美国北阿巴拉契亚地区耕作措施和土地利用管理对土壤团聚体和有机碳的影响

Promoting soil carbon sequestration in agricultural land is one of the viable strategies to decelerate the observed climate changes.However,soil physical disturbances have aggravated the soil degradation process by accelerating erosion.Thus,reducing the magnitude and intensity of soil physical disturbance through appropriate farming/agricultural systems is essential to management of soil carbon sink capacity of agricultural lands.Four sites of different land use types/tillage practices,i) no-till (NT) corn (Zea mays L.) (NTC),ii) conventional till (CT) corn (CTC),iii) pastureland (PL),and iv) native forest (NF),were selected at the North Appalachian Experimental Watershed Station,Ohio,USA to assess the impact of NT farming on soil aggregate indices including water-stable aggregation,mean weight diameter (MWD) and geometric mean diameter (GMD),and soil organic carbon and total nitrogen contents.The NTC plots received cow manure additions (about 15 t ha-1) every other year.The CTC plots involved disking and chisel ploughing and liquid fertilizer application (110 L ha-1).The results showed that both water-stable aggregation and MWD were greater in soil for NTC than for CTC.In the 0-10 cm soil layer,the ＞ 4.75-mm size fraction dominated NTC and was 46％ more than that for CTC,whereas the ＜ 0.25-mm size fraction was 380％ more for CTC than for NTC.The values of both MWD and GMD in soil for NTC (2.17 mm and 1.19 mm,respectively) were higher than those for CTC (1.47 and 0.72 mm,respectively) in the 0-10 cm soil layer.Macroaggregates contained 6％42％ and 13％ 43％ higher organic carbon and total nitrogen contents,respectively,than microaggregates in soil for all sites.Macroaggregates in soil for NTC contained 40％ more organic carbon and total nitrogen over microaggregates in soil for CTC.Therefore,a higher proportion of microaggregates with lower organic carbon contents created a carbon-depleted environment for CTC.In contrast,soil for NTC had more aggregation and contained higher organic carbon content within water-stable aggregates.The soil organic carbon and total nitrogen stocks (Mg ha-1) among the different sites followed the trend of NF ＞ PL ＞ NTC ＞ CTC,being 35％-46％ more for NTC over CTC.The NT practice enhanced soil organic carbon content over the CT practice and thus was an important strategy of carbon sequestration in cropland soils.     

名山河流域黄壤组分对微团聚体吸附解吸镉的影响

选取名山河流域4种土地利用方式（林地、水田、茶园、旱地）的黄壤为研究对象,采用平衡液等温吸附法和NH4OAC、EDTA溶液解吸法,研究土壤组分（有机质、游离氧化铁）对微团聚体吸附解吸Cd2＋的影响。结果表明：去除土壤组分前后,原土及各粒径微团聚体对Cd2＋的吸附量均随Cd2＋初始浓度增大而增大,吸附量均按以下次序递减：（〈0.002mm）〉2～0.25mm〉原土〉0.053～0.002mm〉0.25～0.053mm,与有机质、游离氧化铁、CEC呈极显著正相关。吸附减少量大小关系为：去除有机质〉去除游离氧化铁,有机质的贡献率大于游离氧化铁。Freundlich方程拟合效果最佳,达到极显著水平,分布系数Kd值与Cd2＋初始浓度呈曲线负相关。NH4OAC解吸率随原吸附Cd2＋初始浓度增大而增大,以最大解吸率计,递减规律为：0.25～0.053mm〉0.053～0.002mm〉原土〉2～0.25mm〉（〈0.002mm）;EDTA解吸率随原吸附Cd2＋初始浓度增大而减小,递减规律与NH4OAC解吸率相反。去除土壤组分后,NH4OAC解吸率上升,EDTA解吸率下降,茶园与旱地黄壤非解吸率减小,林地与水田黄壤非解吸率增大。去除土壤组分后,非专性吸附与吸附总量呈极显著正相关,专性吸附与吸附总量呈极显著负相关。     

