Effect of Deficit Irrigation on Common Bean (Phaseolus vulgaris L.) Under Conventional, Fixed and Alternate Furrow Irrigation Systems at West Wellega, Ethiopia

Improving water use efficiency is one important strategy for addressing future water scarcity, which is driven particularly by increasing human population. Enhancing agricultural water productivity is a critical response as it is by far the main consumer of global fresh water. This study investigated the response of common bean (Phaseolus vulgaris L.) to moisture deficit under conventional, alternate and fixed furrow irrigation system over a three years period.  A field experiment was conducted at Haru Agricultural Research sub-center. A randomized complete block design (RCBD) with three replications was used. nine treatments which combined and imposed at all growth stages were used. The three years combined result indicated that there were a highly significant (P<0.01) variation among treatments for grain yield, above ground dry biomass yield, plant height and water productivity. The grain yield of common bean was significantly (P<0.01) affected due to moisture deficit and irrigation methods. Accordingly, the highest grain yield was obtained from conventional furrow 100% ETc irrigating all growth stage treatment followed by conventional furrow 75% ETc and 50% ETc. The highest water productivity of 0.84 kg m -3 was obtained from alternate irrigation system at 75% ETc but the yield loss is not tolerable. conventional furrow 75% ETc and conventional furrow 50% ETc gave a better yield with a moderate water productivity. Therefore, for better water productivity without a significant yield loss, it is recommended to use conventional furrow irrigation with 75% ETc and conventional furrow irrigation 50% ETc. In addition, if the water resource is not scarce in the area, it is recommended to use conventional furrow irrigation with 100% ETc throughout the whole growth stage to obtain optimum yield. Keywords; Water productivity, Deficit irrigation, ETc, Furrow irrigation system, common bean DOI : 10.7176/JNSR/9-1-04

crop along with reducing grain yield and mean weight of hundred seeds following water stress, have been reported (Nielsen et al., 1998 andMolina et al., 2001). Furthermore, common bean cultivar has reported to respond differently to soil moisture stress depending on the severity of water stress (Boutraa et al., 2001). Payero et al., (2008) reported that water deficit can affect growth, development and physiological processes of maize plants, which reduce biomass yield. However, there is a gap on water productivity enhancement and the critical moisture deficit level for optimal production which can help to face the challenge occurs due to water scarcity. Therefore, determination of the effect of deficit irrigation on water productivity is important to utilize the limited water resource without significantly affecting irrigated crop yield. Considering the scarcity of irrigation water, this research was aimed to determine the effect of moisture deficit on water productivity of irrigated common bean.

Materials and Methods Description of the experimental area
The experiment was conducted at Haru agricultural research sub-center during the growing season of 2016 and 2015. It was found in west Wellega zone Gimbi area. The rainfall pattern of the area is bimodal with a short rainy season from February to March and the main rainy season from June to September. The most dominant soil type of the area is clay loam.

Treatments and design
A field experiment was carried out in three seasons of 2016 and 2018. Randomized Complete Block Design (RCBD) with three replications was used following the procedure of Gomez and Gomez (1984). Nine treatments of different deficit irrigation level were factorially combined and randomized in plots as shown in Table 1. The optimal irrigation schedule (ETc) was computed with Cropwat model. Fixed furrow 50% ETc 7 Conventional furrow 100% ETc (Check) 8 Conventional furrow 75% ETc 9 Conventional furrow 50% ETc Each individual plot had area of 3m X 3m = 9m 2 , which consists of 6 rows. Goberasha common bean variety (Phaseolus vulgaris L.) was used as seed source. The recommended spacing of 60 and 10cm between row and plant was employed. Each experimental treatment was fertilized with recommended fertilizer application, that was 100kg/ha and 100kg/ha of DAP and Urea, respectively. All cultural practices were done to all treatments in accordance to the recommendation made for the area. Irrigation water was applied as per the treatment to refill the crop root zone depth close to field capacity.

Data collected
Yield and growth parameter were recorded and the treatments were compared based on grain yield and growth parameter, which includes plant height, above ground biomass and grain yield. Also, water productivity of the crop was estimated.
Grain yield was calculated by harvesting the total number of plants in the net plot (3.75 m 2 ) and grain yield per plot was measured using electronic balance and then adjusted to 10.0% moisture and converted to hectare basis. Above ground biomass was determined by harvesting all the plants from the net plot area at physiological maturity and weighed after sun drying to a constant weight and converted to hectare basis. The water productivity was calculated by the ratio of harvested yield per total water used.

