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Water availability explains a large part of the spatial and temporal yield variability of ware potato in the Netherlands. Climate change is projected to lead to greater variability in water availability. Therefore, an accurate simulation of crop yield as a function of water availability is of high importance. Many crop models can simulate water-limited potato yields, but as detailed experimental data on drought and oxygen stress are scarce, models are often not well calibrated and evaluated. We set up a large experiment and an on-farm observational trial to calibrate and evaluate the simulation of water-limited yield of different potato cultivars across the Netherlands. In addition, we investigated the required model complexity to accurately simulate water-limited potato yields. The crop growth model WOFOST was used for simulations either as a single model or coupled with SWAP. Yields were simulated applying either only drought stress or by including both drought and oxygen stress. We employed two methods for simulating oxygen stress in SWAP-WOFOST. The calibration improved accuracy of simulated water-limited yields as demonstrated in our model evaluation. Both on sandy and clayey soils, water-limited yields were best simulated using SWAP-WOFOST while simulating oxygen stress using a process-based method in combination with a rooting density that decreases linearly with rooting depth. On sandy soils, the bottom boundary condition of free drainage was applicable. On clayey soils measured groundwater levels (or soil water pressure heads when measurements are not available) should be used as bottom boundary condition. On sandy soils both WOFOST and SWAP-WOFOST may be used, as results were similar. On clayey soils, WOFOST is less suitable, as it cannot simulate capillary rise. SWAP-WOFOST however has many options and parameters, which can result in large differences in results. Hence, a careful model set up and evaluation is required for each application. • The models WOFOST and SWAP-WOFOST have been recalibrated for water-limited potato yields. • On clayey soils with shallow groundwater levels SWAP-WOFOST outperformed WOFOST. • On clayey soils there seemed to be an effect of oxygen stress on yield. • Effects of oxygen stress were smallest in WOFOST, and largest in SWAP-WOFOST using a process-based method. • On sandy soils there was an inconsistent benefit of using SWAP-WOFOST over WOFOST. [ABSTRACT FROM AUTHOR]

Laboratory model tests were conducted to investigate the stability of the L-shaped caisson quay wall installed on the sandy soil with clay interlayer. A total of three L-shaped caisson models were cast to explore the effects of the loading position and the position and thickness of the clay interlayer on their stability under plate loading. The ultimate bearing capacity of the L-shaped caisson quay wall on clay interlayer foundation was reduced by a maximum of 41 % compared to sand foundation. The ultimate bearing capacity was significantly reduced when the distance of the clay interlayer to the rubble mound was less than 1/5 of the quay wall height. The applied surcharge made the lateral earth pressure coefficient higher than the active earth pressure coefficients and triangularly distributed along the L-shaped caisson wall. The modified Beton's method considered the effect of the toe length of the L-shaped caisson could more accurately predict the lateral earth pressure. The failure of the L-shaped caisson quay wall on the clay interlayer foundation has three forms Type-I, Type-II, and Type-Ⅲ which are influenced by the loading position, L-shaped caisson dimensions, and positions of the clay interlayer. [ABSTRACT FROM AUTHOR]

This study examines the application of nano-colloidal silica (NCS) in enhancing the mechanical properties of sandy clay soils. Consolidated undrained (CU) triaxial tests were performed on specimens containing varying percentages of NCS (0 %, 5 %, 10 %, and 20 %), which were then cured for different curing periods (1, 7, and 28 days) and subjected to three different confining pressures (50, 100, and 200 kPa). The findings revealed that the inclusion of 10 % NCS resulted in a significant 65 % increase in strength after 28 days compared to the untreated sample. However, higher NCS percentages, exceeding 10 %, led to a decline in strength as the excess NCS was not effectively utilized. The inclusion of NCS and increased curing time led to an increase in the brittleness of the soil and the application of confining pressure was able to reduce this brittleness.Furthermore, the use of 10% NCS and a curing period of 28 days significantly increased the stiffness and absorbed energy of the soil. Despite boosting the peak shear strength, NCS reduced the residual strength. Finally, polynomial modeling (Poly4) provided an excellent fit, enabling the characterization of the stress-strain and pore pressure-stain responses from the triaxial test. • A series of CU tests were conducted to investigate the strength behavior of sandy clay soil with NCS additive. • 10 % was the optimal content of NCS to modify sandy clay soil, which can improve strength. • The addition of NCS to the sandy clay soil enhances the strength and reduces the failure strain. • Empirical models were developed to predict and satisfactorily simulate q-ɛ and u- ε curves. [ABSTRACT FROM AUTHOR]

• Long-term expansion rates of 46 Urban Gullies in Kinshasa and Bukavu are quantified. • Gully widening is responsible for most of the gully expansion. • Expansion rates in sandy soils are mainly controlled by land cover and road density. • Expansion rates in clayey soils appear influenced by landslide dynamics. Urban gullies (UGs) are a growing concern in many tropical cities of the Global South. Addressing this new geo-hydrological hazard requires good insights into the rates and controlling factors of this process. Therefore, we investigate the expansion rates of a representative sample of UGs in Kinshasa (n = 17) and Bukavu (n = 29), two contrasting cities in D.R. Congo. We reconstruct long-term (10–17 years) expansion rates, making a distinction between headcut retreat and sidewall widening, and analyse the environmental factors potentially explaining these rates. Total expansion rates varying between 12.6 and 863 m2y-1. Most of this expansion happens through sidewall widening. In Kinshasa, which is mainly characterized by sandy soils, contrasts in expansion rates are mainly correlated to the characteristics of the upslope drainage area of the gullies. Especially the road density and a hypothetical runoff index (combining drainage area, land use and soil characteristics) explain a significant part of the observed variation. In Bukavu, such trends are less apparent. This is likely because the clayey nature of the soils provides more resistance against gullying, resulting in overall smaller and less actives UGs. Furthermore, the already low infiltration rates of these soils probably make the relative impact of urbanization on runoff production smaller. Our results also indicate that UGs located in recent landslides have higher gully expansion rates. The mechanisms behind remain poorly understood. Overall, our work opens promising perspectives to model and predict gully expansion rates in urban settings but may also guide efforts aiming to stabilize UGs. [ABSTRACT FROM AUTHOR]

Eutrophication has led to the widespread occurrence of cyanobacterial blooms. Toxic cyanobacterial blooms with high concentrations of microcystins (MCs) have been identified in the Lalla Takerkoust reservoir in Morocco. The objective of this study was to evaluate the efficiency of the Multi-Soil-Layering (MSL) ecotechnology in removing natural cyanobacterial blooms from the lake. Two MSL pilots were used in rectangular glass tanks (60 × 10 × 70 cm). They consisted of permeable layers (PLs) made of pozzolan and a soil mixture layer (SML) containing local soil, ferrous metal, charcoal and sawdust. The main difference between the two systems was the type of local soil used: sandy soil for MSL1 and clayey soil for MSL2. Both MSL pilots effectively reduced cyanobacterial cell concentrations in the treated water to very low levels (0.09 and 0.001 cells/mL). MSL1 showed a gradual improvement in MC removal from 52 % to 99 %, while MSL2 started higher at 90 % but dropped to 54% before reaching 86%. Both MSL systems significantly reduced organic matter levels (97.2 % for MSL1 and 95.8 % for MSL2). Both MSLs were shown to be effective in removing cyanobacteria, MCs, and organic matter with comparable performance. [Display omitted] • Cyanobacterial cell removal by Multi-Soil-Layering (MSL) ranged from 99 % to 100 % • Greater degradation capacity of MC-LR in MSL1 (sandy soil) and MSL2 (clay soil) • MC-YR variant was most persistent in substrate of both MSL systems • qPCR detected degrading bacteria in both MSL systems • MSL1 had significant abundance of mlrA gene copies and degrading bacteria [ABSTRACT FROM AUTHOR]

