Journal of Natural Sciences Research www.iiste.org ISSN 2224-3186 (Paper) ISSN 2225-0921 (Online) Vol.8, No.7, 2018 15 Effects of Irrigation Interval on Growth Analysis of Soybean [(Glycine max (L.) Merr.] Lake Mekonnen Southern Agricultural Research Institute, Worabe Agricultural Research Center, department of crop science work process, Ethiopia Abstract A field experiment was conducted with the ultimate goal of irrigation is to utilize added water efficiently on soybean that can give the greatest seed yield per hectare increase from added water in crop year 2015/2016 BC at Hawassa located at 07 0 3'N and 38 0 28'E, and at 1708 masl. Maximum and minimum daily temperature was 27 and 13 o c respectively. This experiment was RCB design with 4 replicates was performed on earth. Each experimental unit with dimensions of 2×2 m and was planted with 5 rows. The irrigation interval includes 3,8,13 days. After collecting data such as stem weight, leaf weight, leaf area, plant weight and plant height. SLA, LAR, NAR and RGR were analyzed. SLA and LAR decreased with age increase under all irrigation intervals and maximum RGR and NAR were achieved at 8 day irrigation interval with a value of 102.5 mg g -1 day -1 and 77.5 mg dm -2 day -1 respectively. The highest biomass of soybean was recorded at irrigation intervals of 3 days with a mean value 176.7163g/m 2 . Keywords: SLA, LAR, RGR and NAR Introduction The origin and early history forms the soybean crop is unknown, it is often said that the soybean is native to East Asia (Adcock and Neill, 2003). Soybean [(Glycine max (L.) Merr.] is a dominant world crop for vegetable oil and protein for animal and human consumption. Interest in soybean production has increased because soybean has a wide range of adaptation in regard to different climatic, soil and growth conditions. Soybean plants under drought stress on field observations indicate that significant amounts of soil water Access during all stages of plant development has an important effect on plant growth imposed. Briyer et al (2000) also concluded that climatic factors have no tangible impact on the spread of soybean roots, but in his view there is some contrary information. However, in most cases it seems that the total numbers of unit roots seriously affected by soil water regime are not seasonal but this does not mean that the rate of soil water availability is not affected. The germination of soybeans, 50 percent of its weight in water requires extra moisture rising from the soil surface is required (John, 2001). Water and nitrogen alone and in interaction, have a negative impact on growth and yield (Taylor et al, 2005).When the grain crop production is desired, a time of tension with the stress intensity is the same (Sarmadnia and Koucheki, 1993). Drought stress reduced nitrogen demand and the need to shoot, also reduce the transfer of solutes such as urea is nitrogen (Astare and Scarisbrick, 1995). Taylor et al (2005) Soybean stem height at the time of the stress factor for predicting tolerance to dehydration cultivars has been introduced. High and stable yields of soybean can reliably be obtained only by supplementing crop water requirement through irrigation. Only optimum conditions permit the plants to use water according to their needs, i.e. to the level of potential evapotranspiration (450-480 mm, Vučić and Bošnjak 1980, Bošnjak 1983). Even though a lot of literatures are recommend to produce soybean by irrigation no optimum irrigation intervals were recommended across different agro ecologies. The objective of this experiment is to conduct appropriate irrigation intervals for maximum growth and grain yield of soybean in a specified location. Material and Methods The experiment was carried out at Hawassa university college of Agriculture experiment field (at 07 0 3'N and 038 0 28'E, and at 1708 masl. Maximum and minimum daily temperature was 27 &13 o c respectively) in the period of 2015/2016 B.C growing season. This experiment was laid in randomized complete block design with 4 replicates. Each experimental unit with dimensions of 2×2 m and was planted with four rows 40cm between rows and 10 cm between plants with recommended NP rate. Treatments in this experiment were irrigation interval i.e. three, eight and thirteen day’s interval. Furrow irrigation method was done for all irrigation intervals. Until the crop was emerged all plots are irrigated equally. Rainfall during the growing season was negligible. Time of seed planting was November 13, 2015 after the land was well prepared. All agronomic practice was done according to the recommendations except irrigation intervals. Collected data: - Plant height, leaf area, leaf weight and stem weight were taken two times in 18 day intervals by taking three individual plants randomly from each rows and at the end of growing season total dry mass were taken from one row of each plot.