Effects of fallow or planting wheat (Triticum aestivum L.) and fertilizing P or fertilizing P and N practices on soil carbon and nitrogen in a low-organic-matter soil

Soil carbon (C) and nitrogen (N) are important for maintaining soil fertility, and they are considerably affected by soil use and management. In the present study, we conducted an 8-year ?eld experiment on loessial dryland soil (Eum-Orthic Anthrosol, Food and Agriculture Organization of the United Nations (FAO)) in the southern Loess Plateau, China. We tested four soil management regimes—i.e., winter wheat (Triticum aestivum L.) cultivation with phosphorus (P) fertilization (WP), winter wheat cultivation with N and P fertilization (WNP), natural fallow (NF) and bare fallow (BF)—to evaluate their effects on soil C and N fractions. After 8 years, compared with the WNP treatment, the total soil organic nitrogen (SON) in the WP treatment decreased by 14.6% and 36.8%, and microbial biomass nitrogen (MBN) by 35.6% and 61.1%, at 0–20 and 20–40 cm soil depths, respectively. The soil heavy fraction nitrogen (HFN) and light fraction nitrogen (LFN) in the WP treatment also decreased by 36.6% and 39.4%, respectively. Furthermore, BF treatment decreased total soil organic carbon (SOC), heavy fraction carbon (HFC), LFN and MBN at both soil depths with average reductions of 43.4%. The NF treatment decreased light fraction carbon (LFC) by 17.0% at 0–20 cm soil depth, as well as MBN by 24.8% and 71.2%, and inorganic C by 29.1% and 23.8%, at 0–20 and 20–40 cm soil depths, respectively. There was no significant difference of microbial biomass C concentration among the WP, NF and BF treatments. These results confirmed that a lack of N fertilization decreased SON, BF reduced both SOC and SON, and NF decreased soil inorganic C. Therefore, the managements of a recommended rate of N fertilizer application and shortened time of bare fallow are critical for maintaining or increasing SON fraction sequestration, and natural fallow management is not a useful method for maintaining soil fertility in dryland in the Loess Plateau in China.

Abbreviations: HFC: heavy fraction carbon; HFN: heavy fraction nitrogen; LFC: light fraction carbon; LFN: light fraction nitrogen; MBC: microbial biomass carbon; MBN: microbial biomass nitrogen; SOC: soil organic carbon; SON: soil organic nitrogen     

尕海湿地植被退化过程中土壤轻重组有机碳动态变化特征

以甘肃省甘南尕海湿地内的沼泽化草甸为研究对象,采用野外取样和室内测试相结合的方法,研究植被退化过程中土壤轻重组有机碳含量及动态变化。结果表明:不同植被退化阶段0—20cm土壤轻组有机碳含量差异显著(P0.05),表现为未退化轻度退化重度退化中度退化;20—100cm土壤轻组有机碳受植被影响较小。整个土壤剖面重组有机碳含量表现为中度和重度退化显著高于未退化和轻度退化(P0.05)。土壤轻重组有机碳含量均随土壤剖面下降显著降低(P0.05)。各退化阶段沼泽化草甸土壤轻重组有机碳均呈现出明显的时间变化,在0—20cm土层,未退化阶段轻组有机碳表现为"降—升—降"的变化趋势,即5月最高,7月和9月最低,其他各退化阶段则在6月降低并趋于稳定;20—100cm土层轻组有机碳变化幅度较小。各退化阶段土壤重组有机碳动态变化较为一致,均随时间延长呈线性下降,不同月份之间差异显著(P0.05)。说明植被退化导致轻组有机碳含量下降,重组有机碳增加,而在植被生长过程中主要消耗轻组有机碳,重组有机碳相对稳定。相关分析表明,地下生物量与土壤含水量的变化对土壤轻重组有机碳影响显著。     