The European bioeconomy is steadily driving an industrial, economic, and social growth looking for sustainable biobased feedstocks able to replace fossil-based materials. In this scenario, there is an urgent and increasing need to produce locally industrial crops, with multiple applications and broad suitability to different pedo-climates. Furthermore, the actual EU legislation imposes to produce industrial crops not competing with food ones, and one possibility is to grow them on marginal land. Among others, camelina [ Camelina sativa (L.) Crantz] has been identified as one of the most suitable options for marginal land in Europe, but so far there is a lack of studies conducted in such conditions able to provide reliable production data, on which it will be possible to build plausible business plans. At this scope different field trials have been established in four European countries, i.e., Italy, Greece, Germany, and Poland, in multiple growing seasons from 2018 to 2021, under different types of marginality. In details, in Italy camelina was tested under steep slopes (25% and 15%), in Greece in a soil with low fertility (pH < 5.5) and adverse terrain conditions (steep slope >12%); in Germany in a soil with limitations in rooting, i.e., rooting depth < 30 cm + stoniness > 15%, and in Poland in two sites one with sand > 40%, and the other with clay > 50% of the texture. Camelina was grown with an autumn cycle in Italy and Greece, and with a spring one in Germany and Poland. Camelina production was impacted by the marginal land, seed yield was on average 0.94 Mg DM ha−1, ranging from 0.38 Mg DM ha−1 for camelina sown in spring in Poland in the sandy soil, up to 1.93 Mg DM ha−1 for camelina sown in autumn in Italy on a 15% slope. Camelina completely failed only in one growing season in the clay soil in Poland, in relation to extreme weed pressure, while in all the other situations it was able to produce seed. Seed quality, that was surveyed only in Italy and Poland, was not negatively impacted by marginality, demonstrating its capacity to cope with harsh growing conditions. Growing camelina in southern European marginal land, in autumn sowing, seemed the most conservative and safe strategy to achieve profitable yields. In terms of agronomic management, the most important choices to optimize the crop in marginal land resulted: weed management, N fertilization, and the harvesting phase. • Camelina confirmed to be adapt to European marginal land. • Under marginal land camelina seed yield ranged between 0.38 and 1.93 Mg DM ha-1. • Seed oil content and 1000-seed weight were not negatively impacted by marginality. • Growing camelina in southern European marginal land was the most conservative and safe strategy to achieve profitable yields. [ABSTRACT FROM AUTHOR]

In this paper, thermomechanical (TM) behavior of laterally loaded energy piles is investigated through analytical and numerical studies. Accordingly, the ultimate lateral load capacity, and the internal moment and horizontal displacement of the pile under service lateral loads, were assessed. Initially, a thermo-elastic-based analytical solution was proposed, and afterwards, a 3D numerical finite element (FE) model was constructed to investigate the effect of different soil parameters, temperature variation and mechanical load conditions on the behavior of energy piles in different soils. Then, the analytical and numerical results were validated against experimental data, and vast analytical/numerical studies were carried out on the TM parameters affecting the behavior of laterally loaded energy piles. Finally, considering the analytical and numerical results, adjusting relationships were introduced to estimate the lateral bearing capacity and the maximum lateral displacement parameters, more precisely. The results showed that in clayey and sandy soils, the ultimate lateral bearing capacity increases by increasing the temperature or by decreasing the external moment. Moreover, heating was found to have an increasing effect on the internal moments and the maximum lateral displacements of the piles embedded in clayey soils, but it had a decreasing effect on the piles embedded in sandy soils. [Display omitted] [ABSTRACT FROM AUTHOR]

Yield gap analyses are useful to assess and benchmark the productivity of cropping systems. Often such analyses are performed at higher aggregation levels. As a result, these studies lack the detail to explain yield gaps at field level and hence make it difficult to translate findings into precise recommendations to farmers and extensionists. This study provides a detailed approach for yield gap assessments at field level through coupling frequent field monitoring in farmers' fields with crop growth modelling. We used ware potato production in the Netherlands as a case to study yield gaps at field level, as average productivity is high whilst yields are still highly variable among fields, and as ware potato is an important cash crop for farmers. Over two growing seasons, 96 ware potato fields were monitored throughout the growing season on a biweekly basis, taking measurements on soil, crop growth and yield. The crop growth model SWAP-WOFOST was used to simulate potential and water-limited potential yields. Various statistical methods were used to quantify yield gap explaining factors. The average yield gap ranged from 20 to 31% depending on the year and soil type. Among fields, the yield gap ranged from 0 to 51%. On clayey soils, the yield gap was attributed mostly to oxygen stress. On sandy soils, the yield gap was determined mostly by drought stress in 2020, a relatively dry year, and by reducing factors (pests, diseases and poor agronomic practices) in 2021, an average year in terms of precipitation. The type of reducing factors differed per field. Furthermore, we found that earlier planting and later harvesting can increase yields, as Yp is radiation-limited. Overall, there is limited scope to narrow the yield gap as current ware potato production is already close to 80% of the potential yield, which is assumed to be approximately the maximum farmers can attain. However, yield and resource use efficiency gains are to be made for individual fields. Furthermore, we conclude that frequent field monitoring coupled with crop growth modelling is a powerful way to assess yield gap variability and to get detailed insight in the yield gap explaining factors at field level. This study showed that coupling frequent field monitoring with crop growth modelling allows to gain detailed insight in yield gap variability among fields. This method provides detailed information about yield gap explaining factors which can be used to improve yield and resource use efficiency at field level. [Display omitted] • Yield gaps were decomposed at field level for ware potato crops in the Netherlands. • The yield gap ranged from 0 to 53% among individual fields. • The yield gap was attributed mostly to oxygen stress on clayey soils. • The yield gap was attributed mostly to drought stress and reducing factors on sandy soils. • Our method provided detailed insight in the yield gap variability at field level. [ABSTRACT FROM AUTHOR]

A generalized water retention curve (WRC) model in a wide suction range considering the initial void ratio is presented in this paper. Both capillary and adsorbed water in soil pores are considered. Based on the experimental results that the adsorbed water content w a is not dependent on the initial void ratio, a new degree of saturation equation of adsorbed water is established. Meanwhile, a new degree of saturation equation of capillary water at various initial void ratios is proposed with a void ratio-related expression of the air entry value. Compared to Lu's model, only one parameter b is introduced in the established model, which can be easily calibrated using WRCs under two initial void ratios. The measured WRC results of 5 soils are used to verify the proposed model in comparison with the other 3 widely used WRC models. The soil used in the model validation covers a wide range of soil types from sandy soil to clay soil, including clayey silty sand, sandy clay till, clayey silt, expansive soil and lateritic soil. The proposed model is well verified for its ability to describe soil water retention characteristics in a wide suction range at various initial void ratios. [ABSTRACT FROM AUTHOR]

Mining operations produce large quantities of tailings that must be handled and stored safely in a technical framework that reconciles economic restrictions and environmental sustainability. Unfortunately, the history of tailings deposits is marked by episodes of catastrophic failures, which is confirmed by the recent tailings dam collapses that occurred in Canada (Mount Polley), Australia (Cadia) and Brazil (Samarco and Brumadinio). Due to this alarming empirical evidence left by the mining industry worldwide, there is international concern and a demand to build these deposits safely from every point of view. In this scenario, the main geotechnical parameter that requires significant attention is the undrained residual shear strength, which is crucial to ensure the physical stability of a tailings dam. The critical state soil mechanic (CSSM) and/or the steady state of deformation provide the conceptual framework for evaluating this strength mobilized by particulate materials. However, despite the fact that these concepts are long established, some important aspects of soil behavior have not been clearly incorporated, which can seriously affect the estimation of the residual undrained shear strength. In this paper the effects of strain rate and reorientation of platy particles in fine-grained soils, the existence of a quasi-steady state (condition of minimum undrained strength) in sandy soils and the limitations of the state parameter are analyzed and discussed. In this context, the main goals are to minimize misjudgments in the estimation of the undrained strength and to introduce an alternative tool, the flow index, I f , to evaluate the susceptibility of the occurrence of flow failure in tailings dams. • The history of tailings deposits is marked by episodes of failures, many of them associated with the occurrence of static liquefaction. • The critical state soil mechanic (steady state of deformation) provides the framework to evaluate static liquefaction. • It is shown that the critical state is more suitable for clayey soils, while the steady state is more useful in sandy soils. • The state parameters do not consider the static shear stress, which in contractive states is responsible for triggering a flow failure. • An alternative state parameter based on the quasi-steady state and the static shear stress is proposed to identify flow failures. [ABSTRACT FROM AUTHOR]

• GeoWATCH performs statistically better in certain soil textures. • Bias correction models were applied to the raw GeoWATCH values. • The bias correction models significantly improved performance of GeoWATCH. The US Army is required to be a good steward of the land per US Army regulation AR 200-1. Based on this regulation, Army installations need to manage lands, to reduce potential damage and impacts to water quality and habitat that may occur from training. Maneuver training does impact the vegetation and soil and this damage is directly related to soil moisture. Soil moisture is an important factor for understanding the potential for soil surface disturbance due to vehicle impacts and predicting soil resilience to vehicle traffic, however, producing accurate estimates of the spatial and temporal variation of soil moisture has historically been elusive. GeoWATCH, which stands for Geospatial Weather-Affected Terrain Conditions and Hazards (formerly DASSP), simulates soil moisture world-wide, at relatively small spatial and temporal scales. GeoWATCH uses a physics-based downscaling approach that uses weather-scale land surface model estimates of soil moisture and land surface water and energy fluxes, with high resolution geospatial data. GeoWATCH soil moisture outputs coupled with vehicle impact models, are anticipated to be useful for near-real-time estimation of ground disturbance, but will require ground validation. To validate GeoWATCH soil moisture estimates, we utilized Soil Climate Analysis Network (SCAN) gauge network soil moisture data from 127 sites across 34 states. Statistical analysis of the raw GeoWATCH output indicated the model performs statistically better in certain soil textures. Model bias is largest for sandy soils, whereas clayey soils were least biased. As a result, bias correction models were applied to the raw GeoWATCH simulated values using linear regression to predict correction factor (CF) values based on physical site characteristics. The bias correction models significantly improved the performance of the GeoWATCH soil moisture model in terms of average performance statistics and number of statistically cally unbiased sites. This process could easily be incorporated into GeoWATCH, allowing for a capability to rapidly estimate vehicle impacts and determine rehabilitation requirements by installation land managers. [ABSTRACT FROM AUTHOR]

