Humus quantity and quality of an entic Haplustoll under different soil‐crop management systems

Abstract

The effects of different management systems on the level and composition of humified organic matter in an entic Haplustoll from the semiarid Pampean region were studied. The systems were: TPc, wheat‐mixed pasture; TV, wheat (Triticum aestivum), oat (Avena sativa), corn (Zea mays) and triticale grasses; TP, wheat‐cattle grazing; and V, virgin, non cultivated. Humic acids were extracted, fractionated, and analyzed for their organic carbon (OC) content, elemental composition, and E4:E6 spectral ratios. The infrared (IR), electron spin resonance (ESR). and ¹³C‐NMR spectra were registered on these humic acids. The TP rotation showed the lowest humic acid‐carbon to fulvic acid‐carbon (HA‐C:FA‐C) ratio. The lower O:C ratio of humic acids from the cropped soils indicates a higher level of oxidation than that of the virgin one. The comparison of the different methodologies allowed us to conclude that crop rotations and conservation tillage were adequate to mantain the level and composition of the soil organic matter and humus which affected the soil fertility and level of productivity     

Macromolecule‐P associations and inositol phosphates in some chilean volcanic soils of temperate regions

Abstract

Total organic P, humic and fulvic acid‐P associations and inositol phosphates in nine volcanic soils of southern Chile were determined. The concentration of organic P (Po) ranged from 654 to 1942 ppm accounting for 49% to 64% of total soil P. Phosphorus associated to humic (HA‐P) and fulvic acids (FA‐P) accounted for 51–68% and 32–49% of Po, respectively. Inositol penta‐ and hexaphosphates represented 42% to 67% of Po suggesting that significant amounts are associated with both humic and fulvic acids. Po content was significantly correlated to organic C, total soil P and HA‐P. HA‐P and FA‐P fractions obtained from the most representative soil were examined by dyalisis and gel filtration. While approximately 96% of HA‐P presented a molecular weight higher than 100,000 daltons, 53% of FA‐P had a molecular weight under 12,000 daltons. It is suggested that these more labile organic P forms would be more easily mineralized, thus increasing the available P pool.     

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.     

Transformation of organic matter from maize residues into labile and humic fractions of three European soils as revealed by 13C distribution and CPMAS-NMR spectra

The dynamics of incorporation of fresh organic residues into the various fractions of soil organic matter have yet to be clarified in terms of chemical structures and mechanisms involved. We studied by ¹³C‐dilution analysis and CPMAS‐¹³C‐NMR spectroscopy the distribution of organic carbon from mixed or mulched maize residues into specific defined fractions such as carbohydrates and humic fractions isolated by selective extractants in a year‐long incubation of three European soils. The contents of carbohydrates in soil particle size fractions and relative δ¹³C values showed no retention of carbohydrates from maize but rather decomposition of those from native organic matter in the soil. By contrast, CPMAS‐¹³C‐NMR spectra of humic (HA) and fulvic acids (FA) extracted by alkaline solution generally indicated the transfer of maize C (mostly carbohydrates and peptides) into humic materials, whereas spectra of organic matter extracted with an acetone solution (HE) indicated solubilization of an aliphatic‐rich, hydrophobic fraction that seemed not to contain any C from maize. The abundance of ¹³C showed that all humic fractions behaved as a sink for C from maize residues but the FA fraction was related to the turnover of fresh organic matter more than the HA. Removal of hydrophobic components from incubated soils by acetone solution allowed a subsequent extraction of HA and, especially, FA still containing much C from maize. The combination of isotopic measurements and NMR spectra indicated that while hydrophilic compounds from maize were retained in HA and FA, hydrophobic components in the HE fraction had chemical features similar to those of humin. Our results show that the organic compounds released in soils by mineralization of fresh plant residues are stored mainly in the hydrophilic fraction of humic substances which are, in turn, stabilized against microbial degradation by the most hydrophobic humic matter. Our findings suggest that native soil humic substances contribute to the accumulation of new organic matter in soils.     

