Rural Industries Research & Development Corporation

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Introduction

A botanical novelty ten years ago, although in its wild form it was reputedly harvested by Aboriginals, it is now produced and marketed commercially in Australia, substituting for the importation of canned produce. For Australia, the Australian produce has the advantage of being marketed fresh (the tinned product lacks quality and consumer appeal) but it is only available over the period June to November, thereby limiting the effectiveness of import substitution.

Premium Australian waterchestnuts are > 4.0 cm in diameter (Photo 1), and better than those from traditional production zones in Thailand (Suphanburi), China (Guai Lin) and Taiwan (Tainan County); but according to connoisseurs, Australian produce at times lacks sweetness and tastes starchy. The crispy texture, which is retained after processing or cooking, is due to the presence of the ferulic acid-containing hemicelluloses in cell walls of the chestnuts. The product is favoured for `fresh' stir-fry mixes, and currently the tinned form is used to supply this product line in supermarkets. It also forms the basis for heavily sweetened drinks in Asia, and is sold in syrup for use as a desert.

A tradition of production in Taiwan and China and the recent introduction of a canning industry in Thailand underpin the world trade in waterchestnut, and the US is the major importer of the canned form.

To assist new and prospective growers, an Australian Aquatic Vegetables Development Committee (Midmore, 1997) has been established to provide information on cooperative establishment of quality assurance, grading, marketing opportunities and coordination of planting and production goals.

Markets and marketing issues

Current levels of canned imports into Australia are unknown because ABS data are pooled with those of true chestnuts and retailers prefer not to divulge such information. Retail prices for canned chestnuts (approx. 90 cents/227 g [gross] tin) are similar to, or less than those in Asian countries—Singapore A$1.20/340g (gross); Thailand A$1.25/227g (gross)—and wholesale prices of canned waterchestnut in Australia (48 cents to 79 cents/230g [gross]) convert to $3.7 to
$6.0/kg of net waterchestnut. Current retail prices of fresh Australian waterchestnuts range from $4.00 to $12.00/kg, which is highly competitive with the net retail cost of canned produce.

The current production in Australia is ca. 20 tonnes per year, with the bulk coming from Mackay and the balance from NSW and Victoria. Most product is marketed through supermarket chains, while small-scale production is sold via country markets. Production in Japan is on the decline (1600 tonnes in 1984 to 1200 tonnes in 1992) as it is in Taiwan (1200 tonnes in 1991 to 860 in 1995).

The best retail prices are gained in Japan from September to December, ranging from A$9.0 to A$30.0/kg while in Taiwan retail price is quite stable at A$6.0/kg, double that of the farm-gate price. Australian production currently pales into insignificance compared with that of Japan and Taiwan, and with that of China which dominates the supply of canned and semi-preserved waterchestnuts to the USA.

Approximately US $35 million as canned and US $8 million as semi-preserved product was imported to the USA in 1996. With an established and potentially larger national market, it is opportune to embark upon export ventures, especially now that the Australian industry draws upon four mechanised harvesting systems which considerably reduce the labour for the crop.
 

Production requirements

Although clay soils favour water retention and puddling, they present serious drawbacks for some harvest systems, particularly since they need more labour for hand-harvesting. In such instances, producers may add sand or composted filter press mud (from sugar mills) to clay soils to ease the harvest burden.

Since the crop is grown in an almost entirely flooded condition, flat or terraced land is necessary. Access to irrigation that will replenish at least the evaporative demand (measured as pan evaporation at standard weather stations) is essential if rainfall during the cultivation season does not exceed evaporation. Often an inland species in the wild, cultivated waterchestnut does not tolerate irrigation water salinity values of greater than 3.3 dS/m without loss of germination and corm yield.

The crop is customarily grown in a sub-tropical to temperate climate, planted in the spring where the growing temperature of 15°C-25° can be maintained, and senescing in autumn in response to plant maturity rather than as a response to low temperature. Generally a 220 day frost-free period is necessary for natural completion of the crop cycle. High daytime air temperature (ca 30°C) favours growth of the crop. Current and potential production areas in Australia are demarcated on the accompanying map.

