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© 2005 Plant Management Network. Evaluation of Weed Control Strategies in Organic Soybean Production Daniel Kluchinski, County Agent II and Associate Professor, Department of Agricultural and Resource Management Agents, Rutgers-The State University of New Jersey, 88 Lipman Drive, New Brunswick, NJ 08901-8525; and Jeremy W. Singer, Research Agronomist, USDA-ARS National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011 Corresponding author: Daniel Kluchinski. kluchinski@rce.rutgers.edu Kluchinski, D., and Singer, J. W. 2005. Evaluation of weed control strategies in organic soybean production. Online. Crop Management doi:10.1094/CM-2005-0614-01-RS. Abstract A 2-year (2001 and 2002) organic soybean [Glycine max (L.) Merr.] study evaluated the contributions of row width (narrow 8-inch and wide 30-inch), mechanical weed control equipment (rotary hoe and cultivator), cultivation frequency (1 to 3 passes with one or both implements), and cultivation timing (early, late, or sequential) to annual broadleaf and grass weed control and grain yield. Narrow row (NR) systems reduced the timeframe available for cultivation compared to wide rows (WR) due to quicker canopy closure. A rotary hoe (RH) was equally or less effective in controlling weeds compared to a cultivator. Weed control was similar for early or late RH treatments, and early or late cultivator treatments. Yield did not differ among treatments in 2001. In 2002, the highest yields were achieved in WR with sequential 1 RH, 2 cultivator passes (54 bu/acre) compared to NR, 1 or 2 RH treatments (27 to 33 bu/acre). WR systems provide greater flexibility in cultivation equipment and timing, and may provide greater yield stability than NR systems. Introduction Exponential increases in organic food sales, increased demand for soy foods due to substantiated health benefits, uniform national organic certification standards, and new and emerging markets are all positive reasons for transitioning some soybean acreage to organic production. Despite these motivating market factors, farmers state that their greatest hesitancy in transitioning to and organically managing crops is weed control. In a national survey, weed control methods were identified as the top information requirement for organic production and the second most common focus of farmers’ own on-farm research activities (10). Organic production requires a complex management system. Various weed control methods can be used including mechanical cultivation (3,6,7); flame weeding and crop rotations (4); companion crops (9); cover crops (1,5,11); and other cultural, mechanical, and biological methods. However, replicated research on mechanical weed control effectiveness in certified organic production systems is limited. Such research is essential to aid growers in evaluating and adopting various components of an organic production system. To that end, combinations of cultural and mechanical weed control practices need to be investigated to identify practical and effective weed control methods in soybean under organic production methods. A study was conducted to determine the contributions of row width, cultivation equipment type, and cultivation frequency and timing to annual broadleaf and grass weed control and soybean grain yield. Field Study Design and Analysis A 2-year field study was conducted during the 2001 and 2002 growing seasons at the Rutgers University Snyder Research and Extension Farm near Pittstown, NJ on a Quakertown silt loam soil (fine-loamy, mixed, mesic Typic Hapludult). The experimental site was certified organic by the Northeast Organic Farming Association of New Jersey (NOFA-NJ). A randomized complete block experimental design with three replicates was used; plot size was 10 by 30 ft. Ohio ‘FG1’ (food grade) soybean were planted at 215,000 plants per acre in Narrow rows (NR) (8-inch) with a small plot research drill and wide rows (WR) (30-inch) with a corn planter. Planting dates were June 27, 2001 and June 4, 2002. Severe soil crusting in 2001 produced unsatisfactory stands that required replanting. Plant populations in 2001 were 190,031 plants per acre in NR hand-weeded control (HWC) treatments and 158,849 plants per acre in WR-HWC; in 2002, populations were 187,667 plants per acre in NR-HWC and 183,333 plants per acre in WR-HWC treatments. The study included 11 treatments to evaluate the effects of row width, cultivation equipment type, timing, frequency, and sequence on annual weed control (Table 1). Mechanical weed control passes were performed with a Kewanne 470 solid-set rotary hoe (RH) (Chromalloy American Corp., Kewanne, IL) or a Buffalo cultivator (Fleischer Manufacturing Inc., Columbus, NE). Most management guides recommend the use of a RH within 5 to 14 days after planting in order to control germinating weed seeds in the "white root" stage as well as to control germinating seedlings through uprooting and desiccation. In our study, a RH was used 12 to 13 days after planting, with sequential RH 4 to 9 days later. Weed seedlings growth stages ranged from white root to an emerged shoot, and from cotyledons showing to formation of the first true leaves. These treatments were used to simulate a "real world" scenario that growers often face with delays due to time, weather, or equipment failure. A cultivator was used alone or in combination with a RH 22 to 35 days after planting. Variations in treatment cultivation timing across years occurred due to planting date, weather, and soil conditions. Table 1. Narrow row (NR) and wide row (WR) mechanical weed control treatments in soybean in 2001 and 2002, near Pittstown, NJ.
