The effect of earthworms on carbon storage and soil organic matter composition in tropical soil amended with compost and vermicompost

The use of organic matter (OM) amendments is widespread in tropical countries and may be beneficial for soil carbon storage. Interactions between earthworms and OM amendments in tropical soils are largely unknown. The aim of this study was to investigate the effect of bioturbation on the quantity and chemical composition of OM in soil amended with compost and vermicompost. Our approach included comparison of soil samples amended with compost, vermicompost or chemical fertilizers in the presence or absence of earthworms during a one-year greenhouse experiment. The soils were submitted to a regular cultivation cycle. After one year, we analysed bulk samples for soil OM elemental composition and characterised its lignin and non-cellulosic carbohydrate components.Our results showed a decrease of the carbon and nitrogen content in soil amended with chemical fertilizers. Vermicompost amendment led to unchanged OC content, whereas the compost amendment increased the soils OC content compared to initial soil. The addition of earthworms reduced OC and N content in soils with organic amendments. This is in contrast to soil amended with mineral fertilizer only, where the presence of earthworms did not have any effect. Bioturbation influenced the lignin signature of the soils, and to a lesser extent the non-cellulosic carbohydrate signature. In conclusion, compost amendment combined with bioturbation influenced the quality and quantity of SOM and as result carbon storage and its biogeochemical cycling in tropical soils. Implications for soil fertility remain to be elucidated.     

Sorption of s-Triazine Herbicides in Organic Matter Amended Soils: Fresh and Incubated Systems

Fresh amendment of soil with sewage sludge and composted sewage sludge resulted in increased sorption of three s-triazine herbicides: atrazine, ametryn and terbuthylazine. The extent of increased sorption (as evaluated by sorption coefficients K_d or K_f) was a function of soil type, such that sorption in amended organic carbon-poor soil (0.4% OC) was more enhanced than in amended organic carbon-rich soil (1.55% OC). Despite significant differences between the organic amendments in terms of humic and fulvic acid content, humin content, soluble organic matter content, total organic matter content, and H/C and O/C atomic ratios, organic matter composition had no discernible effect on either sorption distribution coefficients or on isotherm linearity in amended soils. Soils amended with composted sludge had the same sorption potential as did soils amended with the analogous uncomposted sludge. After incubating soil-sludge mixtures for a year at room temperature, organic matter content decreased to original pre-amendment levels. Sorption coefficients for the three compounds similarly decreased to initial pre-amendment values. Organic carbon normalized sorption coefficients (K_oc) were essentially identical in the soils, amended soils, and incubated amended soils, indicating that sludge and compost derived organic matter does not have a significantly different sorption capacity as compared with the original soils, despite compositional differences.     

土壤中黑碳对农药敌草隆的吸附-解吸迟滞行为研究

采用批处理振荡法和连续稀释法分别测定了敌草隆在人工添加黑碳土壤和自然形成的不同有机质和黑碳含量的土壤中的吸附一解吸行为。吸附结果表明，人工添加黑碳的土壤对敌草隆的吸附强度和吸附容量以及吸附等温线的非线性均随土壤黑碳添加浓度的增加而逐步增大；自然土壤的吸附容量和吸附强度随土壤总有机质含量增加而增加，但吸附等温线的非线性则与土壤中黑碳对有机质的相对含量有关，黑碳比例越高，等温线非线性越大。解吸实验结果表明，无论是人工添加黑碳的土壤还是自然土壤，对敌草隆的解吸迟滞作用均随土壤黑碳含量增高而愈明显。     

Sorption of pesticides in tropical and temperate soils from Australia and the Philippines

