This page provides information on coir (coconut coir). While providing extensive information on coir, there is a section focused specifically on stormwater applications for coir.
Coconut (Cocus nucifera L.) pith or coir, the mesocarp of the fruit, is a waste product that has potential benefits in growth media, including engineered media used in stormwater applications. Coir dust is peat-like and consists of short fibres (< 2 cm). Coir has a large surface area per unit volume, is hydrophilic, and therefore has the ability to absorb water. It's primary components are lignin and cellulose, each making up about 45% of coir's dry weight. Water soluble fractions typically account for about 5% of coir, by weight (Ministry of MSME, Government of India, 2016; Alam, accessed from https://textilelearner.blogspot.com/2014/01/properties-of-coconutcoir-fiber.html on 2/13/20).
There are three basic types of coir material.
Coir production involves separating the husk from the shelled nut and soaking the husk in water. The fibers are then separated from the pith and the resulting material is screened to create a uniform particle size. A dust is created during this process and the dust may be air dried and packaged. Prematurely harvested (green) fruits are often soaked in a saline solution to facilitate the separation process, which in turn affects the chemical properties of the resulting coir dust.
Coir benefits may include but are not limited to the following.
Coir has potential applications for stormwater management. Below is a brief summary.
Beyond erosion control and turf establishment, additional research is needed to identify specific applications in stormwater management.
This section includes a discussion of chemical and physical properties of coir, and potential contaminants in coir.
The physical and chemical properties of coir vary with particle size. Noguera et al. (2003) varied particle size of coir dust, studying the properties of coir passing through sieves 0.125, 0.25, 0.5, 1.0, and 2.0 mm in diameter. They observed the following.
Based on generally recommended plant specifications, the researchers concluded the 0.25-0.5 mm size appears most suited for plant growth, with some addition of larger particles recommended. Abad et al. (2005) similarly concluded that a mix of particle sizes is likely to be optimum for use of coir as a plant medium.
Another factor affecting chemical properties of coir are the conditions under which it is prepared. In particular, if soaking in a saline solution is used in the preparation of coir, concentrations of potassium, sodium, chloride can be very high and may interfere with plant growth.
The following table summarizes data from the literature on physical and chemical properties of coir. Some general conclusions include the following.
Chemical and physical properties of coir.
Link to this table
|Property||Range found in literature1||Median value from literature|
|Total phosphorus (% dry wt)||0.036 - 0.41||0.036|
|Total nitrogen (% dry wt)||0.24 - 0.5||0.45|
|Total potassium (% dry wt)||0.4 - 2.39||0.819|
|Total carbon (%)||42 - 49||47.1|
|Total hydrogen (%)||4.4|
|pH||4.9 - 6.9||5.9|
|Cation exchange capacity (cmol/kg)||31.7 - 130||50|
|Electrical conductivity (ds/m)||39 - 2900||582|
|Total calcium (%)||0.18-0.47||0.40|
|Total magnesium (%)||0.11-0.47||0.36|
|Total copper (mg/kg)||3.1-10.3||4.2|
|Total zinc (mg/kg)||4.0-9.8||7.5|
|Total manganese (mg/kg)||12.5-92||17|
|Bulk density (g/cm3)||0.025 - 0.132||0.06|
|Water holding capacity (% by wt)||137 - 1100||566|
|Total pore space (%)||85.5 - 98.3||95.2|
Primary references for this data:
There are few concerns with contaminants in coir. For coir prepared with saline solutions, sodium and chloride will be elevated and possibly at levels of concern for plants if the coir is not washed. Polyphenols and phenolic acids in coir can be phytotoxic and inhibit plant growth when coir is used without other amendments such as fertilizer or compost (Ministry of MSME, Government of India, 2016). Metal concentrations are well below Tier 1 Soil Reference Values. Organic contaminants, such as polycyclic aromatic hydrocarbons, are not a concern.
In this section we provide information on effects of coir on pollutant attenuation and on physical properties of soil and engineered media.
There are limited studies on coir retention of phosphorus at concentrations typically found in stormwater runoff (less than 0.5 mg/L). Adsorption studies show that phosphorus adsorption at higher concentrations (greater than 1 mg/L) occurs through ion exchange and chemisorption being mechanisms for adsorption, with sulfate competing with phosphate for adsorption sites)(Takaijudin and Ghani, 2014; Kumar et al., 2010; Namasivayam and Sangeetha, 2004).
Shrestha et al. (2019) studied phosphorus leaching from columns containing mixtures of soil, compost, spent lime, and coir. Using tap water with no detectable phosphorus, they observed that adding coir (10% by weight) to a 70-20 soil-compost mix did not decrease phosphorus leaching compared to an 80-20 soil-compost mix. Similar results were observed for media with 40% compost. Hongpakdee and Ruamrungsri (2015) observed reduced phosphorus leaching at the flowering stage, possibly due to increased plant vigor and uptake in treatments containing coir. Herrera Environmental Consultants (2015) conducting flushing and leaching experiments for a variety of media mixtures, including mixtures containing coir. Mixtures of coir and granular activated carbon (GAC) or ash showed orthophosphorus concentrations of 0.021 and 0.052 mg/L, respectively, when flushed with solutions containing less than 0.004 mg/L. For leaching experiments, influent orthophosphate concentrations were 0.323 mg/L and effluent concentrations for coir-GAC and coir-ash mixtures were 0.025 and 0.164 mg/L, respectively. However, the researchers attributed retention of phosphorus to the GAC and ash rather than coir. The researchers also observed decreasing orthophosphorus leachate concentrations with time.
