Chinese Loess Soil Research Articles

A Comparative Study on Soil-Crop Selenium Characteristics in High-Incidence Areas of Keshan Disease in Chinese Loess and Black Soil

With the gradual emphasis on health by people, the research on the pathogenesis of endemic diseases has become increasingly in-depth. Through analyzing the environmental selenium characteristics and conducting a comparative study in typical areas of Chinese loess and black soil in this paper, it is concluded that the environmental selenium in the two regions has different characteristics. The soil in the loess area has the characteristics of high alkalinity, low selenium, and relatively high selenium availability, and the crops are selenium-deficient, while the soil in the black soil area has the characteristics of high organic matter, low selenium availability, and relatively high selenium in crops. The research concluded that the environmental occurrence mechanism of Keshan disease in the loess area and the black soil area is different. Keshan disease can be induced in both low-selenium and sufficient-selenium environments, and environmental selenium should be one of the inducing factors of Keshan disease. This research provides a reference for predicting the areas where Keshan disease occurs and for disease prevention, and it can also serve in the prevention and control of endemic diseases.

Impacts of Adding Municipal Sewage Sludge on Soil Enzyme Activity and Stoichiometry in a Chinese Loess Soil

Impacts of Adding Municipal Sewage Sludge on Soil Enzyme Activity and Stoichiometry in a Chinese Loess Soil

Long-term fertilization affects functional soil organic carbon protection mechanisms in a profile of Chinese loess plateau soil

Crop productivity and soil health are limited by organic carbon (OC), however, the variations in the mechanisms of SOC preservation in a complete soil profile subjected to long-term fertilization remains unclear. The objective of the study was to examined the content and profile distribution of the distinctive SOC protection mechanisms on a complete profile (0–100 cm) of Eumorthic Anthrosols in Northwest China after 23 years of chemical and manure fertilization. The soil was fractionated by combined physical-chemical and density floatation techniques. Throughout the profile, significant variations were observed among fractions. In the topsoil (0–20 and 20–40 cm), mineral coupling with the fertilization of manure (MNPK) enhanced total SOC content and recorded for 29% of SOC in the 0–20 and 20–40 cm layers. Moreover, MNPK increased the SOC content of the unprotected cPOC fraction by 60.9% and 61.5% in the 0–20 and 20–40 cm layer, while SOC content was low in the subsoil layers (40–60, 60–80 and 80–100 cm, respectively) compared with the control (C). The highest OC under MNPK in physically protected micro-aggregates (μagg) (6.36 and 6.06 g C kg−1), and occluded particulate organic carbon (iPOC) (1.41 and 1.29 g C kg−1) was found in the topsoil layers. The unprotected cPOC fraction was the greatest C accumulating fraction in the topsoil layers, followed by μagg and H-μSilt fractions in the soil profile, implying that these fractions were the most sensitive to the fertilization treatments. Overall, the unprotected, physically protected, and physico-chemically protected fractions were the dominant fractions for the sequestration of carbon across fertilization treatments and soil layers.

Immobilization of perrhenate using synthetic pyrite particles: Effectiveness and remobilization potential

Radioactive pertechnetate (TcO4−) has been detected in nuclear waste affected soil and groundwater, posing significant effect on human health and the environment. Yet, cost-effective remediation of Tc-contaminated soil and groundwater remains challenging. To address this critical technology need, we prepared a class of pyrite (FeS2) particles for effective immobilization of pertechnetate. Using perrhenate (ReO4−) as a non-radioactive surrogate of TcO4−, we tested the immobilization effectiveness of the material through batch kinetic experiments, and evaluated the remobilization potential of immobilized Re under anoxic (sealed from air) and oxic (exposed to air) conditions and in the presence of humic acid (HA), EDTA, nitrate, and a Chinese loess soil. The results showed that more acidic pH gave faster Re(VII) removal due to more abundant electron sources (Fe2+ and S22−). X-ray diffraction (XRD) and/or X-ray photoelectron spectroscopy (XPS) analyses confirmed formation of ReO2/ReS2 as the major reduction products. The immobilized Re remained highly stable when aged for 360 days under anoxic conditions at different influence factors. Yet, the immobilized Re was vulnerable to oxygen oxidation, and about 78% of Re was remobilized after 40 days of exposure to air regardless of the initial pH (3.5–9.0) due to excessive pyrite oxidation and the associated pH drop (~2). HA at 120 mg/L inhibited Re remobilization under oxic conditions, which lowered the Re remobilization by ~21% after 40 days of oxic aging. The presence of EDTA facilitated dissolution of Fe but inhibited the dissolution of Re under oxic conditions. Nitrate showed negligible effect on Re remobilization. The presence of a Chinese loess soil effectively inhibited Re remobilization under both oxic and anoxic conditions, lowering the leachable Re by ~32% under oxic conditions. The findings may guide engineered application of pyrite particles as a long-lasting reducing material for immobilization pertechnetate or similar redox-active contaminants in soil and water.

