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Corn producers are likely familiar with the yellowing leaves or stems that can result from nitrogen deficiency, water stress, or disease. But what does it mean when dark purple streaks begin to appear at the tips and margins of older leaves? This purple discoloration Could be a sign of a phosphorus (P) deficiency in corn.
The good news is that proactive soil sampling and subsequent P fertilizer application are generally sufficient to prevent phosphorus deficiency. P deficiency symptoms typically show up early when plants are still young and, unfortunately, by the time these symptoms become obvious, some yield loss may have already occurred.
📸: @Galeanu Mihai via Canva/Featuring the role of vital nutrients, such as phosphorus (P) in corn.
Phosphorus (P) is one of 17 essential nutrients in the life cycle of corn. Although it gets less attention than nutrients than nitrogen or potassium, it is just as crucial for healthy plant growth and development. Data from the Agricultural Research Service at the USDA found that corn hybrids need an average of 580 milligrams of P per plant to reach their maximum grain yield. This would be the equivalent of 40 lbs P per acre for a plant population of 32,000 plants per acre.1
Phosphorus plays a variety of roles in plants, benefiting photosynthesis, respiration, nitrogen fixation, root development, flowering, fruiting and seed production. It also facilitates energy transfer within the plant as a component of adenosine triphosphate (ATP). ATP helps corn transfer and store energy for critical metabolic processes. This energy is particularly crucial during corn’s periods of rapid growth and reproduction, such as seed development and tasseling.2
Phosphorus is also required to form nucleic acids, like DNA and RNA, which guide corn’s development and synthesis of proteins. These nucleic acids are the building blocks of plant structures and enzymes and are essential to a healthy corn plant. That’s not all, though. Phosphorus aids in root development by enhancing the plant's ability to absorb water and nutrients from the soil. Healthy root systems are, of course, a fundamental requirement for corn plants to access the nutrients necessary for their growth. The nucleic acids even enhance corn’s resilience to environmental stressors. In short, phosphorus is indispensable to maximizing corn’s yield potential.
📸: @nikomsolftwaer via Canva/Featuring an agronomist inspecting soil in a corn field.
Phosphorus deficiencies in corn can occur at various stages of the plant's growth, but are most common in younger plants and are influenced by factors such as soil conditions, management practices and climate. Understanding when and where these deficiencies commonly occur can help you implement targeted corrective measures.
Phosphorus deficiencies are often associated with specific soil conditions.
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 compaction may also reduce root growth, leading to reduced P uptake. A reduction of root growth can result in a decrease in P uptake since smaller root systems explore less soil volume and can’t get to available phosphorus.
High-yielding corn requires more phosphorus and, indeed, all nutrients. Because intensive farming practices, such as selecting high-yield hybrids and increasing planting density, can lead to greater nutrient extraction from the soil, adequate phosphorus fertilization is necessary.
Environmental factors such as cold temperatures and waterlogged soils can exacerbate phosphorus deficiencies. Cold soil conditions hinder phosphorus uptake by the roots. Waterlogged soils can also contribute to phosphorus deficiency due to reduced root metabolism. Environmental stressors can reduce phosphorus availability due to their effect on root growth and metabolism
Abnormally high or low pH can also be a cause of phosphorus deficiency. Soil of 6 to 7.2 pH is ideal for phosphorus availability. Acidic soils (pH below 5.5) limit root growth and the availability of P by 30 percent or more. At low soil pH levels P binds with iron and aluminum and at high pH values with calcium. Guidelines from the USDA recommended applying lime to your soil in situations like these to restore a more favorable balance.
📸: @BongkarnThanyakij via Canva/Featuring an agronomist inspecting corn ears for signs of phosphorus deficiency.
Phosphorus deficiencies are most commonly observed during the early growth stages of corn (prior to V6), especially in seedlings. Insufficient phosphorus availability during this critical period can result in stunted growth, delayed maturity, and greater susceptibility to environmental stressors. To the observant grower, symptoms can be identified early, widening the window of opportunity to manage and minimize negative outcomes.
A characteristic symptom of P deficiency in corn is the development of a purple color on the leaves, typically concentrated on the lower parts of the plant. This purple discoloration is attributed to the accumulation of anthocyanins, indicating the plant's struggle to acquire sufficient phosphorus.
📸: @Alandmanson via wikimedia/Featuring purple leaves on corn due to phosphorus deficiency.
Impaired root development can contribute to P deficiency. These roots may appear shallow, sparse and poorly developed, limiting the plant's ability to access phosphorus from the soil.
In the early stages, phosphorus deficiency often results in overall stunted growth. Corn plants may appear smaller compared to their healthy counterparts, with a noticeable reduction in leaf size and plant height.
Phosphorus-deficient plants may exhibit a delay in reaching developmental milestones. This delay can impact the overall maturity of the corn crop, potentially leading to reduced yields.
As the corn plant enters the reproductive stage, phosphorus deficiency can result in poor kernel development. This may lead to incomplete grain filling and ultimately reduce the overall yield potential of the crop.
Inadequate phosphorus can result in weaker stalks and poor cob attachment, making plants more susceptible to lodging and reducing the overall structural integrity of the corn stand.
In severe cases, phosphorus deficiency can lead to necrosis or death of older leaves. This necrosis typically starts at the tips or edges of the leaves and progresses inward. Necrotic tissue further contributes to reduced photosynthetic capacity and hampers overall plant health.
📸: @microgen via Canva/Featuring an agronomy inspector sampling soil for phosphorus deficiency in corn.
While phosphorus often exists in large quantities in most soils, it tends to be present in complex mineral and organic forms, making it less immediately available to corn. The most common ways that phosphorus becomes available to corn is through mineral weathering and microbes breaking down other plants and organic material. Phosphorus is strongly attracted to metallic cations such as iron, aluminum and calcium often forming insoluble compounds at both low and high soil pH levels.
If you determine through a soil test that your soil is lacking in phosphorus, you will need to apply fertilizer and employ other strategies that make phosphorus more available.
Phosphorus fertilizer application through banding can help increase the availability of P to your plants because it is less likely to end up tied up in your soil, especially if you’re dealing with high or low pH soils. There is some debate about the ideal rate of phosphorus application and the ideal distance from the seed for application. One study found that the greatest yield increase for corn occurred when the P band was placed 2 inches from the seed.4
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. The maximum theoretical phosphorus availability is at a pH of 6.8.The closer you are to this pH value, the more available phosphorus is to your plant.
Understanding the symptoms and their variations throughout the corn life cycle greatly expands your ability to intervene in a timely manner. Regular scouting and monitoring, coupled with soil testing, can help you identify phosphorus deficiency early and implement targeted management practices, such as fertilization, to address nutrient imbalances.
Consult with local agricultural extension services, your seed retailer or a seed company professional like your regional BASF representative to get tailored recommendations based on regional soil conditions and specific crop varieties.
📸: @Yevhen Smyk via Canva/Featuring emerged young corn in fertile, rich, healthy soil.
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