Carbon Decomposition in Selected Alabama Soils Amended with Broiler Litter.

Organic carbon is generally low in Alabama soils and varies considerably with cropping systems. Decomposition rates of organic C in ten Alabama soils treated with two broiler litter (BL) samples were investigated under laboratory conditions at room temperature. A 20-g surface (0-15 cm) soil (<2-mm) was mixed with appropriate amounts of BL to give 9 g organic C kg^-1 soil. The soil-BL mixture was transferred into a French square bottle and moistened to 60% water holding capacity. The incubation bottle was connected to a continuous aerobic incubation apparatus. Air from a laboratory outlet was connected to a scrubber consisting of 4 M NaOH, concentrated H₂SO₄, a nanometer to regulate air flow, and a manifold of tygon tubes passing the CO₂-free air through the incubation bottles, and test tubes containing 25 mL of NaOH solution of known molarity (0.2 M) to trap the CO₂ evolved from the incubation bottles. Controls were also included to estimate the CO₂ evolved from untreated soils. The trapping solution was replaced with fresh solution on a regular basis. The CO₂ trapped was determined potentiometrically by titrating 20 mL aliquot of the NaOH solution in the test tube with a standard HCl solution (0.2 M). Before titration, an excess 0.375 M BaCl₂ solution was added to precipitate carbonate. Soil samples obtained from organic farming plots were similarly incubated for 30 days. Generally, the rate constant (k) varied with soils and treatments. The k values of BL-amended soils ranged from 0.022 in Dothan soil to 0.103 in Appling soil, while those of none amended soils varied from 0.00014 in Sucarnoochee soil to 0.031 in Troup soil. The k values of the soils obtained from the organic farming plots were similar to those of none amended soils suggesting that only recalcitrant organic C remained in the soils.