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High Planting Rates Improve Weed Suppression, Yield, and Profitability in Organically-Managed, No-till–Planted Soybean

Published online by Cambridge University Press:  20 July 2017

Jeffrey A. Liebert  and
Matthew R. Ryan
Jeffrey A. Liebert*
Affiliation:
Graduate Student and Assistant Professor, Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853
Matthew R. Ryan
Affiliation:
Graduate Student and Assistant Professor, Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853
*
*Corresponding author’s E-mail: [email protected]
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Abstract

High soybean populations have been shown to hasten canopy closure, which can improve both weed suppression and soybean yield. In conventional soybean production, the high cost of genetically engineered seed and seed treatments have led growers to plant at lower rates to maximize profitability. For organic farmers, market price premiums are typically double the price received for conventional soybean. Without chemical or mechanical weed management, cultural practices are particularly important for adequate weed suppression in cover crop–based organic no–till planted soybean production. In 2014, an experiment was conducted in Aurora and Hurley, New York, to assess the effects of increasing soybean planting rates on weed suppression, soybean yield, and partial economic return. Five planting rates ranging from 195,000 to 914,000 seedsha−1 were arranged in a randomized complete block design. As soybean planting rate increased, weed biomass decreased and soybean yield increased at both sites. An asymptotic model described the relationship between increasing soybean planting rate and yield, and the estimated maximum yield was 2,504 kgha−1 in Aurora and 3,178 kgha−1 in Hurley. Despite high soybean populations, minimal lodging was observed. Partial returns decreased beyond the predicted economically optimal planting rate of 646,000 seeds ha−1 in Aurora and 728,000 seeds ha−1 in Hurley as higher seed costs were no longer offset by yield gains. Based on our results, planting rates that are more than double the recommended rate of 321,000 seeds ha−1 for wide row (≥76 cm) conventional soybean management in New York can enhance weed suppression, increase yield, and improve profitability in organic no-till planted soybean production.

Keywords

SoybeanGlycine max (L.) Merr.Cover cropscultural weed managementmulchorganic rotational no-tillreduced-tillageroller-crimper.
Type
Weed Management-Major Crops
Information
Weed Technology , Volume 31 , Issue 4 , August 2017 , pp. 536 - 549
Copyright
© Weed Science Society of America, 2017 

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Footnotes

Associate Editor for this paper: Robert Nurse, Agriculture and Agri-Food Canada

References

Literature Cited

Alessi, J, Power, JF (1982) Effects of plant and row spacing on dryland soybean yield and water-use efficiency. Agron J 74:851–854 Google Scholar
Arce, GD, Pedersen, P, Hartzler, RG (2009) Soybean seeding rate effects on weed management. Weed Tech 23:17–22 Google Scholar
Archer, DW, Jaradat, AA, Johnson, JMF, Weyers, SL, Gesch, RW, Forcella, F, Kludze, HK (2007) Crop productivity and economics during the transition to alternative cropping systems. Agron J 99:1538–1547 Google Scholar
Ashford, DL, Reeves, DW (2003) Use of a mechanical roller-crimper as an alternative kill method for cover crops. Amer J Altern Agric 18:37–45 Google Scholar
Ball, RA, McNew, RW, Vories, ED, Keisling, TC, Purcell, LC (2001) Path analyses of population density effects on short-season soybean yield. Agron J 93:187–195 Google Scholar
Ball, RA, Purcell, LC, Vories, ED (2000a) Optimizing soybean plant population for a short-season production system in the southern USA. Crop Sci 40:757–764 Google Scholar
