Field-tested methods that work
The Center’s Global Technology Dissemination (GTD) group aims to:
- integrate vegetable technologies from diverse sources to make them readily available to farmers, trainers, consumers and public or private institutions
- provide appropriate training and capacity building activities
- respond to disasters in less-developed countries by providing appropriate short-term development activities in which we have expertise
EXPERIENCE IN THE FIELD
From the study of vegetable crop plants at the biomolecular level to discerning patterns in regional seed distribution, research at the World Vegetable Center encompasses the complex, diverse nature of agricultural production in the developing world. Regardless of their field of inquiry, the Center’s scientists strive to foster productivity, prosperity and health through their research.
Backed by this robust research, the field-tested technologies developed at the Center have been designed to benefit small-scale farmers. Vegetable grafting, starter solution, and rain shelters increase yields in marginal environments. With zero energy cooling chambers and other postharvest methods, farmers maintain the freshness and quality of their vegetables during transport and at the market.
This quarterly bulletin highlighting the application of Center technologies in the field and other topics of interest regarding vegetable production and consumption around the world.
The principle of SST is to raise nutrient concentration in the soil solution by one application of very concentrated nutrient solution immediately after transplanting.
The optimum concentration of starter solution for many vegetables is 240 mg (each) of N-P2O5-K2O in 50 ml water for each plant.
The starter solution can be prepared easily by dissolving soluble fertilizers in water. Any type of locally available soluble fertilizer may be used, but the composition of the fertilizer should include N, P and K — the three essential macro-elements. The N form is of critical importance because some crops prefer NH4+-N but others prefer NO3-N. We suggest that the form best fitted to the crops grown should be chosen. Fertilizers containing urea as N fertilizer should be avoided; Although urea is soluble in water, it needs hydrolysis before plant roots can take it up.
The starter solution can be applied manually to the root zone soil of the plant. It can also be applied by injection, either by manual or mechanized sprayers.
Simple, low-cost drip irrigation systems can ensure small-scale producers benefit from water resources.
This 10-chapter manual provides basic, step-by-step procedures for installing simple drip irrigation systems for different crops, climates, and soils. It addresses common problems, provides troubleshooting and maintenance tips, and offers irrigation scheduling guidelines to avoid under- or over-irrigation. Methods to determine soil types, water quality, water-holding capacity, crop coefficient, and crop water demand are illustrated. The information presented in this guide has been compiled from relevant literature, research and development projects, and is based on practical field experience.
Grafting vegetables can protect crops against a range of soil-borne diseases and can improve crop tolerance to flooding during the hot-wet season. The Center has developed effective grafting techniques for tomato, eggplant, chili, sweet pepper and several cucurbits. Vegetable grafting is used by farmers in Taiwan, Japan, Korea, Vietnam, and Bangladesh, and there are good opportunities to expand this method to other countries.
Grafting technology has been adopted on a large scale in Vietnam to control bacterial wilt in tomatoes that could otherwise completely destroy crops. Grafting susceptible varieties onto resistant rootstock provides good control. Tomatoes are difficult to grow during the hot-wet season, and grafting tomatoes onto eggplant or tolerant tomato rootstocks can minimize problems caused by flooding and soil-borne diseases. More than 10 years of work in the Philippines, Vietnam, Taiwan, and Bangladesh have confirmed the practical value of this technology.
Chili and Sweet Pepper
Grafting can provide crop tolerance to bacterial wilt, Phytophthora blight and root knot nematodes. Grafting of scions is done onto open-pollinated capsicum rootstocks. Only a small proportion of farmers currently use grafted planting materials, even in developed markets such as Japan or Korea. Although they can be costly, grafting onto resistant rootstocks can provide an effective solution to some soil-borne diseases where breeding has not yet produced varieties with effective levels of disease resistance.
Grafting can be used with a variety of cucurbits to provide control of Fusarium wilt and flooding tolerance. Watermelon can be grafted onto bottle gourd to manage Fusarium wilt and provide flooding tolerance when planted in heavy or loam soils. Cucurbits can be grafted onto pumpkin, which will provide some drought tolerance if planted in sandy soil. Disease-susceptible lines of bottle gourd can be grafted onto Luffa (sponge gourd) or pumpkin to improve crop performance.
