农田生态系统不同土地利用方式与管理措施对土壤质量的影响

于2005年在北京市延怀盆地选择农田生态系统中的玉米地、大豆地两种传统土地利用方式,以及近10～20 年由传统农业用地转化而来的蔬菜和果园用地,研究农田生态系统不同土地利用方式与管理措施对土壤质量的影响.结果表明,菜地、果园和高投入玉米地土壤总有机碳(SOC)、全氮(TN)和全磷(TP)含量明显高于中、低投入玉米地和大豆地土壤.在各种土地利用类型中,SOC、TN和TP的变化范围分别为7.67～10.00 g·kg^-1、0.75～1.12 g·kg^-1和0.63～1.00 g·kg^-1;菜地土壤有效磷(AP)含量和电导率(EC)显著高于其他土壤,不同农田生态系统土壤物理性状差异不明显.果园和菜地土壤质量指数分别为0.525和0.503,高于传统农田玉米和大豆土壤(0.417～0.494).菜地土壤的养分有效性最高,水分有效性和根系适宜性低于果园土壤,应注意菜地非点源污染的潜在风险.在传统农业用地中应采取培肥地力等方式提高土壤质量.     

黄土塬区不同土地利用方式土壤水分消耗与补给变化特征

对黄土塬区不同土地利用方式下2012年3—10月7龄果园(挂果初期)、17龄果园(盛果期)、小麦地、玉米地土壤水文状况进行分析,结果显示,0—600 cm试验土层7龄果园土壤贮水量最高,其次为玉米地、小麦地,17龄果园最低,且不同土地利用方式下贮水量随着降水量的变化而上下波动,但其变化滞后于降水。不同土地利用方式均表现为随土壤深度增加土壤含水量变异程度减弱的特征,且其土壤剖面的水分含量变化存在季节变异。农田和7龄果园中不存在土壤干燥化现象,而17龄果园土壤剖面存在较厚的干燥化土层,其分布深度为320—600 cm。不同的土地利用方式的土壤水分的消耗和补充深度有较大差异,17龄果园消耗深度为500 cm,补充深度为200 cm;7龄果园、玉米地和小麦地消耗深度分别为200、300 cm和300 cm,且补充深度均超过了测定的土壤深度,大于600 cm。     

黄土丘陵沟壑区小流域土壤有机碳空间分布及其影响因素

研究局域尺度土壤有机碳空间分布特征,对准确估算大尺度土壤碳库储量和变化具有重要意义。以黄土丘陵沟壑区典型小流域为对象,采集0-10、10-20、20-40、40-60、60-80、80-100cm土层中(898个土壤样品),采用多元线性逐步回归和地理信息系统(GIS)相结合方法,分析了地形(峁顶、峁坡、沟底)、土地利用(农田、果园、川坝地、草地、灌木林、乔木林)等作用下,小流域不同深度土壤有机碳含量的空间分布特征。结果表明:地形因素不仅对表层(0-10cm)土壤有机碳含量空间分布差异影响显著,而且对深层(40-100cm)影响也显著,且空间格局图上40-100cm可以清晰地看地沟底与峁顶和峁坡显著差异。在0-10cm土层,峁顶以中值斑块(50%)和低值斑块(48%)为主;峁坡以中值斑块(62%)为主,其次是低值斑块(22%);沟底中值斑块占70%,其次为低值斑块(23%)。40-100cm均为低值斑块,沟底低值绿色斑块占34%,远高于峁坡(8%)和峁顶(13%)。土地利用对表层(0-40cm)有机碳含量影响显著,对40-100cm土层无影响。在0-10cm土层,乔木林、灌木林、草地上高值斑块分别占18%、47%、10%,川坝地、农田和果园没有高值斑块,中值斑块分别占80%、53%、85%、73%、39%、23%。10-40cm土层,乔木林、灌木林、草地、川坝地、农田和果园中值斑块分别占21%、46%、22%、19%、5%、4%。但在40-100cm土层,各土地利用下有机碳均处于低值斑块区。坡向上0-100cm各层土壤有机碳含量半阴坡(北部、东北、东部)最高,半阳坡(西部、西南、南部)含量较低。     

