Published online 13 May 2005
Published in Agron J 97:919-923 (2005)
DOI: 10.2134/agronj2004.0271
© 2005 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Effect of Row Spacing and Soybean Genotype on Mainstem and Branch Yield
Jason K. Norsworthy* and
Emerson R. Shipe
Dep. of Entomol., Soils, and Plant Sci., Clemson Univ., 277 Poole Agric. Cent., Clemson, SC 29634
* Corresponding author (jnorswo{at}clemson.edu)
Received for publication November 2, 2004.
 |
ABSTRACT
|
|---|
Partitioning of soybean [Glycine max (L.) Merr.] seed yield between mainstem and branch fractions across row widths and genotypes at recommended seeding rates is not well understood. A field experiment was conducted to evaluate the distribution of seed yield between mainstem and branch fractions of eight soybean genotypes grown in narrow (19 cm) and wide (97 cm) rows at recommended seeding rates. In contrast to adequate rainfall throughout the crop season in 2002, a lack of rainfall during reproductive development in 2003 caused differences in mainstem and branch yield components between years. Mainstem seed yields, averaged over years and genotypes, accounted for 45 and 69% of the total yield in wide and narrow rows, respectively. Mainstem seed yields, averaged over years and row widths, ranged from 62 to 142 g m–2 among genotypes. Ranking of mainstem and branch yields among genotypes was stable over environments. Similarly, row width did not influence mainstem yields among genotypes, but genotype branch yields in wide rows were different from those in narrow rows. Branch seed yields in narrow rows, averaged over years, ranged from 14 to 57% of total seed yield while 47 to 74% of total seed yield was produced on branches in wide rows. This research demonstrates considerable differences exist in mainstem and branch yields among genotypes and that genotypes having superior branch yield should be selected for wide rows while mainstem yield should be used as a selection criteria for narrow rows.
|
INTRODUCTION
|
|---|
SOYBEAN YIELD differences between wide and narrow row widths are commonly reported throughout the southern United States (Board et al., 1992; Frederick et al., 1998). However, differences in partitioning of mainstem and branch seed yield among genotypes in wide and narrow rows are not well understood. Since reduced branching at high plant populations has been reported (Carpenter and Board, 1997; Weber et al., 1966), and recommended populations are higher for narrow-row soybean production than in wide-row production (Palmer, 1999), genotypes with superior mainstem yield potential should produce higher yields in narrow rows while genotypes with high branch yield potential should maximize yield in wide rows. However, branch yield has inadvertently, but likely, been used as a major selection criteria to determine currently available soybean genotypes since varietal recommendations of all row widths are primarily based on trials conducted in wide rows. Furthermore, due to the limited availability of seed in the initial stages of genotype selection, branch yield may be the predominant factor allowing progression of a genotype through the selection process. However, the contribution of branch yield to total yield as a component of total yield is thought to diminish under prolonged soil moisture stress, which is common in the southeastern United States (Frederick et al., 2001).
Frederick et al. (2001) found mainstem seed yield of narrow-row soybean stable over environments but branch yield highly contingent on the severity of drought stress during the growing season. These results led them to conclude that mainstem yield is the major contributor to improved yield of narrow- over wide-row soybean following prolonged periods of inadequate soil moisture. Conversely, Alessi and Power (1982) concluded narrow-row soybean enhances water consumption by soybean before flowering, lowering its water use efficiency and reducing yields compared with wider row widths in years in which soil moisture is severely limited. In the absence of severe moisture stress, they found row width had no influence on soybean yield. Differences in results by Frederick et al. (2001) and Alessi and Power (1982) may be due to genotypic differences among cultivars along with determinate versus indeterminate development. The determinate cultivars Northrup King Coker S73-Z5 and Motte were assessed in research by Frederick et al. (2001), and the indeterminate cultivars Clay and Ada were evaluated by Alessi and Power (1982).
