Green agriculture with plastic

Plastic is usually considered to be a big threat to the environment as it is not usually degradable. But a lot of improvement has been made in recent years in the plastic sector and its use in agriculture is increasing very rapidly throughout the world. Bangladesh is no exception in this regard. Its use in agriculture, called plasticulture, in the form of polyvinyl chloride (PVC) pipes for deep tubewell (DTW) and shallow tubewell (STW), buried pipe for underground water distribution system for irrigation, flexible PVC pipes for conveyance of water of STWs and DTWs, and polybags for raising seedlings became very common in Bangladesh. In protected agriculture, vegetables and small fruit are grown giving some kind of protection from adverse weather like rainfall, temperature, wind, diseases, insects, water logging, etc. all of which seriously affect crop yield. In this system, crops are shaded by plastic sheets put on top of structure made of bamboo or galvanized iron pipes. Summer tomato is grown commercially in this system. All these uses have made agricultural operations easier and cost effective.
The first use of plastics in agriculture was in 1948 to make cheaper version of glasshouse. By 1999 almost 12 million hectares worldwide were covered in plastic mulch. The majority of the growth of plasticulture has happened in China, Japan and Korea. In Middle East and Africa, areas are increasing at 15-20 per cent per year compared to 30 per cent in China. In southern Spain around Almeria, the driest area of Europe, plasticulture is growing very rapidly to grow different crops. The area, previously non-cultivable due to shortage of water, became green due to plasticulture.
Technologies developed for other uses of plastics are:
Drip irrigation: In research fields, drip irrigation method has been used in Bangladesh for increasing the water and fertilizer use efficiencies of high value crops like aubergine, papaya, banana, guava, lemon, orange, etc., for more than a decade. It is a technically suitable and economically viable technology. It saves 60 per cent urea and 46 per cent water. Tubes, drippers and water tanks for drip irrigation are made of plastics.
Row covers: For vegetable production, row covers are used as a protective covering to shield plants primarily from the undesirable effects of cold and wind, and also from insect damage. Polyethylene and polypropylene are commonly used, which are very lightweight, often placed on wire loops to form low tunnels. It is left in place for several weeks until crops are well established. Sunlight, rain and air can penetrate through the shading material.
High tunnels: It is a tunnel made of polyethylene and iron or bamboo structure, usually semicircular, square or elongated in shape. Its height is lower than greenhouse and higher than row covers. The interior heats up because incoming solar radiation from the sun warms plants, soil and others inside the tunnel faster than heat can escape. This heating aspect made high tunnels popular in temperate region. In Bangladesh, India and many Asian countries, it is used to grow tomato during rainy season.
Plastic mulches: It is used in similar fashion to other mulches, to reduce evaporation from soil surface and to suppress weeds and insects. Besides, use of drip irrigation in conjunction with plastic mulch allows one to reduce leaching of fertilizers. It keeps ripening fruit and vegetables out of soil that ultimately decreases rotting and keeps them clean. Also it reduces soil compaction and root damage, increases crop yield, and ensures early harvest.
More uses of plasticulture are waiting for Bangladesh. Research and pilot-scale study have recently been started on new types of use.

The writer is former DG, BARI