The sorption behavior of diuron, imidacloprid, and thiacloprid was investigated using 22 soils collected in triplicate from temperate environments in Australia and tropical environments in Australia and the Philippines. Within the temperate environment in Australia, the soils were selected from a range of land uses. The average KOC values (L/kg) for imidacloprid were 326, 322, and 336; for thiacloprid, the values were 915, 743, and 842; and for diuron, the values were 579, 536, and 618 for the Ord (tropical), Mt. Lofty (temperate), and Philippines (tropical) soils, respectively. For all soils, the sorption coefficients decreased in the following order: thiacloprid > diuron > imidacloprid. There were no significant differences in sorption behavior between the tropical soils from the Philippines and the temperate soils from Australia. Sorption was also not significantly related with soil characteristics, namely, organic carbon (OC) content, clay content, and pH, for any of the three chemicals studied. When the data were sorted into separate land uses, the sorption of all three chemicals was highly correlated (P < 0.001) with OC for the rice soils from the Philippines. Sorption coefficients for all three chemicals were highly correlated with OC in temperate, native soils only when one extreme value was removed. The relationships between sorption of all three chemicals and OC in temperate, pasture soils were best described by a polynomial. Sorption coefficients for imidacloprid and thiacloprid determined in the temperate pasture soils remained fairly consistent as the OC content increased from 3.3 to 5.3%, indicating that, although the total OC in the pasture soils was increasing, the component of OC involved with sorption of these two compounds may have been remaining constant. This study demonstrated that the origin of the soils (i.e., temperate vs tropical) had no significant effect on the sorption behavior, but in some cases, land use significantly affected the sorption behavior of the three pesticides studied. The impact of land use on the nature of soil OC will be further investigated by NMR analysis.     

Fate of diuron and terbuthylazine in soils amended with two-phase olive oil mill waste

The addition of organic amendments to soil increases soil organic matter content and stimulates soil microbial activity. Thus, processes affecting herbicide fate in the soil should be affected. The objective of this work was to investigate the effect of olive oil production industry organic waste (alperujo) on soil sorption-desorption, degradation, and leaching of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and terbuthylazine [N2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine], two herbicides widely used in olive crops. The soils used in this study were a sandy soil and a silty clay soil from two different olive groves. The sandy soil was amended in the laboratory with fresh (uncomposted) alperujo at the rate of 10% w/w, and the silty clay soil was amended in the field with fresh alperujo at the rate of 256 kg per tree during 4 years and in the laboratory with fresh or composted alperujo. Sorption of both herbicides increased in laboratory-amended soils as compared to unamended or field-amended soils, and this process was less reversible in laboratory-amended soils, except for diuron in amended sandy soil. Addition of alperujo to soils increased half-lives of the herbicides in most of the soils. Diuron and terbuthylazine leached through unamended sandy soil, but no herbicide was detected in laboratory-amended soil. Diuron did not leach through amended or unamended silty clay soil, whereas small amounts of terbuthylazine were detected in leachates from unamended soil. Despite their higher sorption capacity, greater amounts of terbuthylazine were found in the leachates from amended silty clay soils. The amounts of dissolved organic matter from alperujo and the degree of humification can affect sorption, degradation, and leaching of these two classes of herbicides in soils. It appears that adding alperujo to soil would not have adverse impacts on the behavior of herbicides in olive production.     

Assessing the Potential of Pomegranate Meal and Potato Waste as New Organic Amendments for Vermicompost

Waste disposal has become one of the greatest global concerns, which has high operational costs and might cause environmental pollution. Due to the lack of the organic matter in most of the Iranian agro-ecosystem, recycling organic waste materials favors the environment by reducing chemical fertilizers as well as improving soil structure and fertility. A vermicomposting system using cow manure (CM), pomegranate meal (PM) + sawdust (S), CM + potato waste (PW), PM + PW, CM + PM, and CM + PM + PW was set up to find a viable alternative raw material for improving physico-chemical properties of vermicompost after 60 days. The amended vermicompost of PM + S and PM + PW markedly improved the electrical conductivity (EC), which were below the EC limit (by 1.01 and 2.27 dS m^?1, respectively), pH (by 7.04 and 6.60, respectively), and water holding capacity (respectively 1.9 and 1.2 times higher than CM). Vermicompost amendment led to significant reduction of organic carbon (OC), but nonetheless, PM + S and PM + PW showed higher OC content in the final product probably due to the higher initial carbon to nitrogen (C:N) ratio, raw material origin, and lower decomposition rate. In regard to nutrient value, the total phosphorus content in the end-product of PM + S and PM + PW was, respectively, 19.3 and 7.9 times higher compared with the final product of CM. Additionally, the amended vermicompost of PM + PW markedly improved total nitrogen content as compared with CM. The findings suggested that the additional amounts of nitrogen and potassium to PM + S and also potassium to PM + PW would improve the physico-chemical properties and fertilization of the final vermicompost considerably higher than CM vermicompost. This amendment has the potential to mitigate the adverse effects of vermicompost of CM, for example, salinity and alkalinity; and chemical fertilizers, for example, soil pollution with heavy metals in phosphate fertilizers, as well as the potential for soil rehabilitation.     

