Learn the optimum rate of nitrogen fertilizer when using broiler litter in dryland corn production.

Figure 1. Agronomic optimum N rates (AONRs) for corn following preplant broiler litter applications (2 tons per acre) in selected soil types in Alabama. The field trials also included untreated control without broiler litter or fertilizer N application except for Malbis sandy clay loam soil in 2021 where all plots had accidentally received broiler litter.

Nitrogen (N) is often the most yield-limiting nutrient for corn production. It plays a critical role in forming amino acids, proteins, and chlorophyll molecules, which are essential for plant growth and productivity. Nitrogen fertilizer constitutes a significant portion of the total variable costs in corn production. With rising N fertilizer prices and environmental risks associated with overapplication, applying the optimum rate of N fertilizer is vital to maximize efficiency, profitability, and sustainability.

The southeastern United States is a hub for the poultry industry, with Alabama ranking second in the nation for broiler production. More than a billion broilers are raised annually in Alabama, generating approximately 1.5 to 2 million tons of broiler litter. Broiler litter is an excellent source of essential plant nutrients, with an average fertilizer grade of 3–3–2 (N-P2O5-K2O), making it a valuable resource for crop production.

As established by Auburn University, N recommendations for corn production in Alabama are based on extensive statewide research. These recommendations utilize a yield goal-based approach developed in the 1970s, where the total N requirement is calculated by multiplying the estimated expected yield (bushel acre-¹) by a factor of 1.25 (pounds of N required per bushel) if the yield potential is greater than 120 bushels per acre.

Studies from the Midwest suggest that yield goal-based N recommendations often fail to align with agronomic optimum N rates (AONRs) or economic optimum N rates (EONRs), indicating that yield alone is insufficient to determine EONR. Other site-specific factors, such as soil texture, soil series, and soil organic matter, must also be considered. Moreover, this traditional approach does not account for the N contribution from broiler litter applied before planting, potentially leading to overapplication of fertilizer N.

Six N fertilizer rate trials were conducted in Alabama between 2020 and 2021 to evaluate broiler litter–fertilized corn under rain-fed growing conditions. The trials were established on three soil types: Dothan fine sandy loam, Decatur silt loam, and Malbis sandy clay loam, located at Auburn University Wiregrass, Tennessee Valley, and Gulf Coast Research and Extension Centers, respectively. Broiler litter was applied preplant at a rate of 2 tons per acre. Fertilizer N rates ranged from 0 to 225 pounds N per acre and were side-dressed at the V6–V8 growth stage using liquid urea-ammonium nitrate (28 percent N). The field trials also included untreated control without broiler litter or fertilizer N application. The crop history on coarse-textured soils included cotton rotated with peanuts, while the fine-textured soil primarily supported continuous soybeans. All trials were harvested using a small plot combine, and yields were reported at 15.5 percent moisture content.

Grain yield across treatments ranged from 37 to 113, 85 to 202, and 138 to 210 bushel acre-¹ on Dothan fine sandy loam, Decatur silt loam, and Malbis sandy clay loam soils, respectively. The low grain yield on Dothan fine sandy loam soil highlighted poor growing conditions due to low inherent soil fertility, high N loss potential, and heat and water stress. The carryover of nutrients from repeated application of broiler litter and a wetter growing season likely increased grain yield of the broiler litter alone treatment in 2021 compared to unfertilized control. The AONR values in the trials were 102 (2020), 169 (2021), 130 (2020), 199 (2021), 159 (2020), and 165 (2021) on Dothan fine sandy loam, Decatur silt loam, and Malbis sandy clay loam soils, respectively (figure 1). The AONR differed from region to region and year to year within a single field. This variation in AONR was expected due to variability in available soil N, weather, and losses to leaching, denitrification, or volatilization. Any fertilizer N applied beyond AONR offers no additional yield and will be a monetary loss. Substantial differences often exist in the N rates that maximize economic return compared to the grain yield. The EONR is usually lower than the AONR because of decreased yield gains as the N application rates near the AONR. The EONR should be considered for corn fertilizer recommendations to optimize profit as it accounts for both the expected grain price at harvest and the cost of applied fertilizer N. Tables 1, 2, and 3 provide region-specific EONR for a range of corn and N fertilizer prices. Consult the tables to quickly determine EONR for a particular combination of grain price and N cost in an applicable soil type. For example, the EONR based on $4.50 grain price bushel-¹ and $1.10 N cost pound-¹ in a Dothan fine sandy loam soil is 0.97 and 0.99 pounds N per bushel for the 2020 and 2021 growing seasons, respectively (table 1).

Because broiler litter nutrient content can vary widely depending on farm management operations, representative samples of broiler litter should be analyzed for nutrient concentrations before land application each year. Remember that it is difficult to accurately predict AONR or EONR due to complex biological interactions of N. Nitrogen rate recommendations for a particular field, however, can be fine-tuned with N rate response tests, use of computer models, optical sensors such as chlorophyll meter, and the end-of-season stalk nitrate test.

Tables

View tables 1, 2, and 3 in the corresponding PDF download below.

The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) is an equal opportunity educator, employer, and provider. If you need a reasonable accommodation or free language access services, contact Rishi Prasad at rzp0050@aces.edu.

Rajveer Singh, Research Associate, and Rishi Prasad, Extension Specialist, Associate Professor, both in Crop, Soil, and Environmental Sciences, Auburn University

New June 2025, Optimum Rate of Nitrogen Fertilizer When Using Broiler Litter in Dryland Corn, ANR-3159