THIS week, the National Agricultural Research and Extension Institute (NAREI) continues to share information on onion production with readers.
Irrigation:
Onions require adequate water supply for healthy growth and development during the crop cycle. This crop requires approximately 500,000 gallons of water per acre for proper growth and development during a crop cycle of 110 days. Importantly, moisture stress should be avoided during germination/ emergence and bulbing and farmers should avoid overwatering. A tensiometer could be utilised to properly determine whether onions are receiving optimum irrigation. The farmer should discontinue irrigation when 20 percent of the bulbs have broken necks.
Nutrition:
The important nutrients for onion production are nitrogen, phosphorus, potassium, sulphur, manganese, copper and molybdenum. Prior to any fertilizer application, a soil analysis (chemical, physical, biological) must be done to determine soil texture, pH, organic matter, nematode population, salinity, soil compaction and nutrient availability.
Depending on soil analysis results, all phosphorus should be incorporated four to five days before planting. One-third potassium (if less than 100ppm by soil analysis) can be applied per plant along with nitrogen. Micronutrients, if required, may be incorporated at planting or by foliar application.
When plants are 8.5cm tall, an additional one-third quantity of potassium is to be added, along with nitrogen, and the remainder three to five weeks later. The farmer needs to avoid excessive nitrogen application in the first early months as this can lead to bolting. Nitrogen fertilizers should never be applied after bulbing has started, as this can affect the quality of the bulbs. Sulphur should be applied whenever nitrogen us applied and must be in ratio of one part to 12 parts of nitrogen.