• Agroforestry complexity and soil texture influence ecosystem service provision. • P and Ca cycling through litter and stable soil carbon stocks are synergistic. • Sandy soils are most suited for complex agroforestry. • Agroforestry Complexity Index encompassing diversity, density and management. Agroforestry systems are often promoted as solutions to address land degradation and climate change. However, agroforestry is an umbrella term for a large variety of systems and it is not clear how their degree of complexity influences their provision of soil-based ecosystem services, such as soil organic carbon (SOC) storage and nutrient cycling. Furthermore, a knowledge gap remains whether agroforestry systems perform equally well on all soil types. The objectives of this study were 1) to assess the links between agroforestry complexity, nutrient cycling and SOC fractions, and 2) to assess how soil texture influences these relationships in Brazilian agroforestry systems. We sampled 59 agroforestry plots across 30 sites in Sao Paulo state, Brazil, and 8 monocrop sites (6 pastures and 2 crop monocultures). The 38 sites represented a soil textural gradient, ranging from very sandy to very clayey (clay content range 25 – 620 g kg−1). An Agroforestry Complexity Index (ACI) was defined based on tree species richness, stem density and pruning management. Nutrient (N, P, K, Ca, Mg) and C contents were determined in litter and soil (0–30 cm depth) samples, and mineral-associated organic C (MAOC) and particulate organic C (POC) in soil samples were assessed as well. ACI was positively associated with C, N, P, Ca and Mg stocks in litter, and these litter nutrients were in turn positively associated with the corresponding soil nutrient stocks. Associations between soil nutrients and MAOC were stronger on sandy soils than on clayey soils, particularly for P, Ca and Cation Exchange Capacity (CEC). For POC, robust relationships with nutrients were only found on sandy soils. Structural Equation Models indicated causal relationships between agroforestry complexity, P and Ca cycling, and MAOC and POC stocks in topsoils. Our results indicate that nutrients effectively cycle from in situ mulch into plant-available soil pools and highlight the synergies between nutrient cycling and stable C stocks that can be achieved in complex agroforestry systems. These synergies seem to be particularly strong on sandy soils (<15 % clay). [ABSTRACT FROM AUTHOR]

The atmospheric increase in N 2 O is mainly derived from N fertilisation in agriculture, and improved emission estimates are needed for effective mitigation. This study presents first estimates of country-specific N 2 O emissions from synthetic and liquid organic fertilisers in Denmark. Representative crop rotations were established in four locations across Denmark to provide a realistic context for the estimation of N 2 O emissions, i.e., a dairy farm rotation in Western Denmark, dairy and pig farm rotations in Southwestern Denmark, and an arable rotation in Eastern Denmark. The four sites were light-textured and typical for Northern Europe, whereas rainfall varied considerably among sites and years. A randomised block design was used, and all crops were represented in triplicate each year with monitoring of N 2 O emissions between April 2020 and March 2022. Spring barley was part of all rotations, and here three synthetic fertilisers (NS, NPK and urea ammonium nitrate) and eight organic fertilisers (three cattle slurries, three pig slurries and two digestates) were applied in 1 m2 plots at either two or four sites in order to compare N 2 O emissions from the same N fertiliser materials under contrasting site conditions. Identical methodologies for management, fertiliser application, and N 2 O measurement and flux calculation, were used at all sites to ensure comparability. Manually operated chambers were used for N 2 O flux measurements. The continuous monitoring indicated a strong seasonal pattern across all four sites with the main part of N 2 O emissions during spring. The side-by-side comparison of several N sources at four sites in two years showed for synthetic fertilisers an average N 2 O emission factor for the spring period of 0.15% (95% C.I. −0.17 to 0.37%, n = 16), and for liquid organic fertilisers (pig and cattly slurries, and digestates) an average of 1.02% (95% C.I. 0.75 – 1.30%, n = 44). The higher N 2 O emissions from organic fertilisers, which was significant at each of the four sites, is in opposition to new N 2 O emission factors recently proposed in a refinement of the IPCC methodology for national inventories. The conflicting results are discussed with reference to region-specific site conditions and fertiliser types, and in particular the predominance of soils with a low clay content, and of liquid manure management, may explain the deviations from global estimates. A comparison of annual and spring N 2 O emissions indicated a difference in the order of 0.1 – 0.2% of the N input (n = 8), and the feasibility of estimating N 2 O emission factors based on emissions during the growing season only is discussed. • Annual N 2 O emissions from synthetic and organic fertilisers occurred mainly during spring. • Spring N 2 O emissions from the same fertilisers differed between locations and years. • Much higher N 2 O emissions were observed with organic than with synthetic N. • Sandy soils and liquid manure management may explain deviations from IPCC estimates. • Region- and system-specific N 2 O emission factors may significantly reduce uncertainties. [ABSTRACT FROM AUTHOR]

• A modified KC equation is proposed to calculate hydraulic conductivity in nanopores. • Influence of surface activity and pore size on nano-flow is modelled by MD simulations. • A specific function is proposed to quantify the adsorbed proportion based on MD simulation results. • The modified KC equation is valid to be applied to both sandy and clayey soils. Hydraulic conductivity is a critical parameter for studying the behavior of clay-water systems. However, accurately estimating saturated hydraulic conductivity k in clayey soil by using the Kozeny-Carman (KC) equation is challenging due to the neglect of its active surface properties and nanoscale pores. Clay surfaces can have diverse characteristics resulting from various physicochemical processes such as isomorphous substitution and are typically characterized by the Cation Exchange Capacity (CEC). These properties can significantly impact fluid transport through the clay matrix. To address this issue, this study modifies the KC equation by incorporating an adsorbed water proportion φ that considers the occurrence state of pore water and its correlation with pore diameter, making it applicable to clayey soils. Molecular dynamics (MD) models are established to investigate the influence of surface interaction (CEC) and nanopore size (r) on saturated hydraulic conductivity k of seepage flow in clayey soils. Based on the MD results, a specific function is proposed to quantify the adsorbed proportion φ , which is linearly related to the root of CEC and reciprocal of pore size (r), and then incorporated into a proposed hydraulic correction ratio k * to modify the classical KC equation. The modified KC equation is validated using experimental data from literature, showing a high R 2 value of 0.96. This result demonstrates that the proposed correction ratio k * can extend the application scope of the classical KC equation to clayey soils. [ABSTRACT FROM AUTHOR]

Earthworms are known to improve plant growth in a soil-dependent way, notably via modifications of the rhizosphere microbiota and its functions. We tested the hypothesis that earthworms influence the abundance of microbial genes involved in N cycle according to the type of soil. In three soils with contrasting texture, we quantified five N-cycling genes in different microsites (bulk, rhizosphere or earthworm casts) of microcosms containing (i) neither plants nor eathworms, (ii) plants, (iii) earthworms, (iv) both plant and earthworms. In the presence of earthworms, rhizophere was enriched in nifH (N 2 fixation) and depressed in nosZ or narG (denitrification) in sandy soil, suggesting a shift in N balance towards immobilization; rhizosphere was enriched in nifH but also nosZ and narG in loamy soil; no effect was detected in clayey soil. The pattern of gene abundance across the different soils and microsites suggests that earthworms could favor microorganisms with a potential beneficial effect on plants specifically in sandy soils. [ABSTRACT FROM AUTHOR]