- VIDEO: How to graft tomato
- VIDEO: How to graft pepper
- VIDEO: Build a grafting chamber
- VIDEO: How to graft cucurbits
- Grafting Tomatoes for Production in the Hot-Wet Season
- Grafting Sweet Peppers for Production in the Hot-Wet Season
Today, pheromone traps can be found in fields across Asia, and they are making inroads in Africa. The Center’s entomology team continues to develop specific lures for troublesome agricultural pests, and is working with companies such as RealIPM in Kenya to refine affordable biocontrol products to help farmers produce vegetables safely.
- Select deep red tomato and chili and wash to remove debris and other surface contaminants.
- Blanch fruit in boiling tank or hot steam chamber for 20-30 minutes to ease grinding (chili) or peeling (tomato).
- For chili, add 0.4 liter water for every kg fruit to ease grinding and sort out the seeds and peel.
- Blend the ground chili and tomato flesh (without peel and seeds) separately before mixing them together.
- Prepare the mixture – chili paste (20-30%), tomato paste (15-25%), garlic paste (10-15%), sugar (10-17%), salt (2-4%), cassava starch (0.5-1%), monosodium glutamate (0.1-0.3%), emulsion mixture (0.02-0.06%), ascorbic acid (0.05-0.08%), citric acid (0.1-0.2%), acetic acid (0.3-0.4%), sodium benzoate (0.04-0.06%), sorbic acid (0.08-0.1%), and water (to make 100%).
- Boil the mixture for 3-5 minutes and cool to 65ºC. Acetic acid, sodium benzoate and sorbic acid are added during cooling when the temperature reaches 75-80ºC while ascorbic acid, when temperature reaches 65ºC.
- Pasteurize/sterilize bottles are then fill with the product with temperature not lower than 65ºC.
- Close quickly the filled bottles and keep at ambient for at least one week (during summer) or two weeks (during winter) for appearance of any possible defects. All defective products are sorted away before labeling.
- Store finished products in cool dark area.
- Select good quality, larger defect-free, ripe red fruits.
- Wash thoroughly in clean water to remove debris.
- Slice fruit and remove seeds prior to blanching or the whole fruit can be blanched.
- Blanch fruit in boiling water for 5-10 minutes or fruit slices in steam for 30 minutes (blanching facilitates skin removal).
- Cool fruit in water for about 5-10 minutes, remove skin and scoop out the seeds (seeds impart a bitter taste).
- Homogenize fruit using a blender or a mortar and pestle. Whole fruit can be sliced to facilitate homogenizing.
- Extract juice using stainless steel sieve or meshed netting.
- Cook for 2-3 hours to concentrate the product. Stir using a wooden spoon to prevent the paste from sticking to the cooking pan. Add 2% salt during cooking when the product has thickened substantially, but still easily flows on paper. Continue cooking until the paste is sticky.
- Dispense the paste while still hot into sterilized glass bottles that have been soaked in boiling water for 20 minutes.
- Pasteurize bottles of paste in boiling water for 10-20 minutes.
- Cool the bottles before storage.
- Remove damaged leaves, detach individual leaves of Chinese mustard or slice cabbages into halves or
- Pack vegetables into clay or plastic jars tightly.
- Pour salt solution into jar at 1:1 ratio, e.g. 5 kg vegetables:5 kg salt solution (8% salt solution is prepared by dissolving 80 grams salt per liter water; 10% salt solution is prepared by dissolving 100 gm salt per liter of water).
- Cover the vegetables with slatted material before adding weight to compress the vegetables.
- Allow to ferment (2 days in summer; 4 days in winter).
- After fermentation, remove the vegetables from the jar and wash with clean water to remove excess salt.
- Place the fermented vegetable in clean/pasteurized glass bottles or plastic pouches (300-500 gm per container).
- Add preservative solution fully filling the container and tightly cover/seal (prepare preservative solution by mixing 3% sugar, 5% salt, 0.4% citric acid, 0.05% sorbic acid).
- Pasteurize the bottles/pouches of fermented vegetables by placing them in water heated to 60-65ºC, and continue heating until water temperature increases to 80ºC, and maintain 80ºC for 10 min.
- Cool in water to ambient temperature before storage.
- Assemble the different parts of the hydro cooler.
- Add potable water and place crushed ice until the water temperature reaches 10ºC.