Ball, RA, Purcell, LC, Vories, ED (2000b) Short-season soybean yield compensation in response to population and water regime. Crop Sci 40:1070–1078 CrossRefGoogle Scholar
Bàrberi, P (2002) Weed management in organic agriculture: are we addressing the right issues? Weed Res 42:177–193 Google Scholar
Bartoń, K (2016) MuMIn: Multi-model inference. R package version 1.15.6. http://CRAN.R-project.org/package=MuMIn. Accessed February 27, 2016Google Scholar
Bastiaans, L, Paolini, R, Baumann, DT (2008) Focus on ecological weed management: what is hindering adoption? Weed Res 48:481–491 Google Scholar
Baumann, DT, Bastiaans, L, Kropff, MJ (2001) Competition and crop performance in a leek-celery intercropping system. Crop Sci 41:764–774 Google Scholar
Bernstein, ER, Posner, JL, Stoltenberg, DE, Hedtcke, JL (2011) Organically managed no-tillage rye–soybean systems: agronomic, economic, and environmental assessment. Agron J 103:1169–1179 Google Scholar
Bertram, MG, Pedersen, P (2004) Adjusting management practices using glyphosate-resistant soybean cultivars. Agron J 96:462–468 Google Scholar
Board, J (2000) Light interception efficiency and light quality affect yield compensation of soybean at low plant populations. Crop Sci 40:1285–1294 Google Scholar
Board, JE, Harville, BG (1993) Soybean yield component responses to a light interception gradient during the reproductive period. Crop Sci 33:772–777 Google Scholar
Board, JE, Harville, BG, Saxton, AM (1990) Narrow-row seed-yield enhancement in determinate soybean. Agron J 82:64–68 Google Scholar
Bond, W, Grundy, AC (2001) Non-chemical weed management in organic farming systems. Weed Res 41:383–405 Google Scholar
Bradley, KW (2006) A review of the effects of row spacing on weed management in corn and soybean. Crop Manage. doi: 10.1094/CM-2006-0227-02-RV CrossRefGoogle Scholar
Brandi-Dohrn, FM, Dick, RP, Hess, M, Kauffman, SM, Hemphill, DD Jr, Selker, JS (1997) Nitrate leaching under a cereal rye cover crop. J Environ Qual 26:181–188 Google Scholar
Burnside, OC, Colville, WL (1964) Soybean and weed yields as affected by irrigation, row spacing, tillage, and amiben. Weeds 12:109–112 Google Scholar
Burnside, OC, Moomaw, RS (1977) Control of weeds in narrow-row soybeans. Agron J 69:793–796 Google Scholar
Caldwell, B, Mohler, CL, Ketterings, QM, DiTommaso, A (2014) Yields and profitability during and after transition in organic grain cropping systems. Agron J 106:871–880 CrossRefGoogle Scholar
Carpenter, AC, Board, JE (1997) Branch yield components controlling soybean yield stability across plant populations. Crop Sci 37:885–891 Google Scholar
Coble, HD, Williams, FM, Ritter, RL (1981) Common ragweed (Ambrosia artemisiifolia) interference in soybeans (Glycine max). Weed Sci 29:339–342 Google Scholar
Conley, SP, Binning, LK, Boerboom, CM, Stoltenberg, DE (2002) Estimating giant foxtail cohort productivity in soybean based on weed density, leaf area, or volume. Weed Sci 50:72–78 Google Scholar
Cooper, RL (1971a) Influence of early lodging on yield of soybean [Glycine max (L.) Merr.]. Agron J 63:449–450 Google Scholar
Cooper, RL (1971b) Influence of soybean production practices on lodging environments and seed yield in highly productive environments. Agron J 63:490–493 Google Scholar
Costa, JA, Oplinger, ES, Pendleton, JW (1980) Response of soybean cultivars to planting patterns. Agron J 72:153–156 CrossRefGoogle Scholar
Cousens, R (1985a) A simple model relating yield loss to weed density. Ann Appl Biol 107:239–252 Google Scholar
Cousens, R (1985b) An empirical model relating crop yield to weed and crop density and a statistical comparison with other models. J Agr Sci 105:513–521 CrossRefGoogle Scholar
