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© 2008 Plant Management Network. Influence of Tillage, Row Spacing-Population System, and Glyphosate Herbicide Timing on Soybean Production in the Eastern Great Plains Kenneth W. Kelley and Daniel W. Sweeney, Southeast Agricultural Research Center, Kansas State University, P.O. Box 316, Parsons, KS 67357 Corresponding author: Ken Kelley. kkelley@oznet.ksu.edu Kelley, K. W., and Sweeney, D. W. 2008. Influence of tillage, row spacing-population system, and glyphosate herbicide timing on soybean production in the eastern Great Plains. Online. Crop Management doi:10.1094/CM-2008-1114-01-RS. Abstract Field studies were conducted from 1999 through 2004 in southeastern Kansas to evaluate the influence of tillage method [conventional (CT) and no-till (NT)], row spacing-population system (7.5-, 15-, and 30-inch rows planted at 225,000, 175,000, and 125,000 seeds/acre, respectively), and glyphosate application timing on soybean [Glycine max (L.) Merr.] yield, weed control, and net economic returns. Herbicide treatments were: (i) preplant residual (pendimethalin) followed by glyphosate at 3 weeks after planting (WAP); (ii) glyphosate at 3 WAP; (iii) sequential glyphosate at 3 and 5 WAP; and (iv) glyphosate at 8 WAP. Soybean followed grain sorghum [Sorghum bicolor (L.) Moench] in a 2-year rotation. Tillage method influenced yield very little. Narrower row spacing (7.5- and 15-inch) increased soybean yields 2 to 4 bu/acre in high-yielding environments compared to 30-inch rows and also provided greater weed control. Glyphosate applied sequentially (3 and 5 WAP) provided the highest weed control, but a single glyphosate application 3 WAP often produced the greatest net return, regardless of tillage or row spacing system. The results suggest that the adoption of NT planting will likely increase soybean net returns to a greater extent than reducing row spacing in the eastern Great Plains. Introduction Since the introduction of glyphosate-resistant (GR) soybean in 1996, producers throughout the United States have readily adopted this genetically-engineered technology. Currently, over 90% of the total soybean acreage in the United States is GR varieties (21). Management practices most influenced by the adoption of GR technology in soybean production include weed management, no-tillage, and row spacing and plant population. The use of glyphosate, applied post-emergence (POST) in GR soybean, allows growers greater flexibility in controlling a broad spectrum of both annual and perennial weeds without causing crop injury (17). However, because glyphosate has no residual soil activity, weeds emerging after application may grow and compete with soybean. Producers may delay the time of a single POST glyphosate application to allow more weeds to emerge before treatment, but glyphosate must be applied timely to avoid crop yield loss because of early season weed competition (15,16). The critical time of weed removal in GR soybean has been shown to be earlier when planted in wide rows compared to narrow rows (13,16). A second POST glyphosate application can be used to control weeds that emerge after the initial glyphosate treatment. Sequential glyphosate applications have been shown to improve weed control when compared with single glyphosate applications (19,23,26). However, other research has shown that a single glyphosate application can prevent yield loss in narrow-row GR soybean (5,16,25). Using a residual herbicide applied preplant (PP) or preemerge (PRE) before a single POST glyphosate application may be beneficial in situations where early-season weed competition is severe and a timely glyphosate application is not possible (8). However, tank-mixing residual herbicides with POST glyphosate applications generally has shown no benefit in weed control (5), except for some harder to control species, like morningglory (Ipomoea spp.) (2). Narrower row spacing is often used as a management practice to suppress weed growth and increase grain yield in both glyphosate-resistant (1,11,12,20) and conventional soybean plantings (10). The yield advantage with narrow rows generally has been greater in more northern soybean regions of the United States compared to the southern region. Researchers have