Long-term effects of pasture management and fenced riparian buffers on soil organic carbon content and aggregation

Abstract

Soil organic carbon (SOC) plays a key role in sustaining pasture agroecosystem function and its rate of accumulation can be influenced by management practices including manure deposition and grazing intensity. This study was conducted to determine the impacts of 13-years of different pasture management practices on SOC content and aggregation. The field experiment was conducted in a watershed consisted of five pasture management practices: (i) hayed (H), (ii) continuously grazed (CG), (iii) rotationally grazed (R), (iv) rotationally grazed with a grass buffer strip (RB), and (v) rotationally grazed with a fenced riparian buffer (RBR). Since 2004, all treatments received 5.6 Mg ha−1 of poultry litter annually except the buffer area located at the base of RB and RBR. Starting from the top of hillslope, each plot was divided into three landscape positions (A, B, and C). In addition, the ungrazed, unfertilized riparian buffer strip (RBS) in RBR was also studied. In general, upper landscape positions showed greater SOC than lower positions for most of the treatments, and in particular, soils in the landscape position A had greater SOC than RBS. However, permanganate oxidizable C (POXC) was higher in all poultry litter amended pasture systems compared to the RBS. Rotational grazing practice promoted the formation of large macroaggregates compared to other pasture management practices and RBS. All five pasture management treatments improved large macroaggregate-associated SOC content as compared to RBS, and it was higher in grazed plots than the hayed plots. Overall, this study showed that organic manure addition improved total SOC, POXC and SOC associated with large macroaggregates, while differences in SOC among different pasture management strategies were subtle even after 13 years of continuous management.