A rapid microwave digestion method for colorimetric measurement of soil organic carbon

Abstract

Soil organic matter is an active component of agroecosystems. Rapid and precise measurement of organic carbon (C_org) is essential to monitor changes in organic matter and soil quality. A new semi‐micro wet digestion method for the determination of C_org was developed using rapid microwave energy applied at 500 J mL^‐1 digestion mixture to enhance oxidation of C_org by K₂Cr₂O₇and conc. H₂SO₄. This proposed method and three existing methods of soil C determination were compared with the LECO dry combustion carbon analyzer. The r² value for the proposed microwave method regressed against LECO C was 0.9913. The recovery of C_org by the rapid microwave digestion method for spectrophotometric measurement was 91.7±1.2% (conversion factor 1.09) of C measured by the LECO dry combustion method. Compared to the traditional Walkley‐Black's method, the proposed spectrophotometric with microwave digestion method was rapid and more precise, used smaller reagent volumes, and produced less waste.     

A rapid and precise method for routine determination of organic carbon in soil

Abstract

A simple method for routine determination of organic carbon in soil by a modified Mebius procedure is described. It involves (a) digestion of the soil sample with an acidified dichromate (K₂Cr₂O₇‐H₂SO₄) solution for 30 minutes in a Pyrex digestion tube in a 40‐tube block digester preheated to 170°C and (b) estimation of the unreacted dichromate by titration of the cooled digest with an acidified solution of ferrous ammonium sulfate with use ofN‐phenylanthranilic acid as an indicator. The method is more rapid and precise than the Mebius procedure commonly used for routine analysis of soils for organic carbon, and the only equipment required for its use is equipment now commonly used for routine Kjeldahl analysis of soils for total nitrogen.     

A comparison of wet oxidation methods for determination of total phosphorus in soils

For 15 soils with widely different extractability of phosphorus (P) two newly introduced digestion techniques for determining total P (P_t) were compared with the standard perchloric acid digestion procedure. The two digestion techniques were: (1) concentrated H₂SO₄ plus 30 % H₂O₂ at 360 °C, (2) concentrated HCl plus concentrated HNO₃ in the ratio 3:1 (aqua regia) at 140 °C. Almost equal amounts of P_t were extracted by the two methods (mean = 188.7 mg kg^—1 for H₂SO₄/H₂O₂ and 188.4 mg kg^—1 for aqua regia) which were slightly higher than the standard method (mean = 183.8 mg kg^—1). However, there is no statistical difference among the three digestion methods, suggesting that the tested methods should be useful for estimating P_t in soils with high content of organic C, eliminating the danger of explosion when hot concentrated HClO₄ is used.     

催化氧化法与直接燃烧法测定土壤总碳之比较

土壤碳库由有机碳库和无机碳库两大部分组成。选择黑土和潮土两种不同类型土壤,分别通过直接燃烧和催化氧化方法测定土壤总碳含量,以揭示两种方法测定结果的可比性及其差导显著性,每个样品每种方法重复测定5次。结果表明：催化氧化法和直接燃烧法测定的黑土总碳含量平均值分别为(15.10±0.03) g/kg和(15.38±0.32) g/kg,t检验两种方法的测定结果无明显差异。催化氧化法测定的潮土总碳含量为(15.07 ±0.06) g/kg,直接燃烧法测定潮土总碳含量为(15.76 ±0.18) g/kg,t检验结果差异明显。两种仪器土壤总碳测定结果精密度均较高,相对偏差均小于5%。为采用仪器方法测定土壤总碳含量及土壤碳库量变化提供参考。     

