When something looks off in the field, identifying the root cause can mean the difference between lost yield and timely intervention. For soybeans, nutrient deficiencies often present through distinct visual symptoms, and learning to recognize these is crucial.

Dorivar Ruiz Diaz, Extension nutrient management specialist at Kansas State University, says one of the first clues to identifying nutrient deficiency is where symptoms appear on the plant.

"If it's a mobile nutrient, symptoms typically appear on older, lower leaves first," explains Ruiz Diaz. This is because mobile nutrients - including nitrogen, phosphorus, potassium, and magnesium - can move to newer growth when needed.

In contrast, immobile nutrients such as boron, copper, calcium, iron, manganese, molybdenum, sulfur, and zinc show symptoms in new growth, even if they exist elsewhere in the plant.

Key Deficiency Clues for Soybean Growers

Nitrogen: Look for pale green or chlorotic lower leaves. Soybeans use nitrogen from both soil and root nodules, and symptoms may indicate poor nodulation. This deficiency is common during early vegetative stages.

Iron: Iron is essential for nodule health. Deficiency reduces nitrogen fixation, and symptoms include interveinal chlorosis (yellowing between veins). It's especially problematic in high pH soils or under plant stress, with western Kansas being a hotspot.

Magnesium: Pale green leaves with yellow mottling between veins on lower foliage are key signs. At advanced stages, leaves may show bronzing. This often occurs on sandy soils with low cation exchange capacity.

Manganese: Plants are stunted, with interveinal chlorosis on young leaves. High pH (>7.0), sandy soils, or organic matter above 6% can restrict manganese availability.

Phosphorus: This vital nutrient affects everything from energy transfer to root development. Symptoms include dark green leaves, stunted growth, purple coloration, necrotic spots, and cupping. Deficiency is more visible in cool, wet conditions that limit uptake.

Potassium: Deficiency shows as chlorosis along leaf margins and between veins. It may escalate to nearly all leaves being affected except the youngest. Soybeans demand large quantities of potassium, especially during pod development.

Sulfur: Easily confused with nitrogen deficiency, sulfur deficiency tends to manifest in upper leaves. Symptoms include stunting and a pale green color. It's most common in cool, wet, or sandy soils with low organic matter.

Ruiz Diaz notes an uptick in sulfur issues due to the adoption of high-yield soybean varieties, which have increased nutrient demand.

Actionable Insights for the Growing Season

Understanding these visual clues allows producers to take timely soil or tissue samples, consult agronomists, and apply targeted nutrients. Doing so not only protects the current crop but also informs better fertility planning in future seasons.