保护性耕作对土壤有机碳组分的影响

为了探讨土壤有机碳及活性有机碳组分对不同耕作措施的响应,在黄土高原半干旱区的定西市李家堡镇进行了长期田间定位试验,采用免耕、秸秆覆盖及小麦和豌豆轮作等保护性耕作措施,对0-5 cm,5-10 cm,10-30cm 3层土壤的有机碳(SOC)、易氧化有机碳(ROC)、微生物生物量碳(MBC)的动态进行了系统的研究,结果表明,与传统耕作相比,保护性耕作的3个处理均能不同程度地提高两种轮作次序下SOC,ROC,MBC的含量,这说明保护性耕作有利于碳的固定和生态农业的健康发展,其中免耕和秸秆覆盖两部分结合效果最佳.同时,各处理土层的含碳量均随土壤深度的增加而降低.相关分析表明,ROC,MBC,ROC/SOC,MBC/SOC对不同耕作措施产生的响应与SOC基本一致,它们可以作为对土壤SOC影响的评价指标,与SOC的相关系数大小排序依次为MBCROCMBC/SOCROC/SOC,在表征土壤有机碳变化上它们比SOC更敏感,其灵敏度排序为MBCROC/SOCMBC/SOCROC,因此,在ROC,MBC,ROC/SOC,MBC/SOC等指标中,MBC更要值得重视和采用.     

转变耕作方式对长期旋免耕农田土壤有机碳库的影响

土壤深松是解决长期旋免耕农田耕层浅薄化、亚表层（>15～30 cm）容重增加等问题的有效方法之一,而将长期旋免耕农田进行深松必然导致农业生态系统中土壤有机碳（soil organic carbon,SOC）及碳固定速率的变化。因此,为对比将长期旋免耕转变为深松前后农田土壤有机碳库变化,该研究利用连续12a 的旋耕和免耕长期定位试验以及在此基础上连续6 a旋耕-深松和免耕-深松定位试验,对比了转变耕作方式对农田土壤0～30 cm有机碳含量、周年累积速率及其固碳量的影响。研究结果表明,经过连续12 a的旋耕和免耕处理（2002－2014）,2014年免耕处理土壤0～30 cm有机碳储量比试验初期（2002年）提高38%,旋耕处理降低了30%,而对照常规处理无显著差异。免耕处理土壤0～30 cm有机碳储量比旋耕处理高约2.6倍（2014年）。长期免耕显著提高了土壤0～30 cm的有机碳含量,2002~2014年其土壤0～30 cm固碳量为16.69 t/hm2,但长期旋耕导致土壤0～30 cm SOC含量显著降低,表现为土壤有机碳的净损耗,年损耗速率为?0.75 t/hm2。而长期旋耕后进行深松（旋耕-深松处理）6年其土壤0～30 cm的有机碳含量较原旋耕处理提高32%～67%,且显著提高了土壤固碳量及周年累积速率;免耕-深松土壤0～30 cm的有机碳周年累积速率较免耕处理下降了42%。长期旋耕造成有机碳水平下降的条件下,将旋耕处理转变为深松处理在短期内更有利于促进土壤有机碳的积累,而将长期免耕处理转变为深松措施,降低了土壤有机碳的累积速率和固碳量。     

长期保护性耕作对坡耕地黑土有机碳组分的影响

为对比长期保护性耕作模式与传统耕作模式对黑土有机碳组分的差异化,揭示长期保护性耕作对侵蚀退化黑土质量的恢复作用。基于典型黑土坡耕地连续15 a保护性耕作长期定位田间试验,设置免耕保护性耕作（NT）和旋耕传统耕作（CT）2个田间耕作试验,并实行玉米-大豆轮作模式,测定并分析了两种耕作措施下土壤有机碳及其不同碳组分随土壤剖面的垂直分布及变化特征。结果表明：连续实施15 a的NT与CT相比分别显著提高0～5和>5～10 cm土层的土壤有机碳质量分数（29.54%和22.38%）（P<0.05）,碳储量（31.11%和27.34%）（P<0.05）,全氮质量分数（53.74%和37.60%）（P<0.05）,表层土壤碳氮质量分数提升显著（P<0.05）,深层土壤碳氮质量分数变化不显著;以>5～10 cm土层土壤颗粒有机碳（69.85%）、0～5 cm土层的土壤轻组有机碳（130.81%）和0～5、>5～10 cm土层土壤微生物量碳（85.59%和59.53%）的提升为主,并且对深层土壤有机碳组分也产生一定的积极影响;耕作效应对于土壤团聚体稳定性指标影响显著（P<0.05）,并且土壤团聚体稳定性指标对于SOC质量分数提升也起到了关键作用。研究表明,与传统耕作相比,连续实施15 a保护性耕作,增加的有机碳以活性有机碳为主。长期的保护性耕作对恢复退化农田黑土质量及土壤固碳均具有重要意义。     