黄土高原沟壑区王东沟小流域土壤有机碳空间分布

地貌和土地利用是影响土壤有机碳(Soil organic carbon,SOC)空间变异的重要因素。以黄土高原沟壑区王东沟小流域(8.3 km2)为对象,在考虑地貌单元和土地利用影响的基础上,采集0—20cm样品448个,0—200cm样品33个。研究了地貌单元(塬面、塬坡和沟道)和土地利用方式对SOC含量的影响。结果表明,地貌单元和土地利用对小流域表层和深层SOC的含量分布影响都有显著差异。0—20cm土层的SOC含量,沟道塬面塬坡;塬面表层SOC含量的变化平缓;塬坡和沟道SOC变异大于塬面。0—200cm土层SOC三地貌单元差异达极显著水平(P99.9%),塬面SOC含量最高(5.37g kg-1),塬坡(3.06 gkg-1)最低。不同地貌单元条件下土地利用方式对表层和剖面SOC含量分布的影响也存在明显差异。塬面区,人工草地SOC含量亦明显高于农田和果园,但仅40cm以上土层SOC达到显著差异。在塬坡上,不同土地利用类型间,发生显著差异深度达到140cm。沟道内,林草两种土地利用类型间的SOC含量无显著差异。在估算该地区SOC密度和储量时,需要充分考虑地貌单元和土地利用方式的影响。     

黄土丘陵区小流域尺度土壤有机碳密度及储量

通过对上黄小流域不同土地利用方式下114个样点的采样分析,结合地统计学原理对小流域不同土层土壤有机碳密度的空间变异程度进行研究。研究表明,除表层土壤有机碳密度的空间变异程度较弱外,其余两层均属于中等强度变异。并呈现东部天然草地分布区与中部带状灌丛林地分布区空间变异程度较强的分布特点。不同土层深度和土地利用方式下土壤有机碳密度存在明显差异,土壤有机碳含量随着土层深度的增加而逐渐减小,有机碳密度则表现为10-30cm最高,30-60cm其次,0-10cm最低。不同土地利用方式下,有机碳密度表现为:天然草地 > 果园 > 灌丛林地 > 河滩、河台地 > 撂荒地 > 人工草地 > 耕地。以土地利用方式为基本单元,对上黄小流域土壤有机碳储量进行估算。结果表明,上黄小流域土壤有机碳总储量为46527.12t,其中,灌丛林地(22052.81t)和天然草地(14573.14t)的储量最高,占总储量的78.72%。     

汉中盆地秸秆还田撂荒和林地对土壤碳的影响

农业活动是温室气体重要的排放源,土壤碳库[土壤有机碳(SOC)和无机碳(SIC)]稍微变化会对大气CO_2产生很大影响。汉中盆地是南水北调的重要水源涵养地,在该区域秸秆还田、农田撂荒和林地是目前常见土地利用方式,但缺乏不同利用方式对SIC和SOC影响的研究。该研究采集该区域典型样地土壤,用滴定法和有机碳分析仪分别测定其SIC和SOC含量,研究3种土地利用方式对土壤碳库的影响。结果表明:SOC随土层深度最为敏感的是农田,其次是撂荒地,林地最不敏感。0~140 cm土层SOC碳密度,林地最大,是撂荒田的2.26倍,农田是撂荒田的1.37倍。深土层SOC碳密度,林地是撂荒田的2.44倍,农田是撂荒田的1.07倍。撂荒田的SIC密度最大,其次是农田,林地的SIC碳密度最低。在0~140 cm土层中,SIC密度依次为12.37、11.68和9.77 kg·m~2,撂荒田的SIC碳密度是林地的1.27倍。随着我国农村发展,土地利用管理出现新的方式,今后在估算土地利用管理方式对土壤碳影响时还需要综合考虑SOC和SIC。     

