施用有机肥料对土壤胡敏酸结构特征的影响──胡敏酸的光学性质

本工作通过田间试验和模拟试验研究了施用有机物料对棕壤、草甸土和水稻土中胡敏酸光学性质的影响。结果表明，施用有机物料后使土壤胡敏酸的吸光值和相对色度下降，色调系数升高，甚至发生类型改变。还使胡敏酸紫外２８５ｎｍ和红外２９２０ｃｍ＾－１吸收增强，１７２０ｃｍ＾－１和萤光强度减弱，激发光谱最大强度波长紫移。说明胡敏酸的分子结构变得脂族化，简单化和年轻化。两种有机物料相比，玉米秸杆对胡敏酸的木质素特征作用     

施用有机肥料对胡敏酸结构特征的影响─—胡敏酸的1H-核磁共振波谱

通过在棕壤，草甸土和水稻土上进行田间试验和模拟试验表明，施用有机肥料一般使胡敏酸的脂族Ｈ的相对含量增加，聚亚甲基链长，变短，芳香Ｈ相对含量和由之计算的芳香度下降，从而导致ＨＡ中脂族Ａｌｉ－Ｈ与Ａｒ－Ｈ的比值增加，即发生了脂族化。     

有机物料施用下原生盐碱土胡敏酸结构特征

为研究不同有机物料对原生盐碱土胡敏酸官能团组成的影响,以吉林省大安市原生盐碱地为研究对象,设置空白处理(CK)、颗粒状秸秆处理(KL)、正常玉米秸秆处理(JG)、牧草处理(MC)和羊粪处理(YF),通过红外光谱与主成分分析(Principal component analysis,PCA)相结合,研究不同有机物料施用下土壤胡敏酸红外光谱特征。结果表明,有机物料各处理与CK处理相比增加了土壤胡敏酸中脂肪碳和芳香碳的相对含量,减少了羧基碳的含量。除KL处理外,其他处理均增加了土壤胡敏酸中氨基化合物的相对含量。同时有机物料的施用增加了土壤胡敏酸的脂族碳/羧基碳和脂族碳/芳香碳比值,表征有机物料的施用使得土壤胡敏酸结构缩合度和氧化度下降,脂族性增强,芳香性降低,胡敏酸结构趋于脂族化、简单化、年轻化。对比两种秸秆处理,发现KL处理更有利于土壤新形成结构年轻化、简单化、脂族性强的胡敏酸分子。根据PCA结果,有机物料的施用是土壤中脂族性碳、芳香族碳以及氨基化合物的主要来源之一,为探讨胡敏酸官能团的来源提供依据。通过红外光谱结合PCA,发现了土壤胡敏酸官能团组成对有机物料的不同响应,为研究有机物料的施用对土壤胡敏酸性质的影响机制提供理论依据。     

不同处理牛粪对植菜土壤腐殖质结构特征的影响

通过元素组成分析法、红外光谱分析法(IR)、核磁共振光谱分析法(13 C-NMR)等现代分析方法,研究施用新鲜牛粪、腐解牛粪和蛴螬牛粪2a后对植菜轮作土壤胡敏酸(HA)和富里酸(FA)的影响。结果表明,与单施化肥(CK)相比,不同牛粪处理对植菜土壤胡敏酸和富里酸的元素组成影响有较大的差异,各牛粪处理均引发植菜土壤胡敏酸C含量和C/H降低,O含量、O/C和(N+O)/C升高,富里酸C含量和C/N升高,N、O含量和O/C降低,降低了植菜土壤胡敏酸的缩合程度,升高了土壤胡敏酸的氧化程度和极性,降低了植菜土壤富里酸的氧化程度。不同牛粪处理使植菜土壤胡敏酸的脂肪族化合物减少,且均含有苯基碳、酚羟基C、芳香醚和(或)与O、N等取代基邻、对位的连H芳香C,使芳构化程度增加,富里酸的脂肪族化合物增加,芳香类、羧基类化合物减少,芳构化程度降低。不同牛粪处理的植菜土壤未改变土壤腐殖质的基本结构特征,只引起植菜土壤的结构单元和官能团数量上的差异。     

有机肥施用年限对碱化草甸土腐殖质组成的影响

以黑龙江省肇州县永乐镇15年的长期施用有机肥试验为平台,分析了有机肥不同施用年限对碱化草甸土腐殖质组成和胡敏酸光学性质的影响.农牧结合长期施用有机肥,使土壤中总有机碳含量以及腐殖质中胡敏酸碳、胡敏素碳含量随改良年限的增加而增加,分别提升了116.3％、120.7％和259.2％,与对照比较差异显著,对富里酸碳含量的影响不大;同时胡敏酸与富里酸的比值也提高了129.2％,土壤的理化性质得到了改善;使色调系数(△logK)在15年间总体呈增大趋势,提高了35.7％.为利用农牧结合的方式改良碱化草甸土提供依据.     

