•SIC pool in irrigated dryland of the NCP were estimated as 13.21 kgC·m−2.•SIC accounts for 70% of the soil carbon pool.•Fluvisols area of NCP contributes 4.7% of China's SIC pool with an area of ...2.13%.•Leaching and precipitation result in the concentration of SICs in the lower soil layer.•The potential for inorganic carbon sequestration in the region is 2.58 PgC.
Rapid expansion of irrigated agriculture in semi-arid regions alters the global carbon cycle and terrestrial soil carbon pools, in particular the potential for inorganic carbon sequestration in soils. Current research on soil inorganic carbon (SIC) pools in irrigated farmland focuses on local scale. The impact of irrigated agriculture on soil inorganic carbon pools and sequestration potential at the regional scale should be addressed. This study investigates soil carbon pools and inorganic carbon sequestration potential under intensive irrigated agriculture in alluvial plains in semi-arid climates. We chose the North China Plain (NCP), a traditional intensive agricultural region in China with long-term irrigation practices. Appling the national soil field survey data, we calculated soil inorganic carbon, organic carbon, estimated the content of the total soil carbon pool and the inorganic carbon sequestration potential and assessed the distribution characteristics. The SIC density and storage in fluvisols of irrigated farmland in the NCP were estimated to be 13.21 kgC·m−2 and 2.58 PgC, respectively. SIC densities accounts for 70% of the soil carbon pool. It is inferred that irrigated dryland in semi-arid regions has a considerable soil inorganic carbon pool and inorganic carbon sequestration potentials. The SIC pools in mineral soil horizon beneath plough horizon account for 75.8–78.11% of the total SIC storages. Soil inorganic carbon pools are easily lost through leaching and deposition in the lower part of the soil due to irrigation. We find that due to irrigation and atmospheric precipitation, the top layer of the soil is constantly being replenished with carbonate. Spatial distribution of inorganic carbon pools on floodplains is related to river-related geomorphology. This study provides a SIC perspective for the study of soil carbon pools in agricultural fields and complements the knowledge of carbon sequestration potential.
Global climate change has accelerated the occurrence of agricultural drought events, which threaten food security. Therefore, improvements in the soil water retention capacity (WRC) and crop drought ...resistance are crucial for promoting the sustainability of the agricultural environment. In this study, we explored the effects of applying biochar and water-retaining agent (WRA) on soil WRC and crop drought resistance in a Fluvisols, along with their potential mechanisms. We applied two types of biochar (based on wheat and maize straw) and two WRAs (polyacrylamide and starch-grafted sodium acrylate) to Fluvisols with different textures, and then evaluated soil water retention and crop drought physiological resistance. The combined biochar and WRA treatment increased the WRC in both the sandy loam and clay loam Fluvisols. Biochar and WRA increased the relative content of soil hydrophilic functional groups. Compared with the control (CK), the combined application of biochar and WRA increased the field capacity, reduced soil water volatilization under drought conditions, and slowed water infiltration into the Fluvisols. The soil WRC was higher with the wheat straw biochar (WBC) treatment than with the maize straw biochar (MBC) treatment. It was also higher with polyacrylamide treatment than with the starch-grafted sodium acrylate treatment. The combined application of biochar and WRA improved crop drought physiological resistance by significantly increasing the maize seedling potassium (K) and soluble sugar contents, increasing antioxidant enzyme activity, and reducing the malondialdehyde (MDA) content. The results indicate that the application of biochar and WRA alleviated drought stress by increasing the soil WRC and improving crop drought resistance in Fluvisols.
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•Combined biochar and WRA increased soil WRC and crop drought resistance in Fluvisols.•WBC had better crop drought resistance than MBC in sandy loam and clay loam soils.•Increase in crop K, soluble sugar, antioxidant enzyme activity were key mechanisms.
