metabolic processes. This is the reason why it is called the key to life because it is directly involved in the most life process. Thus, faba bean being a legume it needs phosphorus for better root and nodule development, which is often neglected by farmers. Hence, balanced nutrition of legumes gains significance to harvest better yields, especially under rain-fed cropping conditions, where rainfall quantum and its distribution controls the total crop production system [24].

Phosphorus is among the main limiting nutrients in soil systems in Ethiopia that create high yield gaps [25]. The application of diammonium phosphate to faba bean resulted in either lack of response or negative effects on some on-farm trials in the past in Ethiopia [18]. It was also reported that there was no response to phosphorous fertilizer at Holetta [26]. But, [18] stated that phosphorous fertilization resulted in a significant quadratic response at this location. This study further reported that there was no significant effect on seed yield at Burkitu and Debre Zeit. They reason out that the lack of significant response to the phosphorous application at Debre Zeit is possible since the research field has been fertilized with N and P fertilizers during the past three decades. Seed yield and biomass yield of faba bean was increased from 1338 to 1974 kg/ha and from 3124 to 4446 kg/ha respectively, when phosphorous was changed from 0 to 52 kg/ha at Holeta [27].

Increasing the rate of phosphorus from nil to 40 kg P ha−1 changed the seed yield from 1939 to 3303 kg ha−1 at Bore highlands, Guji zone [28]. Significantly higher mean dry biomass yield (14,158 kg ha−1) and seed yield (6323 kg ha−1) were produced with the application of 40 kg P ha−1 that was at par with 20 kg P ha−1 and 30 kg P ha−1 at Lemu-Bilbilo. The results also showed that the grain yield of faba bean was significantly increased with P fertilizer application rates over the control whereas the application of 30 kg P ha−1 resulted in a higher number of effective tillers plant−1 (1.53), which was at par with all other P rates application except the unfertilized plots [29]. The highest grain yield of 3.2 t ha−1 was obtained from the application of 92 kg ha−1 P205 at the Sekela district of West Gojam [30]. According to [31] fertilization of faba bean with 46 kg P205/ha resulted in a substantial

increase in biological yield (8172 kg/ha) over no fertilizer check (5602 kg/ha haulm yield). Fertilization of faba bean with 46 kg P205/ha resulted in a substantial increase in seed yield (3531 kg/ha) over no fertilizer check (2654 kg/ha seed yield) on vertisols of Ambo University research farm. Harvest index tended to improve with P nutrition (49.7) over no phosphorus (47.4) [31].

On the other hand, the research conducted on phosphorus fertilizer rate at Bore Highlands, Guji Zone revealed that application of 40 kg P ha−1 resulted in the highest plant height of faba bean which was significantly higher by 11.8% than the unfertilized and gave the highest nodule dry weight (170.90 mg/plant) and seed yield (3303.0 kg ha−1), but the faba bean plant height difference between 10, 20, 30 and 40 kg P ha−1, as well as seed yield difference between 30 and 40 kg ha−1 P rate, were statistically the same (**Table 1**). Increasing the rate of phosphorus application from nil to 10 kg P ha−1 did not affect the number of pods produced per plant. However, further increasing to 30 kg P ha−1 application rate resulted in significantly higher numbers of pods per plant−1 than by plots fertilized with 20 kg ha−1, 10 kg ha−1, and nil rates [28].

Faba bean exhibited a significant response in terms of pod weight/plant with the application of 46 kg P205/ha (24.0 g) compared to 21.7 g obtained with no phosphorus (**Table 2**). Test seed weight has a linear relationship with phosphorus fertilization. Phosphorus fertilization at 46 kg P205/ha significantly improved the test seed weight (520 g) over no phosphorus (492 g) at Ambo University research farm vertisols [31].

The total number of nodules per plant increased significantly in response to increasing the rate of phosphorus application. The application of mineral phosphorus fertilizer at the rate of 40 kg (the highest rate) phosphorous ha−1 resulted in the highest number of nodules (94.52) per plant [28].

