You’re familiar with the yellowing corn leaves or stems that can result from nitrogen deficiency, water stress or disease. But what about dark purple streaks at the tips and margins of older leaves? This purple discoloration could be a sign of a phosphorus (P) deficiency in corn.
Proactive soil sampling and P fertilizer application are generally sufficient to prevent phosphorus deficiency. P deficiency symptoms typically show up early when plants are still young. By the time these symptoms become obvious, yield loss may be unavoidable.
Causes of phosphorus deficiency in corn
Phosphorus deficiencies are most common in younger plants and are influenced by soil conditions, management practices and climate.
Soil factors
Soils with both low and high pH levels can experience reduced phosphorus availability, as P tends to form insoluble compounds at either pH extreme. Regular soil testing is essential to assess phosphorus levels and, perhaps more importantly, soil pH to identify potential P deficiencies. Soil of 6.0 to 7.0 pH is ideal for phosphorus availability.¹ Soil pH of less than 5.5 generally limits phosphorus availability of P by 30 percent or more. High amounts of iron oxides, available aluminum, or calcium carbonates or sulfates in soil also bind phosphorus, reducing its availability.²
Soil compaction may also reduce root growth, resulting in decreased P uptake since smaller root systems explore less soil volume and can’t get to available phosphorus.
High-yield environments
High-yield hybrids and increased planting density can lead to greater nutrient extraction from the soil, making adequate phosphorus fertilization necessary.
Environmental stressors
Cold or waterlogged soil hinders phosphorus uptake due to its effect on root growth and metabolism.
Symptoms of phosphorus deficiency in corn
Phosphorus deficiencies typically occur prior to V6, especially in seedlings, resulting in stunted growth, delayed maturity and greater susceptibility to environmental stressors. Early identification aids management and minimizes negative outcomes.
- Symptoms at seedling stage (prior to V6): Purplish discoloration appears on corn leaves, typically concentrated on the lower parts of the plant.
- Symptoms during early vegetative growth: Roots may appear shallow, sparse and poorly developed. Also, overall stunted growth with a noticeable reduction in leaf size and plant height is common. Phosphorus-deficient plants may be delayed in reaching developmental milestones, potentially leading to reduced yields.
- Symptoms during reproductive growth stage: Phosphorus deficiency can cause poor kernel development, incomplete grain filling and ultimately reduced yield potential. Weaker stalks and poor cob attachment from deficient plants make them more susceptible to lodging.
- General symptoms across life cycle: In severe cases, phosphorus deficiency can cause necrosis or death of older leaves, starting at the leaf tips or edges and progressing inward. Necrotic tissue reduces photosynthetic capacity and hampers overall plant health.
How to improve phosphorus availability
If you determine through a soil test that your soil is lacking in phosphorus, there are strategies that make phosphorus more available.
Banding phosphorus fertilizer
Phosphorus fertilizer application through banding can help increase the availability of P to your plants because it is less likely to become tied up in your soil, especially if you’re dealing with high or low pH soils.
Phosphorus and pH balance in soil
Phosphorus availability is influenced by soil acidity. If your soil is too acidic, phosphorus might not be as accessible to your plants. Lime application can help balance the pH and improve nutrient availability. In high pH soils above 7.5, phosphorus is less available due to binding with calcium.
Preventing phosphorus deficiency in corn
Regular scouting and monitoring, coupled with soil testing, and identifying phosphorus deficiency symptoms and their variations throughout the corn life cycle can help you implement targeted management practices, such as fertilization, to address nutrient imbalances.
Consult with your extension agent or your regional BASF representative to get tailored recommendations based on regional soil conditions and specific crop varieties.
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Endnotes
- Larson, Erick. “Corn Fertilization.” Mississippi State University Extension Service, extension.msstate.edu/publications/corn-fertilization. Accessed 14 Apr. 2026.
- “Soil Phosphorus.” USDA, 2022, www.nrcs.usda.gov/sites/default/files/2022-10/Soil%20Phosphorus.pdf. Accessed 14 Apr. 2026.