黄土台塬不同土地利用方式下土壤碳组分的差异

为探讨土地利用方式对土壤碳固定的影响,以乔木、灌木、草和农田等不同植被类型,纯林和混交两种栽培模式的黄土台塬为对象,进行了土壤碳组分研究。结果表明,不同利用方式下林地和天然草地在0—100 cm土层总碳,轻组、重组、可溶性有机碳以及轻组有机碳分配比例(LFOC/SOC)均不同程度高于耕地,而其有机无机复合度(HFOC/SOC)则低于耕地,灌木林地和天然草地这种趋势尤为突出;各种土地利用方式间,土壤总碳和HFOC/SOC在0—20cm差异显著,总碳在60—100 cm也差异明显,轻组、重组及可溶性有机碳在0—40 cm,而无机碳则在40—100 cm差异明显;LFOC/SOC和DOC/SOC在各土层均存在一定差异。土壤总碳、有机碳以及各组分有机碳之间呈极显著正相关,而无机碳则与其呈负相关。轻组和可溶性有机碳均与粗颗粒、易氧化有机碳以及2—0.25 mm团聚体有机碳的相关性高于与细颗粒、稳态有机碳和2 mm团聚体有机碳;而重组有机碳则与之相反。轻组有机碳较有机碳、总碳、重组以及可溶性有机碳能更敏感地反映利用方式之间的差异,可作为土壤质量变化的评价指标。     

培肥措施对复垦土壤轻重组有机碳氮的影响

为揭示复垦土壤轻重组分有机碳氮随复垦年限和培肥措施变化的特征,采用密度分组方法研究了不施肥(CK)、单施化肥(CF)、单施有机肥(M)、有机无机配施(MCF)和生物有机肥与化肥配施(MCFB)5种培肥措施下复垦4,8年土壤轻重组分碳氮含量及碳氮比变化规律。结果表明:复垦土壤总有机碳氮与轻重组有机碳氮含量变化趋势总体均表现为随复垦年限的增加而显著提高。经过8年复垦,不同处理间,单施有机肥对总有机碳(TOC)、总有机氮(TON)、轻组有机碳(LFOC)、重组有机碳(HFOC)与轻组有机氮(LFON)、重组有机氮(HFON)的提高效果总体优于其他处理,与生土相比,增加幅度分别为148.10%,68.09%,163.68%,129.51%,35.00%,92.59%。土壤轻组组分C/N重组组分C/N,土壤轻组组分C/N总体表现为随复垦年限增加而提高,以单施化肥最高,达25.48;重组C/N表现为随复垦年限增加而降低,以单施化肥最低,为6.44。施肥对土壤碳氮库管理指数影响显著,各施肥处理均以生物有机肥与化肥配施处理效果最好。综合来看,在等量养分投入的情况下,单施有机肥更有利于采煤塌陷区复垦土壤总有机碳氮库及轻重组有机碳的积累,单施化肥更大程度促进了轻组组分有机碳和重组组分有机氮的提升幅度。     

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。     

Effect of tillage and rotation on organic carbon forms of chernozemic soils in Saskatchewan

