Corn Fertility in Medium– to High-Yield Environments

Advances in corn agronomic management practices, breeding, and biotechnology continue to have an impact on corn yield potential. Recent research suggests that corn products with rootworm resistance may have increased root growth, leading to increased nutrient uptake and yield potential.1 This increase in nutrient use may lead to changes in fertilizer recommendations.

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Managing soil fertility begins with soil testing. Soil test results help establish nutrient levels available in the soil and provide locally calibrated fertilizer recommendations. Soil testing should be performed annually to help maximize corn yield potential.

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Among others, soil test results provide soil pH values. Soil pH is a measure of soil acidity or alkalinity and can greatly impact crop growth. Optimal soil nutrient availability for corn occurs within a soil pH of 6.0 to 7.0. When soil pH falls below 5.5, corn plants may show signs of nutrient deficiencies. Macronutrients (nitrogen, phosphorous, and potassium) and secondary macronutrients (sulfur, magnesium, and calcium) can become less available to corn plants in low soil pH environments. In addition to reducing nutrient availability, low soil pH can also increase the availability of aluminum and manganese, which can result in plant toxicity and possible plant death. Fertilizer application is necessary in medium- to high-yield environments, but can also increase the probability of soil acidity.

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Soil test results can be used to determine lime requirements for decreasing soil acidity. Soil testing laboratories use buffer pH to determine lime requirements. Buffer pH is a laboratory-derived value used to evaluate the ability of a soil to respond to liming. The larger the difference is between the original soil pH and buffer pH, the more responsive a soil will be to lime application, and the lower amount of lime required to raise soil pH. Lime is recommended to be applied in the fall to allow adequate time to neutralize soil acidity. If lime is unable to be applied in the fall, spring application is recommended.2

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Nitrogen (N). Inadequate fertilization and leaching from heavy rainfall can result in N deficiency. Symptoms appear on leaves as overall light green to yellow coloration and may be observed in a v-shaped pattern that starts at the tip and progresses toward the leaf collar.3

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Nitrogen should be applied according to crop need and is recommended to be applied two to three times per season depending on growing conditions. A split application can reduce the likelihood of N loss from leaching and denitritification during typical wet spring weather. Corn extracts only 15% of required N prior to rapid vegetative growth. To help maximize potential yield, N should be applied prior to rapid vegetative growth, or around the V5 to V8 growth stages. Synchronizing N application timing with rapid N uptake by corn can help improve N use efficiency. A corn plant will need the most N at the V10 growth stage, which occurs about 40 days after plant emergence.4

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Phosphorus (P). Phosphorus deficiency typically occurs in young corn plants after a period of cool soil temperatures. The developing corn roots are unable to uptake enough P for growth, resulting in P deficiency and delayed growth. Symptoms include dark green leaves and purple margins on older leaves, and no symptoms on new, emerging leaves. When optimum growing conditions occur, roots continue to grow and uptake P, symptoms will fade and corn will resume normal growth.2

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Phosphorus can be applied either in the fall prior to tillage or in the spring, depending on local conditions. Phosphorus is nearly immobile in the soil, so incorporation is recommended within the corn root zone. Fertigation may also be an effective method to incorporate P deep into the root zone.5 In dryland fields, if P deficiency is detected early in the season, P may be injected as a sidedress treatment to help the nutrient reach the corn roots; however, care should be taken not to damage roots in the process.

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Potassium (K). Potassium deficiency can be observed on older leaves as chlorotic (yellow), then necrotic (dead) leaf tissue at the leaf tip and migrating toward the stalk.2 Potasium is essential for the plant to move energy from the leaves for grain fill. If K is limited, silk emergence may be delayed, and ears with unfilled tips may result.6 Low K levels can result in yellow leaf margins on lower, older leaves. Because K may be recycled back into the soil through crop residue, deficiencies are common when crop residue is removed from the field.

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Potassium requirements will be higher in production environments with heavy crop removal, such as silage production. Soybean rotations must also be considered as soybean seed production requires more K and will deplete the soil at a faster rate than other crops. Like P, K fertilizer may be applied in the fall as it is relatively immobile in the soil, but caution should be taken when applying K to sandy soils as leaching may occur. Potassium may also be applied in the spring or in-season. A starter fertilizer may help improve N, P, and K availability, especially in conservation tillage systems.

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Although the uptake of nutrients such as sulfur, zinc, and manganese make up less than one percent of fertilizer applied in corn, they are critical for corn development and it is important to identify and manage deficiency symptoms.7

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Sulfur (S). Sulfur deficiency may occur more often in sandy, acidic soils that are low in organic matter. Cool and wet conditions usually found in the spring can also increase the chance of S deficiency. Symptoms include general yellowing, possibly with yellow-white intervein striping. Symptoms appear first on younger leaves as S is relatively immobile in the plant. Plants may also be stunted. If symptoms are a result of cool, wet soils, corn may recover as soon as soil conditions improve.

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Zinc (Zn). Like S, Zn deficiency also occurs more frequently in sandy soils low in organic matter during cool, wet conditions. However, unlike S deficiency, Zn deficiency is more common in alkaline soils. Zinc is also relatively immobile in the plant, so symptoms appear on young leaves as whitish bands that start at the base of the leaf and move toward the tips. Leaf margins and tips typically remain green. Symptoms may be observed several weeks after planting. Internodes may be shortened, but corn typically will recover once favorable conditions return.

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Manganese (Mn). Manganese is often immobile in corn, and can become deficient in high pH soils that may also be high in organic matter or are considered peat or muck soils. Symptoms may be observed in younger plants as streaking and olive in color.3,7 Banded and foliar-applied sources of Mn are available.