Carbon and nitrogen in operationally defined soil organic matter pools

Humic substances [humic acid (HA), fulvic acid (FA), and insoluble humin], particulate organic matter (POM), and glomalin comprise the majority (ca 75%) of operationally defined extractable soil organic matter (SOM). The purpose of this work was to compare amounts of carbon (C) and nitrogen (N) in HA, FA, POM, and glomalin pools in six undisturbed soils. POM, glomalin, HA, and FA in POM, and glomalin, HA, and FA in POM-free soil were extracted in the following sequence: (1) POM fraction separation from the soil, (2) glomalin extraction from the POM fraction and POM-free soil, and (3) co-extraction of HA and FA from the POM fraction and POM-free soil. Only trace amounts of HA and FA were present in the POM fraction, while POM-associated glomalin (POM-glomalin) and POM alone contributed 2 and 12%, respectively, of the total C in the soil. Mean combined weights for chemically extracted pools from POM and from POM-free soil were 9.92 g glomalin, 1.12 g HA, and 0.88 g FA kg⁻¹ soil. Total protein and C, N, and H concentrations showed that glomalin and HA were, for the most part, separate pools, although protein was detected in HA extracts. Even though percentage carbon was higher in HA than in glomalin, glomalin was a larger (almost nine times) operationally defined pool of soil organic C. Glomalin was also the largest pool of soil N of all the pools isolated, but all pools combined only contained 31% of the total N in the soil.     

Long-term effects of farmyard manure and sewage sludge on some soil biochemical characteristics

 Changes in some soil biochemical properties were investigated following repeated applications of aerobically digested sewage sludge (SS) under field conditions over 12 years, and compared with those of an adjacent soil cultivated and amended with 5 t ha^–1 year^–1 (dry weight) farmyard manure (FYM) for at least 40 years, as well as with those of an adjacent uncultivated soil, in order to ascertain changes in soil quality. A short-term aerobic incubation was used to determine the potential of the samples to mineralize the organic C supplied. Results indicated that cultivation caused a reduction in total, humified and potentially mineralizable organic C, total N, light-fraction (LF) C, total and water-soluble carbohydrates, phenolic compounds, cation-exchange capacity (CEC), microbial biomass C, specific respiration, hydrolytic and urease activities, and an increase in the heavy metal content. Total and water-soluble carbohydrates and phenolic compounds expressed as a percentage of total organic C (TOC) were similar in the differently managed plots. Of the two amendments, FYM treatments showed higher amounts of TOC and N, LF-C, total and water-soluble carbohydrates, phenolic substances, CEC, specific respiration of biomass, hydrolytic and urease activities, similar amounts and characteristics of humified organic matter and lower concentrations of Cu, Zn and Cr. Both FYM and SS were inadequate treatments for the restoration of soil organic matter lost as a consequence of cultivation. Received: 20 October 1998     

Using soil organic matter fractions as indicators of soil physical quality

The objective of this study was to evaluate the use of chemical and physical fractions of soil organic matter (SOM ), rather than SOM per se , as indicators of soil physical quality (SPQ ) based on their effect on aggregate stability (AS ). Chemically extracted humic and fulvic acids (HA and FA ) were used as chemical fractions, and heavy and light fractions (HF and LF ) obtained by density separation as physical fractions. The analyses were conducted on medium‐textured soils from tropical and temperate regions under cropland and pasture. Results show that soil organic carbon (SOC ), SOM fractions and AS appear to be affected by land use regardless of the origin of the soils. A general separation of structurally stable and unstable soils between samples of large and small SOC content, respectively, was observed. SOM fractions did not show a better relationship with AS than SOC per se . In both geographical regions, soils under cropland showed the smallest content of SOC , HA and carbon concentration in LF and HF , and the largest HF /LF ratio (proportion of the HF and LF in percent by mass of bulk soil). With significant associations between AS and SOC content (0.79**), FA /SOC (r  = −0.83*^*), HA /FA (r  = 0.58*^*), carbon concentration of LF (r  = 0.69*^*) and HF (r  = 0.70*^*) and HF /LF ratio (r  = 0.80*^*), cropland showed lowest AS . These associations indicate that SOM fractions provide information about differences in SOM quality in relation to AS and SPQ of soils from tropical and temperate regions under cropland and pasture.     