The effects of selected tillage and rotation systems on soil organic carbon and its fractions were studied on Chernozemic soils in south‐western and east‐central Saskatchewan. After practicing a no‐till fallow unfertilized‐wheat rotation for 7 years on an Orthic Brown Chernozem in south‐western Saskatchewan, total soil organic carbon (TOC) in the 0 – 5 cm and 5 – 10 cm layers was slightly lower than the tillage fallow‐unfertilized wheat comparable treatment. However, light fraction of organic carbon (LFOC) was similar in the two treatments. Comparison of the tillage fallow‐unfertilized wheat to a treatment involving conversion to a fertilized continuous cropping system for 10 years showed TOC increased slightly in the two depths and LFOC increased by 24 % and 29 % in the 0 – 5 cm and 5 – 10 cm layer, respectively, of the continuous cropping treatment. Microbial biomass carbon (MB‐C) was increased significantly at the 5 – 10 cm depth. After conversion of fallow‐wheat to alfalfa as perennial forage for 10 years, TOC increased by 80 % and 27 %, LFOC by 245 % and 286 %, and HFOC by 63 % and 20 % at 0 – 5 cm and 5 – 10 cm depths, respectively, compared to the tilled cereal‐fallow system. Meanwhile, water soluble organic carbon (WSOC) was not affected but MB‐C increased significantly. In an Orthic Black Chernozem in east‐central Saskatchewan, the depletion and restoration of organic carbon was observed when native sod was changed into cropland and then back to grassland. For example, the TOC of cropland under cereal‐fallow rotation for 62 years decreased by 42 % and 33 % at 0 – 5 cm and 5 – 10 cm depths, respectively, compared to native sod. The LFOC decreased by 79 % and 74 % in the layers, and reductions in WSOC and MB‐C were even greater. After cropland was re‐seeded to grassland for 12 years, the concentration of total organic carbon was increased by 16 % and 22 % while the mass of organic carbon was the same as the cropland in the two layers. The LFOC and MB‐C amounts in the grass seed‐down were double that of the cropped land, but the amounts of TOC, LFOC, and MB‐C in grass seed‐down were still significantly lower than the native sod.     

耕作方式对稻田土壤有机碳组分含量及其分布的影响

为深入了解耕作方式对土壤碳组分含量的影响,以南方双季稻田为研究对象,研究了翻耕秸秆不还田（CT）、翻耕（CTS）、旋耕（RTS）和免耕（NTS）4种耕作处理对土壤轻组有机碳（LF-OC）、重组有机碳（HF-OC）、土壤轻组组分（LF）和重组组分（HF）的影响。结果表明,不同耕作方式下,土壤轻组中有机碳含量介于191.21～251.54gC·kg-1,fraction之间,轻组有机碳（LF-OC）含量介于3.01～9.27gC·kg-1之间,为土壤总有机碳（TOC）的11.84%～23.31%;耕作扰动导致土壤LF-OC的损失,而秸秆投入能够增加LF-OC;NTS处理利于表层土壤有机碳的积累,但不利于亚表层土壤有机碳的积累;RTS和CTS处理有利于有机碳增加,但LF-OC分解较快;CT处理则导致土壤有机碳的流失。LF-OC与TOC变化相似,呈显著正相关关系（R2=0.84）,且LF-OC对耕作措施的响应比TOC更为剧烈,可以作为指示土壤有机碳库变化的灵敏指标。     

施肥对黑土密度分组中碳、氮的影响

以中国科学院海伦农业生态实验站的长期定位施肥土壤为基础,研究长期施肥对黑土密度分组中碳和氮的影响。结果表明:氮肥能够增加土壤有机碳和全氮含量,但不如NPKOM效果明显。土壤中各组分有机碳含量的变化趋势为重组>游离态轻组>闭蓄态轻组,三者之间差异达极显著水平(p<0.01),重组有机碳的含量最大值为23.72 g/kg,而闭蓄态轻组有机碳的平均值仅为0.69 g/kg;全氮的含量的变化呈重组最大,且极显著大于闭蓄态轻组和游离态轻组,后两者之间无明显差异。不同组分中有机碳浓度和全氮浓度的变化规律一致,为游离态轻组>闭蓄态轻组>重组,且游离态轻组明显大于其它两个组分。NPKOM处理的闭蓄态轻组和重组组分中的有机碳浓度和全氮浓度大于其它施肥处理。碳氮比的变化趋势为游离态轻组>闭蓄态轻组>土壤>重组,重组和土壤中,NPKOM处理的碳氮比最低,CK处理的碳氮比最大,可见有机肥的施用加快了土壤碳的周转速度。     

