effect of timing and amount of irrigation water on bean yield and water use efficiency in arid and semi-arid conditions

introduction: nowadays, due to lack of water resources and increasing demand for water, agricultural water planning issues need further consideration. with proper planning and determination of irrigation depth and time, the effects of stress and yield loss on the plants are reduced. irrigation scheduling is one of the most important factors in crop’s quality and quantity. the main objective of irrigation scheduling is to control crop’s water conditions in order to achieve its optimum yield level. so irrigation timing is the vital factor on which crop water stress and eventually yield's level are dependent upon. moreover, irrigation timing is used in irrigation scheduling. the aim of this study was to evaluate the effect of irrigation time on water consumption, water use efficiency and yield of beans. materials and methods: in order to observe the effect of the amount and the time of the irrigation on water consumption, yields rate and water use efficiency, the current research was carried out at the university of shahrekord during the summer of 2012. the experiment was done as a completely randomized design with 4 repetitions consisting of irrigation time and the amount of irrigation in 4 and 2 levels (at 6, 8, 14 and 18) and (deficit irrigation, full irrigation), respectively. beans seeds were planted in 32 similar vases with a diameter of 45 cm and height of 60 cm, in each experiment. treatments were begun after 37 days from planting. treatments were irrigated when the average moisture in the root zone was equal to the lower border of readily available water of full irrigation. at the end of the experiments, plants were completely harvested. then the plant’s height, number of branches, numbers of pods per plant, pod and seed weight were measured. results and discussion: results showed that irrigating at different times during the day influenced water use efficiency, water consumption, seeds yield and number of pods in the bush. the water consumption was affected by irrigation time. among full irrigation treatments, irrigation at 2 p.m. and 6 a.m. had the highest and lowest water consumption, respectively. the total amount of water used in irrigation at 8 a.m., 2:00 p.m. and 6 p.m. compared to 6:00 a.m. was increased by1.6, 9.5 and 4.1 percent, respectively. the results showed that irrigation at 2:00 p.m., caused a significant reduction in yield. moreover, water use efficiency in 6 a.m. treatments had increased 18.5 percent more than that of the 2:00 p.m. irrigation treatment. the time of irrigation did not have a meaningful effect on bush height, the number of minor branches, the pod's length. the effect of the amount of irrigation water was meaningful on bush height, number of minor branches, seeds yield, the number of pods in the bush, pods length and seed weight. seed yield at 8:00 a.m., 2:00 p.m. and 6:00 p.m. treatments has shown 0.29, 17.1 and 7.6 percent decrease in comparison with 6:00 a.m. irrigation treatment, respectively. moreover, 100-seed weights were significantly affected by the irrigation time. the maximum and minimum weights of 100-seed weights were obtained at 6:00 a.m. and 6:00 p.m. irrigation, respectively. analysis of variance showed that the number of pods per plant was affected by irrigation time. the maximum number of pods per plant was 101 which belong to the 6:00 a.m. treatment. in this experiment in the case of irrigation at 2:00 p.m., the number of pods per plant was significantly decreased in full and deficit irrigation. the results showed that although the irrigation frequency was the same, irrigation at maximum evapo-transpiration caused the plant to be under stress and the yield was reduced. in other word, it can be said that time of irrigation had no meaningful effect on the appearance and shape of the plant while it was effective in terms of the yield. overall assessments showed that maximum of the measured features were obtained in the case of 6:00 a.m. treatment. conclusion: the results showed that irrigation at different times of the day and the applied water stress, reduced water use efficiency. these caused traits such as plant height; number of branches; number of pods per plant; pod and seed weight to be affected by the irrigation depth. based on the results of this experiment it can be stated that, when there is no limit of water supply, it is recommended to irrigate in the early morning, before the steep slope of the temperature rise. however, in the situations with water shortage problems, is better to manage the water and the product.