| dc.description.abstract | This dissertation yielded critical findings on the agronomic use of broiler chicken (Gallus gallus domesticus) litter, a byproduct of the poultry industry, for corn (Zea Mays L.) and cotton (Gossypium hirsutum L.) production in Alabama. Much of the poultry industry is concentrated in the southeastern United States with Alabama ranking second nationwide in broiler production. Consequently, broiler litter is produced in large quantities (an estimated 2 million tons) in the region. Broiler litter is an excellent source of organic matter and contains all essential plant nutrients including nitrogen (N). Utilization of broiler litter as a soil amendment and nutrient-rich fertilizer for row crop production in the southeastern United States is increasing. However, there are no fertilizer N management guidelines for corn and cotton fields that receive broiler litter in Alabama.
The first study investigated the effects of fertilizer N rate on broiler litter–fertilized corn grain yield and nutrient composition. Field experiments were conducted in 2020 and 2021 over three diverse environments (Wiregrass, Tennessee Valley, and Gulf Coast Research and Extension Centers) across Alabama to determine the agronomic optimum nitrogen rate (AONR) for broiler-litter–fertilized corn with five side dress fertilizer N rates (0, 84, 140, 196, and 252 kg N ha−1). Broiler litter (4.48 Mg ha−1 equivalent to 2-ton acre−1) was applied to the study sites before planting each year. The results revealed that the AONRs for grain yield varied by location and year from 114 to 223 kg N ha−1. With the preplant application of broiler litter at a rate of 4.5 Mg ha−1 yr−1, corn producers may require 0.013 to 0.027 kg of fertilizer N per kg of grain yield ha−1. Grain N concentration increased with increasing fertilizer N rate; however, the weak to nonexistent correlation between fertilizer N and other grain nutrient elements suggests that raising the fertilizer N rate does not necessarily lead to higher nutrient levels in corn grain. Overall, these findings are useful for developing N management guidelines for corn fertilized with broiler litter.
The second study evaluated the agronomic response of broiler litter–fertilized cotton to supplemental fertilizer N rate. A five-site-year field study was conducted at Wiregrass and Tennessee Valley Research and Extension Centers from 2021 to 2023 to assess the effects of fertilizer N application (0, 28, 50, 62, 78, and 95 kg ha−1) on broiler litter–fertilized cotton lint yield, above-ground biomass, tissue nutrient concentrations, nutrient uptake, lint turnout, fiber quality, and soil test nutrient changes. Broiler litter was applied at a rate of 4.5 Mg ha−1 yr−1 before planting. The results showed that the lint yield of cotton receiving only broiler litter (i.e., zero fertilizer N treatment) equaled that of the treatments receiving a combination of broiler litter and fertilizer N at relatively low yield potential (968 to 1472 kg ha−1). However, a positive crop response to fertilizer N (up to 50 kg ha−1) was observed at high yield potential (1990 to 2544 kg ha−1). With a few exceptions, fertilizer N had no significant effect on above-ground biomass, tissue nutrient concentrations, lint turnout, or fiber quality measurements in any growing season. Although these results suggest that broiler litter can be used as a primary N fertilizer for optimal cotton production, elevated concentrations of P, K, and Mg (by 14, 90, and 18%, respectively) in surface soil (0–15 cm depth) were observed at the end of study. Therefore, continued land application of broiler litter may be an environmental concern and should be avoided when surface soil test nutrients exceed critical levels.
Complementing the above studies, a third study investigated the effects of broiler litter total cleanout frequency (in other words, the age of broiler litter) on corn grain yield, biomass accumulation, nutrient uptake, and grain nutrient composition. Broiler producers periodically clean their broiler houses to the ground level (i.e., total cleanout) to improve flock health and prevent disease outbreaks. However, the frequency of total cleanout practiced on a broiler farm can impact N content of broiler litter and subsequent N release to crops. A 3-yr field study was established on a Decatur silt loam (Belle Mina, AL) and Malbis sandy clay loam soil (Fairhope, AL) to examine three broiler litter total cleanout frequency periods (<1yr, 1–2yr, and >2yr). The investigation revealed no significant differences in corn growth and grain yield with respect to total cleanout frequency of broiler litter, suggesting that this management practice may not affect the fertilizer value of broiler litter. Information on the crop response to age of broiler litter is important for producers whether utilizing their in-house broiler litter or buying from commercial markets and could help guide producer’s decision on broiler litter choice.
In addition to these field plot studies, the final study explored the impact of extreme rainfall (any heavy or greater-than-normal rainfall with distinct deviation from the mean rainfall level and a low occurrence probability) on runoff, infiltration, total suspended solids (TSS), and nutrient [dissolved reactive phosphorus (DRP), total phosphorus (TP), particulate phosphorus (PP), ammonium N, and nitrate N] losses on three land use systems (pasture, conventional and conservation tillage cropping systems). Extreme rainfall events are becoming more common in many regions of United States, including the southeast U.S. Agricultural systems that prioritize surface residue cover through crop rotation or conservation tillage may be more resilient to climate change-induced rainfall intensification. We conducted a rainfall simulation experiment in which we collected intact soil blocks from cropping systems managed under conventional tillage (CVT) and conservation tillage (CST) as well as pasture fields on silt loam to silty clay loam (Abernathy-Emory, Dewey, and Etowah soil series) and sand to loamy sand (Lucy and Dothan soil series) soils. Two one-acre-inch (0.0245 m) rainfalls were applied 24-hr apart to simulate the intensity of a 10 and 25-yr storm in a 5 min duration. Pasture fields showed little to no runoff; however, they had the highest losses of DRP, TP, and inorganic N (ammonium N + nitrate N) through leaching. The CVT and CST cropping systems had similar runoff volume and associated TSS, TP, and PP losses in both soil types regardless of rainfall intensity. Yet, the CST cropping system showed greatest runoff losses of DRP and inorganic N in silty clay loam soil, likely due to nutrient buildup at the soil surface. Overall, these results suggest that leaching is the dominant loss pathway for P and N in pasture systems and that surface residue cover may protect against runoff losses during extreme rainfalls. | en_US |