宁夏引黄灌区不同类型土壤重组有机碳特征分析

[目的]探究宁夏引黄灌区土壤总有机碳与重组有机碳的特征及相互关系,为研究宁夏引黄灌区固碳效应及碳库稳定性提供科学依据。[方法]以宁夏引黄灌区为研究对象,通过实地采样与分析,测定不同土壤类型总有机碳与重组有机碳含量。[结果]土壤类型是影响宁夏引黄灌区土壤有机碳变化的主要因素,经灌溉耕作后,灌溉土壤总有机碳及重组有机碳含量较对照土壤均有所增加,平均增加量分别为2.27和2.02g/kg,增加量随土层深度增加而减小,增加幅度因土壤类型存在差异;重组有机碳与总有机碳存在显著相关关系(p0.001)。[结论]重组有机碳是总有机碳的重要部分,它与总有机碳之间的相关性随着土层深度的增加而增强,说明灌溉耕作活动及灌溉时间对土壤有机碳具有一定的影响。研究重组有机碳能更好地了解灌区土壤碳库稳定性。     

Influence of tillage and rotation systems on distribution of organic carbon associated with particle-size fractions in Chernozemic soils of Saskatchewan, Canada

The effects of several dominant tillage and rotation systems on soil organic C content of different particle-size fractions were studied in Chernozemic soils from southwestern and east-central Saskatchewan, Canada. In an Orthic Brown Chernozem in southwestern Saskatchewan, 7 years of no-till cereal–fallow, imposed on a long-term tillage fallow–wheat rotation soil, resulted in 0.1 Mg C ha⁻¹ more organic C mass in the sand + organic matter (OM) fraction of the 0- to 5-cm layer, whereas organic C associated with coarse silt (CS), fine silt (FS), coarse clay, and fine clay of 0- to 5- and 5- to 10-cm layers was less than that of the comparable tilled cereal–fallow system. Conversion of tilled fallow–wheat rotation soil to continuous cropping had a slight effect, whereas the organic C mass in all the size fractions was significantly increased in both 0- to 5- and 5- to 10-cm layers after alfalfa was introduced on tilled fallow–wheat as perennial forage for 10 years. In an Orthic Black Chernozem in east-central Saskatchewan that was cultivated and tilled using a cereal–fallow rotation for 62 years, organic C mass decreased in sand + OM, CS, and FS of 0- to 10-cm depth. Conversion of the tilled cereal–fallow cropland soil back to seeded grassland resulted in significantly more soil organic C in sand + OM fraction after 12 years of grass seed-down. The sand + OM fraction appears to be the size fraction pool initially most sensitive to adoption of management practices that are liable to sequester carbon in the soil.     

黄土高原吕梁山不同撂荒年限土壤团聚体稳定性及有机碳分布特征

为探究不同撂荒年限土壤结构及有机碳分布特征,试验选取黄土高原吕梁山自然撂荒1、2、3、5、10、15、20a枣园土壤为研究对象,以清耕作业下的枣园土壤为对照(CK),利用干筛和湿筛法测定并分析各样地0～20 cm 土层中土壤团聚体稳定性、团聚体有机碳与土壤总有机碳含量及其相关性.结果表明:撂荒初期,土壤团聚体含量呈波动...     

添加玉米秸秆对白浆土重组有机碳及团聚体组成的影响

研究添加有机物料后,土壤重组有机碳含量变化及其对土壤团聚体组成的影响,对于科学评价秸秆还田对土壤的培肥作用及其环境效应具有重要意义。采用室内培养试验,培养120 d,研究耕作白浆土耕层土壤和母质层中添加不同比例秸秆对土壤重组有机碳积累量、团聚体组成及各粒级团聚体中有机碳分布的影响。结果表明:随秸秆施用量增加,耕层土壤和母质的重组有机碳含量均呈同步增加趋势,耕层土壤和母质相比,重组有机碳增量差异不大,两者增量差值仅为0.34 g kg-1,但两者的有机碳增率差异很大,耕层土壤仅为85.51%,母质则高达556.23%。说明在成土过程中,耕层土壤中有机质的累积会降低其固碳潜力,而在母质层中,其固碳"位点"处于"空置"状态,因此有很强的固碳潜力。同时,秸秆的添加,促进了土壤中小粒径团聚体(0.25 mm)向大团聚体(0.25mm)的转化,耕层土壤和母质土壤在秸秆添加量为3%和2%时大团聚体中有机碳的贡献率最高,分别为69.90%和65.48%。在白浆土中添加玉米秸秆培养后,其母质的固碳能力大于耕层土壤。     

