Mineral nutrient management for onion bulb crops – a review

The mineral nutrient requirements of onion (Allium cepa L.) largely depend on several factors, such as cultivar, plant density, crop environment, soil fertility, fertilisation methods and managing the distributed quantity of fertiliser by using proper system of water irrigation. Production of bulbs as much as 60 tonnes ha−1 removes108 kg ha−1 of nitrogen (N), 21 kg ha−1 of phosphorus (P) and 120 kg ha−1 of potassium (K) from the field by crop harvest. Taking into account the stock of plant available mineral nutrients in the top 60 cm soil layer (onions also may effectively acquire mineral nutrients from up to 60 cm soil depth) a total supply of 120 to 140 kg N, 22–26 kg P and 150 kg K is recommended for onion production. Peak N, P, K and sulphur (S) uptake occurs during 15 to 60 days after transplanting (DAT) and fertilisers should be applied before 60 DAT for increasing bulb yield and nutrient use efficiency. Drip irrigation systems keep the nutrient solution around roots for a longer period than other systems, so it is more adapted for shallow rooted plants like onion. Adequate plant nutrition strategies involving mineral and organic fertilisers or their combinations are critical for increasing the yield of onion bulbs.