微波消解—ICP-OES法同时测定有机肥、复混肥和尿素中多种元素含量的研究

采用微波消解法处理样品,建立了电感耦合等离子体光谱法同时测定有机肥、复混肥和尿素中铅(Pb)、砷(As)、汞(Hg)、铬(Cr)、镉(Cd)、铜(Cu)、锰(Mn)、钴(Co)、锌(Zn)、镍(Ni)和锑(Sb)11种元素的分析方法。优化了微波消解条件、仪器条件,进行了方法的检出限、精密度、准确性试验。方法检出限为0.003~0.015 mg/L,相对标准偏差均8.1%,回收率为82.4%~103%,通过水系沉积物标准参考样(GBW-07311)及国家标准方法的验证表明,该方法具有简便、快速、准确、灵敏度高等特点,适合有机肥、复混肥和尿素中11种元素的同时测定。     

Dissolved organic carbon in soil solutions: a comparison of collection methods

A field study was undertaken to compare dissolved organic carbon (DOC) concentrations in soil solutions obtained with three different sampling methods over a range of soil types. The sampling devices used were a tension‐free collector, a tension Prenart collector and a tension Rhizon collector. Samples were collected fortnightly for a year at seven sites in northern England, each collection being replicated three times. The soil solution DOC ranged from 1.3 g m^?3 in an acid ranker to 34.7 g m^?3 in a peat. The DOC concentrations obtained with the three methods correlated reasonably well (r² = 0.6–0.8) but with an indication of bias, as the best fit line differed from the 1:1 line. The tension‐free collector gave generally higher DOC concentrations except at very low concentrations (in the acid ranker soil). The DOC concentrations measured with the tension‐free collectors were significantly (P < 0.05) higher than those obtained with Prenart and Rhizon collectors at four and six sites, out of seven, respectively. Subsequent laboratory tests on tension‐free collected samples showed no DOC loss on filtration through 0.1 and 0.22‐μm membranes, whereas a significant loss of DOC occurred when tension‐free collected samples were subsequently passed through Prenart and Rhizon collectors, indicating a probable sampling artefact with the tension devices. The difficulties of acquiring representative soil solution samples are discussed, together with the advantages and disadvantages of tension and tension‐free methods.     

长期施肥下石灰性潮土有机碳变化的DNDC模型预测

为探讨长期不同施肥条件下土壤有机碳的变化规律及DNDC模型的应用,利用封丘石灰性潮土不同施肥措施下的长期定位试验数据,选取CK、NPK、1/2NPK+1/2OM、OM4个处理,分析了15年来作物产量及土壤有机碳(SOC)的变化特征,并用DNDC模型预测了试验地近100年(2000~2099)的SOC变化趋势。结果表明,各施肥处理的多年产量平均值和对照处理差异显著;施用化肥(NPK和1/2NPK+1/2OM)处理和有机肥(OM)处理间也有显著差异;产量最高为NPK处理,达10811 kg/ha,CK处理最低,但1/2NPK+1/2OM处理产量与NPK处理无显著性差异。15年来土壤耕层(0—20cm)有机碳平均值,以OM处理最高,达到7.90 g/kg,显著高于1/2NPK+1/2OM、NPK处理;而CK处理仅为4.15 g/kg。从15年来有机碳的变化看出,CK处理略有下降,NPK处理较为平稳,而1/2NPK+1/2OM和OM处理呈现不断上升趋势,OM处理上升幅度较1/2NPK+1/2OM处理大。对试验地SOC变化趋势长期(100a)的模拟结果显示,与初始土壤SOC含量相比,100a后不施肥处理(CK)土壤有机碳含量下降了52%,化肥(NPK)处理土壤SOC含量较为稳定,而1/2NPK+1/2OM处理和OM处理土壤有机碳增加明显,大约25a后基本上稳定,100a后分别较2000年增加了24%和25%。从实测数据的分析和DNDC模型模拟分析可以看出,有机肥和化肥配施能获得较高作物产量,并能有效地增加土壤SOC含量,从而提高土壤的可持续利用能力。     

