https://orcid.org/0000-0002-1650-4073
Abstract
The rapidly growing world population, inadequate accessible freshwater resources, and frequent erratic changes in climate have stressed human beings and compelled them to take vital initiatives to prevent water wastage. Water conservation efforts are also intensified in the world's largest water-consuming agriculture sector. The water use efficiency in agronomy has already been enhanced by the adoption of the drip irrigation method, intended to supply water directly to the crop, rather than the land around, thereby minimising water losses up to 70% occurring through evaporation and distribution. Mulching in association with drip irrigation in arid crop agronomy leads to mitigating vigorously water stress in agriculture. Mulch is a layer of natural or synthetic or combination material applied to the surface of the soil as a protective medium between the soil and the atmosphere. Entirely, it is an efficient medium for soil moisture conservation, and soil temperature control, adds nutrients to the soil by preventing leaching and more efficient use of fertilisers, resistor to erosion losses, suppressing the weeding and improving the visual look of landscapes. This review paper covers various aspects of mulch, emerging as a dynamic water and soil management tool without affecting the value of crops in agriculture.
HIGHLIGHTS
The rapidly growing world population, inadequate accessible freshwater resources, and frequent changes in climate have stressed human beings and compelled them to take vital initiatives to prevent undue wastage of water.
This covers various aspects of mulch, emerging as a dynamic water and soil management tool without affecting the value of crops in agriculture.
INTRODUCTION
Eighty percent of the total freshwater extracted from rivers and groundwater is used today in producing food and other agricultural products to feed the world's human population. However, agronomists are facing more water constraints than ever before, as the world's average water availability is steeply decreasing. India is a global agricultural powerhouse, and it currently has 4% of the world's total freshwater. But if the available water resources are not used wisely, the day is not far away when India will register as a water-stressed country. This alarming situation requires us to critically reconsider the watering systems and agricultural techniques to save massive quantities of water as well as energy going into the waste. Indeed, an in-depth analysis of prevailing watering systems and their possible Lagunas, ongoing and drafted water-saving techniques and their effects on plant performance is badly needed to meet the pressing need for optimised water usage (Kumar et al. 2005; Dhawan 2017; Rakhecha 2019; Cacal & Taboada 2022). The major agricultural revolution noted in this regard can be broadly divided into two categories:
- (i)
Development of agro-ecological systems.
- (ii)
Use of hybrid seeds/plants which require less water for cultivation.
The agro-ecology system is designed to meet the twin goals of global food safety and conservation of the environment. It emphasises farm production, rainwater and sunlight harvesting, and the elimination of fertiliser, pesticides, and other agrochemicals in order to empower the farming system by significantly lowering cultivation costs. However, agricultural productivity is normally dependent on soil health, which is reflected by biotic and abiotic measures such as soil organic substances, nutrients, moisture, and pH (Karlen et al. 2003; Atkinson et al. 2005; Ngosong et al. 2019). Maintaining healthy soils is thus important in meeting agro-ecological system targets, as its firm aggregates cannot easily scatter water, facilitating improved permeation or water use efficiency, preventing compaction and erosion, recycling nutrients, and supporting the natural biological process. Abdul Rajak (2022) had studied two technologies, Internet of Things and cloud computing, which can be implemented to automate the plant monitoring system.
Mulching made with organic or inorganic materials is one of the agro-ecological management practices. It is designed to manage soil health because it protects soil water evaporation and nutrient losses from sunlight and wind, which is important for crop growth. Mulching reduces runoff and transport capacity by increasing the hydraulic roughness of soil surfaces, as well as entrapping water and soil (Foltz & Wagenbrenner 2010; Montenegro et al. 2013; Shi et al. 2013; Prats et al. 2016; Ngosong et al. 2019). Thus, mulching serves as a tool not only to improve soil health but also soil moisture retention, important for the world passing through serious water crises.
Hence, the main focus of the present review article is related to the first mode of water conservation, the stuff concentrated on the use of novel mulching techniques only. It discusses types of mulching, their working mechanisms and role in water management for the agriculture sector. The article also emphasises on innovative and sustainable approach to prepare mulching with nano level additives, viz., fertiliser, antifungal, and/or pesticides. The incorporation of such additives in mulching is not only beneficial for water conservation but also increases the qualitative and quantitative value of crop as well as soil fertility preservation.
WATER MANAGEMENT
Freshwater is essential for humans' survival. However, its use should be well audited to preserve a healthy demand–supply chain. A brief account of this valuable element on the Earth has been accommodated here.