秸秆还田对再生稻田土壤有机碳组分的影响

  【目的】  在再生稻系统下,探讨秸秆还田对再生稻田土壤有机质组分及其养分含量的影响。  【方法】  试验设置秸秆不还田(CK)、水稻秸秆半量还田(SH)、水稻秸秆全量还田(SW)和水稻秸秆全量还田配施腐熟剂(SWF)共4个处理,分析各处理土壤有机碳及其组分和土壤速效养分含量。  【结果】  与秸秆不还田相比,秸秆还田能提高土壤有机碳及其组分含量。与CK处理相比,在头季和再生季水稻收获期,秸秆还田处理(SH、SW、SWF)土壤中水溶性有机碳含量分别增加了19.62%～22.63%、20.99%～41.48%;土壤中颗粒有机碳含量分别增加了8.47%～20.62%、24.71%～30.90%;三个施秸秆的处理间土壤总有机碳、胡敏酸和富里酸含量无明显差异。秸秆还田可以改变水溶性有机质结构,使其结构趋于简单。秸秆还田下土壤碱解氮、有效磷、速效钾和铵态氮含量均呈增加趋势;在头季水稻收获期,SWF处理的碱解氮、有效磷和速效钾含量显著高于CK处理。在再生季水稻收获期,与头季稻收获期相比,CK处理土壤速效养分含量呈下降趋势,而秸秆还田下各处理速效养分含量均呈增高趋势。  【结论】  秸秆还田可以提高再生稻田土壤有机碳、颗粒有机碳、水溶性有机碳以及腐殖酸组分的含量,促进水溶性有机质结构的变化,从而有效改善土壤养分的供给能力。     

长期垄作免耕对稻田土壤有机碳剖面分布的影响

以稻田免耕长期定位试验为平台,研究长期垄作免耕对稻田土壤有机碳剖面分布的影响。结果表明,垄作免耕(中稻)、垄作免耕(稻油)、常规平作(中稻)和水旱轮作(稻油)4种耕作处理实施20年后,稻田0-60cm土体中各土层有机碳含量最高值和最低值分别出现在垄作免耕(稻油)和水旱轮作(稻油)中,且水旱轮作(稻油)中各土层有机碳含量均显著低于其他耕作处理;垄作免耕(稻油)中0-10cm和40-60cm土层有机碳含量与垄作免耕(中稻)、常规平作(中稻)之间差异不显著,但20-40cm土层有机碳含量则显著高于其他耕作处理(P<0.05),可见同传统耕作相比,长期垄作免耕(稻油)稻田的增碳优势主要体现在20-40cm土层。不同耕作处理连续实施20年后,稻田0-60cm土体有机碳密度的高低顺序为垄作免耕(稻油)>垄作免耕(中稻)>常规平作(中稻)>水旱轮作(稻油),且处理间差异显著(P<0.05)。垄作免耕15～20年期间,稻田0-10cm表层土壤有机碳储量基本稳定,但20-40cm土层有机碳储量仍有增加,其中垄作免耕(稻油)增加最为明显,表明20-40cm土层碳累积是长期垄作免耕下稻田发挥增碳功能的重要机制。     

