Onion Production Guide

 Climatic and Soil Requirements

Bulb onions grow well in friable and well-drained loam soil with good water holding capacity and pH between 5.8 - 6. For best growth and bulb quality, onion requires cooler weather during the early stages of growth and a dry atmosphere to moderately high temperature for bulb development and maturation.

Seed Establishment and Seed Sowing (Nursery)

Seedbed should be located in a well-drained, friable soil with Goodwater holding capacity and with high organic matter content. If soil pH is lower than 5.8, lime applications necessary at the rate of 3 tons/ha., applied one month before transplanting. Land should be prepared by thorough plowings and harrowing's. Level and pulverize the soil to facilitate formation of beds (1 meter wide and 20 m long). Prior to seed sowing, sterilize the beds by burning rice straw on top or by pouring boiling water to prevent pest and disease infestation.

Broadcast decomposed or processed chicken manure or compost at the rate of 4 tons/ha combined with 3 bags14-14-14. Space 10-15 cm between rows and sow seeds evenly in a row at 5-6 seeds/inch. Cover the seeds with rice hull before watering the bed. Approximately, 25 grams of seeds is needed per square meter. Irrigation should be applied adequately in the field right after seed sowing. Seeds will germinate at about 7-10 days after sowing and are ready for transplanting 45 days after sowing.

Land Preparation and Formation of Beds

Prepare the field by 2 plowings and 2 harrowings. Level and pulverize the soil to a fine texture to facilitate formation of beds. Raised beds are constructed at 75 cm wide with 10-15 cm high.

Basal Fertilization and Transplanting

Basal application of chicken dung or compost at the rate of 100 bags/ha combined with 3 bags 14-14- 14 (complete fertilizer) or 2 bags 16-20-0 (Ammonium phosphate) will be applied in the prepared area and cover with rice straw. Transplant one seedling in each hole by pressing downward the base of the seedlings so that the roots will have a good contact with the soil. Irrigate after transplanting.

Side-dressing

Side-dressing will be done ten days after transplanting with 1 bag/ha of Urea plus 2 bags/ha of Muriate of Potash.

Land Preparation

Spray the field infested with “Mutha” and other noxious weeds with any weedicide with the rate of 18-20 tbs per 16 liters of water. Plow the field vertically (1st plowing) followed by harrowing, plow horizontally (2nd plowing) followed by harrowing to attain good tilth and maintain “glomolin” (super glue) in the soil structure.

Fertilization

Four application of fertilizer is required.

• 1st application – basal (organic or inorganic fertilizer 7-10 days before transplanting).

• 2nd application – side dress by band placement (5 cm away from the plant and 8 cm deep from the

root system, Phosphorus Pentoxide (P2O5) must be applied with nitrogen at 20-30 days old.

• 3rd application – apply nitrogen and potassium at 30-40 days. Do not apply Phosphorus Pentoxide

(P2O5) beyond 30 days old plant.

• 4th application – apply nitrogen and potassium 45- 50 days, do not apply any fertilizer beyond 50 days old plant.

Spraying of Foliar Fertilizer

Spray foliar fertilizer when seedlings are 55 days old (formation of bulb). Spray early in the

morning or late in the afternoon. Repeat spraying when the plants are 70 days old.

Irrigation

Bulb onions require adequate moisture for steady, continuous and desirable growth. Depending on soil types, irrigate between 4 and 7 days. The last irrigation should be a light one. Irrigation should be applied after transplanting. Weekly irrigation is done or whenever necessary. Most frequent watering is needed when the bulbs are developing. Do not irrigate 3-5 days before harvesting or when 20-30% of the plant tops fall over naturally.

Cultivation and Hand Weeding

Cultivation and hand weeding should be done 10 days after transplanting to be followed by two to three times more to eliminate weeds and avoid waterlogging.

MANAGEMENT OF INSECTS PESTS AND DISEASES

Pests

• Thrips – Abundant during dry season. Adult and nymphs rasp the leaf surface and suck juice from the leaf. The leaves appear slippery with sunken area that later dry up resulting to weakened plant, reduced growth and lower yields. Examine closely some plants from 14 m perimeter of the field by pulling the leaves apart from the base. If attack is severe, apply chemical control.

