Water availability is the main limiting factor of crop productivity than all of the rests due to its paramount importance for normal plant growth and developments
Fertilizer management problems
Plant nutrient management improvement has an important role in normal plant growth and developments especially for the vegetative plant parts to give optimum yields. The addition of manure, compost and/ or inorganic fertilizer improves the onion production and hence benefits the producers (zeleke and derso, 2015). According to Assefa et al. (2015) finding, using the optimum amount of fertilizer nutrients substantially increases the productivity of onion bulbs beside to using of improved cultivars. Because of Onion is one of the heavy feeders vegetable crop, it requires more mineral fertilizers than other vegetables for a bulb and shot growth (Yohannes et al., 2013). According to Simon et al. (2015) report, three onion varieties (Adama Red, Bombe Red, and Nafis) have been tested at humbo, wolaita zone; Ethiopia was responded to different application of nitrogen and phosphorous fertilizer rates. The finding revealed that the size and onion bulb yield has increased as the level of nitrogen and phosphorous were increased which implies as the optimum nutrient management has a positive contribution to yield improvement of onion production and productivity especially for those areas where a nutrient deficiency is critical. Cara publis jurnal . (2013) also reported a similar finding on the effects of combined application of nitrogen and farmyard manure which has increased the onion bulb yield at Jimma environmental condition.
Furthermore, the effects of nitrogen and phosphorous on onion yield and yield components were studied on the vertisol of Shewa Robit, Northeast Ethiopia, has been responded to a different rate of the fertilizers and recommended based on the optimum yield obtained ( Almas Ikram Kayani ., 2011). According to this research output, the application of nitrogen and phosphorus fertilizer showed a significant response on a fresh bulb yield, dry bulb yield, and total dry biomass and on harvesting index of onion as compared to the non applied treatments. Generally, all the results of different nutrient management practices have been shown that the onion yield production and productivity can be maximized by applying different plant nutrient management systems for the specified soil types at specific locations. Even though, the rate of fertilizers should be determined based on the soil type of the areas, 200kg/ha DAP before transplanting by incorporating with soil and 100kg/ha of urea after 45 days of transplanting has been advised as it is sufficient in most parts of the country ( Andrew Tapiwa Kugedera , 2015).
Crop water requirement problems
Water availability is the main limiting factor of crop productivity than all of the rests due to its paramount importance for normal plant growth and developments. Hence, due to its shallow root system and needs frequent irrigation water after a short interval, onion is susceptible to water stress as compared to other crops (Fitsum et al., 2016). Knowing a number of water requirements of onion based on the specific area is basically important to produce the optimum onion yields. Bossie (2009) elaborated that, knowing of the water requirement and the coefficient values of the crop can help to accurately plan and manage the irrigation water for onion production at different locations even an area where a water shortage is very critical. Therefore, assuming of high irrigation frequency and better scheduling method may be expected to increase the applied fertilizer use efficiency, reduces leaching effects and to improve onion yields by increasing bulb sizes (Serra and Currah, 2002). Currently, from the recommended onion cultivars by Melkassa agricultural research center, Bombay red is the most widely grown onion variety under irrigation water in the country due to its higher bulb yield, earliness and susceptible to the rotting disease under a rain-fed condition at maturity stage (Nikus and Mulugeta, 2013). As a result, knowing of the individual crop water requirements help to produce more than two times per annum to ensure the year-round production of onion in order to get a high return as well as to reduce the susceptibility of the crop to various diseases and insect pests.
1.Esheteu Bekele, E., Azerefegne, F and Abate, T. (2006). Facilitating the Implementation and Adoption of Integrated Pest Management (IPM) in Ethiopia. Planning Workshop, 13-15 October 2003, Melkassa Agricultural Research Center, EARO. Jointly organized by the Association for Advancement of IPM (ASAI) and the Ethiopian Agricultural Research Organization (EARO). DCG, Miljøhuset, Oslo.
2.Farooq U, Sharif M, Erenstein O (2006). “Adoption of Zero Tillage in the Rice- Wheat, Zone of Irrigated Punjab, Pakistan”, Rice-Wheat Consortium for the Indo-Gangetic Plains, CG Block, NASC Complex, DPS Marg, Pusa Campus, New Delhi-110012, India.
3.Kumilachew A., Mengistu K., and Fekadu G (2014). Risks in vegetables production from the perspective of smallholder armers: The case of Kombolcha Woreda, Oromia region, Ethiopia. Agriculture, Forestry and Fisheries 2014; 3(6-1): 1-5
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