轮作结合施肥对土壤有机碳及其组分和土壤养分的影响

研究了轮作结合施肥对土壤有机碳组分及土壤养分的影响,以期为优化眉豆-燕麦轮作体系下施肥措施,实现土壤固碳减排,培肥土壤提供理论依据。本研究设燕麦连作、眉豆-燕麦轮作、眉豆连作模式分别结合不施肥、施化肥、施有机复合肥措施9个处理,三年连续田间定位试验,分析2018年收获后土壤有机碳(SOC)、易氧化有机碳(ROC)、可溶性有机碳(DOC)、重组有机碳(HFOC)、微生物生物量碳(MBC)及养分含量。研究结果表明,各处理团聚体内SOC含量呈现先升高再降低的趋势,其中轮作结合施用有机复合肥处理SOC含量最高,达到41.36 g kg-1。在同一种植模式下ROC、DOC、MBC、碱解氮、速效磷、速效钾含量总体变化趋势为:施用有机复合肥>施用化肥>无肥,轮作结合施用有机复合肥处理较不施肥处理ROC、DOC、MBC、碱解氮、速效磷、速效钾含量分别高7.54%、30.56%、13.35%、9.56%、31.88%、9.52%。HFOC含量总体变化趋势为施用有机复合肥>无肥>施用化肥,轮作结合施用有机复合肥处理较施化肥处理HFOC含量高12.10%。相同施肥条件下轮作模式ROC...     

长期施肥对水稻根系有机酸分泌和土壤有机碳组分的影响

本研究以江西省红壤研究所水稻土长期定位试验田(始于1981年)为对象,分析了不施肥(CK)、单施化肥(NPK)、有机无机配施(NPKM)3种施肥措施对水稻根系有机酸分泌速率及土壤有机碳组分的影响。结果表明:NPK和NPKM处理水稻根系分泌有机酸总量均显著高于CK处理(P0.05,下同),其中NPKM处理最高,提高了54.78%;相对于CK处理,NPK处理水稻根系酒石酸分泌速率显著增加,提高了82.63%,NPKM处理的草酸与苹果酸分泌速率显著增加,分别增加了69.93%、110.98%,而NPK和NPKM处理的柠檬酸分泌速率分别降低了36.57%与40.57%。与CK处理相比,NPKM处理土壤有机碳、颗粒有机碳、微生物生物量碳与可溶性有机碳均显著增加,而NPK处理却无显著变化;可溶性有机碳结构的进一步分析表明,NPKM处理促进了可溶性有机碳中类胡敏酸和类富里酸物质的累积,在可溶性有机碳中所占比例分别为31%、44%,NPK处理可溶性有机碳结构无明显变化;CK和NPK处理中可溶性有机碳的有机物来源主要是植物与微生物的混合源,而NPKM处理主要是微生物代谢所分泌的产物。     

长期撂荒对黑土土壤有机碳组分的影响

为明确长期撂荒对黑土不同土层土壤有机碳及其组分的影响,以吉林公主岭黑土长期定位试验为对象,选取不施肥和撂荒2个处理,采用改良的Walkley-Black土壤有机碳分组方法,研究不同层次(0～0.2、0.2～0.4和0.4～0.6 m)土壤有机碳及其组分的变化.结果表明:(1)0～0.6 m土壤剖面中,撂荒处理下土壤有机...     

化肥减量配施有机肥对土壤有机碳及其组分的影响

为了探究化肥减量配施两种不同黄腐酸钾有机肥对土壤有机碳及其组分的影响,采取盆栽模拟大田种植,以不施肥和纯施化肥为对照,以100%化肥配施100%有机肥、75%化肥配施25%有机肥、50%化肥配施50%有机肥、25%化肥配施75%有机肥和100%有机肥为处理,探讨土壤有机碳（SOC）、可溶性有机碳（DOC）、微生物量碳（MBC）、易氧化有机碳（LOM）和惰性有机碳（ROC）在不同生育期内的含量特征。结果表明：化肥减量配施有机肥各处理有机碳及其组分含量各生育期均表现为：花针期显著高于结荚期和成熟期,其中可溶性有机碳和微生物量碳结荚期含量显著高于成熟期（P＜0.05）;各处理有机碳及其组分含量均表现为：25%化肥配施75%生化黄腐酸钾处理显著高于不施肥、单施化肥和单施有机肥处理,50%化肥配施50%矿源黄腐酸钾处理显著高于不施肥、单施化肥和单施有机肥处理;其中花针期25%化肥配施75%生化黄腐酸钾处理SOC、DOC、MBC、LOM和ROC含量分别为133.0 g·kg-1、284.4 mg·kg-1、269.7 mg·kg-1、30.76 g·kg-1和111.2 g·kg-1,50%化肥配施50%矿源黄腐酸钾处理SOC、DOC、MBC、LOM和ROC含量分别为130.9 g·kg-1、250.5 mg·kg-1、251.7 mg·kg-1、29.86 g·kg-1和110.8 g·kg-1。综上,化肥减量配施生化黄腐酸钾对土壤有机碳及其组分含量的影响整体优于配施矿源黄腐酸钾（P＞0.05）,各生育期有机碳及其组分含量均表现为：化肥减量配施黄腐酸钾花针期显著高于结荚期和成熟期（P＜0.05）,其中25%化肥配施75%生化有机肥处理对提升土壤中有机碳及其组分含量效果最佳,其SOC、DOC、MBC、LOM和ROC含量各生育期分别增加0.15%-13.50%、3.45%-122.11%、15.37%-133.54%、2.56%-60.44%和0.36%-18.80%。     