Linkages between soil structure and physical–chemical soil properties are still poorly understood due to the wide size-range at which aggregation occurs and the variety of aggregation factors ...involved. To improve understanding of these processes, we collected data on aggregate fractions, soil porosity, texture and chemical soil properties of 127 soil samples from three European Critical Zone Observatories. First, we assessed mechanistic linkages between porosity and aggregates. There was no correlation between the fractions of dry-sieved aggregates (>1mm, DSA) and water-stable aggregates (>0.25μm, WSA). Soil microporosity and micro+mesoporosity increased with increasing abundance of aggregates, though this correlation was only significant for the WSA fraction. The fraction of DSA did not affect the overall porosity of the soil, but affected the ratio between micro- and mesopores (θ30kPa/θ0.25kPa), suggesting that micropores are dominantly located within DSA whereas mesopores are located in between DSA and loose particles. Second, we studied the relations between the physical and chemical soil properties and soil structure. Soil texture had only a minor effect on the fractions of WSA and DSA whereas Fe-(hydr)oxide content was correlated positively with both WSA fraction and porosity. This may be attributed to Fe-(hydr)oxides providing adsorption sites for organic substances on larger minerals, thereby enabling poorly reactive mineral particles to be taken up in the network of organic substances. The fraction of WSA increased with an increase in the soil organic carbon (SOC) and Fe-(hydr)oxides content and with a decrease in pH. This pH-effect can be explained by the enhanced coagulation of organically-coated particles at a lower pH. Overall, this study indicates that mechanistic linkages exist between soil chemical properties, aggregate formation and soil porosity.
•We studied the linkages between aggregate formation, porosity and soil chemical properties.•The combination of texture and water-stable aggregates determines the porosity.•Dry-sieved aggregates control the distribution of pores between micro- and mesopores.•Fe-(hydr)oxides are important for the formation of pores and water-stable aggregates.•The combination of Fe-(hydr)oxides, soil organic matter and pH controls aggregate formation.
A vegetation trial was conducted to test, establish and compare the abilities of crimson clover (Trifolium incarnatum L.) and blue alfalfa (Medicago sativa L.) to grow, sequester arsenic and improve ...microbial soil status in soils with deteriorated water and physical properties and with naturally and technogenically reached toxic levels of arsenic. The experiment is based on cultivation of two types of legume crops under the same controlled climatic conditions, but in different soil environments. Contaminated Regosols and control uncontaminated Rhodic Cambisols, ChromicCalcaric Cambisols and Fluvisols, collected from four geographical points, distributed (4 kg.) in a total of 24 pots/samples and sown with the two investigated crops (2x12) were included in the study. Crop growth and development were monitored during the vegetative and reproductive phenological phases, taking timely biometric measurements. According to the observations made and the results obtained, the crimson clover (Trifolium incarnatum L.) is suitable for remediation and improvement of the agrochemical, biological, physical and physicochemical properties of arsenic-contaminated soils - Regosols, by forming a dense root system with a relative abundance of tubers of symbiotic nitrogen-fixing microorganisms in it, in conditions of Interventional contents of arsenic, significant compaction and deteriorated water permeability of the soils. Contamination with arsenic (in association with a number of heavy metals) suppresses the germination of both crops - crimson clover and alfalfa, vegetative phenophases, nutrition, growth and development of clover, but not the fertility of the obtained crop of the studied crops. The main factors limiting the fertility of the two crops in the experiment were the low content of soil colloids (humus and clay) and the poorer soil microbiome. The observed better adaptability in feeding alfalfa in contaminated soils allows this crop to be applied in longer-term remediation measures.