施用生物质炭对黑土腐殖质组成及水稳性团聚体分布的影响

为探究生物炭对土壤腐殖质组成和团聚体特征的影响，以东北黑土区植烟土壤为研究对象，设置了3个处理，2019-2020年连续施用低量生物炭5t/hm2（C1）；高量生物炭25t/hm2（C2）和不施生物炭（CK），分析了不同用量生物炭对土壤腐殖质组分及水稳性团聚体分布的影响，并利用傅里叶红外光谱(FTIR)和13C核磁共振光谱(13C-NMR)对土壤胡敏酸化学结构进行表征。结果表明：C1和C2处理分别使富里酸减少了16.90%和40.85%，胡敏酸含量显著增加了14.86%和33.78%，胡敏酸在腐殖酸中所占比例（PQ值）也显著增加；FTIR和13C-NMR分析表明，C2处理的土壤胡敏酸的2920/1620值降低了11.82%，脂族C/芳香C比值降低了13.04%，表明高量生物炭使胡敏酸芳构化程度增强，脂肪结构比例降低；生物炭的添加促使土壤大团聚体（>0.25mm）比例增加，C2处理提升大团聚体的作用更显著。结合相关性分析发现，胡敏酸含量与2~0.25mm大团聚体含量显著正相关，胡敏酸分子的脂肪族官能团特征与>2mm粒级团聚体显著正相关。此外，C1和C2处理显著提高了烟叶产量。从而表明，生物炭能提升土壤腐殖质中胡敏酸含量和结构，有利于土壤大团聚体形成，提高土壤固碳潜力，对作物有一定的增产效果。     

不同培肥方式黑土腐殖质形态特征研究

针对吉林省黑土区存在的土壤有机质下降、耕地质量退化等问题,利用公主岭国家黑土肥力与肥料效益监测基地连续20年的长期定位试验,采用核磁共振波谱分析法(NMR)、红外光谱分析法(IR)等现代分析方法,研究了不同培肥途径耕层土壤腐殖质的组成、形态结构及动态变化趋势。结果表明:不同培肥途径对耕层土壤腐殖质特征影响明显。施用玉米秸秆处理(S+NPK)和施用有机肥+轮作处理(M+NPK+R)均显著增加了土壤胡敏酸中脂肪族结构成分,单施有机肥处理(M+NPK)显著增加了土壤胡敏酸中羟基含量,S+NPK处理游离羧基含量显著增多。S+NPK、M+NPK及M+NPK+R处理,土壤富啡酸的甲基、亚甲基和次甲基结构成分显著增多,游离羧基含量也显著增多。单施化肥处理,浸提的富啡酸中无机碳酸盐和硅酸盐成分明显增多,化肥长期施用导致土壤中游离富啡酸数量显著减少,土壤的耗竭式利用,导致土壤中铁、铜结合态或络合态的富啡酸增加。不同培肥方式对黑土胡敏酸和富啡酸的元素组成影响有较大的差异,但均可引发胡敏酸C含量降低,N含量增加,富啡酸C、N、H含量增加,O含量降低,可通过不同的培肥方式对土壤腐殖质的元素组成进行调节。     

玉米秸秆分解期间胡敏酸、富里酸动态变化的研究

通过室内培养试验,研究了玉米秸秆在暗棕壤中分解期间(1-15d)胡敏酸(HA)、富里酸(FA)数量与特性的动态变化规律。结果表明:玉米秸秆分解期间,HA的绝对数量先增加后下降,FA的绝对数量下降,可提取腐殖质中HA的比例(PQ)增加,说明最初FA的形成速度大于HA,随培养时间延长FA转化为HA。HA、FA的色调系数(△logK)和活化度下降,而相对色度(RF)增加,表明HA、FA的分子结构逐渐变得复杂化。     

