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© 2007 Plant Management Network. Row Spacing, Plant Populations, and Cultivar Effects on Soybean Production Along the Texas Gulf Coast W. James Grichar, 3507 Hwy 59E, Texas A&M University, Texas Agricultural Experiment Station, Beeville 78102 Corresponding author: W. James Grichar. w-grichar@tamu.edu Grichar, W. J. 2007. Row spacing, plant populations, and cultivar effects on soybean production along the Texas Gulf Coast. Online. Crop Management doi:10.1094/CM-2007-0615-01-RS. Abstract Three soybean (Glycine max L.) cultivars were compared when planted in twin rows (two rows spaced 4 to 6 inches apart on a single bed with 38-inch centers) to soybean produced in single rows on a bed (spaced 38 inches apart) at three seeding rates of 6, 10, and 15 seeds/planted ft at two locations along the Texas Gulf Coast in 2003 and 2004. Soybean yield averaged over cultivars and seeding rates resulted in the twin-row system out-producing the single-row system at two of the four site-years. Soybean yield did not increase as the seeding rate increased with either row spacing. When only seed costs were considered, the twin-row system planted at 6 seeds/ft had the highest net return at three of the four site-years. Introduction Soybean producers are continually searching for methods that will help increase yields, reduce costs, or a combination of the two. The use of twin-row systems have resulted in yield increases over a single row system in several crops including corn (Zea mays L.), cotton (Gossypium hirsutum L.), and peanut (Arachis hypogaea L.) (1,5,10,12,15). Several studies have demonstrated the benefit of decreased row spacing on early season canopy development (6,7,11,17,18). In peanuts, Jaaffar and Gardner (13) reported that narrow and twin-row patterns had greater ground cover, leaf area indices, canopy light interception, crop growth rates, and ultimately higher pod yields when compared to a conventional row pattern. Seedlings in close proximity to each other express phytochrome-mediated responses by developing narrow leaves, long stems, and less massive roots (14). Planting a crop in a pattern that reduces the spacing of plants within and between rows can increase plant biomass and leaf area index (3). Work in the late 1980s showed that reduced row spacing increased the total interception of photosynthetic active radiation by the corn canopy and redistributed the radiation toward the top of the canopy (16). Reduced row spacing are also thought to increase weed control by increasing the competitiveness of a crop with weeds and by reducing light transmission to the soil surface (19). Teasdale (19) showed that reduced row spacing and increased corn populations decreased weed growth in the absence of herbicides and shortened the time of canopy closure by one week. Twin-row systems have been compared in soybean (Glycine max L.) with mixed results. Graterol et al. (9) reported that soybean planted in the twin-row system had no yield advantage over the conventional single-row system in a year with yield-limiting conditions. However, in a year with no yield-limiting conditions, the twin-row planting systems offered yield advantages over a single-row planting system. Other studies have reported on the use of narrow row spacing in soybean. Maturity group V to VII determinate soybean grown in narrow rows (generally 50 cm or less) produced higher yield than soybean grown in wide row spacing in the southern US (4,8,20). Little use of twin-row soybean production has occurred along the Texas Gulf Coast soybean production area. This study was designed to increase the knowledge about twin-row soybean production for this area. The two objectives were: (i) evaluate a mid-group-IV soybean cultivar and an early group V cultivar produced in twin-rows compared to conventional 38-inch rows, and (ii) compare both row spacings when planted at the rate of 6, 10, and 15 seeds per planted foot. Field Procedures Soybean was planted near El Campo and Pt. Lavaca, TX on 24 March 2003 and on 29 March, 2004 near Pt. Lavaca and 21 April 2004 near El Campo. Different planting dates in 2004 occurred due to wet conditions at the El Campo location during the latter part of March. The experimental design for each year was a factorial arrangement using a randomized complete block with three replications at each location. Factors were row spacing (2), seeding rates (3), and soybean cultivars (2). Soybean cultivars used in 2003 at both locations were HBK 5101 and DP 4446 while in 2004 the cultivars at El Campo were HBK 5123 and Pioneer 94M90 and the cultivars at Pt. Lavaca were HBK 5101 and DP 4724. Boundary (S-metolachlor plus metribuzin) was applied preemergence at 1.0 qt/acre for weed control. Select (clethodim) was used postemergence at 10 oz/acre to control any annual grass escapes while Blazer (acifluorfen) was used at 1.5 pt/acre to control any broadleaf weed escapes. Weeds were treated when less than 6 inches tall and all postemergence herbicide treatments included Agridex added at the rate of 0.25% v/v. Each twin-row plot had two sets of twin rows (two rows spaced 4 to 6 inches apart on a single bed spaced on 38-inch centers) that were planted with a Monosem vacuum planter (Monosem ATI Inc., Leneka, KS) equipped with precision seed meters. Conventional planted soybeans were planted in the middle of the raised bed also spaced on 38-inch centers. Two trips were made through each plot to plant the twin-rows since planters were off-set from the row center