Immobilization of hexavalent chromium in soil and groundwater using synthetic pyrite particles

In this study, reactive pyrite (FeS2) particles were prepared through a modified hydrothermal method and tested for immobilization of Cr(VI) in contaminated soil and synthetic groundwater. The addition of a NaAc buffer in the synthetic process resulted in pyrite particles of greater specific surface area, more uniform size, and more crystalline structure. The particles can effectively immobilize Cr(VI) in both water and a model Chinese loess soil. Over 99.9% of Cr(VI) was rapidly removed from water at pH 6.0 (Initial Cr(VI) = 25 mg/L, FeS2 dosage = 0.48 g/L), and the removal remained high (>82%) even at pH 9.5. Both adsorption and reductive precipitation were found operative in the Cr(VI) immobilization, with ∼66% of Cr immobilized due to reduction. Fe(II) ions associated on the FeS2 surface played a key role in the reduction of Cr(VI) to Cr(III), and S22− also facilitated the reductive removal of Cr(VI). The presence of humic acid enhanced Cr(VI) removal at pH 4.0, but the effect was negligible at pH 6.0. Batch kinetic tests showed that treating a Cr(VI)-laden soil with 0.48 g/L (as Fe) of FeS2 decreased the equilibrium water-leachable Cr(VI) by >99.0% at pH 6.0 and by >70.0% at pH 9.0. The distribution coefficient (Kd) value of the pyrite-amended soil was 1477.8 at pH 6.0, which is 306 times higher than that for the untreated soil. Column elution tests showed that installation of a 3-cm reactive layer of FeS2 in a soil column was able to capture the leachable Cr(VI) from the soil, and the retardation factor (Rd) for the 3-cm FeS2 layer sample was 381 times higher than that for the plain soil. The synthetic pyrite particles may serve as a reactive material for effective removal or immobilization of Cr(VI) in contaminated water or soil.

Interactive effects of microplastics and glyphosate on the dynamics of soil dissolved organic matter in a Chinese loess soil

The increased use of plastic films and pesticides on agricultural soil leads to the accumulation of plastic debris and pesticide residues in soil. This accumulation has become a serious environmental issue, as it threatens life of earthworms, inhibits the enzyme activities and microbial diversity, and contributes to the loss of soil microbial carbon and nitrogen. However, little information is available regarding the effects of pesticides on soil dissolved organic matter (DOM). It is also unknown how plastic debris, especially small-sized particles called microplastics, influences the effects of pesticides on soil DOM. In this study, we performed a 30-day soil incubation experiment. Three levels of the common herbicide glyphosate were applied to soil: 0 (control, CK), 3.6 kg ha−1 (G1) and 7.2 kg ha−1 (G2). We also tested four levels of glyphosate and microplastics (homopolymer polypropylene powder) co-addition: 3.6 kg ha−1 + 7% (w/w) (M1G1), 3.6 kg ha−1 + 28% (w/w) (M2G1), 7.2 kg ha−1 + 7% (w/w) (M1G2), and 7.2 kg ha−1 + 28% (w/w) (M2G2). Glyphosate addition slightly increased soil fluorescein diacetate hydrolase (FDAse) and phenol oxidase (PO) activities. Although the glyphosate addition significantly promoted the accumulation of dissolved organic phosphorus (DOP) within the first 14 days, the M2 treatment decreased DOP at day 30. M2G1 and M2G2 increased soil FDAse activity and promoted the accumulation of DOC and DOP relative to G1 and G2 respectively while M1G1 and M1G2 benefited DON accumulation. Our results highlighted that the interaction between glyphosate and low microplastics content negatively affected DOC and DOP dynamics, leading to the loss of bioavailable C and P loss. The interaction between glyphosate and high content microplastics negatively affected DON compared with glyphosate addition, possibly decreasing DON.

