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

Abstract

Achievement of maximum crop yields necessitates the study of factors influencing yields. The influence of irrigation regime and plant population on growth of a Group VII determinate soybean [Glycine max (L.) Merr.] was measured to determine if a particular growth pattern would result in increased yield. In 1980 and 1981, ‘Braxton’ soybeans were grown in 0.91‐m rows on a Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludults) under full‐season irrigation (FSI), irrigation beginning at bloom (BI), and no irrigation (NI). Intrarow spacings ranged from 43 or 61 to 457 mm. At growth stage R2, FSI, BI, and NI plants had attained 72, 66, and 75%, respectively, of maximum height and 38, 35, and 55%, respectively, of maximum vegetative dry weight. Height, stem diameter, and dry weight were greater in the irrigated treatments than in NI. Fullseason irrigated plants were generally taller than BI and NI plants and had 1.7 times more dry weight at R2. With increasing spacing, height decreased while stem diameter increased. Vegetative weight was maximized at spacings of 76 mm or less. Development of canopy cover and LAI was more rapid with decreasing spacing and with irrigation. At least 90% canopy closure was obtained in all spacings of FSI and BI, whereas only 59% was achieved in NI. Yields were the same for FSI and BI, and, within irrigation treatments, there were no yield differences among spacings of 305 mm or less. We conclude that comparable yields can be obtained within a wide range of growth patterns, and that severe reductions in vegetative growth at R2 may have little influence on yield if water is supplied thereafter.

Potential of Early‐Maturing Soybean Cultivars in Late Plantings

“…In these experiments, seed number was associated with both CGR and the length of flowering and pod set. The association with CGR has been widely reported (Ramseur et al, 1985; Egli and Zhen‐wen, 1991; Board et al, 1999) and is consistent with the general concept that seed number is determined by the availability of assimilate from photosynthesis (Egli, 1998). Since the developing seed gets most of its assimilate from current photosynthesis, it is not surprising that sink size (seed number) and eventually the total seed growth rate (g m −2 land area day −1 ) would be related to the daily production of assimilate (i.e., rate of canopy photosynthesis).…”

“…Seeds per unit area in soybean is closely associated with canopy photosynthesis (Christy and Porter, 1982) and CGR (Ramseur et al, 1985; Egli and Zhen‐wen, 1991; Board et al, 1999) during flowering and pod set. The significant ( P = 0.02) linear relationship between seed number and CGR found here (Fig.…”

Soybean Response to Plant Population at Early and Late Planting Dates in the Mid‐South

“…Since soybean yield is determined by canopy photosynthesis during reproductive growth (growth stages R1 through R7) (Jiang and Egli, 1995), maximum levels of light interception and canopy photosynthesis are needed for maximum yield (Wells, 1991). Seed number is related to average crop growth rate during flowering and pod set (R1 through R5) (Ramseur et al, 1985; Egli and Zhen‐wen, 1991; Jiang and Egli, 1995) and reducing photosynthesis for part of this period always reduced seed number (Schou et al, 1978; Kokubun and Watanabe, 1983; Jiang and Egli, 1995). Significant pod production, however, does not begin until 10 to 15 d after R1 (Egli and Bruening, 2006) suggesting that complete ground cover and maximum canopy photosynthesis may not be needed until sometime after R1.…”

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

“…Because of its effects on CGR, drought creates changes in certain growth dynamic and yield component parameters. In general, drought stress during the vegetative growth period (emergence to R5) has adverse effects on LAI, TDM, CGR, and plant height (Scott and Batchelor, 1979;Taylor et al, 1982;Muchow, 1985;Meckel et al, 1984;Desclaux et al, 2000;Pandey et al, 1984;Ramseur et al, 1985;Cox and Jolliff, 1986;Constable and Hearn, 1980;Hoogenboom et al, 1987;Cox and Jolliff, 1987). In a dry growing season, nonirrigated vs. irrigated soybean will begin showing diminished TDM accumulation by the late vegetative or early reproductive period (Scott and Batchelor, 1979).…”

“…In a dry growing season, nonirrigated vs. irrigated soybean will begin showing diminished TDM accumulation by the late vegetative or early reproductive period (Scott and Batchelor, 1979). By R3, LAI differences between irrigated vs. drought-stressed soybeans will be obvious (Cox and Jolliff, 1987), with concomitant effects on LI and CGR (Muchow, 1985;Taylor et al, 1982;Ramseur et al, 1985;Pandey et al, 1984). Among vegetative growth indicators of drought stress, reduced internode length and plant height are the most sensitive (Desclaux et al, 2000).…”