Effect of nitrogen fertilization and bulb spacing on saggai red onion seed production in Berber area, River Nile State, Sudan

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1 Sudanese Journal of Agricultural Sciences (2015) 2, Effect of nitrogen fertilization and bulb spacing on saggai red onion seed production in Berber area, River Nile State, Sudan Sahar I. El Abas a, Abdelazim M. Ali a *, Osman E. Mohamed a, Abdalla H. Nourai b a Faculty of Agriculture, Nile Valley University, Dar Mali, Atbara, Sudan. b Agricultural Research Corporation, Shambat Research station, Sudan. Abstract Field experiments were conducted during the winter seasons of 2009/10 and 2010/11 at Dar Mali in the River Nile State, Sudan, to study the effect of different levels of nitrogen fertilizer and bulb spacing on seed production of the red onion cultivar Saggai Red. Four in row spacings (15, 20, 25, and 30 cm) and four fertilization levels (0, 45, 90, and 180 kg N ha -1 ) were used. Nitrogen was applied in the form of urea in four equal doses (10, 30,50and 70days after planting). The result indic ated that nitrogen fertilization significantly increased the length of leaves, number of leaves, length of flowering stalk and number of flowers per umbel. The highest records for the four growth parameters were obtained by 90 kg N fertilization. The narrow spacing (15 cm) recorded the highest leaves length. However, the number of leaves per plant as affected by spacing was not significant. Bulb spacing of 25 cm resulted in the biggest number of flowers per umbel and the longest flowering stalk. The effects of fertilization and spacing on the number of flowering stalk showed no significant difference. Early flowering was obtained by application of 90 kg Nha -1, and 15 cm bulb spacing. The highest 1000-seeds weight was recorded by 45 kg N ha -1 treatment and 25 cm bulb spacing. The maximum yield of seeds ha -1 was obtained by application of 90 kg Nha -1 and 20 cm bulb spacing. Introduction Onion is one of the important edible crops with an annual world production of more than 54 million tons. United Kingdom, Japan and Gulf countries are net importers, while leading exporters include India, Argentina, The Netherland, Spain, Mexico, and Turkey (Brewister, 2008). Onion is grown in most states of the Sudan. The total area under the crop, as e * Corresponding Author. Tel.: address: azimali58@yahoo.com estimated by Mohamedali (2009), was hectares. Ahmed and George (1984) stated that the weather conditions of central and northern Sudan are quite favorable for seed production of many vegetables including onion. The Northern states are considered the best regions for onion production by virtue of having relatively cool, dry and long winter season which favors onion seed production compared to other parts of the country. In the Sudan, onion production was around one million tons of 35

2 fresh bulbs. In the River Nile State, the area under onion cultivation and total production were estimated to be ha and tons, respectively (Mohamed et al., 2003). Mohamedali and Nourai (1988) reported that an average onion seed yield could reach more than 600 kg ha -1. Planting bulb of optimum size, plant spacing, nutrient application, and a suitable sowing date are considered to be the main factors influencing seed yield and quality (Jilani, 2004). Area under commercial onion production fluctuates from one year to another depending on the total production and the prices of the previous year. Almost all onion genotypes grown at present in the Sudan are of local origin and they are named after localities famous for their production or where seeds are traditionally produced such as Kamlin, Seleim, Hilalliya, Fadasi, and Saggai. Famous and popular cultivars in Sudan are Saggai, Kamlin yellow, and Nassi (Mohamed et al., 2003). Recently, Red Baftaim, a Yemani cultivar has dominated production at least in the River Nile State due to its high productivity, and its preferred cooking qualities, compared to local cultivars. Onion, grown in Sudan, suffers from high percentage of premature bolting, doubling, and splitting because farmers grow inferior quality seeds. No consideration is given to optimum mother bulb size and spacing, no adequate isolation distances between seed crops and commercial bulb is observed. Lastly, the optimum planting time is not known (Ahmed and George, 1984, Mohamedali, 2009, Elhag and Osman, 2013). The objective of this study is to determine the optimum bulb spacing and nitrogen fertilization doses required to obtain good quality onion seeds. Materials and methods The study was conducted for two successive growing seasons (2009/10 and 2010/11) at Dar Mali (13 km north of Atbara) in River Nile State, Latitude 17: 48 N, longitude 34: 00 E and altitude 346 m above sea level. The soil of the experimental site is rivarian alluvial with ph range (Table 1). Onion bulbs of cultivar Saggai Red were bought from a seed producer. Medium size bulbs (40 60 mm), free from doubles, splits and bolters were selected for planting. The treatment tested comprised a factorial combination of four nitrogen levels (0, 45, 90 and 180 kg N ha - 1 ) and four in-row spacings (15, 20, 25 and 30 cm). Split plot design was adopted where the nitrogen levels constituted the main plots, while bulb in-row spacings were the sub plots. The treatments were rep- Table 1 Soil analysis data Item 2009/ /11 Clay % Silt % Sand % ph Ec e (ds m -1 ) CaCo 3 % Ca+Mg (meq/l=mg/kg soil) 4 3 Na (meq/l) N (meq/l)