Varieties

On various occasions superior cultivated lines have been imported to Australia. A summary of the officially reported imports and acquisitions is shown in Table 1. The distinction between varieties currently cultivated is all but lost, and a project is under way to identify cultivated lines using the technique of DNA-based genetic finger-printing. This is of primary importance to maintain quality standards for local and export markets. Prospective growers should be aware of the genetic identity of the material to be planted. It is possible that some lines are more suited to the climatic conditions of Victoria as opposed to those of Queensland, but without clear identification of lines this cannot be confirmed.
 

Agronomy

Corms sprout as ground and water temperature rise above 13°C, and this may be hastened under nursery conditions in cooler climates by the judicious use of clear polyethylene sheet covers. Following direct planting to the wet field, at a depth not exceeding 4 cm, the field is flooded and allowed to drain naturally. Further flooding may be undertaken within three weeks, or when stems are 20 to 30 cm tall. Deeper flooding will usually cool the environment around the corm and delay germination, hence shallow flooding is to be favoured in southern climates, both for plant establishment and during the grand period of growth.

Corms in nurseries are treated similarly to those in the field, and germinate approximately 10 days after planting. They are transplanted into moist or flooded ponds when they reach 20 to 30 cm height, and the tops may be trimmed before transplanting if to tall. Crops from transplants in temperate climates will usually mature 5–6 weeks earlier than crops directly planted to the field on the same date as transplanting. This difference diminishes where temperature, especially at night, is more equable year-round.

Plant spacing in the field depends largely upon climate and planting date (more southerly climates and/or later planting reduces opportunity for rhizome and daughter plant production, therefore should be at closer spacing), but soil fertility and level of fertiliser input will govern plant vigour, and plant spacing should be adjusted accordingly. On average between three and five transplants (or corms) are planted per one square metre, with a triangular arrangement often preferred.

Once established, the crop is continually maintained in a flooded condition, even during the application of the remainder of the inorganic fertiliser, which should conveniently be split and applied eight to ten weeks after planting as the secondary (daughter) plants appear, and just before the development of corms. The application rates of fertiliser is very site-specific, depending upon the natural and organic manure sources of nutrients. Seeding the pond with the water fern Azolla can reduce the overall need for N fertiliser in the subsequent crop. The nitrogen-fixing fern can fix about 50 kg N ha/yr. Azolla is also seeded with the intention of reducing excess soluble nitrogen in ponds and pond water, but the validity of this practice has not been verified. As a rough guide, a waterchestnut crop removes 240 kg N/ha, 33 kg P/ha, 460 kg K/ha, 12 kg Ca/ha and 50 kg Mg/ha; approximately one third to one half of this removal is in the corms. These nutrients must be replenished to minimise ‘mining’ of soil nutrients. Nitrogen fertiliser is best applied in the NH4+ (ammonium) form, for this is the favoured form for uptake by waterchestnut, and is less easily leached than the NO3– (nitrate) form.

The crop requires very little attention after planting other than the fertiliser applications and prophylactic pest/disease control. Once corms have formed they are susceptible to damage from trampling in the field, and the canopy of the crop, (actually the stems as the plants have no true leaves) is so dense as to prevent physical entry to the field without fear of lodging and loss of photosynthetic activity. Stems should as far as possible be kept free from damage by wind, herbivores, and pests and diseases.

Farm-level yields in Australia reach >20 t/ ha but maximum marketable yields (ie. > 2.5 cm corm diameter) are less than
20 t/ha. These values are similar to those reported for China, although small plot yields of up to 40 t/ha have been reported in Australia.
 

