Onions

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Allium cepa L. var cepa

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General Information

Onions (Allium cepa L. var cepa) originate from central Asia. Bulb-forming onions produce a single bulb in a season. There are two basic types of bulb-forming onions: storage onions and “sweet” onions. The difference between storage and fresh onions is that storage onions keep for a longer period of time.

Suitable varieties for organic production

It is recommendable to use fast growing varieties that will shorten the susceptible period for diseases. Onions can be grown from seeds, small dormant onions called “sets”, or onion transplants:

  • Set onion: seeds 90kg per ha, row distance 20cm, 2 - 3cm deep. Harvesting when the set onions have a size of 15-20mm diameter. Store them dry until planting;
  • Plantlets: 4-5 seeds/pot in 4cm cubes or tray with 20-50 cm3/pot; ready to plant with 3 leaves.

Planting

The size of the onion mainly depends on the sawing/planting distance. With low sawing or planting density, you will harvest big onions:

  • Direct sawing: 4-6kg seeds per ha;
  • Planting set onions: 800 - 1000kg per ha, with 5 to 7cm distance in the row.

Crop rotation

Organic onions are planted in a crop rotation schedule. It is not recommendable to plant onions in the same soil for more than one season. Onions can be planted only once within five years in the crop rotation. This is important to avoid diseases. Previous crops can be potatoes, crucifers and field beans, but not carrots or celery. Onions have a good effect as a preceding crop. Onion organic matter residue is about 1 ton per ha, which contains approximately 25kg of nitrogen, 10kg of phosphor and 35kg of potassium. Crops cultivated after onions in the same year include spinach. Harvest and post-harvest handling

Handling

Onions can be stored for several weeks in a cool, dark place. They can be stored in the refrigerator, but not in plastic bags. This will inhibit air circulation and promote rotting of onions.

Storage

The ripe period for storage onions is reached when at least 75% of the crop populations have been laid down. Clearing too early can cause problems during storage. Clearing too late can cause the shell to drop away and induce sprouting. After the harvest, the onions will store better if they are dried outdoors for a week. Leave tops on bulbs during drying. After drying, cut tops within 3 cm of bulb. The onions can be picked up manually or with a full harvester. Onions are stored in dry and well ventilated stores. Storage temperatures should be below 30°C.

Sources and References

Bibliography

FiBL, Research Institute of Organic Agriculture, Switzerland (2011). African Organic Agriculture Training Manual. Soil Fertility Management. [Accessed 19 March 2012]

FiBL, Research Institute of Organic Agriculture, Switzerland (2011). African Organic Agriculture Training Manual. Conversion to Organic Farming. [Accessed 19 March 2012]

FiBL, Research Institute of Organic Agriculture, Switzerland (2011). African Organic Agriculture Training Manual. Crop Management. [Accessed 21 March 2012]

FiBL, Research Institute of Organic Agriculture, Switzerland (2005). Organic Cotton Crop Guide. Authors: Frank Eyhorn (FiBL), Saro G. Ratter (BioSim), Mahesh Ramakrishnan (ICCOA). [Accessed 19 March 2012]

FiBL (2011): African Organic Agriculture Training Manual. Version 1.0 June 2011. Edited by Gilles Weidmann and Lukas Kilcher. Research Institute of Organic Agriculture FiBL, Frick. [Accessed 12 July 2012]

FiBL, Research Institute of Organic Agriculture, Switzerland (2011). African Organic Agriculture Training Manual. Soil Fertility Management. [Accessed 19 March 2012]

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