Result and Discussion Plant height
The statistical analysis showed that different deficit irrigation levels had a highly significant (P<0.01) effect on plant height (Table 2). The maximum plant height was observed at conventional furrow 100% ETc followed by conventional furrow 75% ETc (Table 2). Whereas, the minimum was obtained from fixed furrow 50% ETc. From the current finding, plant height was decreased as a soil moisture content in the root zone decreased. This probably is a natural result of the effect of water deficit resulting from the cell elongation and division, and reflected on the elongation of stem internode (Hillel, 1990). The increasing plant height with adequate depth of irrigation application also indicate the favorable effect of water in maintaining the turgor pressure of the cell which is the major prerequisite for growth (Vaux and Pruit, 1983). On the contrary, shortening of plant height under soil moisture stress may be due to stomata closure and reduced CO2 and nutrient uptake by the plants and, hence, photosynthesis and other biochemical process are hampered, affecting plant growth (El-Noemani et al., 2009). In addition, the plant height shows a decreasing trend for the different furrow irrigation system, the maximum was from conventional furrow irrigation method followed by alternate furrow and fixed furrow irrigation methods (Table 2). Webber et al., (2006) found that common bean (Phaseolus vulgaris) is not well suited to water deficit conditions and alternate furrow irrigation as green gram (Mung bean). Rosadi et al., (2005) revealed that a small level difference in moisture deficit levels did not affect plant height, whereas, it affects when the moisture deficit levels was so high which agrees with the current finding. Emam et al., (2010) and Shenkut and Brick (2003) reported that plant height is affected by severe influence from environmental factors such as water stress.

Above ground dry bio-mass
Different deficit levels and furrow application method has a significant influence (p<0.01) on dry above ground biomass yield. The mean dry biomass at different deficit level showed decreasing trend due to decreasing of irrigation water applied. From table 2, the maximum above ground dry biomass was obtained from conventional furrow 100% ETc followed by conventional furrow 75% ETc. Whereas, the minimum was obtained from fixed furrow 50% ETc (Table 2). From the present study the trend of dry above ground biomass production fairly decreasing as the amount of water applied decreases. This is due to higher biomass production for well irrigated plots since irrigation was applied based on crop water requirement and moisture stress is reduced. Emam et al., (2010) reported that plant dry weight was decreased significantly by increasing water stress. Similar results were reported in the study by Karam et al., (2005). They reported that the applied irrigation water amount reduced dry matter accumulation also reduced. Greater accumulation of dry matter is one of the important inputs to assure total translocation of photosynthate materials to the seed. As reported by several researchers, if water is a deficit factor, there will be a retarded growth in the vegetative and reproductive parts of plants. Terán and Singh (2002) indicated that shoot biomass accumulation is considered as an important trait to attain high seed yield in seed legumes. On the other hand, water deficit can decrease plant height and total biomass (Terán and Singh (2002) and White et al., (1994)) also observed that water deficit retarded plant growth which in turn resulted in production of low biomass and, hence, low grain yield. In addition, the furrow irrigation methods showed a significant difference on above ground dry biomass. Conventional furrow irrigation system is a superior one followed by alternate furrow irrigation and fixed furrow irrigation (Table 2). Mulugeta Mohammed and Kannan Narayanan (2015) and Meskelu et al., (2018) revealed that maize above ground dry biomass is higher for conventional furrow irrigation system than alternate and fixed furrow irrigation system. Over all plant growth is a process of biomass accumulation and is a consequence of the interaction of photosynthesis, respiration, longdistance transport, water relations and mineral nutrition processes. Water deficit stress affects these processes considerably. Many other researchers have also showed that water deficit decreased biomass production of different crops.