Currently, little is known about genotypic differences in ability to partition seed yield between mainstem and branch fractions in response to row widths and across environments at recommended seeding rates. There are substantial genotypic differences in soybean branching and branch yield at lower-than-recommended densities (Rigsby and Board, 2003). If there are also appreciable differences in mainstem yield potential among genotypes, selection of genotypes with superior mainstem yield would be ideal for ensuring high yield in narrow-row culture. Since mainstem yield is believed to be stable across environments (Frederick et al., 2001), it would be advantageous to select genotypes with high mainstem yield since the adoption of narrow-row soybean continues to increase (Norsworthy, 2003) and prolonged periods of yield-reducing drought stress are frequent in the Southeast (Frederick et al., 1998). Therefore, the objective of this research was to evaluate the distribution of seed yield and yield components between mainstem and branch yield of eight soybean genotypes grown in wide and narrow rows at recommended seeding rates.
|
MATERIALS AND METHODS
|
|---|
Studies were conducted at the Edisto Research and Education Center at Blackville, SC, in 2002 and at the Simpson Research Station at Pendleton, SC, in 2003. The soil type at Blackville was a Dunbar sandy loam (fine, kaolinitic, thermic Aeric Paleaquults) with 0.8% organic matter and a pH of 6.1. At Pendleton, the soil type was a Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludults) with 0.9% organic matter and a pH of 6.1. Seedbeds were disked twice and field-cultivated before planting soybean. The Maturity Group VI determinate glyphosate-resistant genotypes Deltapine (DP) 6299, DP6880, Pioneer (P) 96B21, Northrup King (NK) S60-E4, Hartz (H) 6255, Asgrow (A) 6202, SC00-883, and SC00-892 were seeded on 5 May 2002 and 10 May 2003 at 432000 and 272000 seeds ha–1 in 19- and 97-cm row widths, respectively. The six commercial genotypes selected for this study were chosen because of their widespread use in South Carolina. The two experimental lines under development were selected because of their potential availability. Wide-row soybean was seeded in four-row plots, whereas narrow-row plots consisted of 10 rows. All plots were 7.6 m in length. The entire study was treated with 0.42 kg a.e. ha–1 glyphosate [N-(phosphonomethyl)-glycine] at 2, 4, and 6 wk after soybean emergence. Late-emerging and noncontrolled weeds were removed by hand throughout the remainder of the growing season.
At soybean physiological maturity, 10 plants were harvested and oven-dried, and then seed yield from mainstem and branch fractions was determined from these plants. Plots were trimmed to a 3.6-m length and harvested using a small-plot combine, and seed yield was expressed at 130 g kg–1 seed moisture. Mainstem and branch seed yield per unit area were determined by multiplying the proportion of each seed fraction by total yield. Individual seed weight was determined by counting and weighing 100 seeds from each fraction. Seed numbers were calculated from seed yield and individual seed weight of each fraction.
All data were subjected to analysis of variance as a split-split plot design using the PROC GLM function of SAS to test all main effects and possible interactions (SAS Inst., 2000). The factors evaluated were year (main plot), row width (subplot), and genotype (sub-subplot). Each treatment was replicated four times. Treatment means were separated using Fisher's protected LSD test at P < 0.05. Correlation analyses using PROC CORR in SAS were conducted using plot data to determine the relationship between measured parameters and total, mainstem, and branch seed yields in wide and narrow rows.
|
RESULTS AND DISCUSSION
|
|---|
Soybean densities in 2002 averaged 14 and 28 plants m–2 in wide and narrow rows, respectively, whereas wide rows contained an average of 20 plants m–2 and narrow rows 31 plants m–2 in 2003 (data not shown). No differences were detected in soybean population among genotypes in either year. Frequent rainfall occurred throughout the 2002 growing season, resulting in soybean yields of 277 g m–2, averaged across genotypes and row widths. Although frequent rainfall also occurred during soybean vegetative development in 2003, little precipitation occurred during soybean reproductive development. Consequently, soybean yields in 2003 were reduced to 141 g m–2, averaged across genotypes and row widths.