## *2.1.2 Nitrogen*

Nitrogen is an essential nutrient for plant growth, development, and reproduction. It is so vital because it is a major component of chlorophyll, amino acids, energy-transfer compounds, such as ATP (adenosine triphosphate), and significant component of nucleic acids such as DNA, the genetic material that allows cells (and eventually whole plants) to grow and reproduce. Adequate amounts of nitrogen in the plant are also essential for the absorption of other nutrients [32]. It is involved in cell multiplication, giving rise to the increase in size and length of


#### **Table 1.**

*Effect of mineral phosphorus fertilizer application rate on plant height, number of pods plant−1, nodule dry weight and seed yield of faba bean during 2015 and 2017 main cropping season at bore.*

*Faba Bean Agronomic and Crop Physiology Research in Ethiopia DOI: http://dx.doi.org/10.5772/intechopen.101542*


#### **Table 2.**

*Main effects of phosphorus rates on effective tillers plant−1, dry biomass yield, and seed yield of faba bean in Lemu Bilbilo district of Arsi zone.*

leaves and stems and especially the stalks of grains and grasses; increases chlorophyll, giving the leaves their dark green color, plays a part in the manufacture of proteins in the plant, and is part of many compounds in the plant including certain types of basic acids and hormones [33]. Therefore, the application of nitrogen below optimum has a profound influence on crop growth and may lead to a great loss in grain yield [34].

Nitrogen is among the main limiting nutrients in soil systems in Ethiopia that create high yield gaps [25, 31]. Applying starter nitrogen from 0 to 27 kg/ha has slightly increased faba bean yield but, a further increase of nitrogen has indicated a decline of yield. The highest biological yield was recorded at the highest nitrogen level at Arsi zone [35]. Faba bean seed yield increased at Adet, Holeta, and Sheno when nitrogen increased from 0 to 36 kg/ha [18].

#### *2.1.3 Sulfur*

Sulfur is another important nutrient required by plants essentially required to form proteins and coenzymes [36]. Sulfur as a protein component is an essential element. Soil sulfate may originate from atmospheric deposition, fertilizer addition, or mineralization of soil organic S, which is the main sulfur fraction. In recent years the importance of appropriate nourishment of plants with sulfur has grown, which is chiefly related to a decrease in the deposition of this element in soils because of a reduction in industrial emissions [37]. The shortage of this component in the soil reduces the yield level and quality of leguminous plants [38, 39]. Sulfur fertilization, moreover, improves the yield quality, increasing the content of protein and sulfur amino acids in seeds [40, 41].

#### **3. Plant population and patterns**

Plant density is a major determinant of proper plant development and growth [42]. It has a remarkable capacity to exploit the environment with varying competitive stresses [43]. Both high and low crop densities reduce yield and total revenue. When planting density is too low, each individual plant may perform at its maximum capacity, but there are not enough plants as a whole to reach the optimum yield. If the planting density is too high, plants may compete against each other, known as intra-specific competition. Under those conditions, the performance of individual plants becomes a limiting factor for maximum crop yield [44].

It has been reported that among a various package of improved production technology proper plant population with appropriate adjustment of inter and intra-row spacing play a key role in enhancing faba bean production [45]. Optimum plant density differs from each variety and location since the different location has different soil type, soil moisture, soil fertility, and relative humidity [46]. In line with these findings, the research conducted on plant densities on faba bean varieties at Lemu-Bilbilo district of Arsi zone, Ethiopia indicated that the highest seed yield of faba bean (4649, 4594, and 4162 kg ha−1) was obtained at 90, 70, and 50 plant m−2 for Degaga, Moti and Gora varieties, respectively [47]. The authors also stated that the highest total biomass of 9 t ha−1 was recorded from the highest plant population (90 m−2), but did not show significant differences to the total biomass obtained from 70, 50, and 25 (control) plants m−2. It was reported that 25 plants population density m−2 was economically recommended for Degaga and Moti varieties whereas, 50 plant population density m−2 was for Gora variety at the study site and similar agro-ecologies**.**

