| Popis: |
Water erosion results in the mobilization and depletion of soil organic carbon (SOC), but studies providing direct experimental evidence of eroded C mineralization and its linkage to the global C cycle are lacking. A study was conducted to determine the mineralization of SOC in runoff from a southwestern Ohio Crosby soil (fine, mixed, mesic Aeric Ochraqualf) that had been under no-till (NT), chisel till (CT) and moldboard plow (MP) for 38 years. To simulate present and future soil erosion conditions, the 0–3 and 5–8 cm soil layers from triplicate soil blocks extracted from each tillage practice were used. Soil layers were transferred to runoff trays and simulated rainfall (30±5 mm h −1 ) was applied for 1 h. Runoff was collected at 20, 40 and 60 min following initiation of rainfall event. Carbon dioxide production was monitored for 100 days in runoff samples incubated without and with N (0.15–0.20 g NH 4 -N kg −1 sediment) amendment to simulate situations where water erosion coincides with high soil mineral N availability. The data show that soil layer depth and time of runoff sampling had no significant effect on any of the parameters considered. Sediment delivery (g sediment m −2 h −1 ) was significantly lower in the NT (17.4) than in the other tillage (CT: 48.9, MP: 34.1) practices; it was inversely related to degree of soil aggregation and sediment C content. The average of C export ranged between 0.6 and 1.1 g C m −2 h −1 , and was highest in the CT soil. Mineralization of runoff C followed a first-order kinetics and proceeded at rates significantly higher in NT and N-amended runoff. Nearly half of the total runoff C mineralization recorded during the entire incubation occurred during the first 20 days suggesting that under field conditions, most of the erosion-induced CO 2 production will occur in the days immediately following rainfall events. Potentially mineralizable carbon ( C 0 ) in runoff was significantly greater with NT (13.5 g C kg −1 sediment) than with the other tillage practices, and was positively correlated with sediment C content ( R 2 =0.76) and cumulative C mineralized ( R 2 =0.77–0.97). The data presented showed that 29–35 and 33–46% of the C exported in runoff was mineralized in 100 days without and with N amendment, respectively. These results are the first quantitative evidence that a significant fraction of the SOC released through water erosion is mineralizable and, therefore represents an additional source of atmospheric CO 2 . |
Full Text from ScienceDirect