LAUSR

Em Abstract Twin-rowplanting in soybean ( L.) has been proposed for optimizing Glycinemax resource use and seed yield. Experiments were conducted in  and  on a Dundee silt loam to assess soybean seed yield and irrigation water use efficiency (IWUE) in response to single-row (SR) and twin-row (TR) planting geometries under rainfed (RF), all row or full irrigation (FI), and alternate row or half irrigations (HI). Averaged across two crop years and three irrigation regimes, TR enhanced seed yield by % over SR (. vs. . Mg ha). The final plant stands established in the FI, HI, and RF under TR were , , and  plants m, whereas , , and  plants m were established under SR. Under both SR and TR, irrigations produced a higher number of pods per plant than of RF. Averaged across crop years, yields in the irrigation–planting geometry combinations were . Mg ha in FI-TR, . in Mg ha in HI-TR, . Mg ha in FI-SR, . Mg ha each in RF-TR and HI-SR, and . Mg ha in RF-SR. The HI-TR combination had the highest IWUE of about .Mg ha mm of water, followed by HI-SR with . Mg hamm . The seed yield in FI-TR was not significantly higher than that of HI-TR. Thus, conversion from FI-TR to HI-TR can save half the amount of irrigation without compromising yield or economic returns. Conversion from SR to TR is profitable regardless of the irrigations.