Abstract
The agricultural industry is one of the main economic contributors in developing countries, especially in tropical regions. Extensive land clearing has led to severe erosion within the watersheds, which increases the vulnerability of water catchments to natural disasters, such as floods. Cellulosic fibers, such as jute, sisal, kenaf, hemp, and coir, are gaining increasing worldwide attention for their potential application in controlling soil erosion, principally due to their remarkable biodegradable and physical properties. Nonetheless, the research on biocomposites in controlling soil erosion is limited compared to the natural fibers. This is perhaps due to poor availability and high cost of biodegradable polymers compared to natural fibers, which are abundant and inexpensive. Poor adhesive interactions between the matrix and natural fibers due to the hydrophilic characteristic of the fibers is another major drawback that limits the development of biocomposites for controlling soil erosion.
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Application of Cellulosic Fiber in Soil Erosion Mitigation: Prospect and Challenges
M. I. Syakir,a,b,* Yazan Al Manasir,a Nurin Syahindah Syasya Nor Ashikin,a Shaiful Yusuff,a Mark Zuknik,a and H. P. S. Abdul Khalil a
The agricultural industry is one of the main economic contributors in developing countries, especially in tropical regions. Extensive land clearing has led to severe erosion within the watersheds, which increases the vulnerability of water catchments to natural disasters, such as floods. Cellulosic fibers, such as jute, sisal, kenaf, hemp, and coir, are gaining increasing worldwide attention for their potential application in controlling soil erosion, principally due to their remarkable biodegradable and physical properties. Nonetheless, the research on biocomposites in controlling soil erosion is limited compared to the natural fibers. This is perhaps due to poor availability and high cost of biodegradable polymers compared to natural fibers, which are abundant and inexpensive. Poor adhesive interactions between the matrix and natural fibers due to the hydrophilic characteristic of the fibers is another major drawback that limits the development of biocomposites for controlling soil erosion.
Keywords: Cellulosic fiber; Biomass wastes; Soil stabilizer; biocomposite; Environment; Sustainable
Contact information: a: School of Industrial Technology, Universiti Sains Malaysia, Penang, Malaysia 11800; b: Centre for Global Sustainability Studies (CGSS), Universiti Sains Malaysia, Penang, Malaysia 11800; *Corresponding author: misyakir@usm.my
GRAPHICAL ABSTRACT
INTRODUCTION
Awareness of the potential replacement of synthetic polymers with biodegradable sources first arose in the late 1970s. This was due to the oil crisis that occurred during that era and the difficulties in composting synthetic polymers relative to natural polymers (Hatakeyama et al. 1977). The proliferation of synthetic polymers and the extensive dumping of such waste into the ocean and landfills have led to various environmental problems, such as the ingestion of plastic materials by wildlife in the ocean and land that ultimately causes fatalities (Huang et al. 1990). The United States became the world’s top leader for environmental innovation in the late 1960s, whereas environmental interest and action in Europe began only during the 1980s (Lampe and Gazda 1995). In Asia, Japanese researchers began to replace synthetic plastic with fermented carbohydrate polymers in the 1970’s (Glass) (John et al. 1998). Since then, various studies and research have been conducted globally to fully utilize natural resources and recycled waste materials to replace petroleum-based non-biodegradable polymers.
The evolution of natural fiber as a reinforcement material in biodegradable composites has been growing tremendously in industrial and research fields. Natural fiber is a fiber that originates from any natural resource, which includes plants and animals (Ticoalu et al. 2010). Natural fibers have good mechanical properties, especially when compared to synthetic fibers (May-Pat et al. 2013). Natural fibers, particularly from plants, such as sisal, hemp, flax, bamboo, coconut, kenaf, jute, and ramie (Ticoalu et al. 2010), are relatively low density, low weight, low cost, energy-efficient, non-toxic, renewable, recyclable, and biodegradable (Herrmann et al. 1998; Wambua et al. 2003; Cheung et al. 2009; Thomas and Pothan 2009). Therefore, natural fibers are both environmentally friendly and cost-effective.
Natural fibers have been innovatively embedded with biopolymer matrices made up of cellulose, starch, and lactic acid to form biocomposites since the 1980s (Herrmann et al. 1998). The biopolymer matrix in a biocomposite functions to stabilize the shape of the structure, transfer the pressure between the fibers, and functions as a coating to protect the composite from damage (Moser 1992; Luo and Netravali 1999). Formerly, biocomposites have been used in packaging and agricultural industries (Herrmann et al. 1998). However, due to growing demand, they have also been used in the automotive industry. Due to their equivalent cost with glass fiber-reinforced plastics, biocomposites have also been applied in the building industry as door panels, as they offer aesthetic value and are resistant to scratching and ultraviolet degradation (Marsh 2003).