青藏高原生态系统土壤有机碳研究进展

作为"世界第三极"的青藏高原,高寒生态系统是青藏高原主要的生态系统之一.它本身是一个复杂而又特殊的系统,因其独特的自然地理环境而形成的高寒土壤更有其独特的性质.本文首先综述了青藏高原高寒生态系统的土壤有机碳储量、估算方法的研究进展及造成估算结果差异的原因,随后对高寒土壤有机碳排放的观测试验进行了综述,探讨了气候变化对高寒生态系统土壤有机碳源汇效应的影响.目前,全球变暖的趋势正在加剧,40 年来,青藏高原气温平均上升了约 0.3 ～ 0.4℃,冻土面积正广泛退缩,这直接导致青藏高原高寒生态系统发生了以植被覆盖度减少、高寒草原草甸面积萎缩等为主要形式的显著退化,植被生产力和土壤有机碳输入量都减少,而温度升高加快了土壤有机碳分解速率,从而影响到高寒生态系统的碳循环和碳储量.青藏高原土壤有机碳的源汇效应问题已成为研究的热点,但是到目前为止,温度升高到底如何影响土壤有机碳的动态变化没有明确的定论,为此,我们必须从长期的观测试验来说明气候变化对土壤碳库的源汇效应.     

Long-term effects of agronomic practices on the soil organic carbon sequestration in Chernozem

The study was based on data from selected long-term field trials established at the Experimental Fields of the Institute of Field and Vegetable Crops, Novi Sad (Serbia). The effect of tillage systems on SOC concentration and SOC stock was most pronounced at 0–10 cm depth. In a 0–40 cm soil layer, in a 7-year period, no-till (NT) sequestrated 863 kg SOC ha^?1 yr^?1 more compared to moldboard plow tillage (PT), while the effects of disc tillage (DT) and chisel tillage (CT) were not significantly different. Unfertilized three-crop rotation (CSW) compared to two-crop rotation (CW) enhanced SOC storage in a 0–30 cm soil layer by 151 kg C ha^?1 yr^?1 in a 56-year period. Within fertilized treatments, SOC concentration was highest under continuous corn (CC). Mineral fertilization (F) non-significantly increased the SOC stock compared to no fertilization in corn monoculture in a 32-year period. The incorporation of mineral fertilizers and harvest residues (F + HR) and mineral fertilizers and farmyard manure (F + FYM) sequestered 195 and 435 kg C ha^?1 yr^?1 more than the unfertilized plot, respectively, in a 0–30 cm soil layer, in a 35-year period. Irrigation did not significantly affect SOC sequestration.     

有机培肥与耕作方式对稻麦轮作土壤团聚体和有机碳组分的影响

为了明确不同外源有机物和耕作方式对土壤地力培育的影响,以水稻-小麦轮作系统为对象,通过2个年度(2016—2018年)大田试验研究了外源有机物(秸秆和有机肥)和耕作方式及其交互作用[稻麦秸秆还田配合旋耕(SR),稻麦秸秆还田配合翻耕(SP),秸秆不还田、增施有机肥配合旋耕(MR),秸秆不还田、增施有机肥配合翻耕(MP),秸秆不还田、不施用有机肥、旋耕深度15 cm(CKR)]对土壤团聚体和有机碳组成的短期影响。结果表明:SR处理能够降低水稻季土壤容重并增加总孔隙度。相比CKR,小麦季SR处理显著增加0.05mm水稳性团聚体含量,增加量为7.2%。此外,外源有机物和耕作对土壤有机碳活性组分具有显著影响。其中,易氧化有机碳(EOC)主要受耕作与有机物交互作用影响,酸水解有机碳(LPIc和LPII_c)主要受耕作措施的影响, SR处理的土壤EOC和LPI_c含量比CKR提高0.3～2.6 g·kg~(-1)。颗粒有机碳(POC)主要受外源有机物的影响,并且秸秆还田处理POC平均含量高于增施有机肥处理,增加量为0.75g·kg~(-1)。短期内,外源有机物和耕作及其交互作用对稳定性有机碳(黑碳和矿物结合态有机碳)的影响较小。综上,秸秆还田配合旋耕有助于提高土壤水稳性团聚体和活性有机碳的含量(EOC、LPI_c和POC)。     