3 licated four times. The nitrogen fertilizer was applied as four equal split doses at 10, 30, 50, and 70 days after bulb planting in the form of urea (46 % N). Bulbs were planted in the first week of November in rows 70 cm apart. Leaf length (cm) Length of leaves of randomly selected 10 bulbs per plot was measured using a ruler, four, six and eight weeks after bulbs planting. Number of leaves plant -1 The number of leaves, of randomly selected 10 bulbs per plot, was counted four, six and eight weeks from planting. Flower stalk length (cm) The length of flower stalk of randomly selected 10 plants was determined using a ruler. Number of flowering stalks plant -1 The number of flowering stalks per plant was taken after ten weeks from planting. Ten, randomly selected plants in each plot, were used for counting the flowering stalks. Days to 50% flowering Days from bulb sowing to 50% flowering, was determined, for each plot, when 50% of plants reached blooming. Total flowers umbel -1 The total number of flowers umbel -1 was calculated from two umbels selected randomly from each plot. Seed yield (kg ha -1 ) One row from the center of the plot was harvested. Seed yield in kg ha -1 was calculated according to the following formula. Seed yield (kg ha -1 ) = Weight of seed (g) per row m Length of row in m 1000 g 1000-seed weight (g) After threshing, 1000 seeds from each treatment were weighed using a sensitive balance. Data collected were analyzed using SAS computer program, and the Least Significant Difference was used to compare treatment means. Results and discussion Seed yield Nitrogen fertilization significantly affected seed yield in both seasons (Table 2). The highest seed yield was obtained by the application of 90 kg N ha -1 ( kg ha -1 in season 2009/10 and kgha -1 in season 2010/11. The lowest seed yield was obtained by the control treatment ( kg ha -1 in season 2009/10 and kg ha -1 in season 2010/11). Differences in seed yield, due to spacing effect, were not significant in the first season (2009/10), however it was significant in the second season. The highest seed yield in both seasons was obtained by 20 cm spacing; however, spacing bulbs between cm yielded almost similar results. The lowest seed yield in both seasons was recorded by 15 cm spacing. The interaction among treatments was significant only in the second season. Fertilization using rates above 90 kg N ha -1 yielded heavier seeds in large spaced plots compared to the 15 cm spaced ones. Increasing fertilizer dose up to 90 kg N ha -1 increased seed yield, however, there was no significant increment in seed yield with higher fertilizer dose. The result agreed with those of El-Hilo et al. (1970); Ahmed and Abdalla (1984); Mohamedali and Nourai (1988) and Nandphuri et al. (1968) who indicated that increase in onion seed 37

4 yield, realized as a result of high nitrogen level, might be due to more nutrients being available for plant growth and seed development and yield per plant. Nourai et al. (2003) attributed the increase in seed yield, to the increase in nitrogen and the increase of seed yield of individual plants. Also the study indicated that 20 cm row spacing produced maximum seed yield. El-Hilo and Nourai (1975) reported similar results. Weight of 1000-seed: There was significant variation with respect to seed weight due to the influence of nitrogen fertilization and bulb spacing effects in both seasons (Table 2). With respect to nitrogen, in both seasons, the highest seed weight was obtained by 45 kg N ha -1 treatment and the control treatment, showed the lowest seed weight. The 25 cm and 15 cm spacing treatments recorded the highest and the lowest seed weight, respectively. There was no significant interaction between fertilization and bulb spacing. Both narrow spacing and low nitrogen regime resulted in reduced 1000-seed weight. Increasing plant density with no fertilizer applied reduced 1000-seed weight. Results of this study were in conformity with that conducted by Chaudhary et al. (1990) who reported that 1000-seed weight was significantly higher in plants spaced 30 cm apart and also with that of Gamie et al. (1996) and EL -Hilo and Abu Gough (1973) who reported that whenever nitrogen is added, relatively heavy seeds are expected to be produced. Number of flowers umbel -1 The highest number of flowers was obtained by the application of 90 kg N ha -1 and the lowest by the control treatment in both seasons. Regarding the spacing effect, no significant differences were observed in the first season (2009/10). In the second season (2010/11), the highest number of flowers (573), and the lowest (459) were recorded in the 30 cm and 15 cm bulb spacing, respectively. This result agree with Jilani (2004) and Hassan and Ayoub (1978) who reported an increase in percent bolters and in number of flowers in onion with the application of nitrogen. In contrast, El-Hilo and Mohamedali (1971) and Nourai (1982) repor ted that nitrogen application reduced the developing flowers. With respect to spacing, the study indicated that the wide spacing resulted in increased number of flowers umbel -1 compared with the smallest spacing. Mean length of flowering stalks The tallest flowering stalk was obtained by the application of 90 kg N ha -1 and the shortest by the control treatment in both seasons. Different bulb spacing significantly affected the flowering stalk length only in the first season. The tallest flowering stalk in the first season (86.1 cm) was recorded by 25 cm spacing and the shortest flowering stalk (84.08 cm) was recorded by 30 cm spacing. The interaction effect was significant only in the first season. The increased length of flowering stalk was obtained by the higher level of nitrogen. However, closer spacing produced tall flowering stalks, in the presence of nitrogen, while wider spacing gave the same results in the absence of nitrogen (Table 2). Nandpuri et al. (1968) reported similar results. Abu- Sarra (2006) found similar results indicating that the increase in nitrogen level resulted in increased stalk height in small and mid size bulbs compared to- that 38