Our work addresses a neglected aspect of heavy metal (HM) pollution of sediments in small floodplain reservoirs. Very little is known about this type of water bodies, in contrast to oxbow lakes or ...old river beds. The study examines the spatial horizontal distribution of HM and the effect of texture, organic carbon (OC) content, morphometric and location features on HM concentrations. Moreover, the data from the assessment of sediment toxicity were analysed with respect to recent years' droughts to estimate the potential toxicity of sediments as soils. The statistical analyses showed that the texture and the OC content had a significant impact on the HM concentrations. Fine-grained and OC-rich sediments exhibited higher HM pollution. Only one morphometric/location factor was shown to affect HM levels in sediments – the angle between the reservoir axis and the riverbed. The angle value affected the texture and, consequently, the HM content: with a rising angle the share of the coarse-grained fraction increased leading to a decrease in the HM concentration. The spatial horizontal HM distribution did not show statistically significant results, nonetheless, HM content was found to rise along with the distance from the initial part of reservoir. The toxicity levels were not exceeded in sediments, however, the evaluation of the material as soil showed that, according to European Union guidelines, the content of at least one HM was toxic in 80% of the samples. Contaminated floodplain reservoirs should be regarded as a double threat to riverine ecosystems. On the one hand, they are one of the main non-point sources of river valley pollution; on the other hand, given the drying up of reservoirs, sediments become soils and the soil-bound heavy metals become more toxic to the environment.
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•Knowledge about the functioning of small water reservoirs is very limited.•Features influencing heavy metal content are established.•Climate change causes drying out of reservoirs.•Non-toxic sediments transform into toxic soils.
Surface-water irrigation is one of the most important irrigation methods in areas with abundant surface water. Although this method of irrigation is both economical and convenient, many contaminants ...are also introduced into the soil-water systems such as organophosphorus pesticides (OPPs). To study the influence of surface-water irrigation on the distribution of OPPs in soil-water systems, 42 water samples (38 groundwater and four surface water) and 85 soil samples (78 profile soil samples and seven topsoil samples) were taken from Shahu in the Jianghan Plain, China. Shahu is a typical Chinese surface-water irrigation district. During sampling, three types of areas were considered: surface-water irrigated areas, groundwater-irrigated areas away from rivers, and non-irrigated areas adjacent to rivers. The results showed that the concentrations of OPPs in the groundwater and soil in the surface-water irrigated farmland were higher than those in groundwater-irrigated farmland. The groundwater flow field and surface-water irrigation were responsible for the OPPs. Thus, it is clear that the surface-water irrigation had a strong influence on the distribution of OPPs in soil-water systems. Principal component analysis for OPPs content in groundwater showed that the key influencing factors on the distribution of OPPs in groundwater were the groundwater flow field and current pesticide use.
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•Methamidophos, Diazinon and Omethoate were the main OPPs in the soil-water system.•OPPs in the topsoil and subsoil had adverse effects to the safety of agricultural products.•OPPs in the subsoil and groundwater had significant spatial distribution characteristics.•Surface-water irrigation influenced the distribution of OPPs in the study area.•Groundwater flow field and current pesticide use were two major influencing factors.
In the last 30years, a number of large-scale multi-ecological projects have been implemented on the Chinese Loess Plateau, where there has been a significant trend toward ecological restoration, ...which will certainly affect the spatial distribution of soil cabon sequestration. We investigated 180 topsoil sites (to 20cm depth) to enhance the understanding of the spatial patterns of soil organic carbon (SOC) and its dominant influencing factors in the Luoyugou watershed (72km2), which is a typical watershed in the gully-hill area of the Loess Plateau, China. The results indicate that the SOC in the Luoyugou watershed follows a distinct spatial pattern, whereby the SOC increases as altitude increases. The SOC of the mountain ridge area (high elevation area) is measurably higher than that of the sides of the valley. Four spatially interpolated methods (IDW, Ordinary Kriging, land use types and multiple linear regression) were used to express the SOC spatial patterns, but all of them have low estimate accuracy because the SOC in the hilly loess area is highly heterogeneous given the complex topography and land use/cover. The estimate accuracy should improve with the Normalized Difference Vegetation Index (NDVI), given auxiliary information. SOC in the Luoyugou watershed is influenced by altitude, land use, and NDVI. Altitude has a significant relationship with SOC in the Luoyugou watershed. Annual precipitation significantly increases with increased altitude, and land use/vegetation cover changes between terraced cropland, orchard to grassland, and woodland. The SOC of Luoyugou has no significantly correlated relationship to topographic indices (slope, upslope area, and TWI), which have been profoundly disturbed by human activity, particularly by the conversion from sloped land to terraced cropland. The study results show that afforestation can significantly increase SOC. The SOC in immature forests (10years old) is 17.91% higher than that in terraced cropland, but 32.25% lower than that in 30-year-old forests. The SOC concentration of 30-year-old forest is significant higher than that in other land cover. On a 10-year time scale, orchard is not a good ecological restoration type for increasing SOC; the contribution to enhancing SOC is not obvious and even shows a weak decreasing trend. In general, the SOC sink role of the Loess Plateau is being enhanced by ecological restoration.