Highlights • Soil thrust of underwater tracked vehicles on clayey seafloor should be properly estimated. • Two different failure modes exist in the development of soil thrust on clayey seafloor. • Previous prediction models tend to overestimate the soil thrust of clayey seafloor. • A reliable soil thrust prediction model for clayey seafloor is newly developed. Abstract As the soil traction of the track system consisting of a track plate and protruded grousers is generally higher than that of a comparable wheel system, underwater tracked vehicles are the favored platforms for heavy-weight remotely operated vehicles (ROVs). When an underwater tracked vehicle moves on the seafloor, the track system laterally transmits an engine torque to the soil-track interface, resulting in slip displacement and an associated soil thrust acting as a traction force. Therefore, to evaluate the mobility of underwater tracked vehicle, it is critical to evaluate the soil thrust of the track system based on the soil-track interaction. Unlike the soil thrust of sandy soils, a reliable soil thrust assessment method accounting for the failure mechanism of clayey soil has yet to be developed in spite of its significance. An experimental study on the mechanism of the soil thrust of clayey soil was thus performed. Model track experiments were conducted on a model track system with clayey soil. Based on the experiment results, the mechanism of the soil thrust of clayey soil was investigated and was compared with the mechanism of soil thrust derived from the previous soil thrust assessment methods using sandy soil. Particular attention was given to the development of a new soil thrust prediction model for the track system on clayey soil using the limit equilibrium analysis technique. [ABSTRACT FROM AUTHOR]

Abstract Soil water repellency affects vast regions of agricultural and native land across the globe. Sandy soils are most likely to develop non-wetting characteristics with susceptibility decreasing with clay content. This study uses molecular dynamics simulations combined with laboratory scale experiments to study the interactions and assembly of saturated C 16 straight chain alcohol and carboxylic acid molecules on a range of soil surfaces. The development of severe water repellency on sand at low loading levels of palmitic acid (0.75 × 10−6 mol g−1) is explained in terms of favourable H-bonding with silica surfaces and the development of 2–3 layers of lateral aligned organic molecules on the mineral surface. The efficacy of kaolinite in lowering soil water repellency is attributed to the higher surface area of this mineral and favourable surface chemistry, which hinders formation of persistent organic multilayers. Highlights • Molecular dynamics simulations identify interactions of fatty acids on sand and clay. • H-bonding interactions between the molecules and surfaces differ for clay and sand. • A parallel arrangement of molecules with the mineral surfaces is kinetically favourable. [ABSTRACT FROM AUTHOR]

Abstract The increasing use of nanoparticles (NPs) in recent years has posed a potential threat to the natural ecosystem. The aim of this study was to determine the C and N mineralizations of different textured (clay and sandy) soils at increasing doses of (25, 50 and 100 mg kg−1) TiO 2 NPs and ZnO NPs that are biological synthesized from Peganum harmala L. plant extract, and to reveal their potential effects on the soil ecosystem. The carbon (C) and nitrogen (N) mineralizations were respectively determined by the CO 2 respiration method and the Parnas-Wagner method under the controlled laboratory conditions for 42 days (28 °C, 80% of field capacity). The highest carbon mineralization among all applications was in clay soils mixed with 100 mg kg−1 TiO 2 NPs. In clay soils treated with ZnO NPs, the treatment of 50 mg kg−1 ZnO NPs increased microorganism activity (P < 0.001). Carbon mineralization rates were found to be higher in sandy soils compared to clay soils (P < 0.05). It was observed that these rates were higher in the TiO 2 NPs treated soils compared to the ZnO NPs treated soils. The nitrogen mineralization ratios were found to be higher in clay soils compared to sandy soils. All of these results indicate that the microorganisms affected from both the presence of TiO 2 NPs and ZnO NPs and differences of texture in these two soils. Highlights • Carbon and nitrogen mineralization of two different textured soils treated with TiO 2 and ZnO nanoparticles were studied. • Soil physical and chemical characteristics varied significantly between the clay and sandy soils. • C and N mineralization were observed higher in the clay soils than the sandy soils. • The microbial activities affected from the different dosages of TiO 2 and ZnO nanoparticles. [ABSTRACT FROM AUTHOR]

Conservation agriculture (CA), with reduced tillage, permanent soil cover and diversified cropping systems, is advocated in southern Africa to improve soil quality, reduce input costs and mitigate climate-induced risks. However, improvements in terms of yield and soil organic carbon (SOC) under CA are slow and variable and many small-scale farmers are unable to buffer themselves against potential short-term financial losses. In this study we examined the effects of CA-related management practices on SOC sequestration and productivity at two medium-term sites on a sandy soil (eight year trial) and clay soil (six years) in maize producing areas of South Africa. Using field data, current input costs and market prices for crops, we calculated the gross margin for each system. Treatments compared conventional ploughing under maize monoculture with reduced tillage, intercropping and crop rotation. On the clay soil, SOC was increased under reduced tillage (57.6 t C ha −1 ) compared to conventional tillage (54.9 t C ha −1 ) while there was no difference for the sandy soil (19.7 t C ha −1 average across treatments). Profitability was most strongly influenced by seasonal rainfall, but was higher on the sandy soil than the clay soil, with an average gross margin of R11,344 ha −1 and R5,686 ha −1 , respectively. This study has demonstrated that while certain CA practices can create site-specific benefits for farmers, it is highly dependent on local weather and soil conditions. For the clay soil an additional payment scheme would be required to reward farmers in southern Africa for C-sequestration to make CA profitable and achieve increased C-mitigation through soil sequestration. [ABSTRACT FROM AUTHOR]

This paper presents the influence of temperature on the residual strength by analyzing shearing tests carried out in a temperature- and velocity-controlled ring shear apparatus. Temperature was applied in steps of cooling and heating ranging between 6 °C and 50 °C at a constant shearing velocity of 0.442 mm/min. Additional tests include the evaluation of the strength at 0.890 mm/min before and after the imposed temperature change. Six basic soil types characterized by different mineralogy, grain size and plasticity, as well as, mixture soils having different proportions of sand and clay, are evaluated and the results are interpreted in terms of their properties. The experimental results reveal that the temperature effect becomes relevant when fine particles and plasticity increase being negligible in the case of the sandy soil. Shear strength reacts immediately to temperature changes and a new residual strength establishes soon. The temperature effect is symmetric. An increase in temperature leads to a decrease in strength, and an equal and opposite trend is observed when temperature decreases. The magnitude of the strength variation is significant in clayey soils. For the case of high plasticity soils, the residual friction angle variation observed during cooling and heating (±50 °C) is around 2°. The strain rate effect evaluated in a smaller number of tests indicated a strain rate strengthening in all the materials tested except for the case of the sandy soil, which also was not reactive to temperature changes. The experiments are calibrated with a velocity, state, and temperature-dependent friction model. • Influence of temperature on residual shear strength have been characterized. • Heating leads to decrease in friction and cooling leads to an increase for high shearing rates. • Relevance of residual friction change with respect of temperature correlates with the soil plasticity. • No effect of temperature was measured for the clean sand tested. • The friction constitutive model developed by Chester (1994) can reproduce the tests performed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil sampling methods were assessed using 720 samples at two locations. • Calculated composite sampling decreased significant effects especially in sandy soils. • Sampling in-row resulted in greater crop effect on research results. • Soil enzyme activities required more samples compared to other soil properties. • A Monte Carlo simulation can be used to estimate needed sample size. A wide variety of soil sampling methods have been adopted, yet limited research has addressed how sampling methods can impact research results particularly for spatially variable soil properties. To address these concerns, we intensively sampled two existing soil health trials in Texas for analysis of soil extracellular enzymatic activities (EEAs), permanganate oxidizable C (POXC), soil organic C (SOC), and pH. The data generated was used to quantify the effect of composite sampling, sampling position (in-row vs between-row), and number of samples on statistical results. We compared a Monte Carlo simulation approach with a traditional power analysis to quantify the impact of the number of samples on our results. Calculated composite sampling resulted in lower statistically significant results compared to discrete sampling, demonstrating lower sensitivity of composite sampling. Sampling in-row resulted in greater values specifically for EEAs, pH, POXC, and SOC. Simulation generated estimated number of samples were mainly driven by the effect size and spatial variation. EEAs were highly variable, resulting in a higher estimated number of samples as compared to other soil properties such as POXC and SOC. In our study with two sites, soil with greater clay content resulted in overall lower estimated number of samples compared to a relatively sandy soil, demonstrating a greater sampling requirement for sandy soil. The simulation approach had a weak correlation with traditional power analysis. The simulation predicted lower estimated number of samples when compared to power analysis, which can help save cost in the long run. Overall, factors like composite sampling, sampling in-row vs between-row, and number of samples taken did impact research results. The impact of these sampling strategies on soil parameters of interest needs to be investigated to achieve the most accurate research results in soil science. [ABSTRACT FROM AUTHOR]

