Yield and Yield Components of ‘Braxton’ Soybeans as Influenced by Irrigation and Intrarow Spacing¹

Abstract

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 Hapludults). 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 bloom in both years, full‐season irrigation gave no yield advantage over bloom irrigation.

Soybean Yield Formation: What Controls It and How It Can Be Improved

“…Although some have reported mild adverse effects of drought on seed per pod (Ramseur et al, 1984;Pandey et al, 1984), others have shown no effect (Lawn, 1982;Elmore et al, 1988). In contrast, consistent reports have shown pod m -2 is reduced by drought during the R1-R6 seed formation period (Sionit and Kramer, 1977;Ramseur et al, 1984;Pandey et al, 1984;Snyder et al, 1982;Neyshabouri and Hatfield, 1986;Cox and Jolliff, 1986;Ball et al, 2000). Based on these results, we conclude that reduced seed m -2 from drought stress is derived predominately from reduced pod m -2 rather than seed per pod.…”

“…Thus, when confronted with drought stress, soybean reduces seed m -2 so that normal seed size can be maintained. Although some have reported mild adverse effects of drought on seed per pod (Ramseur et al, 1984;Pandey et al, 1984), others have shown no effect (Lawn, 1982;Elmore et al, 1988). In contrast, consistent reports have shown pod m -2 is reduced by drought during the R1-R6 seed formation period (Sionit and Kramer, 1977;Ramseur et al, 1984;Pandey et al, 1984;Snyder et al, 1982;Neyshabouri and Hatfield, 1986;Cox and Jolliff, 1986;Ball et al, 2000).…”

“…This shortens the seed filling period causing reduced seed size and yield (De Souza et al, 1997). When soybean faces seasonal drought or drought initiated by R1, yield loss results predominately from reduced pod and seed numbers and seed size is relatively unaffected (Sionit and Kramer, 1977;Ramseur et al, 1984;Pandey et al, 1984;Meckel et al, 1984;Cox and Jolliff, 1986;Constable and Hearn, 1980;Lawn, 1982;Ball et al, 2000). Thus, when confronted with drought stress, soybean reduces seed m -2 so that normal seed size can be maintained.…”

Drought‐Stress Effects on Branch and Mainstem Seed Yield and Yield Components of Determinate Soybean

“…Planting soybean late results in less branch vegetative growth, lower branch yields, and lower total yield per plant, which can usually be compensated for by planting at a higher seeding rate in a more narrower row‐width configuration (Board, 1990; Ramseur et al, 1984a; Frederick et al, 1998). In contrast, branch seed‐yield reductions due to drought stress probably can not be compensated for by planting at a higher plant seeding rate in narrow rows because of the greater evapotranspiration and severity of drought stress that can occur with narrow row culture (Frederick et al, 1998).…”

“…Less is known about the effects of drought stress on soybean branch growth and branch seed yield or how drought stress affects the distribution of seed yield between the main stem and branches. Ramseur et al (1984a)(b) reported that, for the determinate cultivar Braxton, most seed yield was located on branches originating from lower mainstem nodes and that increases in seed yield with irrigation were due to increases in the number of seeds per square meter and seed weight on both the mainstem and branch fractions. Full‐season irrigation and irrigation beginning at initial flowering had the same effect on seed yield in their study, suggesting that the major factors affecting seed‐yield increases with irrigation do not come into effect until near initial flowering.…”