•Altitude influences the spatial pattern of soil organic carbon (SOC) in the Chinese Loess Plateau.•Vegetation restoration has significantly enhanced SOC sequestration in recent decades.•Spatial variability of SOC is highly heterogeneous due to complex topography and landscapes.•NDVI can improve the prediction accuracy of the spatial pattern of SOC in the Loess Plateau.
The determination of geochemical fractions of heavy metals (HM) in soils is a key issue when studying their mobility. Therefore, we have determined the geochemical fractions and the vertical ...distribution of chromium (Cr), copper (Cu), and zinc (Zn) in seven floodplain soil profiles in relation to flooding conditions and relevant soil properties. These soil profiles represent two different soil groups (Mollic Fluvisols and Eutric Gleysols) which differ significantly in flooding duration and soil properties. The metals were fractionated sequentially to seven fractions as follows: F1: soluble+exchangeable, F2: easily mobilizable, F3: bound to Mn oxides, F4: bound to soil organic matter (SOM) (might include sulphides), F5: bound to low crystalline (amorphous) Fe oxides, F6: bound by crystalline Fe oxides, and F7: residual fraction.
The total Cr, Cu, and Zn concentrations ranged from 54.4 to 134.1, 165.2 to 215.7, and 128.5 to 1097.8mgkg−1, respectively, and exceeded the precautionary values of the BBodSchV (1999). Total metal concentrations correlated significantly to soil organic carbon (SOC), total sulphur (St), and cation exchange capacity (CEC), as well as crystalline and amorphous Fe- and Mn-oxides. The residual fraction was dominant for Cr, the organic bound for Cu, and crystalline Fe oxides for Zn. The potential mobile fraction (PMF=∑F1–F6) ranged from 38.4 to 71.4, 63.9 to 85.1, and 51.5 to 83.3% of the total Cr, Cu, and Zn, respectively. However, the mobile fraction (MF=∑F1–F2) ranged from 0.96 to 1.84, 2.1 to 4.1, and 9.1 to 28.7% of the total concentrations of Cr, Cu, and Zn, respectively. The order of the PMF in the studied soil profiles was Cu>Zn>Cr, while the order of the MF was Zn>Cu>Cr. The PMF of the three metals was positively correlated with SOC and Mn oxides. The PMF was positively correlated with CEC (Cr, Zn), St (Cr), and Fe oxides (Zn). The PMF of Cu and Zn correlated negatively with clay. The MF of the three metals was correlated negatively with soil pH. The MF of Zn was correlated positively with clay, SOC, and St. The MF of Cr was correlated positively with clay, while it correlated negatively with SOC, St, CEC, and Fe–Mn oxides. The Fluvisols revealed higher total concentrations and potential motilities of Cr, Cu, and Zn compared to the Gleysols. However, the Gleysols had a higher metal mobility compared to Fluvisols due to their longer flooding duration. The solubility of Cr below the average water level in the studied profiles was higher than above the water level, while the solubility of Cu and Zn above the water level was higher than below the water level in both soil groups. The potential mobility of the studied metals (especially of Cu followed by Zn), and thus the transfer of these metals into the grassland and food chain, should be high, which might be harmful to the floodplain ecosystem.
•Geochemical fractions of Cr, Cu, and Zn in floodplain soil profiles were determined.•Total metal concentrations exceeded frequently the precautionary values.•Long term flooded soils (Gleysols) show a higher metal mobility than Fluvisols.•The order of potential mobile fraction (PMF) was: Cu>Zn>Cr.•The order of the mobile fraction (MF) was: Zn>Cu>Cr.