土壤矿物吸附和土壤团聚体对土壤有机碳含量的影响研究

Soil organic carbon (SOC) can act as a sink or source of atmospheric carbon dioxide; therefore, it is important to understand the amount and composition of SOC in terrestrial ecosystems, the spatial variation in SOC, and the underlying mechanisms that stabilize SOC. In this study, density fractionation and acid hydrolysis were used to assess the spatial variation in SOC, the heavy fraction of organic carbon (HFOC), and the resistant organic carbon (ROC) in soils of the southern Hulunbeier region, northeastern China, and to identify the major factors that contribute to this variation. The results showed that as the contents of clay and silt particles (0--50 μm) increased, both methylene blue (MB) adsorption by soil minerals and microaggregate contents increased in the 0--20 and 20--40 cm soil layers (P < 0.05). Although varying with vegetation types, SOC, HFOC, and ROC contents increased significantly with the content of clay and silt particles, MB adsorption by soil minerals, and microaggregate content (P < 0.05), suggesting that soil texture, the MB adsorption by soil minerals and microaggregate abundance might be important factors influencing the spatial heterogeneity of carbon contents in soils of the southern Hulunbeier region.     

种植模式对核桃幼林土壤微团聚体组成与分形维数的影响

【目的】筛选核桃林下适宜的复合种植模式,并分析其对培肥土壤和提高林地经济效益的影响。【方法】在四川省雅安市大渡河干热河谷区,于核桃林下设置了4种种植模式,即核桃+甘蓝+甘蓝(HGG)、核桃+甘蓝+马铃薯(HGM)、核桃+白菜+大豆(HBD)、核桃纯林(HCK),并以农地(玉米+马铃薯,NCK)为对照,测定不同种植模式林下土壤的微团聚体组成和分形维数(D)、物理性质、养分含量和微生物数量,并探讨D和特征微团聚体组成比例(PCM)、微团聚体各粒级含量及土壤理化性质、微生物数量的关系。【结果】与NCK相比,4种复合种植模式林下土壤中的粒径0.25 mm土壤微团聚体含量均显著增加,粒径0.02 mm土壤微团聚体含量显著降低;不同种植模式林下土壤的D和PCM值由大到小依次表现为NCKHCKHBDHGMHGG。与NCK相比,HGG、HGM、HBD、HCK种植模式的土壤自然含水量及非毛管孔隙度、毛管孔隙度和总孔隙度分别增加12.2%～50.4%,2.4%～14.8%,2.8%～29.1%和2.6%～23.1%,体积质量降低4.6%～17.6%;有机质、全氮和碱解氮含量分别增加5.1%～14.9%,3.9%～12.5%和25.1%～112.5%;细菌、放线菌、真菌和总微生物数量分别增加21.4%～54.3%,19.2%～58.1%,17.8%～58.4%和21.2%～54.6%。相关分析表明,D和PCM值与土壤自然含水量、孔隙度、养分含量和微生物数量均呈极显著负相关,与体积质量呈极显著正相关。【结论】大渡河干热河谷区采用"核桃+甘蓝+甘蓝"种植模式,能有效改善核桃幼林林下土壤微团聚体组成,降低土壤D和PCM,提高土壤养分含量和微生物数量,是该地区最佳的核桃林下复合种植模式。     

红壤恢复林地微团聚体形成与稳定的影响机制研究进展

微团聚体是土壤团粒结构的基本组成单元,较大团聚体具有更强的稳定性,其形成与稳定对于土壤有机碳的长期吸存起着决定性作用。目前关于微团聚体形成与稳定性的研究多专注于农业土壤,红壤侵蚀地植被恢复后土壤团聚体稳定性、有机碳分布及微生物群落特征研究也主要集中在大团聚体上,而土壤微团聚体的动态变化及其主要影响因素尚不明确,对于其内在机制更缺乏了解。通过总结土壤微团聚体的形成过程及稳定性,综述了凋落物、根系和菌根对土壤微团聚体形成与稳定的影响,阐述了土壤微团聚体内微生物群落、化学结合态有机碳及有机碳结构是土壤有机碳稳定的重要机制,并提出了未来微团聚体研究方向,以期揭示红壤侵蚀退化地森林恢复过程中微团聚体形成和稳定的生物化学机制,从而为深入阐明有机质—土壤团聚结构—微生物—化学耦合作用和森林土壤碳吸存机制提供参考。     

土壤有机培肥对微团聚体组成及其碳,氮分布和活性的影响

本文通过田间试验研究了土壤有机培肥(ISFOM)对棕壤和黑土微团聚体组成及其碳、氮分布和活性的影响。并对本文所用的制备微团聚体的方法进行了评价。结果表明:①棕壤和黑土的优势粒级和次优势粒级分别为10～50μm和50～250μm,C、N分布一般为10～50μm>50～250μm≥0～5μm>5～10μm。②随粒级的增加,棕壤的碳活性(C_A)和氮活性(N_A)提高。③ISFOM后一般使50～250μm粒级含量、各级微团聚体的C_A和N_A增加。④在没有更好的方法以前,用沉降虹吸法制备微团聚体是可行的。     