Today natural fiber has gained attention from various industries due to its abundance availability and good mechanical properties. The scope of this manuscript is to discuss the natural fiber derived from agricultural byproducts and its potential applications as soil cover for erosion mitigation. Various strategies have been implemented to stabilize soil structure, including mechanical, physical, and chemical reaction techniques. Soil reinforcement, soil replacement, compaction, and chemical soil stabilization are some of the techniques to enhance the mechanical properties of soil (Tabatabaee 1985). In review, the efficiency of controlling soil erosion by using natural resources, such as EFB, oil palm frond, eco-mat, and leguminous cover crop plants, are discussed. However, cellulosic-soil mixing strategies are outside of the scope of this manuscript. As well, this review aimed to study the current trends in the applications of biodegradable materials and biocomposites in soil erosion mitigation.
The agricultural industry is one of the main economic contributors to developing countries, such as Malaysia and Indonesia. Malaysia and Indonesia are among the biggest producers of oil palm in the world, with 5.64 million hectares (Malaysian Palm Oil Council, 2015) and 8 million hectares (Indonesia Investments 2016) of plantation area, respectively. Furthermore, these numbers are projected to increase annually. However, in Malaysia, annual flood events have become more severe, particularly in the East Coast of Peninsular Malaysia. Agricultural activities, such as deforestation and the replanting season of palm oil, have been suspected to be main contributors to these flood events (Zafirah et al. 2016).
Although the increasing exploitation of oil palm brings many advantages to nations engaged in oil palm cultivation, especially economic advantages, environmental impacts must be considered. During the critical stage of oil palm establishment, the exposed surface soil is most vulnerable to erosion, particularly during the rainy season. Soil erosion is one form of soil degradation and is mainly driven by water and wind factors. Although soil erosion is a natural process, anthropogenic activities can increase rates of erosion up to 40%. Soil erosion leads to surface runoff due to the impact of rainfall. Water runoff transports eroded soil into river basins, which eventually causes sedimentation. In addition to deteriorating water quality and aquatic ecosystems, sedimentation also causes shallowing of water bodies until they can no longer sustain any water loads, which leads to overflow of the water bodies and consequent flood disasters.
Therefore, as soil erosion is a worldwide issue, researchers have studied various initiatives to prevent soil erosion from worsening for several decades (Leknoi and Likitlersuang 2020). Research has been carried out is the application of materials, particularly natural fibers, through various methods, such as mulching, spraying, coating, and matting methods. Borst and Medersk (1957) used manure and straw mulching to increase the infiltration rate of water into soil. In a more recent study, Deshmukh et al. (2015) used rice straw blankets to promote vegetation growth and increase soil moisture content. However, the cellulosic material application on soil not only can mitigate the soil erosion, but it can also play important role in pest management if applied systematically (Jabran 2019).
CELLULOSIC FIBER FOR SOIL EROSION CONTROL
The zero burning policy currently employed in many types of plantations is a good example of the development of more sustainable agricultural practices. Therefore, mulching and matting with natural fibers are used in the agricultural industry to control erosion and promote vegetation growth in a wide variety of situations, such as plantations or construction sites (Likitlersuang et al. 2020). In general, attributes of natural fibers such as strength, length, biodegradability, stiffness, size, and weight play important role for the effectiveness of natural fiber application in soil erosion.
In general, attributes of natural fibers such as strength, length, biodegradability, stiffness, size, and weight play important roles for the effectiveness of natural fiber application in soil erosion. Today most of natural fibers applied on soils are in the form of geotextile, i.e. kenaf, sisal, hemp, and bagasse. Others like jute, oil palm empty fruit bunch (OPEFB), wood fiber, and straw are applied directly (Clark 2010). These approaches are employed because they are cost-effective, provide a nutrient supply, and increase the organic matter content in soil with minimal usage of fertilizers and pesticides. The strength and weaknesses of cellulosic fibers used to control soil erosion, i.e. jute, kenaf, oil palm empty fruit bunch, hemp, coir, wood, and straw, are compared and summarized in Table 1.
