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Jongtae Lee, Jinseong Moon, Heedae Kim, Injong Ha and Sangdae Lee

The effect of nitrogen (N), phosphorus (P), and potassium (K) supply on the growth and nutrient uptake of intermediate-day onions (Allium cepa L.) was investigated in a double cropping system of rice and onion in which rice straw had been annually applied. The experiment consisted of three sets of treatments: N (0, 120, 240, 360 kg·ha−1 N), P (0, 18, 35, 52 kg·ha−1), and K (0, 67, 133, 200 kg·ha−1) with the addition of 8.0 t·ha−1 of decomposed pig manure. The rice straw was incorporated with tillage after harvest. Foliage weight of the onion plant was affected by N rate on 21 Apr. and on 23 May. Bulb weight was also influenced by N rate on 23 May and at harvest. The only difference (P ≤ 0.05) in onion yield was observed between the zero N rate and all the other N levels. Soil pH was correlated with rate of N fertilization. Soil NO3-N for 240 and 360 kg·ha−1 N rates ranged from 36.6 to 113.7 and 49.9 to 148.6 mg·kg−1, respectively, which was at least twice as high as that at 120 kg·ha−1 N rate. The highest fertilizer use efficiency of nitrogen was 36.0% at 120 kg·ha−1 followed by 240 kg·ha−1 at 28.0% and 360 kg·ha−1 at 20.6%. There was no clear effect of P or K rates on P or K concentration in the onion bulbs. K concentration and uptake in the onion leaf tissue increased with higher K rates. In conclusion, compost and rice straw provided sufficient P and K to grow onions without additional P and K fertilizer, and under these conditions, the fertilizer level of 120 kg·ha−1 N produced as much onion bulb yield as higher N levels.

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Jongtae Lee, Sunkyoung Hwang, Seongtae Lee, Injong Ha, Haejun Hwang, Sangdae Lee and Juyeon Kim

This study aimed to compare agricultural practices, soil physical and chemical properties, growth characteristics, and nutrient uptake of bulb onions from organic and conventional farms in southeastern Korea during the 2011–12 growing season. Soil and plant samples were collected from eight certified organic fields managed organically for more than 5 years and eight conventional fields adjacent to the organic fields. The amounts of nutrients applied to onion fields were approximately two times greater with the conventional methods than with organic methods. However, the soil physical and chemical properties were not significantly different between the organic and conventional systems, except for NO3-N in early May. Growth characteristics were significantly different in early April with organic bulb yield of 55.9 t·ha−1, which was 21.8% lower than conventionally produced onions. Yield reduction in organic onions was the result of lower large-sized (8 cm or greater) bulb yield compared with conventional production. In the conventional system, phosphorus (P) and potassium (K) content of leaf tissue in early April, and nitrogen (N) and P content of bulb tissue in early May were higher than those in the organic system. Uptake of all nutrients was greater in the conventional onions compared with the organic onions, except for leaf tissue at harvest. In conclusion, organic onions began to grow and absorb soil nutrients later than the conventional onions in the initial vegetative growth stage. Moreover, it led to an organic onion producing a lower bulb yield. To accelerate the initial growth of the organic onion plant, agricultural practices need to be modified. Modifications that may help include using larger sized seedlings at transplanting, covering the plants with nonwoven fabric or transparent plastic film to increase warmth during winter, and harvesting the onions 1 week later than the conventional onions.