Fresh water and its importance
The social and productive significance of water is reflected in two major setups; its liquid form is used to fulfil hygienic, health and economic requirements like irrigation, whereas its second form in unfiltered rainwater gets accumulated into the soil and operates the production chain of food and other biomass. Water security in terms of its consistent availability in a sufficient quantity is regarded as a key factor for the survival of living creatures, especially human beings. When societal water demands become higher in relation to water availability, it is regarded as water scarcity, generally resulting in user struggles (Peter 1993; Butts 1997; Chaplin 2001; Falkenmark 2013; Grey et al. 2013). As such, out of the total available fresh water on the earth, a major share of 97% is in the oceans. Only three percent of the water on the earth is fresh and, of this, more than two percent is unavailable to satisfy the needs of humans as it is locked away in the deep groundwater aquifers, polar ice caps or glaciers. Only 0.36% of the world's water in rivers, lakes, and swamps is sufficiently accessible to be considered a renewable freshwater resource (Peter 1993; Butts 1997).
Impact of societal changes on the water cycle
Human civilisation has rapidly accelerated urbanisation and industrialisation; widespread use of electronic luxury and automobiles has resulted in the emission of toxic gases and liquid waste, which is frequently dumped illegally into freshwater bodies or soil rather than barren land. All of this has pushed the barometer for both air pollution and water pollution of natural resources to an all-time high. Unanimously, these factors have caused undesirable global warming and frequent climatic changes such as high temperature differences, hostile weather changes, cyclones, and so on badly, disrupting the regularity of the water cycle as well as dropping surfeit level, and thus increasing pressure on the already available but limited water resources (Butts 1997; Patil et al. 2013; Colak et al. 2015; Kader et al. 2017a).
Importance of water conservation in today's scenario for the agriculture sector
The situation of freshwater scarcity worsens day by day, and as a part of remedial measures, the ‘water conservation’ concept is gaining more and more importance in all the sectors related to human life. Some of the popular water conservation methods interlaced with human life are rainwater harvesting, water metering, greywater recycling and pressure reducing valves. (Dhawan 2017; Saroha 2017). Following the same footprints, the agricultural sector which accounts on average for 70–80% of the globe has prevalently adopted drip irrigation systems (Kumar et al. 2005; Dhawan 2017; Rakhecha 2019). However, installation of drip irrigation demands higher capital investment in the beginning but operating with due water economy (60–70%) than flood irrigation in an efficient manner, thereby in the long run it turns out to be cheaper. It is thereby regarded as an appreciable initiation taken towards freshwater sustainability for the balanced agro-ecological systems (Mendelsohn & Dinar 2003; Gyssels et al. 2005; Rajbir et al. 2009; FAO of the UN Rome 2017; Kader et al. 2017a).
The agronomy sector in addition to water costing is highly influenced by the human population count, which is, unfortunately, growing steeply day by day. Innumerable surveys predicted that the world population will be increasing from 7 billion now to 8.3 billion in 2025, and feeding such a huge chunk is going to create a big challenge for agrarian communities in the future. Looking at the growing pace of the world population, forecasts are also made about a 70–100% hike in the food demand by the year 2050, substantiating the stated fear well (Kumar et al. 2005; Rosegrant et al. 2009; Ajmeri & Ajmeri 2016; Dhawan 2017; FAO of the UN Rome 2017; Ahirwar et al. 2019; Rakhecha 2019). The upcoming threatening situations can be tackled by practicing new but scientific ecofriendly agricultural methods for sustainable food production. These require vigorous study of the soil biological system for a better understanding of the complex processes and interactions dominating in the stability of crop production as well as soil health (Khan et al. 2009; Bahadur et al. 2014; Ajmeri & Ajmeri 2016; Ahirwar et al. 2019). The frequent use of surface and groundwater resources, together with the use of greenhouse agriculture, led to an increase in crop yield (Jabal et al. 2022).
AGRO-ECOLOGICAL MULCHING SYSTEM
An Agronomy tool for Controlled Water Consumption ‘Mulch’ is basically an English word, and is derived from the original German word ‘molsch’, meaning soft or beginning to deteriorate, whereas the word mulching means covering, protecting, and insulating (Kasirajan & Ngouajio 2012; Ngosong et al. 2019; Iqbal et al. 2020; Prem et al. 2020). Accordingly, mulch used in scientific agriculture can be defined as a material that is spread or laid over the soil surface between rows of crops or around the tree trunk in order to cover the surface of the soil for plant growth, development and competent crop production (Patil et al. 2013; Kader et al. 2017a; Iqbal et al. 2020; Prem et al. 2020).
Historical development of mulching
Types of mulching.