Depth‐dependent soil organic carbon dynamics of croplands across the Chengdu Plain of China from the 1980s to the 2010s

Agricultural soils have tremendous potential to sequester soil organic carbon (SOC) and mitigate global climate change. However, agricultural land use has a profound impact on SOC dynamics, and few studies have explored how agricultural land use combined with soil conditions affect SOC changes throughout the soil profile. Based on a paired soil resampling campaign in the 1980s and 2010s, this study investigated the SOC changes of the soil profile caused by agricultural land use and the correlations with parent material and topography across the Chengdu Plain of China. The results showed that the SOC content increased by 3.78 g C/kg in the topsoil (0–20 cm), but decreased in the 20–40 cm and 40–60 cm soil layers by 0.90 and 1.26 g C/kg respectively. SOC increases in topsoil were observed for all types of agricultural land. Afforestation on former agricultural land also caused SOC decreases in the 20–60 cm soil layers, while SOC decreases only occurred in the 40–60 cm soil layer for agricultural land using a traditional crop rotation (i.e. traditional rice–wheat/rapeseed rotation) and with rice–vegetable rotations converted from the traditional rotations. For each agricultural land use, SOC decreases in deep soils only occurred in high relief areas and in soils formed from Q4 (Quaternary Holocene) grey‐brown alluvium and Q4 grey alluvium that had a relatively low soil bulk density and clay content. The results indicated that SOC change caused by agricultural land use was depth dependent and that the effects of agricultural land use on soil profile SOC dynamics varied with soil characteristics and topography. Subsoil SOC decreases were more likely to occur in high relief areas and in soils with low soil bulk density and low clay content.     

城市沿江土地覆被变化对土壤有机碳和轻组有机碳的影响

采用Vario EL III型元素分析仪,2007年7月分析了福州城市沿江3种土地覆被类型（芦苇湿地以及草坪和片林）土壤有机碳（SOC）与轻组有机碳（LFOC）的垂直分布特征.结果表明：3种土地覆被类型SOC和LFOC含量均表现为在土壤表层富集并向下层递减的趋势,且人工绿地在土壤剖面（0～60 cm）不同层次的SOC和LFOC含量均显著高于沿江芦苇湿地,其中,草坪0～20 cm土层的SOC含量显著高于片林;沿江芦苇湿地转为草坪和片林后,其SOC储量分别增加了94.8%和72.0%,LFOC储量分别增加了225%和93%;城市沿江湿地转变为城市人工绿地后,因植物物种、密度以及周期性人工管理等变化,使土壤质量得以改善、SOC和LFOC储量增加,其中LFOC对土地覆被变化的响应较SOC敏感,以表层(0～20 cm)土壤LFOC受到土地利用/覆地变化的影响最大.     

设施菜地重金属的剖面分布特征

以山东省寿光市种植1～12年的蔬菜大棚及相邻的小麦地为对象,研究了设施菜地中As、Cd、Cu、Zn、Cr、Ni 6种重金属在土壤剖面中的分布特征.结果表明：在0～150 cm土层内,随着土层深度的增加,设施菜地与小麦地中6种重金属含量均呈下降趋势;与小麦地相比,相同土层设施菜地中6种重金属的含量均明显较高,设施菜地0～20 cm土层中As、Cd、Cu、Zn、Cr、Ni的含量分别比小麦地相同土层高出35.0%、146.2%、65.6%、36.4%、21.5%和14.0%,120～150 cm土层分别高出10.6%、.5%、19.4%、20.2%、15.2%和9.3%,20～120 cm各土层中的含量亦高于小麦地.设施菜地0～20 cm土层中,Cd、Cu、Zn含量与种植年限呈显著正相关,随着种植年限的增加,其累积速率分别为0.027、1.153和2.830 mg·kg^-1·a^-1;设施菜地中6种重金属的含量与土壤有机碳、全氮含量呈正相关,除Ni和As外的4种重金属含量亦与土壤全磷含量呈极显著相关,有机肥等的施用可能在一定程度上导致设施菜地中重金属的累积.     

