The Effect of Nitrogen Fertilization and Plant Density on Growth, Yield, Quality and Shelf-life of Bulb Onions (Allium Cepa L)

Abstract

Two experiments were conducted at the field station of the University of Nairobi, Kabete and at the National Horticultural Research Centre, Thika during the Short rains and Long rains, 1990 and 1991 respectively. In the first experiment, the response of four (three recently introduced and one local onion cultivars) to application of four levels of nitrogen fertilizer (0, 13, 26 and 39 N Kg/ha) applied as CAN (26%) was studied. The 4x4 factorial experiment was laid out in a split-plot design with three replicates. Nitrogen was applied in the mainplots and the cultivars in the sub-plots. Data on days to maturity, total and marketable yield, bulb weight and size, neck-thickness, splitting and doubling, total soluble solids (TSS) and shelf-life was collected. The results showed that total and marketable yield significantly increased with increasing nitrogen levels. However, the magnitude of this increase differed with locations, cultivars, and seasons. The highest bulb yield of 70.4 tons/ha was recorded at the highest level (39 Kg N/ha) of nitrogen. Increasing nitrogen upto 26 Kg/ha • ... rA significantly reduced duration to maturity by about 4 days. Application of upto 13 Kg N/ha significantly reduced the number of bulbs in Grade 3 but had no significant effect on the number of bulbs in Grade 1 and 2. Nitrogen application had no significant effect on percentage splitting and doubling, bulb weight, neck-thickness and shelf-life. Significant differences were observed between the cultivars in terms of maturity period, total and marketable yield, bulb weight and shelf-life. The newly introduced cultivars (KON5.KON6 and KON7) were all superior to the local cultivar (Tropicana F, xviii hybrid) in all these aspects. Significant location differences were also detected where total and marketable yield, bulb weight and size and splitting/doubling were all significantly higher at Kabete than at Thika. Significant interactions between nitrogen and cultivars on total yield were and also between locations and nitrogen on splitting /doubling and TSS. The interaction between locations and cultivars on number of days to maturity, total yield, bulb weight and marketable yield was significant. A significant interaction between locations, nitrogen and cultivars was observed in total yield. In the second experiment, the four onion cultivars were grown at three plant densities (38, 56 and 111 plants/m2 to study the effect of plant density on bulb yield and quality. The experiment was laid out in a split-plot design with three replicates. Cultivars were planted in the mainplots and the density in the sub-plot. Results showed that increasing plant density significantly increased total and Marketable yield. The percentage of splits and doubles significantly increased with plant density while the number of bulbs in Grade 1 was significantly reduced with increased plant density. Increasing plant density had no significant effect on maturity period , neck- thickness and bulb weight. The newly introduced cultivars (KON5, KON6 and KON7 ) were again significantly superior to the locally grown Red creole in terms of buib yield, maturity period (they matured earlier) and had larger bulbs. Red creole showed a strong tendency to split especially at high plant density. Significant locational differences were observed in splitting/doubling, bulb weight and maturity period. The interaction between locations, plant density and cultivars on splitting and doubling was significant.