Cowbrough, MJ, Brown, RB, Tardif, FJ (2003) Impact of common ragweed (Ambrosia artemisiifolia) aggregation on economic thresholds in soybean. Weed Sci 51:947–954 Google Scholar
Cox, WJ, Cherney, JH (2011) Growth and yield responses of soybean to row spacing and seeding rate. Agron J 103:123–128 Google Scholar
Cox, WJ, Cherney, JH (2014) Soybean seed treatments interact with locations for populations, yield, and partial returns. Agron J 106:2157–2162 Google Scholar
Crowder, DW, Reganold, JP (2015) Financial competitiveness of organic agriculture on a global scale. Proceedings of the National Academy of Sciences of the United States of America 112:7611–7616 Google Scholar
De Bruin, JL, Pedersen, P (2008a) Effect of row spacing and seeding rate on soybean yield. Agron J 100:704–710 Google Scholar
De Bruin, JL, Pedersen, P (2008b) Soybean seed yield response to planting date and seeding rate in the Upper Midwest. Agron J 100:696–703 Google Scholar
Devlin, DL, Fjell, KL, Shroyer, JP, Gordon, WB, Marsh, DH, Maddux, LD, Martin, VL, Duncan, SR (1995) Row spacing and seeding rates for soybean in low and high yielding environments. J Prod Agric 8:215–222 CrossRefGoogle Scholar
Doll, H (1997) The ability of barley to compete with weeds. Biol Agric Hortic 14:43–51 Google Scholar
Duncan, WG (1986) Planting patterns and soybean yields. Crop Sci 26:584–588 CrossRefGoogle Scholar
Eckert, DJ (1988) Rye cover crops for no-tillage corn and soybean production. J Prod Agric 1:207–210 Google Scholar
Eckert, DJ (1991) Chemical attributes of soils subjected to no-till cropping with rye cover crops. Soil Sci Soc Am J 55:405–409 Google Scholar
Edwards, JT, Purcell, LC (2005) Soybean yield and biomass responses to increasing plant population among diverse maturity groups: I. Agronomic characteristics. Crop Sci 45:1770–1777 Google Scholar
Egli, DB (1988) Plant density and soybean yield. Crop Sci 28:977–981 CrossRefGoogle Scholar
Epler, M, Staggenborg, S (2008) Soybean yield and yield component response to plant density in narrow row systems. Crop Manage. doi: 10.1094/CM-2008-0925-01-RS Google Scholar
Esker, PD, Conley, SP (2012) Probability of yield response and breaking even for soybean seed treatments. Crop Sci 52:351–359 Google Scholar
Ethredge, WJ, Ashley, DA, Woodruff, JM (1989) Row spacing and plant population effects on yield components of soybean. Agron J 81:947–951 Google Scholar
Gaspar, AP, Mitchell, PD, Conley, SP (2015) Economic risk and profitability of soybean fungicide and insecticide seed treatments at reduced seeding rates. Crop Sci 55:924–933 Google Scholar
Harder, DB, Sprague, CL, Renner, KA (2007) Effect of soybean row width and population on weeds, crop yield, and economic return. Weed Technol 21:744–752 Google Scholar
Harris, TC, Ritter, RL (1987) Giant green foxtail (Setaria viridis var. major) and fall panicum (Panicum dichotomiflorum) competition in soybeans (Glycine max). Weed Sci 35:663–668 Google Scholar
Hartzler, RG, Battles, BA, Nordby, D (2004) Effect of common waterhemp (Amaranthus rudis) emergence date on growth and fecundity in soybean. Weed Sci 52:242–245 Google Scholar
Helms, TC, Deckard, E, Goos, RJ, Enz, JW (1996) Soybean seedling emergence influenced by days of soil water stress and soil temperature. Agron J 88:657–661 Google Scholar
Hicks, DR, Pendleton, JW, Bernard, RL, Johnston, TJ (1969) Response of soybean plant types to planting patterns. Agron J 61:290–293 Google Scholar
Hock, SM, Knezevic, SZ, Martin, AR, Lindquist, JL (2006) Soybean row spacing and weed emergence time influence weed competitiveness and competitive indices. Weed Sci 54:38–46 Google Scholar
Hovermale, CH, Camper, HM, Alexander, MW (1979) Effects of small grain stubble height and mulch on no-tillage soybean production. Agron J 71:644–647 Google Scholar
Jannink, JL, Orf, JH, Jordan, NR, Shaw, RG (2000) Index selection for weed suppressive ability in soybean. Crop Sci 40:1087–1094 Google Scholar
