A good nutrient management program is one of the keys to high-yield corn production. Instituting best management techniques to ensure adequate nutrient availability throughout the growing season can pay real dividends at the end of the year and minimize the adverse effects of nutrient runoff and leaching on the environment.
Nitrogen
Timing and Sources
Nitrogen fertilizer applications for corn production can be challenging to manage effectively. Fall application of nitrogen is not recommended, but if nitrogen is to be applied in the fall, make certain that soil temperatures are below 50 degrees Fahrenheit and that anhydrous ammonia with an appropriate stabilizer is used. Do not apply nitrogen fertilizers that contain nitrate in the fall, as the risk of loss is high due to leaching. Application of nitrogen in the spring is more efficient and less susceptible to loss. Nitrogen stabilizers may be used for early spring application, but the benefit of such compounds is inconsistent. The application of sidedress nitrogen is a good alternative to preplant applications of nitrogen. In-season applications move fertilization away from the busy planting period and are closer to actual crop uptake of nitrogen. Sidedressing also minimizes the risk of nitrogen loss—especially on poorly drained clay soils, which are subject to denitrification, and sandy soils, which are susceptible to leaching. The main risk of inseason application is the possibility of delayed application due to wet conditions.
When selecting a nitrogen source, remember that a pound of nitrogen is a pound of nitrogen; make selections based on risk and cost. For example, it would be risky to apply urea to the surface of no-till ground due to the potential loss of nitrogen by volatilization. Surface dribble banding of liquid nitrogen or subsurface injection are better alternatives. This is not to say that urea is not a good source of nitrogen, but it should be placed below the soil surface. Always consider material cost as well as the field environment to get the most efficient use of nitrogen fertilizers.
Rates
Current nitrogen recommendations for corn production are based on a simple economic model, the Maximum Return To Nitrogen (MRTN). In an era of variable grain and nitrogen fertilizer prices, this model strives to maximize farmer profitability. The MRTN takes into account a ”typical” yield response curve, the price of nitrogen fertilizer, and the price of corn grain. A simple tool with Ohio data to generate MRTN nitrogen rate recommendations is online at cornnratecalc.org. The background and justification for this approach are laid out in this regional publication: store. extension.iastate.edu/product/12240.
Phosphorus and Potassium
Application Methods
Phosphorus and potassium are more straightforward than nitrogen when it comes to application methods. Phosphorus and potassium are not subject to the same loss mechanisms as nitrogen, thus application concerns are not as restrictive. The main loss mechanism for phosphorus is through soil erosion. Utilization of conservation practices that minimize the risk of soil runoff to surface waters is adequate for good phosphorus management. More guidance on reducing phosphorus losses can be found at ohioline.osu.edu/factsheet/agf-509. Phosphorus and potassium can be applied either broadcast prior to planting or banded—near the row or over the row (pop-up)—as a starter when planting. If applying starter in a band 2 inches to the side and 2 inches below the seed, the total amount of salts applied (N + K2O) should not exceed 100 pounds per acre. If a starter is applied with the seed—not recommended due to potential salt problems—the total salts (N + K2O) applied should not exceed 5 pounds per acre for low CEC soils or 8 pounds per acre for high CEC soils. The benefit of starter fertilizers increases when soil test levels and soil temperatures are low and when soil surface residues are high. Soils that have moderate to high levels of soil test phosphorus and potassium show little to no benefit from starter fertilizer.
Sources
Little difference exists between commonly used forms of phosphorus and potassium regarding nutrient uptake. Ortho- and poly-phosphate formulations perform equally well, even though the crop takes up the ortho form (poly forms convert to ortho forms rapidly). It should be mentioned that if dry formulations of phosphorus are to be applied in contact with the seed, monoammonium phosphate (MAP) is a somewhat safer form of phosphorus to apply than diammonium phosphate (DAP). DAP produces more ammonia (NH3), which is toxic to germinating seeds. When banding MAP, DAP, or ammonium polyphosphate (APP), do not exceed more than 40 pounds of nitrogen per acre. If soil test phosphorus and potassium are high on no-till soils, then only nitrogen should be applied as a starter, unless 40 to 60 pounds of nitrogen per acre has been applied preplant.
Rates
Soil test levels below the critical value are considered deficient and warrant the application of fertilizer (Table 4.14). Current recommendations for phosphorus and potassium are presented in Tables 4.15 and 4.16. Buildup and maintenance recommendations are designed to increase soil test levels to the critical value or maintain current soil test levels. Considering it takes 8 to 20 pounds of P2O5 and 5 to 10 pounds of K2O (added or removed) to change the soil test level by one unit (depending largely upon soil texture), soil test levels above the critical value will be adequate for crop production for at least a few years (depending upon the soil test level).
Sulfur
Sulfur deficiencies are not common, but deficiencies increasingly are being reported, especially on sandier soils with low organic matter. Historically, sulfur was deposited in large quantities from atmospheric rainfall. However, emission standards on industrial activities have resulted in a sharp decrease in sulfur deposition from the atmosphere. As this trend continues, sulfur fertilization may become more important. Sulfur fertilization rates have not been established in Ohio. Corn grain removes a relatively low amount of sulfur: approximately 14 pounds of sulfur for 180 bushels per acre of corn. Accordingly, 15 to 30 pounds per acre of sulfur should be adequate for soils suspected of being deficient. Sulfur fertilizer options include ammonium sulfate, ammonium thiosulfate, and gypsum.
For comprehensive information on corn fertilization and soil fertility management, see OSU Extension bulletin 974 Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa, which is available online at extensionpubs.osu.edu/tri-state-fertilizerrecommendations-for-corn-soybean-wheat-and-alfalfa.
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