查看更多>>摘要：Reflectance spectroscopy in the visible-infrared and shortwave infrared (450-2500 nm) wavelength region is a rapid, cost-effective and non-destructive method that can be used to monitor heavy metal (PTE, potential toxic elements) contaminated areas. Due to the PTE pollution that has accumulated in the course of wastewater treatment, the existence of Technosols presents an environmental problem, a potential source for PTE uptake by vegetation, or even the release of PTEs into groundwater. In this study, multivariate procedures using Partial Least Squares Regression (PLSR) and Random Forest Regression (RFR) are applied to quantify relationships between soil heavy metal concentration (Cr, Cu, Ni, Zn) and reflectance data of highly contaminated Technosols from a former sewage farm near Berlin, Germany. Laboratory measurements of 110 soil samples in four different preparation steps were acquired with HySpex hyperspectral cameras. The impact of the different preparation steps, namely "oven-dried", "sieved", "ground", "LOI", was evaluated for its potential to enhance the method performance or to reduce the time-consuming soil sample preparation. Furthermore, different spectral preprocessing methods were evaluated regarding improvements of spectral modelling performance and their ability to minimise noise and multiple scattering effects. Considering the optimal coefficient of determination (R-2), PLSR shows an improving performance and accuracy with increasing preparation steps such as ground or LOI for all metals of interest (R-2_Cr: 0.52-0.78; R-2_Cu: 0.36-0.73; R-2_Ni: 0.19-0.42 and R-2_Zn: 0.41-0.74). RFR shows a weaker estimation performance for all metals, even when using higher sample preparation levels (R-2_Cr: 0.36-0.62; R-2_Cu: 0.17-0.72; R-2_Ni: 0.20-0.35 and R-2_Zn: 0.26-0.67). The results show that an application of methods such as PLSR for the prediction of PTE concentration in Technosols is still a challenge but provides more robust estimations than the user-friendly RFR method. Additionally, this study shows that PTE estimation performance in heterogeneous soil samples can be improved by increased laboratory soil preparation steps and further spectral pre-processing steps.
查看更多>>摘要：Understanding farmer local knowledge of soil management practices and their fertility is vital to maintaining soil fertility in agricultural areas, which contributes to maintaining sustainable agro-ecosystems. In this study, soil fertility indicators and the farmer's management practices were investigated, while local knowledge was contrasted with scientific understanding. For this, 610 surveys were conducted with dichotomous and open questions that were applied in the 16 localities of the province of Loja in southern Ecuador; for their comparison, carbon and texture maps were generated utilizing the respondents' main indicators. Farmers visibly identify various soil parameters such as texture (53.9% sandy soils), color (64.3% black soils), workability (81.3% workable soils), and stoniness (64.6% soils do not have stoniness), as indicators of soil productivity, while applying soil management practices inherited mainly from their parents and grandparents. As such, there are many concordances such as some of the practices that respondents use that pollute the soil and others that conserve the soil; also some disagreements in certain study places between soil color according to local knowledge and carbon stocks, other disagreements were between the texture according to the perception of the respondents and the textural classes. The findings demonstrate respondents identify soil fertility through their experience using visible indicators; some practices to soil management can contribute to soil conservation, which is very important for future management practices and soil fertility conservation that can significantly influence the techniques that farmers implement.