Johnson, BJ, Harris, HB (1967) Influence of plant population on yield and other characteristics of soybeans. Agron J 59:447–449 Google Scholar
Jordan, N (1993) Prospects for weed control through crop interference. Ecol Appl 3:84–91 Google Scholar
Knake, EL, Slife, FW (1969) Effect of time of giant foxtail removal from corn and soybeans. Weed Sci 17:281–283 Google Scholar
Krausz, RF, Young, BG, Kapusta, G, Matthews, JL (2001) Influence of weed competition and herbicides on glyphosate-resistant soybean (Glycine max). Weed Technol 15:530–534 Google Scholar
Lee, CD (2006) Reducing row spacing to increase yield: why it doesn’t always work. Crop Manage. doi: 10.1094/CM-2006-0227-04-RV CrossRefGoogle Scholar
Lee, CD, Egli, DB, TeKrony, DM (2008) Soybean response to plant population at early and late planting dates in the Mid-South. Agron J 100:971–976 Google Scholar
Lee, CD, Renner, KA, Penner, D, Hammerschmidt, R, Kelly, JD (2005) Glyphosate-resistant soybean management system effect on Sclerotinia stem rot. Weed Technol 19:580–588 Google Scholar
Liebl, R, Simmons, FW, Wax, LM, Stoller, EW (1992) Effect of rye (Secale cereale) mulch on weed control and soil moisture in soybean (Glycine max). Weed Technol 6:838–846 Google Scholar
Lueschen, WE, Hicks, DR (1977) Influence of plant population on field performance of three soybean cultivars. Agron J 69:390–393 Google Scholar
McWhorter, CG, Hartwig, EE (1972) Competition of johnsongrass and cocklebur with six soybean varieties. Weed Sci 20:56–59 Google Scholar
Mickelson, JA, Renner, KA (1997) Weed control using reduced rates of postemergence herbicides in narrow and wide row soybean. J Prod Agric 10:431–437 Google Scholar
Mirsky, SB, Curran, WS, Mortensen, DA, Ryan, MR, Shumway, DL (2009) Control of cereal rye with a roller/crimper as influenced by cover crop phenology. Agron J 101:1589–1596 Google Scholar
Mirsky, SB, Ryan, MR, Curran, WS, Teasdale, JR, Maul, J, Spargo, JT, Moyer, J, Grantham, AM, Weber, D, Way, TR, Camargo, GG (2012) Conservation tillage issues: cover crop–based organic rotational no-till grain production in the mid-Atlantic region, USA. Renew Agr Food Syst 27:31–40 Google Scholar
Mirsky, SB, Ryan, MR, Teasdale, JR, Curran, WS, Reberg-Horton, CS, Spargo, JT, Wells, MS, Keene, CL, Moyer, JW (2013) Overcoming weed management challenges in cover crop–based organic rotational no-till soybean production in the eastern United States. Weed Technol 27:193–203 Google Scholar
Mohler, CL (1996) Ecological bases for the cultural control of annual weeds. J Prod Agric 9:468–474 Google Scholar
Mohler, CL, Callaway, MB (1995) Effects of tillage and mulch on weed seed production and seed banks in sweet corn. J Appl Ecol 32:627–639 Google Scholar
Monks, DW, Oliver, LR (1988) Interactions between soybean (Glycine max) cultivars and selected weeds. Weed Sci 36:770–774 Google Scholar
Moschler, WW, Shear, GM, Hallock, DL, Sears, RD, Jones, GD (1967) Winter cover crops for sod-planted corn: their selection and management. Agron J 59:547–551 Google Scholar
Munawar, A, Blevins, RL, Frye, WW, Saul, MR (1990) Tillage and cover crop management for soil water conservation. Agron J 82:773–777 Google Scholar
Murphy, SD, Yakubu, Y, Weise, SF, Swanton, CJ (1996) Effect of planting patterns and inter-row cultivation on competition between corn (Zea mays) and late emerging weeds. Weed Sci 44:865–870 Google Scholar
Nakagawa, S, Schielzeth, H (2013) A general and simple method for obtaining R 2 from generalized linear mixed-effects models. Methods Ecol Evol 4:133–142 Google Scholar
Nave, WR, Wax, LM (1971) Effect of weeds on soybean yield and harvesting efficiency. Weed Sci 19:533–535 Google Scholar
