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Spring Considerations for Soybean

Crop Production News - 2018

By Dale Risula, PAg, Provincial Specialist, Special Crops, Regina

May 2018

Iron chlorosis deficiency symptoms on soybean leaves
Iron chlorosis deficiency symptoms
on soybean leaves
Soybean requires high heat and high moisture, yet variety improvements have led to very successful crops here in Saskatchewan. Soybean produced in Saskatchewan are mostly crushed for oil and high-protein meal used in animal feed. Soybean production has been increasing at a rapid rate in Saskatchewan, with acres reaching more than 800,000 in 2017.

The biggest issue facing soybean is selecting the right variety for maturity and yield. Inoculation is also very important, since the rhizobium bacterium (Bradyrhizobium japonicum) associated with soybean is not indigenous to Saskatchewan soils. Ideal field fertility leads to improved pod clearance and plant growth. Fertility requirements for soybean can be found in the following table.


Suggested Level



< 50 lbs*


Medium to High

10 to 20 ppm Olsen


Medium to High

> 1120 ppm



< 0.5 mmhos/cm



< 2.5%

*Especially important for first-time fields

Soybean is subject to the condition known as iron deficiency chlorosis. Breeding work has aimed to reduce the sensitivity of soybean varieties to iron deficiency; however, there is still a lot of variability in how varieties perform. Growers are encouraged to choose a variety that is tolerant to iron chlorosis deficiency. Some preliminary work conducted by Dr. Jeff Schoenau showed that in a dry year, iron (Fe) fertilization had no effect in helping alleviate iron deficiency chlorosis; however, in a wetter year (more conducive to iron deficiency chlorosis), a sensitive variety showed positive response to Fe fertilization. Overall, the best defense is to choose a tolerant variety.

Soybean should be planted one to 1.5” (2.4 to 3.8 cm) deep, targeting 40 plants/m2 (150 to 160k plants/acre). The critical weed-free period is early from emergence of the seedlings to the V-3 stage (three trifoliate leaves originating from the main stem that are completely unrolled). Some of the rationale behind early weed control is related to early weeds being small and easier to control and environmental conditions not being too hot or dry for better herbicide efficacy. 

Phytophthora root rot symptoms
Phytophthora root rot symptoms.

Seedling blight and root rot are other problems that soybean may encounter. There are a few common organisms that cause root rot to pulse crops that may also affect soybean, including Phytophthora sojae, and PythiumRhizoctonia and Fusarium species. Unlike some of the other root rot pathogens, P. sojae, the causal agent of phytophthora root rot, does not affect other crops grown in Saskatchewan. Phytophthora root rot is favoured under wet conditions. Early infection of soybean plants by P. sojae can result in pre- and post- emergent damping off. The stems of the infected seedlings will appear water soaked, the leaves may become chlorotic and the affected plants will wilt and die. On older plants, the most characteristic symptom is a dark brown lesion on the lower stem that extends up from the taproot. The lesion may eventually girdle the stem and cause the plant to become stunted or die.

For information on soybean production, please contact your regional crops extension specialist or the Ag Knowledge Centre.

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