岩溶区不同土地利用方式对土壤有机碳及其组分的影响

选择重庆市中梁山岩溶槽谷中5种土地利用方式(弃耕地、草地、菜地、橘园地和林地)为研究对象,在野外调查和室内分析的基础上,采用方差分析法对比分析了土壤总有机碳、溶解性有机碳、易氧化性碳、轻组有机碳、颗粒有机碳及矿物结合态有机碳的含量变化,并用相关分析法分析了土壤有机碳各组分之间的关系。结果表明:不同土地利用方式土壤总有机碳(TOC)含量随土层深度增加而降低,上下层土壤TOC含量在2.69~13.88g/kg之间,不同植被覆盖类型、耕作方式和施肥是影响土壤TOC分布的重要因素。不同土地利用方式下有机碳各组分(DOC、EOC、LFOC、POC和MOC)含量在垂直分布上均呈现出随土壤深度的增加而降低的趋势,但不同土地利用方式之间的差异较大,主要与植被类型、施肥管理、耕作方式以及人为干扰有关。弃耕地含量均比较低,林地和草地受人为干扰较少含量较高,菜地土壤受施肥和翻耕影响,上下层土壤含量差异不大,橘园地上下层土壤5种有机碳组分含量差异均是最大的。弃耕地受之前耕作影响,弃耕时间短,有机质输入量少,POC/MOC值相对较低,菜地受施肥和翻耕影响上下层土壤POC/MOC值相对比较稳定,草地、橘园地和林地0—20cm土壤POC/MOC值均高于20—40cm,下层土壤有机碳比较稳定。0—20cm和20—40cm土壤有机碳及组分之间存在相关关系,0—20cm土壤TOC与LFOC和MOC之间呈显著正相关,LFOC与POC之间也呈现显著正相关;20—40cm土层,土壤TOC与EOC、LFOC和MOC之间呈显著正相关性,MOC与TOC以及EOC和LFOC均呈现正相关性,LFOC与POC之间关系由表土层的显著正相关转变为极显著正相关。下层土壤比上层土壤有机碳稳定性强,尤其是土壤TOC、LFOC和MOC能够敏感地反映土壤碳库的变化,可以作为土壤有机碳稳定性的敏感性指标。     

稻田垄作免耕对土壤团聚体和有机质的影响

该文以1990年建立的耕作制定位试验田紫色水稻土为研究对象,分析了冬水田（FPF）、水旱轮作（CR）和垄作免耕（RNT）3种耕作方式对土壤团聚体组成和有机质的影响。结果表明,垄作免耕减少了对土壤大团聚体的破坏,在0～10 cm土层,垄作免耕大团聚体含量分别是冬水田和水旱轮作的1.48和1.32倍,微团聚体含量则显著降低;在 ＞10～20 cm土层有相同的趋势。3种耕作条件下,有机碳和氮在团聚体中的分布模式类似,均有向大团聚体富集的趋势,但垄作免耕条件下土壤有机碳和氮质量分数显著高于冬水田和水旱轮作。对土壤颗粒有机质（POM）的分析结果表明,垄作免耕0～10 cm土层轻质组分（LF）的质量分数（1.92 g/kg）与水旱轮作（1.70 g/kg）差异不显著,但显著高于冬水田（1.42 g/kg）。冬水田、水旱轮作和垄作免耕的0～10 cm土层,团聚体内总颗粒有机质（total iPOM）质量分数分别为0.96,1.12,2.14 g/kg;垄作免耕土壤团聚体内细颗粒有机质（fine iPOM）分别为冬水田和水旱轮作土壤的3.02和2.46倍,占总POM差异的57%和66%。垄作免耕土壤团聚体内粗颗粒有机质（coarse iPOM）分别为冬水田和水旱轮作土壤的1.56和1.40倍,占总POM差异的18%和19%。在＞10～20 cm土层有相似的趋势,但在＞10～20 cm层土壤粗iPOM的差异对总POM差异的贡献较0～10 cm层大。垄作免耕减少了对大团聚体的破坏并促进微团聚体向大团聚体团聚;降低了团聚体的周转速率,促进了细iPOM的固定,利于紫色水稻土对碳的固定和积累。     