while conventionally planted soybeans were centered directly over the row. Plots were planted at a rate of 6 (82,700 seeds/acre), 10 (137,400 seeds/acre), and 15 (206,100 seeds/acre) seed per planted foot; therefore the twin-row actually had 12 (165,400 seeds/acre), 20 (274,800 seeds/acre), and 30 (412,200 seeds/acre) seed planted per linear foot. Seedling emergence counts were taken approximately six weeks after planting. Pod height measurements (mean difference from the ground to the first node on the main stem with the pod attached) were taken in 2003 but not 2004. Lowest pod were measured prior to harvest. Five plants per plot were measured and an average recorded. Harvesting was accomplished mechanically with a small plot combine and plot yields adjusted to 13% moisture. Net returns were based on seed costs only and did not include land preparation, herbicide, or insecticide costs. Seed costs were calculated based on calls to local seed representatives. Seed costs were based on a cost of $35.00 per bag at 150,000 seeds per bag count while the soybean price was calculated at $5.88/bu based on the close of the market on 21 February, 2006. Data were analyzed using PROC GLM with SAS (SAS Institute, Inc., Cary, NC) and a model statement appropriate for a factorial design. Treatments means were separated by Fisher’s protected least significant difference test at P = 0.05. Data for the two years were analyzed separately due to changes in soybean varieties. Yearly Rainfall In 2003 at El Campo, below average rainfall was received for March through May with average to above average rainfall for June through July, while in 2004 rainfall was above average for all months except March and July (Table 1). At Pt. Lavaca, in 2003, very little rainfall was received in April, May, and August with below average rainfall for June and July. In 2004, only April resulted in above average rainfall while the other months were extremely dry (Table 1). Table 1. Rainfall amounts at the two locations in 2003 and 2004.
Plant Populations Row spacing interacted with seeding rate for each year at both locations. Plant populations increased when seeding rates were increased from six to ten seeds/ft but a decrease in plant populations was noted when the seeding rate was increased from ten to fifteen seeds/ft at both the twin and 38-inch row spacings (Table 2). Other research has shown that optimal plant populations vary from 12,000 to 202,000 plants per acre (4,8). The optimal soybean plant population can vary by as much as 100% across years, even when the same cultivar is grown in the same location (20). This variability can be explained by environmental conditions, with the optimal plant populations increasing under adverse conditions (20). Table 2. Soybean plant populations (plants/planted foot) as influenced by row spacing and seeding rates in 2003 and 2004 at El Campo and Pt. Lavaca.
Row Spacing Effects on Pod Height. Lowest pod height was significantly higher in twin rows than single rows for HBK 5101 and DP 4446 at El Campo in 2003 while at the Pt. Lavaca location no response was seen to the twin-row effect with either variety (Table 3). No response to pod height was seen with seeding rate (data not shown). Bowers et al. (2) reported that soybean plant and pod heights were generally greater in the twin rows than in the single row planting system; however, in general, row spacing had no measurable effect on pod height. Table 3. Soybean pod height (lowest pod height) response to twin-
Soybean Yield Row spacing by variety response was noted for three of the four site years, with the only exception being Pt. Lavaca in 2003 (Table 4). HBK 5101, Pioneer 94M90, and DP 4724 all had a positive yield response to the twin-row system while HBK 5123 had a negative yield response to the twin-row spacing. Yields were not different for DP 4446 with either system at the two locations. Bowers et al. (2) reported significant yield differences due to row spacing in 3 of 4 years. In 2 of those years, yield was greater from the twin-row system while in one year the reverse was true. They also reported that late-season rainfall also affected yield response to row spacing. In their study the twin-row system produced a yield advantage in the 2 years receiving the most late-season rainfall. Graterol et al. (9) reported that twin-row planting systems yielded more than single-row systems only in environments without yield limitations. Rainfall near El Campo in 2003 was below average for March through May but above average for June and July. At Pt. Lavaca in 2004 all months except April had below-average rainfall (Table 1). Rainfall during late fall of 2003 and winter of 2004 can be characterized as above average (data not shown); therefore, sub-soil moisture was present at Pt. Lavaca to help maintain plant growth and development. Partial Net Dollar Returns Partial net returns were greatest with 6 seeds/ft either planted in the twin-row or 38-inch row system (Table 5). At El Campo in 2003 and Pt. Lavaca in 2004, the twin-row system planted at 6 seeds/ft resulted in the highest partial net return while at Pt. Lavaca in 2003 and El Campo in 2004, the 38-inch row system at 6 seeds/ft produced the highest returns. The 10 seeds/ft rate was intermediate in partial net return with both the twin- and 38-inch row system. The 15 seeds/ft rate planted in the twin-row produced the lowest partial net return in 2 of 4 site years. Table 5. Partial net returns for row spacing and seeding rate effects on yield based on seed costs only.