Emissions of greenhouse gases (GHGs), such as carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) have great impact on global warming and atmospheric chemistry. Biochar addition is a potential option for reducing GHGs emissions through carbon (C) sequestration and N 2 O mitigation. However, the influences of biochar on C and nitrogen (N) transformations in soil are still unclear, resulting in a poor understanding of the mechanisms of N 2 O mitigation effects of biochar. Here we carried out two soil incubation experiments to investigate the influence of two common biochars addition (corn cob and olive pulp) with ammonium sulfate on CO 2 and N 2 O emissions from two contrasting soil types (acidic sandy and alkaline clay soil). Furthermore, four extracellular enzymes activities that related to C and N cycling, i.e. cellobiohydrolase, chitinase, xylanase and β-glucosidase, were analyzed to gain insights into the underlying mechanisms of biochar’s effects on CO 2 and N 2 O evolutions. Contrasting effects of two biochars on CO 2 and N 2 O emissions were observed in the two different soils. The corn biochar addition had no significant effect on CO 2 and N 2 O emissions in the alkaline clay soil, but significantly decreased CO 2 emissions by 11.8% and N 2 O emissions by 26.9% in the acidic sandy soil compared to N-fertilizer only treatment. In contrast, olive biochar addition showed no significant effect on CO 2 emissions but decreased N 2 O emissions by 34.3% in the alkaline clay soil, while in the acidic sandy soil addition of olive biochar triggered about a twofold higher maximum CO 2 emission rate and decreased N 2 O emissions by 68.4%. Up to 50–130% higher specific CO 2 emissions (per unit of C-related enzyme activity: cellobiohydrolase, chitinases and β-glucosidase) were observed after addition of olive biochar compared to corn biochar addition in the acidic sandy soil. We concluded that biochar’s effects on N 2 O and CO 2 emissions are more pronounced in acidic soils. Alkaline biochar’s N 2 O mitigation potential in acidic soils seems to be dependent on soil NO 3 − content as drastically higher N 2 O emissions were measured in early phase of the experiment (where soil NO 3 − was high) and significantly lower N 2 O fluxes were obtained in later phases (with lower soil NO 3 − content). [ABSTRACT FROM AUTHOR]

The determination of soil hydraulic properties is laborious and expensive, especially in large-scale applications. One often used substitute for measured hydraulic properties are pedotransfer function (PTFs) estimates. Most PTFs, however, are statistical models that tend to produce biased results for data outside their –often limited– calibration databases. In addition, most PTFs have been established on data derived from temperate regions causing the question whether such models are applicable to soils in tropical regions. This work aimed to evaluate the performance of the Splintex PTF to predict the hydraulic functions for sandy and clayey soils from several tropical and subtropical Brazilian datasets. Splintex is somewhat unique in that it is based on physical principles using a modification of the Arya-Paris method while allowing the estimation of van Genuchten parameters from limited data. In addition, Splintex has an option to include measured soil water retention points, in principle allowing it to produce accurate estimates for a variety of soils. Estimates by Splintex were compared with the empirical Rosetta PTF, which also has an option to use one (or two) retention points. Estimates by both PTFs were compared to observed retention data and field capacity, available water capacity, hydraulic conductivity, and diffusivity using metrics such as Pearson correlation ( r ), mean absolute error (MAE) and root mean square error (RMSE). Both Splintex and Rosetta yielded similar results and sometimes produced significant biases in estimated quantities. In the majority of cases it appears that Splintex produced somewhat better estimates than the 2001 version of Rosetta , indicating that Splintex is a viable, physically-based, alternative to estimating hydraulic properties. [ABSTRACT FROM AUTHOR]

• The semi-analytical solutions of three-dimensional ground movements are proposed. • The nonuniform convergence and the ovalization are considered. • The accuracy and efficiency of the proposed method are verified. • The influences of typical factors on the ground movements are illustrated. This paper presents the semi-analytical solutions to predict the three-dimensional ground movements of shallowly buried tunnels in clayey and sandy soils based on the virtual image technique. Both the ground nonuniform convergence and the tunnel ovalization are taken into account in the proposed method. The accuracy of the proposed method is verified by comparing with the results from field monitoring, numerical simulation and existing solutions. The results indicate that the transverse surface settlements mainly occur within H /tan(45° + φ /2) + R from the tunnel axis on both sides of the tunnel, and the variations of the longitudinal surface settlements are mainly produced within ± 2 H from the tunnel face. The internal friction angle, Poisson's ratio, cover depth and tunnel diameter have significant effects on the surface and subsurface movements according to the parametric analysis. The proposed method can serve as a practical tool in the preliminary design of tunnels and provide a theoretical basis for ensuring the construction safety of actual engineering. [ABSTRACT FROM AUTHOR]

• Thermal conductivity for frozen soil is higher than that of unfrozen soil. • Higher thermal conductivity of frozen and unfrozen soils at higher clay content. • Current models cannot predict correctly thermal conductivity of frozen sandy soil. Thermal conductivities of five sandy soils subjected to freezing-thawing and drying-wetting cycles were determined. Specimens were prepared at five different clay contents of 0, 5, 10, 15, 20% prior to compaction at the Proctor maximum dry density. Soil specimens were saturated prior to freezing-thawing and drying-wetting experiments. During a freezing-thawing cycle, soil's thermal conductivity and unfrozen water content were measured at different temperatures ranging from -3 °C to 0 °C. During a drying-wetting cycle, soil's thermal conductivity was measured at different water contents. The experimental results were then compared with predictions by two of the most appropriate existing models, namely De Vries's and Johansen's models, in order to provide insights into the effects of clay content on soil thermal conductivity at (saturated and unsaturated) unfrozen and frozen states. [ABSTRACT FROM AUTHOR]

Global climate change is predicted to intensify temperature and precipitation extremes, exposing soils to frequent and/or intense alternate wetting and drying regimes. Rewetting a dry soil causes a burst of CO 2 known as the "Birch effect". This spike in respiration can be attributed to: (i) release of cellular solutes (metabolites) accumulated during drought due to rapid increase in water potential upon re-wetting; (ii) sudden death of certain microbes serving as carbon (C) sources for surviving microbes, leading to microbial community shifts; and (iii) release of physically protected C due to aggregate breakdown upon repeated drying-wetting. The relative importance of these mechanisms may change in different soil textures, but very few studies examine all three processes. In this study, we evaluated the effects of repeated drying and wetting cycles (transient state moisture conditions) on the Birch effect and elucidated the mechanisms that contributed to this effect in different textured soils. Soils of three distinct textures (sandy, loamy, and clayey) were incubated for 140 days under five alternate cycles of drying (10% WHC) and wetting (100% WHC) conditions. Control soils were held at 55% WHC for the same duration. Microbial biomass C (MBC), extractable organic C (EOC), metabolites, microbial community structure, and changes in aggregate associated C were determined at each time point. Sandy soil had the lowest respiration rate followed by loamy and clayey soils, and cumulative CO 2 loss was higher under transient moisture state compared to steady state. In sandy and clayey soils, changes in bacterial abundance controlled the Birch effect, while in loamy soil, the release of aggregate protected C majorly controlled the Birch effect. • CO 2 loss in changing soil moisture conditions is higher than steady conditions. • Soil texture is a major controller of microbial activity leading to the Birch Effect. • Bacterial community compositional changes contributed to the Birch Effect in all soils. • In sandy soils, metabolite accumulation controlled the Birch Effect. • In loamy and clayey soils, aggregate disruption fueled the Birch Effect. [ABSTRACT FROM AUTHOR]

• Surface activity on chronically subsided relief was analysed in a coal mining region. • Overall subsidence of 4–9 m from 1966 to 2013 pre-determined near-surface displacements. • Tree-ring records from Larix decidua Mill. showed the strongest activity in the 1970s. • One-year compression wood was discussed as a specific dendrogeomorphic signal. • Extreme rainfall contributes to surface activity in an area with more clayey soils. Tree-ring records from sites affected by underground mining provide valuable data on the long-term development of subsidence troughs. However, due to complexity of local conditions, it is unclear whether the surface displacements are actually the result of mining operations or shallow landslides caused by extreme rainfall. This paper compares surface movements at two nearby sites in the Upper Silesian Coal Basin (Central Europe) that have been affected by underground coal mining. Dendrogeomorphic data on subsidence-related movements were obtained from 360 increment cores (90 trees) of European larch (Larix decidua Mill.). Subsidence between 1966 and 2013 was calculated from the corresponding digital elevation models and the actual morphometric parameters of the sites were related to tree-ring records. The effect of precipitation on surface displacements was evaluated using logistic regression models incorporating rainfall data from a nearby meteorological station and dendrogeomorphic event years. The subsidence at the edges of subsidence troughs (study sites) between 1966 and 2013 reached 4–9 m, which is relatively low compared to nearby (5 km radius) directly undermined sites with subsidence up to 22 m. Most events were dated to the 1930s, 1970s, 1990s, and late 2000s with a peak of activity in 1973 and other noteworthy events in 1986, 1995, and 2009. Event years at the site with a flatter topography, and more waterlogged and clay soils are well explained by higher triennial precipitation and higher Simple daily intensity index, suggesting a possible influence of near-surface displacements on the chronology of recorded events, whereas the elevated site with step-block topography showed no relationship between precipitation extremes and event years. We concluded that not only the time of mining operation, but also the site-specific conditions are crucial for characterization of surface displacements in the forested post-mining landscape. [ABSTRACT FROM AUTHOR]

