Food and Fertilizer Technology Center - publications

Apr. 01, 1999

Protective Structures for Improved Crop Production

MOST VEGETABLE GROWERS in Asia have a land holding which is smaller than one hectare (2.4 acres). They are interested in any technology which helps them to produce more crops each year from their land, particularly during the off season when prices are higher. For this reason, greenhouses and other types of structures have become popular among Asian growers.

Production under structures not only increases the total annual yield per unit area, but also improves the quality. Vegetables have a better flavor and appearance when they are grown in a controlled environment, where growers can make precise adjustments of nutrients and other inputs.

The kinds of protective structures used by growers in Asia range from simple structures such as rain shelters, shadehouses, mulches, row covers and plastic tunnels, to permanent structures covered in plastic or glass with computerized environmental controls. Growers in countries where typhoons are common over the summer tend to prefer low-cost structures which can be quickly and cheaply replaced. Greenhouses in such countries generally have walls and roof of plastic rather than glass, over a metal or even a bamboo framework.

The discovery and development of the polyethylene polymer in the late 1930s, and its subsequent introduction in the early 1950s in the form of plastic films, mulches, and drip-irrigation tubing and tape, revolutionized the commercial production of many vegetable crops. The later discovery of other polymers, such as polyvinyl chloride, polypropylene, and polyesters, and their use in pipes, fertigation equipment, filters, fittings and connectors, and row covers, further extended the use of plastic in agriculture.

In general, structures are used to overcome low temperatures in temperate Asian countries, and high temperatures in tropical ones. Modifying the temperature is required, not only for crop protection, but also to provide growers with more comfortable working conditions. A common use of structures in both cool and hot climates is for the nursery production of high-quality and/or early seedlings for transplanting. In May, FFTC held a seminar for the exchange of information about improved ways of using protective structures for the production of horticultural crops.

Production under Structures in Asia: An Overview

In Japan, greenhouses were first introduced to protect crops from cold weather. Now greenhouses are commonly used all year round. High summer temperatures are modified by good ventilation, shading and evaporative cooling. New covering materials are being developed which block solar radiation.

In Malaysia, the area used for the protected cultivation of horticultural crops has expanded rapidly over the last decade. The most important constraint is marketing. In general, vegetables produced under structures cannot successfully compete with those produced in the open field imported from neighboring countries, unless stringent measures are taken by the authorities to safeguard the quality and safety of vegetables. These include specifying the maximum levels of pesticide residues, and accurate labeling.

Greenhouse production of vegetables in Korea has made much progress in terms of the external design and the construction of modernized glasshouses. However, there is still a need to reduce the labor cost of operations such as transplanting and harvesting. Protected cultivation of vegetables takes 2-3 times more labor than open field cultivation. Mechanization of some operations may be necessary. This in turn implies standard facilities where machines can be used.

In Taiwan, some fruits such as peaches are being produced under structures. Establishing a permanent orchard structure is expensive, and needs a considerable amount of technical skill. The system must be able to meet the environmental requirements of the fruit grown, so that trees produce a stable yield of high-quality produce.

In Thailand, protective structures are being used to produce flowers by the hill tribes of northern Thailand, under the Royal Project Foundation. At present, the Royal Project Foundation has a large planting area under plastic in Thailand, 90% of which is used for flower production. Greenhouse designs developed by the Foundation have already been widely used nationwide. Structures for some fruit crops such as grape and peach are under investigation and show promising results, while research on vegetables under structures is also under way.

While greenhouse production increases the net income of farmers in Northern Thailand, they still need a great deal of outside technical support. Greenhouse production is so different from their traditional agriculture, that it will take some time for growers to acquire all the needed technical skills. This is a common problem elsewhere in Asia. Production under structures requires good management. Proper planning and attention to detail are needed, if the grower is to succeed

Another widespread problem is that small-scale farmers may find it difficult to finance the investment cost of even a simple structure. In the Philippines, for example, the initial cost of establishing protective structures such as greenhouses and plastic houses is considerable, and not within the reach of ordinary farmers. Designs using cheaper materials are needed. Furthermore, mulching materials which are durable and biodegradable must be developed to protect the environment. Further studies are also needed on protective structures which can withstand typhoons, and which have a better ventilation system for a tropical climate.

Mechanized Production

Whereas many Asian smallholders have adopted machinery for rice production, machines are not much used under structures. There are several reasons for this. Firstly, most farms are too small. Even if suitable machines were available, the utilization rate would be very low. Secondly, growers produce a wide range of crops. It is not easy to develop machines that can take care of a wide range of needs of a variety of crops. Thirdly, most greenhouses are temporary structures with narrow walkways which are difficult for machines to enter.