Changes in the sorption–desorption of fungicides over time in an amended sandy clay loam soil under laboratory conditions

Purpose

The aim of this work was to study the temporal changes in the sorption?Cdesorption of fungicides in a sandy clay loam soil amended with spent mushroom substrate (SMS) under controlled laboratory conditions and the influence that fungicides properties and soil characteristics have on these processes. Soil amendment with SMS is becoming a widespread management practice since it can effectively solve the problems of uncontrolled SMS accumulation and disposal and improve soil quality. However, when simultaneously applied with pesticides, SMS can significantly modify the environmental behaviour of these compounds.

Materials and methods

Sorption?Cdesorption isotherms of metalaxyl, penconazole, pyrimethanil and iprovalicarb for unamended and amended vineyard soils from La Rioja (Spain) were obtained. Composted SMS (C-SMS) and fresh SMS (F-SMS) from cultivation of different mushrooms were used as amendments at 2?% and 10?% rates. Soil parameters (organic carbon (OC), dissolved organic carbon (DOC), humic acid (HA) and fulvic acid (FA)) and sorption (Kf, nf, Kd, Koc) and desorption (Kfd, nfd, H) parameters of fungicides were determined over 0, 6 and 12?months of soil incubation with SMS under controlled conditions.

Results and discussion

Addition of amendments to soil increased soil sorption capacity of fungicides. Kd values increased with the hydrophobic character of fungicides (metalaxyl?<?iprovalicarb?<?pyrimethanil?<?penconazole) at both amendment rates. The lower content of DOC and the higher degree of OC humification enhanced sorption of all fungicides by the soil?+?C-SMS with regard to the soil?+?F-SMS. In general, sorption of fungicides decreased after 6 and 12?months of soil?+?SMS incubation, although the humification degree of the remaining OC expressed by HA/FA increased. This might indicate that the OC content was more important for fungicide sorption than the changes in its nature with the incubation time. SMS addition favoured desorption of metalaxyl and iprovalicarb, in general, whereas irreversible sorption of penconazole and pyrimethanil increased. However, the opposite trends were observed when the soil?+ SMS incubation time increased.

Conclusions

The results show an increase in sorption of all fungicides by amending soil with composted or fresh SMS. However, desorption of fungicides increases or decreases depending on the properties of fungicides and soil?+ SMS. Changes in both processes with the incubation time are more related to the OC content of the amended soil than to the evolution of its nature. These outcomes are of interest for extending SMS application to soil with minimal or no environmental risk when used simultaneously with fungicides.     

Comparative sorption and leaching study of the herbicides fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) in a soil amended with biochars and other sorbents

Biochar, the solid residual remaining after the thermochemical transformation of biomass for carbon sequestration, has been proposed to be used as a soil amendment, because of its agronomic benefits. The effect of amending soil with six biochars made from different feedstocks on the sorption and leaching of fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) was compared to the effect of other sorbents: an activated carbon, a Ca-rich Arizona montmorillonite modified with hexadecyltrimethylammonium organic cation (SA-HDTMA), and an agricultural organic residue from olive oil production (OOW). Soil was amended at 2% (w/w), and studies were performed following a batch equilibration procedure. Sorption of both herbicides increased in all amended soils, but decreased in soil amended with a biochar produced from macadamia nut shells made with fast pyrolysis. Lower leaching of the herbicides was observed in the soils amended with the biochars with higher surface areas BC5 and BC6 and the organoclay (OCl). Despite the increase in herbicide sorption in soils amended with two hardwood biochars (BC1 and BC3) and OOW, leaching of fluometuron and MCPA was enhanced with the addition of these amendments as compared to the unamended soil. The increased leaching is due to some amendments' soluble organic compounds, which compete or associate with herbicide molecules, enhancing their soil mobility. Thus, the results indicate that not all biochar amendments will increase sorption and decrease leaching of fluometuron and MCPA. Furthermore, the amount and composition of the organic carbon (OC) content of the amendment, especially the soluble part (DOC), can play an important role in the sorption and leaching of these herbicides.     