查看更多>>摘要：To reveal the influence of shell sand content on soil physical properties and salt ion changes under simulated rainfall leaching conditions, various ratios of shell sand to fluvo-aquic soil were simulated to change the particle composition of shell sand. Basic physical and chemical properties, such as soil particle-size composition, soil bulk density, soil porosity, soil pH, soil electrical conductivity, and soil salt ions were determined and analyzed. Fuzzy mathematics was used to evaluate the potential for soil water storage and salt suppression by altering the shell sand-to-fluvo-aquic soil ratio. The results showed that with decreasing shell sand content, the soil particle composition with different ratios of shell sand to fluvo-aquic soil changed significantly. With decreasing shell sand content, bulk density and capillary porosity of the soils with different ratios increased, and the total porosity and noncapillary porosity decreased. The soil pH first decreased and then increased, following the order 0:1 > 1:0 > 1:1 > 1:2, while the electrical conductivity increased. Cl-, NO3-, Na+, Ca2+, and Mg2+ showed a trend of first decreasing and then increasing with decreasing shell sand content, following the order 0:1 > 1:0 > 1:2 > 1:1. The mixed soil with a 1:1 ratio of shell sand and fluvo-aquic soil has the largest leaching loss of salt segregants. A comprehensive evaluation of the soil improvement performance with respect to the ratio of shell sand to fluvo-aquic soil revealed a trend of 1:1 > 1:0 > 0:1 > 1:2, and the mixed soil with a 1:1 ratio of shell sand to fluvo-aquic soil showed the greatest improvement. The shell sand content can significantly affect soil water and salt transport, and a suitable shell sand content can effectively improve soil water storage and salt inhibition effects.
查看更多>>摘要：Carbon (C) and nitrogen (N) are closely coupled to regulate the cycle of soil organic carbon (SOC) and its feedback to climate change in terrestrial ecosystem. However, the response of SOC content to N input in different soil types on time scales is still less understood. Here, we did a meta-analysis by collecting global farmland data across 60 years based on soil taxonomy, as well as our long-term field agricultural experiment from 2006 to 2019 (total number of observations, n = 301). The results showed that N addition promoted the increase of SOC content on an average of 9.1% in agrosystem, but varied considerably in different soil types (5.2%-12.0%). The SOC content of Alfisols and Mollisols soils showed a significant increasing response along the time scale. Furthermore, random forest model and structural equation model analysis indicated that climate factors and soil types indirectly affect the temporal response of SOC to N application through soil properties such as TN and C:N. This study emphasizes that the temporal response of SOC content to long-term N addition depends on soil type, with an scale-up effect in soil types with relative high SOC content (like Alfisols and Mollisols), which provides a new perspective for better understanding the C sequestration as the consequence of coupling effect of C and N in farmland system under long-term human activities.
查看更多>>摘要：Grazing-based production systems are a source of soil greenhouse gas (GHG) emissions triggered by excreta depositions. The adoption of Urochloa forages (formerly known as Brachiaria) with biological nitrification inhibition (BNI) capacity is a promising alternative to reduce nitrous oxide (N2O) emissions from excreta patches. However, how this forage affects methane (CH4) or carbon dioxide (CO2) emissions from excreta patches remains unclear. This study investigated the potential effect of soils under two Urochloa forages with contrasting BNI capacity on GHG emissions from cattle dung deposits. Additionally, the N2O and CH4 emission factors (EF) for cattle dung under tropical conditions were determined. Dung from cattle grazing star grass (without BNI) was deposited on both forage plots: Urochloa hybrid cv. Mulato and Urochloa humidicola cv. Tully, with a respectively low and high BNI capacity. Two trials were conducted for GHG monitoring using the static chamber technique. Soil and dung properties and GHG emissions were monitored in trial 1. In trial 2, water was added to simulate rainfall and evaluate GHG emissions under wetter conditions. Our results showed that beneath dung patches, the forage genotype influenced daily CO2 and cumulative CH4 emissions during the driest conditions. However, no significant effect of the forage genotype was found on mitigating N2O emissions from dung. We attribute the absence of a significant BNI effect on N2O emissions to the limited incorporation of dung-N into the soil and rhizosphere where the BNI effect occurs. The average N2O EFs was 0.14%, close to the IPCC 2019 uncertainty range (0.01-0.13% at 95% confidence level). Moreover, CH4 EFs per unit of volatile solid (VS) averaged 0.31 g CH4 kgVS(-1), slightly lower than the 0.6 g CH4 kgVS(-1) developed by the IPCC. This implies the need to invest in studies to develop more region-specific Tier 2 EFs, including farm-level studies with animals consuming Urochloa forages to consider the complete implications of forage selection on animal excreta based GHG emissions.