- Dip produce in crates into the cooled water until the internal fruit temperature reaches 10-13ºC. Ordinary bulb thermometer can be used to monitor fruit temperature.
- Remove the cooled fruit, remove excess water, and store at ambient or cold condition.
Brick walled and box type evaporative cooling systems for vegetable storage
Simple evaporative coolers (EC) create cool and humid conditions to slow quality deterioration of fresh vegetables caused mainly by moisture loss. When used for tomato, chili, cabbage, Chinese kale, Chinese mustard and aromatic mustard they can reduce weight loss by 50-80% compared with storage under ordinary room conditions.
Two types of EC have been tested: The brick-walled EC is made of clay bricks designed to neatly fit the containers of produce to be placed inside. The structure is double-walled, and the 10-20 cm space between walls can be filled with sand as insulator and kept moist with water. A jute sack covering a wooden frame over the structure is kept moist with water. The box EC is made of wooden slats and covered with a tight fitting jute sack kept moist with water.
- Use good quality, unblemished vegetables.
- Wash with clean water or 100-200 ppm chlorine-treated water (except cabbage, as washing could favor decay).
- Air-dry the produce and then place in the EC.
- Keep insulator (sand and jute sack) moist throughout the storage period.
- Periodically inspect produce and cull out decayed, yellowed or overripe produce.
Lime paste, alum solution or guava leaf extract control bacterial soft rot in harvested cabbage
Bacterial soft rot is the most serious postharvest problem of cabbages and other crucifers in the humid tropics. The disease usually starts at the cut butt end of cabbage. It can be prevented or minimized by simply applying lime paste, 15% alum or guava leaf extract at the butt before packing and handling. The techniques are very simple and cheap but very effective (sometimes eliminating the problem completely) and can yield high returns.
- Prepare lime paste by mixing lime powder and water at 1:1 ratio.
- Prepare 15% alum solution (saturated solution) by dissolving 15 gm alum granules in 100 ml water. If weighing scale is not available, prepare the solution by adding and dissolving alum into a small volume of water until such time that the alum will not dissolve anymore (saturated).
- Prepare guava leaf extract by extracting pure extract from mature leaves of guava (slice the leaves and extract juice using mortar and pestle) and add water at 1:1 mixture.
- Apply the lime paste, alum solution or guava leaf extract at the cut butt end of cabbage using any suitable, clean applicator (e.g. soft, fine brush, cotton, cotton cloth).
- Allow to dry before packing and subsequent handling.
Modified atmosphere packaging (MAP)
Polymeric films reduce spoilage of vegetables during transport and storage. Commercially available plastic films, such as low-density polyethylene, high-density PE and polypropylene bags can be used to increase the shelf life of fresh vegetables by reducing weight loss, wilting or shriveling and delaying fruit ripening. Films should be 25-micron thick; commercially labeled as 001 bags.
- Sort good quality and damage-free vegetables.
- Place vegetables inside the plastic bag and seal.
- Store at ambient temperatures for 6-10 days or until when first sign of decay is observed.
Using the sun to produce high value vegetable products
Solar dryers can reduce the time to dry cabbage or chili by half to three-quarters compared with sun-drying and they are more hygienic. Selling dried chili can earn up to a third more income than selling fresh produce. Dryer designs can include a heating chamber (using charcoal or firewood) for use in the absence of sunlight, or cabinet types with glass-walled drying chambers and were produced in conjunction with the Royal University of Agriculture in Cambodia and the National University of Laos.
Processing Chili (Lao PDR):
- Sort good quality and damage-free fruit, preferably red-ripe.
- Weigh fruit.
- Spread fruit in drying trays and place inside the drying chamber of the solar dryer.
- Periodically inspect the fruit until the desired moisture content is reached, usually 10% or less (chili may have 80-85% moisture content; if 1 kg fresh chili is being dried, the weight of the dried product at about 10% moisture content would range from 250-300 gm).
Processing Cabbage (Cambodia):
- Clean cabbage by removing damaged parts.
- Chop the cabbage into small slices.
- Place slices in suitable container and add 5% salt solution for overnight incubation.
- Spread the slices thinly on drying trays and place inside the drying chamber of the solar dryer.
- Periodically inspect the cabbage slices to determine the desired dried product (same procedure as chili).