Yield and Yield Components of ‘Braxton’ Soybeans as Influenced by Irrigation and Intrarow Spacing

Yield and yield components of ‘Braxton’ soybeans [Glycine max (L.) Merr.], Maturity Group VII, were measured for differing irrigation regimes and intrarow spacings. Soybeans were planted in 0.91 m rows in mid-May, 1980 and 1981 on a Cecil sandy loam soil (clayey, kaolinitic, thermic Typic Hapluddts). Prior to the V3 growth stage, plots were thinned to achieve intrarow spacings of 61,76,102, 152,305, and 457 mm in 1980 with spacings of 43 and 51 mm added in the 2nd year. Soil water regimes were full-season irrigation (FSI), irrigation beginning at bloom (BI), and no irrigation (NI). Beginning at R4, plants from a 0.5-m section of row were removed at 10- to 14-day intervals for determination of seed growth rate and effective filling period. Yield components (pod number, seed number, seeds per pod, and single seed weight) were determined at R7 or maturity. Final seed yields were determined by harvesting bordered rows following end trimming. Seed yields for the 2 years, averaged over all spacings, were 3023,2876, and 1322 kg/ha for the FSI, BI, and NI higation treatments, respectively. While yields were increased significantly with irrigation, no significant difference in yield was measured between FSI and BI treatments. Yields among plant spacings were not significantly different for any irrigation treatment either year with the exception that the yield of the 457-mm spacing of the BI treatment was significantly reduced in 1981. Seed number was highly correlated with seed yield, whereas single seed weight was not significantly correlated with yield. Increases in seed number under the irrigation treatments were due to increases in both pod number and seed per pod. Seed growth rate was increased and effective filling period was decreased by irrigation. We concluded that intrarow spacings up to 457 mm had little influence on yield. Even though rainfall was low during vegetative growth prior to blpom in both years, full-season irrigation gave no yield advantage over bloom irrigation.