Changes in the chemical composition of soil organic matter after application of compost

Is the composition of soil organic matter changed by adding compost? To find out we incubated biowaste composts with agricultural soils and a humus‐free mineral substrate at 5°C and 14°C for 18 months and examined the products. Organic matter composition was characterized by CuO oxidation of lignin, hydrolysis of cellulosic and non‐cellulosic polysaccharides (CPS and NCPS) and ¹³C cross‐polarization magic angle spinning nuclear magnetic resonance (CPMAS ¹³C‐NMR) spectroscopy. The lignin contents in the compost‐amended soils increased because the composts contained more lignin, which altered little even after prolonged decomposition of the composts in soil. A pronounced decrease in lignin occurred in the soils amended with mature compost only. Polysaccharide C accounted for 14–20% of the organic carbon at the beginning of the experiment for both the compost‐amended soils and the controls. During the incubation, the relative contents of total polysaccharides decreased for 9–20% (controls) and for 20–49% (compost‐amended soils). They contributed preferentially to the decomposition as compared with the bulk soil organic matter, that decreased between < 2% and 20%. In the compost‐amended agricultural soils, cellulosic polysaccharides were decomposed in preference to non‐cellulosic ones. The NMR spectra of the compost‐amended soils had more intense signals of O–alkyl and aromatic C than did those of the controls. Incubation for 18 months resulted mainly in a decline of O–alkyl C for all soils. The composition of the soil organic matter after compost amendment changed mainly by increases in the lignin and aromatic C of the composts, and compost‐derived polysaccharides were mineralized preferentially. The results suggest that decomposition of the added composts in soil is as an ongoing humification process of the composts themselves. The different soil materials affected the changes in soil organic matter composition to only a minor degree.     

Dissolved organic carbon interactions with sorption and leaching of diuron in organic-amended soils

Diuron ( N '-[3,4-dichlorophenyl]- N,N -dimethylurea) is one of the most frequently used herbicides in olive groves in Spain and other Mediterranean countries. The main objective of this work was to investigate the effect of the dissolved organic carbon (DOC) from a commercial humic amendment, derived by composting the liquid waste of the olive-mill process (LF), and a solid residue from the olive oil production industry (AL) on the sorption and leaching behaviour of diuron in soil. For this purpose, a clay and a sandy soil were selected. Soil sorption coefficients of diuron increased with LF (32%) and AL (76%) amendment in the sandy soil, whereas sorption decreased in the clay soil upon amendment, especially in the case of the liquid LF (52%). The DOC from LF and AL is composed of very poorly humified molecules, which are strongly sorbed onto the clay soil and thus compete with diuron for the same sorption sites. Dialysis experiments revealed that diuron forms stable complexes with DOC from LF and AL. Leaching of diuron in columns of the sandy soil treated with the organic amendments caused earlier breakthrough and maximum concentration peaks at fewer pore volumes when compared with leaching with 0.01 m CaCl₂. Competition between diuron and DOC molecules for sorption sites and diuron–DOC interactions can both account for the enhanced leaching of diuron.     

An assessment of subsoil organic carbon stocks in England and Wales

It is estimated that half the soil carbon globally is in the subsoil, but data are scarce. We updated estimates of subsoil organic carbon (OC) in England and Wales made by Bradley et al. (2005) using soil and land‐use databases and compared the results with other published data. We estimated that the soils of England and Wales contained 1633, 1143 and 506 Tg of OC at 0–30, 30–100 and 100–150 cm depths, respectively. Thus, half of the soil OC was found below 30 cm depth. Peat soils accounted for the largest proportion, containing 44% of all the OC below 30 cm despite their small areal extent, followed by brown soils, surface‐water gley soils, ground‐water gley soils and podzolic soils. Peat soils had more than 25% of their profile OC per unit area in the 100–150 cm depth, whereas most other soils had <8% at this depth. The differences between soil types were consistent with differences in soil formation processes. Differences in depth distributions between land uses were small, but subsoil OC stocks in cultivated soils were generally smaller than in soils under grassland or other land uses. Data on subsoil OC stocks in the literature were scarce, but what there was broadly agreed with the findings of the above database exercise. There was little evidence by which to assess how subsoil OC stocks were changing over time.     