Pests and diseases and their control

Insect pests of waterchestnut are known, but with few exceptions are not devastating. Green and long-horned grasshopper and snout moth larvae bite the bases of stems and the rice water weevil (Lissorhoptrus oryzophilus) damages corms, as do mole crickets (Gryllotalpa sp.). Stem damage may be prevented by use of Lorsban 500EC but there is no easy remedy for corm damage in the field.

In 1997 outbreaks of Nisia grandiceps (a sucking insect) and Scirpophaga (a moth species) were reported, and also controlled by use of Lorsban 500 RC. A rust (Uromyces sp.) attacks waterchestnut, and is controlled in its early stages by sulphur dust. Stem blight present on acid soils (pH 5.5) caused by Cylindrosporium eleocharidis (Lentz) is chemically controlled by corm dressings or spray with Benomyl, Thiophanate and Amban, and can be controlled by rotation with non-host crops. Waterchestnut wilt, reported in China and caused by a specific race of Fusarium oxysporum, is not present in Australia, which reinforces the need to maintain effective quarantine protocols for the import of fresh waterchestnut materials.

Ducks are a major worry to some producers (30% of respondents in an industry survey) and netting, sound and lights are effectively used to reduce damage. Bandicoots and mice also cause damage to corms if ponds have been drained.
 

Harvest, handling and postharvest

In-field storage can extend the harvest period, but once temperatures around the corms rise to 13°C, shoot formation occurs and the retail attractiveness of the corms is reduced.

Waterchestnuts are readily bruised during harvest, leading to saprophytic fungal and bacterial activity and at times fermentation; so they must be handled with care. Following harvest, corms are washed, cleaned, and graded by size according to market outlet. Likewise, packaging form and size also depends on market outlet, with types ranging from 200 g plastic bags to 5 kg cartons. Currently corms are not graded for sweetness, but within three years a new non-invasive near infra-red apparatus will probably provide this service to producers and their customers.

Cool storage is essential for the holding of produce in Queensland, while ambient winter temperature storage suffices in Victoria and the south of NSW for short periods. Air-dried sound corms may be stored for up to six months at 1–4°C, and surface sterilising with sodium hypochlorite reputedly extends that period. A small proportion of the harvest is saved for next year’s crop, and is usually stored in this manner. To gain chain-store markets for fresh produce in Australia, it is important to have it available throughout the year—hence the interest in extending the storage life of fresh waterchestnut.
Currently no large-scale peeling of Australian produce is undertaken, although core punching of small waterchestnuts is used as a means of value-adding for the low-priced small-size category. A range of bottled produce, at the cottage industry level, is niche-marketed.
 

Economics of production

Research imperatives

Key contacts

Greg Cahill
Dept. National Resources and Environment Victoria
Bendigo Agriculture Centre
Box 2500
Bendigo Delivery Centre,
Vic. 3654

Michael Coles
Australian Waterchestnut Producers Association
P.O. Box 169
Maldon, Vic 3463

Hans Erken
Earthcare Enterprises
P.O. Box 500
Maleny, Qld 4552

Greg Gunning
Gunnings Australian Waterchestnut
P.O. Box 897
Mackay, Qld 4740

Geoff Lodge
Murray Valley Waterchestnut Growers Group
RMB 1235
Murchison North, Vic. 3610
Email:lodgeg@netc.net.au

Daryl Trott
Aquanut
RSD 813
Spring Hill Road
Lauriston, Vic. 3444
 

Key references

Cahill, G. 1997 Australian Waterchestnut Industry. Outcomes of Producer Survey and National Industry Workshop. Mimeograph. 23 pp.

Hodge, W.H. and Bisset, D.A. 1955 The Chinese Waterchestnut. Circular 956, US Dept. Agric., Washington, DC.

Morton, J.F., Sanchez, C.A. and Synder, G.H. 1998 Chinese Waterchestnuts in Florida—past, present, and future. Proc. Fla. State Hort. Soc., 101, 139–144.

Midmore, D.J. 1997 Putting the ‘Australian’ into waterchestnuts. New Crops Newsletter, 8, 19–20.
 
 

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