Influence of microplastic addition on glyphosate decay and soil microbial activities in Chinese loess soil

The intensive use of pesticide and plastic mulches has considerably enhanced crop growth and yield. Pesticide residues and plastic debris, however, have caused serious environmental problems. This study investigated the effects of the commonly used herbicide glyphosate and micrometre-sized plastic debris, referred as microplastics, on glyphosate decay and soil microbial activities in Chinese loess soil by a microcosm experiment over 30 days incubation. Results showed that glyphosate decay was gradual and followed a single first-order decay kinetics model. In different treatments (with/without microplastic addition), glyphosate showed similar half-lives (32.8 days). The soil content of aminomethylphosphonic acid (AMPA), the main metabolite of glyphosate, steadily increased without reaching plateau and declining phases throughout the experiment. Soil microbial respiration significantly changed throughout the entirety of the experiment, particularly in the treatments with higher microplastic addition. The dynamics of soil β-glucosidase, urease and phosphatase varied, especially in the treatments with high microplastic addition. Particles that were considerably smaller than the initially added microplastic particles were observed after 30 days incubation. This result thus implied that microplastic would hardly affect glyphosate decay but smaller plastic particles accumulated in soils which potentially threaten soil quality would be further concerned especially in the regions with intensive plastic mulching application.

Response of soil dissolved organic matter to microplastic addition in Chinese loess soil

Plastic debris is accumulating in agricultural land due to the increased use of plastic mulches, which is causing serious environmental problems, especially for biochemical and physical properties of the soil. Dissolved organic matter (DOM) plays a central role in driving soil biogeochemistry, but little information is available on the effects of plastic residues, especially microplastic, on soil DOM. We conducted a soil-incubation experiment in a climate-controlled chamber with three levels of microplastic added to loess soil collected from the Loess Plateau in China: 0% (control, CK), 7% (M1) and 28% (M2) (w/w). We analysed the soil contents of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), NH4+, NO3−, dissolved organic phosphorus (DOP), and PO43− and the activities of fluorescein diacetate hydrolase (FDAse) and phenol oxidase. The higher level of microplastic addition significantly increased the nutrient contents of the DOM solution. The lower level of addition had no significant effect on the DOM solution during the first seven days, but the rate of DOM decomposition decreased in M1 between days 7 and 30, which increased the nutrient contents. The microplastic facilitated the accumulation of high-molecular-weight humic-like material between days 7 and 30. The DOM solutions were mainly comprised of high-molecular-weight humic-like material in CK and M1 and of high-molecular-weight humic-like material and tyrosine-like material in M2. The Microplastic stimulated the activities of both enzymes. Microplastic addition thus stimulated enzymatic activity, activated pools of organic C, N, and P, and was beneficial for the accumulation of dissolved organic C, N and P.

Effects of straw and biochar amendments on aggregate stability, soil organic carbon, and enzyme activities in the Loess Plateau, China

