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On-Farm Soybean Cultivar Evaluation for Suitability to

Organic Production in Southern Manitoba

Michelle Carkner, M.Sc. Candidate (defended)

Advisor: Martin Entz

Natural Systems Agriculture Lab, Department of Plant Science, University of Manitoba

Introduction and Objective

Organic legume field crops are becoming important to the organic industry as an organic

protein feed source to meet demand for organic livestock increases in Canada and globally

(soy2020, 2005; IFOAM, 2016). Additionally, legume field crops are a valuable contribution to

organic farm rotations as they are able to supply their own nitrogen demands and provide

income. Currently, the Canadian prairies account for 99% of organic protein crops grown in

Canada (COTA, 2016).

Soybean (Glycine max Merr.) is not a common grain legume field crop grown on

Canadian organic prairie farms, as only 119 hectares of soybeans were sown in 2014 (COTA,

2016). Increasing organic soybean hectares requires technical knowledge and suitable cultivars

that have been tested under organic conditions. At the moment, non-genetically modified (GM)

cultivars are bred and performance tested under conventional conditions. The results may not

be suitable for organic farms as conditions on these farms differ from conventional farms in a

variety of ways. Murphy et al. (2007) reported that sub-optimal performance of conventionally

bred wheat (Triticum aestivum L.) cultivars under organic conditions may be due to biased

selection of cultivars that perform well under chemical intensive conditions.

The objective of this research was to evaluate the performance of 12 non-GM short-

season soybean cultivars on organic farms in Manitoba.

One of the qualities given special attention to was weed competitiveness. Past literature

has pointed to early vigour as an important indication of cultivar competitiveness in cereals and

legume grain crops (Lemerle et al., 1996; Jannink et al., 2000; Place et al., 2011). Therefore,

cultivars with increased biomass and height early in the season may be more competitive with

weeds.

Materials and Methods

The research compared 12 non-GM short-season soybean cultivars sourced across

Canada and North Dakota (Table 1), and took place at six locations (Carman, Elie, St. Pierre-

Jolys, Somerset, Swan Lake, and Woodmore) in southern Manitoba between 2014 and 2015

(Figure 1). The experiment was a randomized complete block design with four replicates, each

cultivar representing a treatment. Within each treatment, a sub-plot was kept weed-free by

hand to compare relative weed competitiveness of cultivars. Additional weed control included

pre-emergence harrow, and inter-row cultivation at V1-V2.

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Stand density, early (V3) (approx. first week of July) and late (R5) (approx. second week

of August) soybean and weed biomass and height, pod height, 100-seed weight, and yield from

weedy and weed-free sub-plots were recorded. The following summary will focus on early (V3)

biomass production, height, and yield.

Figure 1: Location of field study sites in southern Manitoba.

Table 1: Soybean cultivar, source, company heat units, and maturity ratings included in the study

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Results

Early season vigour

Early season biomass production (taken only in 2015) differed among cultivars (Table 2).

Early biomass accumulation was inconsistent among cultivars between sites which was

indicated by a site-cultivar interaction. ‘SK0007’ averaged the highest biomass production, but

was not one of the highest biomass producers at Woodmore 2015 and St. Pierre 2015.

Differences in early biomass production was also observed with ‘OAC Prudence’, which was the

highest biomass producer at Somerset 2015, but had among the lowest biomass at Carman

2015.

This site-cultivar interaction shows that cultivars respond differently to different

environmental conditions. Differing early soybean biomass accumulation could be due a

response in differing weed densities and species present. For example, Somerset 2015 weed

biomass at early growth was at about 2015 kg ha-1 whereas early weed biomass at Carman

2015 amounted to 863 kg ha-1. Additionally, the principle weed species at Somerset 2015 were

Sinapsis arvensis (wild mustard) and Avena fatua (wild oat) whereas the principle weed species

present in Carman 2015 were Amaranthus retroflexus (redroot pigweed), Cirsium arvense

(Canada thistle), and Setaria lutescens (yellow foxtail).

Table 2: Early season biomass production sampled at the V3 stage of development.

Cultivar Carman 2015*

St. Pierre 2015 Somerset 2015 Woodmore

2015 --- kg ha-1 ---

Auriga 561 760 731 de 792

DH 401 929 953 776 cde 664

DH 863 701 890 1015 abc 662

Jari 878 867 857 bcd 884

Krios 622 635 702 de 803

OAC Petrel 531 880 753 cde 890

OAC Prudence 655 1110 692 de 797

Savanna 707 757 1176 a 818

SK0007 1366 990 1103 ab 744

SVX14T0053 706 852 533 e 620

Toma 929 977 860 bcd 622

Tundra 982 939 856 bcd 735

CVⱡ (%) 38 31 29 22

P > F 0.0546 0.4846 0.0013 0.2124

*Means within a column followed by the same letter are not significantly different at the 0.05 level of significance ⱡCoefficient of variation (CV) represents the extent of variability in relation to the mean of the cultivars at that site. Large numbers highly variable

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Across all site-years, the same cultivars were tallest at V3. ‘SK0007’ and ‘Tundra’ were

among the tallest cultivars at early growth. This indicates that despite the differing

environmental conditions across sites, V3 soybean height was consistent across cultivars.