黄土丘陵区不同土地利用类型土壤水分变化特征

土壤水分是制约黄土丘陵区生态建设和土地可持续利用的关键因子,认识不同土地利用类型的土壤水分状况对该地区植被恢复和土地资源的有效利用具有重要的理论和实际意义.本研究采用EC-5土壤水分传感器,对黄土高原园则沟流域坡耕地、梯田、枣园和草地生长季内(5—10月)0~160 cm土壤剖面含水量进行连续监测,探讨这4种典型土地利用类型的土壤水分变化特征.结果表明:在降水常态年和干旱年,不同土地利用方式土壤水分的季节变化、蓄水特征及垂直分布均存在差异.在2015年干旱年,梯田表现出良好的蓄水保墒效果,0~60 cm土层生长季平均土壤含水量分别比坡耕地、枣园和草地高2.6%、4.2%、1.8%(P<0.05),0~160 cm土层储水量分别比坡耕地、枣园和草地高43.90、32.08、18.69 mm.在2014年常态年,枣园0~60 cm土层生长季平均土壤含水量分别比坡耕地、梯田和草地低2.9%、3.8%、4.5%(P<0.05);在干旱年,0~160 cm土层有效水储量仅占土壤总储水量的35.0%.不同土地利用方式下均是表层(0~20 cm)与中层(20~100 cm)土壤水分的灰色关联度较大,且土壤水分变化态势的相似程度表现为梯田>草地>坡耕地>枣园.对于试验区内的坡耕地,可考虑改造为梯田,以提高雨水资源的有效利用、促进生态农业建设;而针对黄土丘陵区旱作枣园土壤缺水严重的现象,需采取适当水分管理措施以降低枣树自身耗水和其他无效耗水,实现枣园可持续发展.     

不同土地利用类型下氮、磷在土壤剖面中的分布特征

在北京市东南郊大兴区采取了44处0～20cm,20～40cm,40～60cm,60～80cm,80～100cm5个不同深度的土壤剖面样品。按土地利用类型,采样点可分为农田、菜地、果园、林地、草地。土壤剖面中,由表层向深层,pH值升高,有机质、速效磷、全磷、硝态氮、全氮降低,且在20～40cm处有较大变化。表层土壤受土地利用影响,不同土地利用类型的土壤性质差别较大,尤以菜地土壤,pH为8.01低于其他类型土壤的平均值8.27,有机质、速效磷、全磷、硝态氮、全氮都高于其他类型的土壤,分别是其他类型土壤的110%～198%,355%～1629%,162%～224%,724%～1540%,130%～248%,速效磷和硝态氮远高于其他土壤。深层土壤性质差异不大,各项土壤性质差异随深度而变小,但菜地80～100cm处,硝态氮含量为18.8mgkg-1,是同深度其他类型土壤的175%～389%。土壤中硝态氮的积累情况,菜地>农田、果园、林地>草地。磷的积累与氮不同,速效磷在0～20cm大量积累,不同类型的土壤,速效磷积累差异显著,在40～60cm处,菜地速效磷含量是其他利用类型土壤的161%～602%;在80～100cm处,不同利用类型的土壤中速效磷无显著性差异。这一情况表明,菜地的过量施用氮、磷肥导致了土壤中的磷和氮大量积累,并以速效磷、硝态氮的形态向下淋溶并在深层土壤中积累。硝态氮在80～100cm的积累仍相当严重,有继续向下淋溶的可能,速效磷的淋溶在80～100cm处已较为微弱,其淋溶过程主要在0～60cm处。对速效磷和硝态氮的累积进行多元线性回归分析,发现速效磷与全磷含量有着良好的线性相关性,而与有机质和全氮含量关系不大。硝态氮则受土壤中pH、有机质和全氮3因素的共同影响。     