The geochemistry of black water in selected coastal streams of the Southeastern United States

Abstract

An investigation was conducted in a watershed formed by the tributaries of the Little River in South Georgia to study the nature of the humic and inorganic fractions of black water, and their influence on stream water quality. Large amounts of black colored water were sampled during 1983 to 1984 according to streamflow pattern in December, March, June and September. Measurements of air and water temperature and dissolved oxygen were made at the gaging sites, whereas water analysis for conductivity, Cl, NO₃‐N, NH₄‐N, P, total N, and other macro‐ and microelements were conducted in the laboratory. Fulvic (FA) and humic acid (HA) were isolated from the water samples, and analyzed by infrared and ¹³C NMR spectroscopy. Suspended clay from the water samples were collected and determined by x‐ray diffraction analysis. The results showed that black water was characterized by low conductivity and low ion concentrations indicating satisfactory chemical quality. The Na content was half the amount of other rivers in the Southeastern United States, whereas the ? content was similar to the world average. A seasonal fluctuation was noticed for Ca and Mg concentration. The increase of these ions during high streamflow in spring and summer was attributed to agricultural practices in the surrounding lands. Dissolved organic matter (DOM) concentration was highest in December during low streamflow. As DOM content decreased during high streamflow, water pH increased. A large part of the humified DOM was composed of fulvic acid, which was more aromatic in nature than soil‐fulvic acid as determined by ¹³C NMR. The suspended clay had a composition reflecting the clay mineralogy of Tifton soils in the surrounding uplands. It is believed that the Tifton soil, with its low activity clay and hence low CEC, may not be able to buffer the effect of acid leaching of black water.     

矿化垃圾中植物大量营养元素含量的剖面分布特征

对经长期填埋后已稳定化的垃圾进行开采和资源化利用,能增加现有填埋场库容,对解决城市生活垃圾填埋场紧张的现状具有重要意义。以一个已运行10a以上的垃圾填埋场为研究对象,对已填埋6、8、10a的矿化垃圾中一些植物大量营养元素的剖面分布进行了测定。结果表明：（1）矿化垃圾中氮、磷、钾养分的浓度总和已达到国家有机肥养分含量标准,有机质含量也明显高于土壤的有机质含量,从植物养分供应的角度看,矿化垃圾可具有资源化利用的价值;（2）矿化垃圾中养分主要以氮素为主,磷、钾营养元素的总量较低,但速效态含量相对较高;（3）不同填埋深度的矿化垃圾中,主要营养元素的含量大部分在填埋8~10a后达到相对稳定的状态,但受矿化垃圾组成成分复杂性的影响,部分形态营养元素的变化规律不明显。     

Application of Near Infrared Reflectance Spectroscopy for the Assessment of Soil Quality in a Long‐Term Pasture

Abstract

The objective of the present study was to assess the ability of near infrared reflectance spectroscopy (NIRS) to analyze chemical soil properties and to evaluate the effects of different phosphorus (P) and potassium (K) fertilization rates on soil quality in different layers of a long‐term pasture. The NIRS calibrations were developed for humus, total Kjeldahl nitrogen (N_Kjeldahl), and several humic substances (HA1, “mobile” humic acids fraction; ΣHA, sum of humic acids; FA1, “mobile” fulvic acids; ΣFA, sum of fulvic acids, etc.) using soil samples of rather heterogeneous origin, collected during 1999–2003. Different spectral preprocessing and the modified partial least squares (MPLS) regression method were explored to enhance the relation between the spectra and measured soil properties. The equations were employed for the quality prediction of a sod gleyic light loam (Cambisol) in five PK fertilization treatments. The soil was sampled in 2000 and 2003 in three field replicates at depths of 0–10, 10–20, 20–30, and 30–50 cm, n=60 samples yr^?1. The best coefficients of correlation, R², between the reference and NIRS‐predicted data were as follows: for N_Kjeldahl, 0.965; humus, 0.938; HA1, 0.903; HA2, 0.905; HA3, 0.924; ΣHA, 0.904; and FA1, 0.911; and ΣFA, 0.885. Our findings suggest that it is feasible to use NIRS for the assessment of the effects of the inorganic PK fertilizer on the soil quality in different depths of a long‐term pasture.     

