Abstract:
Soybean [Glycine max (L) Merrill] is among the most important legume crops produced in western Ethiopia. However, declining soil fertility as well as poor soil fertility management practices has limited its yields. A field experiment was conducted in Bako Agricultural Research center during 2018 main cropping season to investigate the effect of NPS rates on yield and yield components of soybean varieties and to identify economically feasible rates of blended NPS rate that increase the productivity of soybean varieties. The treatment consists of three varieties of soybean (Dhidhessa, Ethio-yugoslavia and Wello) and five rates of NPS (0, 50,100,150 and 200 kg ha-1). The experiment was laid out in factorial arrangement in randomization complete block design (RCBD) with three replications. Significant differences were obtained on days to 50% flowering, number of primary branches per plant and hundred seed weight due to the main effect of variety. Number of days (53.47days) to 50% flowering was hastened by variety Wello and delayed (55.87 days) by variety Dhidhessa. Variety Dhidhessa and variety Wello gave the highest (5.74) and lowest (5) number of primary branches, respectively. The highest hundred seed weight (16.9g) was recorded from variety Ethio-yugoslavia and the lowest (15g) from variety Wello. Significant effect was exhibited on days to 50% flower, above ground biomass yield and seed yield due to main effects of NPS rate. The highest (55.78) and the lowest (53.78) numbers of days to flowering were recorded due to application of 200 kg NPS ha-1 and 0 kg NPS ha-1, respectively. The tallest (81.63cm) and the shortest (65.60 cm) plants were recorded under 200 kg NPS ha-1 and 0 kg NPS ha-1, respectively. The highest (8718 kg ha-1) above ground dry mass was obtained at the highest rate of 200 kg NPS ha-1 and the lowest (6910 kg ha-1) was due to 0 kg NPS ha-1. The highest (2763 kgha-1) seed yield was recorded from the application of 100 kgha-1NPS rate and the lowest (1935kgha-1) seed yield was recorded from nil application of NPS fertilizer rate. Moreover, the highest net benefit (21,457.2Birr ha-1) was obtained from combination of variety Dhidhessa with application of 100 kg ha-1of blended NPS rate and the lowest (14327.9 Birr ha-1 ) was obtained from variety Ethio-Yugoslavia with nil application of fertilizer. The best combination with with high grain yield and economic benefit is 100kgha-1 NPS fertilizer rate with Didhessa Variety, The major measured parameters contributing for grain yield were above ground biomass ,number of pod per plant and no of primary branch per plant. This experiment generally confirmed as 100kgha-1 NPS for soybean was appropriate. This trial was conducted at strong acid soil, these it is expected as the plants might not have access to use the applied fertilizer and if it was conducted with lime application the responses might be changed. Thus, it can be concluded that combined application of 100 kg ha-1 of blended NPS with variety Dhidhessa could be used at Bako district and similar agro ecology. However, since the study was conducted for one season at one location, it has to be repeated over seasons and locations to make a conclusive recommendation.
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