shown that the increased yield associated with narrow rows is due primarily to a greater crop growth rate during vegetative and early reproductive growth stages (4,18), resulting in a more dense crop canopy that is able to intercept more solar radiation as well as providing more shading of the soil surface. However, seeding rates for narrow-row soybean can be 20 to 45% greater than for wide-row soybean (1,14), which increases input cost. Greater economic returns, however, have been reported in narrow-than wide-row GR soybean production when similar weed management systems were implemented (17) and water is not limited (9). An extensive literature review on the influence of tillage on corn and soybean yields in the United States and Canada showed that no-till (NT) has a different effect on soybean yields relative to conventional tillage (CT), depending on the region of soybean production (6). The review showed that NT tended to have greater yields than CT in the south and west regions of the United States, whereas, CT and NT had similar yields in the central United States, and NT typically produced lower yields than CT in the northern United States and Canada. For the eastern Great Plains soybean-producing region, which is located between the corn and soybean belt of the Upper Midest and the soybean-producing region of the mid-southern United States, information is lacking concerning the optimum management practices that result in greatest economic returns in glyphosate-resistant soybean production systems. Thus, the objectives of this research study were to investigate the effects and interactions of three different management practices (tillage method, row spacing-population system, and glyphosate herbicide timing) on grain yield, weed control, and net economic return. Field Study in a Soybean and Grain Sorghum Rotation Site information. Field studies were conducted from 1999 through 2004 at the Columbus Unit of the Kansas State University Southeast Agricultural Research Center. The soil was a Parsons silt loam (fine, mixed, active, thermic, Mollic Albaqualf) consisting of a shallow topsoil (< 12 inch) overlaying a thick "clay-pan" subsoil. Initial soil chemical characteristics at the 0- to 6-inch depth included a pH (1:1 soil/water) of 6.5, organic matter (OM) of 2.0%, Bray-1 phosphorus of 15 lb/acre, and exchangeable potassium (1 M ammonium acetate extract) of 80 lb/acre analyzed by the procedures recommended by North Central Region Agricultural Experiment Stations (3). Wheat and double-crop soybean preceded the grain sorghum crop before study establishment. Monthly rainfall and average maximum and daily air temperature during the growing season and the 30-year average are shown in Table 1. Table 1. Monthly rainfall totals and average maximum and daily air temperature for Columbus, KS during the growing season.
Experimental design. Soybean treatments were evaluated each year by alternating the 2-year rotation of soybean and grain sorghum in two adjacent sites. The experimental design was a split-plot arrangement of a randomized complete block with three replications. Main plots (40 by 40 ft) consisted of a 2 × 3 factorial combination of two tillage methods (conventional and no-tillage) and three soybean row spacing and population systems (7.5-, 15-, and 30-inch rows planted at 225,000, 175,000, and 125,000 seeds/acre, respectively). Subplot treatments (10 by 40 ft) consisted of three glyphosate herbicide treatments applied at different times and one glyphosate treatment that included a preplant residual herbicide (pendimethalin) (Table 2). All POST glyphosate treatments were applied with a CO2-pressurized backpack sprayer equipped with a 10-ft boom and XR8003 VS extended flat-fan nozzles (Spraying Systems Co., Wheaton, IL) at 30 psi to deliver 20 gal/acre. POST treatments were applied by walking in the plot border areas with the backpack sprayer rather than using a tractor-mounted sprayer to reduce plant damage and possible yield reduction. All tillage and herbicide treatments were imposed on the same plots in each year of the study and three complete 2-year cropping cycles were evaluated at each site, giving six years of soybean data. Table 2. Summary of herbicide treatments, rate of application, and timing.
