SOIL REQUIREMENTS. Onions grow best in well-drained, friable loam soils with good water holding capacity and soil pH of 6 to 7. But with proper land preparation and management practrices like fertilization, irrigation and good drainage, onions can be grown in a range of soils like rice fields. In Central Luzon, for example, onions are grown right after harvesting rice to take advantage of residual moisture at the same time making use of the rice straw as mulching material. For bigger-sized bulbs and better yield, onions are also best grown during the month of October to February.
SEEDLING ESTABLISHMENT. Onions are usually grown using seeds. They are either direct-seeded in the field or grown in the nursery before transplanting. One benefit of direct seeding is that one saves on labor but the disadvantages far outweigh this benefit. Direct seeding requires more seeds, more efficient management to produce satisfactory yield, and results in bulbs of more variable sizes. As such, transplanting is recommended, especially if onions are intended for fast food chains or for export, which are very strict on the quality of onion bulbs that they buy.
To prepare the seedbed, plow and harrow the soil twice. The plowing should be at least one inch deep. Organic fertilizers such as green manure crops can be applied and mixed with the seedbed to increase the organic matter of the soil. Then make seedbeds that are 30 to 40 cm high and 0.5 to 1 meter wide at any convenient length. Make sure that the soil on top of the seedbeds is well pulverized and then level the surface.
Make rows 15 to 20 cm apart along the seedbed. Distribute the seeds evenly on the rows then cover thinly with soil. Cover the seedbed with rice straw or dry grass or rice hull to conserve moisture. Three to five kilos of seeds will give seedlings enough to plant one hectare.
Water the seedbeds just enough to maintain sufficient moisture but be careful not to overwater as this favors development of diseases. Seeds will germinate 5 to 11 days after sowing. Seedlings are ready for transplanting 40 to 45 days after emergence. A day before transplanting, water the seedbeds thoroughly so that the seedlings can be pulled easily without damaging their roots.
FIELD PREPARATION & TRANSPLANTING. Start land preparation 35 to 45 days before transplanting. For conventional land preparation, cut rice stubbles close to the ground and set aside the stubbles for use later as mulching material. Plow the field once and harrow twice then level the soil to form beds. The furrows between the prepared beds will serve as irrigation and drainage canals. A week before transplanting, spread the stubbles on the prepared beds. Make holes on the mulched beds 8x8 cm to 15x15 cm apart. Transplant one seedling per hole making sure that seedlings are planted deep enough to prevent drying out easily. Press the soil around the base of the seedlings to ensure good soil contact. Irrigate the field after transplanting.
FERTILIZATION. To ensure efficient nutrient uptake, fertilizer should be applied close to the plants but not close enough to cause damage. For every hectare, sidedress two bags of 50-kg urea and 3 bags of complete (14-1414) fertilizer 14 days after transplanting (DAT) and at 50 DAT.
WEEDING. Hand weeding may start one month after transplanting. Succeeding operations may be repeated as the needed arises. Selective herbicide may also be used to control weeds.
IRRIGATION. The frequency of irrigation depends upon soil moisture. But it is recommended to first irrigate at 7 or 14 DAT, at 50 DAT which coincides with the early bulb development, and at 60 DAT which is the bulbing stage.
INSECT PEST & DISEASE CONTROL. Insect pests such as cutworm and armyworm can be controlled using Sugod 2.5 EC while leafminer and thrips with Cardinal 50 SP and Kilabot 50 EC, respectively. Diseases such as purple blotch and fusarium rot can be controled by either Pilarich or Pilarzeb.