Understanding the differential fertilizer N fates among soil textures is important to optimize crop nitrogen (N) management for reducing N losses while enhancing crop yields and N use efficiency. In this study, two-year field experiments were conducted on three contrasting soil textures (clay, sandy and loamy soils) with an identical climate in Northeast China, to quantify fertilizer N fates in the maize cropping system and evaluate their responses to N rates (168, 240, and 312 kg N ha−1) under different soil textures using 15N tracer technique, further to model fertilizer N fates with soil properties using multiple linear regression. In two seasons, both grain yields and plant N accumulation were the highest on loamy soil, followed by clay soil, while the lowest on sandy soil. Compared with loamy and clay soils, the plant N accumulation derived from fertilizer (Ndff%) was significantly higher (47 %) on sandy soil in the 1st season, meanwhile its poor soil structure increased environmental N losses (ENL) while decreasing crop N recovery (CNR) and soil N residual (SNR); together with higher in-season ENL, this further significantly lower Ndff% (6%) on sandy soil in the 2nd season. Relative to loamy soil, the SNR on clay soil was significantly higher in both seasons due to the denser and heavier soil texture, but its CNR was lower in the 1st season while both CNR and ENL were higher in the 2nd season. Throughout two growing seasons, the total CNR of loamy, clay and sandy soil was 44 %, 34 % and 28 %, the total ENL was 41 %, 46 % and 64 %, and the final SNR was 15 %, 20 % and 8 %, respectively. With increasing N rates, total CNR decreased while final SNR increased on all three soils, and ENL increased in the 1st season but decreased in the 2nd season. Moreover, the N responses of CNR and SNR were higher on sandy soil, indicating that its fertilizer N fates were more susceptible to N rates. Therefore, crop N management strategies are required to be adjusted according to differential fertilizer N fates among soil textures. By establishing the model between fertilizer N fates with soil properties and N rates, we provided a promising approach to understand and predict fertilizer N use and loss for precisely optimizing N managements on different soil textures. [Display omitted] • Crop 15N recovery was higher on loamy soil (43.8 %) relative to clay soil (34.4 %) and sandy soil (28.1 %). • Soil 15N residual was higher on clay soil (19.6 %) relative to loamy soil (14.9 %) and sandy soil (7.6 %). • Total 15N loss was higher on sandy soil (64.3 %) relative to clay soil (46.0 %) and loamy soil (41.2 %). • The higher Ndff in 1st year but the lower Ndff in 2nd year were obtained on sandy soil than other soils. • Modelling the relationships between fertilizer 15N fates and the soil structure and N rates. [ABSTRACT FROM AUTHOR]

Heavy metal contaminated soils pose a serious threat to the environment, and preparing ceramsite using contaminated soils was proposed as an effective method to address this threat in this study. Specifically, two typical soils (i.e., contaminated clay and sandy soil) were mixed with different ratios and calcined at temperature 1000–1200 °C to prepare ceramsite. Special attentions were paid to evaluating the immobilization of heavy metals in ceramsite and identifying the corresponding immobilization mechanisms. Using the leachability of heavy metals from ceramsite as evaluation criteria, the optimum mixing ratio of clay/sandy soil and sintering temperature were determined as 0.6:0.4 and 1200 °C. Moreover, based on the spectroscopic characterizations and thermodynamic calculation, high sintering temperature well facilitated the liquid phases formation, promoting the reactions between heavy metals and aluminosilicates and the valence state conversion of heavy metals. Accordingly, heavy metals were well immobilized in ceramsite by forming thermodynamically stable minerals, being encapsulated in solid matrix, and transforming to valence states with low mobility. The leaching conditions including pH and temperature had minimal effect on the immobilization of heavy metals in ceramsite. In summary, ceramsite prepared by contaminated soils was environmentally friendly and had good potential in engineering application as building materials. [Display omitted] • Co-utilization of polluted clay and sandy soil for ceramsite production is presented. • The optimum ratio of clay/sandy soil and sintering temperature are 0.6:0.4 and 1200 °C. • The immobilization effectiveness of heavy metals in ceramsite is evaluated. • The immobilization mechanism of heavy metals in ceramsite is determined. [ABSTRACT FROM AUTHOR]

Natural and man-made slope failure has been a phenomenon that has caused many deaths, destruction, and environmental damage. The use of bioengineering technique (grasses) has been widely approached for slope remediation work. However, slope failure still occurs even though it has been protected by a few grasses. Many previous findings have reported on root pull out and root tensile strength for different plant species. However, the type of soil was not taken into account. Therefore, this research was carried out to investigate the function of root mechanical properties in different types of soil. The dry and wet sieve analysis tests were performed to know the classification of the soil. In addition to that, the soil mineralogy test was also conducted to support the soil classification. Root tensile strength tests were carried out on well-grown and poorly-grown Bermuda grass toward sandy and clay soil in dry and wet conditions. The dry condition is considered the condition of Bermuda grass in hot weather, while the wet condition is the condition after the raining season. Bermuda grass was chosen since this type of grass is widely applied for slope stabilization. The site locations were chosen in Temerloh, Maran which consist of clay soil. The other locations chosen were Karak, Gambang, Kuantan, Dengkil, Batang Kali, Ulu Yam, Kuala Pilah, Gombak and Sabak Bernam consist of sandy soil. The results show that the single root of Bermuda grass has higher tensile strength in sandy soil with range values from 0.47 to 185 Mpa compared to clay soil with range values from 0.12 to 159.10 Mpa. In conclusion, the results indicate that soil is one of the factors that influence the growth of bioengineering techniques for slope reinforcement. • A bioengineering method is being used as an alternative for slope stabilization. • The soil stability will increase with time as the root grows. • The pull out force was much affected by tensile strength. • In term of tensile strength, the value decreases with increasing root diameter. • Roots have a great impact on tensile and pull out strength. [ABSTRACT FROM AUTHOR]

Scour is ubiquitous in offshore wind farms and threatens the stable state of the natural frequency of offshore wind turbines. The foundation of offshore wind turbines is a layered seabed, which mainly consists of clay, silt, and fine sand layers. However, little published literature can be found on the natural frequencies of monopiles in layered foundations with scour. The objective of this study was to reveal the influence of scour in layered foundations on the natural frequencies of monopoles and study its mechanism based on the dynamic characteristics of layered foundations. Therefore, based on an actual layered seabed, three typical layered foundations were established, and the first natural frequency of the monopile in terms of sensitivity to scour as well as the ability to resist continuous scour in the layered foundations were revealed. Moreover, the experimental results were analysed based on the stiffness and damping variations of the layered foundations under scour conditions. Importantly, a competitive relationship between the stiffness and damping of the layered foundations on the variation of the first natural frequency with scour was found and elaborated for the first time. The competitive relationship was influenced by the proportion of clay in the layered foundation. • The first natural frequencies of monopiles in different layered foundations present different responses to scour and different resistance to continuous scour. • The stiffness characteristics and damping characteristics of the layered foundations present a competitive relationship in the response of first natural frequency of monopile to scour. • The competition relationship between the stiffness characteristics and damping characteristics is influenced by the proportion of sandy soil and clay in the layered foundations. [ABSTRACT FROM AUTHOR]

Wetland environments may have hypersulfidic soils, that contain pyrite, which can generate extreme acidity and form sulfuric soils (pH < 4), when exposed to oxygen which poses a threat to the environment. Management of sulfuric soils by addition of neutralising agents such as lime or inundation with seawater may be uneconomical or ineffective in inland environments. In this study, we tested the effects of the addition of three clayey soils with different net negative acidities to a sulfuric sandy soil as an amelioration option. The aim of this experiment was to investigate the effect of addition of hyposulfidic clay soils to a sulfuric sandy soil on pH changes in reduced and oxidised conditions. A sulfuric sandy soil (pH 4.1) was mixed with three hyposulfidic clay soils (with clay contents ranging between 38 and 72%) to give clay soil proportions of 0, 25, 50, 75 and 100 (%dry soil). According to their net negative acidity, the three clay soils are referred to as: NA-334, NA-54 and NA-8 (values in mol H + tonne − 1 ). All soils were collected in a Ramsar wetland in South Australia. The soils were amended with wheat straw at 10 g of C kg − 1 and then incubated for 14 weeks under reducing conditions (wet period) followed by 11 weeks incubation under oxidising conditions (dry period) during which they were maintained at 100% of maximum water holding capacity. The pH of the sulfuric soil alone increased during the wet period by about two pH units (to pH 6) and decreased by more than two pH units (to pH < 4) during the dry period. In the clay soils alone and treatments with sulfuric soil, the pH during the wet period decreased by 0.5 to 1 unit with NA-334 and NA-54 and increased by one unit with NA-8. The pH was > 6 in all clay treatments at the end of the wet period. During the dry period, the pH remained above pH 7 with NA-334 and decreased by about one unit (to pH 5.5) with NA-8. In treatments with NA-54, the pH decrease during the dry period depended on the proportion of clay soil, ranging from 0.5 pH unit with 75% clay soil to two pH units with 25% clay soil. The capacity of the clay soil treatments to maintain stable pH during wet and dry periods depended mainly on the negative net acidity of the added clay soils, but was not related to their concentration of reduced inorganic sulfur or clay content. It can be concluded that addition of clay soils with high negative net acidity could be used to ameliorate acidity in acid sulfate soils with sulfuric materials. [ABSTRACT FROM AUTHOR]