Mulching materials
There are various types of mulching materials used for surface mulching or vertical mulching, viz., polythene mulching, gravel mulching, dust mulching, live vegetative barriers, hay mulching etc. (Patil et al. 2013; Kader et al. 2017a; Ngosong et al. 2019; Iqbal et al. 2020; Prem et al. 2020). However, broadly they are divided into two main categories; organic and inorganic. The organic mulches are those sourced from nature, either animal residue (manure, stubbles) or agricultural/ forestry domain waste (maize stalks, jowar stalks, groundnut stovers, cotton stovers, and pine needles) or crop cover (live mulch like creepers). Apart from these, traditional components like bark, grass clippings, wood chips, dry leaves, and paper are also accommodated into this class (Smith et al. 1997; Rathore et al. 1998; Kasirajan & Ngouajio 2012; Sathiyamurthy et al. 2017). Basically, they cover their attributes from the formerly living materials. While inorganic mulches are made up of petroleum-based synthetic polymeric sheets: linear low-density polyethylene (LLDPE), ethylene butyl acrylate (EBA), low-density polyethylene (LDPE), and ethylene vinyl acetate (EVA) are some of the commercially used materials in this regard. They are either camouflaged or contrasted with the crop colours but a popularly used economical one in India is black polyethylene sheet (Rollo 1997; Rathore et al. 1998; Lamont 1999; Amin 2001; Hussain & Hamid 2003; Espi et al. 2006; Kasirajan & Ngouajio 2012; Yang et al. 2015; Adhikari et al. 2016; Ajmeri & Ajmeri 2016; Tan et al. 2016; Sharma & Bhardwaj 2017). Nowadays experimentations are also ongoing with biodegradable polymers to control soil contamination caused by these synthetic but non-biodegradable materials (Shogren 2000; Halley et al. 2001; Shogren & David 2006; Kasirajan & Ngouajio 2012).
Adding to the conventionally practiced mulching, nowadays researchers are exploring the feasibility of new types of mulching material. They also fall into the organic category since they are sourced from environmentally friendly natural textile fibres in the form of nonwoven, woven or knitted structures. The fibres tested to date include; jute, coir, cotton waste, wool, palm leaves, bagasse, flax, jute, Alfa, and Agave (Dinu & Saska 2006; Rawal & Anandjiwala 2007; Subaida et al. 2008; Zhang et al. 2008; Bhattacharyya et al. 2009; Pandey 2012; Saha et al. 2012; Luo et al. 2013; Asma 2014; Debnath 2014; Bhavani et al. 2017; Das et al. 2017; Sunilkumar 2017; Manna et al. 2018; Abidi et al. 2019). The entire research domain aimed to synthesise mulches which can serve as substitutes for the harmful plastic for the soil as well as the environment. Thereby either null or least harmful techniques and constituents are preferred in their manufacturing course also. They are usually manufactured by either pure mechanical means; needle punched nonwoven or stitch bonded nonwoven, or produced with a minimum viable add-on of environmentally harmful components via thermal bonding or adhesive bonding techniques (Lamont 1999; Debnath 2014; Das et al. 2017; Manna et al. 2018; Annapoorani & Saranya 2019). Hence, each mulching material possesses specific characteristics. Thereby, the choice of suitable mulching material is usually affected by local climate, cost-effectiveness and feasibility for the crop (Rathore et al. 1998; Lamont 1999; Rawal & Anandjiwala 2007; Debnath 2014; Wang et al. 2015; Marasovi & Kopita 2019). Mohd Za'im et al. (2021) studied that HTMS-treated polyester fabric has great potential as water repellent fabric and it can be used for mulching. A comparative status between two popular categories of mulching has been given in Table 1.