Soil from the Loess Plateau of China is typically low in organic carbon and generally has poor aggregate stability. Application of organic amendments to these soils could help to increase and sustain soil organic matter levels and thus to enhance soil aggregate stability. A field experiment was carried out to evaluate the effect of the application of wheat straw and wheat straw-derived biochar (pyrolyzed at 350-550°C) amendments on soil aggregate stability, soil organic carbon (SOC), and enzyme activities in a representative Chinese Loess soil during summer maize and winter wheat growing season from 2013 to 2015. Five treatments were set up as follows: no fertilization (CK), application of inorganic fertilizer (N), wheat straw applied at 8tha-1 with inorganic fertilizer (S8), and wheat straw-derived biochar applied at 8tha-1 (B8) and 16tha-1 (B16) with inorganic fertilizer, respectively. Compared to the N treatment, straw and straw-derived biochar amendments significantly increased SOC (by 33.7-79.6%), microbial biomass carbon (by 18.9-46.5%), and microbial biomass nitrogen (by 8.3-38.2%), while total nitrogen (TN) only increased significantly in the B16 plot (by 24.1%). The 8tha-1 straw and biochar applications had no significant effects on soil aggregation, but a significant increase in soil macro-aggregates (>2mm) (by 105.8%) was observed in the B16 treatment. The concentrations of aggregate-associated SOC increased by 40.4-105.8% in macro-aggregates (>2mm) under straw and biochar amendments relative to the N treatment. No significant differences in invertase and alkaline phosphatase activity were detected among different treatments. However, urease activity was greater in the biochar treatment than the straw treatment, indicating that biochar amendment improved the transformation of nitrogen in the soil. The carbon pool index and carbon management index were increased with straw and biochar amendments, especially in the B16 treatment. In conclusion, application of carbonized crop residue as biochar, especially at a rate of 16tha-1, could be a potential solution to recover the depleted SOC and enhance the formation of macro-aggregates in Loess Plateau soils of China.

Effects of elevated CO2 and drought on the microbial biomass and enzymatic activities in the rhizospheres of two grass species in Chinese loess soil

Elevated CO2 and drought are key consequences of climate change and affect soil processes and plant growth. This study investigated the effects of elevated CO2 and drought on the microbial biomass and enzymatic activities in the rhizospheres of Bothriochloa ischaemum and Medicago sativa in loess soil. Drought exerted significant species-specific negative effects on root and shoot biomass and microbial properties except for the soil basal respiration in the rhizospheres of B. ischaemum and M. sativa. Increased CO2 exerted weak effects on plant biomass and enzymatic activities but demonstrated significant effects on the amounts of carbon and nitrogen in soil microbial biomass, basal respiration, substrate-induced respiration, and the metabolic quotients in the rhizospheres of M. sativa and B. ischaemum. The rhizosphere soil microbial index was a good aggregative indicator of the general state of the microbial properties of the rhizospheres. The interactive effects of elevated CO2 and drought on plant growth and microbial properties significantly differed, indicating that elevated CO2 significantly alleviated the effects of drought stress on the microbial properties of the rhizosphere. In addition, the effects of elevated CO2 and drought on microbial biomass and enzymatic activities considerably varied between the two selected species. M. sativa generally experienced a better ameliorative effect than B. ischaemum.

Characteristics and mechanisms of Ni(II) removal from aqueous solution by Chinese loess

Nickel is a toxic heavy metal among trace elements which has a detrimental impact on living organisms. There is growing need of finding an economic and effective solution for Ni(II) immobilization in environments. Chinese loess was selected as adsorbent to remove Ni(II) from aqueous solution. Adsorbent dosage, reaction time, solute concentration, temperature, and solution pH also have influences on efficiency of Ni(II) removal. The monolayer adsorption capacity of loess towards Ni(II) is determined to be about 15.61 mg/g. High temperature and pH favor the removal of Ni(II) using Chinese loess soil and the optimal dosage of loess is determined to be 10 g/L. The kinetics and adsorption isotherms of the adsorption process can be best-fitted with the pseudo second order kinetics and Langmuir isothermal model, respectively. The thermodynamic analysis reveals that the adsorption process is spontaneous, endothermic and the system disorder increases with duration. Nickel ions can be removed with the removal efficiency of 98.5% at pH greater than or equal to 9.7. Further studies on loess and Ni(II) laden loess (using X-Ray diffraction, Fourier transform infrared spectroscopy) and Ni(II) species distribution at various pH have been conducted to discuss the adsorption mechanism. Loess soils in China have proven to be a potential adsorbent for Ni(II) removal from aqueous solutions.