长期施肥对土壤有机碳和无机碳的影响

利用18年长期定位试验,研究了在不同施肥条件下,土壤有机碳和无机碳在0~50 cm土层分布特征。结果表明,施肥对土壤有机碳的影响随着土层深度的增加而下降,0~7.5 cm土层的土壤有机碳比7.5~15 cm、15~30 cm、30~50 cm分别增加了4.6%、22.0%、63.1%,而无机碳含量随着土层深度的增加而增加,与有机碳的变化规律正好相反。不同种类的肥料对土壤有机碳的影响也不相同,化肥、有机肥长期配合施用和长期施用有机肥可以在0~30 cm土层增加土壤有机碳含量,降低土壤中的无机碳含量,而长期单施化肥对土壤的有机碳和无机碳含量无明显差异。     

Soil organic carbon distribution in relation to land use and its storage in a small watershed of the Loess Plateau, China

Soil organic carbon (SOC) is an important component in agricultural soil, and its stock is a major part of global carbon stocks. Estimating the SOC distribution and storage is important for improving soil quality and SOC sequestration. This study evaluated the SOC distribution different land uses and estimated the SOC storage by classifying the study area by land use in a small watershed on the Loess Plateau. The results showed that the SOC content and density were affected by land use. The SOC content for shrubland and natural grassland was significantly higher than for other land uses, and cropland had the lowest SOC content. The effect of land use on the SOC content was more significant in the 0-10 cm soil layer than in other soil layers. For every type of land use, the SOC content decreased with soil depth. The highest SOC density (0-60 cm) in the study area was found in shrublandII (Hippophae rhamnoides), and the other land uses decreased in the SOC density as follows: natural grassland > shrublandI (Caragana korshinskii) > abandoned cropland > orchard > level ground cropland > terrace cropland > artificial grassland. Shrubland and natural grassland were the most efficient types for SOC sequestration, followed by abandoned cropland. The SOC stock (0-60 cm) in this study was 23,584.77 t with a mean SOC density of 4.64 (0-60 cm).     

皖北平原蒙城县农田土壤有机碳空间变异及影响因素

以皖北平原典型农业生产大县亳州市蒙城县为代表,运用统计学、地统计学方法和GIS技术研究了其农田耕作层(0～20 cm)土壤有机碳(SOC)含量的空间分布及其影响因子。结果表明:研究区SOC含量为10.41±2.52 g kg-1,近30年来提高了55.61%,SOC变异系数为24%,属于中等变异程度。SOC含量在空间分布上表现为东北部、中部和西南部含量高,由西北向东南先逐渐增加后逐渐降低,变异程度较高。整个县域范围内SOC空间变异的主要影响因素为土壤机械组成(粉粒和砂粒含量),其次为秸秆还田。     

不同地表覆盖栽培对旱地土壤有机碳、无机碳和轻质有机碳的影响

通过田间长期定位试验,分层采集冬小麦-休闲种植体系0—40 cm土层的土样,研究了常规、地表覆膜和覆草栽培对土壤有机碳、无机碳和轻质有机碳的影响。结果表明,覆膜或覆草可以显著增加地上部小麦生物量和子粒产量。不同地表覆盖对0—40 cm土层的无机碳含量和分布无显著影响,但与常规栽培相比,地表覆膜使0—5 cm土层的有机碳含量显著降低,0—40 cm各土层轻质有机碳表现出明显降低趋势,平均降低 C 6.1~74.5 mg/kg;地表覆草却表现出明显增加土壤轻质有机碳的趋势,0—5,5—10,10—20 cm土层的轻质有机碳含量分别增加C 235.2、190.0和144.9 mg/kg,相当于常规的38.7%,32.9%和34.5%。同时,覆草栽培还表现出降低0—10 cm土层轻质有机质含碳量的趋势,并使0—20 cm土层轻质有机碳占有机碳的比例显著高于常规栽培和地表覆膜处理。可见,地表长期覆膜不利于旱地土壤有机碳累积,覆草不仅可以增加表层土壤的轻质有机碳累积,还可改善土壤碳氮组成。     

