Nutrient Deficiency Identification Basics

• Nutrient deficiencies can look like other field issues and may potentially impact corn and soybeans at any time during the season.
• Identifying deficiencies, especially early in the season, may help with management practices to help mitigate the nutrient issues in the future.

Importance

Macro and micro soil nutrient deficiencies may be observed due to low soil nutrient levels or presence of environmental conditions that restrict plant nutrient uptake. Diagnosing plant symptoms can be the first step in identifying and correcting future problems. The following is a review of common causes and symptoms of deficiencies of the 6 essential macronutrients in soil.

Nitrogen (N): Major component of amino acids, the building blocks of proteins. Important component of chlorophyll, which is used in photosynthesis and fuels plant stem, leaf and ear structure growth.

Symptoms:

• Pale, yellowish corn plants with spindly stalks
• Corn leaves with V-shaped yellowing on lower (older) leaves starting at tip and progressing down the mid-rib (Figure 1)
• Yellow and premature death of lower leaves, restricted ear and kernel development

Causes:

• Environmental conditions causing soil nitrogen loss (leaching, volatilization or denitrification)
• Under fertilization
• Sandy soils
• Soybean plants with little or no early root nodulation

Phosphorous (P): Important early in the plant life cycle to initiate growth and carry out photosynthesis.

Symptoms:

• Purple tint that spreads across entire leaf, starting on lower leaves (Figure 2)
• Observed only at early growth stages
• Some hybrids will show similar purpling symptoms even with sufficient P available

Causes:

• Low P testing soils
• Cool soils that are excessively wet or dry, limiting availability
• Compaction

Potassium (Potash or K): Known as the plant health nutrient. Important for regulating plant water use and increasing disease tolerance, stalk quality and standability.

Symptoms:

• Yellowing and chlorosis of leaf margins on lower leaves in corn and soybeans (Figure 3)
• Chlorosis of corn leaf tip highly noticeable
• Excessive yellowing and chlorosis of entire lower leaves continue with ongoing deficiency, progressing up the plant
• Upper leaves will remain unaffected due to K being translocated from lower leaves
• Will weaken stalk strength, often causing late-season lodging

Causes:

• Low K testing soils
• Compaction or other conditions restricting root growth
• Excessively dry soil conditions

Sulfur (S): Has a key role in protein synthesis and many plant functions, including photosynthesis, chlorophyll formation and nitrogen fixation.

Symptoms:

• General yellowing of leaves, which can be seen in new growth since sulfur is not as mobile within the plant
• Stunting, slow growth
• Interveinal chlorosis (loss of green color) in newer growth sometimes (Figure 4)
• Symptoms tend to disappear as soils warm and sulfate mineralization increases

Causes:

• Low soil pH
• Sandy, low organic matter soils
• Cold soil delaying mineralization of S from organic matter

Magnesium (Mg)

Symptoms

• Yellow to white interveinal striping of lower corn leaves
• Dead, round spots later, with beaded streaking appearance (Figure 5)
• Older leaves may become reddish-purple with tips and margins of leaf later becoming necrotic

Causes:

• Acidic, low soil pH
• Sandy, low organic matter soils in high rainfall environments
• Can be induced with high potassium availability

Calcium (Ca)

Symptoms:

• Tips of leaves don’t unroll and stick together (Figure 6)
• Severe stunting
• Very rarely observed

Causes:

• Acidic or low soil pH levels < 5.0
• Sandy, low organic matter soils