Hydrophobic sorption of polar organics by low organic carbon soils

The sorption of three groups of polar organic compounds capable of H bonding with inorganic soil surfaces (phenols, alcohols, and ketones) by three soils having different organic-carbon (OC) contents was compared with the sorption of nonpolar compounds by the same soils. Soil OC content and compound hydrophobicity were observed to be of value in predicting sorption coefficients for all groups of compounds except phenols. The higher OC soil (1.2% OC) exhibited a significant relationship between sorption coefficient and hydrophobicity for all compound classes; the very low OC soil (0.06% OC), however, exhibited a relatively weak relationship between sorption coefficient and hydrophobicity. The data support the application of hydrophobicity-based predictions of soil/sediment sorption coefficients to compounds capable of weak H-bond interactions with mineral surfaces and soils of ≥0.1% OC.     

The effect of warming on the vulnerability of subducted organic carbon in arctic soils

Arctic permafrost soils contain large stocks of organic carbon (OC). Extensive cryogenic processes in these soils cause subduction of a significant part of OC-rich topsoil down into mineral soil through the process of cryoturbation. Currently, one-fourth of total permafrost OC is stored in subducted organic horizons. Predicted climate change is believed to reduce the amount of OC in permafrost soils as rising temperatures will increase decomposition of OC by soil microorganisms. To estimate the sensitivity of OC decomposition to soil temperature and oxygen levels we performed a 4-month incubation experiment in which we manipulated temperature (4–20 °C) and oxygen level of topsoil organic, subducted organic and mineral soil horizons. Carbon loss (C_LOSS) was monitored and its potential biotic and abiotic drivers, including concentrations of available nutrients, microbial activity, biomass and stoichiometry, and extracellular oxidative and hydrolytic enzyme pools, were measured. We found that independently of the incubation temperature, C_LOSS from subducted organic and mineral soil horizons was one to two orders of magnitude lower than in the organic topsoil horizon, both under aerobic and anaerobic conditions. This corresponds to the microbial biomass being lower by one to two orders of magnitude. We argue that enzymatic degradation of autochthonous subducted OC does not provide sufficient amounts of carbon and nutrients to sustain greater microbial biomass. The resident microbial biomass relies on allochthonous fluxes of nutrients, enzymes and carbon from the OC-rich topsoil. This results in a “negative priming effect”, which protects autochthonous subducted OC from decomposition at present. The vulnerability of subducted organic carbon in cryoturbated arctic soils under future climate conditions will largely depend on the amount of allochthonous carbon and nutrient fluxes from the topsoil.     

致谢审稿专家

Two agricultural soils were collected from Dahu and Pinchen counties and swine manure compost (SMC) from Pingtung County in Taiwan, China to investigate the sorption and dissipation of three tetracyclines (TCs), i.e., oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC), in compost, soils and soil/compost mixtures with different organic carbon (OC) contents. There were seven treatments in total. TCs were most strongly adsorbed to SMC in all treatments due to the high OC content. When SMC was present in the soils, the sorption of TCs was significantly enhanced, which might be attributed to the increased OC content and CEC. The adsorption of TCs showed non-linear adsorption isotherms and fitted well to the Freundlich model. After 49 d of incubation at 25 oC in soils and soil/compost mixtures in the dark, TCs elapsed in all substrates, with the time required for 50% degradation (DT50) between 20 and 41 d, and the time for 90% degradation (DT90) between 68 and 137 d. Soil amended with compost enhanced the stability of TCs and reduced their mobility. The dissipation of TCs in a soil environment was slow, indicating that these compounds might be persistent in soil.     