Additional research is needed to understand the phosphorus retention or leaching from media containing coir. Research to date suggests coir will not retain phosphorus in stormwater runoff but will not significantly contribute to leaching from engineered media.
There is limited research on retention and leaching of pollutants from coir. Shrestha et al. (2019) observed that media containing coir performed similar to spent lime for ammonium and nitrate retention and leached significantly less of these chemicals than treatments containing compost. Herrera Environmental Consultants (2015) observed similar results and also observed that mixtures of coir and either granular activated carbon or ash reduced copper and zinc leaching compared to media mixtures consisting of just soil and compost. Because concentrations of potential pollutants are low in coir, leaching at concentrations of concern appears unlikely. An exception is coir that was soaked in salt water, which may contribute to high sodium, potassium, and chloride concentrations.
Coir has several properties that may improve soil physical and hydraulic properties (Cresswell; Noguera et al., 2003; Abad et al., 2005; Small et al., 2018; Lodolini et al., 2018; Arachchi and Somasiri, 1997).
|Advantages of coir over peat (Source:Ministry of MSME, Government of India. 2016)|
|Requires lesser amount of lime due to high pH|
|Quick and easy rewetting after drying, while peat becomes hydrophobic on drying|
|Requires short time for irrigation to replace loss of water and drainage from pot, saving fertilizer due to non leaching of nutrients|
|Higher capillary wetting property|
|Able to provide aeration in base of mix|
|Very resilient and exceptional physical stability when wet or dried|
Pure coir is not suitable for plant growth. It has a high C:N ratio (>100) and a high lignin content, resulting in slow decomposition and immobilization of plant nutrients. In addition, polyphenols and phenolics acids in the coir can be phytotoxic and inhibit plant growth (Ministry of MSME, Government of India, 2016).
When composted and added as an amendment to a growing media, coir improves plant growth, with coir outperforming peat in several studies. In the absence of composting, nitrogen and phosphorus additions will likely be necessary, depending on plant requirements. Calcium and magnesium additions may also be needed. Concentrations of other nutrients and micronutrients are generally acceptable for most plant species (Cresswell; Asiah et al., 2004; Noguera et al., 2003; Abad et al., 2002; Meerow, 1997; Lodolini et al., 2017; Hongpakdee and Ruamrungsri, 2015; Small et al., 2015; Scagel, 2003; Arachchi and Somasiri, 1997). Noguera et al. (2003) showed that, based on generally recommended plant specifications, 0.25-0.5 mm diameter coir particles appear most suited for plant growth, with some addition of larger particles recommended. Abad et al. (2005) similarly recommended a mix of particle sizes.
|Recommended values for coir used in a growth media (Source: see reference list in this section)|
|pH||5.2 - 6.8|
|Electrical conductivity (ms/cm)||0.50 – 1.20 (lower part of range typically preferred)|
|Cation exchange capacity (meq/100g)||20 - 40|
|Copper (% minimum)||1.5|
|C:N ratio (minimum)||110|
|Lignin (%)||30 - 35|
|Total organic matter (% minimum)||75|
|Moisture (%)||15 - 20|
|Ash content (%)||1.0 - 1.5|
|Expansion||> 12 l/kg|
|Water holding capacity||3-4 l/kg|
Recommended specifications for coir when used in a growing media are shown in the adjacent table and include the following.
Coir should be composted or incorporated into media containing a nutrient (N and P) source, such as compost. Alternatively, liming or addition of microorganisms may enhance decomposition of coir, which subsequently aids in release of nutrients from the coir. The Ministry of MSME, Government of India (2016) provide a discussion of different composting materials and methods, including specifications.
References containing specifications are provided below. Note that most of these references include information on the packaged material (e.g. bags, blocks, briquettes), such as weight and size.
Distributors of coir for use in bioretention media (e.g. horticultural use) can readily be found on the internet and we do not make specific recommendations. When purchasing coir, the following questions should be asked.
Packaged coir is typically tested and meets specifications as described above. Standardized testing does not appear to exist for coir, but several methods for testing different characteristics appear to be appropriate.
The following references provide information on testing of coir.
Coir has a high C:N ratio, ranging from 75 to 186, with a median of 115 (Abad et al., 2002; Abad et al., 2005; Shrestha et al., 2019; Meerow, 1997; Arenas et al., 2002). It also contains a high lignin content and therefore decomposes relatively slowly unless nutrients, primarily nitrogen and phosphorus, are added to the media (Amlan and Devi, 2001). Composting is recommended to increase nutrient availability, which in turn may increase the rate of decomposition. Similarly, liming or addition of specific microorganisms can enhance decomposition (Prabhu and Thomas, 2002). Even when decomposition is facilitated, the life expectancy of coir exceeds two years (Newman 2007).
Prabhu and Thomas (2002) provide an extensive discussion of coir decomposition.
There are few handling concerns. Dust may be an eye irritant. Examples of material and safety data sheets can be found at the following links.
Coir dust is a sustainable alternative to peat. Historically, little coir has been utilized and has therefore been disposed as a waste. Prabhu and Thomas (2002), for example, estimated that in India alone, 1.5 million tonnes of coir pith could be obtained annually but only 500,000 were produced at the time of their study. More recently coir production in India has been estimated at about 1 million tonnes annually (Ministry of MSME, Government of India, 2016). Studies are underway to expand existing markets and develop technologies for manufacturing coir dust from coir fiber (Praveenkumar and Agamoorthi 2017; Varma, 2018).