Decay characteristics and erosion-related transport of glyphosate in Chinese loess soil under field conditions

The decay characteristics and erosion-related transport of glyphosate and aminomethylphosphonic acid (AMPA) were monitored for 35d at different slope gradients and rates of application in plots with loess soil on the Loess Plateau, China. The initial glyphosate decayed rapidly (half-life of 3.5d) in the upper 2cm of soil following a first-order rate of decay. AMPA content in the 0–2cm soil layer correspondingly peaked 3d after glyphosate application and then gradually decreased. The residues of glyphosate and AMPA decreased significantly with soil depth (p<0.05) independently of the slope inclination and application rate. About 0.36% of the glyphosate initially applied was transported from plots after one erosive rain 2d after the application. Glyphosate and AMPA concentrations in runoff were low while the contents in the sediment were much higher than in the upper 2cm of the soil. CapsuleAlthough the rate of glyphosate decay is rapid in Chinese loess soil, the risks of glyphosate and AMPA need to be taken into account especially in the area with highly erosive rainfall.

Short-term transport of glyphosate with erosion in Chinese loess soil — A flume experiment

Repeated applications of glyphosate may contaminate the soil and water and threaten their quality both within the environmental system and beyond it through water erosion related processes and leaching. In this study, we focused on the transport of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) related to soil erosion at two slope gradients (10 and 20°), two rates of pesticide with a formulation of glyphosate (Roundup®) application (360 and 720mgm−2), and a rain intensity of 1.0mmmin−1 for 1h on bare soil in hydraulic flumes. Runoff and erosion rate were significantly different within slope gradients (p<0.05) while suspended load concentration was relatively constant after 15min of rainfall. The glyphosate and AMPA concentration in the runoff and suspended load gradually decreased. Significant power and exponent function relationship were observed between rainfall duration and the concentration of glyphosate and AMPA (p<0.01) in runoff and suspended load, respectively. Meanwhile, glyphosate and AMPA content in the eroded material depended more on the initial rate of application than on the slope gradients. The transport rate of glyphosate by runoff and suspended load was approximately 14% of the applied amount, and the chemicals were mainly transported in the suspended load. The glyphosate and AMPA content in the flume soil at the end of the experiment decreased significantly with depth (p<0.05), and approximately 72, 2, and 3% of the applied glyphosate (including AMPA) remained in the 0–2, 2–5, and 5–10cm soil layers, respectively. The risk of contamination in deep soil and the groundwater was thus low, but 5% of the initial application did reach the 2–10cm soil layer. The risk of contamination of surface water through runoff and sedimentation, however, can be considerable, especially in regions where rain-induced soil erosion is common.

Effects of Coal Gangue Content on Water Movement and Solute Transport in a China Loess Plateau Soil

AbstractThe mining industry has grown strongly in China in recent decades, resulting in large amounts of coal gangues, which cause water and soil pollution, soil erosion, and various other environmental problems. They are often used in reclamation projects in attempts to restore land damaged by mining, hence they are frequently present (in widely varying proportions) in the topsoil in areas around mines. Their presence can strongly affect key soil variables, including its bulk density, structure, water retention, water movement, and solute transport rates. In the study presented here, the effects of gangue contents on infiltration, saturated hydraulic conductivity, and solute transport parameters of a Chinese Loess plateau soil were examined. The results show that infiltration rates and saturated hydraulic conductivity decreased with increasing gangue content. The Peck–Watson equation modeled these relationships well, but Bouwer–Rice equations provided poorer matches with the acquired data. Cumulative infiltration over time was described well by both the Philip equation and Kostiakov equation. Both the simplified convection–dispersion equation and a two‐region model described the solute transport processes well. In addition, the dispersion increased, while both the Peclet number and mobile water fraction decreased, with increases in gangue contents.

Experimental Validation of Retardation of Tritium Migration in the Chinese Loess Media

Retardation of tritium migration in the Chinese loess media was studied through column experiments by comparison of the migration velocity with other three “non-adsorptive” tracers of Br−, 99Tc, and 131I. Results showed that the transport peak of Br− was 1.25 times earlier than that of tritium when the tracers were simultaneously injected into the column, and the migration of 99Tc was even 1.60 times faster than 3H when the tracers were simultaneously injected. For iodine, it was only 1.02 times faster than that of tritium, but it should not be ignored. It reflected that the transport of 3H, compared to that of Br−, 99Tc, or 131I in the loess media, was retarded. In order to validate the adsorption behavior of tritium on loess, batch tests were carried out using Chinese loess soil. The experimental results indicated that the adsorption of tritium was actual existence, and the distribution coefficient of tritium is influenced by initial activity of tritium, pH, water/solid ratio, and the content of humic and fulvic acids.