Changes in the organic matter forms in chernozems of the Kamennaya Steppe under different land uses, locations, and hydromorphism degrees

The soils of the Kamennaya Steppe (Voronezh oblast) were studied. The rate of changes in the contents of C_org and the particular forms of organic matter (labile, microbial, and stable) were revealed in the quasi-natural soils of the fallows and shelterbelt and in the arable soils (rainfed farming for 12, 55, 85, and 115 yrs and irrigated farming for 40 yrs) of different positions on the watersheds and slopes. The effect of the increased soil moistening in the recent decades was also studied. In the upper 50 cm of the fallow soils that were not plowed since 1882, the relative C_org accumulation in the recent 30 yrs has amounted to 5%. The soils of the shelterbelt planted in 1903 were similar to the fallow soils. As compared to the soil of the unmown fallow, the C_org loss from the 1-m soil layer under the shelterbelt and the 12-year-old cropland were less than 9%; the losses from the plowed soils (used for 55–115 yrs) were 21–27% on the watersheds and 37–46% on the slopes. In the first decade, the rate of the Corg losses in the 0- to 20-cm layer of the cultivated chernozem was 120 g C/m². With the increasing duration of the soil plowing (from 55 to 115 yrs), the C_org losses decreased from 45 to 28 g C/m² per yr in the watershed soils and from 51 to 35 g C/m² per yr in the soils on the slopes. The maximum loss of C_org was found for the soils on slopes, waterlogged soils, and irrigated soils. In the slope soils, the C_org loss due to erosion was 9–18% of the total. In the upper horizons of the old agrogenic soils, compared to the soil of the unmown fallow, the C_ha/C_fa increased, since the content of fulvic acids (FA) faster decreased than that of the humic acids (HA); the C content of the nonhydrolyzable residue was reduced. The slope and waterlogged soils differed from the watershed soils in the smaller amounts of HA and FA and in the greater content of humin carbon. In the 0- to 20-cm layer of the soils studied, the rate of the basal respiration (BR) was 0.2–0.5 μg C/g soil per h, the content of the microbial biomass (C_micr) was 326–1073 μg C/g, and the share of C_micr amounted to 1.0–1.9%. These values were minimal in the irrigated soil and maximal in the fallow ones. A high correlation coefficient (r = 0.88–0.92) was found between the C_micr content and the BR, between the contents of C_org and HA, and between the contents of C_org and mobile C. The correlation coefficient between the contents of C_org and FA and C_org and humin C was 0.67.     

Carbohydrates as Chemical Constituents of Biowaste Composts and their Humic and Fulvic Acids

The decomposition of organic matter of source-separated biowaste during composting was followed during 18 months. Compost samples were fractionated into three parts: (i) hot water soluble extract (HWE) (ii) bitumen fraction and (iii) humic substances (humic acids (HA) and fulvic acids (FA)). Original compost samples and the HA and FA fractions were hydrolyzed with sulfuric acid for hexoses and pentoses. Quantitative spectrophotometric and qualitative GC/MS analyses of monosaccharides as trimethylsilyl ethers of the corresponding alditols were carried out.

During composting, the amount of HA in the organic matter of the compost increased, the amounts of HWE and bitumen decreased and the amount of the FA fraction changed only a little. Carbohydrates were found to be important constituents of biowaste composts and their HA and FA fractions. Elemental analysis (C, N and H) of compost and HA samples showed an increase in the C:H ratio and in unsaturation of compounds during composting. The decrease in the C:N ratio was marginal.

The amounts of hexoses and pentoses in original compost samples and the HA and FA fractions decreased during composting. The sugar alcohols erythritol, xylitol, L-arabitol, ribitol, L-rhamnitol, L-fucitol, D-mannitol, D-glucitol and galactitol were identified in both the HA and FA fractions. 2-Deoxy-D-erythro-pentitol was identified in one HA fraction and inositol in two FA fractions. An analysis of gas chromatographic data for relative abundances showed that, in every sample except one and in every stage of composting D-glucitol was the main sugar alcohol. In general, the relative amount of D-glucitol decreased during composting, while the relative amounts of all other sugar alcohols increased.

As chemical indicators of compost maturity, carbohydrates would appear to be a important group of compounds. Most informative as a general indicator would be the ratio of the amount of HA to the amount of organic matter in the total compost samples.

