Carbon decomposition in broiler litter-amended soils

Abstract Organic carbon (OC) is generally low in Alabama (U.S.A.) soils and varies considerably with cropping systems. Information on decomposition rates of the added C is a prerequisite to designing strategies that improve C sequestration in farming systems. Different models including exponential models have been used to describe OC mineralization in soils as well as to describe its potential as CO 2 to be released into the environment. We investigated the decomposition of broiler litter added to ten non-calcareous soils (Appling, Troup, Cecil, Decatur, Sucarnoochee, Linker, Hartsells, Dothan, Maytag, and Colbert soils). A non-linear regression approach for N mineralization was used to estimate the potentially mineralizable OC pools (C o ) and the first-order rate constant (k) in the soil samples. Results showed that the non-amended soils have distinct differences in their ability to release their native OC as CO 2 and can be divided into four groups depending on their potentially mineralizable C (C o ) and their ability to protect stable organic matter. Sucarnoochee soil represents the first group and contains a moderate amount of OC (11.4 g C kg −1 ) but had the highest C o (7.30 g C kg −1 soil). The second distinct group of soils has C o varying between 5.50 and 5.00 g C kg −1 soil (Decatur, Hartsells, Dothan, and Maytag). The third group has C o between 5.00 and 4.00 (Appling, Cecil, and Linker). The fourth group has C o less than 4.00 g C kg −1 soil (Troup and Colbert). Half-life of C remaining in non-amended soils varied from 26 days in Maytag soil to 139 days in Cecil soil. The OC in these non-amended soils represents a very stable form of organic C and thus, not easily decomposed by soil microorganisms. In the broiler litter-amended soils, the C o varied from 3.82 g C kg −1 in Appling soil amended with broiler litter 1–7.04 g C kg −1 soil in Maytag amended with broiler litter 2. Decomposition of the added OC proceeded in two phases with less than 31% decomposed in 43 days. Potentially mineralizable organic C (C o ) was related to soil organic C ( r  = 0.661**) and soil C/N ratio ( r  = 0.819*).