Journal of Natural Sciences Research www.iiste.org ISSN 2224-3186 (Paper) ISSN 2225-0921 (Online) Vol.5, No.15, 2015 79 Effect of Intra-Row Spacing on Haricot Bean (Phaseolus vulgaris L.) Production in humid Tropics of Southern Ethiopia. Yacob Alemayehu * Mieso Kaweti Ararsa Boki Department of Plant Science, College Agriculture and Natural Resource, Dilla University. P.O. Box 419, Dilla, Ethiopia ABSTRACT Field experiment was conducted at the research farm of Dilla University in 2015 main cropping season, with the objective of determining the optimum plant spacing for better productivity of haricot bean under the humid conditions of Dilla, southern Ethiopia. A well-adapted haricot bean variety namely, Hawassa-Dume, was tested at 5, 10, 15 and 20 cm intra-row spacing with 40 cm inter-row spacing for each treatment. The analysis of variance (ANOVA) revealed that plant height, number of branch plant -1 , pod plant -1 , total biomass and grain yield were significantly (p < 0.05) influenced by varying intra-row spacing. In contrary, number of leaves plant - 1 , seed pod -1 and thousand seed weight were insignificant in all intra-row spacing. Increasing the intra-row spacing beyond 10 cm resulted in significant reduction in grain and biomass yields, but consistent increase in number of branches plant -1 and pod plant -1 . Compared with the grain yield obtained at widest intra-row spacing (20 cm), increase in the grain yield was recorded at 5 cm and 10 cm intra-row spacing that were 22.9% and 33.2%, respectively. In general, the result suggests that narrow intra-row spacing at 10 cm which corresponds to plant population density of 266,667 plants ha -1 was better for achieving optimum grain yield under humid environment. To confirm this, similar investigations should repeated in multi- locations and years. Keywords: Yield, yield components, Haricot bean, Intra-row spacing 1. INTRODUCTION Haricot bean (Phaseolus vulgaris L.) is one of the major legume crops produced in various parts of Ethiopia. The total area and production estimated to be 366,876.94 ha and 46,300.9 tons respectively (CSA, 2013). Haricot bean is grown highly for consumption as a food crop (an important source of protein) (MoARD, 2009), and consumed highly in traditional dishes: such as nefro (boiled grain mixed with maize), and wet (local soup). Despite its tremendous importance, the current national average yield of haricot bean is low 1.26 t ha -1 (CSA, 2013), which is far lower than its yield potential, mainly owing to various production constraints. Among the constraints, lack of well adapted varieties, fertilizers levels, planting date, row spacing (population density), weed and disease control and weather conditions are important factors determining the productivity and quality of bean crops (Chemeda, 1997; Solomon, 2003; Essubalew et al., 2014; Gebremedhin, 2015). The grain yield of haricot bean is highly affected as a result of many complex morphological and physiological processes occurring during the growth of the crop, which ultimately influence the yield and yield components. Based on climatic conditions, several researchers obtained different response of haricot bean in relation to spacing. Solomon (2003) observed seed yield increase from 42.44 to 56.89 g plant -1 with increasing 7 x 40 and 16 x 40 cm intra-row spacing. Results obtained by the same author indicated that grain yield was highest (778.2 kg ha -1 ) at 10 cm intra-row spacing. Similarly, Essubalew et al. (2014) reported that pod yield [of green been] increased consistently from 3473 kg ha -1 to 2574 kg ha -1 with an increase in intra-row spacing ranging from 7 x 40 - 15 x 40 cm. On the other hand, Bakry et al. (2011) and Mtaita and Mutetwa (2014) indicated that seed yield and biomass tends to decrease in wider row spacing (row spacing of 7, 10 cm). Mehmud et al. (1997) indicated that increased row spacing manifested increase in the seed weight/plant, pod weight/plant, and 1000 seed weight, but decreased plant height and seed yield/unit area. Kumar et al. (1997) and Mureithi et al. (2012) obtained the highest seed yield (1.09 t ha -1 ) and plant dry weight (15 g) with plant spacing of 15 cm and 20 cm, respectively. However, Mishra and Mishra (1995) concluded that seed yield was not affected by row spacing. According to Davi et al. (1995) seed yield of haricot bean increases as plant density increases (narrow spacing), but high plant densities can lead to low aeration, high humidity and prolonged periods of dampness. These are ideal conditions for the development of white mold (Sclerotinia). The environment within a canopy of given plant density will be affected both by plant and row spacing. As seed is a major input cost for dry bean production, optimum plant density should maximize yield while minimizing seed cost. In Ethiopia, a standard spacing of 40 cm x 10 cm has been adopted; irrespective of the growing conditions and locations which was not clear how this spacing was considered as the standard spacing without having planting density study. In Dilla area, production of haricot bean covers about 334.91 ha (15%) of the total area of land for pulses (2,209.9 ha) under cultivation, with annual production of 3303.27qt (CSA, 2013). However, most farmers are not sure of the appropriate planting density to use. They either use very high or very low plant density, which consequently results in poor grain yield in quality and quantity. Hence, optimization of