According to our studies, the carbohydrates in composts are covalently bound to the structures of FA and HA. Carbohydrate determination clearly deserves more attention in the structural elucidation of FA and HA.     

Effect of fulvic and humic acids on nitrificationPart 1: In vitro production of nitrite and nitrate

Abstract

Mixed opinions exist on the effect of organic matter on nitrification in soils as well as the lack of data on the effect of fulvic (FA) and humic (HA) acids on this biochemical process. This in vitro investigation was conducted to study the effect of FA and HA on oxidation of NH⁺ ₄ and NO^‐ ₂ by soil nitrifiers and on the delay period (t') and maximum nitrification rate (K_max). Soil extracts containing an ammonium‐oxidizer population were incubated in vitro for 3 weeks at 25C in the presence of (NH₄)₂SO₄and 0 to 320 mg FA or HA/L at pH 7.0 or 8.0. A similar experiment was conducted with soil extracts containing a nitrite‐oxidizer population, but with KNO₂ as the N source. An additional experiment was conducted with the nitrite‐oxidizer extracts for the determination of t’ and K_max values. Nitrite production tended to increase linearly as a result of FA and HA treatments from 0 to 320 mg/L at pH 7.0 or 8.0. Fulvic acid appeared to be more effective than HA in increasing the oxidation process. Differences in pH had only a slight effect. On the other hand, nitrate production was decreased linearly by FA or HA treatments from 0 to 320 mg/L which provided some justification for reports of lower nitrate, but higher nitrite concentrations in soils high in organic matter content. Humic acid treatments increased the delay period (t¹), and at the same time decreased the maximum nitrification rate (K_max). The latter suggests that in the presence of HA more time is required to reach a maximum nitrification rate.     

Characterization of organic matter fractions in the top layer of soils under different land uses in Central‐Eastern Europe

The objective of this study was to investigate differences in organic matter fractions, such as dissolved organic carbon and humic substances, in soils under different land uses. Soil samples were collected from the upper layer of arable lands and grasslands. Humic substances (HS) were chemically fractionated into fulvic acids (FA), humic acids (HA) and humins (HUM), and based on the separated fractions, the humification index (HI) and the degree of HS transformation (DT) were calculated. Dissolved organic carbon (DOC) was determined by cold (CWE) and hot water (HWE) extractions. Regardless of land use, the results indicated significant differences in soil organic carbon (SOC) and HS composition, with HA and HUM as the dominant fractions. Total SOC was higher in grassland (median = 17.51 g kg^?1) than arable soils (median = 9.98 g kg^?1); the HI and DT indices did not differ significantly between land uses (HI = 0.3–10.3 and DT = 0.2–6.2 for grasslands, p > 0.05; HI = 0.3–3.9 and DT = 0.2–20.1 for arable lands, p > 0.05). This indicates the relatively high stability of organic carbon and efficient humification processes in both land uses. Additionally, in arable soils lower CWE‐C (0.75 g kg^?1) and higher HWE‐C (2.59 g kg^?1) than in grasslands (CWE‐C = 1.13 g kg^?1, HWE‐C = 1.60 g kg^?1) can be related to farming practice and application of soil amendments. The results showed that both labile and humified organic matter are better protected in grassland soils and are consequently less vulnerable to mineralization.     

下拉秀剖面有机碳赋存特征

以位于青藏高原三江源地区的下拉秀剖面为对象,按剖面自然分异的颜色层次分层采集样品,研究了三江源腹地沉积土壤的有机碳。结果表明:各层位有机碳含量差异显著(P<0.05),现代生草层总有机碳(TOC)、易氧化碳(LOC)、胡敏素(HM)碳含量最高。全剖面可见LOC和水溶性物质(WSS)存在,WSS和45cm以下的LOC的相对含量随剖面深度的增加总体呈上升趋势。富里酸(FA)和HM含量在各层位间差异显著(P<0.05),胡敏酸(HA)在个别层位存在绝对含量差异不显著(P>0.05)的现象。HA/FA在0.14～2.72范围内变化,总体表现为剖面上半部分大于1,下半部分小于1,最大值未出现在现代生草层。FA的E4/E6变化幅度大,HA的E4/E6波动小。综合表现为剖面有机物质腐殖化程度各层异质各向的特征,现代生草层的腐殖质化程度所代表的年代在剖面各层位当中既不是最高的时期亦不是最低的时期。     

