Response of onion (Allium cepa L.) to sowing date and plant population

Abstract

Field trials were conducted on the West Campus facility of the Department of Soil, Crop and Climate Sciences of the University of the Free State in Bloemfontein during 2009 and 2010. The first trial during 2009 investigated the response of onion (Allium cepa L.) cultivars to sowing date. Cultivars namely; Charlize, Jaquar, Python and South Wester were used in 2009. Onions were sown on 31 April, 7 May and 21 May during 2009. The second trial was conducted during 2010, where cultivar Ceres Gold was used to replace South Wester as the latter was no-longer available in the market and sowing was done on 11 May, 25 May and 8 June. In both seasons, experiments were laid out as a randomized complete block design with each treatment combination replicated three times. During 2009, plant population of 41 plants m-2 was used, while in 2010 plant population of 61 plants m-2 was used. Plots of 1.8 m2 were used with each plot having five rows. Each row had fifteen plants during 2009 and twenty two plants during 2010. Before planting, soil sampling and analysis were made, thereafter, fertilizers were applied as per soil analysis results. A third field trial was conducted in 2010 to evaluate the three sowing dates (11 May, 25 May and 8 June) with a combination of five plant populations (95, 83, 74, 67 and 61 plants m-2) using one onion cultivar (‘Jaquar’). The experiment was laid out as a randomized complete bock design, with three replications having 1.8 m2 plots. In each plot there were five rows. A bulb storage trial was also conducted under room (±25°C) and cold room temperatures (±5°C). This was done for all field trial in both seasons. In a trial investigating response of cultivars to sowing date, better plant height, number of leaves, bulb fresh mass, and yield were observed when sowing was done from the end of April to the end of May. Sowing date significantly influenced bulb and neck diameters only during 2009. Bulbs were becoming more firm as sowing date was delayed, and the opposite was observed for bolting. Cultivar South Wester bolted more, followed by cultivar Jaquar while other cultivars did not bolt. The shape of bulbs was not significantly influenced by sowing date but it showed to be cultivar authentic. No split bulbs were observed. In a trial of sowing date and plant population, significantly taller plants were obtained with early sowing date than the two later sowing dates. Leaf production was not significantly influenced by sowing date. Sowing date and plant population affected bulb fresh mass, yield, bulb and neck diameters as well as firmness. Sowing date did not influence bulb shape while plant population did. None of the bulbs bolted from this trial. Mid-intermediate day cultivars (‘South Wester’ and ‘Ceres Gold’) recorded the shortest duration (105 days and 63 days respectively), while on average other cultivars were stored for 126 days in 2009 and 105 days in 2010. Storage disease (black mould), sprouting and loss of moisture from the bulbs were the contributing factors for reduction in storage duration. These factors were promoted by both field and storage conditions. Onion producers should have adequate information on the cultivars and the production.