Jute Fiber
Jute is a natural fiber that is long, shiny, and golden in color, and it is commercially obtained from two species, which are the white jute plant (Corchorus capsularis) and the tossa jute plant (C. olitorius). Jute fibers, which are mainly comprised of cellulose and lignin, are extracted via a natural microbial process known as retting (Gupta et al. 1976; Majumdar and Day 1977). Retting is an important process, as the quality of the jute fibers is largely dependent on retting efficiency (Chi et al. 1966; Ahmed and Akhter 2001). Retting involves the immersion of jute bundles in slow running water, such as a channel, streamlet, tank, lake, or reservoir, for 14 d to 28 d to break down the pectin materials, hemicellulose, and lignin (Banik et al. 2003; Paridah et al. 2011). However, as the retting process causes environmental pollution and heavy competition in the fiber market, innovative methods have been introduced to enhance final product quality, reduce labor needs, and decrease the costs (Jahan et al. 2016) of jute production.
The Bangladesh Government has recommended a ribbon retting method that improves fiber quality (Banik et al. 2003), requires half the amount of water needed in conventional retting, shortens production time by 4 d to 5 d, and reduces environmental pollution (Alam 1998). The production of jute is mainly concentrated in India, China, and Bangladesh. Jute fiber is in high demand due to its availability, durability, biodegradability, low thermal conductivity, and fiber uniformity. In India, jute has been traditionally used for packaging materials, such as strings, hessian, carpet backing, gunny bags, and canvas. Jute is used globally in diverse industries, which include the automobile, construction, transportation, furniture, textile, and cosmetic industries (Gon et al. 2012; Jirawattanasomkul et al. 2019)
In addition, jute fiber is used in the agricultural industry for land restoration during the process of natural vegetation establishment. The fiber is applied alone or blended with other polymers (both natural and synthetic). Jute geotextile is used for various civil engineering applications, such as controlling topsoil erosion, protecting river and canal banks, stabilizing slopes, and strengthening road pavements (Jadvani and Gandhi 2013). A case study in India found that, when compared with synthetic erosion control materials, jute geotextiles increased vegetative cover 80%, retained soil nutrients and soil moisture, and reduced maximum dry density (Barooah and Goswami 1997; Datta 2007; Mathur et al. 2008; Jual and Sharda 2008; Aggarwal and Sharma 2010; Islam et al. 2013; Sonthwal and Sahni 2015). This was due to the capacity of jute geotextiles to retain 375% more water than their dry weight (Islam 2013), which increased the shear strength of the soil (Zaidi et al. 2016) where the root system of plants anchored the soil together, which decreased soil erosion. Jute geotextiles have also been reported to foster vegetation growth due to their outstanding hydrophilic property of absorbing 4.5 times to 6 times more water more than their dry weight (Rickson and Loveday 1998). Due to their various characteristics, jute geotextiles can fully stabilize a slope in only 1 y (Choudhury and Sanyal 2010). Jute net absorbs raindrop impacts and kinetic energy, which reduces surface runoff and its erosion potential (Ingold and Thomson 1990; Mathur et al. 2008) and adds nutrients to the soil upon its decomposition (Mathur et al. 2008).
Kenaf Fiber
Kenaf or roselle (Hibiscus cannabinus), which is widely commercialized in the southern United States (Kugler 1996; Webber, III et al. 2002) is also known as Java jute, due to its similarity with jute fibers (Feng et al. 2001). Kenaf is comprised of cellulose (the main reinforcing element), lignin, and hemicellulose, which are the binding elements (Feng et al. 2001). Kenaf is a popular cellulosic source that has economic and ecological benefits (Nishino et al. 2003). It is a biennial herbaceous plant that takes 2 y to complete its biological lifecycle. Kenaf can grow under a wide range of weather conditions and can reach a height over 3 m three months after sowing the seeds (Terry and Reichert 1999). In South Africa, the United States, and Malaysia, kenaf is typically cultivated for its fiber, which is traditionally used to manufacture ropes and sacks.
Kenaf is unique because the stem produces two types of fiber, including coarser fibers (bast fiber) and finer fibers (core fiber), which are located in the outer layer and inner layer, respectively. Bast fiber comprises 35% of the kenaf plant, and the rest of the plant is comprised of core fiber (Sellers et al. 1993). The properties of kenaf fiber are dependent on the sources, age, separating technique, and history of the fibers (Akil et al. 2011). In addition to its other uses, kenaf fiber is used as an alternative raw material to manufacture paper (Akil et al. 2011), non-woven mats in automotive industries (Magurno 1999), textiles (Ramaswamy et al. 1995), and mats for grass seeding and erosion control (Kaldor et al. 1990; Ramaswamy and Easter 1997; Webber, III et al. 2002).