5 with large size bulbs. Number of flowering stalks bulb -1 In both seasons, no significant differences were observed in the number of flowering stalks 10 weeks after planting, neither to fertilization, nor to bulb spacing. The interaction effect was also not significant (Table 2). Results of this study with regard to number of flowering stalk per bulb contradicted Abu-Sarra s (2006) findings and agreed with that of Ahmed (1982), who found that nutrient regime did not affect the number of stalks (inflorescence) per bulb. Mishar (1994) performed similar experiment on the seed production and found that fertilization rate of 120 kg N ha -1 significantly increased the number of flowering stalks. With respect to spacing, Nourai et al. (2003) and Gamie et al. (1996) found that low plant density resulted in more stalks per bulb. Days to 50 % flowering There was a significant variation in the number of days to flowering due to nitrogen dose (Table 2). In both seasons, differences were highly significant. The longest time to blooming, in both seasons, was recorded by the control and the shortest time was obtained by the application of 90 kg N ha -1. On the other hand, bulb spacing affected time to blooming, and the effect was significant in season (2010/11) only. The longest time was recorded by 30 cm spacing and the shortest time by 15 cm spacing. Application of fertilizer reduced days to flowering compared to the control treatment. This might be due to the fact that the application of nitrogen led to increased rate of vegetative growth which in turn resulted in early flowering. Smaller bulb spacing enhanced the period to blooming. Wider spacing (30 cm) delayed flowering, while closer spacing (15 cm) resulted in earlier flowering, probably due to competition inducing earlier flowering. Leaf length The addition of nitrogen significantly increased the length of leaves 4, 6 and 8 weeks after planting (Table 3). This result is similar to those of Kadamas and Amans (1991), Perez et al. (1996), Chakrabatri et al. (1980), Singh and Dhankhar (1988) Singh and Mohanty (1998), Osman et al. (1992) and Nandpuri et al. (1968) who stated that addition of nitrogen fertilizer enhanced vegetative growth of onion plants. Kumar et al. (1998), Bhardwaj et al. ( 1991) and Bokshi et al. (1989) found also that nitrogen application increased length of leaves bulb -1. However, the result obtained was not similar to that of Leghari et al. (1997) who found that nitrogen had no effect on length of leaves bulb -1. With respect to spacing, the study indicated that narrow spacing resulted in increased leaf length compared with wider spacing, at least in one season. The interpretation of this result was possibly due to competition for nutrient, moisture and light as indicated by Jilani (2004). It seems that densely planted bulbs, when-ever moisture and nutrients are sufficient, seems to grow taller seeking for light. Leaves number per planted bulb Nitrogen fertilization significantly affected leaves number in both seasons. The higher number of leaves was obtained by application of 90 kg N ha -1, and the lowest was recorded by the control. Regarding the bulb spacing and interaction effect, differences were not significant (Table 3). 39

6 Table 2 Means of seed yield (kg ha -1 ), 1000 seed weight (g), number of flowers umbel -1, flowering stalk number plant -1, flowering stalk length (cm) and days to 50 % flowering of Red Saggai onion cultivar as affected by N fertilizer and spacing Seed yield (kg ha -1 ) 1000 Seed weight (g) Number of flowers umbel -1 Flowering stalk number plant -1 Flowering stalk length (cm) Days to 50 % flowering Season 2009/ / / / / / / / / / / /11 Nitrogen level (kg N ha -1 ) Mean Plant spacing (cm) Mean CV 5.47 % 7.62 % % 9.44 % % 4.63 % % % 1,79 % 3.56 % 1.36 % 1.86 % LSD (Nitrogen) NS NS LSD (Spacing) NS NS NS NS 1.00 NS NS 0.79 LSD (Interaction) NS NS NS NS NS NS 1.13 NS NS NS NS: Not significant 40

