Lehrstuhl für Grünlandlehre, Technische Universität München, Germany.
Institut für Geographie, Universität Augsburg, Germany.
Sci Total Environ. 2019 Apr 15;661:481-491. doi: 10.1016/j.scitotenv.2019.01.200. Epub 2019 Jan 16.
Changing soil use from cropland to grassland influences organic carbon storage in a highly complex way. This includes the root/shoot allocation, the root depth distribution, the incorporation of shoot biomass and lateral organic carbon fluxes, by erosion and removal of harvested carbon, and finally the aeration by tillage. An experiment was designed allowing resampling a number of soils 18 yr after conversion to grassland (either pasture or meadow or set-aside) only 20 cm apart from the original sampling to exclude site variation. Before conversion to grassland the cropland was prone to erosion, with a mean lateral carbon flux during 20 yr prior to conversion of 13 t ha. Harvest had removed another 29 t ha of carbon at eroding sites. Colluvial carbon inputs had been up to 18 t ha while harvest had removed 38 t ha at colluvial sites. The carbon fluxes by erosion were negligible during the 18 yr period after conversion. After conversion the carbon losses by harvest also ceased at set-aside grassland and pastures while the net losses on meadows were 45 t ha. Conversion to grassland significantly changed depth functions of carbon, stones, bulk density and porosity. Despite the large changes in carbon fluxes, carbon stocks did only change significantly within 18 yr under poorly drained, gleyic soils. Well-aerated soils did not show a significant increase in SOC stocks. This was even true for heavily eroded soils, where conversion from cropland to grassland (without erosion) should foster dynamic replacement of SOC. The widespread drainage of wet grassland soils prior to conversion to cropland thus can cause a large release of carbon, while an influence of tillage by either increasing aeration or erosion could not be detected in this study. Therefore, fostering carbon sequestration by conversion of cropland to grassland requires restoring former draining conditions.
土壤使用由耕地转为草地会以非常复杂的方式影响有机碳储存。这包括根/茎分配、根深度分布、通过侵蚀和收获碳的去除以及耕作的通气来整合地上生物量和侧向有机碳通量。进行了一项实验，允许在将耕地转为草地（牧场、草地或休耕地） 18 年后，仅从原始采样点 20 厘米处重新采集一些土壤样本，以排除采样点的差异。在转为草地之前，耕地易受侵蚀，在转为草地前 20 年，平均侧向碳通量为 13 吨/公顷。在侵蚀地，收获又去除了 29 吨/公顷的碳。在堆积地，堆积碳输入量高达 18 吨/公顷，而收获则去除了 38 吨/公顷的碳。在转为草地后的 18 年内，侵蚀引起的碳通量可忽略不计。转为草地后，休耕地和牧场的收获引起的碳损失也停止了，而草地的净损失为 45 吨/公顷。转为草地显著改变了碳、石头、容重和孔隙度的深度函数。尽管碳通量发生了很大变化，但在排水不良、潜育土壤中，碳储量仅在 18 年内才发生显著变化。通风良好的土壤中 SOC 储量没有显著增加。即使在严重侵蚀的土壤中也是如此，在这些土壤中，从耕地转为草地（无侵蚀）应该会促进 SOC 的动态替代。在转为耕地之前，广泛排水的湿草地土壤会导致大量碳的释放，而在本研究中，没有检测到耕作通过增加通气或侵蚀的影响。因此，通过将耕地转为草地来促进碳固存，需要恢复以前的排水条件。
