Soybean agronomy highlights from western Canada: the new frontierKristen P. MacMillan1*(kristen.macmillan@umanitoba.ca, @kristenpodolsky ), Bryan J. Cassone2a, Don Flaten3b, Robert H. Gulden1c, Yvonne Lawley1d, Ramona Mohr4e

1Dept. of Plant Science, University of Manitoba, Winnipeg, Canada; 2Brandon University, Brandon, Canada; 3Dept. of Soil Science, University of Manitoba, Winnipeg, Canada; 4Agriculture and Agri-Food Canada, Brandon, Canada

Table 2. Most abundant weeds (L, source: Leeson, AAFC, 2016) and most commonly diagnosed diseases (R, source: Manitoba crop diagnostics lab, 2011-17)

in Manitoba soybeans.

Canola (Brassica napus L.) Seedling diseases

Wild buckwheat (Polygonum convolvulus) Phytophthora sojae

Barnyard grass (Echinochloa crus-galli) Septoria brown spot

Dandelion (Taraxacum officinale) Bacterial blight (Pseudomonas sp.)

Redroot pigweed (Amaranthus retroflexus) Phyllosticta leaf spot

Spring wheat (Triticum aestivum) Downy mildew (Peronospora manshurica)

Green foxtail (Setaria viridis) Pod and stem blight (Phomopsis sp.)

Yellow foxtail (Setaria pumila) Anthracnose (Colletotrichum spp.)

Wild oats (Avena fatua) Alternaria leaf spot

Broad leaved plaintain Sclerotinia white mould

Table 1. Growing conditions of soybean growing regions in Canada and USA.

US Mid-West Ontario Manitoba

Frost-free period (total days)

May 1-Sept 30(145+)

May 5-Sept 25(125+)

May 15-Sept 20(105-125)

Heat units (CHU) 3500+ 2500-3500 2200-2500

Annual Precip. (in) 36 36 18

July-August Precip. (in) 8.0 6.8 5.8

Average yield (bu/ac) 49 46 38

Major crops (80% of acres)

Corn, SoybeanSoybean, Corn,Winter Wheat

Wheat, Canola, Soybean, Oats

Soils and Fertility

Manitoba agricultural soils are generally calcareous with a neutral to high pH.These factors along with salinity, imperfect drainage and early season moisture contribute to severe iron deficiency chlorosis across expansive acres in some years. Variety selection is used to prevent IDC and an iron chelate product is being tested in on-farm trials. Soybeans are often grown without additional fertilizer - recent studies have shown a very low frequency of response to P, regardless of rate, placement or timingb. A rotational P management strategy is recommended in w. Canada, where the focus is to maintain soil P levels in a medium range to ensure agronomic productivity and minimize environmental risk. New studies are investigating the response of soybean to K fertilization on sandy, deficient soils in Manitobab and ongoing studies are exploring supplemental Ne. Currently, additional N fertilizer is only used when nodulation failure occurs (<5 nodules per plant) and crop is showing N deficiency.

Introduction

Canadian soybean acres reached a record 7.3M acres in 2017, up 33% from 2016. The increase is attributed to expansion in w. Canada where 3.1M acres were planted in 2017, a two-fold increase since 2014. Short season variety development (00 to 000), favorable growing conditions and steady markets are important contributing factors. Agronomy research is a priority to develop region-specific best management practices for w. Canada where canola is a major rotational crop, soils are often calcareous, and the growing season is relatively short and cool (Table 1).

Crop Establishment

Soybeans are primarily planted after wheat, followed by canola, soybean and corn. Short-term crop sequence studies have found few significant effects of preceding crop on soybean yield, thus far, but have found significant impacts on soil microorganisms, namely, mycorrhizalcolonization and biological nitrogen fixationd. Long-term crop sequence studies are underway to further elicit impacts on yield and diseased,e. Residue and soil management is an emerging topic as soybeans expand into zero-till production areas of w. Manitoba and Saskatchewan where soils tend to be cool in spring. Tillage is being looked at again as a method to dry out and warm the soil to facilitate earlier, improved soybean establishment. On the other hand, the traditional practice of fall and spring tillage in the Red River valley is being tested in an effort to reduce tillage for this low residue crop. In on-farm tests conducted on sandy soils, no significant yield differences have been found in wheat following till or no-till soybean residue, nor soybean following till vs. no till corn residued.The next step is establish tillage trials on clay soils. In regards to crop inputs at planting, the use of seed treatment and inoculant varies by field history. Double inoculation (i.e. liquid on-seed and granular in-furrow) is common for fields with <2 previous soybean crops, while single inoculation (liquid on-seed) is considered a gradual step for fields with >2 previous soybean crops. To determine if inoculation is still required in established soybean fields, on-farm trials are comparing liquid on-seed

