Effect of nitrogen rate on growth, yield and quality of green bean (Phaseolus vulgaris L.) Varieties at bishoftu, central Ethiopia

Abstract

Green beans take the highest share among the leading exportable vegetables and recently, it is becoming one of the most important vegetables in local markets as well. However, several biotic and abiotic factors are contributing to the low yields and quality. Among others, soil nitrogen content is low on most part of the bean growing areas of the country and also there is no adequate application of nitrogen fertilizer. In addition, there is lack of adequate suitable varieties for specific or wider production locations. Therefore, an experiment was conducted at Bishoftu in the year 2011/2012 with the objective of determining the optimum level of N and identifies appropriate green beans (Phaseolus vulgaris L) varieties for higher yield and quality. A 4x5 factorial experiment arranged in Randomized Complete Block Design (RCBD) with three replications was used. The treatments consisted of four bush type bobby bean varieties namely, Melka 1, Melka 3, Melka 5 and Contender blue and five levels of N (0, 40, 80, 120 and 160 kg N ha-1 ). In view of that, data were collected pertaining to growth, yield and quality of green beans and analyzed using SAS statistical software version 9.2 (SAS Institute Inc., 2008). The results revealed that the difference between the four varieties was highly significant (P<0.05) for all parameters studied. Variety Melka 3 gave highest plant height (37.41cm), total leaf area (2839.28 cm2 /plant), shoot and root dry weight (31.83 g/plant), total pod yield (14.04 t/ha), marketable pod yield (11.40 t/ha), average marketable pod weight (5.70g), pod dry weight (5.86 g/plant), pod straightness value (2.81) and pod length (13.56cm). The highest pod diameter (9.93mm) and pod protein content (19.71%) was obtained from Melka 5 and in the case of 50% flowering, Contender blue required shortest time (46.40 days). Application of N had a highly significant (P<0.05) effect on all studied parameters except for the tap root length and pod straightness. Application of 160 kg N ha-1 increased plant height by 9.36 cm, total leaf area by 50.62%, shoot and root dry weight by 45.9%, pod protein content by 10% and delayed days to 50% flowering by five days over the control and also highest value for pod color (3.39) and lower pod fiber content (2.93) was observed. The application of 120 kg N ha-1 increased the total pod yield by 49.85%, marketable pod yield by 52.33%, number of pods per plant by 42.48%, average marketable pod weight by 19.3%, pod dry weight by 90.79%, pod length by 15.25%, pod diameter by 37.99% over the control. The application of 120 kg N ha-1 produced a statistically similar result with 80 kg N ha-1 on total and marketable pod yield. Total pod yield had significantly positive correlation with plant height (r=0.63**), total leaf area (r=0.62**), days to 50% flowering (r=0.48**), number of primary branches (r=0.27* ), marketable pod yield (r=0.96**), unmarketable pod yield (r=0.40**), total number of pods per plant (r=0.64**), average marketable pod weight (r=0.57**), pod length (r=0.61**) and pod diameter (r=0.68**). The statistical analyses it was evident that application of 80 kg N ha-1 with variety Melka 3 could improve productivity and quality of green beans around the study area while on the basis of partial budget analyses has also indicated that variety Melka 3 with 40 kg N ha-1 produced the highest MRR (1306.67%). However, repeating the experiment for more seasons would help us draw sound conclusions and recommendations. Hence, future studies should look in to these factors to develop fertilizer recommendations for optimum yield and quality of green bean in Bishoftu area.