菜地土壤有机碳分级以及总量变化的动态特征研究

Fertilisers significantly affect crop production and crop biomass inputs to soil organic carbon（SOC）. However, the long-term effects of fertilisers on C associated with aggregates are not yet fully understood. Based on soil aggregate and SOC fractionation analysis, this study investigated the long-term effects of organic manure and inorganic fertilisers on the accumulation and change in SOC and its fractions, including the C concentrations of free light fraction, intra-aggregate particulate organic matter（POM） and intra-aggregate mineral-associated organic matter（MOM）. Long-term manure applications improved SOC and increased the concentrations of some C fractions. Manure also accelerated the decomposition of coarse POM（cPOM） into fine POM（fPOM） and facilitated the transformation of fPOM encrustation into intra-microaggregate POM within macroaggregates. However, the application of inorganic fertilisers was detrimental to the formation of fPOM and to the subsequent encrustation of fPOM with clay particles, thus inhibiting the formation of stable microaggregates within macroaggregates. No significant differences were observed among the inorganic fertiliser treatments in terms of C concentrations of MOM, intra-microaggregate MOM within macroaggregate（imMMOM） and intra-microaggregate MOM（imMOM）. However, the long-term application of manure resulted in large increases in C concentrations of MOM（36.35%）, imMMOM（456.31%） and imMOM（19.33%） compared with control treatment.     

连续五年生物垃圾堆肥施用后地中海蔬菜种植系统中土壤有机碳的变化

Biowaste compost can influence soil organic matter accumulation directly or indirectly. A 5-year experiment was conducted to assess the influence of biowaste compost on the process of soil aggregation and soil organic carbon(SOC) accumulation in a Mediterranean vegetable cropping system. The study involved four treatments: biowaste compost(COM), mineral NPK fertilizers(MIN), biowaste compost with half-dose N fertilizer(COMN), and unfertilized control(CK). The SOC stocks were increased in COM, COMN, and MIN by 20.2, 14.9, and 2.4 Mg ha~(-1)over CK, respectively. The SOC concentration was significantly related to mean weight diameter of aggregates(MWD)(P 0.05, R~2= 0.798 4) when CK was excluded from regression analysis. Compared to CK, COM and COMN increased the SOC amount in macroaggregates( 250 μm) by 2.7 and 0.6 g kg~(-1)soil, respectively, while MIN showed a loss of 0.4g kg~(-1)soil. The SOC amount in free microaggregates(53–250 μm) increased by 0.9, 1.6, and 1.0 g kg~(-1)soil for COM, COMN, and MIN, respectively, while those in the free silt plus clay aggregates( 53 μm) did not vary significantly. However, when separating SOC in particle-size fractions, we found that more stable organic carbon associated with mineral fraction 53 μm(MOM-C) increased significantly by 3.4, 2.2, and 0.7 g kg~(-1)soil for COM, COMN, and MIN, respectively, over CK, while SOC amount in fine particulate organic matter(POM) fraction(53–250 μm) increased only by 0.3 g kg~(-1)soil for both COM and COMN, with no difference in coarse POM 250 μm. Therefore, we consider that biowaste compost could be effective in improving soil structure and long-term C sequestration as more stable MOM-C.     