Floodplain soils are important reservoirs of organic carbon (OC) in the terrestrial carbon cycle. Few rivers and floodplains in the world and particularly in central Europe are in a natural state. ...They are regulated, stabilised from erosion behind artificial levees, drained and used for agriculture. Fluvisols store high amounts of OC from the topsoil to the subsoil, but little is known about the soil organic matter (SOM) quality and its vulnerability to decomposition. In this study, two regulated floodplains originating from different parent materials under grassland use in Southern Germany (Alpine Foreland and the Bavarian Forest) were sampled and analysed for the quantity and quality of inherent SOM in the topsoil and two subsoil levels. We characterised bulk soil (pH, texture, inorganic carbon and total nitrogen) and applied a combined density and size fractionation scheme to obtain six fractions. The chemical composition of the fractions was further determined using solid-state 13C NMR spectroscopy (SOM composition), as well as X-ray diffraction (clay mineralogy) and N2-BET (specific surface area (SSA)). Contributions of light fractions and especially of occluded particulate organic matter (oPOMfine) to the total OC were remarkably high in the subsoils. Organo-mineral associations (OMFfine) highly contributed to total OC at both sites but only in the topsoils. The highest OC concentrations of OMFfine were found in calcareous parent material, which shows that polyvalent cations promote OC storage. However, the inter-site as well as intra-site heterogeneity of oPOMfine and OMFfine OC contribution was highly variable. In the Bavarian Forest, oPOMfine was enriched in lipids in the subsoil. This was most probably due to a limited supply of oxygen in the aggregates through fluctuating groundwater levels that retarded decomposition and selectively preserved aliphatic compounds. In the Alpine Foreland, soil biota had mixed fresh SOM into the subsoil. There, oPOMfine contained all the functional C-groups, particularly carbohydrates. A changing global climate jeopardises OC reservoirs in floodplains, due to increased flooding and associated river bank erosion. Such disturbances not only cause losses of productive land but also release OC stored in light fractions that could be oxidised to CO2, depending on its chemical composition, thus adding to global warming.
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•Floodplain subsoils store high amounts of organic carbon in light fractions.•Strongly decomposed, lipid-rich light fractions occur in less-aerated subsoils.•Weakly decomposed light fractions in well-aerated soils with high bioturbation•Polyvalent cations promote mineral-bound OC storage in calcareous soils.
This study aimed to (i) select the endophytic bacteria from maize roots for their N2-fixing ability and (ii) evaluate the efficacy of potent indigenous bacterial strains on soil fertility, nitrogen ...(N) uptake, and growth and yield of maize. A total of 31 maize root samples were collected from An Giang province in Vietnam to isolate the bacteria. The pot experiment was conducted in nine treatments: (i) 100% N of the recommended fertiliser formula (RFF), (ii) 85% N of RFF, (iii) 70% N of RFF, (iv) 55% N of RFF, (v) 85% N of RFF plus a mixture of two potent strains of nitrogen-fixing endophytic bacteria (NFEB), (vi) 70% N of RFF plus a mixture of two potent strains of NFEB, (vii) 25% N of RFF plus a mixture of two potent strains of NFEB, (viii) 0% N of RFF plus a mixture of two potent strains of NFEB, and (ix) 0% N of RFF. The experiment was conducted in the greenhouse to collect soil and plant samples at harvest and observe their growth and agronomic parameters. The results showed that two acid-resistant endophytic bacterial strains were selected and identified as Enterobacter cloacae ASD-21 and E. cloacae ASD-48. At 85% N level, a mixture of the two endophytic bacteria strains was applied as biofertilisers and proved their ability to significantly enhance NH4+ content and N uptake, with an increase of 14.8 mg NH4+ kg-1 and 0.26 g N pot-1, respectively. A mixture of the two potent strains of NFEB produced higher values in plant height, stem diameter, cob length, and cob diameter compared to 100% N of RFF. It replaced 15% N of RFF but still maintained the maize grain yield.