Crude oil products are among the most common pollutants of soils which can drastically affect the engineering properties of soils. In the current study, a series of laboratory tests were conducted to investigate the interaction between crude oil and sandy soil with clay and the effect of crude oil, crude oil residence time, absorbent additives type and content, microwave power, specimen weight, maximum grain size and fine grain fraction on the removal efficiency of pollution through microwave radiation to extract optimum values for potential and high efficiency in hydrocarbon removal. The present study also investigated geotechnical properties, including cohesion, internal friction angle, shear strength in three conditions before and during pollution and after cleanup utilizing direct shear and static triaxial tests. The results showed that the presence of clay particles, oil content and saturation effect in the soil could significantly control the engineering soil behavior. In the presence of 4% crude oil in direct shear tests, the whole oil content is accumulated on clay particles due to the high specific area of clay particles, reducing the cohesion and the internal friction angle. By contrast, beyond the 4% of crude oil, sand particle in the soil was the controlling factor of the whole behavior of the mixture. In triaxial tests, the trend of soil parameters is almost similar to direct shear tests by increasing crude oil, except that, with an increase of 4% of oil, the friction angle of the soil increases due to the presence of a large number of flocculated clay particles. • Microwave heating was considered as a potential option to remediate the polluted soil. • The highest removal efficiency was obtained from effective microwave parameters. • Soil strength parameters were evaluated before, during and after cleanup. • Clay particles, oil and water in the soil control the polluted soil behavior. [ABSTRACT FROM AUTHOR]

This paper describes the application of the Italian chabazite-rich tuff of Sorano (Grosseto) as a soil conditioner and slow nutrient fertilizer to a silty-clay soil and a sandy soil. The study was developed by means of batch and column experiments. The objectives of the study were: (1) to evaluate and compare the physical and hydraulic properties of mixtures of soil and natural zeolitite (95:5% v/v) with those of unamended soils, (2) to determine the effects of applying NH 4 + -enriched zeolitites on soils and (3) to model water and solutes movement in two different scenarios, with and without amendment incorporation. Results of column experiments were then modelled to obtain the physical–chemical and hydraulic parameters representative of the soils amended with the NH 4 + -enriched zeolitites. Using synthetic rainwater as eluent, NH 4 + was never detected in the water phase of batches and columns; NO 3 − and PO 4 3 − were both present at high concentrations in batch tests and were leached in column elution tests. NO 3 − displayed very high concentrations at the beginning of the elution whereas PO 4 3 − showed low concentrations and retarded peaks in both amended soil columns. The rationale of the study lies in the belief that inorganic amendments, which improve the physical and hydraulic properties of soils, can lead to minimized leaching of nutrients. [ABSTRACT FROM AUTHOR]

This paper examines the ultimate bearing capacity of energy piles in sandy and clayey soils by conducting numerical modeling under different thermal loads, fluid-pipe configurations and fluid characteristics. Accordingly, U and W-shaped fluid-pipes with different diameters were simulated using ANSYS-FLUENT software, under different inlet flow rates, fluid temperatures and ground temperatures. Moreover, a semi-empirical analytical solution is proposed for predicting the outlet temperature for different pipe configurations. Then, the energy piles were modeled using ABAQUS FE-software, and the effect of temperature distribution in U, double-U and W-shaped pipes on the ultimate bearing capacity was studied, in heating/cooling conditions. Both numerical simulations and the analytical solution were validated against experimental data. Results showed that under constant flow rate, initial inlet temperature and pipe diameter, the differences between the inlet and outlet temperature of the heat exchange fluid in the U-shaped pipes was less than that obtained for the W-shaped pipes. Also, for constant inlet temperature and pipe diameter, the temperature difference decreased when the inlet flow rate increased. It was found that under constant thermal loading conditions, the changes in the ultimate bearing capacity were higher in piles with double U-shaped pipes, followed by U-shaped pipes, and lowest for W-shaped pipes. [Display omitted] • The ultimate bearing capacity of energy piles in different soils is investigated. • Different fluid characteristics and various pipe configurations are examined. • CFD and TM simulations are conducted and validated versus experimental data. • An empirical-analytical solution is proposed for predicting the outlet temperature. • Functional graphs are presented for calculations of the ultimate bearing capacity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biogas residues and cattle slurry shifted bacterial community in sandy, clay and organic soils. [•] Biogas residues and cattle slurry reduced substrate-induced respiration in organic soil. [•] Biogas residues and cattle slurry affected soil microbial system, differently. [ABSTRACT FROM AUTHOR]

137Cs is one of the most persistent radioactive contaminants in soil after a nuclear accident. It can be taken up by plants and enter the human food chain generating a potential human health hazard. Although a large amount of literature has highlighted the role of the different processes involved in Cs uptake by plants, there is still no simple way to predict its transfer for a specific plant from a particular soil. Based on the assumption that the concentration ratio (CR) of Cs can be predicted from one plant taxon if the CR of another taxon is known and taken as reference, whatever the supporting soils, a series of plant/soil Cs transfer experiments were performed on Rhizotest during 21 days using three soils with different textures, clay and organic matter contents and two plants (millet and mustard) with potentially contrasting Cs uptake capacity based on their phylogeny. CRs of each plant varied by 2–3 orders of magnitude depending on the soil and contrary to expectations, the CRs of mustard were either higher (for clay soil), equal (for clay-loam soil) or lower (for sandy soil) than the one of millet. Considering Cs availability in soils and defining a new CR based on the amount of Cs available in the soil (CR avail) decreased the range of variation in CR between the different soil types for a given plant by one order of magnitude. Differences in Cs (and K) translocation to shoots, possibly specific to millet within Poales, could partly explain the relative CRs of millet and mustard as a function of soils. • Soil/plant Cs transfer experiments on Rhizotests with three soils and two plants. • The Cs CR of mustard is not always the highest, contrary to plant phylogeny predictions. • Differences in CRs may partly relate to the translocation capacities of millet. • Calculating CR based on the available Cs pool in soils reduce the range of CR variation. [ABSTRACT FROM AUTHOR]

This paper proposes a combined-loading elastoplastic constitutive model (CL model) for a unified description of the mechanical behavior of soil materials, including clay, sand, and intermediate soil. This mathematical model combines the super-subloading yield surface Cam-clay model and the non-associated Drucker–Prager (DP) model. The first model introduces the skeleton soil structure concept into the Cam-clay model based on critical-state soil mechanics. It describes the mechanical behavior of naturally deposited clay more accurately than the existing model does. The non-associated DP model considers the frictional properties of granular materials and is widely used to describe the undrained shear behavior, particularly that of sandy soil. The newly proposed model is one in which these two independently existing models simultaneously or independently work in loading states according to the loading criterion, which can be derived as a natural result from plastic multipliers. This framework allows for a unified description of a wide range of soil materials, including naturally deposited clayey soils and sandy soils. [ABSTRACT FROM AUTHOR]

Abstract: This is the first attempt to report the gaseous nitrogen emissions from landfill leachate filtration methods by irrigating the aged refuse. A first-order reaction model was a good fit for the increase in ammonia emissions from aged refuse, clay and sandy soil incubated for 120h after adding the leachate-N solution. The emissions of ammonia and N2O by the three experimental materials fit well to first-order and zero-order models, respectively. The maximum ammonia emission from aged refuse was approximately 1.17mg d.w. and the calculated emission factor was 1.95‰, which was 3.76 and 2.67 times lower than that of sandy and clay soils, respectively. The tendencies of nitrification and generations fit well to the zero-order reaction model and the net nitrification rate by the aged refuse was 1.30 (p <0.05) and 1.71 (p <0.05) times that of clay soil and sandy soil, respectively. At the same time, the net generation rate by the aged refuse was 1.56 (p <0.05) and 2.33 (p <0.05) times that of clay soil and sandy soil, respectively. The quantity of nitrogen emitted by aged refuse as N2O was 2.46 times greater than that emitted as ammonia. The emission factor for N2O from aged refuse was 8.28 (p <0.05) and 16.11 (p <0.05) times greater than that of clay and sandy soils, respectively. For the leachate irrigation, N2O emissions should be of greater concern than ammonia emissions. [Copyright &y& Elsevier]