The kenaf plant has the potential to reduce soil erosion due to its dense and deep root system that holds soil particles together (Lauriault and Puppala 2009). In 1994 and 1995, the United States Department of Agriculture (USDA) spent approximately $100,000 to study the structural composite of kenaf fiber and its application in controlling soil erosion (Kugler 1996). The low water absorption characteristics and good mechanical properties of kenaf fiber make it a good candidate for soil reinforcement (Artidteang et al. 2012). Artidteang et al. (2012) studied the impact of kenaf geotextile’s waving patterns on soil reinforcement applications, and the results demonstrated that the plain pattern of woven kenaf has the highest tensile strength, followed by hexagonal and knot-plain patterns.
Oil Palm Empty Fruit Bunch (OPEFB) Fiber
The oil palm (Elaeis guineensis) tree, which is commonly used in commercial agriculture to produce palm oil, has a life-span of 25 y to 30 y and can grow up to 20 m in height. It is cultivated, produced, and commercialized worldwide but mostly by Malaysia and Indonesia, which together account for approximately 85% of global palm oil production (Indonesia Investment 2016). An oil palm tree consists of approximately 90% biomass waste and 10% oil. Every year, billions of tonnes of waste products, particularly OPEFB and palm oil mill effluent (POME), are produced after the sterilization and stripping process of fresh fruit bunches (FFBs) (Abdullah and Sulaiman 2013). For every ton of crude palm oil (CPO) produced, 1.1 tons of OPEFB is disposed of (Karina et al. 2008) due to the difficulty of managing these wastes (Abdullah and Sulaiman 2013).
This abundant major byproduct is sometimes disposed of via incineration, which causes extensive air pollution. Oil palm empty fruit bunch, which is primarily comprised of cellulose, hemicellulose, and lignin (with cellulose contributing the highest percentage of biomass of 49% to 65%), offers the best prospects to be an effective reinforcement material in composites (Rozman et al. 2000; Sreekala et al. 2004; Norul Izani et al. 2013). Many studies have been conducted to sustainably utilize biomass wastes from the oil palm industry. Among these studies, the use of OPEFB in the pulp and paper industry to replace the existing paper from wood sources was explored (Ibrahim 2003; Tanaka et al. 2004).
Studies have also been carried out on the application of OPEFB as a raw material for the production of various materials, such as super capacitor electrodes (Farma et al. 2013), glucose, and xylose (Lim et al. 1997; Rahman et al. 2006), activated carbon (Alam et al. 2007), bio-diesel (Feng 2013), bioethanol (Sudiyani et al. 2013; Chiesa and Gnansounou 2014), and microbial oil (Ahmad et al. 2016). Conventionally, EFB is used as mulching material. Empty fruit branch can also be incinerated to obtain oil palm ash (OPA), which has a high potassium content (Thambirajah et al. 1995; Husin et al. 2002; Farma et al. 2013) and can be applied as soil conditioner and organic fertilizer in estates and plantations. When applied as a soil conditioner, EFB increases the soil’s pH, cation exchange capacity, soil moisture, organic carbon, and nutrient contents (Teh et al. 2010; Comte et al. 2013; Frazão et al. 2014), and can thus function as a replacement for chemical nitrogen fertilizers, which tend to increase the acidity of the soil in oil palm plantations due to the removal of base cations (Nelson et al. 2011).
Upon decomposition, OPEFB acts as a compost fertilizer that aids nutrient cycling, primary productivity, and soil carbon stabilization (Hättenschwiler et al. 2005; Tao et al. 2016). Compost fertilizers derived from OPEFB also enhance soil fauna feeding activity through the presence of decomposer microbes, and they increase the concentration of base cations and soil moisture, which improves soil quality (Tao et al. 2016). Empty fruit bunch can retain water and release it gradually into the soil, and it can improve soil fertility and productivity due to better aeration and decrease soil erosion due to the improvement of the physical and chemical characteristics that contribute to sturdy soil structure (Abdullah and Sulaiman 2013; Syakir et al. 2016).