Long‐term no‐till and stover retention each decrease the global warming potential of irrigated continuous corn

Over the last 50 years, the most increase in cultivated land area globally has been due to a doubling of irrigated land. Long‐term agronomic management impacts on soil organic carbon (SOC) stocks, soil greenhouse gas (GHG) emissions, and global warming potential (GWP) in irrigated systems, however, remain relatively unknown. Here, residue and tillage management effects were quantified by measuring soil nitrous oxide (N₂O) and methane (CH₄) fluxes and SOC changes (ΔSOC) at a long‐term, irrigated continuous corn (Zea mays L.) system in eastern Nebraska, United States. Management treatments began in 2002, and measured treatments included no or high stover removal (0 or 6.8 Mg DM ha^?1 yr^?1, respectively) under no‐till (NT) or conventional disk tillage (CT) with full irrigation (n = 4). Soil N₂O and CH₄ fluxes were measured for five crop‐years (2011–2015), and ΔSOC was determined on an equivalent mass basis to ~30 cm soil depth. Both area‐ and yield‐scaled soil N₂O emissions were greater with stover retention compared to removal and for CT compared to NT, with no interaction between stover and tillage practices. Methane comprised <1% of total emissions, with NT being CH₄ neutral and CT a CH₄ source. Surface SOC decreased with stover removal and with CT after 14 years of management. When ΔSOC, soil GHG emissions, and agronomic energy usage were used to calculate system GWP, all management systems were net GHG sources. Conservation practices (NT, stover retention) each decreased system GWP compared to conventional practices (CT, stover removal), but pairing conservation practices conferred no additional mitigation benefit. Although cropping system, management equipment/timing/history, soil type, location, weather, and the depth to which ΔSOC is measured affect the GWP outcomes of irrigated systems at large, this long‐term irrigated study provides valuable empirical evidence of how management decisions can impact soil GHG emissions and surface SOC stocks.     

基于景观尺度下的鄱阳湖湿地浅层土有机碳的空间特征

湿地土壤有机碳研究是全球碳循环研究的基础性工作, 对于准确评估湿地固碳增汇和全球温室气体减排都具有重要意义。以鄱阳湖国家自然保护区为研究区域, 选择六种景观类型(湿地洲滩景观包括受人工控制的碟形湖泊常湖池、半人工控制的碟形湖泊蚌湖、不受人工控制的洲滩前缘泗洲头以及岗地景观包括林地、田地和菜地), 湿地洲滩景观在各1 m高程(泗洲头和蚌湖采样高程10-17 m, 常湖池采样高程12-17 m)内的浅土壤采取3个土壤样品, 岗地景观浅层土壤各采取3个土壤样品, 分析浅层土壤有机碳含量。结果表明, 鄱阳湖不同景观类型的浅层土壤有机碳含量差异性显著。湿地洲滩浅层土壤(特别是0-10 cm土层)的有机碳随高程梯度变化呈现倒U型变化, 即低海拔与高海拔土壤有机碳的含量较中海拔土壤有机碳的含量低, 泗洲头洲滩土层0-10 cm的有机碳含量最高值出现在13-14 m高程, 其中0-10 cm土层的土壤有机碳含量变化值为1.56-12.29 g·kg-1, 10-20 cm土层的土壤有机碳含量变化值为0.96-8.19 g·kg-1; 蚌湖洲滩土层0-10 cm的有机碳含量最高值出现在14-15 m高程, 其中0-10 cm土层的土壤有机碳含量变化值为6.36-23.32 g·kg-1, 10-20 cm土层的土壤有机碳含量变化值为4.14-8.88 g·kg-1; 常湖池洲滩土层0-10 cm的有机碳含量最高值出现在16-17 m高程, 其中0-10 cm土层的土壤有机碳含量变化值为6.51-18.91 g·kg-1, 10-20 cm土层的土壤有机碳含量变化值为3.83-10.05 g·kg-1。岗地浅层土壤有机碳(特别是0-10 cm土层)田地的土壤有机碳含量最高, 菜地土壤有机碳含量最低。比较六种景观类型的浅层土壤有机碳含量, 泗洲头洲滩浅层土壤有机碳含量最低, 蚌湖洲滩浅层土壤有机碳含量最高。六种景观类型的浅层土壤有机碳含量呈现一致的现象是土层0-10 cm的机碳含量明显高于土层10-20 cm的有机碳含量, 说明鄱阳湖国家自然保护区内土壤有机碳含量主要富集在土壤浅层的特征。土壤pH值对湿地土壤有机碳呈显著负相关性, 而土壤含水量、地上部分生物量与土壤有机碳呈显著正相关性。     

