Identifying Nutrient Deficiency Symptoms in Soybeans

Jul 16, 2021

By Dorivar Ruiz Diaz and Dave Mengel

This time of year, soybeans may begin showing signs of chlorosis or other leaf discoloration in all or parts of the field. There may be many causes of discoloration. Nutrient deficiencies are one possibility.

General considerations

The relative mobility of the nutrient within the plant will determine if the deficiency symptom will first be noticeable on the lower leaves or upper leaves.

Mobile Nutrients: These nutrients can be transferred from older tissues to the youngest tissues within the plant. Deficiency symptoms are first noticeable on the lower, oldest leaves.

Nitrogen (N)
Phosphorus (P)
Potassium (K)
Magnesium (Mg)

Immobile Nutrients: These nutrients are not easily transferred within the plant. Therefore, symptoms occur first on the upper, youngest leaves.

Boron (B)
Calcium (Ca)
Copper (Cu)
Iron (Fe)
Manganese (Mn)
Molybdenum (Mo)
Sulfur (S)
Zinc (Zn)

Possible causes of nutrient deficiencies:

Low soil levels of the nutrient
Poor inoculation (in the case of N deficiency)
Unusually low or high soil pH levels depending on the nutrient in question
Roots are unable to access sufficient amounts of the nutrients - due to poor growing conditions, excessively wet or dry soils, cold weather, or soil compaction
Root injury due to mechanical, insect, disease, or herbicide injury
Genetics of the plant

The following is a brief description of the symptoms of some of the most common nutrient deficiencies in soybeans.

Nutrient deficiency symptoms

Nitrogen. Chlorotic or pale green plants starting with the lower leaf (Figure 1a). Within the plant, any available nitrogen (N) from the soil or from nitrogen fixation within nodules on the roots goes to the new growth first. Soybeans prefer to take up N from the soil solution as much as possible, since this requires less energy than the nitrogen fixation process. However, both sources of N are important for soybeans since they are a big user of N. Nitrogen deficiency can be associated with poor nodulation (Figure 1b).

Soybean field showing signs of chlorosis

Figure 1a. Soybean field showing signs of chlorosis.

Lack of nodulation on far right soybean plants

Figure 1b. Lack of nodulation on far right soybean plants.

Iron. Iron chlorosis, occurs in calcareous soils (contains calcium carbonates) with high soil pH. The classic symptom is chlorosis (yellowing) between the veins of young leaves since iron is not mobile within the plant (Figures 2 and 3). A side effect of iron deficiency can be N deficiency, since iron is necessary for nodule formation and function. If iron is deficient, N fixation rates may be reduced. Iron deficiency occurs on calcareous soils, in addition to high pH, plant stress can favor the development of iron chlorosis, and therefore the severity can vary significantly from year to year in the same field.

Iron chlorosis in soybeans; the upper leaves become chlorotic

Figure 2. Iron chlorosis in soybeans; the upper leaves become chlorotic.

Close-up of iron chlorosis in soybeans

Figure 3. Close-up of iron chlorosis in soybeans.

Magnesium. Lower leaves will be pale green, with yellow mottling between the veins. At later stages, leaves may appear to be speckled bronze. This deficiency may occur on very sandy soils.

Manganese. Stunted plants with interveinal chlorosis (Figure 4). Can be a problem in soils with high pH (>7.0), or on soils that are sandy or with a high organic matter content (>6.0% OM). Manganese activates enzymes which are important in photosynthesis, as well as nitrogen metabolism and synthesis. Symptoms are hard to distinguish from iron chlorosis.

Manganese deficiency symptoms are similar to symptoms of iron chlorosis in soybeans

Figure 4. Manganese deficiency symptoms are similar to symptoms of iron chlorosis in soybeans.

Phosphorus. Phosphorus deficiency may cause stunted growth, dark green coloration of the leaves, necrotic spots on the leaves, a purple color to the leaves, and leaf cupping. These symptoms occur first on older leaves. Phosphorus deficiency can also delay blooming and maturity. This deficiency may be noticeable when soils are cool and wet, due to decrease in phosphorus uptake.