Comparison of mulching
| Subject | Organic Mulching | Inorganic Mulching |
|---|---|---|
| Materials | Traditional: paddy straws, wood chips, leaf, paper Textile Fibres Nonwoven: Jute, Coir, Sisal, Palm leaves, bagasses, Cotton etc. | Traditional: Stones Petroleum-based Polymeric Sheets: Acetate, polyethylene, polymeric material, Sprayable polymer plastic film, LLPE etc. |
| Thickness | 30–50 mm, defined based on crop cycle | 15–20 μm |
| Serviceability Colours Weeding Solarisation Fragments Availability Costing Labour Degradability Plant growth Water infiltration | Temporary and decompose with time Natural Effective but some grass material grows Not effective Degradable to soil adds to nutrient values to the soil Available Easily Cheap Less laborious as required for laying only Naturally decompose and add nutrients to the soil Moderate growth Increases | 2–3 crop seasons Contrast to crop: Black, Red, Silver, yellow, etc. High weed competition except the transparent colour Most effective as boosting soil temperature Contaminates after 1–2 seasons Easily not available Expensive More laborious as required for laying and removing Buried resulted into polluted soil Fast growth and earlier harvesting Restricts water flow |
| Subject | Organic Mulching | Inorganic Mulching |
|---|---|---|
| Materials | Traditional: paddy straws, wood chips, leaf, paper Textile Fibres Nonwoven: Jute, Coir, Sisal, Palm leaves, bagasses, Cotton etc. | Traditional: Stones Petroleum-based Polymeric Sheets: Acetate, polyethylene, polymeric material, Sprayable polymer plastic film, LLPE etc. |
| Thickness | 30–50 mm, defined based on crop cycle | 15–20 μm |
| Serviceability Colours Weeding Solarisation Fragments Availability Costing Labour Degradability Plant growth Water infiltration | Temporary and decompose with time Natural Effective but some grass material grows Not effective Degradable to soil adds to nutrient values to the soil Available Easily Cheap Less laborious as required for laying only Naturally decompose and add nutrients to the soil Moderate growth Increases | 2–3 crop seasons Contrast to crop: Black, Red, Silver, yellow, etc. High weed competition except the transparent colour Most effective as boosting soil temperature Contaminates after 1–2 seasons Easily not available Expensive More laborious as required for laying and removing Buried resulted into polluted soil Fast growth and earlier harvesting Restricts water flow |
Resources: (Debnath 2014; Kader et al. 2017a, 2019; Prem et al. 2020).
It is apparent from the comparison that natural and in that organic-based material meets the objective of mulch in a more ecofriendly-way. This should be considered in the support of a plastic free nation or world for the survival and betterment of living beings in addition to soil safety.
Mulch laying methods and their efficacy in water preservation
Various types of mulching material available to date are laid in the application field mainly by two methods; flat mulching, and ridge-furrow mulching. However, each method has its subgroups in terms of preparation of lay as per the type of crop and soil, but undeniably each is intended to maximise yield along with water and soil erosion preservation (Kader et al. 2017a; Kader et al. 2019; Prem et al. 2020).
Flat mulching
Mulch laying techniques.
Ridge mulching
The ridge mulching is used to harvest rainwater in splash rainfall areas. In ridge mulching the soil is covered with plastic films, here the ridge of soil is covered with plastic mulch, hence it is referred to as ridge mulching. In this technique the ridge channels rainwater into furrows, reducing surface water runoff, thus increasing water use efficiency (Zegada-Lizarazu & Berliner 2011; Gan et al. 2013). Generally, as a ridge mulching inorganic polymeric sheets are utilised. These sheets are applied by ridge-furrow or raised bed systems (Figure 2(III–IV)) for harvesting maximum rainwater (Gan et al. 2013). This system is commonly utilised for crops like potatoes, and corn commonly planted on the ridge part covered with mulch materials (Zhao et al. 2014), and many a time crops are also planted in the furrow part either with mulch or without it.
Water and soil management mechanism of mulching
Steps of mulch laying.
Main types of irrigation system.
This selection plays an important role in water saving by mulching, especially when every drop of water is accounted for. Hence, drip irrigation delivers water slowly to the plant root zones only making them moist without causing water logging, additionally, no water is supplied between rows or non-productive areas, resulting in substantial water saving along with due weed control. Generating a good balance between water and air around roots is necessary for optimal plant growth, and these conditions are well attained. The drop-wise water supply of the system gives great relief to root stress from flooding, drying cycles and fertiliser loss, that's why it has been established as a water efficient system [Figure 4]. Additionally, it can cut down energy costs by as much as 50%, even though it works with high-pressure, high-energy as its counterparts. The statistics published by Natural Resources Conservation Service (NRSC) Irrigation Guide 2020 state that drip irrigation can bring about a remarkable 40–70% water saving for farmers compared to conventional flood irrigation substantiating its efficacy (NRSC 2020). Thereby aggregate saving in water becomes much higher when mulching is done along with the drip irrigation system. The findings of Iqbal et al. (2020), Kader et al. (2019), Ahmad et al. (2015), Ahmad et al. (2020) endorse it well; according to them irrigation requirements of crop plants are reduced with mulches, and sometimes they can totally diminish the need of irrigation. To date, standardised statistics are not published in terms of water consumption quantity during crop cultivation done with and without mulching except for the work done by researchers. Rajbir et al. (2009) studied the influence of drip irrigation at 80% evapotranspiration and polyethylene (black) mulch to compare with surface irrigation, on the growth, yield, water use efficiency and economics of tomatoes. He found drip irrigation with black mulch registered all-time highest fruit yield (57.87 tonnes/ha), much better plant growth along with significantly higher water use efficiency (1.23 tonne/ha-cm) as compared to flood irrigation (29.43 tonnes/ha, 0.42 tonnes/ha-cm) as well as drip irrigation alone (45.57 tonnes/ha, 0.97 tonnes/ha-cm). Thus, drip irrigation with mulching has not only saved water consumption but also resulted in higher fruit yield compared to surface irrigation.
