BY: Christopher Forsythe, Agronomist – On-Farm Network, MPSG
To capture greater profit, many Manitoban farmers grow food-grade soybean varieties destined for a global human food market. Food-grade soybeans are grown under identity preserved contracts most often with a prescribed non-genetically modified or conventional variety and are subject to higher traceability and quality standards. Farmers get a price premium on food-grade soybeans over commodity herbicide tolerant soybeans for the crush market. There’s growing interest in diversifying into food-grade soybeans in Manitoba, but there are some important management considerations.
One consideration is iron deficiency chlorosis (IDC) where the plants develop interveinal chlorosis, which reduces yield. Soybeans grown in Manitoba can be prone to developing IDC due to our high calcium carbonate soils. This season’s cool and wet weather made IDC symptoms even worse than normal. Often, soybeans will grow out of IDC but yield loss from IDC will occur if symptoms persist past the sixth trifoliate (V6) staging.
Soybean cultivars differ in their ability to acidify their root zone and uptake iron, because of this, variety selection is the best strategy to manage IDC in higher risk fields. The soybean industry has worked hard to develop high yielding food-grade varieties bred for Manitoba, however, there are fewer food-grade varieties available on the market rated “tolerant’’ to IDC than herbicide tolerant soybeans.
This makes matching the right IDC tolerance important in fields that are higher risk to developing IDC. To understand your risk, a soil test can determine the calcium carbonates and soluble salts. If your field has high calcium carbonate (less than five per cent) and soluble salt levels (less than one millimhos (mmhos) per centimeter ) (see Table 1.) there is an extreme risk of IDC. If your soils are in the high risk category choose the most tolerant variety available (refer to the Manitoba Pulse and Soybean Growers Pulse & Soybean Variety Guide and Seed Manitoba).
Another IDC prevention tool available is an in-furrow chelated iron (Fe EDDHA) product that has shown to provide some protection. Farmers can also reduce IDC by growing soybeans in wider row widths and increasing seeding rates, but these impacts are relatively minimal and can vary across different environments.
This year, the On-Farm Network (OFN) was approached by a food-grade soybean farmer who has struggled with IDC and wanted to test an in-furrow chelated iron product. The OFN helped the farmer set up an on-farm replicated strip trial (see Photo 1). The seed was a food-grade variety with an IDC rating of 2.1 (semi-tolerant). The field was in the high IDC risk category (soluble salts of 0.56 mmhos/cm and calcium carbonate of 5.6 per cent). A granular iron chelate product was applied to treated strips at a rate of four pounds per acre. The results showed that the iron chelate product didn’t increase yield over the untreated strips. Iron chelate products have been shown to improve IDC symptoms through trials in North Dakota, however, this was our first OFN trial and additional research in Manitoba is required.
Ultimately, iron chelate products won’t turn a susceptible variety into a tolerant variety, so the best strategy if your field has a history of IDC is to choose the most tolerant variety available.
Soil testing to determine a field’s overall IDC risk is good practice however, bear in mind IDC often only affects pockets of a field. Ensure you aren’t overlooking these pockets during soil sampling. As shown in this year’s OFN trial, there’s no evidence the pockets can be successfully farmed separate from the rest of the field. As a result, the best advice may be to first avoid planting an IDC susceptible variety on a high-risk field, and where IDC is present but judged to be less of a threat, consider the above points to make an informed decision on pairing the variety with the field.
Food-grade soybeans present a fantastic diversifying opportunity, and we look forward to seeing more IDC tolerant varieties to compliment effective IDC management strategies.
If you are interested in conducting an in-furrow iron chelate product trial in 2025 please get in touch with please contact Chris, On-Farm Network agronomist, at chris@manitobapulse.ca or (204) 751-0439.