Mainstem Fraction
Due to differences in rainfall between years, a significant row width x year interaction influenced mainstem seed yield and seed number (Table 1). In 2002, when precipitation was adequate throughout the growing season, mainstem seed yield was 211 g m–2 in narrow rows compared with 107 g m–2 in wide rows (Table 2). Mainstem seed yield accounted for 70% of the total yield in narrow rows and only 42% of the total yield in wide rows. In 2002, the average soybean population in wide rows was 50% less than in narrow rows, which is similar to the 49% reduction in mainstem yield of wide rows compared with narrow rows. Therefore, mainstem yield differences between mainstem seed yield per plant are likely due to population differences rather than differences between mainstem seed yield per plant between row widths. Conversely, in 2003, when rainfall was absent during reproductive development, mainstem seed yields and seed number were statistically similar between row widths, indicating narrow-row soybean was less able to maintain mainstem yield per plant compared with the lower-population, wide-row soybean. Rapid canopy formation of narrow-row soybean was likely detrimental to mainstem yield because of the absence of rainfall during reproductive development, lowering the water use efficiency of the high population (Alessi and Power, 1982). Mainstem seed yield was also highly correlated with total seed yield (r = 0.731 to 0.865) and mainstem seed number (r = 0.860 to 0.930) in both row widths (Table 3), which explains the significance of the main effects of year and row width and year x row width interaction for seed number (Table 1).
View this table:
[in this window]
[in a new window]
|
Table 1. Analysis of variance for mainstem and branch seed yield, seed number, and seed weight for eight soybean genotypes grown in 19- and 97-cm row widths at Blackville, SC, in 2002 and Pendleton, SC, in 2003.
|
|
View this table:
[in this window]
[in a new window]
|
Table 2. Effect of soybean row width and genotype on mainstem seed yield, seed number, and seed weight, averaged over 2002 and 2003.
|
|
View this table:
[in this window]
[in a new window]
|
Table 3. Pearson correlation coefficients (r) for total, mainstem, and branch yield and yield components (n = 62) for 19- and 97-cm row widths, averaged over eight genotypes and 2 yr.
|
|
Mainstem soybean seed weight was influenced by environment (Table 1). The lack of rainfall during soybean reproductive development in 2003 led to a 31% reduction in seed weight compared with 2002 (Table 4). Row width did not influence seed weight (Table 1).
View this table:
[in this window]
[in a new window]
|
Table 4. Effect of year and row width on mainstem seed yield, seed number, and seed weight, averaged over eight genotypes.
|
|
Mainstem seed yields were not influenced by interactions involving genotype (Table 1). The lack of these interactions allows determination of genotypes with high mainstem yield potential across a range of environments and row widths, assuming an optimal planting date. However, the main effect of genotype was significant for seed yield, seed number, and seed weight (Table 1). Mainstem seed yields and seed numbers among genotypes averaged over years and row widths ranged from 62 to 146 g m–2 and 515 to 1181 seed m–2, respectively, indicating considerable range in mainstem yield potential among genotypes (Table 2). Mainstem seed weights varied among genotypes, ranging from 116 to 141 mg seed–1.
Branch Fraction
A significant row width x genotype interaction influenced branch seed yield (Table 1), indicating that some genotypes are capable of partitioning more resources to increase branch seed yield in response to row width while some genotypes exhibit relatively stable branch seed yields across row widths (Table 5). For example, branch seed yield in narrow rows, averaged over years, ranged from 31 g m–2 for NKS60-E4 to 112 g m–2 for DP6299, comprising 14 to 57% of the total seed yield (Table 5). In wide rows, 46 to 74% of the total seed yield was produced by branches, with DP6880 again producing the highest average yield of 139 g m–2. Although NKS60-E4 produced the lowest branch seed yield in narrow rows, it ranked third in contribution of branch seed yield to total yield in wide rows, illustrating the capability of some genotypes to alter partitioning of seed yield between mainstem and branch fractions in response to row width. Since yield components were not influenced by significant year x genotype interactions, branch seed yields by genotype appear to be stable across environments (Table 1).