Nord, EA, Ryan, MR, Curran, WS, Mortensen, DA, Mirsky, SB (2012) Effects of management type and timing on weed suppression in soybean no-till planted into rolled-crimped cereal rye. Weed Sci 60:624–633 Google Scholar
Norsworthy, JK, Oliver, LR (2001) Effect of seeding rate of drilled glyphosate resistant soybean (Glycine max) on seed yield and gross profit margin. Weed Technol 15:284–292 Google Scholar
Northeast Regional Climate Center (2016) CLIMOD 2: Monthly Summarized Data. http://www.climodtest.nrcc.cornell.edu. Accessed April 10, 2016Google Scholar
Oplinger, ES, Philbrook, BD (1992) Soybean planting date, row width, and seeding rate response in three tillage systems. J Prod Agric 5:94–99 Google Scholar
Orlowski, J, Cox, WJ, DiTommaso, A, Knoblauch, W (2012) Planting soybean with a grain drill inconsistently increases yield and profit. Agron J 104:1065–1073 Google Scholar
Parvez, AQ, Gardner, FP, Boote, KJ (1989) Determinate- and indeterminate-type soybean cultivar responses to pattern, density, and planting date. Crop Sci 29:150–157 Google Scholar
Pedersen, P, Lauer, JG (2002) Influence of rotation sequence on the optimum corn and soybean plant population. Agron J 94:968–974 CrossRefGoogle Scholar
Peigné, J, Ball, BC, Roger-Estrade, J, David, C (2007) Is conservation tillage suitable for organic farming? A review. Soil Use Manag 23:129–144 Google Scholar
Peters, EJ, Gebhardt, MR, Stritzke, JF (1965) Interrelations of row spacings, cultivations and herbicides for weed control in soybeans. Weeds 13:285–289 Google Scholar
Pinheiro, J, Bates, D (2000) Mixed-Effects Models in S and S-PLUS. New York: Springer-Verlag. Pp 337–410 Google Scholar
Pinheiro, J, Bates, D, DebRoy, S, Sarkar, D, Core Team, R (2016) nlme: Linear and Nonlinear Mixed Effects Models. R Package Version 3.1-126. http://CRAN.R-project.org/package=nlme. Accessed March 28, 2016Google Scholar
Place, GT, Reberg-Horton, SC, Carter, TE Jr, Smith, AN (2011) Effects of soybean seed size on weed competition. Agron J 103:175–181 Google Scholar
Place, GT, Reberg-Horton, SC, Dunphy, JE, Smith, AN (2009) Seeding rate effects on weed control and yield for organic soybean production. Weed Technol 23:497–502 Google Scholar
Probst, AH (1945) Influence of spacing on yield and other characters in soybeans. J Am Soc Agron 37:549–554 Google Scholar
Purcell, LC, Bass, RA, Reaper, JD 3rd, Vories, ED (2002) Radiation use efficiency and biomass production in different plant population densities. Crop Sci 42:172–177 Google Scholar
RCore Team (2016) R: A Language and Environment for Statistical Computing. Vienna, Austria: R Foundation for Statistical Computing Google Scholar
Rose, SJ, Burnside, OC, Specht, JE, Swisher, BA (1984) Competition and allelopathy between soybeans and weeds. Agron J 76:523–528 Google Scholar
Ryan, MR, Mirsky, SB, Mortensen, DA, Teasdale, JR, Curran, WS (2011) Potential synergistic effects of cereal rye biomass and soybean planting density on weed suppression. Weed Sci 59:238–246 Google Scholar
Ryan, MR, Smith, RG, Mortensen, DA, Teasdale, JR, Curran, WS, Seidel, R, Shumway, DL (2009) Weed–crop competition relationships differ between organic and conventional cropping systems. Weed Res 49:572–580 Google Scholar
Salado-Navarro, LR, Sinclair, TR, Hinson, K (1986) Yield and reproductive growth of simulated and field-grown soybean. II. Dry matter allocation and seed growth rates. Crop Sci 26:971–975 Google Scholar
Schwinning, S, Weiner, J (1998) Mechanisms determining the degree of size asymmetry in competition among plants. Oecologia 113:447–455 Google Scholar
Shibles, RM, Weber, CR (1965) Leaf area, solar radiation interception and dry matter production by soybeans. Crop Sci 5:575–577 Google Scholar
Shibles, RM, Weber, CR (1966) Interception of solar radiation and dry matter production by various soybean planting patterns. Crop Sci 6:55–59 Google Scholar