a NR = narrow row, WR = wide row; HWC = hand weeded control, NWC = no weed control; RH = rotary hoe, C = cultivator; E = early, L = late Weed control data for annual grasses and broadleaves were collected August 2, 2001 and July 12, 2002, approximately 5 weeks after planting. Control of each weed species was determined through visual evaluation using a rating scale of 0 to 100% control, where 0 = no control and 100 = total control; data were pooled across species within broadleaf and grass weeds and average % control was calculated. Weed control data were then classified with ratings of poor = 20 to 60% control, fair = 60 to 80% control, and good to excellent = 80 to 100% control. Soybean stand counts were determined for a 1/1000-acre area in each plot on the same dates as weed control data. Plots were harvested on November 12, 2001 and November 4, 2002 with a small plot combine (Massey Ferguson 8 research combine, AGCO Corp., Duluth, GA). In NR plots, areas of 5 rows by 30 ft were harvested for grain yield; in WR plots, areas measuring 2 center rows by 30 ft were harvested. Yield (bu/acre) were corrected to 13% moisture. Statistical analysis was performed using analysis of variance, and mean separation was accomplished using a protected LSD at a 0.05 probability level. Orthogonal contrasts were also used to compare NR and WR systems, excluding no weed control (NWC) and HWC treatments. Weed Control Annual broadleaf and grass weeds included galinsoga (Galinsoga ciliata), common lambsquarter (Chenopodium album), redroot pigweed (Amaranthus retroflexus), Pennsylvania smartweed (Polygonum pensylvanicum), common ragweed (Ambrosia artemisiifolia), barnyardgrass (Echinochloa crus-galli), crabgrass (Digitaria spp.), and giant foxtail (Setaria faberi). Weed control data are presented in Table 2 for annual broadleaves and annual grasses in 2001 and 2002. Table 2. Broadleaf and grass weed control in narrow row (NR) and wide row (WR) mechanical control treatments in 2001 and 2002, near Pittstown, NJ.
a NR = narrow row, WR = wide row; HWC = hand weeded control, NWC = no weed control; RH = rotary hoe, C = cultivator; E = early, L = late. b NS = not significant. In both years, most of the WR mechanical weed control treatments resulted in good to excellent control, while NR treatments resulted in poor to fair control. Both annual broadleaf and grass weed control were generally higher each year in WR soybean treatments that included a cultivator compared to NR RH treatments. Although more rapid canopy closure in NR could result in greater weed control, NR-NWC treatments resulted in 51% control for broadleaf weeds in 2001 and 0% control for broadleaf and grass weeds in 2002. The high level of grass weed control in the NR-NWC treatment in 2001 is due to the variability in the grass weed population in the study area rather than solely crop-weed competition. Treatment effects on broadleaf weed control were significant in 2001 (P = 0.0032) and 2002 (P < 0.0001). In 2001, all WR treatments with cultivator alone or sequentially following 1 or 2 RH passes resulted in greater weed control than WR with 2 sequential RH passes. In 2002, WR RH followed by a cultivator had greater weed control than NR 2 RH pass treatments (Fig. 1). In 2001, broadleaf weed control in all NR RH treatments was not different than that obtained in the NR-NWC treatment; in 2002 all were greater than the control.