Tillage effect on organic carbon in a purple paddy soil

The distribution and storage of soil organic carbon （SOC） based on a long-term experiment with various tillage systems were studied in a paddy soil derived from purple soil in Chongqing, China. Organic carbon storage in the 0-20 and 0-40 cm soil layers under different tillage systems were in an order： ridge tillage with rice-rape rotation （RT-rr） 〉 conventional tillage with rice only （CT-r） 〉 ridge tillage with rice only （RT-r） 〉 conventional tillage with rice-rape rotation （CT-rr）. The RT-rr system had significantly higher levels of soil organic carbon in the 0-40 cm topsoil, while the proportion of the total remaining organic carbon in the total soil organic carbon in the 0-10 cm layer was greatest in the RT-rr system. This was the reason why the RT-rr system enhanced soil organic carbon storage. These showed that tillage system type was crucial for carbon storage. Carbon levels in soil humus and crop-yield results showed that the RT-rr system enhanced soil fertility and crop productivity. Adoption of this tillage system would be beneficial both for environmental protection and economic development.     

Tillage and residue management effects on temporal changes in soil organic carbon and fractions of a silty loam soil in the North China Plain

Soil degradation and associated depletion of soil organic carbon (SOC) have been major concerns in intensive farming systems because of the subsequent decline in crop yields. We assessed temporal changes in SOC and its fractions under different tillage systems for wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping in the North China Plain. Four tillage systems were established in 2001: plow tillage (PT), rotary tillage (RT), no‐till (NT), and plow tillage with residues removed (PT0). Concentrations of SOC, particulate organic carbon (POC), non‐POC (NPOC), labile organic carbon (LOC), non‐LOC (NLOC), heavy fraction carbon (HFC) and light fraction carbon (LFC) were determined to assess tillage‐induced changes in the top 50 cm. Concentrations of SOC and C fractions declined with soil depth and were significantly affected by tillage over time. The results showed that SOC and its fractions were enhanced under NT and RT from 0 to 10 cm depth compared with values for PT and PT0. Significant decreases were observed below 10 cm depths (P < 0.05) regardless of the tillage system. The SOC concentration under NT for 0–5 cm depth was 18%, 8%, and 10% higher than that under PT0 after 7, 9, and 12 yr of NT adoption, respectively. Apparent stratification of SOC occurred under NT compared with PT and PT0 for depths >10 cm. All parameters were positively correlated (P < 0.01); linear regressions exhibited similar patterns (P < 0.01). Therefore, to maintain and improve SOC levels, residue inputs should be complemented by the adoption of suitable tillage systems.     

Long‐term cropping systems and tillage management effects on soil organic carbon stock and steady state level of C sequestration rates in a semiarid environment

A calcareous and clayey xeric Chromic Haploxerept of a long‐term experimental site in Sicily (Italy) was sampled (0–15 cm depth) under different land use management and cropping systems (CSs) to study their effect on soil aggregate stability and organic carbon (SOC). The experimental site had three tillage managements (no till [NT], dual‐layer [DL] and conventional tillage [CT]) and two CSs (durum wheat monocropping [W] and durum wheat/faba bean rotation [WB]). The annually sequestered SOC with W was 2·75‐times higher than with WB. SOC concentrations were also higher. Both NT and CT management systems were the most effective in SOC sequestration whereas with DL system no C was sequestered. The differences in SOC concentrations between NT and CT were surprisingly small. Cumulative C input of all cropping and tillage systems and the annually sequestered SOC indicated that a steady state occurred at a sequestration rate of 7·4 Mg C ha⁻¹ y⁻¹. Independent of the CSs, most of the SOC was stored in the silt and clay fraction. This fraction had a high N content which is typical for organic matter interacting with minerals. Macroaggregates (>250 µm) and large microaggregates (75–250 µm) were influenced by the treatments whereas the finest fractions were not. DL reduced the SOC in macroaggregates while NT and CT gave rise to higher SOC contents. In Mediterranean areas with Vertisols, agricultural strategies aimed at increasing the SOC contents should probably consider enhancing the proportion of coarser soil fractions so that, in the short‐term, organic C can be accumulated. Copyright © 2010 John Wiley & Sons, Ltd.     