x Seed costs were calculated based on a cost of $35.00 per bag at 150,000 seed per bag count while soybean price was calculated at $5.88/bu. When seeding rates were compared, at a planting rate of 6 seeds/ft, only at the El Campo location in 2004 was there a significant increase in net returns with either system. The single row 38-inch system had almost a $40/acre return over the twin-row system. At 10 seeds/ft, no difference in net returns were noted between the two systems while at a seeding rate of 15 seeds/ft, both locations in 2003 showed a net increase with the 38-inch spacing over the twin-row system. No differences were noted in 2004 at either location with a seeding rate of 15 seeds/ft (Table 5). Partial net returns were not different between the two systems at a lower seeding rate in three of four site-years. As seeding rates increased, the 38-inch system had a higher partial net return than the twin-row system in 2003 but not 2004. However, if a twin-row system is to be used, seeding rates should be no greater than 6 seeds/planted ft to avoid a substantial increase in seed cost and a reduction in net returns in most years. Acknowledgments The Texas Soybean Board provided funds for this research. Kevin Brewer, Dwayne Drozd, Bill Klesel, and A. J. Jaks provided technical assistance. Literature Cited 1. Baldwin. J. A., Beasley, J. P., Jr., Brown, S. L., Todd, J. W., and Culbreath, A. K. 1998. Yield, grade, and tomato spotted wilt virus icidence of four peanut cultivars in response to twin versus single row planting patterns. Proc. Amer. Peanut Res. Educ. Soc. 30:51. 2. Bowers, G. R., Rabb, J. L., Ashlock, L. O., and Santini, J. B. 2000. Row spacing in the early soybean production system. Agron. J. 92:524-531. 3. Bullock, D. G., Nielsen, R. L., and Nyquist, W. E. 1988. A growth analysis comparison of corn growth in conventional and equidistant plant spacing. Crop Sci. 28:254-258. 4. Costa, J. A., Oplinger, E. S., and Pendleton, J. W. 1980. Response of soybean cultivars to planting patterns. Agron. J. 72:153-156. 5. Cox, W. J., and Cherney, D. R. 2002. Evaluation of narrow-row corn forage in field scale studies. Agron. J. 94:321-325. 6. Culpepper, A. S., and York, A. C. 2000. Weed management in ultra narrow row cotton (Gossypium hirsutum). Weed Technol. 14:19-29. 7. Esbenshade, W. R., Curran, W. S., Roth, G. W., Hartwig, N. L., and Orzolek, M. D. 2001. Effect of row spacing and herbicides on burcumber (Sicyos angulatus) control in herbicide-resistant corn (Zea mays). Weed Technol. 15:348-354. 8. Egli, D. B. 1988. Plant density and soybean yield. Crop Sci. 28: 977-981. 9. Graterol, Y. E., Elmore, R. W, and Eisenhauer, D. E. 1996. Narrow-row planting systems for furrow-irrigated soybean. J. Prod. Agric. 9:546-553. 10. Grichar, W. J., Besler, B. A., Lemon, R. G., and Pigg, D. J. 2004. Comparison of conventional and twin-row production systems on cotton growth and development. Proc. Beltwide Cotton Conf. p. 2119-2203. 11. Heitholt, J. J., Tettigrew, W. T., and M. T. Meredith, Jr., W. R. 1992. Light interception and light yield of narrow-row cotton. Crop Sci. 32:728-733. 12. Hutmacher, B., Wright, S. D., Vargas, R. N., Marsh, B. H., Munk, D. S., Weir, B. L., Keeley, M. P., and Banuelos, G. 2005. Double-row 30 inch cotton in California: long-term summary. Proc. Beltwide Cotton Conf. p. 1975-1980. 13. Jaaffar, Z., and Gardner, F. P. 1988. Canopy development, yield and market quality in peanut as affected by genotype and planting pattern. Crop Sci. 28:299-305. 14. Kasperbauer, M. J., and Karlen, D. L. 1994. Plant spacing and reflected far-red light effects on photosynthesis allocation in corn seedlings. Crop Sci. 34:1564-1569. 16. Ottman, M. J., and Welch, L. F. 1989. Planting patterns and radiation interception, plant nutrient concentration, and yield in corn. Agron. J. 61:279-282. 17. Reddy, K. N. 2001. Broadleaf weed control in ultra narrow bromoxynil-resistant cotton. Weed Technol. 15:497-504. 18. Tharp, B. E., and Kells, J. T. 2001. Effect of glufosinate-resistant corn (Zea mays) population and row spacing on light interception, corn yield, and common lambsquarters (Chenopodium album) growth. Weed Technol. 15:413-418. 19. Teasdale, J. R. 1995. Influence of narrow row/high population corn (Zea mays) on weed control and light transmittance. Weed Technol. 9:113-118. 20. Wells, R. 1991. Soybean growth response to plant density: relationship among canopy photosynthesis, leaf area, and light interception. Crop Sci. 31: 755-761. |
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