连续提取对土壤腐殖质组分数量与特性的影响

以暗棕壤为供试土壤,研究了NaOH和NaOH+Na4P2O7连续提取对土壤腐殖质组分数量和特性的影响。结果表明:用两种提取剂得到的土壤腐殖质组分总量相差不大,并且其中HA组分的数量均高于FA组分。随提取次数增加,胡敏酸(HA)、富里酸(FA)和胡敏素(HM)的绝对数量均下降,HA、FA的相对数量也下降,而HM的相对数量则增加。以NaOH为提取剂时,最后得到的腐殖质组分中FA的相对比例高于HA;而用NaOH+Na4P2O7为提取剂时,最后得到的腐殖质组分中HA的相对比例则高于FA。连续提取过程中,HA、FA的色调系数(Δlogk)和活化度(AD)通常呈增加趋势,而相对色度(RF)下降,说明后提取出的HA、FA的缩合度较低,脂族性较强。用RF来表征HA、FA特性变化更为合适。     

稻草腐解过程中形成胡敏酸的组成和结构研究

通过稻草腐解实验,采用化学分析方法,研究了稻草腐解过程中土壤胡敏酸的化学特征的动态变化,旨在丰富农作物秸秆还田过程中的胡敏酸化学组成、性质与结构变化的特征。在试验培养条件下,施用稻草后土壤的有机碳含量提高了31.71%,腐殖质含量增加了51.93%,都在90d时达到最大值。施用稻草45d时的PQ值(HA在HS中所占的比例)明显降低,在90d和135d时的PQ值与45d时变化不大。施用稻草后土壤胡敏酸的色调系数(ΔlogK)逐渐减少,相对色度(RF)值迅速增大,胡敏酸的氧化程度和芳构化程度增强。胡敏酸的元素组成以碳为主,含量在52%左右,其次为氧。H/C的比值逐渐降低,O/C的比值不断增大。羧基和酚羟基为主要的酸性基团。羧基含量先降低,后随着腐解的进行,其含量不断升高;酚羟基的含量变化与羧基的含量变化趋势相反;羰基含量逐渐增加。施用稻草会引起紫色水稻土胡敏酸化学组成和结构的变化。     

小麦玉米秸秆连续还田对土壤有机质红外光谱特征及氮素形态的影响

通过6年的田间定位试验,探讨了CK(不施肥,秸秆不还田)、SF(施肥,秸秆不还田)、T1(施肥,玉米秸秆还田)、T2(施肥,小麦秸秆还田)、T3(施肥,玉米小麦秸秆还田)5种处理对土壤氮素形态和有机质红外光谱特征的影响。结果显示:与SF相比较,T1、T2、T3处理使土壤有机氮含量分别增加3.7%、15.9%和18.5%,土壤无机氮含量分别减少15.5%、15.9%和24.0%,其中铵态氮分别降低11.3%、6.0%和12.0%,土壤硝态氮含量分别降低19.3%、22.9%和32.1%;与SF相比较,T1、T3处理土壤有机质(SOM)的C/N分别降低2.8%和1.4%,T2处理SOM的C/N提高1.4%;C/O分别提高9.2%、12.8%和12.1%;而H/C分别降低4.6%、5.5%和4.6%。红外图谱分析显示,T1、T2、T3处理引起3 500~3 200 cm?1处的吸收峰增加,2 924 cm?1处出现了新的弱峰,表明SOM的脂肪族特征增加,且以1 630 cm?1处为中心的宽带吸收峰强度明显增加,SOM芳构化程度增强。研究表明,施肥显著提高了土壤有机氮、无机氮含量,以及土壤有机质的C/N和C/O。而秸秆还田降低了土壤无机氮,提高了土壤有机氮,使SOM的C/N、H/C下降,C/O上升,同时提高了SOM中酚基、羟基、羧基、芳香碳和酰胺含量,其中以小麦、玉米秸秆双季还田的效果最为显著。     