Smith, RG, Barbercheck, ME, Mortensen, DA, Hyde, J, Hulting, AG (2011) Yield and net returns during the transition to organic feed grain production. Agron J 103:51–59 Google Scholar
Spitters, CJT (1983) An alternative approach to the analysis of mixed cropping experiments. I. Estimation of competition effects. Neth J Agr Sci 31:1–11 Google Scholar
Tharp, BE, Kells, JJ (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 Google Scholar
[USDA-AMS] US Department of Agriculture, Agricultural Marketing Service (2016) National Organic Grain and Feedstuffs: Bi-weekly Reports. https://www.ams.usda.gov/market-news/search-market-news. Accessed April 10, 2016Google Scholar
[USDA-NASS] US Department of Agriculture, National Agricultural Statistics Service (2016) Prices Received for Soybeans by Month – United States. http://www.nass.usda.gov/Charts_and_Maps/Agricultural_Prices/pricesb.php. Accessed April 11, 2016Google Scholar
Villamil, MB, Bollero, GA, Darmody, RG, Simmons, FW, Bullock, DG (2006) No-till corn/soybean systems including winter cover crops: effects on soil properties. Soil Sci Soc Am J 70:1936–1944 Google Scholar
Walker, ER, Mengistu, A, Bellaloui, N, Koger, CH, Roberts, RK, Larson, JA (2010) Plant population and row-spacing effects on maturity group III soybean. Agron J 102:821–826 Google Scholar
Wax, LM, Nave, WR, Cooper, RL (1977) Weed control in narrow and wide-row soybeans. Weed Sci 25:73–78 Google Scholar
Wax, LM, Pendleton, JW (1968) Effect of row spacing on weed control in soybean. Weed Sci 16:462–465 Google Scholar
Weaver, SE (2001) Impact of lamb’s-quarters, common ragweed and green foxtail on yield of corn and soybean in Ontario. Can J Plant Sci 81:821–828 CrossRefGoogle Scholar
Weber, CR, Shibles, RM, Byth, DE (1966) Effect of plant population and row spacing on soybean development and production. Agron J 58:99–102 Google Scholar
Weber, CR, Staniforth, DW (1957) Competitive relationships in variable weed and soybean stands. Agron J 49:440–444 Google Scholar
Weiner, J (1990) Asymmetric competition in plant populations. Trends Ecol Evol 5:360–364 Google Scholar
Weiner, J, Griepentrog, H, Kristensen, L (2001) Suppression of weed by spring wheat Triticum aestivum increases with crop density and spatial uniformity. J Appl Ecol 38:784–790 Google Scholar
Wells, R (1991) Soybean growth response to plant density: relationships among canopy photosynthesis, leaf area and light interception. Crop Sci 31:755–761 Google Scholar
Wells, MS, Brinton, CM, Reberg-Horton, SC (2015) Weed suppression and soybean yield in a no-till cover-crop mulched system as influenced by six rye cultivars. Renew Agr Food Syst. doi: 10.1017/S1742170515000344 CrossRefGoogle Scholar
Wiggans, RG (1939) The influence of space and arrangement on the production of soybean plants. J Am Soc Agron 31:314–321 Google Scholar
Wilcox, JR (1974) Response of three soybean strains to equidistant spacings. Agron J 66:409–412 Google Scholar
Williams, MM 2nd, Mortensen, DA, Doran, JW (2000) No-tillage soybean performance in cover crops for weed management in the western Corn Belt. J Soil Water Conserv 55:79–84 Google Scholar
Wortman, SE, Francis, CA, Bernards, MA, Blankenship, EE, Lindquist, JL (2013) Mechanical termination of diverse cover crop mixtures for improved weed suppression in organic cropping systems. Weed Sci 61:162–170 Google Scholar
Yelverton, FH, Coble, HD (1991) Narrow row spacing and canopy formation reduces weed resurgence in soybeans (Glycine max). Weed Technol 5:169–174 Google Scholar
Young, FL, Wyse, DL, Jones, RJ (1982) Influence of quackgrass (Agropyron repens) density and duration of interference on soybeans (Glycine max). Weed Sci 30:614–619 Google Scholar
Zadoks, JC, Chang, TT, Konzak, CF (1974) A decimal code for the growth stages of cereals. Weed Res 14:415–421 Google Scholar