轮作休耕模式对土壤团聚体及有机碳含量的影响

为探究轮作休耕模式对红壤坡耕地团聚体稳定性及有机碳含量的影响,通过田间试验设置了休闲地、玉米单作、玉米-豌豆-玉米和玉米-苕子-玉米4个处理,分析了不同种植模式下土壤团聚体稳定性及有机碳含量,结果表明:(1)不同种植模式下土壤机械稳定性和水稳定性团聚体组成均以≥0.25 mm粒径占比最高,机械稳定性团聚体占比在80.68%以上,水稳定性团聚体达到了77.05%以上,且≥0.25 mm团聚体所占比例大小顺序为:休闲地>玉米-豌豆-玉米>玉米-苕子-玉米>玉米单作。(2)根据不同团聚体稳定指数(MWD,GMD,R_0.25和PAD)显示,休闲地的团聚体稳定性最好,与玉米单作之间差异显著,且休闲地和玉米轮作两种模式下团聚体稳定性均优于玉米单作。(3)玉米单作土壤团聚体有机碳含量最低,玉米轮作和休闲地能显著提高有机碳含量,并且玉米-苕子-玉米轮作效果最优; ≥0.25 mm粒径范围的团聚体储存的有机碳含量最高。(4)通过对土壤水稳性团聚体稳定指数与有机碳含量的相关性分析表明,4个不同团聚体稳定指数与有机碳含量都呈极显著正相关关系,与R_0.25相关程度最高。研究结果可为试验区域坡耕地水土流失防治提供理论依据。     

土壤生物活性有机碳库及其表征指标的研究

土壤生物活性有机碳库 (C0)的大小和周转可以指示土壤供应养分的能力以及养分的循环状况。对浙江省 11个土壤的研究表明 ,生物活性有机碳库的变化幅度为 184.87～ 3022.41mg/kg ,占土壤总有机碳的2.91%～8.94% ,生物活性有机碳库的周转速率k为0.0070～0.0199d-1。C0与土壤总有机碳、全氮、有效氮、CEC、重铬酸钾易氧化有机碳、微生物生物量碳、微生物生物量氮、水溶性有机碳、热水提取有机碳、轻组有机碳都呈显著性正相关 ,k与这些指标均无相关性。C0与重铬酸钾易氧化有机碳、微生物生物量碳、微生物生物量氮、水溶性有机碳、热水提取有机碳、轻组有机碳占土壤总有机碳的百分比均无相关性 ,k只与水溶性有机碳占土壤总有机碳的百分比呈显著性正相关 (R2=0.4684 ,P0.025)。水溶性有机碳占土壤总有机碳的百分比是表征土壤生物活性有机碳库周转的较好指标。     

黄土高原半干旱区不同土地利用下的土壤有机碳、碳组分和土壤营养

Cropland (CP), native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L. ) (ST), and branchytamarisk (Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China. Total organic carbon (TOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), total N (TN), nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N), ammonium nitrogen (NH₄⁺-N), total P, and available P (AP) were measured. The results showed that SOC in NG, ST and BT were 12.7%, 27.7% and 34.8% higher than that of the cropland, respectively. LFOC, light fraction (LF) dry matter, ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland. Cropland had the highest TN, the sum of NO₃^--N and NO₂^--N, TP and AP due to the use of chemical fertilizers. TOC significantly correlated with LFOC, HFOC and C/N. LFOC significantly correlated with dry matter of the LF and C/N. TN, the sum of NO₃^--N and NO₂^--N and AP were significantly negatively correlated with TOC and LFOC. Therefore, land use conversion from cropland to shrub land, or maybe grassland, contributed to SOC sequestration and improved soil nutrients stabilization.     

