RAIN SHELTER is a new technology introduced in Malaysia for commercial production of selected high value crops such as tomato. The production of tomatoes during the hot-wet season in Malaysia and other tropical and subtropical climates is limited by unfavorable conditions such as high temperature, flooding, strong winds and high incidence of diseases. These conditions can significantly reduce tomato yields. Rain shelters protect tomato plants against the impact of heavy rainfall and prevent frequent periods of leaf wetness. The shelters are generally used in conjunction with raised plant beds to minimize flooding and water logging. Sometimes the use of rain shelters can make a difference between harvesting a good crop and harvesting no crop at all. This article I would like to discuss the rain shelter technology based on my observations and field experience which referred to few technical books.
There are many types of simple structure in Malaysia introduced by Department of Agriculture and private sector for Lowland and Highland requirements. Rain shelters can vary in size, shape and structural materials. I would like to discuss the two types described herein are a singlebed type with an arched roof and a doublebed type with an A-shaped roof . These are constructed with galvanized iron (GI) pipe. The singlebed shelter has a width of 2.4 m which able to accommodate a 1.5-m-wide plant bed with adequate furrows for good drainage. The double-bed shelter has a width of 4.8 m, which will accommodate two 1.5- m-wide beds. Height at the center of both shelter types is 2.4 m, which provides head space for workers and adequate height to grow indeterminate tomato varieties. The length of the shelters is variable and can be adjusted to the row length. The prototype shelters described herein are stand alone structures with a fixed length of 5 m for the single-bed type and 6 m for the double-bed type.
From my field experience shows that the structural components of a rain shelter consist of foundation posts (vertical pipes), arches (curved pipes), stringers (horizontal pipes), and braces (diagonal flat irons or pipes). The posts and arches are 1/2-inch inner diameter galvanized iron pipes whereas the stringers can be made of lighter material such as galvanized electrical conduit or ridged polyvinyl chloride (PVC) pipes of 1/2-inch inner diameter. Wood or bamboo can also be used to construct semi-permanent rain shelters for those construct simple rain shelter structure with less capital and availability of natural resources. The covering materials are made of ultraviolet (UV)-resistant clear or transparent polyethylene (PE) film, 0.1 mm thick. Connecting and fastening materials are made of PE and steel clips (1/2 inch), and plastic-wire belts.
The Principles of construction of Rain shelters should be built to withstand strong wind in locations where severe storms occur. Reinforce the structure against wind by connecting the arched top members and foundation posts with horizontal pipes. Center posts (not in single-bed type structures) sustain the pressure from the top due to heavy rainfall while the side linkage pipes reduce the damage by wind. Secure the covering materials (plastic film) with clips and plastic-wire belts. The Establishing foundation posts must first step in construction is to mark the position of the posts. Dig holes with a post digger and bury the two corner posts 30 cm deep. To ensure the same level and height, the two ends of a transparent plastic tube filled with red solution are placed against the posts . When the liquid reaches the same height on both ends, the two posts are of the same height. Bury the rest of the foundation posts on both sides of the bed at 30 cm deep about every 70 cm. To connect the arch tops into the foot pipes (foundation posts) by inserting both ends at 5 cm to the pointed end of the foot pipe post. Strengthen the two sides of the structure with horizontal side pipes . Attach the pipes using steel clips. Reinforce the side of the structure by installing diagonal side pipes on both sides . Install the center top pipe to the arch top).
The next process is to install the plastic film cover . First cut the UV polyethylene film cover to fit the arched top roof. For a single bed rain shelter, one sheet measuring 5.3 m long x 3.75 m wide will cover a bed 5 m long. Attach the PE film to the arch and side braces GI pipes using 1/2-inch PE plastic clips. The plastic cover is installed and then secured with plastic clips. To reinforcing plastic sheets and cover use steel clips to reinforce the plastic sheet on the side horizontal pipes and upright post . After the plastic sheet cover is secured on all sides, reinforce the top against strong wind by tying with plastic-wire belt. Installation of nylon netting along the ides is optional. The netting may be used to exclude insect pests and prevent rain from blowing in. Usually 32- mesh is used, but 60-mesh netting is recommended if whitefly-transmitted viruses are a problem during the offseason. For a 5.0-m-long singlebed shelter, cut sheets of nylon netting 5.3 m long x 1.8 m high to fit two sides. To cover front and back ends of rain shelter, cut sheets of nylon netting 2.7 m wide x 2.7 m high. Install nylon netting on all sides using plastic clips.