Figure 2: Early season soybean height aggregated from Carman 2015, St. Pierre 2015, Somerset 2015, and Woodmore 2015

Final Yield

The final performance of soybean cultivars differed depending on the site in which it

was grown. For simplicity, three sites (Carman 2015, Woodmore 2015, and Somerset 2015) will

be used an example.

The top yielding site out of all nine site-years was Carman 2015 (Figure 3), with yields

ranging from 2386 – 3200 kg ha-1. At this site, yields matching or even exceeding conventional

soybean yields were observed. The top producing cultivars were ‘Savanna’, ‘Toma’, and ‘OAC

Prudence’. Woodmore 2015 was a ‘medium’ yielding site (Figure 4), ranging from 1279 – 1729

kg ha-1. The top yielding cultivars at Woodmore 2015 were ‘Savanna’, ‘SVX14T0053’, and

‘Toma’. The yields at the ‘lower’-yielding site, Somerset 2015 (Figure 5), ranged from 880 –

1215 kg ha-1. The top producers in Somerset 2015 were ‘Toma’, ‘SK0007’, and ‘SVX14T0053’.

Interestingly, cultivar yield significantly differed from each other at Carman 2015 and

Woodmore 2015, but not at Somerset 2015. Yield loss due to weeds was the highest at

Somerset 2015, with approximately 44% lower yields in the weedy than weed-free. Carman

2015 saw a 20% yield reduction and Woodmore 2015 experienced a 28% yield loss due to

weeds. These results could provide some evidence to suggest that intense weed competition

stifled the potential for genetic expression. This is valuable to organic farmers in the Canadian

Prairies, as cultivar choice may not be as important as a rigorous, well-timed weed control

regiment isn’t in place. The weeds present at Somerset 2015 are representative of the most

challenging weeds organic farmers in Manitoba deal with (Entz et al., 2001).

CD BC FG CDE E EF E DE

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Figure 3: Final soybean yield at Carman 2015, Differences in letters indicate significant differences between cultivars.

Figure 4: Final soybean yield at Woodmore 2015 Differences in letters indicate significant differences between cultivars.

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Figure 5: Final soybean yield at Somerset 2015

Conclusions

High organic soybean yields are attainable in southern Manitoba, but this hinges on the ability

for proper weed management and environmental conditions. See organic soybean weed

management experiment results our lab has done here.

Soybeans are not very competitive against cool season weeds such as wild mustard or wild oat,

but may be able to compete against warm season weeds such as redroot pigweed fairly well. If

an organic farmer is planting soybeans in a known wild mustard problem area, they should have

a very good weed control program in place.

While past research has pointed to choosing soybean cultivars that are competitive at early

growth, this work found that on average, cultivars that were most vigorous at early growth

were usually the lowest yielding at most sites. All organic farmers should keep relative maturity

in mind to avoid frost damage.

For more information on this research please contact Michelle Carkner at

carknemk@myumanitoba.ca

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Acknowledgements

The author is greatly appreciative of the financial support provided by the Natural Sciences and

Engineering Research Council of Canada, Growers International Organic Sales Inc., and the

Manitoba Pulse and Soybean Growers.

Immense thanks to the organic farmers who collaborated and donated their land for this work.

References

Canadian Organic Trade Association (COTA) 2016. Growing Organic in the Prairies.

Entz, M.H., R. Guilford, and R. Gulden. 2001. Crop yield and soil nutrient status on 14 organic farms in the eastern portion of the northern Great Plains. Can. J. Plant Sci. 81: 351–354.

International Federation of Organic Agriculture Movements (IFOAM). 2015. The World of Organic Agriculture.

Jannink, J.L., J.H. Orf, N.R. Jordan, and R.G. Shaw. 2000. Index selection for weed suppressive ability in soybean. Crop Sci. 40: 1087–1094.

Lemerle, D., B. Verbeek, R.D. Cousens, and N.E. Coombes. 1996. The potential for selecting wheat varieties strongly competitive against weeds. Weed Res. 36(6): 505–513.

Murphy, K.M., K.G. Campbell, S.R. Lyon, and S.S. Jones. 2007. Evidence of varietal adaptation to organic farming systems. F. Crop. Res. 102: 172–177.

Place, G.T., S.C. Reberg-Horton, D.A. Dickey, and T.E. Carter. 2011. Identifying soybean traits of interest for weed competition. Crop Sci. 51: 2642–2654.

Soy2020. 2005. Organic Soybean Processing Facility Value Proposition. : 1–4.

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Photos from the field

Soybeans after inter-row cultivation at St. Pierre-Jolys 2015

Differing maturities at Woodmore 2015

Intense weed pressure at Somerset 2015

Soybeans at R5 development stage in Carman 2015