坡耕地黑土不同密度的土壤有机碳组分的空间分布特征

以东北黑土区一典型漫岗坡耕地为研究对象,通过测定不同侵蚀程度地形部位的轻组、重组有机碳含量,分析土壤侵蚀和沉积过程对土壤不同密度组分有机碳的影响。研究结果表明:在各地形部位,表层土壤(0～20cm)轻组有机碳(LF-C)含量显著高于亚表层土壤,介于45.3～65.8mgkg-1之间,占土壤总有机碳(TOC)的2.91%～5.87%。侵蚀严重的坡肩部位LF-C、重组有机碳(HF-C)和TOC分别比侵蚀微弱的坡顶部位减少了27.4%、17.2%和18.1%,表明LF-C对土壤侵蚀和沉积过程的响应比土壤总有机碳更为强烈,土壤TOC的减少是土壤LF-C和HF-C减少共同作用的结果。LF-C/TOC的变化和LF-C的变化相似,说明土壤侵蚀优先导致LF-C的损失。各地形部位表层土壤LF-C和微生物量碳显著正相关,在沉积部位富集的LF-C的最终归宿问题还有待于进一步研究,沉积部位仍以惰性的HF-C为主。     

民勤绿洲区撂荒农耕地土壤有机碳变化特征及影响因素

对民勤绿洲区不同撂荒年限农耕地0-60cm土体4个土层中土壤总有机碳（TOC）、轻组有机碳（LFC）和重组有机碳(HFC)剖面分布以及与土壤主要属性的关系进行比较研究。结果表明:(1)撂荒区0-60cm土层土壤,TOC、LFC和HFC含量分别介于3.21-5.23g/kg、0.34-1.51 g/kg、2.55-4.30 g/kg之间,相对于常规耕作,撂荒过程中土壤TOC 、LFC和 HFC的下降主要发生在耕层（0-20cm）,撂荒50年间,TOC 、LFC和 HFC年均减幅分别为1.94%,5.46%和2.13%;20-60 cm土层土壤TOC和HFC含量总体呈现缓慢增长的趋势,撂荒50年TOC和HFC年增幅分别为0.31%和0.88%,LFC持续减少,年均减幅为1.18%。(2)撂荒地HFC对TOC的贡献大于LFC,土壤TOC和HFC分别与粘粒百分比（Clay）和粉粒百分比（Silt）呈极显著正相关,与沙粒百分比（Sand）呈极显著负相关,LFC与Silt、Sand和Clay均未达到统计学上的显著水平,但LFC分别与土壤pH、EC和SAR达到显著或极显著水平,说明LFC对土壤盐碱化较为敏感。(3)逐步回归分析表明,土壤全氮（TN）,总碳氮比（TOC/TN）对土壤TOC 、LFC和 HFC影响较大。（4）随撂荒时间延长,耕层土壤逐步趋于粗质化,粘粉粒含量不足,容重降低,盐碱化提高,不利于土壤有机碳的积累,随土层加深,粘粉粒含量提高,有助于土壤有机碳的固持。     

Organic matter in size‐density fractions after 16–50 years of grass ley,cereal cropping and organic amendments

