The ManicaPost
Master Farmer By Seed Co Technical Team
Seed may be sown directly on land which is sprinkler-irrigated. The crop matures earlier than with transplanted seedlings and there is also less premature bolting.
The soil must be thoroughly and finely prepared for good germination. It is here that most difficulty is experienced, as the soil must be kept moist until germination occurs. Sprinkler irrigation must be applied every two days in the field. Onion seedlings are extremely tender and will only develop normally when conditions are favourable in the early stages of growth.
The viability of the seed must be known in order to determine the seeding rate. Efficient small seed planters can be used and the seeding rate will be approximately 4 kg per hectare. A uniform stand is desirable.
An advantage of direct sowing is the elimination of labour costs involved in transplanting. However, considerable labour is required to thin out seedlings in the field. Thinned seedlings may be used for transplanting. If the onions are left unthinned high yields may be obtained but, where crowded, the bulbs will remain very small and may be deformed due to clustering and completion between the bulbs.
Onion Sets
The use of onion sets is another method of production which aims at producing onions for the winter market. The seed is sown out of season from early August to mid-September. The climate at this time of the year stimulates the plants to form bulbs immediately, which limits the size of the bulb. The seedlings are left in the bed until they ripen normally in December, or approximately three months after sowing. The bulblets are suitable for transplanting, although those over 4 cm in diameter tend to produce a high proportion of split bulbs.
At the onset of ripening, the leaves start drying from the tips and the weak stem collapses. Following the collapse of the majority of the tops, the bulblets are lifted. Direct exposure to the sun should be avoided as they are easily damaged. They should be dried in shade, preferably on half-inch wire netting, and then stored in a dry place. The dry roots and leaves are removed before planting out.
The bulblets are planted out in the field at the beginning of February at the normal onion spacing, 5 – 10 cm in the row and 15 – 25 cm between rows. They are planted into shallow furrows. Although the precise positioning of the bulb is not important, bulbs placed upside down or at an angle will take longer to sprout.
Sprouting starts after a few weeks and then they grow rapidly since the food reserves in the bulblets are high. Harvesting will commence about mid-June.
This method of production presents a number of problems as the final quality is comparatively poor. Defects such as split bulbs, thick neck and uneven ripening occur frequently. However, these onions are well accepted at times of shortage.
Time to sow
The successful growing of onions depends mainly on the correct time of sowing. This is influenced by various factors and a thorough knowledge of these is required by the producer.
Onions are grown mainly by sowing in seedbeds, between late January and mid-April, and transplanting after six to eight weeks. These onions are grown during winter. The tendency is to try to sow earlier but it must be appreciated that early sowings do not necessarily mean harvesting any sooner. Bulb formation is determined by day length and temperature. Onions sown earlier tend to produce a higher proportion running to seed and to develop split bulbs. Later sowings tend to eliminate these defects.
The occurrence of bolting depends largely on time of sowing. Early sowings usually produce considerably more bolters than later sowings. Although this is a hereditary characteristic
(The choice of cultivar from Seedco is important), it is affected by environmental factors. Where onions have been sown directly into the land (i.e. not transplanted), the influence of sowing time on bolting is reduced. As directly sown onions develop faster than transplanted onions, they should not as a rule set seed in June/July due to the low prevailing temperatures.
Irrigation
Light irrigation should be applied daily after transplanting until the seedlings are standing straight. Thereafter irrigation is reduced depending on soil type. Water consumption during the first 10 weeks after transplanting is low. During bulb initiation, however, water requirements are critical and the plant should never be allowed to wilt.
Harvesting
It must be borne in mind that the onion bulb continues to increase in weight until the foliage collapses. This collapse is caused by a weakening and shrinkage of the stem immediately above the bulb when the plant is mature. The bulb is then at maximum weight.
Earlier harvesting, to obtain a higher selling price, will generally lead to lower yields and quality. Therefore harvesting should start when the plants collapse. The mature onion will also keep better.
Onions are usually lifted by hand. If the soil is hard a light irrigation prior to lifting will help.
Drying
Onions for immediate sale are not dried and are usually marketed within a week of lifting. Foliage is usually cut in the field and the bulbs are left for two to three days to dry out before marketing.
However, onions for storage must be thoroughly dried. This is achieved by stacking in windrows in the lands. The foliage must protect the bulbs from the direct sun. In the event of rain, these windrows should be turned to facilitate drying. Bulbs lying on wet soil start sprouting and their keeping quality is impaired.
Seed Co Technical Team:
Silas Mutota is Seed Co Regional Sales Manager.
+263 773 473 948/ silas.mutota@seedcogroup,com
John Basera is Seed Co Agronomy and Extension Services Manager.
+263 772 413 184/ [email protected] <mailto:[email protected]>.
Kudakwashe Mashanda is Seed Co Product Development Manager.
+263 775605 057/[email protected]