Fig. 1. The WR-1RH,2C resulted in the highest level of broadleaf weed control both years (99% in 2001, 95% in 2002). The WR provided the longest timeframe for sequential cultivation, as compared to NR-2RH(1L) which only resulted in 65% broadleaf weed control in 2001 and 57% in 2002. (A) Wide row-1 rotary hoe, 2 cultivations (WR-1RH, 2C)-2002. (B) Narrow row-2 rotary hoeings (1 late) (NR-2RH(1L)-2002. Annual grass weed control did not differ among treatments in 2001 (P = 0.1446) and were rated as fair or good to excellent. In 2002, the weed control ratings were significant (P = 0.0002). Control was similar for all treatments except NR-2 RH(1E), NR-2 RH(1L) and WR-1C(L) which were not effective in controlling grasses. Early or later RH cultivations in NR were similarly effective, as were early or late cultivator treatments in WR. All single or sequential RH treatments resulted in 47 to 78% control of broadleaves and 33 to 83% control of grasses. This level of weed control compares to or exceeds that reported by Renner and Woods (1999) who concluded that when used at an appropriate time, a RH can reduce weed populations by as much as 70%. A cultivator, used by itself or in combination with a RH, resulted in good to excellent control of annual broadleaf weeds in both years (84 to 99% in 2001; 89 to 95% in 2002). These levels of control were better than treatments utilizing a RH once or sequentially, which resulted in poor to fair control (55% to 74% in 2001; 47 to 78% in 2002). RH effectiveness may have been reduced as weed seedlings were primarily beyond the white root stage. In addition, RH effectiveness may have been further reduced by wet weather, with rainfall during the first 3 weeks after planting totaling 5.1 inches in 2001 and 4.1 inches in 2002. Successful weed control in a NR system can also depend on the mechanical weed control equipment available. The RH used in this study was solid set rather than having independent, floating, ground-driven wheels (hoes) that follow the contours of the field. This limited the ability to control weed seedlings located in channels and contours in the field and may have influenced season long weed control. Grain Yield Soybean yield (Table 3) ranged from 36 to 50 bu/acre in 2001, but yields were not different among treatments (P = 0.3553). It is unclear why the WR-HWC yielded so low in 2001. Even though poor weed control ratings occurred in certain treatments in 2001, the late planting date may have reduced the weed density and competitiveness (2). In 2002 (P < 0.0001), yields ranged from 23 to 54 bu/acre; the highest yield occurred in WR soybean with one pass of a RH and two passes of a cultivator (WR-1RH+2C). The lowest yields in 2002 were in NR with one or two passes with a RH; of these treatments, NR-1RH and NR-2RH(1E) were the same as the NR-NWC treatment. Yields were greater for all WR treatments, except the 2RH(1L) treatment, regardless if RH, cultivator or a combination was used. Yield differences were not related to plant density because there was no difference in plant density among treatments in either year (data not presented). Averaged across NR and WR systems, excluding the NR-HWC, NR-NWC, and the WR-HWC treatments, no difference was detected in 2001 between NR (42 bu/acre) and WR (45 bu/acre) systems (P = 0.3037), although in 2002, WR yielded (43 bu/acre) higher than NR (28 bu/acre; P < 0.0001). This indicated that WR systems may provide greater yield stability than NR systems. Table 3. Soybean yield (bu/acre) in narrow row (NR) and wide
a NR = narrow row, WR = wide row; HWC=hand
weeded control, b NS = not significant. Conclusions Acceptable weed control is possible in NR organic soybean production, although WR systems allow greater flexibility in cultivation equipment and timing. However, our results suggest that WR weed control systems may provide greater yield stability than NR systems. Additional research to determine how to best integrate cultivation equipment selection, and cultivation timing and frequency in NR and WR organic soybean production is needed. Acknowledgments The authors would like to thank the New Jersey Soybean Board for their financial support and the staff of the Rutgers University Snyder Research and Extension Farm for their technical assistance. Literature Cited 1. Ateh, C. M., and Doll, J. D. 1996. Spring planted winter rye (Secale cereale) as a living mulch to control weeds in soybean (Glycine max). Weed Technol. 10:347-353. 2. Buhler, D. D., and Gunsolus, J. L. 1996. Effect of date of preplant tillage and planting on weed populations and mechanical weed control in soybean (Glycine max). Weed. Sci. 44:373-379. 3. Gunsolus, J. L. 1990. Mechanical and cultural weed control in corn and soybeans. Am. J. Altern. Agric. 5:114-119. 4. Lampkin, N. 1990. Organic Farming. Farming Press, Ipswich, United Kingdom. 5. Liebl, R. A, Simmons, F. W., Wax, L. M., and Stoller, E. W. 1992. Effect of rye (Secale cereale) mulch on weed control and soil moisture in soybean (Glycine max.). Weed Tech. 6:838-846. 6. Lovely, W. G., Weber, C. R., and Staniforth, D. W. 1958. Effectiveness of the rotary hoe for weed control in soybeans. Agron. J. 50:8621-625. 7. Parish, R. L., Bracey, R. P., Wells, D. W., and Bergeron, P. E. 1990. A comparison on cultivation methods for commercial vegetable crops. Am. J. Agric. Eng. 6:565-568. 8. Renner, K. A., and Woods, J. J. 1999. Influence of cultural practices on weed management in soybean. J. Prod. Agric. 12:48-53. 9. Thelen, K. D., Mutch, D. R., and Martin, T. E. 2004. Utility of interseeded winter cereal rye in organic soybean production systems. Agron. J. 96:281-284. 10. Walz, E. 1999. Final Results of the Third Biennial National Organic Farmers' Survey. Org. Farming Res. Foundation, Santa Cruz, CA. 11. Westgate, L. R., Singer, J. W., and Kohler, K. A. 2005. Method and timing of rye control affects soybean development and resource utilization. Agron. J. 97:806-816 . |
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