Potassium. Soybean typically requires large amounts of potassium. Like phosphorus deficiency, potassium deficiency occurs first on older leaves. Symptoms are chlorosis at the leaf margins and between the veins (Figure 5). In severe cases, all but the very youngest leaves may show symptoms.

Potassium deficiency

Figure 5. Potassium deficiency: chlorosis of the lower leaves. Photo by Dave Mengel, K-State Research and Extension.

Sulfur. Stunted plants, pale green color, similar to nitrogen deficiency except chlorosis may be more apparent on upper leaves. Plant-available sulfur is released from organic matter. Deficiency is most likely during cool wet conditions or on sandy soils with low organic matter content.

Source : ksu.edu

Video: The 15-Year Bet Behind Every New Variety!

Canada is trying to decide how much agricultural research capacity it can afford to lose. Brian Rossnagel believes the better question is whether the country can afford to rebuild it.

The longtime barley and oat breeder makes the case with a simple fact about his profession: the consequences of today’s decisions may not become visible for 10 or 15 years.

“Pick the right parents. That’s the biggest thing,” Rossnagel says. “If you pick the wrong parents, you’re not going to get anywhere—and you don’t know that until 10 years, 15 years later.”

That warning carries particular weight as Agriculture and Agri-Food Canada moves to reduce spending and streamline parts of its science operations. The department’s 2026–27 plan anticipates the loss of approximately 665 positions by 2028–29 and says some research will be reduced where capacity exists in academia or industry. AAFC says the changes will make its science operations more cost-effective over the long term.

For Canada’s seed industry, Rossnagel’s career illustrates what is at stake.

This fall, the retired University of Saskatchewan breeder will be inducted into the Canadian Agricultural Hall of Fame. During his 35-year career at the Crop Development Centre, he helped develop more than 100 barley and oat varieties, including CDC Austenson—one of Western Canada’s most widely grown feed barleys. His induction recognizes not only those varieties, but the collaboration and research system that made them possible.

Rossnagel is quick to emphasize that none of it was the work of one person.

“The first thing I thought about was all the other people who contributed to whatever success I and my program had over the years,” he says. “We know that it’s not an individual who does this. It’s a group—a team.”

That team extends well beyond the breeder whose name appears beside a variety. It includes technicians, pathologists, quality specialists, statisticians, regional testing sites, seed growers and industry partners. It also includes the breeders who came before and those who will carry the germplasm forward.

CDC Fraser barley, for example, moved through three breeding careers. Its parents came from Brian Harvey’s program. Rossnagel advanced the material after Harvey retired, and Aaron Beattie later guided it through registration and release.

That kind of handoff is normal in plant breeding. The person who makes the original cross may never see the resulting variety reach farmers.

It also explains why lost research capacity cannot simply be switched back on when budgets improve.

“If you shut it off, it’s very, very difficult—and particularly costly—to start it up again,” Rossnagel says. “If you have to start from scratch, it’s going to be at least 10 years before anybody notices whether you’re getting anything done or not.”

The concern is not simply how many experimental lines Canada can process. Modern equipment, statistical tools and genetic technologies allow today’s breeding programs to evaluate tens of thousands of lines—far more than Rossnagel could handle when he entered the field in the early 1970s.

But efficiency and automation do not generate every idea.

“If you pare back down, and instead of having six or seven individual scientists concentrating on wheat breeding, you go down and say three people could handle all this, well, that’s half the ideas gone,” he says. “Particularly if you happen to lose the three people who had the really neat and innovative ideas, boy, that’s a problem.”

It is a timely distinction for Canadian agriculture. Consolidating programs may preserve the volume of material moving through a system, at least initially. It may not preserve the diversity of thinking, regional knowledge or willingness to pursue unconventional crosses.

That regional knowledge matters because Canadian agriculture is not one uniform production environment. A variety suited to southern Alberta may face different disease, moisture and maturity pressures than one grown in Manitoba, Ontario or Atlantic Canada.

“Agriculture is applied biology,” Rossnagel says. “Biology, all around the Earth, moves from the poles to the equator. It does not move from Newfoundland to B.C. like politics do.”