Properties and bioavailability of particulate and mineral‐associated organic matter in Arctic permafrost soils,Lower Kolyma Region,Russia

Permafrost degradation may cause strong feedbacks of arctic ecosystems to global warming, but this will depend on if, and to what extent, organic matter (OM) is protected against biodegradation by mechanisms other than freezing and anoxia. Here, we report on the amount, chemical composition and bioavailability of particulate (POM) and mineral‐associated OM (MOM) in permafrost soils of the East Siberian Arctic. The average total organic carbon (OC) stock across all soils was 24.0 ± 6.7 kg m^?2 within 100 cm soil depth. Density fractionation (density cut‐off 1.6 g cm^?3) revealed that 54 ± 16% of the total soil OC and 64 ± 18% of OC in subsoil horizons was bound to minerals. As well as sorption of OM to clay‐sized minerals (R² = 0.80; P < 0.01), co‐precipitation of OM with hydrolyzable metals may also transfer carbon into the mineral‐bound fraction. Carbon:nitrogen ratios, stable carbon and nitrogen isotopes, ¹³C‐NMR and X‐ray photoelectron spectroscopy showed that OM is transformed in permafrost soils, which is a prerequisite for the formation of mineral‐organic associations. Mineral‐associated OM in deeper soil was enriched in ¹³C and ¹⁵N, and had narrow C:N and large alkyl C:(O‐/N‐alkyl C) ratios, indicating an advanced stage of decomposition. Despite being up to several thousands of years old, when incubated under favourable conditions (60% water‐holding capacity, 15°C, adequate nutrients, 90 days), only 1.5–5% of the mineral‐associated OC was released as CO₂. In the topsoils, POM had the largest mineralization but was even less bioavailable than the MOM in subsoil horizons. Our results suggest that the formation of mineral‐organic associations acts as an important additional factor in the stabilization of OM in permafrost soils. Although the majority of MOM was not prone to decomposition under favourable conditions, mineral‐organic associations host a readily accessible carbon fraction, which may actively participate in ecosystem carbon exchange.     

Influence of organic amendment on the adsorption and leaching of ethametsulfuron-methyl in acidic soils in China

The sorption and leaching of ethametsulfuron-methyl by an acidic soil, after organic amendment with humic acid (HA) and a commercial peat, were studied in batch and soil column experiments. Adsorption capacity (K_f) values, obtained by fitting the experimental data to the Freundlich equation, ranged from 4.39 for the original soil containing 1.02% OC to 10.56 for the organic amended soils containing 2.61% OC. The increase in herbicide adsorption by organic amendment addition to soil was attributed to the high adsorptive capacity of the insoluble organic matter added to the soil. Evidence provided by FT-IR analysis suggested multifunctional hydrogen bonds were involved in the adsorption of ethametsulfuron-methyl on organic matter. The distribution of ethametsulfuron-methyl along the soil profile, obtained from soil column experiments, indicated that the amount of ethametsulfuron-methyl retained ranged from 68.4% for the column filled with the original soil to 92.4% for that filled with the organic amended soil. Amounts of ethametsulfuron-methyl recovered in the leachates, which ranged from 7.7% (organic amended soil) to 23.7% (unamended soil) of that applied, depended upon the loading rate and the source of organic amendment. Organic amendments significantly reduced the leaching of ethametsulfuron-methyl, and humic acid showed the higher potential than peat. This research suggests that organic amendment may be an effective management practice for controlling pesticide leaching.     

Response of sorption processes of MCPA to the amount and origin of organic matter in a long-term field experiment

Changes in farming practices over long times can affect the sorption behaviour of MCPA ((4‐chloro‐2‐methylphenoxy)acetic acid). We studied the adsorption–desorption mechanisms of MCPA on soil with varied amounts and origins of soil organic matter obtained from a long‐term field experiment with various organic amendments. The origin of the soil organic matter seems to be crucial for the sorption behaviour of MCPA. Samples of soil amended with sewage sludge sorbed MCPA more strongly than the soil under any other treatment. Peat‐amended soil was second followed by soil receiving animal manure, green manure, mineral fertilizer without N and the fallowed soil. Both the carbon content and the origin of the organic matter are important for the sorption. A decrease of carbon content of a soil does not necessarily imply a reduction of sorption capacity for polar organic acids such as MCPA. Nevertheless, our adsorption–desorption experiments suggest that with decreasing carbon content the role of mineral sorption mechanisms could become more pronounced. Our results showed that interactions of soil organic matter and soil minerals distinctly influence adsorption properties for MCPA.     