Size‐density fractionation, which was originally developed to examine short‐term decomposition of added material in sandy soil, was highly sensitive to medium‐ to long‐term changes in loam and clay soils. Materials from different size classes (>1 mm, 0.1–1 mm, 0.05–0.1 mm and <0.05 mm) were separated by density into light (ρ < 1.0 g cm⁻³), medium (1.0 < ρ < 1.85 g cm⁻³) and heavy (ρ > 1.85 g cm⁻³) fractions. In 16–18‐year cropping experiments the 0.1–1‐mm heavy fraction contained 17–19% of total carbon in ley soils compared with 7% in continuously cropped soils. Greater N‐mineralization rates after sieving of ley cropped soils could not be related to differences in C:N ratios of fractions, but this was assumed to be related to exposure of aggregate‐binding agents. In a 50‐year trial 40% of total soil carbon was contained in the 0.1–1‐mm heavy fraction in soil treated with sewage sludge compared with 7–9% in the fallow and ‘zero N’ treatments. Thus, the soils studied expressed an aggregate hierarchy dependent on organic carbon dynamics. The relative abundance of carbon in heavy organo‐mineral fractions >0.1 mm was inversely related to the relative abundance of C in black‐brown medium density material <0.1 mm, defined as uncomplexed particulate organic matter that was presumably released during ultrasonic disruption deterioration of finer (<0.1 mm) aggregated organo‐mineral particles. The size density fractionation allowed identification of materials of contrasting visual appearance, chemical qualities and, by inference, biological turnover times. However, they were found to be predominantly composite fractions and may be too complex to be represented by unique model pools.     

不同冬种模式对稻田土壤碳库管理指数的影响

长江中下游地区是我国水稻生产的重要基地,在保障我国粮食安全中占有重要地位,但该地区农田可持续性不高,稻田冬季利用率较低。本研究通过探讨不同冬季种植模式对土壤质量的影响,为冬闲田合理开发利用,提高稻田可持续性提供理论依据。设置5种冬种模式,分别为冬季休闲、冬种紫云英、冬种油菜、冬种大蒜和冬季轮作（马铃薯、紫云英、油菜）模式,通过测定不同土层土壤养分、土壤有机碳、活性有机碳和微生物生物量碳等,进一步分析不同冬种模式的土壤碳库管理指数及其综合效应。结果表明,在0~30 cm稻田土壤,与冬闲处理相比,不同冬季种植模式土壤有机碳提高6.12%~7.17%、活性有机碳提高13.56%~20.76%、微生物生物量碳提高0.13%~14.34%、可溶性有机碳提高3.49%~19.15%,土壤活性有机碳有效率提高6.74%~17.20%,冬季轮作（马铃薯、紫云英、油菜）模式能显著促进稻田土壤总有机碳及可溶性有机碳的积累;不同冬种模式提高了稻田土壤碳库活度指数和碳库指数,并且土壤碳库管理指数增加14.37%~27.29%。土壤有机碳与活性有机碳呈极显著相关（P<0.01）,土壤碳库管理指数与总有机碳呈显著相关（P<0.05）、与活性有机碳间存在极显著（P<0.01）的相关性。对土壤碳库管理指数影响因素的灰色关联度综合分析表明,冬季轮作（马铃薯、紫云英、油菜）模式排名第1。可见,不同冬季种植模式能增加土壤有机碳含量和提高土壤碳库管理指数,冬季轮作（马铃薯、紫云英、油菜）模式的综合评价最好,其次为冬种大蒜模式。     

长期施肥对土壤活性有机碳指标的影响

以棕壤长期肥料定位试验地土壤为试材,研究和对比了不同施肥处理耕层土壤各项活性有机碳指标对长期施肥的响应。研究结果表明,长期施用化肥、有机肥以及有机肥配施化肥均显著改变了土壤总有机碳(TOC)含量。与此同时,土壤的轻组有机碳(LFOC)、易氧化有机碳(ROC)和微生物量碳(MBC)含量亦对长期施肥产生与TOC基本一致的响应。相关分析结果表明,土壤的LFOC、ROC和MBC可以作为长期施肥对土壤TOC影响的评价指标,且三者的指示灵敏度依次为MBC>LFOC>ROC。