x Ammonium sulfate applied at 3 lb/acre to all glyphosate treatments. y fb = followed by. z WAP = weeks after planting. Soybean planting. The soybean cultivar (NC+ 5A45) used was maturity group (MG) V and glyphosate-resistant. Planted seed size varied some with year, but averaged 3,000 seeds/lb. Soybean in 7.5- and 15-inch rows were planted with a Great Plains NT drill (model 1005NT, Great Plains Mfg., Salina, KS), and 30-inch rows were planted with a John Deere (conservation model 7000 Maxi-emerge). Soybean was planted in June in all years, which is the normal full-season planting date for this region of Kansas. Average plant population was determined by taking random triplicate counts of the number of plants within a hula-hoop (34-inch diameter) for the narrow row spacing and the number of plants in 3-ft sections of row in the 30-inch row spacing. Cultural practices. Conventional tillage operations for soybean following grain sorghum consisted of fall disking, late-winter chiseling, early spring disking, and one or two field cultivations prior to planting to remove emerged weeds and incorporate the preplant residual herbicide treatment. In no-till plots, the preplant residual herbicicde was tank-mixed with a burn-down herbicide treatment (0.75 lb ae/acre of glyphosate and 0.5 lb ai/acre of 2,4-D, low volatile ester) and applied with a tractor-mounted compressed air sprayer approximately 10 days prior to planting. The residual preplant incorporated herbicide treatment in CT also was applied at the same time as the burn-down and residual treatment in the NT system. Weed species. Weed species in NT plots at the time of preplant burn-down application consisted primarily of various winter annual types and small annual weeds. Weed species after planting consisted primarily of smooth crabgrass (Digitaria ischaemum) and common waterhemp (Amaranthus rudis). Weed control ratings at 6 WAP were based on a visual rating of 0 to 100, with 0 equal to the weed control in 30-inch row spacing plots that had not yet been sprayed (glyphosate at 8 WAP) and 100 equal to complete control. The weed control rating at 6 WAP provided the best estimate of weed competition among treatments because of later soybean canopy closure. However, visual weed control ratings also were taken at 3 and 10 WAP (data not shown) to evaluate herbicide effectiveness of the preplant residual herbicide before the early glyphosate application (3 WAP) and after the late glyphosate treatment (8 WAP). Pendimethalin was chosen for the preplant residual herbicide treatment because of relative low cost, ability to surface apply in NT systems as well as incorporate in CT, and proven performance for the control of weed species targeted in this study (crabgrass and common waterhemp). Data collection. Grain yields were determined by machine-harvesting 5-ft by 40-ft from the center of each plot and adjusting to constant moistures of 13%. Grain yield data were analyzed using the Proc Mixed procedure in SAS (SAS Institute Inc., Cary, NC). All factors except REP were considered fixed. Year was treated as a strip-plot fixed effect, so that across years the data were analyzed as a strip-split plot. Treatment means were compared by using Fisher’s protected LSD (0.05). Economic budgets. Economic budgets were developed annually for all treatments. Input costs (seed and herbicide) were based on local costs in each year of the study. Costs for tillage, herbicide application, planting, and harvesting were based on average custom rates for eastern Kansas (22). Interest expense (8%) was calculated on one-half of non-land costs. Costs for land, management, and general farm overhead were not included because those costs were assumed to be the same for all treatment combinations. Gross income was calculated each year by multiplying crop yield by average yearly grain price. Net returns represented gross returns minus specified variable costs. Government program benefits were not included in this study. Growing conditions. Rainfall and average maximum and daily air temperature during the growing season differed yearly over the 6-year period (Table 1), which influenced grain yield responses. In 1999 and 2000, low rainfall in August and above-normal air temperatures during the reproductive stage of development resulted in poor yields. In 2002, yields also were below normal due to low rainfall and cooler than normal air temperatures during October. In 2001 and 2003, grain yields were average for this growing region of Kansas (38°N latitude); whereas in 2004, grain yields were above average because of cooler air temperatures during July and August. Soybean plant population. Soybean populations within the same row spacing were similar for NT and CT systems each year (data not shown). Plant population per acre averaged 147,000 in 7.5-inch rows, 119,000 in 15-inch rows, and 97,000 in 30-inch rows. In this study, soybeans were planted at different populations to simulate a systems approach that likely would be used by most producers. Treatment Effects on Grain Yield Tillage Method. Soybean yields were not significantly influenced by tillage method (Table 3). Over the 6-year period, soybean yields averaged 26 bu/acre for CT and 27 bu/acre for NT (Table 4). Results agree with a recent survey showing that CT and NT often have similar soybean yields in the central United States (6). With the adoption of continuous NT, grain yields during the initial years of establishment have been reported to be lower than for CT (24); however, in this study, the early yield drag was not observed possibly because of the low-yielding environments experienced in 1999 and 2000 (Table 4). Table 3. Analysis-of-variance significance levels for the effect of tillage method, row spacing-population system, and glyphosate herbicide timing on grain yield and weed control.