Potential water and soil management benefits with mulching
- i.
Minimising evaporation: The mulch laid on the soil behaves like a moisture barrier and does not allow seepage of soil moisture, thereby this moisture cannot evaporate beneath the mulch film but gets condensed, and goes back into the soil as water droplets. Such moisture is well-retained by the soil for many days, reducing the frequency of water supply or the irrigation demand throughout the crop cultivation period (Kader et al. 2017b). This characteristic of mulching is well realised in the reporting done by various researchers to date. Researchers found that mulches have the ability to retain moisture in the root zone of plants, consequently, water may be accessible for an extended period for the plants. Hydrophobic plastic mulching and inorganic gravels act more as a buffer and are said to be more effective in this regard as compared to hydrophilic cellulosic textile fibre base nonwovens or organic mulching (Smith et al. 1997; Duryea et al. 1999; Koski & Jacobi 2004; Pakdel 2010; Li et al. 2013a, 2013b). Thereby the importance of suitable mulching material selection as per climatic conditions, soil, and crop type should not be disregarded to decrease the irrigation frequency in crop cultivation (Chalker-Scott 2007).
- ii.
Moderation of soil temperature: The mulch insulates the soil and shields it against heat and cold temperatures, the major culprits in restricting overall crop growth. Hence, extreme temperature conditions can adversely impact the growth of the newly developed roots of the plants by dropping the uptake of nutrients and water, and put the plants under stressed conditions (Goulet 1995; Chalker-Scott 2007). Therefore, the sensible maintenance and regulation of soil temperature are crucial for optimum plant growth. It was found that the application of mulch can regulate soil temperature by keeping the soil cool during very hot climatic conditions and warm on chilling winter days (Kudinov 1972; Einert et al. 1975; Fraedrich & Ham 1982; Long et al. 2001; Kader et al. 2019). Temperature control via mulching is relative and influenced by its basic characteristics. In spite of their higher soil water consumption, the cover (live) mulch releases more water vapours through the evapotranspiration process and decreases the soil surface temperature due to its evaporative cooling effect compared to the non-living mulch materials (Montague & Kjelgren 2004). Gravel mulch is proven to be more temperature restraining amongst inorganic solid-type mulch; say as concrete (Iles & Dosmann 1999; Montague & Kjelgren 2004). Synthetic mulches were found incompetent in temperature regulation as these could increase the soil temperature rather than regulating it at a favourable level (Duncan et al. 1992; Litzow & Pellett 1993; Walsh et al. 1996; Montague & Kjelgren 2004; Chalker-Scott 2007; kader et al. 2019). Similarly, hydrophobic natural mulches like pine bark caused the nearest leaves to leak more water through the leaves and increased the soil surface temperature (Zajicek & Heilman 1994). Thereby, the selection of suitable mulch as per climatic conditions and its basic characteristics is far more important. The thickness of the mulch should also be sorted properly, the heavy mulches have shown more positive impacts on temperature maintenance as compared to thin mulch application on soil surface (Van Nierop & White 1958; Horowitz & Thomas 1994).
- iii.
Suppress water-stealing weeds: Germination of seeds as well as weeds is prevented by the mulch as it prevents sunlight from reaching the top layer of soil. So, fewer or no weeds are there to compete with the main crop interest in terms of water and nutrients, as well as to be pulled out, facilitating better growth of the crop by improving soil aeration and drainage along with reduced soil erosion (Sharma & Bhardwaj 2017). Downer & Hodel (2001) reported on the competition provided by the cover crops to the main crop interest in water resources and concluded that mulches have more benefits over the cover crops.
- iv.
Improve water retention capacity of soil: Hence, organic mulches have multifaceted and darker faces; they result in less reflection of light. The rate of evaporation thereby observed with the organic mulches in agricultural lands is less, permitting higher percolation and water retention of soil (Kader et al. 2019). But a higher rate of light reflection is observed with inorganic mulches, especially rocks, thereby they are not found suitable for too sensitive plants. However, both organic and inorganic mulches can serve better in soil water conservation as compared to synthetic and control soil (Kacinski 1951; Arthur & Wang 1999; Lakatos et al. 2000). Generally used mulch materials for soil moisture retention are the livestock wastes, residues of the crop, and different types of stone gravels (Buban et al. 1996; Siipilehto 2001).
- v.
