Effect of year, location, compost, and mixed oilseed cake on bulb and scale characteristic, nutrients and organic compounds in bulb and leaf, and storage quality in organic bulb onion

Abstract

This study aimed to evaluate the effect of years and different locations, beef cattle manure compost (BCMC) and mixed oilseed cake (MOC) application rates on bulb and scale characteristics, nutrient content and nutrient uptake in bulb and leaf, and storage quality of intermediate-day onions (Allium cepa L.) at two organic onion growers' fields during the 2012/2013 and 2013/2014 growing seasons. Treatments included BCMC applied at rates of 0, 30 tonha(-1) and MOC applied at rates of 0, 3, 6, 9 tha(-1). Average temperature at two experimental locations during the growing season in 2013/2014 was 1.2 degrees C higher than in 2012/2013, while total rainfall was 206.6 mm higher in 2012/2013 than in 2013/2014. Onion bulb diameter, bulb fresh weight, scale thickness and fresh leaf weight were significantly greater in 2013 than in 2014, but bulb dry matter was greater in 2014 than in 2013. Nitrogen, potassium (K) and magnesium (Mg) contents and uptakes in bulb were significantly higher in 2013/2014 than in 2012/2013. BCMC application at 30 tha(-1) rate increased K and Mg contents in bulb and leaf as compared with no BCMC. Total soluble solids (TSSs), pyruvic acid (PA), total phenolics (TPs) and total flavonoids (TFs) contents were higher in 2013/2014 than in 2012/2013. BCMC application at 3 tha(-1) decreased TSSs and PA content compared with no BCMC. MOC application increased PA content. Rot and weight loss on 8 September in cold room storage were lower in 2013/2014 than in 2012/2013, but the loss on 14 October and 10 December were not significantly different between two years. In conclusion, high air temperature and low rainfall in Mar. and Apr. increased fresh bulb weight and bulb thickness, while high temperature, low rainfall and long sunshine duration increased TSSs, PA, TPs and TFs contents. Compost and oilseed cake application increased fresh bulb weight, scale thickness, while they decreased TSSs and did not affect organic compounds.