In situ comparisons of ammonia volatilization from N fertilizers in Chinese loess soils.

Ammonia volatilization loss from mineral N fertilizers was determined on a calcareous Chinese loess soil with a pH (CaCl2) of 7.7. An original in situ method that required no electricity or laboratory analyses was used. By means of a bellows pump, ambient air was drawn through four conical cups placed onto the soil (total area 400 cm2) and subsequently through an NH3-specific detector tube with direct colorimetric indication of the ammonia concentration (measuring range, 0.05–700 vol.-ppm NH3). Duration of measurement was about 3 min. Following N fertilization to winter wheat in 1990 and to summer maize in 1991, the application methods surface broadcast, uniform incorporation into the 0–15-cm layer, and for maize, a point placement at 10 cm depth were investigated. Ammonium bicarbonate and urea were applied at rates of 100 and 200 kg N ha−1. In the autumn of 1990, ammonia losses following NH4HCO3 application were more than twice as large as with urea, fertilizer incorporation reduced NH3 losses 15-fold, and doubling the nitrogen application rate resulted in a 1.7-fold increase in the percentage of nitrogen loss. Cumulative ammonia fluxes were about 2 times higher in the summer of 1991. Comparing application methods in summer, losses were significantly (3 times) lower only with point placement. The above differences were all significant at the P<0.05 level. Due to the very low air exchange rate (0.9 volumes min−1), actual volatilization rates were underestimated by this method. Though not yielding absolute amounts, the Drager-Tube method proved very suitable for comparing relative differences in ammonia fluxes. The measurements clearly reflected the characteristic flux patterns for the different treatments and the effects of environmental factors on their time course.

A direct link between the China loess and marine δ18O records: aeolian flux to the north Pacific

MOST studies of Quaternary climates conducted during the past 150 years have focused on glacial sequences, and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates. An important goal of palaeoclimatology, however, to link the well-known detailed continental records to marine records of similar resolution, has yet to be realized. The classic loess sequences of China provide an apparently continuous record of continental climate over the past 2.4 million years1,2. The oxygen isotope, δ18O, timescale developed from the marine record3 gives us a global chrono-stratigraphy of late Pleistocene climates. Previously, it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north-west Pacific downwind from China4,5. Here we report the results of such an effort for core V21-146 (Fig. 1) and tie the last 500,000 years of the Chinese loess–soil sequence directly to the δ18O timescale and, in so doing, refine the dating of regional loess and soil horizons.

Micromorphological comparison of three soils derived from loess in different climatic regions

Three soil profiles derived from Pleistocene eolian loess were compared according to their micromorphological properties. One soil was chosen from The Netherlands, with a temperate humid climate, one from Poland with a slightly drier climate, and one from China, having a semi-arid climate. The investigations lead to the following conclusions: (1) Typologically the soils examined show different development stages according to the environmental conditions, including the climatic and anthropogenic soil-forming factors. These are expressed by differentiation of horizons and by their micromorphological properties; (2) The soil profiles derived from Dutch and Polish loess show permanent trends towards vertical translocation of the clay fraction, together with iron oxides. In The Netherlands soil the plasma illuviation is more distinctly expressed than in the Polish one due to the climatic conditions; (3) In the soil profile derived from the Chinese loess, only weak trends towards plasma translocation were observed. The illuviation of plasma is restricted by the occurrence of various forms of calcium carbonate and only re-orientation is present. The higher clay content is due to the higher amount of original clay in the loess sediments; (4) In the Chinese loess soil there is a lot of lublinite in the whole profile. The actual presence of lublinite in the surface horizon points to a secondary accumulation of the component in the A 1-horizon. It is probable that the material originating from the subsoil has been brought upward by agricultural practices.