Organic carbon quantity and forms as influenced by tillage and cropping sequence

Abstract

Soil organic matter and its chemical fractions have a profound impact on soil chemical and physical properties. In turn, the effect of management (cropping and tillage) on the quantity and chemical properties of soil organic matter can be substantial. The objective of this study was to compare the effects of specific tillage regimes and crop sequences commonly used in the central Great Plains of the United States on the quantity, quality, and distribution with depth of soil organic carbon (SOC). Soils were sampled in 1 cm or 2 cm increments to a depth of 10 cm from experimental field plots on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll). The plots had been under 6 continuous tillage regimes since 1978 and cropped to continuous corn, continuous soybean, or corn‐soybean in rotation since 1985. Soils were analyzed for total SOC, fulvic acid (FA) carbon, and humic acid (HA) carbon. No‐till and continuous corn (Zea mays L.) management generally had the highest SOC, with a sharp reduction in SOC below 2 cm. Only no‐till increased FA, which also decreased with depth, especially between 2 and 4 cm. Humic acid concentration was highest under continuous corn but was unaffected by tillage. Humic acid also was highest in the 1‐ to 2‐cm increment of continuous corn. Two ratios which are used as indices of degree of humification, HA/FA and (HA+FA)/SOC, gave different estimates of the effect of management. Only continuous com increased HA/FA, suggesting increased humification. No treatment affected (HA+FA)/SOC. Overall, continuous corn and no‐till contributed the greatest amounts of residue and maintained a soil environment conducive to preserving the resulting organic matter. These management options increase not only total SOC, but also alter the quality of that SOC as measured by HA and FA. These changes in SOC characteristics may have implications for long‐term soil quality and soil productivity.     

Characterization of water soluble organic matter in soils by size exclusion chromatography and fractionation with polyvinylpyrrolidone

Water extracts were obtained from four types of soils (Brown Lowland soil, Yellow soil with manure application for 6 years, non-allophanic Andosol, and allophanic Andosol), and the organic matter in the water extracts was fractionated according to the solubility in acid and adsorption onto polyvinylpyrrolidone (PVP). For the water extracts and their fractions, the amounts of organic C, total N, and anthrone-reactive C (ARC) were analyzed, and high performance size exclusion chromatography (HPSEC) was carried out. The PVP-non-adsorbed fulvic acid (FA) fraction accounted for the largest proportion of the total water-soluble organic C, ranging from 52% for the Yellow soil to 96% for the allophanic Amdosol, followed by the PVP-adsorbed FA and humic acid (HA) fractions. The water extract of the allophanic Andosol was characterized by the lack of HA fraction and a small proportion of PVP-adsorbed FA fraction. For all the water extract samples, more than 90% of the ARC was recovered in the PVP-non-adsorbed FA fraction. The proportion of ARC in the total organic C in the fraction was also highest in the PVP-non-adsorbed FA fraction. The molecular weight (MW) of the humic substances (HS) at peak maximum was estimated at 1,300 Da for the water extracts and their fractions from the Brown Lowland soil and non-allophanic Andosol samples by HPSEC using polyethylene glycols as MW standards. Manure application increased the MW of HS in the HA and PVP-adsorbed FA fractions. On the other hand, only a small amount of HS was found in the water extract of the allophanic Andosol by HPSEC.     

Humic matter isolated from soils and water by the XAD‐8 resin and conventional NaOH methods

