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Lesson Note

Subject: Agricultural Science
Topic: Production of Onion (Allium cepa)
Lesson Objective: At the end of the lesson, learners should be able to discuss the stages involved in producing onions.

Lesson Discussions


Scientific Classification

Uses: Onion serves as a human food, can be fed to livestock and have local medicinal uses.

Ecology: Onion does best in fertile, friable and well-drained loamy soil with a pH of 6.0 – 7.0. The production of bulbs is controlled by the photo period and the critical day-length ranges from 11 – 16 hours depending on the cultivar. With optimum water regime, cool conditions are desired for early growth while maturation, harvesting and curing require warm and drier conditions.

Husbandry: Onions are propagated by direct seeding or through transplants. In direct seeding, sow the seeds at a depth of 1cm in rows of 30cm apart. The seedlings are later thinned to 7.5cm apart. Direct seedling requires a seed rate of 4.5kg/ha. For transplants, the seeds are dressed with Thiram or Captan and are sown in well tilled beds of 7.62 × 1.22m in rows about 20cm apart. Prior to planting, a groove of 1.5cm deep is made along the row and a germination mixture is spread evenly on it. The groove is covered lightly with fine sand after planting. Watering and mulching are required to raise good seedlings. The onion field should be well tilled before transplanting. Transplanting is done at about 8 weeks after sowing at a spacing of 7.5 – 10cm along the rows which are 30cm apart. Potassic and phoshatic fertilizers may be applied before or at sowing while a dressing of ammonium sulphate is applied after transplanting or the crops could be dressed with 1:1:2 NPK at the rate of 400kg/ha.

The image below shows the features of onion plant:

Credit: quora.com

Harvesting: Maturity is reached when the leaves turn brown, fall over and begin to die back. It is advisable to plan the planting so that maturity is reached during dry warm weather conditions. The onion is lifted with the tops removed or retained. Curing may be by sun drying for about 4 days or by the use of artificial heat. Onions are stored in well-ventilated places under dry conditions and a moderate temperature of 24 – 30°C. Maleic hydrazide may be used to improve storage life and reduce the incidence of sprouting during storage.
Pests: Onion pests are thrips, maggots and nematodes.

Diseases: Downy mildew, purple blotch, pink and neck rot.

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