Improving food safety in Vietnam using soilless vegetable production

S. E. Parks and S. M. Newman, L. M. Pham, H. T. Ngo and T. K. Thi
National Centre for Greenhouse Horticulture, Fruit and Vegetable Research Institute
NSW Department of Primary Industries, Hanoi, Vietnam
Gosford, New South Wales, Australia

Key words: cocopeat, safe vegetables, vegetable quality, hydroponics

Abstract
There are food safety concerns in Vietnam in terms of pesticide and heavy
metal residues in vegetables. Soilless vegetable production is one solution to
eliminating pest and disease pressure from soil and the exposure to soil
contaminants such as heavy metals. An Australian aid project (AUSAID-CARD)
investigated the suitability of some locally available materials in Vietnam as soilless
substrates. This paper reports on the results of two experiments carried out at the
Fruit and Vegetable Research Institute in Hanoi, Vietnam. Four media were used as
substrates for the production of tomatoes and cucumbers. The media included coir,
or mixtures of three components including sugar cane waste, peanut husks, soybean,
peat or volcanic rock. For both the tomato and cucumber crop yield was
significantly increased by the use of coir as a substrate. The two crops were grown
without the use of pesticides. In this experiment, the medium of sugar cane waste,
peat and volcanic rock proved unsuitable for cucumber production as it produced
fruit with lead levels above the maximum residue limit of 0.2 mg/kg in three out of
five replicates. These results demonstrate that soilless culture can be used
successfully in Vietnam as a means of reducing residues in vegetables but highlight
that substrates can potentially be a source of contaminants.

INTRODUCTION
Vietnam has food safety issues concerning pesticide and heavy metal residues in
vegetables. These affect the health of farmers using the pesticides, and consumers eating

plants between experimental units. Before planting seedlings, substrates were placed in
grow bags. Nutrient solution was delivered via drippers. The nutrient solution input was
around 1.8 dS/m for cucumbers and 2.2 dS/m for tomatoes, depending on weather
conditions.
Yield measurements included total fruit number and total fruit weight per plant.
Quality measurements were made on 10 fruits per experimental unit and included nitrate,
vitamin C and lead concentrations, expressed on a fresh weight basis. These
measurements were carried out according to the standard methods developed at FAVRI.

RESULTS AND DISCUSSION
Yield, measured in total fruit number and fruit weight per plant, for cucumbers
(Fig. 1) and tomatoes (Fig. 2), was greatest in the coir substrate. Mean fruit weight was
also higher for cucumbers and tomatoes grown in coir (data not shown). Yield was similar
for the three other substrates. Physical and chemical characteristics of these media were
not measured, so it is not known how these characteristics may have contributed to crop
performance.
Fruit quality characteristics were affected differently by the substrates. The nitrate
concentration of cucumber fruits (Fig. 3) was generally higher than tomato fruits. As
cucumber fruit skin contains chlorophyll, it is not surprising that cucumbers have a higher
nitrate concentration than tomatoes. The chlorophyll concentration of leaves is sometimes
used to manage crop nitrate (Shapiro, 1999). Nitrate concentration was particularly high
for medium 2 (sugar cane waste, peanut husks and peat), suggesting that this medium was
contributing an additional source of nitrate to plant roots. Since this extra nitrate did not
result in extra growth by plants in this medium, nitrate was probably at supra-optimal
supply levels. Fruits generally have a lower concentration of nitrate compared with other
plant parts such as leaves and do not pose a food safety risk. However, if green leafy
vegetables were to be grown using similar substrates it would be useful to identify
potential sources of nitrate in the substrate to reduce the risk of nitrate accumulation in
vegetables.
Tomatoes were, not unexpectedly, higher in vitamin C content than cucumbers,

of heavy metals and persistent organic pollutants from soil. Environmental Pollution.
Elsevier Science Ltd, Oxford, UK: 2003. 124: 3, 375-378. 9 ref.
Shapiro, C. A. 1999. Using a chlorophyll meter tom managem nitrogen application sto
corn with high nitrate irrigation water. Com. Soil Sci. and Plant Anal. 30:1037-1049.
Thi, T. K. and Ha, T. T. T. 2003. Safe vegetable research and development in Vietnam:
status and prospective. Vietnam J. of Ag. and Rural Devel. 1:115-118.
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