Sisal Fiber
Sisal (Agave sisalana), which constitutes 2% of global plant fiber production, originates from southern Mexico and is extensively cultivated and naturalized in many other countries, particularly in tropical and subtropical countries with temperatures above 25 °C, and it has a life span from 7 to 10 years. It cannot be cultivated in moist, saline soil conditions, such as clay. Each of its sword-shaped leaves consists of approximately 1000 fibers, which constitutes 4% of the total fiber in the plant. Sisal fiber is extracted by stripping off the leaves using a rotating wheel set with blunt knives. The drying process is the most crucial part, as moisture content determines the quality of the fiber. Although artificial drying is reported to yield better grades of fiber compared to sun drying, it is not practical in developing countries where sisal is produced. The sisal fiber is traditionally used for manufacturing string, rope, and twine. Presently, sisal fiber is used in the automotive industry as a strengthening agent in composite materials and in the paper industry due to its high cellulose and hemicellulose contents.
Sisal fiber is also used for marine and agricultural cordage and in the carpet and textile industries. In addition, Sisal fiber is used to make sisal geotextiles, which are designed to protect soil by creating a micro-climate for seedlings until vegetation is established. Sisal fiber has a longer life span than jute; thus, sisal geotextiles are beneficial when applied on riverbanks or for extreme applications where plant growth is gradual (Smith 2000). When tested on a 17% land slope, sisal geotextile demonstrated better erosion control than jute and coir geotextiles due to its high-water absorption capacity (Ram et al. 2009). Similar to kenaf fiber, sisal fiber has low moisture absorption (Giridhar and Rao 1986; Methacanon et al. 2010) and high strength (Methacanon et al. 2010).
These two unique properties indicate the good performance of sisal geotextiles, as strength and durability are vital characteristics in soil erosion control (Methacanon et al. 2010). Sisal fiber reinforced soils with cement increased the tensile behavior (Mattone 2005; Mwasha 2009) and decreased the bulk density of soil (Mattone 2005). Sisal fiber also significantly improved the shear stress of soil via earth reinforcement, as an increase in fiber length reduces the shear stress, which leads to the interlock failure between soil and fiber particles to cooperate as a single coherent matrix (Prabakar and Sridhar 2002).
Hemp Fiber
Cannabis sativa or hemp is typically found in the northern hemisphere and grows to a height of 6 to 12 ft. It is cultivated for the industrial uses of its derived products, including its stalk, which consists of two type of fibers, long fibers (bast) and short fibers (core). In contrast with other trees, hemp is ready to be harvested 2 to 4 months after being planted. In addition, it can grow in most types of soil and climates with moderate nursery management. Extraction of hemp fiber can be completed by two methods, which include retting (traditional method) or thermo-mechanical pulping (modern method). There have been controversies regarding the prohibition of cultivation and usage of hemp fiber in the U. S., as it was claimed to be the main source for the recreational drug marijuana. However, it has been verified that industrial hemp and marijuana come from different breeds of Cannabis sativa. Thus, industrial hemp has no value as a recreational drug (Yonavjak 2013). The superior properties of hemp fiber, such as its strength, durability, and absorbency are currently in demand in a wide range of industries and applications. It is typically blended with other fibers, such as wheat straw or flax, to increase its mechanical properties for use in textiles, rope, twine, paper, and building materials.
Hemp fiber is also used to control soil erosion. Geotextiles made from hemp fiber are designed to prevent soil erosion by stabilizing new plantings while they develop root systems along the slope, thus reducing the growth of weeds on bare soils. However, unlike geotextiles made from coir fiber, hemp degrades rapidly over a few months when exposed to water and soil, which makes it unsuitable for long-term applications (Karus et al. 2000). However, Small and Marcus (2002) disapproved of this statement and stated that a long-life span is an undesirable attribute in geotextiles, and the most vital aspect is the choice of a vegetation crop type that has the ability to develop root systems in a short period of time (Lekha 2004). The hemp plant possesses long tap roots that help to hold soil particles together, inhibit soil erosion, and increase soil aeration. Organic matter originating from hemp plants also improves soil fertility and helps decrease the usage of fertilizers in farmland. In this way, soil damaged by compaction and erosion can be repaired and restored. In addition, this method can reduce nitrogen pollution in water bodies due to soil leaching.