On the other hand, [48] reported that the significantly highest seed yield (2495 kg ha−1) of faba bean was obtained at the combination of 30 cm × 15 cm spacing (the lowest and highest inter and intra-row spacing, respectively). The lowest grain yield (1329 kg ha−1) was recorded at 30 cm × 5 cm spacing (**Table 3**). They also reported that significantly the highest dry biomass yield (8738 kg ha−1) was recorded at the combination of 30 cm inter by 5 cm intra-row spacing. This was statistically similar with the dry biomass obtained due to 40 cm by 5 cm inter and intra-row spacing combination, and the lowest dry biomass yield (3812 kg ha−1) was obtained at 50 cm × 15 cm inter and intra-row spacing interaction in the Duna district of Hadiya zone [48].

According to [49] significantly higher seed yield (4222 kg/ha) was observed in the 40 cm inter-row spacing as compared to 50 cm inter-row spacing which gave the lowest seed yield per hectare (3138 kg/ha) at fluvisols of Haramaya University. Seed yield (kg/ha) is significantly affected by inter and intra-row spacing. The higher seed yield was observed in the narrowest as compared to the wide spacing which gave the lowest mean seed yield at vertisols of Haramaya [45]. Another experiment conducted to see the effect of plant spacing on faba bean at Ambo University vertisols research farm revealed plant spacing had a significant effect on seed yield of faba bean [48]. Plots sowing by 30 × 7.5 cm spacing resulted in greater faba bean seed yield (3814.8 kg/ha) than that sowing by 40 × 5.0 cm (3074.1 kg/ha) and 60 × 5.0 cm (2388.9 kg/ha), respectively.


#### **Table 3.**

*Interaction effect of inter and intra-row spacing on seed and dry biomass yield of faba bean at Duna district of Hadiya zone in 2015.*

*Faba Bean Agronomic and Crop Physiology Research in Ethiopia DOI: http://dx.doi.org/10.5772/intechopen.101542*

Further research accompanied on plant spacing at fluvisols of Haramaya University also indicated that significantly the highest numbers of seeds per pod and seed yield per plant were obtained in wider row spacing [48]. At the same location, but different soil types (vertisols) also reported that an increase in the number of seeds per pod with wider plant spacing could be due to less competition for nutrients and water [49]. This is consistent with the results of [45] who stated wider spacing tended to improve the seeds/pod as compared with narrow spacing. These results might be due to the fact that widely spaced plants suffer less from competition than closely spaced plants.

Many literatures report that as plant density decreases (inter and intra-row spacing increases) number of pods/plant increases. For example [45] found a significant increment of the number of pods per plant by increasing inter and intrarow spacing in which the highest number of pods/plant (28.6) was obtained from the widest (50cm × 12cm) inter and intra-row spacing on vertisols at Haramaya University. The authors also state that a decrease in inter and intra-row spacing increases competition which eventually leads to a reduction in the number of pods on the individual plant. An increase in the competition for light and nutrients in high population leads to a decrease in photosynthesis and so more abscission and lower pods per plant.

## **4. Cropping system**

#### **4.1 Intercropping**

Intercropping is the agricultural practice of cultivating two or more crops in the same land at the same time [50]. It is intensive management for crop production which aims to match efficiently crop demands to the available growth resources and labor [51]. It is relatively common in tropical and temperate areas because of the effective utilization of water [50], nutrients [52, 53], and solar energy [54]. The most common advantage of intercropping is the production of greater yields on a given piece of land by making more efficient use of the available growth resources. This could be due to different rooting characteristics, canopy structure, height, and nutrient requirements or resource use at different times [55].

