Onion Nutrition

Onions require a fertile but well balanced soil. Manure is not recommended as weeds are a serious problem for this crop and also  due to variable nitrogen content. Soils must have a pH of 6.5 to 6.8 for satisfactory crops. On peat soils, pH of 5.5 is sufficient. The soil must contain adequate calcium for crop growth. This means that calcium must be evenly distributed and incorporated into the field. Crop failure is common on fields with inadequate liming. Also, some cultivars may be more sensitive than others to low pH. 

  • Nitrogen

Apply most of the nitrogen pre-plant incorporated (at least 2/3 of the required amount). Side-dress the remainder in mid- to late June after the seeded onions are about 15 cm tall. Excessive nitrogen especially in July can cause delayed maturity (thick necks) and soft bulbs.

  •  Phosphorus

Should be banded if possible at the time of seeding. Otherwise relatively heavy applications of phosphorus must be broadcast and pre-plant incorporated. 
Potash - Potash should be broadcast and pre-plant incorporated. Application rates depend on the level in the soil.

  • Micronutrients
  • Copper

deficiency occurs on acid or peat soils. Copper may be mixed with the fertilizer and applied. On peat soils (as an initial application), 50 kg of copper sulphate per hectare is recommended. Copper Sulphate can be applied by spraying it onto the soil surface and incorporating it into the soil (this material is extremely corrosive to metal).

  • Manganese

At high soil pH's a deficiency may show up. Soil application of this element is not suggested due to the large amounts required. Foliar applications of manganese sulphate are recommended, starting when the plants are about 15 cm tall with 1.5 to 2.75 kg manganese per hectare in 300 L of water and repeated in 4 to 5 sprays 10 days apart. Use the low rate on small plants increasing the rate as the season progresses.

  • Fertilizer Application 

For seedbeds, apply basal fertiliser Compound S (7:21:7 9S 0.04B) at the rate of 45g/m2. After 2 to 3 weeks of emergence, apply Ammonium Nitrate (34.5% N) as top dressing at the rate of 35 g/m2.
For lands, apply basal fertiliser of Compound C (5:15:12 11S.01B) fertiliser at the rate of 600 kg/ hectare. Apply Ammonium Nitrate (34.5% N) at the rate of 100 kg per hectare after 4 to 6 weeks after transplanting. 

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