Coir Fiber
Coir or coconut fiber is extracted from the mesocarp tissue or husk of the coconut (Cocos nucifera). One thousand coconuts can supply enough raw material to produce 10 kg of coir. Coir fiber has high concentrations of lignin and lower decomposition rates than other natural fibers, which makes it the most suitable candidate for outdoor applications. Coir fiber can be divided into two types: brown fiber and white fiber. Brown fiber is extracted from mature coconuts and thus contains more lignin and less cellulose, whereas white fiber is extracted from immature green coconuts, which causes it to be smoother and finer but less durable. Conventionally, retting is conducted for several months to extract coir from coconut fruits. As technology has advanced, coconut defibering machines have been widely used on account of their practicality and time efficiency.
Coir fiber is used in rope, sack, brushes, doormats, rugs, insulation panels, packaging, and automobile body panels. Typically, brown coir is more frequently used than white coir due to its high durability. Coir fiber is an abundant and renewable resource with a very low decomposition rate as and higher shear stress than other natural fibers, which makes it suitable for controlling soil erosion. In a soil burial test with identical soil humidity and temperature conducted by the German Federal Institute for Material Testing, cotton and jute fibers took only 6 w and 8 w, respectively, to disintegrate, whereas coir fiber took more than a year to degrade (Rao 2002). In addition, it has an outstanding tensile strength that is resistant in various climates and conditions (Karus et al. 2000).
Geotextiles made from coir fibers were reported to successfully initiate vegetation growth in a short period of time due to the presence of sufficient water and light that encouraged seed germination. Compared to flax and hemp fibers that disintegrate rapidly in a few months, coir fiber has long-term stability due to its high lignin content (40% to 50%) and low cellulose content, and it is cheaper than flax and hemp fibers (Gupta 1991; Pritchard 1999; Karus et al. 2000). The tensile strength of coir geotextile decreases to 70% after 7 months of application (Vishnudas et al. 2008). Vishnudas et al. (2012) stabilized cultivated slope land by using coir geotextiles and found that slopes with crops treated with geotextiles had higher moisture content and less soil erosion than the control plots with geotextiles alone and no crops.
In addition, coir fiber is naturally resistant to seawater; therefore, it can be used to protect coastlines from erosion and prevent further deterioration along shores. It also has high endurance against high velocities of water flow and is suitable for application on steep slopes, as it increases soil water infiltration and provides sufficient protection from erosion by impeding rapid water flow (Gupta 1991). For instance, compared to unprotected soil, coir nettings decrease soil erosion 99.6% during the pre-monsoon season, 95.7% during the monsoon season, and 78.1% during the post-monsoon season (Lekha 2004). Beyond the enhanced infiltration of soil, coir-based rolled erosion systems delay the time for soil runoff, reduce intensity of rill incision, and reduce soil loss compared to bare soil (Sutherland and Ziegler 2007). Yadav and Tiwari (2016) reinforced clay soil with alkaline-treated coir fiber (1%) and pond ash (10%). They found that the addition of pond ash and fiber decreases the dry unit weight and increases water retention capacity, compressive strength, split tensile strength, and axial strain at failure of soil mixtures. Lekha (2004) found that soil structure is improved and the total organic carbon content in soil is enhanced through the application of coir fiber.
Bagasse
Sugarcane (Saccharum officinarum) can grow up to 3 m to 5 m in height and is typically cultivated in tropical and subtropical climate zones, such as China, Brazil, and Thailand. The sugarcane plant produces sugar (mainly in the form of sucrose). The fibrous waste residues that remain after the squeezing of sugarcanes during sugar production are known as bagasse. Generally, bagasse contains approximately 40% to 60% cellulose (Alavez-Ramirez et al. 2012). Globally, the output of bagasse fibers is estimated to be 75 million metric tons per year (Rowell 1998). Bagasse is currently used in various industries such as the construction, packaging, disposable tableware, paper and pulp, agricultural, and fuel industries. In addition, bagasse is used to generate heat and electricity in sugar mills, to control soil erosion by mulching, and produce geotextile mats (Fortes et al. 2012; Carvalho et al. 2013). Bagasse mulch improves carbon and nutrient cycling (Fortes et al. 2012), water retention (Dourado-Neto et al. 1999), and the structure of the soil (Graham et al. 2002). In addition, bagasse contains beneficial nutrients needed by plant growth, including N, P, K, and Ca (Graham et al. 2002; Fortes et al. 2012; Trivelin et al. 2013).