长期施肥对红壤性水稻土有机磷组分的影响

以19年肥料长期定位试验为背景,应用Bowman和Cole的有机磷分组方法,对红壤性水稻土有机磷组分及其变化进行了研究。结果表明:红壤性水稻土耕层有机磷含量较高,为225.93～322.47mgkg-1,占土壤全磷的28.59%～42.34%。土壤有机磷各组分中以中度活性有机磷含量最高,平均为134.80mgkg-1,占有机磷总量的51 58%;中度稳定性有机磷(92.46mgkg-1)占35.38%;高度稳定性有机磷(20.35mgkg-1)占7.79%;活性有机磷含量最低(13.67mgkg-1),占5.23%;长期施肥对土壤各组分有机磷量产生影响,耗磷处理,主要是中度活性有机磷和活性有机磷下降,降低量以CKNK处理。施磷主要促进中度稳定性有机磷和高度稳定性有机磷的增加,增加幅度以NPK+OMPNPK处理。不同施肥措施对土壤有机磷和无机磷库的耗竭或积累速度是不同的,耗磷条件,土壤有机磷/无机磷的比值上升,施磷使有机磷/无机磷比值下降.土壤供磷强度与有机磷/无机磷的比值呈显著负相关(r=-0.9497* ,r0.05=0.878)。     

Effect of organic matter applications on 13C-NMR spectra of humic acids of soil

Much attention has been paid to improving soil fertility with organic matter (OM) application, which not only deals with organic wastes and protects the environment, but also maintains soil fertility and increases crop yields. Much research has also been on the effects of OM applications on the soil’s physical, chemical and biological properties, but relatively less attention has been spent on humic substance (HS). In order to clarify the mechanism of improving soil fertility by applying OM, we analysed the changes of structural characteristics of humic acid (HA) from OM applications to soils by ¹³C‐NMR, chemical analysis, thermal analysis, optical properties, IR and fluorescence spectroscopy. Samples of a brown soil (Paleudalf) and a paddy soil (an anthropogenic soil originating from Udifluvents) were collected from the plough layer of the long‐term field experiment at Shenyang Agricultural University and Liaoning Provincial Alkali‐Saline Soil Institute, respectively. Both field experiments included three treatments each: (i) brown soil, zero‐treatment (CK_br) and two pig manure (PM) applications (O₁ and O₂) at annual rates of 0.9 t ha^?1 and 1.8 t ha^?1 of organic carbon, respectively; and (ii) paddy soil, zero‐treatment (CK_pad), pig manure (O_p) and rice straw (O_r) at annual rates of 2.62 t ha^?1 and 1.43 t ha^?1 of organic carbon, respectively. An incubation experiment was also carried out to test the field experiment on the brown soil, namely four treatments: zero‐treatment (CK_c), and three pig manure applications at rates of 30 g kg^?1 (C₁), 50 g kg^?1 (C₂) and 70 g kg^?1 (C₃), respectively. The total incubation was 180 days. The results indicated that number‐average molecular weights (M_n), total acidity, aromaticity, excitation maximum wavelength (λ_Exmax), and the heat ratio of the high to moderate temperature exothermic regions (H₃/H₂) of the HA all decreased after OM application. The degree of activation (AD), the absorption intensity ratio of 2920 cm^?1 to 1720 cm^?1 in infrared spectra (IR_2920/1720), alkyl C and O‐alkyl C of the HA increased. The HA structure tended to become simpler and more aliphatic.     

不同水分状况下施锌对玉米生长和锌吸收的影响

选择潮土(砂壤)和土(粘壤)两种质地不同的土壤,进行盆栽试验,研究不同土壤水分条件下施锌对玉米生长和锌吸收的影响。结果表明,施锌显著增加了玉米植株根、茎、叶以及整株干物质重;缺锌条件下玉米植株根冠比、根叶比和根茎比趋向增大。施锌显著提高了玉米植株各器官中锌的浓度和吸收量,并明显促进锌向地上部运移。干旱胁迫抑制了玉米植株生长,根冠比、根茎比、根叶比增大;随着土壤水分供应增加,植株生长加快,各器官生物量以茎和叶增加大于根。水分胁迫下,在潮土上玉米叶片中锌浓度上升;在土上叶片中锌浓度下降。但增施锌后,根和茎锌浓度增加幅度较大,叶片增加幅度较小;施锌和水分胁迫对根和茎锌浓度的交互作用极显著。水分胁迫下,玉米植株对锌的吸收总量减少。水分胁迫和锌肥施用对玉米叶片、茎锌吸收量的交互作用十分显著,但对根锌吸收量的交互影响不显著。     