Assessment of land use changes on woody cover and landscape fragmentation in the Orinoco savannas using fractal distributions

The effect of land use changes on the woody cover and patchiness of the Orinoco lowlands was analyzed from 1951 to 1997 by using a stretched exponential model in terms of the patch size distribution. We selected five production systems on the basis of the following components: policy option, technology and environment. They are: (a) high-input pasture in deep soil (DL-HIGraz), (b) low-input cropping in deep soil (DH-LOCrop), (c) high-input cropping in deep soil (DH-HICrop), (d) low-input cropping in shallow soil (SL-LOCrop) and (e) extensive cattle grazing in shallow soil (SL-LOGraz). For comparison, stands with similar soil depth and woody density (DL-Fallow, DH-Fallow and SL-Fallow) were selected at the protected Biological Reserve in the Calabozo region. Results indicate that the distribution of the patches was described by the stretched exponential distribution model with c as the exponent distribution. The magnitude of c reflected the effect of land use changes over time. Thus, the parameter c for human impacted stands was higher than that for the fallow stands. The stretched exponential model implies that the human impact had a multiscalar effect on the Orinoco mosaic, in terms of the multiplicative processes. There is a generic mechanism exhibiting an anomalous distribution of the patches such as has been proposed for physical systems. Therefore, the number of generation of the multiplicative processes (i.e. inverse of c) for impacted stands was lower than that in the fallow stands. As the time from fallow establishment proceeded, there was a tendency to patch re-organization by biotic effects.     

不同蔬菜种植方式对土壤固碳速率的影响

近年来蔬菜地面积快速增加已成为我国农田土壤碳库变化的重要驱动因素,研究蔬菜种植方式对农田土壤固碳影响,对于揭示我国农田土壤碳库变化具有重要意义。通过实地调查与采样分析,研究了山东省苍山县3种蔬菜种植方式(大田种植、季节性大棚和长年性大棚种植)对农田土壤固碳速率影响及其随种植时间的变化规律。结果表明,3种种植方式下蔬菜地土壤有机碳含量均随种植时间的增加而增加;长年性大棚、季节性大棚和大田种植方式下0—100 cm土层土壤平均固碳速率分别达到1.44、2.73、1.60 Mg.hm-2.a-1;表层土壤(0—20 cm)平均固碳速率依次为0.64 Mg.hm-2.a-1、0.36 Mg.hm-2.a-1、0.20Mg.hm-2.a-1,3种蔬菜种植方式的土壤固碳速率存在显著差异。同样为蔬菜地,选择合理种植方式是提高农田土壤固碳速率的重要途径。     

Soil C,N, P and Its Stratification Ratio Affected by Artificial Vegetation in Subsoil,Loess Plateau China