However, the scale of farming in most Asian countries is expected to increase, particularly in highly industrialized ones. Many growers are enlarging the size of their operations through group farming or producers' associations. Designs for greenhouse machinery should focus on attachments which can be adapted to various crops and different operations, and simple, lightweight machinery suitable for a rural labor force which includes many women and old people. Eventually, new cultivation models with uniform beds and standardized seedling trays can be expected for mechanized operations.

Grafting of Vegetable Seedlings

In vegetable production in greenhouses, continuous cultivation leads to heavy losses, particularly from soil-borne diseases and nematodes. Grafted seedlings have become popular in Japan. Grafting gives greater disease tolerance and increased vigor to crops, to an extent which justifies the higher cost of such seedlings. In 1990, in areas producing watermelons, cucumbers, melons, tomatoes and eggplants, 59% of plants were grafted. A range of rootstock species and varieties are used, and various grafting methods. Recently, tube grafting has become popular in the manual grafting of tomato, eggplant and cucumber plants, because it is faster. Grafting robots and healing chambers have been developed for use in plant nurseries.

Plug Culture System

In plug culture, vegetables are sown by direct seeding into small cells or plugs. Usually a single seed is planted in each plug. When the seedlings have grown to the 2-3 leaf stage, they are transplanted into flats. These may contain from 18 to more than a hundred cells full of growing medium. The flats are usually left to grow under netting or some kind of structure. The plug system is widely used in Taiwan for the production of leafy vegetables, which are harvested at an early stage when they are still young and tender.

Consumers like the flavor of the vegetables, and the fact that they are free of field soil. From the grower's point of view, plug seedlings have a faster growth rate, a shorter cropping period and a longer storage life. Research data also shows that vegetables grown in a porous medium have better root and shoot growth than those grown in field soil, resulting in higher yields. However, the system is labor intensive, particularly transplanting the plugs into the flats and taking them to the field. Future research should focus on mechanization and automation of the system to reduce the labor demand. Another useful innovation would be biodegradable or photodegradable flats that are more environmentally friendly. The possibility of using colored flats which reflect light, thus promoting plant growth and repelling insects, should also be explored.

Plug production technology was introduced into Korea in 1992, and is now an important industry. The technology was first used for the mass production of vegetable seedlings to be transplanted into greenhouses and the open field. This gave growers a steady supply of high-quality seedlings, and relieved them of the burden of having to produce their own planting materials. Recently, there has been growing interest in flower plug transplants.

Soilless Culture

Since the early 1980s, many soilless growing systems have been developed in Asia, some suited to tropical countries and some to temperate ones. Some of these were based on hydroponics. Early types were open systems. More recent ones are closed. Drained water is collected and brought to a central poinmt for reuse, after the water has been disinfected and its EC and pH adjusted.

Nowadays, however, 80% of greenhouse producers are using some kind of artificial medium for their crops. Soilless systems using media of various kinds systems give growers good control over plant nutrients, so that produce has good appearance, flavor and nutritive value. Porous media also offer an ideal environment for root growth.


To be competitive in today's marketplace, vegetable growers must strive for high-quality produce and extended production cycles. The use of structures enables vegetable producers to realize greater returns per unit of land. Yields under structures may be two or three times higher than those of field crops. Production under structures also offers other benefits, including early harvests which earn higher prices, cleaner and better quality produce, more efficient use of water and fertilizer, reduced leaching of fertilizers (especially on light, sandy soils), and better management of pests, weeds and diseases

Production under structures is well suited to Asia, because it can be used effectively by growers with either small or large farms. The basic principles and intensive management are much the same, regardless of the size of the operation. The disadvantage is that it involves higher investment and production costs than growing crops in the open field, especially if it uses advanced techniques such as plug culture or grafting. A higher level of management skills is needed, including planned production for prearranged marketing outlets.

One important constraint in production under structures is the high labor input, and the fact that most operations in Asia are still being carried out by hand. The development of suitable machinery to be used under structures would do much to overcome this problem.

Given the economic growth in Asian economies, the need for higher incomes from farming and better quality produce is likely to continue. Protected cultivation is one way of achieving these goals. However, technical improvements should emphasize, not only yield increases, but also cost effectiveness in the context of a dynamic and often rapidly changing market situation.

International Seminar on Protective Structures for Improved Crop Production

Held in Suwon, Korea, April 13 _ 16

No. of Participating Countries: 7 (Japan, Korea, Malaysia, Philippines, Taiwan ROC, Thailand, U.S.A.)

No. of Papers: 13

No. of Participants: 80 plus observers

Co-sponsor: Rural Development Administration (RDA), Korea

Index of Images

  • ac1999a1.jpg

    Figure 1 Greenhouse with Rolled-up Shade Curtain, and an Open Panel at the Back to Admit Cooler Air

  • ac1999a2.jpg

    Figure 2 Plug Seedlings Ready for Transplanting, 20 Days after Sowing.

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