|Gale, W - IOWA STATE UNIVERSITY|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 26, 1999
Publication Date: N/A
Interpretive Summary: Soil organic matter levels frequently increase under no-till farming practices. These increases in organic matter are commonly thought to occur as a result of leaving crop residue on the soil surface. The contribution of root residue to soil organic matter accumulation is usually ignored, or at best, underestimated. The objective of our research was to study no-till practices and determine the contribution of surface residue and roots to the recent accumulation of carbon in soil organic matter. Our results showed that 75% of the new carbon moving into the soil after one year came from roots and only 25% from surface residue. We also observed that two thirds of the carbon contained in the surface residue had been released into the atmosphere after one year. In contrast, a greater proportion of the carbon contained in the roots remained in the soil. These results clearly indicate that plant roots contribute more to soil organic matter than the plant residue that is left on the soil surface in no-till. With the increased emphasis on carbon storage in soil, these results help define the role that plants and tillage have in changing soil carbon content. This information will help scientists develop agricultural management strategies that enhance soil quality and decrease carbon dioxide in the atmosphere through the storage of organic carbon in soil.
Technical Abstract: No-till (NT) practices have the potential to increase soil organic C, but little is known about the relative contribution of surface residue and roots to soil organic C accumulation. In a simulated NT experiment, we studied the fate of**14C-labeled surface residue and in situ roots during a one year incubation in a silt loam soil. Soil samples collected during the eincubation were chemically dispersed and separated into four particle size and density fractions. The weight, organic C, **14C, and total N content of each fraction were determined. Alkali traps were used to measure **14C losses due to respiration. After 360 d, 66% of the **14C contained in the surface residue on d 0 had been respired as **14CO2, 12% remained in residue on the soil surface, and 16% was in the soil. In comparison, 56% of the root-derived **14C in the soil was evolved as **14CO2 and 42% remained in the soil. The large (500- to 2000-um) and small (53- to 500-um) particulate organic matter (POM) fractions together contained 28-42% of the root-derived **14C in the soil. A greater proportion of surface residue-derived **14C in the soil was associated with silt- and clay-sized particles. POM contained only 9-19% of the surface residue-derived **14C in the soil. At the end of one year, 75% of the new-C that moved into the soil came from the roots and 25% from the surface residue. These data show clear differences in the partitioning of surface residue- and root-derived C during decomposition and imply that the beneficial effects of no-till on soil organic C accrual are primarily due to the increased retention of root-derived C in the soil.