• Armyworms – The larvae bore into the onion leaves and fed leaving the exterior almost intact. Damage is worst in weedy fields. Thorough land preparation is done to destroy the egg laying sites and feeding source. Chemical control is recommended especially when population in high.

• Cutworms – Larvae feed at night and hide near their feeding site during the day. They roll when disturbed. Apply chemical insecticide.

Diseases

• Purple Blotch – Fungal disease occurs on the leaves, bulbs, flowers. Lesions start at small sunken area with dark purple center. Infection of the bulb occurs as the plant approaches maturity. A combined approach involving cultural and chemical control is necessary.

• Sooty Mold – Occurs generally after the bulbs have been harvested. This is favored by high temperature and humidity. Curing the onions quickly with good ventilation is necessary.

• Bacterial Soft Rot – Bulbs that have mechanical injuries/bruises are susceptible. Make sure that plants are mature before harvest. Provide proper ventilation during the curing, packing and transport. Fungicide spraying is done to prevent fungal diseases. Spraying starts 12 days from sowing or as needed.

Harvesting and Curing

Harvest the crops as soon as the necks of the plants tends to fall down or when 75% of the stems are fallen over. Harvesting is done manually by pulling the matured bulbs. After harvest cut the leaf by using sharp knife up to the neck and place in red bag and bring them to the curing house. The curing house should be well ventilated and relatively dry. Harvested bulbs are cleaned by cutting the remaining roots before sorting. Remove or cut tops with shears 1.5-2.5 cm from stem end of the bulbs. Do not remove outer scales. Place the bulbs on racks made of tiers of bamboo, wood or netted wire. Put the racks in a well-ventilated shed. For easier harvesting system, pull the bulbs, then pile in group, followed by cutting of leaves up to the neck, and placing in red bag before bringing to the packing house. At the packing house, remove the bulbs inside red bag and trim onion roots by cutting through the use of scissors. Place onion bulbs cleaned in a sorting table and sort by size before packing on red bag and pile ready for market.

Post harvest

Cure harvested bulb for 10-14 days in a sunny wellventilated area. Align onions so that the leaves of one onion can be parallel to another. Grade bulbs according to size and quality. Pack bulb onions in net sacks for storage and/ or immediate disposal.

This Publication is a project of the Department of Agriculture,

Regional Field Office No. 02, High Value Crops Development Program.

Plant Propagation: Orthotropic Clonal Propagation thru air layering/marcotting

Marcotting or air layering, an asexual or vegetative method of plant propagation of orthotropic shoots (stem growing vertically). It can be easily performed by the induction of root development and usually done by wounding the part of the plant to be rooted.

How it is done?

1. First, select a stem or shoots of a semi-woody plant species that growing vertically. The orthotropic shoots is an ideal one because the leaves are arrange radially around the stem.

2. Put a girdle around the stem by moving the knife in circular motion around the stem, then remove a strip of bark, the portion of the stem to be rooted at around 1 inch length.

Girdled Part (1 inch length)

3. Further remove the cambium layer using a sharp knife, a cambium is slippery coating on the wood. This is to prevent the the upper and lower barks wound from healing and reconnecting

4. Mold a slightly wet soil media, preferably clay loam soil, and put the soil around the portion of the stem that has been girdled. The rooting medium may be as thick depending on the time of the roots to be developed. The longer is the time required to induce rooting and the bigger is the stem, the thicker should be the rooting medium.

5. Then secure the media using a plastic wrapper or coconut coir dust and tie the upper and bottom portion using a wire or cable keeper. If you're using a plastic don't forget to put a minute whole around, this is to ensure the inflows of air and water within the media.

6. Frequently monitored the moisture content of soil media and watered if necessary. Maintaining the moisture content of the soil media allows the earliness of the roots to developed and easy for penetration.

7. Separation of the rooted shoots from mother plant should be done upon observing the emergence of roots or roots are quite plenty enough.  New shoots will also have sprouted from the portion of the stem immediately below the rooting medium.

8. Potting of rooted shoots, upon separation, promptly transplant the rooted cuttings in a pot proportion to it’s' size, trimmed the leaves into half part to lessen transplanting shock, stress and transpiration rate. Put the potted plants into shaded area, high humidity and avoid direct sunlight.