Coconut coir: Consistency in quality

Dr. N.Yogaratnam, Chairman, Tree Crops Agro Consultants

In 1949, E. P. Hume wrote an article in the Journal Economic Botany, extolling the horticultural virtues of a by-product of the coconut husk fibre processing industry. Coir is the name given to the fibrous material that constitutes the thick mesocarp (middle layer) of the coconut fruit (Cocos nucifera).

The long fibers of coir are extracted from the coconut husk and utilized in the manufacture of brushes, automobile seats and mattress stuffing, drainage pipe filters, twine and other products.

Traditionally, the short fibers (2mm or less) and dust (“pith”) left behind have accumulated as a waste product for which no industrial use had been discovered.

The excellent growth obtained with various plants when this coir dust or, as was called, “cocopeat,” was used as the growing medium (this word has now been registered as a trademark by one manufacturer of the material).

It is only in the last 15 to 20 years that this has percolated through the often conservative ways of international horticulture. In the 1970s and 80s, initial tests in Australia and Europe indicated that coir dust could function remarkably well as a substitute for various peat products in soil-less container media for plant growth.

Several Dutch companies have in fact been using coconut coir dust in production media since the 1980s, and the Royal Botanic Gardens at Kew has been shifting most of its plant production into coir dust-based media.

Sri Lanka (where over 2.5 billion coconut fruits are processed each year) has become the leading processor of what had previously been considered a waste product into a form suitable for horticultural use.

While other sources may be available, companies in Sri Lanka have invested heavily in an infrastructure to guarantee consistency and quality of the product, though this still lacks perfection.

Problems that can occur with coir dust where attention to quality control is not a priority include contamination with animal manures (with the attendant possibility of salmonella) and excess salinity.

The former can be a problem in countries, where cows often range free. The latter can occur anywhere where “green” coconuts are harvested for coir extraction.

Unripe nuts are usually soaked in brine to make the fibre easier to extract, while fresh water is used with fully ripe coconuts.

Coir dust accumulates in large piles or “dumps” outside of the mills which process the husks for extraction of the industrially valuable long fibers.

The high lignin and cellulose content of the pith prevents the piles from breaking down further.

Some of the piles in Sri Lanka are reportedly a century old!

It is this same characteristic that prevents oxidation and resultant shrinkage of coir dust when it is used as a growing medium.

It had been reported that the superior (and much more expensive) sphagnum peat has shown wide swings in both price and availability in the last decade. Subsequently, it was considered that a high quality peat alternative that is consistently available and also satisfies heightened environmental concerns would be a “natural” in the market place.

Coir dust fitted into this requirement and was considered as a cheaper substitute and effective in performance.

Compared to Asia, there was little coir production in tropical America, and, consequently, low supplies of coir dust. Growing acceptance of the material in the horticultural market place has changed this, and we now see start-up companies in the west attempting to compete with Sri Lanka, India and the Philippines.

Quality parameters

The following qualities of coir dust have been recognized by the agricultural and horticultural industries for their use: 1) high water holding capacity, 2) excellent drainage, 3) absence of weeds and pathogens, 4) greater physical resiliency (withstands compression of baling), 5) renewable resource; no ecological drawbacks to its use, 6) decomposes more slowly , 7) acceptable pH, cation exchange capacity and electrical conductivity, and 8) easier wetability.

Coir dust may well be a product that will have huge potential in agriculture and horticulture.

The key issues in developing widespread use of this material in horticulture will be price and insuring consistent quality of the coir dusts that enter the market.

Recently there have been numerous complaints regarding inconsistency in the quality of the products supplied to overseas markets, in terms of performance in the farm.

Variation in quality

Although Sri Lanka is the leading manufacturer of horticultural substrates derived from coir dust, other countries in Asia, Africa are also major coconut producers and processors.

Yet, research into variation in coir dust properties and the study of its potential for use in horticulture is scarce and incomplete and most of the results of these studies in general are inconsistent.

Manual Abad reported in 2007, the results of their studies done to characterize the main physico-chemical and chemical properties of 13 coconut coir dusts from different sources. Samples from Costa Rica, India, Ivory Coast, Mexico, Sri Lanka and Thailand were used in this study.

Based on this study, they concluded that the physico-chemical and chemical properties studied, Viz pH, Electrical conductivity, CEC, Organic matter content, C/N ratio, Cellulose, Hemi-cellulose, Lignin, Nutrients; N,P, K, Ca, Mg, Cl, SO4 and Na differed significantly between and within the coir dust sources tested.

They argue that the variability was probably due to differences in the raw coconut fruit, the husk processing method applied to remove fibre, and the stock piling period of the coir dust.

Michael R. Evans (1996), studying source variation, reported that chemical properties of 12 sources of coconut coir dust from Philippines, Sri Lanka and Indonesia viz. pH, and EC were significantly different among sources. But, no significant differences occurred among samples with respect to, Fe, Mn, Zn, B, Cu, NH4- N and Mg, although significant differences occurred between sources for Ca, Na, and NO3- n. The widest range recorded by them was for K and Cl. Sources also differed with respect to CEC from 38.9 to 60.0 meq/ 100g.

Coconut husk and processing effects on chemical properties of coir dust was studied by Sreenivas Konduru (1990), and they also reported similar differences, although there were variations in some parameters.

It is not clear as to how raw coconut fruit source, husk processing method and coir dust age affect both physico-chemical and chemical properties of coir fibre dust. If this is known, a consistent product with acceptable characteristics may be made available.

In another report, Alan W Meerow (An Associate Professor) has reported in 1993, that coir dust tends to be high in both sodium (Na) and potassium (K), compared to other peats, but Na is leached readily from the material under irrigation.

The high levels of K present in coir dust are interesting to note, and may actually prove more a benefit than any detriment to plant growth.

Coir dust from sources other than Sri Lanka have also reportedly contained chlorides at levels toxic to many plants, thus it is very important that salinity in the raw material be monitored before processing into a horticultural amendment.

pH, another quality determinant of coir dust, if at high level, may allow less lime to be added to a coir dust-based medium, though adding lime to container soils is important for Ca and Mg nutrition than elevating pH.

A small amount of nitrogen drawn occurred with coir dust, but typical production fertilization practices would likely compensate for the small amount of resulting N loss.

Although at present, it is unclear, yet it is important that fertilization regimes need to be manipulated, in media composed chiefly of coir dust.

SAR Tharanga, from Sri Lanka, reported in 2005, the results of their study on variation in chemical are physical properties of raw coir dust with reference to age, origin and extraction method.

They concluded based in this study that salinity ( Electrica Conductivity (EC)) reduced with aging but increased with reducing particle size. The ionic composition varied among areas of origin with no relationship with the other chemical properties.

Aging reduced the particle size distribution ( PSD). Even through other physical properties were closely related with PSD, aging had no significant effect on these parameters. However, aging negatively influenced the expansion characteristics of coir dust.

Although, the method of fibre extraction, influenced PSD, it had no effect on expansion property. It was concluded that coir dust from areas within safety margins as given in Sri Lanka standards specification with regard to salinity ( EC) and alkalinity ( pH) are suitable.

Use of new coconut husk with favourable chemical properties and extracted through decorticator method might provide raw coir dust for the production of good quality value-added growing medium.

However, frequent watering may be required to overcome lower Water Holding Capacity (WHC) and to wash out tannins present in the new coir pith.