查看更多>>摘要：Paddy soils experience long-term redox alternations affecting the interactions between the biogeochemical cycling of iron (Fe) and carbon (C). Differences in particle aggregation and soil organic matter (SOM) turnover are likely to both affect and be affected by the trajectory of Fe mineral evolution/crystallinity with redox fluctuations. We hypothesized that the legacy effects of redox cycling under paddy management affects particle aggregation, the distribution and mineralogy of Fe (hydr)oxides between particle-size fractions, and the interaction with SOM stabilization. Moreover, we expected underlying processes to be different in paddy eluvial and illuvial horizons, particularly due to the different inputs and redox conditions these horizons experience. To test these hypotheses, we evaluated the distribution of Fe species and organic C between different aggregate and particle-size fractions in topsoil (eluvial) and subsoil (illuvial) horizons of soils under long-term paddy and nonpaddy management in NW Italy, as well as mineralogical changes in Fe phases by Fe K-edge Extended X-ray Adsorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) spectroscopy. Our findings indicate that although paddy topsoils are depleted in hydrous Fe oxides with respect to non-paddy soils, they can stabilize important amounts of C through mineral associations, particularly with finer particle-size fractions rich in less crystalline Fe phases. We also show that redox cycling can influence microaggregate stability and consequently the distribution of Fe phases and OC between intra and inter-micmaggregate fractions. On the other hand, illuvial horizons under paddy management were enriched in short-range ordered hydrous Fe oxides and this contributed to enhanced microaggregate formation and C stabilization with respect to non-paddy subsoils.
查看更多>>摘要：Organo-mineral association and water-stable aggregation in finely textured tailings are critically important to the eco-engineered soil formation from alkaline Fe ore tailings for sustainable mine site rehabilitation. Arbuscular mycorrhizal (AM) symbiosis plays important roles in soil aggregate formation and organic matter (OM) stabilization. However, it is unknown if AM symbiosis could enhance aggregate formation and OM stabilization in alkaline Fe ore tailings. The present study aimed to investigate the establishment of AM symbiosis and their role in tailing aggregate formation coupled with OM stabilization, as well as the underlying mechanisms. After initial eco-engineering (OM amendment and pioneer plant cultivation) to improve physicochemical conditions for plant survival, Sorghum spp. Hybrid cv. Silk inoculated with/without AM fungi (Glomus spp.) were cultivated in the tailings under glasshouse conditions for 14 weeks. The results indicated that AM fungi formed symbiotic association with Sorghum spp. plants, improved mineral nutrient (e.g., P) acquisition and root growth in the eco-engineered tailings. The AM symbiosis significantly improved aggregate formation. The association of organic carbon and nitrogen with tailing minerals of the aggregates was enhanced by the AM symbiosis. As revealed by synchrotron-based C 1 s near edge X-ray absorption fine structure (C 1 s NEXAFS) and Fe K edge X-ray absorption fine structure (Fe K edge XAFS) spectroscopy, the AM symbiosis favoured carboxyl and aromatic C association with secondary Fe-Si minerals, which may have been formed from AM driven mineral weathering. Overall, the study revealed that the AM symbiosis could not only improve the growth of pioneer plant species in the early eco-engineered tailings, but also advance soil formation through enhancing organic C and N sequestration and physical structure development via water-stable aggregation. These findings help to advance our understanding of the importance of AM symbiosis in the eco-engineering of tailings into functional soil (or technosols) for sustainable rehabilitation of Fe-ore tailings.
Campo, JulianCammeraat, Erik L. H.Gimeno-Garcia, EugeniaAndreu, Vicente...
