Soybean Glycine max (L.) Merr is important to the agricultural economy in Canada where nearly 5,100,000 tonnes of soybean are produced on approximately 1,700,000 ha with an approximate farm gate value of $1,000,000,000 [1] [2] . Globally, Canada ranked 7th in the world with 2% of soybean production in 2012-2013 [1] . Ontario soybean growers need to implement optimal agronomic practices, including proper weed management and plant nutrition, to maximize their production efficiency.

Various biostimulants have been available for a number of years [3] - [8] . Biostimulants have been defined as compounds, substances and other products such as microorganisms, trace elements, enzymes, plant growth regulators that when applied in small quantities to plants or soils can enhance plant growth and development by increasing the efficiency of physiological process within plants [3] [4] . Some studies have reported that biostimulants enhance nutrient availability, increase water-holding capacity, increase antioxidants, enhance metabolism and increase chlorophyll production in plants [4] - [11] .

AX13-04-4, Crop Booster and RR Soy Booster are three biostimulants developed by Axter Agro sciences Inc. (895, Chemin Benoit, Mont-St-Hilaire, Quebec, J3G 4S6, Canada) for use in various crops to increase seed yield through enhancement of crop vigor and foliage development [12] - [14] . These biostimulants contain approximately 15% total nitrogen, 3% phosphoric acid (P₂O₅), 6% soluble potash (K₂O), 0.02% boron, 0.05% chelated manganese, 0.05% molybdenum, 0.05% chelated zinc, and 0.5% E.D.T.A. (chelating agent) [13] [14] .

According to the Axter Agro sciences Inc., AX13-04-4, Crop Booster, and RR Soy Booster have the ability to compensate for plant’s inability to take up sufficient nutrients under stressed conditions and decrease herbicide induced stress that may be caused by post emergence herbicides [12] .

The effects of these biostimulants, added to commonly used post emergence herbicides, in soybean production in Ontario are not known. Ontario growers need scientific data on effect of these biostimulants to make informed decisions on their use in their production system. In absence of such data, growers rely on their “best guess” when using these products which may result in application of ineffective products that reduce net return and cause unnecessary loading of chemicals into the environment.

The objective of this study was to evaluate the effect of adding a biostimulant to glyphosate, glyphosate + chlorimuron, glyphosate + imazethapyr, glyphosate + fomesafen and glyphosate + quizalofop applied post emergence on crop injury, weed control and soybean yield under Ontario environmental conditions.

A total of 69 field experiments were conducted in soybean at the Huron Research Station, Exeter, Ontario and University of Guelph Ridgetown Campus, Ridgetown, Ontario. All field trials were established as a randomized complete block design with four replications. Herbicide and biostimulant treatments are listed in Tables 1-9.

Abbreviations: AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambs quarters; SETVI, green foxtail; SINAR, wild mustard; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate alone with glyphosate + Crop Booster denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Abbreviations: AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambs quarters; SETVI, green foxtail; SOLPT, Eastern black nightshade; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate alone with glyphosate + Soy Booster denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Abbreviations: AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambsquarters; SETVI, green foxtail; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate + chlorimuron alone with glyphosate + chlorimuron + AX13-04-4 denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Abbreviations: AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambsquarters; SETVI, green foxtail; SINAR, wild mustard; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate + chlorimuron alone with glyphosate + chlorimuron + Crop Booster denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Abbreviations: ABUTH, velvetleaf; AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambsquarters; SETVI, green foxtail; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate + chlorimuron alone with glyphosate + chlorimuron + Soy Booster denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Abbreviations: AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambsquarters; SETVI, green foxtail; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate + imazethapyr alone with glyphosate + imazethapyr + Crop Booster denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Abbreviations: ABUTH, velvetleaf; AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambsquarters; SETVI, green foxtail; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate + imazethapyr alone with glyphosate + imazethapyr + Soy Booster denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Abbreviations: AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambs quarters; SETVI, green foxtail; SINAR, wild mustard; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate/fomesafen alone with glyphosate/fomesafen + Crop Booster denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Abbreviations: AMASS, green or redroot pigweed; AMBEL, common ragweed; CHEAL, common lambsquarters; SETVI, green foxtail; WAT, weeks after herbicide application. Significance of contrasts comparing glyphosate + quizalofop alone with glyphosate + quizalofop + Crop Booster denoted by * for P < 0.10 and ** for P < 0.05 beside the means.

Studies with the addition of Crop Booster to glyphosate (total of 12) were conducted at Exeter in 2003, 2004, 2014 and 2015 and at Ridgetown in 2002 (2 trials), 2003, 2004, 2005 (2 trials), 2014 and 2015 (Table 1). Studies with the addition of RR Soy Booster to glyphosate (total of 8) were conducted at Exeter in 2003 and 2004 and at Ridgetown in 2002 (2 trials), 2003, 2004 and 2005 (2 trials) (Table 2).