The procedure for constructing this shelter is very similar to that of a single-bed shelter, with the most notable exception being the addition of center posts . Mark the position of foundation posts on both sides. Drill holes 40 cm deep and insert side and center posts. Cover holes with soil. Put a three-way adapter GI pipe (3/4 inch diameter) on the center post. For a 6-m long shelter, link nine adapters into slats with screws. Link and connect side iron posts to the center post using 3/4-inch elbow pipe. Install the plastic film cover following similar procedures used for a single-bed rain shelter. Strengthen the plastic film cover on side pipes using zigzag wire clips . Use plastic-wire belts to secure the plastic cover against strong winds.
From my observation in Cameroon Highland vegetable growing area to prepare the land by tilling with a small farm rotovator or hand tiller or manually done. After beds are made than apply basal fertilizer either by broadcast or band. Basal fertilizer rate varies with crop and location, so apply fertilizer based on recommendation for tomato in your area. A combination of organic and inorganic fertilizers, including micronutrients such as boron, is recommended for basal application. The fertilizer is incorporated by rototilling before making raised beds. When fertilizer is banded in furrows in the center of the bed, cover the furrows with soil immediately after application.
The transplanting process by using a grafted tomato seedling are used during the off-season. Use eggplant rootstocks when flooding or waterlogged soils are expected. Eggplant roots can survive for days under water. Use tomato as a rootstock only if flooding and water logged soils are not expected. Select rootstocks that resist bacterial wilt and other soil-borne diseases. Drill holes 10 cm deep on mulched beds using a hole puncher and insert tomato transplants. Cover the hole with soil taking care that the graft union (stem joint of rootstock and scion) stays above the soil line. Tomato plants should be staked 2–3 weeks after transplanting. When planting an indeterminate variety, support plants by tying side branches with plastic tape on an A-frame bamboo trellis. Retain two main stems and prune side branches regularly. For a determinate variety, use the cradle staking system . No pruning is necessary. For both systems, it is important that plants be securely supported on the trellis. This will prevent vines from sliding down and the scion (if grafted) contacting the soil, where it may become infected.
On grafted plants it is important to remove suckers that develop on the eggplant rootstocks near the cotyledons. Removal of adventitious roots that develop on the scion before they reach the soil. As stated earlier, to prevent infection from soil-borne diseases, the scion tissue must not come into contact with the soil. Spraying activities is important to enhance fruit setting. The high temperatures during the off-season can reduce fruit yields. The use of heat-tolerant varieties plus applications of a commercial fruit-set hormone such as Tomatotone or Tomatolan are recommended. Use a 15 ppm solution CPA (ISK tomatotone 0.15% diluted 1:100). Treat each flower cluster one time after two or three of the flowers are open. Apply two pumps of the solution (about 1 ml) per flower cluster using a handheld mist sprayer after 3:00 PM.
Tomato among crop susceptible to the attack of diseases and insects can ruin a crop. Common diseases during the hot, wet season include early blight, southern blight, black leaf mold, gray leaf spot , bacterial wilt, and bacterial spot. Whitefly-transmitted viruses are emerging as major problems, especially when the season is dry. Resistant varieties, if available, and crop rotation are ecommended to prevent most disease problems. Commonly observed insects are tomato fruitworm , tobacco cutworm, beet armyworm, and leaf miner. Monitor your crops closely and take appropriate control measures. The plastic cover and side netting will accumulate dust and algae. To keep the materials clean and long lasting, wash them with water or a detergent solution. Add bleach if necessary to kill algae. Use a highpressure hose to spray water or detergent solution.
The rain shelter technology are the latest technology in Malaysia for commercial high value crop in highland and lowland. The local material components are produce locally and lower price compare those imported.
(Adapted from ADVRC technical paper.)