* = Significant at the 0.05 probability. ** = Significant at the 0.01 level of probability. NS = Nonsignificant. Table 4. Main effects of tillage method, row spacing-population system, and glyphosate herbicide treatment on soybean yield, 1999-2004, Columbus, KS.
x PP (residual) = preplant (pendimethalin); Glyph = glyphosate;
Row spacing-population systems. The effect of row spacing-population system on soybean yields was significant (Table 3), although yield differences were greatest during the high-yielding environments of 2001, 2003, and 2004 (Table 4). During those years, soybean yields in 7.5- and 15-inch rows averaged 2 to 4 bu/acre higher than 30-inch rows. In the low-yielding environment of 1999, 2000, and 2002, row spacing-population system had no significant effect on grain yield. Other research conducted in Kansas also showed that the yield advantage in narrower row spacing was greatest in high-yielding environments (7). The tillage by row spacing-population system interaction with year was not significant for grain yield (Table 3), indicating that row spacing-population effects were similar for both CT and NT over the duration of the study. Herbicide application. Grain yields were significantly reduced by late applications of glyphosate (8 WAP) most years (Table 4). Grain yields were typically highest for sequential applications of glyphosate (3 + 5 WAP). Grain yields for pendimethalin + glyphosate at 3 WAP and single glyphosate at 3 WAP were within 2 bu of the sequential glyphosate treatment. The significant interaction of herbicide treatment and row spacing-plant population system with year (Table 3) was largely due to small yield variations in some years between row spacing-plant population systems and individual herbicide treatments (year interactions not shown). On average, the sequential glyphosate treatment at 3 and 5 WAP resulted in slightly higher grain yields in the 15- and 30-inch row spacing-population systems compared to 7.5-inch (Table 5). Table 5. Interaction effects of row spacing-population system and glyphosate herbicide timing on grain yield and weed control, 6-year average (1999-2004), Columbus, KS.
x 7.5-inch rows planted at 225,000 seeds/acre; 15-inch rows planted at 175,000 seeds/acre; and 30-inch rows planted at 125,000 seeds/acre. y PP (residual) = preplant (pendimethalin); Glyph = glyphosate;
Treatment Effects on Weed Control Similar to grain yields, crabgrass and waterhemp weed control was affected by row spacing-population system and glyphosate herbicide treatment, but not by tillage (Table 3). Weed control ratings at 6 WAP were averaged across year and tillage and are reported for the various weed management and crop arrangement treatments (Table 5). Regardless of row spacing-population system, both crabgrass and common waterhemp weed control were highest when glyphosate was sequentially applied at 3 and 5 WAP, followed by pendimethalin + glyphosate at 3 WAP, and then single glyphosate at 3 WAP. But, differences in weed control at 6 WAP among plant arrangements were 10% or less for all treatments that included glyphosate at 3 WAP. The level of weed control resulting from the preplant pendimethalin treatment prior to the early glyphosate application at 3 WAP ranged from 60 to 70% in most years for both crabgrass and common waterhemp, regardless of tillage system (data not shown). Weed control at 6 WAP was improved when soybean were arranged in row spacing systems less than 30 inches (Table 5). Weed control at 6 WAP was 20% higher in narrow row systems when no herbicide had been applied (glyphosate at 8 WAP), which resulted in greater yields compared to 7-inch rows. Weed control at 10 WAP (data not shown) indicated that the late glyphosate treatment (8 WAP) gave greater than 80% control of both crabgrass and common waterhemp, but early weed competition significantly reduced yield potential. Weed competition varied with year (data not shown), ranging from light in 2002 (< 5 and < 10 plants/yd² for common waterhemp and crabgrass, respectively) to moderate (20 to 30 and 40 to 60 plants/yd² for common waterhemp and crabgrass, respectively) in most other years; however, herbicide treatment effects on weed control were similar across years. In this study, where soybean was planted in June, overall weed competition may have been reduced somewhat compared to an earlier planting date because the initial flush of weeds likely was controlled with tillage in CT and by the burn-down herbicide treatment (glyphosate + 2,4-D, low volatile ester) in NT systems. Treatment Effects on Economic Returns Average net returns along with high (year 2003) and low (year 2000) values are shown in Table 6. Regardless of row spacing-population system, net returns generally averaged $20 to $30/acre greater with NT than CT because of fewer trips across the field. In addition, overall, net returns were greater when planted in 15- or 30-inch row systems compared to 7.5-inch rows because of the greater seed cost associated with the higher planting rate in 7.5-inch rows. Table 6. Net annual returns ($/acre) for soybean at different row spacing-population systems, tillage method, and herbicide treatments from 1999 through 2004, Columbus, KS.