耕作与轮作方式对黑土有机碳和全氮储量的影响

土壤有机碳(SOC)及全氮(TN)对土壤肥力、作物产量、农业可持续发展以及全球碳、氮循环等都具有重要影响。为探索不同耕作和轮作方式对耕层黑土SOC和TN储量的影响,本文以吉林省德惠市进行了8 a的田间定位试验中层黑土为研究对象,对免耕、垄作和秋翻三种耕作方式及玉米-大豆轮作和玉米连作两种轮作方式下SOC和TN在各土层的含量变化进行了分析,并采用等质量土壤有机质储量计算方法,对比分析了不同处理对0～30 cm SOC和TN储量的影响。结果表明,与试验开始前相比,玉米-大豆轮作系统中,秋翻下SOC和TN储量均有所降低;免耕显著增加了0～5 cm SOC及TN含量,但SOC在亚表层亏损,导致其储量并未增加;而垄作处理下SOC及TN含量在0～5、5～10 cm的均显著增加,0～30 cm储量亦分别增加了4.9%和10.7%。玉米连作系统的两种耕作处理(免耕和秋翻)下SOC和TN储量均有所增加,且TN储量增幅均高于玉米-大豆轮作系统,其中免耕下TN储量增幅是玉米-大豆轮作的3.2倍。所有处理下C/N均呈降低趋势,其中垄作0～5 cm C/N由12.05降至11.04,降低幅度分别是免耕和秋翻的3.2和2.8倍。综上可知,对质地黏重排水不良的中层黑土,玉米-大豆轮作系统下免耕并不是促进SOC固定的有效形式,而垄作则促进了黑土SOC和TN的积累,这不仅有利于土壤肥力的改善,而且是使农田黑土由CO2"源"变为"汇"的有效形式之一。与玉米-大豆轮作相比,玉米连作下三种耕作方式都有利于SOC和TN积累。     

耕作方式对干旱绿洲滴灌复播大豆农田土壤有机碳的影响

为探讨不同耕作措施对不同层次土壤碳的影响,从而评价出滴灌条件下最有利于复播大豆农田固碳的耕作方式,于2012-2014年开展了冬小麦收获后土壤采取翻耕覆膜(tillage plough,TP)、翻耕(tillage,T)、旋耕(rotary tillage,RT)和免耕(no-till,NT)4种不同耕作方式的复播大豆田间试验,研究麦后不同土壤耕作方式对复播大豆农田0~100 cm土层土壤容重、总有机碳(soil organic carbon,SOC)及碳库管理指数(carbon pool management index,CPMI)的影响。结果表明,各处理土壤SOC和易氧化有机碳(easily oxidized organic carbon,EOC)含量随着土层的加深基本呈不断下降趋势。免耕、旋耕处理显著增加了表层0~10 cm土壤的SOC和EOC含量,而TP处理显著增加了耕层20~30 cm的SOC和EOC含量,60~100 cm土层TP处理的SOC含量显著低于其他处理,但各处理间EOC含量差异不显著;土壤容重与总有机碳含量呈显著负相关关系(P0.01);0~60 cm土层不同耕作方式CPMI平均值以免耕处理最高,分别比旋耕、翻耕覆膜、翻耕处理的增加了4.41%、9.90%、22.06%,表明免耕、旋耕能够提高0~60 cm土壤的总体CPMI,而耕翻覆膜显著提高20~30 cm耕层土壤CPMI值。该研究为干旱绿洲滴灌条件下选择最有利于复播大豆农田固碳的耕作方式提供了理论依据。     

Landuse impacts on soil organic carbon fractions in different rainfall areas of a subtropical dryland

