Crop carbon contribution to the soil with different cropping and livestock systems

ABSTRACT:

The level of organic matter or carbon in agricultural soils depends on additions from crop residues and manures and on losses from erosion and decomposition. The supply of C to soils is dependent on biomass yields, harvest index, and the proportion of feed C retained in the manure with different crops. A simple mathematical procedure was used to estimate quantities of C supplied to the soil with different livestock systems. This procedure involved the partitioning of C into residue, root, and animal components. Mere were uncertainties, however, about the quantities of C originating from crop roots and C losses during manure storage. Two typical livestock farm systems were compared; a swine system emphasizing grain crops, and a dairy system with grain and forage crops each in a typical rotation. This study revealed that manure contributes a relatively small proportion of the C to soil compared to crop roots and residue, especially in swine systems, unless straw bedding is included. The total quantity of C supplied to the soil was generally greater with the dairy system, primarily because of the inclusion of a legume/grass crop in the rotation.