不同物料蚓粪对土壤酸度和Cu、Pb化学形态的影响

以两种常见的有机废弃物牛粪和稻秆为原料,利用Eisenia foetida生产蚓粪,采用室内培养试验,研究了蚓粪在重金属污染的酸性土壤中对有机碳含量和形态、土壤酸度及Cu、Pb形态的影响。结果表明:在2.5%~10%的蚓粪用量下,土壤总有机碳含量增加了25%~83%,除牛粪蚓粪组的可溶性有机碳显著高于稻秆蚓粪外(P0.05),其余形态两种蚓粪间土壤有机碳含量无显著差异。蚓粪使土壤pH(H2O)值提升0.38~1.13个单位,同时交换性氢和铝的含量分别降低41%~77%和57%~94%,显著降低了土壤酸度,且较对照高出0.35~4倍;牛粪蚓粪仅在10%用量下降低土壤酸度的效果高出稻秆蚓粪22%。蚓粪使土壤中水溶-交换态Cu和Pb含量分别降低22%~70%和29%~70%,使有机结合态Cu和Pb含量分别提高19%~56%和10%~40%,表明蚓粪可以显著降低土壤中Cu和Pb的活性。蚓粪降低土壤Cu、Pb活性的效果分别较对照物料高出0.58~9.6倍和0.16~3.4倍。稻秆蚓粪降低土壤Cu、Pb活性的效果分别比牛粪蚓粪高出11%~61%和1%~32%。综上所述,蚓粪降低土壤酸度和Cu、Pb活性的效果优于对照,牛粪蚓粪降低土壤酸度的效果较好,稻秆蚓粪降低土壤Cu、Pb活性的效果更佳。在降低土壤酸度和Cu、Pb活性方面,蚓粪中的总有机碳、微生物量碳、胡敏酸碳和富里酸碳均具有重要作用,并且蚓粪中有机碳的作用效率高于对照中等量的有机碳。     

Changes in nutrient content,enzymatic activities and microbial properties of lateritic soil due to application of different vermicomposts: a comparative study of ergosterol and chitin to determine fungal biomass in soil

In this experiment, vermicomposts, prepared from five different waste materials, were applied to acid lateritic soil under field conditions and soil samples were collected after 90 days to study the effect of vermicomposts on different chemical and biochemical. Results suggest that vermicompost prepared from paddy straw is most effective to improve nutrient content, enzymatic activities and microbial properties of lateritic soil. Vermicompost application significantly (P ≤ 0.05) increased the concentration of organic C, mineralizable N, available P and exchangeable K in soil. Amylase, protease, urease and acid phosphatase activities were also significantly (P ≤ 0.05) higher in vermicompost treated soils compared with the control. Both basal and substrate‐induced microbial respiration, microbial biomass C and N and fungal population in lateritic soil were increased due to vermicompost application. Ergosterol and chitin content were significantly (P ≤ 0.05) higher in vermicompost treated soils over the control. Application of vermicompost increased the proportion of fungal biomass in total soil microorganisms.     

半干旱土添加有机改良剂后有机质的化学结构变化

A 9-month incubation experiment using composted and non-composted amendments derived from vine pruning waste and sewage sludge was carried out to study the effects of the nature and stability of organic amendments on the structural composition of organic matter (OM) in a semi-arid soil.The changes of soil OM,both in the whole soil and in the extractable carbon with pyrophosphate,were evaluated by pyrolysis-gas chromatography and chemical analyses.By the end of the experiment,the soils amended with pruning waste exhibited less organic carbon loss than those receiving sewage sludge.The non-composted residues increased the aliphatic-pyrolytic products of the OM,both in the whole soil and also in the pyrophosphate extract,with the products derived from peptides and proteins being significantly higher.After 9 months,in the soils amended with pruning waste the relative abundance of phenolic-pyrolytic products derived from phenolic compounds,lignin and proteins in the whole soil tended to increase more than those in the soils amended with sewage sludge.However,the extractable OM with pyrophosphate in the soils amended with composted residues tended to have higher contents of these phenolic-pyrolytic products than that in non-composted ones.Thus,despite the stability of pruning waste,the composting of this material promoted the incorporation of phenolic compounds to the soil OM.The pyrolytic indices (furfural/pyrrole and aliphatic/aromatic ratios) showed the diminution of aliphatic compounds and the increase of aromatic compounds,indicating the stabilization of the OM in the amended soils after 9 months.In conclusion,the changes of soil OM depend on the nature and stability of the organic amendments,with composted vine pruning waste favouring humification.