x Net returns equal gross returns minus variable costs. y CT = conventional tillage; NT = no-tillage. z High (2003), Low (2000), and Avg. (1999 through 2004) net returns; The effects of the different glyphosate herbicide treatments on net returns varied with row spacing-population system and tillage method. For the weed competition in this study, glyphosate applied 3 WAP generally gave the highest net return, regardless of tillage or row spacing-population system. The grain price for soybean during this 6-year study averaged $5.20/bu; but, soybean prices have increased dramatically since this study ended and are currently (2008) over $10/bu. Similarly, input costs are nearly 25% greater than when this study was conducted. A projected soybean budget that included the current economic conditions (data not shown) did not change the economic benefit of NT over CT. However, in the projected economic budget, the difference in net returns between narrow and wide row systems was smaller, especially with NT. With CT, net returns in the projected budget were still greater in 15- and 30-inch rows than for the 7.5-inch row spacing. Reducing the plant population in 7.5-inch rows to 175,000 seeds/acre (same rate as 15-inch rows), however, would increase net return nearly $10/acre based upon current soybean seed cost and likely would not affect soybean yield because of soybeans ability to compensate for lower plant populations by producing more branches (1,9). Conclusions Soybean yields were influenced very little by tillage method when weeds were adequately controlled. However, net returns likely will be greater with NT because of fewer trips over the field, potentially leading producers to adopt NT. Even though narrow row spacing-population systems tend to increase soybean yield and provide greater weed control, especially in high-yielding environments, net returns may favor 15- or 30-inch over 7.5-inch row systems because of greater seed cost. However, additional research may be needed to address lower seeding rates in narrow row spacing systems. Timing of glyphosate herbicide did not result in large grain yield or weed control differences unless glyphosate was delayed until 8 WAP. Even though a preplant residual herbicide treatment did not improve yield or weed control compared with a single glyphosate treatment at 3 WAP, systems such as this may provide producers a flexible application window and a different herbicide mode for controlling the weed spectrum. Acknowledgments Contribution no. 08-300-J from the Kansas Agriculture Experiment Station, Manhattan, KS. The authors express appreciation to Michael Dean for his technical assistance. Literature Cited 1. Bertram, M. G., and Pedersen, P. 2004. Adjusting management practices using glyphosate-resistant soybean cultivars. Agron. J. 96:462-468. 3. Brown, J. R., ed. 1998. Recommended chemical soil test procedures for the North Central region, Missouri Agric. Exp. Stn. SB 1001. Missouri Agric. Exp. Stn., Columbia, MO. 4. Bullock, D., Khan, S., and Rayburn, A. 1998. Soybean yield response to narrow rows is largely due to enhanced early growth. Crop Sci. 38:1011-1016. 5. Corrigan, K. A., and Harvey, R. G. 2000. Glyphosate with and without residual herbicides in no-till glyphosate-resistant soybean (Glycine max). Weed Tech. 14:569-577. 7. Devlin, D. L., Fjell, D. L., Shroyer, J. P., Gordon, W. B., Marsh, B. H., Maddux, L. D., Martin, V. L., and Duncan, S. R. 1995. Row spacing and seeding rates for soybean in low and high yielding environments. J. Prod. Agric. 