In Ethiopia, food production for a rapidly growing population from a continually shrinking farm size is a prime developmental challenge. Researches indicated that inter-cropping is a good way of using land efficiently. A 3 years study of sorghum/groundnut and sorghum/soybean intercropping in Asosa (Ethiopia) showed that sorghum/groundnut intercrop had the highest sorghum yield at all growing seasons. The gross income and land equivalent ratio indicates greater economic benefit with intercropping of groundnut in 1: 1 proportion and simultaneous planting than sole planting [56].

The spatial arrangement of faba bean with barley around Debre Birhan area revealed that a significantly greater land equivalent ratio (LER) was obtained in intercropping than both crops when planted as sole. The 2B:1FB (one row of faba bean intercropped in two rows of barley) was more productive than other planting patterns (1B:1FB and 1B:2FB). All spatial arrangements had the LER values of more than one (LER > 1). It indicated that intercropping had economic advantages in land-use efficiency [57].

Mixed intercropping of wheat with faba bean was compared with sole culture of each species in 2002 and 2003 at Holetta Agricultural Research Center, in the central highlands of Ethiopia, and intercropping increased the land equivalent ratio by +3% to +22% over sole cropping [58]. The authors' findings showed that as faba

bean seed rate in the mixture increased from 12.5 to 62.5% the wheat grain yield was reduced from 3601 kg/ha to 3039 kg ha−1 whereas faba bean seed yield was increased from 141 kg ha−1 to 667 kg ha−1. However, the maximum total grain yield of 4031 kg ha−1 of wheat, gross monetary value of US\$ 823, system productivity index of 4629, and crowding coefficient of 4.70 were obtained when wheat at its full seed rate was intercropped with faba bean at a rate of 37.5%. The field research conducted on planting ratio in faba bean and wheat intercropping at Kulumsa showed grain yield of faba bean was significantly affected by planting ratio plus wheat intercropping and additional income of 18.5% and 40% was gained than planting sole faba bean and wheat, respectively [59].

### **4.2 Crop rotation**

Crop rotation is the most among factors significantly increased soil organic matters [60]. Legumes contribute to the maintenance and restoration of soil fertility by fixing N2 from the atmosphere [61]. The input of fixed N from grain legumes may be a significant contributing factor in relation to sustaining productivity in smallholder systems [62]. The researches findings so far indicated that faba bean can enhance the yield of the following crop and increase the economy of the farmers [63]; can mark residual phosphorus available that otherwise would remain fixed [64] and may indirectly make more phosphorus and potassium available for subsequent crops [65] and the rotational benefit of faba bean to improve the P availability for subsequent crops also is considered to be closely related to the mineralization of its P-rich crop residues rather than to residual effects of root exudates on soil chemistry.

Faba bean improve the structure of poorly structured soil by stabilizing soil aggregates compared to continuous cotton and cereals as pre-crops [66]. Its roots and stubble contributed 44–50 kg N ha−1 to the requirements of the following crop in a temperate climate [67]; produce high levels of rhizome deposition which will improve the soil N balance which assists in maintaining soil organic fertility, and appear to provide an important source of N for following crops in the rotation [20].

Other findings revealed that yields of malting barley were greater with some pulse rotations than with continuous barley at Jeldu and Holetta [58]. Mean grain yield advantages of malting barley over the two locations after faba bean, field pea, and rapeseed were greater by 67, 43, and 53%, respectively, than malting barley after barley indicating that the lack of crop rotation has already been manifested in the continuous barley plots. The authors also showed that the highest biomass yield of 7348 (kg ha−1) and protein content (11.3%) of malting barley were recorded from malting barley following faba bean which was 9.5% protein content greater than that of following malt barley.

## **5. Biological nitrogen fixation**

Many studies conducted in Ethiopia and elsewhere in Africa have suggested that biological nitrogen fixation in different legume crops supplies sufficient N for optimum and sustainable crop production [39, 68]. Many studies also confirmed that different legumes have different nodulation and biological nitrogen fixation potentials [69]. Faba bean can fix about 69 kg/ha nitrogen in Northern Ethiopia [70].