Studies with the addition of AX13-04-4 to glyphosate + chlorimuron (total of 6) were conducted at Exeter and Ridgetown in 2008-2010 (Table 3). Studies with the addition of Crop Booster to glyphosate + chlorimuron (total of 13) were conducted at Exeter in 2008, 2010, 2013, 2014 and 2015 (2 trials) and at Ridgetown in 2008, 2009, 2010, 2013, 2014 and 2015 (2 trials) (Table 4). Studies with the addition of RR Soy Booster to glyphosate + chlorimuron (total of 5) were conducted at Exeter in 2008 and 2010 and at Ridgetown in 2008, 2009 and 2010 (Table 5).

Studies with the addition of Crop Booster to glyphosate + imazethapyr (total of 9) were conducted at Exeter in 2008, 2010 and 2015 (2 trials) and at Ridgetown in 2008, 2009, 2010 and 2015 (2 trials) (Table 6). Studies with the addition of RR Soy Booster to glyphosate + imazethapyr (total of 5) were conducted at Exeter in 2008 and 2010 and at Ridgetown in 2008, 2009 and 2010 (Table 7).

Studies with the addition of Crop Booster to glyphosate + fomesafen (total of 6) were conducted at Exeter in 2011, 2012 and 2013 and at Ridgetown in 2012 (2 trials) and 2013 (Table 8).

Studies with the addition of RR Soy Booster to glyphosate + quizalofop (total of 5) were conducted at Exeter in 2010 and 2011 and at Ridgetown in 2009, 2010 and 2011 (Table 9).

Field plots were 2 m wide and 8 or 10 m long. Soybean was seeded at 370,000 seeds ha⁻¹ in rows that were spaced 0.75 m apart at a depth of 4 cm in May or early June of each year. Herbicide treatments were applied with a CO₂ pressurized back-pack sprayer equipped with Hypro ULD120-02 nozzle tips (Hypro, New Brighton, MN) calibrated to deliver 200 L∙ha⁻¹ of water at 200 kPa. Herbicide applications were made with a 1.5 m boom with four nozzles spaced 50 cm apart.

Crop injury 1 and 4 weeks after herbicide treatment (WAT) and weed control (4 and 8 WAT) were visually estimated on a scale of 0 (no injury/control) to 100% (complete plant death/complete weed control). Soybean was harvested from each plot with a small plot combine, weight and moisture were recorded, and yields were adjusted to 13% moisture.

Data were analyzed as an RCBD using PROC MIXED in SAS 9.4. Herbicide treatment was considered a fixed effect, while environment (year-location combinations), the interaction between environment and herbicide treatment, and replicate nested within environment were considered random effects. Significance of the fixed effect was tested using F-test and random effects were tested using a Z-test of the variance estimate. The UNIVARIATE procedure was used to test data for normality and homogeneity of variance. The untreated check was excluded from the analysis for weed control data. Data were arcsine square root transformed when necessary to satisfy the assumptions of the variance analyses. Treatment comparisons were made using contrasts. Data compared on the transformed scale were converted back to the original scale for presentation of results.

Prominent weed species in this study included velvetleaf (Abutilon the ophrasti Medic.; ABUTH), redroot pigweed (Amaranthus retroflexus L.; AMARE), common ragweed (Ambrosia artemisiifolia L.; AMBEL), common lambsquarters (Chenopdium album L.; CHEAL); green foxtail (Setaria viridis L.; SETVI) and annual grasses. Weed control for each species were analyzed only when they existed in at least 50% of field plots (Tables 1-9).

There was no increase in soybean injury with the addition of the biostimulants evaluated when added to glyphosate, glyphosate + chlorimuron, glyphosate + imazethapyr, glyphosate + fomesafen, or glyphosate + quizalofop. Also, the addition of biostimulants to glyphosate, glyphosate + chlorimuron, glyphosate + imazethapyr, glyphosate + fomesafen and glyphosate + quizalofop did not affect weed control except for a slight increase in the control of common ragweed with the addition of RR Soy Booster to glyphosate + imazethapyr, a slight increase in the control of common lambsquarters with the addition of Crop Booster to glyphosate + fomesafen, a slight increase in the control of green foxtail with the addition of Crop Booster to glyphosate + fomesafen and a slight increase in the control of common lambsquarters with the addition of Crop Booster to glyphosate plus chlorimuron or fomesafen or quizalofop. There was generally a small numeric increase in soybean yield with the addition of biostimulants to the herbicides evaluated, but this increase in yield was not statistically significant at the p < 0.05 level.

The authors would like to acknowledge Todd Cowan and Lynette Brown for their expertise and technical assistance in these studies.

Soltani, N., Shropshire, C. and Sikkema, P.H. (2016) Evaluation of Biostimulants Added to Post Emergence Herbicides in Soybean. American Jour- nal of Plant Sciences, 7, 1729-1740. http://dx.doi.org/10.4236/ajps.2016.713162

Abbreviations: ABUTH, velvetleaf;

AMASS, green or redroot pigweed;

AMBEL, common ragweed;

CHEAL, common lambsquarters;

SOLPT, Eastern black nightshade;

SINAR, wild mustard;

SETVI, green foxtail;

WAT, weeks after herbicide treatment.

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