Abstract

Differences were studied in humic (HA) and fulvic acid (FA) extracted from soils and streams in South Georgia by the Amberlite XAD‐8 resin and conventional NaOH method. Characterization analysis was performed by liquid ¹³C NMR, infrared (IR) spectroscopy, scanning electron microscopy (SEM), and chemical analysis. The NMR spectra indicated that the resin method yielded black water HA and FA with spectroscopic, chemical and elemental characteristics different from those isolated by the conventional NaOH method. Humic acids from both the resin and conventional NaOH methods were composed of aliphatic, aromatics and carboxyl groups, but the “resin”; HA contained more aliphatic groups. These differences were also noticed between the FA fractions obtained by the two methods. The differences corresponded to differences in IR spectra. The IR spectrum of “resin”; FA exhibited only a weak shoulder at 1625/cm for the COO”; stretching vibration, in contrast to that of FA isolated by the conventional NaOH procedure. Apparently, the high aliphatic‐CH₃ group content has blocked the vibration above, as evidenced by methylation of HA. Fulvic acid extracted by the resin method was also higher in total acidity, but considerably lower in N content than FA obtained by the conventional NaOH method. Both methods yielded black water FA which was less aromatic in nature than black water HA, or soil FA.     

Modifications of degradation-resistant soil organic matter by soil saprobic microfungi

Modifications of humic (HA) and fulvic (FA) acids in their solutions and in sterile soil by microfungal species and two well-known HA degraders were studied by measurement of total oxidizable carbon (OC), absorbances, enzyme activities and CO₂ release. The effect of glucose on FA and HA, and also minerals on FA utilization was also observed. Microfungi affected HA more than FA. Common microfungal species decolorized HA and decreased their molecular size (evaluated in terms of A₄/A₆ ratio). Some of them decreased aromaticity of HA and FA as the only carbon sources. They did not affect OC, although released CO₂ from FA. Under higher availability of mineral nutrients, the FA aromaticity increased and FA decolorization decreased. The molecular size of HA decreased in the presence of glucose. In the FA medium complemented by minerals, the known basidiomycete HA degrader, Trametes versicolor, decreased the amount of aromatic compounds in contrast to microfungal species Alternaria alternata, Clonostachys rosea, Exophiala cf. salmonis, Fusarium coeruleum, F. redolens, Penicillium canescens, Phoma sp. and another basidiomycete Phanerochaete chrysosporium. No microfungal species exhibited lignin peroxidase activity. On the other hand, activities of manganese peroxidase (MnP) were recorded for all species incubated in FA. Carbon dioxide produced from soil inoculated by microfungi negatively correlated with the decolorization, aromaticity and OC of/in FA reisolated from the soil. The results support the hypothesis that soil microfungi can attack both HA and FA and can represent an important factor in their transformations in arable soils. The enzyme involved in FA modifications is probably fungal MnP. We enriched a group of known HA and FA degraders and showed some abilities of a few frequent soil microfungal species. This can be one of the first but important step towards learning the functioning of carbon release from the big reservoir represented by humic substances in arable soils.     

Centrifugal extraction and determination of free amino acids in soil solutions by TLC using tritiated 1-fluoro-2,4-dinitrobenzene

A method is described to separate and quantitate free amino acids from soil solutions extracted rapidly by centrifugation at 10,000 g for 5 min. Centrifugation of soil samples with forces up to 20,000 g did not affect the content of ammonium and water soluble organic carbon in solution, therefore it was concluded that the integrity of microbial cells was unaffected.The method of amino acid analysis involved treatment of the soil solution with tritiated 1-Fluoro-2,4-dinitrobenzene under alkaline conditions after addition of a known concentration of a standard mixture of amino acids. After extraction, the dinitrophenyl (DNP)-amino acids were separated by two-dimensional thin layer chromatography. Quantification was effected by counting the ³H-activity of each spot and comparing it to that of spots of a standard amino acid mixture of known concentration. The method has been tested and found satisfactory on a variety of cultivated soils, except for an Andept soil with a high content of metallic ions in solution.The total free amino acid content in cultivated and virgin soil samples ranged between 0.32 and 4.72 μg g^?1 soil.Alanine, phenylalanine and threonine were the most abundant followed by valine and the aspartic-glutamic acid complex. Basic amino acids, those containing S (methionine and cystine), and the isoleucine-leucine pair were the least abundant and frequently not detected. With the Chernozemic order the total amino acid content decreased in the following order: Brown > Dark Brown > Black. Virgin soil samples contained more but not always a wider range of free amino acids than did cultivated soils. A Luvisolic soil cropped for 50 yr to a 5-yr rotation contained fewer and a narrower range of free amino acids than did the same soil cropped to a wheat-fallow rotation.