View this table:
[in this window]
[in a new window]
|
Table 5. Effect of soybean row width and genotype on branch seed yield, seed number, and seed weight, averaged over 2002 and 2003.
|
|
Branch seed yield was also influenced by a significant year x row width interaction (Table 1). However, branch seed yields, averaged over genotypes, were 47 and 51% less in narrow and wide rows, respectively, in 2003 than in 2002. Thus, the contribution of branch yield to total yield showed some stability over two diverse years, regardless of row width. For instance, 30% of the total seed yield was contributed by the branch fraction in 2002 compared with 34% in 2003 in narrow rows (Table 6). In wide rows, total yield depended more on branch yield, with 58% of the total yield produced on branches in 2002 while 50% of the total yield was contributed by branches in 2003. These findings indicate that for full-season soybean planted in accordance with recommended planting dates and seeding rates, precipitation has little impact on partitioning of seed yield between mainstem and branch fractions, regardless of row width. These findings differ from those of Frederick et al. (2001), who concluded that the contribution of branch yields to total yield is highly influenced by available moisture while mainstem yields are quite stable. If mainstem yields are stable over environments, but branch yields are not, then the mainstem contribution to total yield would be considerably greater than that of the branch fraction in years of low rainfall. The research by Frederick et al. (2001) was conducted in narrow rows (19-cm row width) with a single genotype each year; therefore, they were only able to evaluate the effect of moisture stress on yield components from mainstem and branch fractions, rather than interactions involving year, row width, and genotype as investigated in this study. Based on our results, branch seed yields are drastically influenced by row width x genotype interactions. Also, the absence of a genotype x row width x year interaction for mainstem or branch yield in our study and total yield in other studies (Board and Harville, 1996; Parker et al., 1981) lends evidence that changes in branch yield are closely linked to changes in mainstem yield, regardless of environmental stresses. Furthermore, if extensive branching was detrimental during drought, the contribution of branch yield to total yield would be less in years of moisture stress while mainstem contribution would increase. Only minimal changes in the contribution of branch yield to total yield were observed in our study.
View this table:
[in this window]
[in a new window]
|
Table 6. Effect of year and row width on branch seed yield, seed number, and seed weight, averaged over eight genotypes.
|
|
Similar to the mainstem fraction, branch seed numbers closely followed trends in branch seed yield between row widths in both years. Regardless of row width, branch seed yield was more closely correlated with seed number (r = 0.882 to 0.949) with more than a threefold difference among genotypes for seed number (Table 5). While branch seed weights did not differ between row widths in either year, branch seed weights were correlated with branch seed yield (r = 0.510 to 0.523) (Table 3). The lack of rainfall in 2003 resulted in differences in seed weight between years; however, the year x row width interaction and row width effect were nonsignificant, indicating row width has no effect on branch seed weight, regardless of moisture differences over years.
|
CONCLUSIONS
|
|---|
This research illustrates substantial differences in mainstem and branch yield among genotypes. Use of this knowledge in selecting genotypes for wide or narrow rows may improve total yields. Similarly, Rigsby and Board (2003) found total soybean yield differences among genotypes planted at lower-than-recommended populations, mainly due to the ability of genotypes to partition dry matter into branches. While branch yield is highly dependent on population (Norsworthy and Frederick, 2002), there is some uncertainty about the stability of branch yield relative to mainstem yield during prolonged periods of moisture stress. Frederick et al. (2001) concluded that most branch growth occurs between initial flowering and beginning seed fill. Furthermore, moisture stress during this period is extremely detrimental to branch yield but less influential on mainstem yield. In our research, the lack of rainfall throughout most of the soybean reproductive development in 2003 reduced yields; however, the contribution of branch and mainstem yields to total yield were only slightly different from 2002, a year in which moisture was adequate throughout the growing season. Furthermore, both mainstem and branch seed yield fractions were closely correlated with seed number per square meter over both environments, which is in agreement with the findings of others that seed number is impacted more by moisture stress than seed size (Ball et al., 2000).