长施马粪对暗棕壤团聚体腐殖质数量和质量的影响

运用元素和红外光谱分析研究了暗棕壤长期施用马粪(每3年施肥1次)、施低量化肥和马粪配施高量化肥对水稳性大团聚体(2 mm和2~0.25 mm)、微团聚体(0.25~0.053 mm)和粉/黏粒粒级(0.053 mm)中腐殖物质-胡敏酸(HA)的分布及其结构特征的影响,探讨施肥对农田土壤肥力的贡献及其团聚体的固碳机制。施用马粪和马粪配施高量化肥分别提高(49.06%)和降低(31.04%)了2~0.25 mm大团聚体比例,3种施肥措施均提高了土壤有机碳(SOC)数量,但对土壤HA数量影响不显著。不同施肥措施对不同粒级团聚体中HA的分子结构特征影响不同,3种施肥措施均降低了2~0.25 mm大团聚体HA的缩合度,芳香性增加;微团聚体HA缩合度降低,脂族性增强;施用马粪提高了粉/黏粒HA的缩合度和脂族性,马粪配施高量化肥提高了粉/黏粒HA的缩合度和芳香性,施用低量化肥,粉/黏粒HA缩合度下降,芳香性提高。因此,长施马粪提高了土壤SOC数量,促进2~0.25 mm大团聚体的形成,大团聚体中HA的稳定性提高,利于土壤固碳,而0.25~0.053 mm微团聚体和0.053 mm粉/黏粒HA的活性增强,利于土壤肥力供给,这些团聚体是评估长施马粪对腐殖质质量产生影响的重要粒级。     

Chemical structure of humic acids in biosolids-amended soils as revealed by NMR spectroscopy

We used NMR spectroscopy to characterize humid acids extracted from soils that had received long-term application of 2 levels of biosolids to evaluate the soil organic matter (SOM) stability in biosolids-amended soils. The study also quantified fulvic acids (FAs), humic acids (HAs) and Fe/Al oxides. The soils were collected in 2004 from 7 fields, in Fulton County, southwestern Illinois, which received biosolids at a cumulative rate of 0 (control), 554 (low biosolids) and 1,066 (high biosolids) Mg ha⁻¹. The application of biosolids increased both FA and HA contents, but biosolids-amended soil and control soil did not differ in FA/HA ratio. Biosolids application had no effect on water-soluble organic carbon content. Biosolids application increased the presence of Fe/Al in the SOM complex and lowered its C/Fe and C/Al ratios. ¹³C NMR spectra showed increased alkyl C and decreased aromatic C content in soil HAs with the application of biosolids, and the extent of such changes was higher with high than low biosolids treatment. Under biosolids application, the soil HAs’ C structure shifts from O-alkyl-dominant to alkyl-dominant. Biosolids application does not decrease SOM stability but rather increases the stability of soil humic substances.     

有机物料对白土土壤胡敏酸结构特征的影响

【目的】研究有机物料施入对白土土壤的腐殖质含量组成和胡敏酸(HA)结构特征的影响,为明确不同腐殖质组分对土壤肥力的影响提供理论依据。【方法】供试土壤为江苏省溧阳市南渡镇"白土改良大田示范试验核心区"的南方中低产水稻土(白土)。试验设秸秆还田(ST)、施有机肥(OM)和对照(CK,不施有机物)3个处理,培肥3年。同时采集试验田周围相邻的江苏省耕地质量监测点(2007~2013年)的每年施化肥(LAF)和长期不施肥(NF)的两种处理土壤进行比对研究。分别测定土壤的基本理化性质及其腐殖质含量的组成,并提取土壤胡敏酸(HA)固体样品利用红外光谱和元素分析来进行结构表征。【结果】秸秆还田和施有机肥处理的有机碳、全氮含量明显高于对照;与对照相比,施有机物料土壤HA的E4/E6比值增加,且秸秆还田施有机肥对照。红外光谱显示,试验区域和耕地监测点的不同处理土壤HA均在1650 cm-1处(酰胺I带)和1550 cm-1处(1500~1580 cm-1酰胺II带伸缩振动)有特征吸收。施有机肥和秸秆还田处理土壤HA的2920/1720、2920/1650比值显著大于对照。在元素组成上,OM、ST处理的土壤腐殖质(HA)中C、H、N的含量比均高于CK,相对长期施化肥(LAF)和不施肥(NF)的土壤有明显提高,而氧元素的含量呈降低的趋势;OM和ST处理土壤HA的[H]/[C]和[O]/[C]原子数比均低于CK;与LAF和NF处理相比,试验区域各处理土壤腐殖质的[H]/[C]和[O]/[C]原子数比均有明显降低。【结论】有机物料施入土壤后可增加土壤有机碳含量,改善土壤理化性质,提高作物产量和品质,且施入土壤的有机物料可转化为新的腐殖质,降低土壤的腐殖化程度。土壤腐殖质(HA)的红外光谱分析说明,白土土壤HA具有明显的酰胺类化合物特征。有机物料施入后使得土壤脂族性增强,羧基量减少,芳香度降低;秸秆还田和施有机肥处理与对照相比,土壤HA的[H]/[C]和[O]/[C]比均有下降的趋势,且HA的氮素含量明显增加,这显示有机物料施入后白土土壤腐殖质发生"脱水"过程,同时也反映了白土土壤腐殖质形成的特征。     