Soil erosion control: The mulching materials cover up the barren soil and act as a buffer against the direct striking impact of wind and rainwater preventing soil erosion, thus enhancing the nutrient status of soil by preventing leaching and more efficient use of fertilisers as well as soil nutrients. Mulch can directly break the kinetic energy of rainwater in hilly areas and increase soil infiltration rate as well as stabilise slope (Chalker-Scott 2007) [90]. Apart from this, it can lessen the compaction of soil caused due to the heavy weight of feet and tires of heavy implements which can adversely affect the roots of crops, and consequently reduce the growth and development of plants. According to the annotations of Donnelly & Shane (1986) mulching should be performed before the development of soil compaction otherwise it will not be helpful in overcoming soil aggregation. The problem of compaction can be well resolved with living mulch materials such as growing grass, and bark, especially on sloppy surfaces as it can aggregate the soil particles by binding in a complex unit (Sartz 1963; Samarappuli & Yogaratnam 1984; Oliveira & Merwin 2001; Tanavud et al. 2001). Borst & Woodburn (1942) reported that soil erosion got reduced by about 86% with the use of 0.6 inches thickness mulch. Similarly, the straw mulch and erosion net combination was also found efficient enough to decrease soil erosion by 95% in comparison to the barren soil in forest areas (Megahan 1974).
- vi.
Soil fertility improvement: Organic mulches and biodegradable plastic mulches ultimately break down in the appropriate environment and add nutrients to the soil surface, improvement in moisture retention capacity and increment in the humus layer. However, these beneficial effects, whether earned or not, and to what extent, are purely influenced by the type of mulch, soil characteristics and climatic conditions. Just for an example; wood chips, straw, green manures, and bark mulches have been found to deliver more nutrients as compared to inorganic mulches (Singh et al. 1991; Pickering & Shepherd 2000; Ansari et al. 2001; Downer & Hodel 2001). However, Chalker-Scott (2007) suggested the preferred use of organic mulches for landscaping and also warned about their extensive use on agricultural lands in spite of their higher nutrient supply capability, as they can damage sensitive crops, living organisms, and water resources.
Water and soil management with and without mulch.
BRIEF SUMMARY OF RESEARCH ABOUT MULCHING
Ahirwar et al. (2019) have studied biodegradable plastic mulch for water conservation in horticulture. They found that the increase in soil temperature under biodegradable plastic mulch was almost equal to that observed under non-degradable plastic mulch; as a result, water consumption remained identical. Regarding yield, no significant difference in total and marketable yield over the season was seen. Four days early yield for melon was required but yield timing for bell pepper has shown no effect. Performance-wise biodegradable plastic mulch behaved similarly to black polyethylene mulch but with the advantage that due to its biodegradation starting in about 45–50 days on laying, its removal from the field at the end of the season is not required. Mulching boosts water preservation in comparison to un-mulched soil; this fact is supported by various researchers irrespective of the type of mulch used (McMillen 2013; Ogundare et al. 2015). Manna et al. (2018) evaluated the effect of different GSMs of nonwoven jute mulches in winter in the dry lateritic soil of Eastern India. They found that the soil moisture was conserved in all GSMs of mulch compared to the control (no mulch). Sardar et al. (2016) analysed the effect of different mulches, viz., plastic sheet, rice straw, grass clippings and sawdust on soil physical conditions, growth and development of Rosa Centifolia. Black plastic mulch was found to be very effective for the maximum conservation of soil moisture. Alapati & Shaik (2018) developed sisal fibres based on a 3 mm thick agro mat structure to use at the nursery level where regular watering is required. They have found that the sisal mulch mat holds good moisture content and thereby conserves 40–50% moisture content of the soil compared to black sheet (PP) and control (un-mulched) samples. Li et al. (2013a) conducted field experiments in the Weibei Highlands of China. They have studied the effects of cultivation with ridge and furrow mulching. Ridges were covered with plastic film in all the treatments and different furrow treatments were mulched with plastic film (PE film), biodegradable film, maize straw, and liquid film. For the control sample, ridges were covered with plastic film and the furrows without mulching. They had observed that ridge and furrow mulching cultivation did not significantly change seasonal evapotranspiration but rather regulated water availability during critical growth stages. Contrasting results are reported about soil moisture retention under different mulching materials. Ogundare et al. (2015) reported plastic mulch has shown superiority over organic mulch. Li et al. (2013b) have conducted a field trial in a dry sub-humid area to study the effect of