Bagasse geotextiles are among the natural fiber geotextiles that are fully biodegradable due to their high lignin content, which provides a natural adhesive to entangle the fiber mat together (Collier et al. 1997). The cited authors found that bagasse mat maintained its superior structure even after being tested in heavy rains, whereas woven coir net shrank after the first rainstorm. However, bagasse mats have a slow vegetation growth rate due low light penetration. Dang et al. (2016) found that the mixture of bagasse fiber and hydrated lime enhanced the compressive strength of expansive soil.
Wood Fiber
Wood fibers are cellulosic elements that are obtained from trees and commonly used to make various materials, including paper. Typically, wood fibers are used in the paper and pulp, construction, and wood industries. They are also applied to control soil erosion. Hydraulic mulch is a temporary way to protect exposed soil from erosion with a mixture of shredded wood fiber and a stabilizing emulsion (California Stormwater Quality Association 2003). Isrealsen and Urroz (1990) tested the efficiency of different mulches (wood fiber/tack, silva fiber, straw tack, and regular fiber) in preventing soil erosion by using a rainfall simulator. Results revealed that wood fiber/tack mulch had the lowest soil erosion rate after silva fiber, whereas straw tack mulch showed the highest soil erosion rate of the remaining mulches.
Water runoff rate was also notably reduced by the wood fiber/tack mulch, followed by silva fiber, straw tack, and regular fiber mulches. The data for the germination of barley seeds, the dry weight, and height of the barley plant showed that the wood fiber/tack mulch and the silva fiber mulch were superior to the straw tack and regular fiber mulches. This was due to the greater degree of seed protection provided by these mulches, which encouraged germination of seeds under warm temperatures. The study also found that long-fibered products performed better than short-fibered ones, whereas products with tackifiers were more efficient than products without tackifiers.
The authors included a disclaimer that the results presented were not conclusive due to the small number of replications (Isrealsen and Urroz 1990). Prats et al. (2017) added that sieved wood fiber was more effective in reducing soil erosion, as a smaller fraction of shredded wood led to a lower soil erosion mitigation capacity and was less cost effective than sieved wood fiber for large-scale applications (Foltz and Wagenbrenner 2010). Mulch application at a rate of 2.6 Mg ha-1 over 70% ground cover significantly reduced soil erosion and resulted in less formation of drainage channels during intensive rainfall.
Straw
Agricultural straw is one of the most frequently used materials for soil erosion mitigation, as it is commonly recognized to be the most practical, cheapest, and simplest way to impede soil loss (Foltz and Dooley 2003). Past studies mainly evaluated the effects of straw mulching on the stability of post-fire soil. Straw mulching is more viable than erosion barriers for decreasing soil erosion after severe wildfires, despite low rate application (Fernández and Vega 2016). Many studies agree that at least 60% of ground coverage is exposed to soil erosion after fires (Johansen et al. 2001; Vega et al. 2005; Cerdà and Doerr 2008). In agreement with Vega et al. (2014), straw mulch that covered approximately 60% of the affected area reduced soil erosion 70% during the first month after the fire, whereas erosion barriers reduced soil loss by only 32% during the first year of application and decreased rapidly afterwards (Fernández and Vega 2016).
However, Fernández-Fernández et al. (2016) claimed that straw mulching has no remarkable impact in reducing soil erosion, which may be due to the moderate rainfall intensity and erosion rates at the time the study was conducted. Prosdocimi et al. (2016) stated that the use of straw mulch resulted in delayed ponding and runoff generation and decreased median water and sediment concentration runoff, which consequently reduced soil erodibility and surface runoff overall. In addition, straw mulching increases water retention, organic content, and the availability of nutrients in soil, which improved the production yield of the crops (Stagnari et al. 2014). In a study conducted by Muñoz et al. (2017) on the physicochemical properties of soil, the application of a plastic mulching system showed positive impacts relative to straw mulching, such as high soil carbon content and soil stability.
However, the eco-physiological conditions for bacteria growth under plastic mulching were less suitable than under straw mulching, where there was a decline in the number of bacteria and soil fungi and an increase in the production of mycotoxins as a stress sign response by the fungi. Although straw mulch is widely available and has a low specific weight, recent studies have revealed the downsides of straw mulch, which include that its low specific weight allows it to be easily removed by strong winds (Robichaud et al. 2014). In addition, it decomposes easily, especially when compared to wood fibers (Robichaud et al. 2014; Fernández and Vega 2016).