14页
查看更多>>摘要：Forest fires cause many changes in the physical, chemical and biological soil properties such as aggregation and soil organic carbon contents (SOC) as well as on soil hydrology and erosion processes. Most studies on post-fire soil erosion in Mediterranean environments have been plot-based and research at hillslope or broader scale is scarce. Understanding SOC nature, distribution and modifications, as produced by forest fires and erosion, has become crucial to model and define the role of soil erosion as source or sink of C, and to sustainably manage ecosystem services related to the soil resource. This research provides data about the loss and redistribution of soil and SOC in a Mediterranean forest hillslope burned with high severity, at the Natural Park of Sierra de Espadan, Spain. Soil was sampled in coupled hillslopes (ca. 0.25 ha) (BU: burned, CO: control) at bottom (depositional), middle (transport) and top positions (eroding) at two depths (0-2 cm, 2-5 cm), and under two environments (UC: under canopy soil, BS: bare soil). Sediments were collected after each erosive event along one year, and yields were calculated. Samples were analysed to assess aggregate stability (AS), size and density fractionations, SOC contents and stocks. The main hypothesis is that fire affects soil characteristics related to aggregation and SOC stabilization and, together with erosion processes, may modify SOC distribution within aggregates and the burned hillslope.
Qi, JianyingJensen, Johannes L.Christensen, Bent T.Munkholm, Lars J....
11页
查看更多>>摘要：Maintaining good soil structural stability is an important element in agricultural sustainability. Incorporation of cereal straw and use of cover crops improve soil structural stability but the long-term individual and interactive effects of these management practices is poorly understood. We examined the impact of four rates of straw incorporation in spring barley (0, 4, 8 and 12 Mg ha(-1)-, annually) combined with a ryegrass cover crop under-sown in the barley in spring. Soil was sampled after four decades of treatments in the Askov (Denmark) straw incorporation experiment situated on a sandy loam with 12% clay. We assessed clay dispersibility measured on two macro-aggregate size fractions (ClayDis 1-2 mm and ClayDis 8-16 mm), wet-stability of aggregates, and clay dispersibility of < 8 mm field-moist soil and aggregate strength. Soil structural stability and strength were related to soil organic carbon (SOC), SOC/Clay and root biomass. The SOC content increased with straw rate and when ryegrass cover crops were grown. Root biomass was marginally greater (P = 0.068), when cover crops were included. The soils receiving 8 and 12 Mg straw ha(-1)- had a significantly lower ClayDis 1-2 mm and ClayDis 8-16 mm than soil with straw removal. Inclusion of a ryegrass cover crop did not affect ClayDis 1-2 mm, but decreased ClayDis 8-16 mm marginally (P = 0.054) and decreased clay dispersibility of field-moist soil. The results suggest, that binding agents from cover crops such as roots increase stabilization of large macroaggregates, while the increased stability due to straw incorporation was related to SOC irrespective of aggregate size.
Lai, XiaomingZhu, QingCastellano, Michael J.Liao, Kaihua...
15页
查看更多>>摘要：Soils with a significant proportion of rock fragments (RFs, with diameter >2 mm) are widely distributed in terrestrial ecosystems. However, a lack of quantitative information about RF characteristics restricts our ability to explain and predict the related soil carbon (C) and nitrogen (N) processes, and induces biases of C and N investigations in areas where soils contain significant RFs. In this paper, we reviewed the direct and indirect effects of RFs on soil C and N cycles, including via affecting soil C and N stocks, hydrology, temperature, and via chemical weathering that releases C, N, cations and anions, consumes CO2 and regulates pH. Based on this, we discussed current challenges and potential solutions in investigating C and N cycles of high RF content soils. First, we proposed a series of approaches to quantifying the effects of RFs on C and N stocks and soil hydrology across scales. Second, we emphasized the evolutions of soil RFs' properties over time, and recommended including RF physicochemical properties in the routine soil inventory. Third, we suggested that both the effects of RFs and the evolutions of soil RFs over time should be considered in model simulation. Finally, we provided a framework by coupling monitoring, mapping and modelling to investigate the roles of RFs on soil C and N cycles from earth's critical zone to global scale. This review will improve our understandings of RFs and terrestrial C and N cycles, and their responses to global change.
NSTL
Elsevier