Response of Five Onions (Allium cepa L.) Cultivars to Fertilizer Type and Season Reflected on Growth, Yield, Quality and Storability under Khartoum State Conditions

Abstract

Two experiments were carried out during the 2015 /16 and 2016/17 summer seasons at the Experimental Farm of Shambat Research station, Agricultural Research Corporation, Khartoum, Sudan. The purpose was to investigate the performance of five onion cultivars; Baftaim (S), Saggai lmproved, Abu-Freaiwa, Kamleen, Texas Early Yellow Grano under five fertilizers regimes (control, urea, organic, NPK and ammonium sulphate). The experimental design was in split plot with three replications. The Studies addressed three aspects which were; vegetative growth, bulb yield, quality and storability. Vegetative growth parameters used were plant height, number of leaves per plant and leaf length. Yield and quality the parameters assessed were single bulb fresh weight, total and marketable yield, doubling, bolting, bulb diameter, length, neck diameter, number of rings, total soluble solids and dry matter content. Storability evaluated using the parameters of rotting, sprouting, total bulb weight loss and diseases susceptibility (black mold infected bulbs). The results indicated that there were no significant differences among fertilizers on growth, yield and quality of onion cultivars. Whereas for cultivars both Baftaim (S) and Kamleen had ample vegetative growth while Texas Early Yellow Grano had sparse vegetative growth; however, both Baftaim (S) and Texas Early Yellow Grano were the high yielding ones. It could be explained that both have high capacities of partitioning large portions of the vegetative growth (biological yield) to the sink (bulb) which is the economic yield. Lack of cultivar and fertilizers interaction could be attributed to the cultivar genetic make-up and/or the levels and type of fertilizers used or possibly the experimental sites. All quality characters were not significantly affected by fertilizers and that could be due the fact that they are mostly genetically controlled, however, the minor differences observed could be due the selection intensity or degree of purification attained during development of cultivars, in addition to possible cultivar – environment interactions. Onion bulb Storability is correlated with dry matter and pungency both being genetically controlled with factors affected with management practices like harvesting, curing and the storage environment especially temperature and relative humidity. The Sudanese onion cultivars evaluated Baftaim (S), Kamleen, Saggai Improved and Abu-Freaiwa are high dry matter (≥15%) and TSS cultivars that are also pungent, consequently stored well for four months in traditional store. On the other hand the results showed that the introduced cultivar Texas Early Yellow Grano, a mild low dry matter (≤ 10%) cultivar had bad storability of 4-8 weeks under the same conditions, it recorded the highest percentage of rotted, sprouted and black mold infected bulbs. It can be concluded that both cultivars Baftaim (S) and Kamleen showed vigor growth and gave the highest yield, quality and storability compared to other cultivars. Cultivar Texas Early Yellow Grano although showed the lowest growth and storability, gave high total and marketable yield.