不同土地利用方式对棕壤及其各级微团聚体中有机磷组分的影响

采用Bowman-cole有机磷分级法研究了典型棕壤及其各级微团聚体中有机磷组分在林地、柞树林地、耕地3种土地利用方式下的变化情况.结果表明,有机磷总量在3种利用方式下表现为林地＞耕地＞柞树林地,有机磷占全磷的比例却为林地＞柞树林地＞耕地.土地利用方式对棕壤活性有机磷和高稳性有机磷的含量及有效性影响甚微,开垦为耕地可保持中活性有机磷含量并提高其有效性,开垦为柞树林地则显著降低其含量,耕垦可显著降低耕地中中稳性有机磷含量及其比例.耕垦可以降低有机磷总量在各级微团聚体中的含量,且降低率随粒级的增大而增加,提高50～250 μm粒级活性有机磷的有效性,降低＜10 μm和50～250 μm粒级中的中活性有机磷含量,开垦为耕地有利于＜10 μm粒级中其有效性的保持,可显著降低10～50 μm和50～250 μm粒级中稳性有机磷含量,尤其显著降低耕地中其占有机磷的比例,开垦为柞树林有地有利于高稳性有机磷在各粒级中的分解转化,开垦为耕地的却有利于高稳性有机磷在10～50 μm和50～250 μm粒级中累集.     

黄土丘陵区不同恢复年限草地土壤微团粒分形特征

运用分形理论研究黄土丘陵区不同恢复年限草地土壤微团粒的粒径组成、分形维数特征及与土壤理化性质关系,使分形学在土壤微团粒性状与土壤肥力特征研究中得到进一步应用,并为评价草地生态系统土壤特征及生态恢复提供新方法。结果表明:表土层分形维数随植被恢复年限的增加而减少;剖面土壤沙粒含量越高,微团粒分形维数越低,粘粒规律相反,而粉粒与分形维数相关性不显著;土壤质地由粗到细使得分形维数由小到大变化;分形维数也可有效地表征不同植被恢复年限的草地土壤结构和养分的变化趋势;分形维数与土壤容重、非活性孔度、全磷、速效钾及氨态氮之间存在正相关性,与土壤活性孔度、孔隙比、有机质、全氮、碱解氮及硝态氮表现出负相关。     

Long-term straw return influenced ammonium ion retention at the soil aggregate scale in an Anthrosol with rice-wheat rotations in China

Soil aggregates are an important controlling factor for the physico-chemical and biological processes such as ammonium (NH₄⁺) retention. Straw return to the field is increasingly recommended to promote soil carbon (C) sequestration and improve crop yields. However, the effects of straw return on NH₄⁺ retention at soil aggregate level in agricultural soils have seldom been investigated. This study aimed to evaluate the influences of long-term straw return on NH₄⁺ adsorption and fixation in microaggregates (<0.25 mm) with or without soil organic carbon (SOC) oxidization. Soil samples were collected from plots of three treatments, i.e., no fertilizer (CK), inorganic NPK fertilizers (NPK), and inorganic NPK fertilizers with rice straw return (NPKS), from a 20-year-old field trial with rice-wheat rotations in Taihu Lake Region, China. Soil aggregates were separated using wet-sieving method. The SOC of microaggregates was oxidized by H₂O₂. The results showed that long-term straw return significantly increased SOC and NH₄⁺ adsorption, but inhibited NH₄⁺ fixation in microaggregates. NH₄⁺ adsorption potential and strength - obtained from adsorption isotherms - increased, but NH₄⁺ fixation decreased along with increasing SOC in microaggregates, indicating the important role of SOC in NH₄⁺ adsorption and fixation. This was verified by the SOC oxidization test that showed a relative decrease in NH₄⁺ adsorption potential for the NPKS treatment and an increase in NH₄⁺ fixation in all three treatments. Therefore, long-term straw return influences NH₄⁺ adsorption and fixation by enhancing SOC content and could improve N availability for crop uptake and minimize applied N fertilizer losses in rice-wheat cropping systems.