Benjamin Senyo Bey Abstract

Trace Elements in Broiler Litter-Treated Soils: Fate and Effects on Nitrogen Transformations
Benjamin Senyo Bey
Advisor: Dr. K. Kpomblekou-A

       Broiler production has increased tremendously over the past decade in the U.S. Consequently, a significant amount of broiler litter is generated each year. In the year 2000, for instance, 8.2 billion broilers were produced, generating about 9.84 million tons of broiler litter. Excessive application of inorganic fertilizers to farmlands has raised health and environmental concerns to consumers, soil and environmental scientists, policymakers, and the government. Organic fertilizers, such as broiler litter, are vigorously being promoted as sources of plant nutrients. Trace elements are routinely added to poultry feed and water as additives to improve disease resistance and feed conversion efficiency. These are eventually found in poultry droppings, unconsumed feed and water and thus become part of broiler litter. Considerable amounts of As (37 ppm), Zn (377 ppm), Mn (655 ppm), Cd (20 ppm), Cu (390 ppm), and Pb (35 ppm) were reported in broiler litter. Metal contents of the litter may vary according to poultry production management practices. Studies conducted in our laboratory using 33 broiler litter samples collected in 12 Alabama counties showed variable amounts of trace elements. Prolonged and over application of broiler litter to agricultural lands may result in accumulation of trace elements. The toxicological effect of these trace elements on microbial population, enzymatic activities, biochemical reactions and, to a larger extent, on human health cannot be underestimated. When present in sufficient concentrations, trace elements may become toxic to soil microorganisms and severely affect microbially-mediated soil processes. Preliminary results obtained in our laboratory in the Appling soil showed that, some trace elements, such as As, Cd, Co, Cr, Se, and Zn exhibited inhibitory effects on N transformations at concentrations higher than 1.0 mmol g-1 soil. For instance, As effectively inhibited nitrification from 62 to 20 mg kg-1 soil. The objectives of this research work were to: 1) use equimolar concentrations (1.0 mmol g-1 soil) of ten trace elements to enable us to compare their inhibitory effects on nitrogen transformations across 10 Alabama soils having wide range of physical and chemical properties, 2) investigate the kinetics of nitrogen transformations in soils treated with broiler litter in the presence of trace elements, and 3) investigate the fate of trace elements in broiler litter-treated soils using sudax (Sorghum bicolor) as a test grass. Preliminary results from the current studies showed that the inhibitory effects of the trace elements on N transformations varied from soil to soil. Cadmium and Cr showed inhibitory effects in most soils with percentage inhibition of about 52 and 29%, respectively, in the Dothan soil. In most of the soils, ammonification was inhibited by the presence of the trace elements. Nitrification inhibition correlated significantly with soil organic C in the presence of Mn (r2 =