Center for Global Change and Earth Observations, Michigan State University, East Lansing, Michigan, 48823, USA.
Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, Michigan, 48824, USA.
Ecol Appl. 2018 Jul;28(5):1362-1369. doi: 10.1002/eap.1745. Epub 2018 Jun 1.
Land use conversions into and out of agriculture may influence soil-atmosphere greenhouse gas fluxes for many years. We tested the legacy effects of land use on cumulative soil nitrous oxide (N O) fluxes for 5 yr following conversion of 22-yr-old Conservation Reserve Program (CRP) grasslands and conventionally tilled agricultural fields (AGR) to continuous no-till corn, switchgrass, and restored prairie. An unconverted CRP field served as a reference. We assessed the labile soil C pool of the upper 10 cm in 2009 (the conversion year) and in 2014 using short-term soil incubations. We also measured in situ soil N O fluxes biweekly from 2009 through 2014 using static chambers except when soils were frozen. The labile C pool was approximately twofold higher in soils previously in CRP than in those formerly in tilled cropland. Five-year cumulative soil N O emissions were approximately threefold higher in the corn system on former CRP than on former cropland despite similar fertilization rates (184 kg N·ha ·yr ). The lower cumulative emissions from corn on former cropland were similar to emissions from switchgrass that was fertilized less (57 kg N·ha ·yr ), regardless of former land use, and lowest emissions were observed from the unfertilized restored prairie and reference systems. Findings support the hypothesis that soil labile carbon levels modulate the response of soil N O emissions to nitrogen inputs, with soils higher in labile carbon but otherwise similar, in this case reflecting land use history, responding more strongly to added nitrogen.
土地利用向农业的转化和退出可能会影响到多年来土壤-大气温室气体通量。我们测试了土地利用对 22 年历史的保护储备计划（CRP）草地和传统耕作农田（AGR）转变为连续免耕玉米、柳枝稷和恢复草原后 5 年累积土壤氧化亚氮（N O）通量的遗留效应。未转换的 CRP 草地作为对照。我们在 2009 年（转换年）和 2014 年使用短期土壤培养法评估了上层 10cm 的可利用土壤 C 库。我们还使用静态室法从 2009 年到 2014 年每两周测量一次原位土壤 N O 通量，但当土壤冻结时除外。以前处于 CRP 状态的土壤中的可利用 C 库比以前处于耕作农田状态的土壤高约两倍。尽管施肥率相似（约 184kg N·ha·yr），但在前 CRP 上种植玉米的 5 年累积土壤 N O 排放量比在前农田上种植玉米高出约三倍。尽管以前的土地利用情况不同，但在施肥量较少的柳枝稷（约 57kg N·ha·yr）上，前农田上玉米的累积排放量较低，与施肥量较少的柳枝稷相似，而未施肥的恢复草原和对照系统的排放量最低。研究结果支持这样一种假设，即土壤可利用碳水平调节土壤 N O 排放对氮素输入的响应，在这种情况下，土壤中可利用碳水平较高但其他方面相似，反映了土地利用历史，对添加的氮素反应更强烈。