8:215-222. 8. Ellis, J. M., and Griffin, J. L. 2002. Benefits of soil-applied herbicides in glyphosate-resistant soybean (Glycine max). Weed Tech. 16:541-547. 9. Harder, D. B., Sprague, C. L., and Renner, K. A. 2007. Effect of soybean row width and population on weeds, crop yield, and economic return. Weed Tech. 21:744-752. 10. Heatherly, L. G., Elmore, C. D., and Spurlock, S. R. 2001. Row width and weed management systems for conventional soybean plantings in the Midsouthern USA. Agron. J. 93:1210-1220. 11. Hock, S. M., Knezevic, S. Z., Martin, A. R., and Lindquist, J. L. 2006. Soybean row spacing and weed emergence time influence weed competitiveness and competitive indices. Weed Sci. 54:38-46. 12. Johnson, W. G., Kendig, J. A., Massey, R. E., DeFelice, M. S., and Becker, C. D. 1997. Weed control and economic returns with postemerge herbicides in narrow-row sosybean (Glycine max). Weed Tech. 11:453-459. 13. Knezevic, S. Z., Evans, S. P., and Mainz, M. 2003. Row spacing influences the critical timing for weed removal in soybean (Glycine max). Weed Tech. 17:666-673. 14. Kratochvil, R. J., Pearce, J. T., and Harrison, M. R., Jr. 2004. Row-spacing and seeding rate effects on glyphosate-resistant soybean for Mid-Atlantic production systems. Agron. J. 96:1029-1038. 15. Krausz, R. F., Young, B. G., Kapusta, G., and Matthews, J. L. 2001. Influence of weed competition and herbicides on glyphosate-resistant soybean (Glycine max). Weed Tech. 15:530-534. 16. Mulugeta, D., and Boerboom, C. M. 2000. Critical time of weed removal in glyphosate-resistant Glycine max. Weed Sci. 48:35-42. 17. Nelson, K. A., and Renner, K. A. 1999. Weed management in wide- and narrow-row glyphosate resistant soybean. J. Prod. Agric. 12:460-465. 18. Parvez, A. Q., Gardner, F. P., and Boote, K. J. 1989. Determinate- and indeterminate-type soybean cultivar responses to pattern, density, and planting date. Crop Sci. 29:150-157. 19. Payne, S. A., and Oliver, L. R. 2000. Weed control programs in drilled glyphosate-resistant soybean. Weed Tech. 14:413-422. 20. Steckel, L. E., and Sprague, C. L. 2004. Late-season common waterhemp (Amaranthus rudis) interference in narrow- and wide-row soybean. Weed Tech. 18:947-952. 21. USDA. 2007. Adoption of genetically engineered crops in the U.S. Online. Data sets, Economic Research Service, USDA, Washington, D.C. 22. USDA. 2007. Custom machinery rates for Kansas. Online. Data sets, National Agricultural Statistics Service, USDA, Washington, D.C. 23. Wait, J. D., Johnson, W. G., and Massey, R. E. 1999. Weed management with reduced rates of glyphosate in no-till, narrow-row, glyphosate-resistant soybean (Glycine max). Weed Tech. 13:478-483. 24. West, T. D., Griffith, D. R., Steinhardt, G. C., Kladivko, E. J., and Parsons, S. D. 1996. Effect of tillage and rotation on agronomic performance of corn and soybean: Twenty-year study on dark silty clay loam soil. J. Prod. Agric. 9:241-248. 25. Wiesbrook, M. L., Johnson, W. G., Hart, S. E., Bradley, P. R., and Wax, L. M. 2001. Comparison of weed management systems in narrow-row, glyphosate- and glufosinate-resistant soybean (Glycine max). Weed Tech. 15:122-128. 26. Young, B. G., Young, J. M., Gonzini, L. C., Hart, S. E., Wax, L. M., and Kapusta, G. 2001. Weed management in narrow- and wide-row glyphosate-resistant soybean (Glycine max). Weed Tech. 15:112-121. |
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