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West Central Africa 2020 | English Version

Step 2 Land preparation

Step 2 Land preparation and transplanting Step 3 Watering Step 4 Weed and nutrient management Soils for transplanting have to be thoroughly ploughed to eliminate debris and soil clods. All crop debris belonging to the alliaceae family must be removed or burnt to avoid possible risks of disease build up. Depth of beds should be 20-30 cm and manure should be applied at a rate of 25-40 tons/hectare at least 1-2 weeks before transplanting. • For drip or sprinkler irrigation, make beds of at least 1 m wide and raise the beds to a 15 cm height. • For basin irrigation make sunken squares of 1 to 4 meters with convenient height. • Transplant seedlings after 5-8 weeks when they have a height of between 10-20 cm, or the thickness of a pencil and at least 3-5 well-formed leaves. • 25 to 50% of the tops must be trimmed off before or during transplanting to avoid losses after transplant. • Transplant early in the morning or late in the evening to minimize the transplant shock and water immediately after transplanting. • Transplant seedlings in a 3-5 cm deep. • Transplant immediately or as soon as possible after digging up the seedlings. • Plant spacing can vary but should be approx. 15-20 cm between rows and 6-10 cm between plants. • Optimal plant density is 300,000 to 500,000 plants per hectare and yields of 50 to 60 tons should be achieved but can even reach up to 90-100 tons. Onions require frequent light irrigation. Onion roots will mostly feed in the top 40 cm of soil so when watering takes place it should be to a depth of at least 60 cm depending on the soil type. Excessive moisture must be avoided at bulbing stage. Ensure enough water is available while the bulbs are swelling. Apply 25 mm of water over a weekly period for the first 6-7 weeks and thereafter 35 mm per week until one week before lifting. Irregular watering can lead to spit bulbs. These recommendations are very approximate, you should determine your own irrigation frequency depending on soil moisture, temperature (more frequent irrigation in hotter weather) and soil type (lighter soils need more frequent irrigation). The surface of the soil should never be hard and dry in a growing onion crop, but should never be too wet and flooded. The onion canopy cannot shade out weeds and since it has a very shallow fibrous root system, care should be taken when using hoes to take out weeds. The onion bulb is a heavy feeder of manure or organic content. The general principle is to apply any basal phosphate fertilizer for better root development before transplanting. During bulbing a combination of calcium and boron base fertilizers is needed. Total fertilizer application should be determined by soil and tissue testing. Generally plant onions with 80 kg of Phosphorus, 100 kg Potassium and 50 kg of Nitrogen per hectare (including nutrition from any manure or compost added). Throughout the rest of the growing season an additional 100-150 kg of Nitrogen and 20-50 kg of P and small amounts of K can be added as topdressings every week or fortnight until after bulb initiation (generally 2-3 months after transplant in Africa). After bulb initiation you should mainly apply K (total around 100-180 kg/ha) and smaller amounts of Nitrogen and Calcium. No fertilizer should be applied during bulb maturation (around 2 weeks before top fall). Step 5 Harvesting and curing It takes between 3 to 4 months for onions to mature from transplanting in West and Central Africa. When 80% to 100% of the tops have fallen over and the bulbs are well-filled, loosen the soil with a blade below the roots or lift them by hand. The drying process is called curing and it is a preventive measure to avoid moisture loss and disease attack which helps to prolong shelf-life. When harvests are done in a dry season that is not too hot, bulbs can be cured in the field by cutting the tops and placing in rows with leaves partially covering the bulbs to prevent sun burn or greening. Field curing can take 2-3 weeks depending on weather condition and should be packaged when outer leaves and neck are completely dry. For harvests in hotter or wetter seasons onions need a dry area with good ventilation such as in an open walled shed. Cut between 25-50 mm above the bulb and tie the top of the bulbs in bunches. Hang them in a horizontal pole in well-ventilated shade. Grading should be done before and after storage before packaging. 10 | Enza Zaden Enza Zaden | 11

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