Soil Organic Matter Quality and Zinc and Lead Sorption as Affected by a Sewage Sludge Or a Sewage Sludge Compost Application

Sewage sludge (SS) or sewage sludge compost (SSC) were applied to soil under controlled conditions, at rates of 0 or 200 Mg ha^?1, to investigate changes in dissolved organic matter (DOM), humic acids (HA), and Pb and Zn sorption in the soil. Infrared spectroscopy, visible spectrophotometry, and sorption isotherms (mono-metal and competitive sorption systems) methods were used to assess the changer. The E₄/E₆ ratio (λ at 465 / λ at 665 nm) and the infrared spectra of DOM and HA showed aromatic behaviour in compost-soil (SSC-S); in contrast sewage sludge-soil (SS-S) showed an aliphatic behaviour. Application of either SS or SSC increased the Pb and Zn sorption capacity of soil. The Pb and Zn sorption increased in soil and soil mixtures with a competitive metal system. The metal affinity sequence for soil, SS-S, and SSC-S was compared with the predicted affinity sequences obtained from metal properties. Poor correspondence was observed between the metal affinity sequence and the metal affinity sequence predicted by ionic potential, indicating that metals bonding to soils were not predominantly electrostatic. An affinity sequence based on Pearson's theory agreed with the metal affinity sequences for soils. A statistical analysis showed that the bands assigned to esters (1080 cm^?1) of DOM, phenolic OH (1420 cm^?1), amide I (1650 cm^?1), carboxyl and carbonyl C=O stretches of different nature, C=O stretch of aromatic esters, aliphatic cetone, aldehyde (1720 cm^?1), ethers and esters (1230 cm^?1), aliphatic alcohols (1125 cm^?1), and lignin (1380 cm^?1) of HA were correlated with Zn constants of Langmuir adsorption isotherm (P < 0.05).     

Characterization of DAX‐8 adsorbed soil fulvic acid fractions by various types of analyses

We investigated the optical absorption properties (A ₄₀₀/C and A ₆₀₀/C values), elemental composition, weight-averaged molecular weight (Mw), and liquid-state carbon-13 (¹³C) nuclear magnetic resonance (NMR) spectroscopy of DAX-8 adsorbed fulvic acid fractions (DAX-8 FAs) in various soils (n?=?36) to establish the general trends in their chemical characteristics. We also compared our results with those of humic acids (HAs) obtained from the same soils used in this study and other published data to discuss the differences between them. Our results clearly indicate that DAX-8 FAs with high carboxyl C content have small Mw and low hydrogen to carbon (H/C) ratio. In addition, DAX-8 FAs with high carbonyl C and alkyl C content have high A ₄₀₀/C values and H/C ratios, respectively. These results strongly suggest that DAX-8 FAs with high aliphatic chemical properties have low carboxyl C content, large Mw and high H/C ratio. There are significant differences in chemical characteristics among the various soil types in almost all data; e.g., DAX-8 FAs from Podzols showed significantly higher A ₄₀₀/C values, larger Mw, higher carbonyl C and O-aryl C content than those obtained from Andosols. However, these two C functional groups are relatively low values in the total C content among all soil types, suggesting that DAX-8 FAs may exhibit only small differences in chemical properties among the various soil types. The comparison with published data regarding soil HAs shows that DAX-8 FAs are characterized by smaller Mw; lower C, H, and nitrogen (N); higher oxygen (O) content; higher O/C; lower O/H ratios; higher carboxyl C content; and lower aryl C content in total C.