7 Table 3 Means of leaf length and leaf number 4, 6 and 8 weeks after planting of Red Saggai onion cultivar as affected by N fertilization and spacing Leaf length (cm) Leaf number 4 weeks 6 weeks 8 weeks 4 weeks 6weeks 8 weeks Season 2009/ / / / / / / / / / / /11 Nitrogen level (kg N ha -1 ) Mean Plant spacing (cm) , Mean CV 4.80 % 2.26 % 5.07 % 2.45 % 2.35 % % 5.21 % % 4.35 % 3.57 % LSD (Nitrogen) NS LSD (Spacing) NS NS NS NS NS NS NS NS NS NS LSD (Interaction) NS NS NS NS NS NS NS NS NS NS NS: Not significant 41

8 The positive effect of fertilization on leaves number per plant agreed with results reported by Levy et al. (1978) and Kumar et al. (1998). They reported that the number of leaves per plant were increased in onion with the application of nitrogen up to 150 kg ha -1. Jilani (2004) also found that the highest rate of nitrogen ( and 100 kg ha -1 ) delayed flowering, however, it increased the number of leaves per plant. In contrast, Leghari et al. (1997) found that nitrogen levels did not affect the number of leaves per plant. The study indicated that the optimal dose of nitrogen fertilizer for onion seed production, in continuously cultivated rivarian type of soil, as Dar Mali area, was about 90 kg N ha -1. No significant results were obtained at higher nitrogen doses. To obtain heavy seeds with high total yield, 70 cm rows, cm within row spacing is recommended. References Abu-Sarra, A.F. (2006). Effect of mother bulb size and nitrogen fertilization on production of red onion seed at Rahad scheme. Crop Husbandry Committee proceedings. ARC, Sudan. Ahmed, A.A. (1982). The influence of mineral nutrition on seed yield and quality of onion (Allium cepa L.). Ph.D Thesis, University of Bath. Ahmed, A.A.E., George, A.T.R. (1984). The effects of mineral nutrition on seed yield and quality in onion. ActaHorticulturae 143, Ahmed, L.H., Abdalla, A.A. (1984). Nitrogen and phosphorus fertilization in relation to seed production in onion (Allium cepa L.) ActaHorticulturae 143, Bhardwaj, M.L., Rattan, R.S., Kohli, U.K. (1991). Effect of nitrogen, phosphorus and depth of bulb planting on seed production in onion. Indian Journal of Horticulture 48, Bokshi, A.I., Mondal, M.F., Pramanik, M. (1989). Effect of nitrogen and phosphorus nutrition on the yield and quality of onion seeds. Bangladesh Horticulture 17, Brewister, J.L. (2008). Onions and other vegetable alliums. 2 nd Edition, Oxford, UK. Chakrabarti, A.K., Choudhury, B., Singh, C. (1980). Effect of nitrogen and phosphorus on seed production of onion (Allium cepa L.). Seed Research 8, 1 4. Chaudhary, F.M.K., Mehmood, A.M., Qadir, A. (1990). Effect of plant density on plant growth size and yield of onion. Pakistan Journal of Agricultural Research 11, Elhag, A.Z., Osman, H.M. (2013). Effect of plant spacing on onion seed quality. Universal Journal of Applied Science 1, El-Hilo, A.H., Ayoub, A.T., Abulgasim, A. (1970). Effect of fertilizer and number of rows per ridge on onion seed yield. Agricultural Research Corporation, Miscellaneous Horticultural Reports, , El-Hilo, A.H., MohamedaIi, G.H. (1971). Effect of plant population and nitrogen; level on yield of onion seed at Girba. Agricultural Research Corporation, Miscellaneous Horticultural Reports , 50. EL-Hilo, A.H., Abu Gough, A.A. (1973). Onion seed yield from whole and differential cut bulbs Agricultural Research Corporation, Miscellaneous Horticultural Reports , 48. El-Hilo, A.H., Nourai, A.H. (1975). Effect of population on onion yield. Annual Reports, Hudeiba Research Station, Sudan. Gamie, A.A., El-Rahim, G.H.A, lmam, M.K. (1996). Effect of bulb size and plant density on the onion seed production under upper Egypt condition. Asuit Journal of Agricultural Sciences 27,

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