plastic film and wheat straw mulch on water loss by evaporation under unplanted and cropped conditions as well as water use by transpiration under cropped conditions. They observed plastic mulch was more effective for the conservation of soil water than wheat straw mulch in all situations. For lettuce crop cultivation during dry periods, Jenni et al. (2004) found plastic film to be more effective for conserving soil moisture than paper mulch. Khan et al. (1988) and Begum et al. (2001) found mulching with rice straw to be more effective than plastic mulch in terms of obtaining the highest soil moisture storage. Munn (1992) has compared the effect on soil temperature with various mulching materials as well as bare soil for maize, soybean and tomato cultivation in the USA, and found cooler soil temperature with the highest soil moisture conservation with newspaper mulching. Similar soil moisture behaviour was noted by Daene (2005) and Haapala et al. (2014) with paper mulching treatment, and according to them the reason behind this is the inherent porosity and hygroscopic nature of the paper, which resulted in its expansion and shrinkage with the change in moisture content. Bittellia et al. (2008) and Abouziena & Radwan (2015) stated about highly dynamic moisture change behaviour in the upper surface layer (0–10 cm) of soil due to water vapour fluxes across the soil-atmospheric interface. However, the application of mulch acts as a barrier and reduces the fluctuation of soil moisture and soil temperature (Qin et al. 2018). Debnath (2014) analysed soil moisture retention and erosion control performance of jute woven and nonwoven mulches made of different fabric GSMs and compared them with the bare soil as well as plastic mulch for three vegetables: cauliflower, tomato, and beans, and one fruit sweet lime. Jute nonwoven fabrics of 250 GSM have shown lower permeability and higher water-holding capacity and thereby lower soil temperature than their woven fabrics. Qin et al. (2018) conducted three years of continuous field experiments in the maize field in Northwest China and concluded that the water-saving effect of the plastic mulch mainly occurred during the daytime, but promoted soil water evaporation in the nighttime. Additionally, they proposed that the coating of the covering (mulch) material, can control the energy and water transfer process between soil and atmosphere and thereby enhance the effect of plastic mulch, such as increasing water transfer resistance in the daytime and promoting a warming effect in the nighttime. Going in the same line Decoteau et al. (1988) varied plastic mulch surface colour, black and white, and studied their effects on reflected light and thereby root-zone temperature in the tomato plant growth. The soil temperature was measured 2.5 cm below the mulch, and found 1 °C higher temperature within the biologically acceptable range for tomatoes for black surface colour than white. Rudich et al. (1978) have carried out drip irrigation experiments under conditions of mulching and plastic tunnels to see the responses of muskmelon and watermelon plants to irrigation during different growth stages. They observed that neither crop was affected by irrigation applied during the stages of vegetative growth, flowering, or fruit set. However, irrigation in the fruit development stage, which continues for about a month with watermelon and 1.5 months with muskmelon, resulted in increases in yield. Irrigation during fruit development did not affect fruit quality. Ahmed et al. (2013) conducted field trials at the National Cereals Research Institute, Badeggi to compare the effect of coloured polyethylene mulch and one without mulch as a control on the growth and yield of industrial sugarcane of a variety NCS 008 in Nigeria. Their results show that polyethylene mulch increases soil temperatures and accelerates plant growth and development which gives better sugarcane yield compared to the plants in the control plots. Therefore, the use of polyethylene coloured mulch for industrial sugarcane should be encouraged in estates, especially in areas where the annual rainfall duration is short to enable the crop to utilise the maximum water available. Chavan et al. (2010) have observed the maximum soil moisture and minimum soil temperature were obtained in case of the sugarcane trash mulch compared with wheat straw mulch, soybean straw mulch and intercropping over no mulch for the rabi sorghum grain.
Advantages and disadvantages associated with mulching
It is apparent from the above mentioned outputs of various research that the choice of mulching material and its method of laying is greatly influenced by crop type, soil type, weather conditions and definitely water management practices. The appropriate selection of mulching techniques could be fruitful for agro-ecological systems. However, each system undergoes contradictions; accordingly for mulch materials some researchers also favoured mulches and others have pointed out the damaging effects caused by mulches (Bedford & Pickering 1919; Patil et al. 2013; Kader et al. 2017a; Ahirwar et al. 2019; Ngosong et al. 2019; Ajmeri et al.; Iqbal et al. 2020; Prem et al. 2020). They are briefly summarised in Table 2.