耕地土壤有机碳组分的季节变化

Carbon fractions in soils apparently vary not only in space, but also over time. A lack of knowledge on the seasonal variability of labile carbon fractions under arable land hampers the reliability and comparability of soil organic carbon(SOC) surveys from different studies. Therefore, we studied the seasonal variability of two SOC fractions, particulate organic matter(POM) and dissolved organic carbon(DOC), under maize cropping: POM was determined as the SOC content in particle-size fractions, and DOC was measured as the water-extractable SOC(WESOC) of air-dried soil. Ammonium, nitrate, and water-extractable nitrogen were measured as potential regulating factors of WESOC formation because carbon and nitrogen cycles in soils are strongly connected. There was a significant annual variation of WESOC(coefficient of variation(CV) = 30%). Temporal variations of SOC in particle-size fractions were smaller than those of WESOC. The stocks of SOC in particle-size fractions decreased with decreasing particle sizes, exhibiting a CV of 20%for the coarse sand-size fraction(250–2 000 μm), of 9% for the fine sand-size fraction(50–250 μm), and of 5% for the silt-size fraction(20–50 μm). The WESOC and SOC in particle-size fractions both peaked in March and reached the minimum in May/June and August, respectively. These results indicate the importance of the time of soil sampling during the course of a year, especially when investigating WESOC.     

Assessing the effect of crop residue removal on soil organic carbon storage and microbial activity in a no‐till cropping system

Changes in agricultural management strategies have received much attention in recent years with a view to increasing or maintaining the amount of carbon (C) sequestered as soil organic C (SOC). In many parts of the world, minimum or no‐till management has been promoted as a means of improving soil quality, reducing losses of erosion and potentially increasing SOC stocks. However, no‐till systems can become problematic and potentially disease‐prone, especially due to high crop residue loadings. Consequently, residue removal either by harvesting or burning off may be employed to reduce these pressures. Here, we examined the effect of crop residue removal on C storage in soil that had been under no‐till management for 20 yr. We predicted improved physical properties (i.e. lower bulk density) and greater microbial activity under the residue retention soils due to greater readily available C and nutrients derived from crop residues. In contrast, we predicted relative reductions in SOC in the no residue soils due to a lack of available residue‐derived C for microbial use. Residue removal caused a relative C loss from the soil, which was related to C input, amount of nutrient availability and microbial activity. We demonstrate the importance of maintaining crop residue cover in no‐till cropping systems for soil function and highlight the potentially deleterious effects of changing management strategy to increased residue harvesting or removal by burning.     

免耕和秸秆还田对东北黑土区土壤团聚体组成及有机碳 含量的影响

为解决东北黑土区因不合理耕作导致的土壤结构性状变差及有机碳含量下降的问题,该研究于2015年开始,在黑龙江省哈尔滨市东北农业大学向阳试验基地开展。设置免耕+秸秆还田（NTS）、免耕（NT）、翻耕+秸秆还田（CTS）、翻耕（CT）4种处理,于2018、2019年采集土样,研究免耕措施及秸秆还田对东北薄层黑土区0～10、>10～20 cm土壤团聚体稳定性、土壤有机碳含量、各粒径团聚体内有机碳含量的影响。结果表明：2018和2019年0～10、>10～20 cm土层NTS处理>5 mm水稳性团聚体百分比含量及平均重量直径显著高于其他3种处理,NTS及NT处理土壤有机碳含量显著高于CTS及CT处理（P?<0.05）,4种处理各粒径水稳性团聚体有机碳含量峰值总体出现在1～2 mm处,NTS及NT处理>5、2～5、1～2 mm有机碳贡献率整体高于CTS及CT处理。研究表明,免耕与秸秆还田有利于薄层黑土坡耕地耕层土壤团聚体稳定性的提高和各粒级下团聚体有机碳的积累,与其他3种处理相比,免耕+秸秆还田效果更佳。     

Effect of ultrasonic power on soil organic carbon fractions

Ultrasonic dispersion is a prevalent tool for soil fractionation. It is widely ignored that variation in ultrasonic power might lead to significantly different dispersion. We evaluated the effect of power variation with constant energy on the fine fraction mass, its organic C content and quality. All parameters increased significantly with power. The term “stable aggregates” as used in fractionation schemes cannot be defined by ultrasonic energy alone but power needs to be standardized, too.