Artificial vegetation restoration can induce variations in accumulation and distribution of soil carbon (C), nitrogen (N) and phosphorus (P). However, little is known about variations in soil C, N and P nutrient fraction stratification following artificial vegetation in Loess Plateau China. Based on the hypothesis that re-vegetated can improve soil quality and stratification ratios (SR) can be used as an indicator to evaluate soil quality. This study measured contents and storages of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and their SRs in topsoil (0–20 cm) and subsoil (20–60 cm) in three 30-year re-vegetated lands that had been converted from arable land (Robinia pseudoacacia L., Caragana Korshinskii Kom. and abandoned cropland with low interferences and few management measures) and one slope cropland (SC) as a control for three soil profiles(0–20 cm, 20–40 cm and 40–60 cm) from June 2009 to June 2013. The results showed that the contents and storages of SOC, TN and TP in re-vegetated land were significantly higher than those in the SC in both topsoil and subsoil. The storages of SOC, TN and TP in the topsoil (0–20 cm) of the re-vegetated lands increased by 16.2%-26.4%, 12.7%-28.4% and 16.5%-20.9%, respectively, and increased by smaller but significant amounts in subsoil from 2009 to 2013. The SRs for SOC, TN and TP in the re-vegetated lands were mostly >2 (either for 0–20:20–40 cm or 0–20:40–60 cm) and greater than that in the SC. The SRs showed an increasing trend with increasing restoration age. The results also showed that the land use type and soil depth were the most influential factors for the SRs and storages, and the SRs of SOC and TN had significantly positive correlations with their storages. The SRs were concluded to be a good indicator for evaluating the soil quality, which can be significantly enhanced through vegetation restoration. Moreover, vegetation restoration can significantly enhance SOC, TN and TP accumulation in both topsoil and subsoil.     

Carbon Sequestration in Reclaimed Minesoils

Minesoils are drastically influenced by anthropogenic activities. They are characterized by low soil organic matter (SOM) content, low fertility, and poor physicochemical and biological properties, limiting their quality, capability, and functions. Reclamation of these soils has potential for resequestering some of the C lost and mitigating CO₂ emissions. Soil organic carbon (SOC) sequestration rates in minesoils are high in the first 20 to 30 years after reclamation in the top 15 cm soil depth. In general, higher rates of SOC sequestration are observed for minesoils under pasture and grassland management than under forest land use. Observed rates of SOC sequestration are 0.3 to 1.85 Mg C ha^{? 1} yr^{? 1} for pastures and rangelands, and 0.2 to 1.64 Mg C ha^{? 1} yr^{? 1} for forest land use. Proper reclamation and postreclamation management may enhance SOC sequestration and add to the economic value of the mined sites. Management practices that may enhance SOC sequestration include increasing vegetative cover by deep-rooted perennial vegetation and afforestation, improving soil fertility, and alleviation of physical, chemical and biological limitations by fertilizers and soil amendments such as biosolids, manure, coal combustion by-products, and mulches. Soil and water conservation are important to SOC sequestration. The potential of SOC sequestration in minesoils of the US is estimated to be 1.28 Tg C yr^?1, compared to the emissions from coal combustion of 506 Tg C yr^{? 1}.     

滇南喀斯特断陷盆地土地利用方式对土壤有机碳及其活性组分的影响

土地利用方式是影响土壤有机碳库的重要因素,为探究喀斯特断陷盆地土壤有机碳库对土地利用方式及环境因素的响应,以滇南喀斯特地区5种典型土地利用方式(耕地、草地、灌丛、人工林、天然林)为研究对象,分析不同土地利用方式土壤有机碳(SOC)及活性有机碳(LOC)组分,即可溶性有机碳(DOC)、易氧化性有机碳(EOC)及微生物量碳(MBC)的含量、储量及分配比例在土壤垂直剖面(0-60 cm)的变化特征。结果表明：5种土地利用方式的SOC含量随土层深度的增加逐渐降低,其储量依次为灌丛(191.77 t/hm²)、草地(166.86 t/hm²)、耕地(142.47 t/hm²)、人工林(134.31 t/hm²)和天然林(102.62 t/hm²);EOC和MBC的平均含量及储量均以草地及灌丛最高、人工林及天然林次之,二者在土壤垂直剖面上与SOC含量的变化特征一致,但EOC和MBC含量在土层间的下降幅度大于SOC;土地利用方式和土层深度对DOC无显著影响(P>0.05);活性有机碳的分配比例受土地利用方式及土层深度的显著影响(P<0.01),其中人工林的EOC/SOC和MBC/SOC显著低于草地、灌丛及天然林。通径分析指出SOC和EOC主要受C/P比、全磷、砂粒和交换性钙的影响,砂粒和C/P比是影响MBC的主要因子。研究阐明在喀斯特断陷盆地地区EOC和MBC对土地利用方式的响应比SOC更敏感。另外,今后在土壤碳库的研究中应更多关注土壤磷和物理结构对其的影响。     