vs. no inoculation in fields with >4 previous soybean crops. To date, 16 out of 18 trials have shown no yield response to inoculantf. The first plant population study for soybeans in w. Canada led to recommendations to aim for a final plant stand of 30-40 plants/m2 or 140-160,000 plants/ac to achieve 95-100% of optimum yield (Figure 1). The same study investigated row spacing and confirmed that narrow rows (8-12”) yield the same or higher than wide rows (16-30”) and found no population x row spacing interactione. Air seeders are primarily used for seeding in w. Canada with planters more commonly used in Manitoba for corn and other row crops. Actual seeding rates vary depending on equipment, seed quality and seedbed.

Figure 1. Relationship between relative soybean yield and measured plant

stand based on 13 site-years in Manitoba (2011-2013) and is the mean between

wide and narrow rows (source: R. Mohr).

Acknowledgements Pest Management

Kochia scoparia is currently the only confirmed glyphosate resistant weed in w. Canada, but several other species lurk in North Dakota and Minnesota. The most common weed in Manitoba soybean fields is volunteer Roundup Ready canola (Table 2). This crop-weed is intensively studied in Manitoba where work has shown that canola has relatively high harvest losses and a persistent seedbankc. In soybean, an economic threshold of 2-3 plants/m2 has been identified. Early fall disturbance following canola harvest has been found to increase fall recruitment and reduce the canola seedbank. Efficacy of chemical control options are also being evaluated. With over 95% of soybeans grown in w. Canada being RR, farmers have shifted to liberty-tolerant canola systems. Recent field surveys have shed light on disease pathogens in MB soybeans. In 2016, next-generation sequencing was utilized to diagnose foliar diseases, leading to the first confirmation of frogeye leaf spot (Cercospora sojina) in w. Canadaa. Leaf spot diseases are common (Table 2) but are generally of minor economic importance and fungicide is not widely used. Root rots are currently the most important economic concern. Collaborative efforts are underway to survey the race distribution of Phytophthora and to investigate cross-pathogenicity of Fusarium spp., which affects the major crops grown in w. Canada. Soybean cyst nematode has not yet been detected.

Future

Soybean production has been a Manitoba success story and further expansion into w. Canada is likely, although dryland soybean yield relative to short, cool season crops may be limited by moisture deficit and cool night-time temperatures from R3-R6; work is underway to address this challenge. Yields were limited in 2017 by iron chlorosis, moisture deficit and aphids, raising some new questions. A newsoybean and pulse agronomy research program* has been established to increase capacity to study and enhance soybean and pulse production practices and cropping systems for Manitoba and western Canada. Seeding dates, crop phenology, cropping system, hail damage, seed depth and fertility are among the current projects.

Figure 2. Soybean is generally unresponsive to P fertilizer in MB: only 1 out of 28 site-years showed a significant yield response.

Figure 3. Iron deficiency chlorosis is a challenge in MB: in this field, a tolerant and non-tolerant variety was grown.

Photos by K. MacMillan

Literature CiteddSanders, D. 2017. The effect of preceding crop on soybean grain yield, mycorrhizal colonization and biological nitrogen fixation. MSc thesis, University of Manitoba, Winnipeg. Online.dWalther, P. 2017. Corn (Zea mays L.) residue management for soybean (Glycine max L.) production: On-farm experiment. MSc thesis, University of Manitoba, Winnipeg. Online.dBartley, G. and Y. Lawley. 2016. Early season soybean response to wheat residue management in Manitoba. Poster. Manitoba Agronomists Conference. Online.

f Manitoba Pulse & Soybean Growers On-Farm Network, www.manitobapulse.ca.eMohr, R et al. 2014. Effect of row spacing and seeding rate on soybean growth, yield and quality in Manitoba. Poster. Manitoba Agronomists Conference. Winnipeg, MB. Online.bBardella, G. 2016. Phosphorus management practices for soybean production in Manitoba. MSc thesis, University of Manitoba, Winnipeg. Online.

cGregoire, P. 2017. Volunteer canola (Brassica napusL.) interference with soybean (Glycine max L.). MSc thesis, University of Manitoba, Winnipeg. Online.cGeddes, C and R. Gulden. 2016. Volunteer canola seedbank disturbance in western Canada: is timing everything? Poster. Manitoba Agronomists Conference, Winnipeg, MBaCassone, B and G. Diaz Cruz. 2017. An innovative technology for early detection of foliar soybean diseases in Manitoba. Pulse Beat 81: 30-32.