Abstract
<p>The broad objective of this study was to test Deficit Irrigation (DI) as an appropriate irrigation management strategy to improve crop water productivity and give optimum onion crop yield. A field trial was conducted with drip irrigation system of six irrigation treatments replicated three times in a randomized complete block design. The crop was subjected to six water stress levels 100% ETc (T100), 90% ETc (T90), 80% ETc (T80), 70% ETc (T70), 60% ETc (T60) and 50% ETc (T50) at vegetative and late season growth stages. The onion yield and quality based on physical characteristics and irrigation water use efficiency were determined. The results indicated that the variation in yield ranged from 34.4 ton/ha to 18.9 ton/ha and the bulb size ranged from 64 mm to 35 mm in diameter for T100 and T50 respectively. Irrigation water use efficiency values decreased with increasing water application level with the highest of 16.2 kg/ha/mm at T50, and the lowest being13.1 kg/ha/mm at T100. It was concluded that DI at vegetative and late growth stages influence yields in a positive linear trend with increasing quantity of irrigation water and decreasing water stress reaching optimum yield of 32.0 ton/ha at 20% water stress (T80) thereby saving 10.7% irrigation water. Onion bulb production at this level optimizes water productivity without significantly affecting yields. DI influenced the size and size distribution of fresh onion bulbs, with low size variation of the fresh bulbs at T80.</p>
Highlights
The ever increasing world population and the demand for additional water supply by industrial, municipal, and agricultural sectors exert a lot of pressure on renewable water resources forcing the agricultural sector to use the available irrigation water efficiently to produce more food to meet the increasing demand (Andarzian et al, 2011; Valipour, 2014a)
Optimum yield is achieved by balancing between Irrigation water use efficiency (IWUE), yield reduction and water saving. These findings indicate that T80 results in 10.7% water saving without substantial negative effect on irrigation water use efficiency of the crop (Figure 6)
It was further concluded that production at this level optimizes water productivity without significantly affecting crop yields
Summary
The ever increasing world population and the demand for additional water supply by industrial, municipal, and agricultural sectors exert a lot of pressure on renewable water resources forcing the agricultural sector to use the available irrigation water efficiently to produce more food to meet the increasing demand (Andarzian et al, 2011; Valipour, 2014a). To achieve sustainable use of limited water resources available for agriculture, it is necessary to develop guidelines for irrigation applications to be used by extension service providers and farmers (Geerts, Raes, & Garcia, 2010). This study was conducted in Nandi County, in the western part of Kenya which experiences water scarcity during the dry season from October to March, often resulting in conflicts. During this season vegetable supply is low while its demand is high. Deficit irrigation (DI) strategy was chosen for use in the study as it maximizes irrigation water productivity and optimizes crop yields (English & Nakamura, 1989; Zhang & Oweis, 1999; Fereres & Soriano, 2007; Geerts & Raes, 2009)
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