Smallholder farms have and can store more carbon than previously estimated

Increasing soil organic carbon (SOC) stocks is increasingly targeted as a key strategy in climate change mitigation and improved ecosystem resiliency. Agricultural land, a dominant global land use, provides substantial challenges and opportunities for global carbon sequestration. Despite this, global estimates of soil carbon sequestration potential often exclude agricultural land and estimates are coarse for regions in the Global South. To address these discrepancies and improve estimates, we develop a hybrid, data-augmented database approach to better estimate the magnitude of SOC sequestration potential of agricultural soils. With high-resolution (30 m) soil maps of Africa developed by the International Soils Database (iSDA) and Malawi as a case study, we create a national adjustment using site-specific soil data retrieved from 1160 agricultural fields. We use a benchmark approach to estimate the amount of SOC Malawian agricultural soils can sequester, accounting for edaphic and climatic conditions, and calculate the resulting carbon gap. Field measurements of SOC stocks and sequestration potentials were consistently larger than iSDA predictions, with an average carbon gap of 4.42 ± 0.23 Mg C ha⁻¹ to a depth of 20 cm, with some areas exceeding 10 Mg C ha⁻¹. Augmenting iSDA predictions with field data also improved sensitivity to identify areas with high SOC sequestration potential by 6%—areas that may benefit from improved management practices. Overall, we estimate that 6.8 million ha of surface soil suitable for agriculture in Malawi has the potential to store 274 ± 14 Tg SOC. Our approach illustrates how ground truthing efforts remain essential to reduce errors in continent-wide soil carbon predictions for local and regional use. This work begins efforts needed across regions to develop soil carbon benchmarks that inform policies and identify high-impact areas in the effort to increase SOC globally.     

基于最小限制水分范围评价不同耕作方式对土壤有机碳的影响

以2009年吉林省德惠市中层黑土上进行了8a的田间定位试验小区土壤为研究对象,对免耕和秋翻两种耕作方式及玉米-大豆轮作和玉米连作两种种植方式下耕层有机碳进行分析,分别采用加权平均和分层两种方法计算最小限制水分范围(LLWR),用其评价不同耕作方式对土壤有机碳的影响.结果表明,免耕在玉米-大豆轮作和玉米连作下0-5 cm土壤有机碳含量分别比秋翻增加了15.2％和11.5％ (P＜0.05).采用加权平均法计算的LLWR值为0.148-0.166 cm3/cm3,不同耕作方式下玉米-大豆轮作的LLWR高于玉米连作且在两种种植方式下均表现出免耕小于秋翻的特点;利用分层法计算得到的LLWR值介于0.130-0.173 cm3/cm3之间,玉米-大豆轮作和玉米连作下免耕0-5 cm LLWR均显著小于秋翻,而5-30 cm LLWR数值免耕大于秋翻(P＞0.05);玉米-大豆轮作下0-30 cm各层LLWR均高于玉米连作.由于LLWR可以评价不同耕作方式对土壤有机碳的影响,因此采用加权平均法计算的LLWR可以客观的反映不同耕作处理尤其是种植方式对土壤有机碳的影响;而采用分层法计算的LLWR则更清晰的刻画了土壤表层与亚表层固碳能力的差异.