Landuse can alter soil organic carbon (SOC) fractions by affecting carbon inflows and outflows. This study evaluated changes in SOC fractions in response to different landuses under variable rainfalls. We compared cropland, grassland and forest soils in high rainfall (Islamabad ~1142 mm) and low rainfall (Chakwal ~667 mm) areas of Pothwar dryland, Pakistan. Forest soils in both rainfall areas had highest SOC (11.32 g kg^?1), particulate organic carbon (POC, 1.70 g kg^?1), mineral-associated organic carbon (MOC, 7.17 g kg^?1) and aggregate-associated organic carbon (AOC, 7.86 g kg^?1). However, in rangeland and cropland soils, these varied with rainfall. Under high rainfall, SOC and MOC were 12% and 17% higher in rangeland than in cropland while POC and AOC were equal. Under low rainfall, SOC and MOC were higher in rangeland than in cropland by 7.21 and 1.79 g kg^?1 at 0–15 cm and equal at 15–30 cm depth. POC and AOC were higher in rangeland than in cropland, in both depths. Averagely, SOC, POC, MOC and AOC were 26%, 68%, 76% and 30% higher in high rainfall than in low rainfall soils. Sensitivity of SOC fractions to landuses observed under different rainfalls could provide useful information for soil management in subtropical drylands.     

不同有机物料还田对华北农田土壤固碳的影响及原因分析

中国农业面临着废弃物数量大、污染严重,农田土壤生产力低的现实问题。该研究以增加农田土壤固碳为目标对砂质农田进行有机物料还田,将秸秆、猪粪、沼渣和生物炭4种物料用尿素调节等氮还田,对农田土壤有机碳、颗粒有机碳、可溶性有机碳和微生物量碳的含量进行测定,并探究不同有机物料还田对土壤有机碳的影响原因。研究结果表明:物料还田3a后,生物炭、猪粪和沼渣处理土壤有机碳(SOC)比秸秆处理分别高262.4%、26.8%和20.7%;2014—2015年生物炭处理的土壤微生物量碳(MBC)较秸秆处理降低2.9%~35.5%,猪粪处理和沼渣处理的土壤可溶性有机碳(DOC)分别提高17.1%~60.1%和7.2%~64.8%;2014—2015年生物炭、猪粪和沼渣处理土壤颗粒有机碳(POC)较秸秆处理提高10.8%~148.2%、9.5%~58.3%和11.3%~57.6%;物料还田后,土壤总有机碳(TOC)和POC呈极显著的回归关系(R2=0.67,P0.001),土壤DOC与MBC有极显著相关性(R2=0.52,P0.001)。与秸秆还田相比,生物炭还田有利于土壤POC的累积进而促进土壤有机碳的提升,猪粪和沼渣则通过提高土壤MBC、DOC和POC的含量,促进土壤有机碳的周转和固定。从农田土壤固碳角度而言,生物炭,猪粪和沼渣还田优于秸秆还田。     

黑碳添加对土壤有机碳矿化的影响

通过室内培养试验,向土壤中分别添加不同温度制备的黑碳,热解温度分别为350℃(T350)、600℃(T600)和850℃(T850),研究了黑碳添加对土壤有机碳矿化的影响。结果表明,不同温度条件制备的黑碳在15℃和25℃培养条件下,土壤CO2释放速率总的趋势是前期分解速率快,后期缓慢。在整个培养过程中(112天),随着培养时间的延长,土壤CO2释放速率下降趋势逐渐降低,CO2释放速率相对值的大小随着培养温度的的升高而增大。在不同温度培养条件下,添加黑碳后土壤CO2-C累计量均是T350>T600>T850,T350土壤CO2-C累计量最高分别为415.26 mg/kg和733.82 mg/kg。添加不同黑碳后,土壤有机碳矿化增加率存在极显著差异(p<0.01),表明不同温度制备的黑碳对土壤有机碳矿化的影响显著。