Soybean is a vital oil crop in Ethiopia to attract foreign income. In southwest Ethiopia's irrigated conditions, phosphorus fertilization and water stress limits soybean yield. A three-year field experiment (2018/19–2020/21) assessed the impact of deficit irrigation (DI) and phosphorus rate (P rate) on crop water productivity (WPc), agronomic efficiency of phosphorus (AEP) and soybean yields. It included two DI levels and one control treatment (I50 = 50 % ETc, I75 = 75 % ETc, and I100 = 100 % ETc) in the main plot and five P rates (P0 = 0, P10 = 10, P20 = 20, P30 = 30, and P40 = 40 kg ha−1 P) in the subplot, arranged in a randomized split plot design with three replicates. P rates were optimized for each DI level using a quadratic polynomial regression model, predicting maximum agronomic yield and economically optimal P rate based on yield and cultivation cost. The study's results demonstrated a highly significant difference in soybean yield, WPc, and AEP among various P treatments. Furthermore, the highest WPc (0.63 kg m−3) and AEP (31.67 kg kg−1) were achieved with treatments with 30 kg ha−1 P and 10 kg ha−1 P. Among DI treatments, 75 % ETc reduced water usage by 25 % and increased WPc by 13.3 %. The application of 30 kg ha−1 P improved WPc and increased yield by 91 % and 90 %, respectively. The combined effect of I100×P30 significantly increased plant height (68.23 cm), dry matter (4.4 t ha−1), and yield (2965.49 kg ha−1) by 40.3 %, 104.3 %, and 215.2 %, respectively. The maximum WPc (0.83 kg m−3) and the lowest (0.30 kg m−3) were achieved at I50×P30 and I100×P0, respectively. The lowest AEP (9.36 kg ha−1) was obtained at I50×P40, while AEP (64.49 kg kg−1) significantly improved by 85 % at I100×P10. The maximum agronomic yields ranged from 1842.5 to 2895 kg ha⁻¹, with the corresponding combined treatments of I50×P26 to I100×P32. Economically optimal P rates ranged from 26 kg ha−1 (I50) to 31 kg ha−1 P (I100), giving net returns of $1666.1 to $3028.4 ha−1. Efficient management of DI and P can optimize irrigation, reduce P losses, and mitigate economic and environmental risks. Based on the result of this finding, applying 31 kg ha−1 of P under 100 % ETc and 28 kg ha−1 of P under 75 % ETc is recommended as the optimal P application strategy to achieve higher yield, WPc, AEP, and maximize economic returns in southwest Ethiopia. In addition, the breeder needs to develop soybean varieties that are more resistant to water stress and efficient in P uptake.

中文翻译：

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埃塞俄比亚西南部吉马大豆生产亏缺灌溉水位和磷肥用量优化


大豆是埃塞俄比亚吸引外国收入的重要油料作物。在埃塞俄比亚西南部的灌溉条件下，磷肥和水分胁迫限制了大豆产量。一项为期三年的田间试验（2018/19-2020/21）评估了亏缺灌溉 （DI） 和磷肥用量 （P 肥量） 对作物水分生产力 （WPc）、磷农艺效率 （AEP） 和大豆产量的影响。它包括主小区中的两个 DI 水平和一个对照处理（I50 = 50 % ETc、I75 = 75 % ETc 和 I100 = 100 % ETc），子小区中包括五个 P 率（P0 = 0，P10 = 10，P20 = 20，P30 = 30 和 P40 = 40 kg ha-1 P），以随机分裂区设计排列，有三个重复。使用二次多项式回归模型针对每个 DI 水平优化 P 用量，根据产量和栽培成本预测最大农艺产量和经济上最优的 P 用量。研究结果表明，不同 P 处理之间的大豆产量、WPc 和 AEP 存在非常显著的差异。此外，用 30 kg ha-1 P 和 10 kg ha-1 P 处理实现了最高的 WPc （0.63 kg m-3） 和 AEP （31.67 kg kg-1）。在 DI 处理中，75% 的 ETc 减少了 25% 的用水量，并将 WPc 增加了 13.3%。施用 30 kg ha-1 P 提高了 WPc，产量分别提高了 91 % 和 90 %。I100×P30 的综合效应显着提高了株高 （68.23 cm）、干物质 （4.4 t ha-1） 和产量 （2965.49 kg ha-1） 分别增加了 40.3 %、104.3 % 和 215.2 %。最大 WPc （0.83 kg m-3） 和最低 （0.30 kg m-3） 分别在 I50×P30 和 I100×P0 处实现。在 I50×P40 获得最低的 AEP（9.36 kg ha-1），而在 I100×P10 获得 AEP（64.49 kg kg-1）显着提高了 85%。最大农艺产量从 1842 年开始。5 至 2895 kg ha⁻¹，以及相应的 I50×P26 至 I100×P32 联合处理。经济上最优的磷肥量范围为 26 kg ha-1 （I50） 至 31 kg ha-1 P （I100），净回报率为 1666.1 美元至 3028.4 美元 ha-1。DI 和 P 的有效管理可以优化灌溉，减少 P 损失，并减轻经济和环境风险。基于这一发现的结果，建议在埃塞俄比亚西南部施用 31 kg ha-1 的 100 % ETc 和 28 kg ha-1 的 P在 75 % ETc 下施用磷作为最佳施用策略，以实现更高的产量、WPc、AEP 和最大化经济回报。此外，育种者需要开发更耐水胁迫和高效吸收磷的大豆品种。