Advantages and disadvantages of mulching
| Benefits | Drawbacks | |
|---|---|---|
| Natural Material-based: I) organic mulch | Reflects solar radiation. Reduces water evaporation rate and keeps soil cool. Prevent germination. Reduces runoff, increases moisture retaining power of soil. Improves infiltration and percolation of water. Restrict weed growth and prevent soil erosion. Increase the soil nutrients. | Restricts oxygen supply nearby the root region of poorly drained soil due to more moisture retention. If mulching is done close to the stem, moisture in the stem of the plant can create habitat for various microorganisms and diseases. Mulches like grass clipping, grain straw, cotton waste etc. having seed can encourage germination of weeds. |
| ii) Inorganic mulch | Cost efficient because they cannot be replaced frequently. More durable compared to organic mulches because they do not degrade early. Conserves soil moisture, saves time. Control the growth of the weeds. Maintains soil temperature, Prevents attack of insects and diseases. | Inorganic mulches, except in biodegradable plastic mulches, do not augment any nutrient to the soil because they do not decompose. Increase temperature of soil if established in large areas. Rubber mulch may harm plants as it is toxic in nature. |
| Synthetic material-based | Totally impervious to water. Reduces the rate of evaporation. Improves moisture holding capacity. It stops the rise of water containing salts, repels insects and pests. Prevents weed growth. Maintain soil structure and reduce soil erosion. Increase the crop germination speed. | Economically less viable compared to organic mulches. Black mulch can develop the risk of scorching of early plants because of increased temperature. Toxic for animals. Hinder development of roots of the succeeding crop. Continuous use of plastic mulch for successive 5–20 years can result in 122–146% increase in salt content of topsoil. |
| Benefits | Drawbacks | |
|---|---|---|
| Natural Material-based: I) organic mulch | Reflects solar radiation. Reduces water evaporation rate and keeps soil cool. Prevent germination. Reduces runoff, increases moisture retaining power of soil. Improves infiltration and percolation of water. Restrict weed growth and prevent soil erosion. Increase the soil nutrients. | Restricts oxygen supply nearby the root region of poorly drained soil due to more moisture retention. If mulching is done close to the stem, moisture in the stem of the plant can create habitat for various microorganisms and diseases. Mulches like grass clipping, grain straw, cotton waste etc. having seed can encourage germination of weeds. |
| ii) Inorganic mulch | Cost efficient because they cannot be replaced frequently. More durable compared to organic mulches because they do not degrade early. Conserves soil moisture, saves time. Control the growth of the weeds. Maintains soil temperature, Prevents attack of insects and diseases. | Inorganic mulches, except in biodegradable plastic mulches, do not augment any nutrient to the soil because they do not decompose. Increase temperature of soil if established in large areas. Rubber mulch may harm plants as it is toxic in nature. |
| Synthetic material-based | Totally impervious to water. Reduces the rate of evaporation. Improves moisture holding capacity. It stops the rise of water containing salts, repels insects and pests. Prevents weed growth. Maintain soil structure and reduce soil erosion. Increase the crop germination speed. | Economically less viable compared to organic mulches. Black mulch can develop the risk of scorching of early plants because of increased temperature. Toxic for animals. Hinder development of roots of the succeeding crop. Continuous use of plastic mulch for successive 5–20 years can result in 122–146% increase in salt content of topsoil. |
Novel sustainable mulching approach
This deals with the preparation of natural fibre-based mulching with additives. These additives can be fertiliser, antifungal matter, pesticides, and UV protector. They can be used as per the need of the healthy crop yield, and may be one or a combination of more than one functionality at a time. They can be resourced from nature; plants: Azadirachta indica, Calotropis gigantea; waste: used tea leave etc. via green nano synthesis (Shaikh et al. 2017; Radadiya et al. 2021). Their incorporation in mulching can be done at a micro or nano level without hampering its aesthetic. It releases nano/micro soil nutrients in a metered way and enhances soil fertility apart from the benefit of water conservation. Thus, it can become an economical sustainable tool for agro-ecology.
5. SUMMARY
Globally, mankind is facing increasing threats of fresh water shortages due to increased population count, deforestation, urbanisation and industrialisation. At the same time, the freshwater supply chain becomes vulnerable due to unpredictable climatic changes inviting frequent drought and floods, which directly or indirectly affect water and energy consumption in the agriculture sector.
Mulching in such a scenario emerged as a very useful practice, especially in low rainfall regions by limiting water usage wisely in the agriculture sector which is accounted as the biggest consumer of water. The successful application of natural and synthetic mulching has been practiced in farms, horticulture, nursery and landscapes to date. In today's world natural textile fibres as well as the textile belonging to the organic category in various forms has potential application in the area of mulching. This exercise will support the nation to become plastic free, a major source for contamination of the soil as well as hazardous to the environment.
Mulches have resulted in reduced soil evaporation, soil moisture conservation, suppressed weed growth, controlled soil structure and temperature, positively contributed to soil microorganisms, increased yield with better fruit quality, and above all sound aesthetically pleasing with the least usage of irrigation water.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.
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