Additionally, differences in mainstem and branch yield between row widths were greatest when moisture was adequate throughout the growing season. Factors that contribute to increased yield of narrow-row soybean, such as greater biomass accumulation, light interception, and leaf area development (Board and Harville, 1992), may likewise be detrimental during periods of moisture stress, resulting in increased water consumption of narrow-row soybean, lowering its water use efficiency and seed yield compared with wide-row soybean with lower populations (Alessi and Power, 1982).
The largest portion of seed yield from wide-row soybean was generally contributed by the branch fraction, regardless of genotype. Since the seeding rates for wide-row soybean are less than those of narrow-row soybean (Palmer, 1999), the ability of soybean to branch is greater in wide rows. Conversely, in narrow rows, mainstem yield is the primary contributor to total yield; therefore, mainstem yield should be used as a criteria for selecting superior soybean genotypes for narrow rows.
|
REFERENCES
|
|---|
- Alessi, J., and J.F. Power. 1982. Effects of plant and row spacing on dryland soybean yield and water-use efficiency. Agron. J. 74:851–854.[Abstract/Free Full Text]
- Ball, R.A., L.C. Purcell, and E.D. Vories. 2000. Short-season soybean yield compensation in response to population and water regime. Crop Sci. 40:1070–1078.[Abstract/Free Full Text]
- Board, J.E., and B.G. Harville. 1992. Explanation for greater light interception in narrow- vs. wide-row soybean. Crop Sci. 32:198–202.[Abstract/Free Full Text]
- Board, J.E., and B.G. Harville. 1996. Growth dynamics during the vegetative period affects yield of narrow-row, late-planted soybean. Agron. J. 88:567–572.[Abstract/Free Full Text]
- Board, J.E., M. Kamal, and B.G. Harville. 1992. Temporal importance of greater light interception to increased yield in narrow-row soybean. Agron. J. 84:575–579.[Abstract/Free Full Text]
- Carpenter, A.C., and J.E. Board. 1997. Branch yield components controlling soybean yield stability across plant populations. Crop Sci. 37:885–891.[Abstract/Free Full Text]
- Frederick, J.R., P.J. Bauer, W.J. Busscher, and G.S. McCutcheon. 1998. Tillage management for doublecropped soybean grown in narrow and wide row width culture. Crop Sci. 38:755–762.[Abstract/Free Full Text]
- Frederick, J.R., C.R. Camp, and P.J. Bauer. 2001. Drought-stress effects on branch and mainstem seed yield and yield components of determinate soybean. Crop Sci. 41:759–763.[Abstract/Free Full Text]
- Norsworthy, J.K. 2003. Use of soybean production surveys to determine weed management needs of South Carolina farmers. Weed Technol. 17:195–201.
- Norsworthy, J.K., and J.R. Frederick. 2002. Reduced seeding rate for glyphosate-resistant, drilled soybean on the southeastern Coastal Plain. Agron. J. 94:1282–1288.[Abstract/Free Full Text]
- Palmer, J.H. 1999. South Carolina soybean production guide. Ext. Circ. 501. Clemson Univ. Coop. Ext. Serv., Clemson, SC.
- Parker, M.B., W.H. Marchant, and B.J. Mullinix, Jr. 1981. Date of planting and row spacing effects on four soybean cultivars. Agron. J. 73:759–762.[Abstract/Free Full Text]
- Rigsby, B., and J.E. Board. 2003. Identification of soybean cultivars that yield well at low plant populations. Crop Sci. 43:234–239.[Abstract/Free Full Text]
- SAS Institute. 2000. SAS user's guide. Version 8. SAS Inst., Cary, NC.
- Weber, C.R., R.M. Shibles, and D.E. Byth. 1966. Effect of plant population and row spacing on soybean development and production. Agron. J. 58:99–102.[Abstract/Free Full Text]
TOP
ABSTRACT
INTRODUCTION
