Protective Structures for Improved Crop Production in Asia
Small-scale farmers can produce crops all year round with the help of simple plastic greenhouses.
Introduction
With less than one hectare of land for their crops, small-scale growers in Asia are vitally interested in technology which makes cropping more intensive. Simple structures of plastic are widely used for this reason. Not only do they help growers produce more crops each year, with higher yields. Vegetables grown under structures are usually of better quality than those grown in the field. What is more, growers can harvest crops in the off season, when prices are at their peak.
Types of Structure
Simple plastic structures include rain shelters, nethouses which screen the crops from the sun, mulches or row covers, plastic tunnels and plastic greenhouses. The extent to which they improve the yield depends largely on the extent to which advances in crop protection, plant breeding and crop cultivation have been applied to production under structures.
Polyethylene plastic was first developed in the 1930s. In the early 1950s it came into agricultural use, made into plastic films, pipes for drip irrigation and various kinds of plastic film. New kinds of plastic were developed in later years- polyvinyl chloride, polypropylene and polyesters _ which were cheaper, more durable, and opaque or transparent as needed.
Major Problems
A major concern now is the disposal of used plastic in rural areas. Researchers are trying to develop new plastics which are biodegradable. The ideal is agricultural plastics which will break down after use into harmless residues - or even into fertilizer!
The production of vegetable crops using plasticulture is a production system that requires high input costs and good management. Whether it is economically viable depends on the price of the structures and the price paid for the crops. Even when these are favorable, proper planning and attention to detail are needed if the grower is to succeed.
Mechanized Production under Structures
It is not easy to develop machines that can meet the precise needs of a range of crops within a confined space. Another problem is that most Asian farms are too small for efficient mechanization. Even if suitable machinery were available, the utilization rate would be very low.
The area of vegetables grown under structures is growing rapidly. This trend is likely to continue, as consumers demand high-quality fresh produce. Mechanization will be much easier if growers can achieve economies of scale by group farming, or by joining producers' associations.
Designs for greenhouse machinery in Asia should focus on increasing the adaptability of attachments for various crops and different operations. It should also aim at simple, lightweight machinery suitable for a rural labor force which includes many women and old people.
Eventually, the problem of mechanization will probably be solved by new cultivation models with uniform beds and standardized seedling trays.
Plug Culture
Fresh leafy vegetables, eaten when they are very young, are popular in Taiwan. These crops are often grown by plug culture. Vegetable seeds are sown into plugs. When the seedlings reach the 2-3 leaf stage, they are transplanted into flats. Each flat contains up to 18 plugs. The flats are then laid out in a greenhouse, or in the open field under protective netting, until the vegetables are ready to harvest.
This may seem a labor-intensive system. However, sowing is automated, and transplanting into flats is done on a moving conveyor belt.
Plug culture has a number of advantages . More crops can be grown each year. Growing seedlings in a porous medium with a good nutrient supply not only speeds up the growth rate, but extends the storage life. Lettuce, Chinese kale and water convolvulus grown in flats had a lower transpiration rate, and a storage life 2-6 days longer, than ordinary crops.
Work is now in progress on flats which are photodegradable, and on colored flats which reflect light and repel insects.
(For more information about plug culture, See FFTC Extension Bulletins No. 477 and No. 479 on this database).
Hydroponic Systems
Over the past 20 years, many growing systems have been developed which do not use soil. Instead, the plant roots are immersed, or sometimes periodically soaked, in a nutrient solution. Initially, the main aims in developing these soilless systems were to achieve higher yields and quality, better control of plant growth, energy savings, and control of soil-borne pathogens.
Recently it is the environmental aspect which has become important. Soilless culture is seen as a recycling system which does not burden the environment with fertilizers and pesticides. The first soilless culture was based on open systems. Superfluous drainage water flowed directly into the subsoil, polluting surface and ultimately, groundwater too. Now, all soilless culture needs to be a closed system. Drainage water is collected in troughs and brought to a central point for reusing, after the water has been disinfected and its pH and EC adjusted.
Index of Images
Figure 1 Harvested Leafy Vegetables. the Vegetables Grown in a Plug System (Left) Still Have Their Roots Intact. This Gives Them a Longer Shelf Life.
Figure 2 Newly Transplanted Flats Out in the Field
Figure 3 Vegetables Grown in a Hydroponic System