#### **5.1 Rhizobium inoculation**

Inorganic fertilizer is an immediate supply of nitrogen, but by far the most important source of fixed nitrogen derives from the activity of certain soil bacteria

#### *Faba Bean Agronomic and Crop Physiology Research in Ethiopia DOI: http://dx.doi.org/10.5772/intechopen.101542*

that absorb atmospheric N2 gas and convert it into ammonium. According to [71] soil bacteria reduce approximately 20 million tons of atmospheric nitrogen to ammonia. Integration of multipurpose, N-fixing legumes into farming systems commonly improves soil fertility and agricultural productivity through symbiotic associations between leguminous crops and Rhizobium [8]. They also suggested that the contribution of N fixation to soil fertility varies with the types of legumes grown, the characteristics of the soils, and the availability of key micronutrients in the soil to facilitate fixation, and the frequency of growing legumes in the cropping system.

It is widely acknowledged that inoculation of legumes with effective rhizobia can improve yields and provide a substitute for inorganic fertilizers. Research has recognized inoculation with effective and appropriate rhizobial strain is necessary to improve symbiotic nitrogen fixation and optimize faba bean productivity [72]. These authors also revealed that inoculation affects microbial community by increasing desired rhizobia strain population in the rhizosphere and for successful establishment, inoculants strain must be able to survive in the soil environment and take advantage of an ecological niche to be offered by the roots of the host plant.

Since the soil may harbor certain ineffective nodule forming native rhizobia, effective nodule formation largely depends upon the competitiveness of inoculants strain. This upholds that strain competitiveness is key for successful inoculation under field conditions. Therefore, symbiotic performance depends on the abundance of effective rhizobia strain and its competitiveness for nodulation. It is evident that there are diversified faba bean cultivars in Sub-Saharan Africa that are likely to be accompanied by symbiotically effective nitrogen-fixing indigenous Rhizobium strains [72].

Rhizobium inoculation resulted in significantly taller plants (55 cm) compared to not inoculated plants (43 cm). No significant difference in grain yield and biological yield of faba bean were recorded among not inoculated and inoculated faba bean with strain FB-1017 at Arsi Zone [35]. Faba bean grain yield was decreased from 2.65ton/ha to 2.55ton/ha when it was inoculated with rhizobium across locations (Agarfa, Farta, and Sinana) [73].

## **6. Prospects of agronomic research for enhancing sustainable intensification in Ethiopia**


## **7. Conclusion and future outlook**

The outcomes of this review revealed that faba bean yield showed an increasing trend as a result of technology improvements by different researchers. Among different fertilizers study phosphorus is a very important nutrient for faba bean production. To know the optimum amount of this nutrient research study should be conducted across locations, soil types and also repeated based on soil test results. Applying a small amount of nitrogen which is different across locations as starter

nitrogen is required for faba bean production and productivity. Intercropping faba bean with cereals can increase income by about 50% over sole cropping component crops. On the other hand, rotating faba bean with cereals increased soil fertility which is can increase the yield of the subsequent crop. A slight decrease of faba bean grain yield was observed when it was inoculated with rhizobium at Agarfa, Farta, and Sinana. In general, it was revealed that there was still a drawback of research done on faba bean yield improvement in Ethiopia. Therefore, further studies on soil acidity, secondary and micronutrients, organic fertilizer study should need focus on across locations, soil type, and weather conditions in Ethiopia.

## **Conflict of interest**

There is no conflict of interest among authors.

## **Author details**

Dereje Dobocha\* and Debela Bekele Kulumsa Agricultural Research Center, Ethiopian Institute of Agricultural Research, Ethiopia

\*Address all correspondence to: derejegoda@gmail.com

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Faba Bean Agronomic and Crop Physiology Research in Ethiopia DOI: http://dx.doi.org/10.5772/intechopen.101542*

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## **Chapter 15**