Grain yield
The three years over year analysis of grain yield shows a highly significant difference (P<0.01) on the use of different furrow system as well as on different deficit levels of irrigation. The result revealed that conventional furrow 100% ETc gave the highest grain yield (2393.5 K.g ha -1 ) followed by conventional furrow 75% ETc (2053.7 K.g ha -1 ) ( Table 2). The minimum grain yield was obtained from fixed furrow 50% ETc (822.3 K.g ha -1 ) followed by alternate furrow 50% ETc (900.5 K.g ha -1 ) ( Table 2). The interesting finding from the present study is conventional furrow irrigation 75% ETc had a minimum yield loss (14.75%) over the control treatment. The result indicated that the irrigation water applied to the highest yielding treatment next to the control was 25% less than that of applied to the control. As the moisture deficit level increased up to 75% of the control one the yield loss goes up to 65.65% on fixed furrow irrigation water application method. It is well known that the ultimate effect of drought in legumes and cereals is reduction of grain yield. In the present study, the stress at the 75% deficit had affected seed yield so severely, far from normal size and weight and also shriveled in morphology. Simsek et al., 2011 revealed that when the moisture deficit levels increased the seed production of the common bean cultivars reduced significantly. The findings of this study agree with the findings of most researchers, who had proved the fact that water deficit can decrease seed yield to the different levels depending on the extent of the stress and on growth stage at which the stress occurred. Ghassemi-Golezani et al., (2009) obtained a 20% yield reduction with stress during early and late vegetative growth and 50% reduction when stressed during early pod filling stage. Timsina et al., (1993) also reported a yield reduction of 40% -89% in water stressed bean genotypes. Additionally, Taddese and Amare (1994) studied the effects of water limitation on growth and grain filling of faba bean cultivars and found out that water deficit stress considerably reduced grain yields due to large reductions in growth, grain filling duration, grain weight and grains per plant. Researches conducted on maize (Jonghan Ko and Giovanni Piccinni, 2009) and on onion (Enciso et al., 2009) revealed that, as the moisture deficit level increased the production of the crop will declined, which agrees with the current finding. When we compare the method of water application conventional furrow is best suited for common bean production, as the irrigation method changed to alternate furrow and fixed furrow the yield loss is become 47.11% and 52.81% respectively. Manal and Abdallh (2013) research work on maize revealed that, the highest grain yield was obtained with conventional furrow irrigation while, the lowest yield was obtained with fixed furrow irrigation which agreed with the current finding. As indicated by many researchers, water stress decreases the final leaf area, net photosynthesis, light use efficiency (Egli, 1998, Husain et al., 1990and Grashoff, 1990, pod retention and filling by reducing the availability of assimilates and distorting hormonal balance (Hura et al., 2007) and final yield reduction will be the consequence.

Water productivity
From the results of analysis of variance (Table 2), there were highly significant difference at (P<0.01) between the three irrigation systems in water productivity. This is because of the difference in percentage of water actually converted to evapotranspiration out of the total amount applied. This is consistent with the significant improvements in water productivity that have been associated with alternate furrow irrigation (Zhang et al., 2000). From the table 2, the maximum water productivity obtained from alternate furrow 75% ETc followed by fixed furrow 75% ETc. whereas, the minimum was obtained from fixed furrow 50% ETc. From the current study, the maximum water productivity was obtained at 66.5% of soil moisture deficit from the control treatment, as a moisture deficit level increased up to 75% of the control one the water productivity becomes low. The reason for this finding is may be the grain yield produced by the applied water is very low because of a high level of moisture stress generated in the root zone. Different research conducted by Kirnak et al., (2005) and Sarkar et al., (2008) stated that higher water productivity will be obtained on maximum water deficit level which contradict with the current findings. Yalew (2007) investigated that although yield increment is generally accompanied with an increase in the total water use, higher water productivity was recorded with the deficit application. 8.8 Means with the same column followed by the same letters are not significantly different. *significant (p<0.05), **significant (p<0.01), ***significant (p<0.001), ns not significant (p<0.05).

Conclusion and Recommendation
The result of this study confirm that water availability plays a major role in plant height, dry above ground biomass and grain yield weight of growing common bean. Common bean production depends mainly on soil water condition. A high level of soil water availability usually ensures an optimal common bean growth. Any restriction in the supply of irrigation water induces decrease plant growth. Overall, as a moisture deficit level increased the grain yield, above ground dry bio-mass yield and plant height decreased. On water productivity issue, as a moisture deficit level increased as mid stress level the water productivity enhanced, whereas, when the deficit level goes to sever moisture stress level the water productivity becomes minimum. Regarding of furrow irrigation methods, there were major differences among conventional, alternate and fixed irrigation in terms of studied traits. Regarding less water consumption of alternate and fixed irrigation compared with