Times and Frequencies of Additional Fertilization to Improve Nutrient Efficiency of Organic Liquid Fertilizer for Onion Organic Cultivation

The objective of this study was to improve the fertilization efficiency of organic fertilizer as a unique nutrient source for organic cultivation. A solid type of organic fertilizer (SOF) was applied before transplanting and then additional either or both solid and liquid type fertilizers were applied to organic cultivation of onions (Allium cepa). A liquid organic fertilizer (LOF) for additional fertilization was applied separately 4 times in Feb. and Mar. (LOF Ⅰ), 6 times in Feb. and Mar. (LOF Ⅱ) and 9 times in Feb., Mar. and Apr. (LOF Ⅲ). The combined treatments of SOF and LOF as additional fertilizers were applied as 1 time solid and 3 times liquid (SOF+LOF Ⅳ) in Feb. and Mar., or 1 time solid and 6 times liquid (SOF+LOF Ⅴ) in Feb., Mar., and Apr. The last category of treatment was application of organic fertilizer only as base. The onion growth in treatments LOF Ⅰ, LOF Ⅱ, and LOF Ⅲ was better than that of both SOF+LOF Ⅳ and SOF+LOF Ⅴ treatments. The change in leaf weight showed similar trend to that in plant height; also, the leaf weight in treatment CF (chemical fertilizer) was two-fold of those in organic fertilization treatments at the peak growth stage, the 183rd day after transplanting, although there was not significant difference in the number of leaves. After then, bulb weight showed a remarkable contrast between CF and organic group. All nutrient uptakes of leaves in CF were greater than those in treatments of organic fertilization. However, in case of the bulbs, only N and P₂O∧5 uptakes were different between CF and organic group. The marketable yield in treatment CF was 64.5 ton ha-¹, while that in treatment LOF Ⅱ was 46.4 ton ha-¹, which was 72% of treatment CF. The organic fertilizer was comprised of multiple elements such as sesame oil cake, rice bran, fish meal etc. Basal organic fertilizer contained 31 gㆍkg-¹ of N, 28 gㆍkg-¹ of P₂O∧5, 19 gㆍkg-¹ of K₂O and 405 gㆍkg-¹ of organic matter. The contents of liquid organic fertilizer were 634 mgㆍkg-¹ of N, 68.1 mgㆍkg-¹ of P₂O∧5 and 453 gㆍkg-¹ of K₂O. The organic fertilizer increased pH, organic matter and exchangeable calcium in soil more than CF. Even though organic fertilizer was not readily available as chemical fertilizer, the application of organic fertilizer as the base and 6 times liquid additional fertilization in Feb. and Mar. (LOF Ⅱ) was the most effective among the other organic fertilization treatments.