Abstract: In the humid tropics, conversion of forests into croplands has the potential to alter the flux of dissolved organic matter (DOM) and influence C balance and N availability in soil. Sites located on a clay-rich Ultisol in Thailand and a highly acidic and sandy Ultisol in Indonesia were used to quantitatively evaluate effects of land use change on fluxes of dissolved organic C (DOC) and N (DON) in cropland and adjacent forest. The DOC flux from surface soil horizons was lower in cropland (poultry manure-amended) than in the forest on the sandy Ultisol (Indonesia), while DON flux increased in cropland due to release of DOM enriched in N from the decomposed SOM and manure. In contrast, DOC and DON fluxes in cropland (non-fertilized) and forest on the clay-rich Ultisol (Thailand) were consistently low due to high adsorption of DOM and rapid DON mineralization. Total dissolved N (TDN) in soil solution was dominated by nitrate for both cropland soils; DON represented a major fraction of TDN in the sandy cropland soil due to lower DOM adsorption capacity and slower DON mineralization. The conversion of forests to croplands could enhance SOM decomposition and produce DOM enriched in N, but leaching losses of DOC and DON were small under low-input agriculture in tropical region. The effects of agricultural use on DOC and DON fluxes could vary depending on application rates of manure and adsorption and mineralization capacities of soils. [Copyright &y& Elsevier]

Abstract: Eutrophication caused by phosphorus (P) rich leachate from sandy soils has been one of the major agro-environmental issues in the world. In predicting P bioavailability in soils, P reactivity in soil clay fractions (e.g., iron oxyhydroxides) has been a major focus of soil chemistry research in the past. However, the role of sand fraction has been rarely investigated to accurately understand the retention and release mechanisms of P in soils, and remains poorly understood. In this case study, we report here on macroscopic and spectroscopic evidence for environmentally important P partitioning mechanisms in soil sand fractions. In the high P sandy soils, total desorbable P from the sand fraction was as high as ~50% of total desorbable P from the whole soils, and these bioavailable P were associated with ammonium oxalate extractable Al and Fe. Scanning transmission electron microscopy/energy-dispersive X-ray analysis further revealed that P was associated with amorphous mixed Fe/Al/Si precipitates in the sand grain coating, and was not present with crystalline iron oxyhydroxides like goethite. Bulk- and microfocused-Fe K-edge X-ray absorption spectroscopy analysis showed that average FeO6 coordination environments in the grain coating did not exactly coincide with that in synthetic goethite, hematite, and ferrihydrite. The coordination numbers of second and third Fe shells were slightly larger/smaller than those in reference iron oxyhydroxides (hematite and goethite), suggesting the perturbation of local chemical structure of FeO6 linkages by Si/Al/P. Our research findings suggest that amorphous Al/Si/Fe grain coatings in soil sand fractions might be important in predicting the release of labile P in the surface and subsurface environment. [Copyright &y& Elsevier]

Abstract: Clay and organic matter, when incorporated together in a sandy soil, improved soil aggregation in association with both microbial activity and soil strength. Incorporation of clay into sandy agricultural soils in south-western Australia is a practice used to overcome water repellence, but the addition of high levels of clay can cause hardsetting. We investigated the extent to which addition of clay and organic matter would improve aggregate stability of a sandy agricultural soil from Meckering, Western Australia without negatively affecting soil strength. Four levels of subsoil clay and three levels of lucerne hay were compared in topsoil incubated for up to 42days at two temperatures. Addition of both clay and lucerne hay together increased stable aggregation and the longer the period of incubation, the greater the macroaggregate stability. A decrease in soil respiration associated with increasing level of clay added may be related to protection of organic matter. Soil strength increased when the amount of clay alone was increased, but addition of both clay and organic matter decreased soil strength. Soil amelioration with 5% clay and 0.8% organic matter was most effective at improving the stability of macroaggregates without hardsetting. The non-linear relationships observed demonstrate the importance of understanding interactions between biological and physical components of soil fertility in relation to the sustainability of land management practices. [Copyright &y& Elsevier]

Abstract: The fragmentation of larger soil aggregates to smaller fractions is a fundamental physical process that may occur naturally or be imposed. Soils that naturally re-structure themselves following structural damage from a homogeneous mass into a heterogeneous matrix of fine, granular and stable aggregates and pores are of great benefit. A key driving force is shrink–swell processes, particularly wet–dry cycles. Models of dynamic fragmentation have been devised. A promising model based on a threshold limiting size distribution of aggregates, with temporal- and scale-invariance, has been developed recently. We sought to assess this model with soil fragmentation test data. We sampled 12 soils from a 2km transect (Bedfordshire, UK), subjected them to physical damage by shearing and kneading, and then imposed up to 3 or 5 wet–dry cycles. We measured the aggregate size distribution and mean weight diameter (MWD) of both the whole soil fraction and the fine-scale (<5mm) aggregate fraction, selected as a key threshold size, as they fragmented. A subset of four soils was examined in more detail to assess the model predictions. Clayey soils fragmented considerably more than sandy soils, and resulted in an accumulation of fine-scale aggregates. This suggested that fragmentation was induced by shrinkage and swelling stresses impacting upon the clay fraction and that the wet–dry cycles were not able to reverse the structural damage imposed on the sandy soils. In the clayey soils the form of the distribution of fine-scale aggregates showed clear signs of temporal invariance over the wet–dry cycles. In addition, as the cumulative distributions of the fine-scale aggregates followed a power law relationship, this suggested invariance in scale. In fragmenting soils, the MWD of the fine-scale aggregates was a convincing asymptote for the MWD of the whole soil fraction. We demonstrated temporal- and scale-invariance in clayey soils that fragment upon wetting and drying and the accumulation of a resistant set of fine-scale aggregates. Such soils are likely to be better-able to recover naturally from any physical damage to their structure and will require less remedial work, and hence a lower energy input, compared to non-fragmenting sandy soils. [Copyright &y& Elsevier]

Abstract: Geo-electrical sensors are often used as auxiliary variables with sparse direct measurements to estimate soil properties. Using a single sensor is not ideal in some circumstances. For example, sandy, sandy gravelly, sandy salt-affected and clayey soils are poorly identified using an EMI or gamma-ray sensor singularly. The complementary use of these sensors should improve interpretation in landscapes containing these soils. Analysis of multi-sensor data is however problematic. Several methods have been developed to integrate multi-sensor data but there is currently no unequivocally accepted methodology. The objectives of this work were: 1) to define a combined approach of geostatistics and sensor data fusion to integrate field data from electromagnetic induction (EMI) measured with EM38 and EM31, gamma (γ)-ray and RTK GPS sensors for delineating areas of homogeneous soil; 2) to show the potential of gamma radiometric sensor by estimating a relationship for crop available soil potassium (K) from the γ-ray signal. The geophysical survey was carried out on an 80-ha cropping field in Corrigin, Western Australia. Seventy-seven soil samples were collected at the nodes of a 100×100m-mesh grid and analysed for different properties. The EM38 and EM31 data were strongly correlated with each other and so were γ-radiometric counts from thorium (Th), uranium (U) and all elements (TC). The multi-sensor data were split into 4 subgroups, based on their similarities: 1) EMI data; 2) γ-radiometric counts from potassium (emitted from all forms of K including readily plant available, non-exchangeable and structural K); 3) γ-radiometric counts from Th, U and TC and 4) RTK GPS height. Each group of data was separately analysed using geostatistical techniques. The soil samples and geophysical data were jointly interpolated using multi collocated cokriging. The EMI data showed anisotropy and an anisotropic Linear Model of Coregionalization was fitted before cokriging. The EM31 and EM38 maps looked quite similar. The maps of γ-U, Th and TC were also similar, suggesting that they reflected the same soil properties, but were somewhat different from the γ-K maps. High values of EMI coincided with both low γ-radiometric values at the valley bottom, due to moist sandy salinity-prone soil of varying depth to texture contrast, and high γ-radiometric values at the elevated areas of the field due to emission from finer textured soil. High γ-radiometric values coincided also with low values of EMI over gravelly sands. Only the use of a multi-sensor platform could discriminate soils that gave similar outputs to one sensor. The first two principal components of the geophysical data were used to partition the field into homogeneous areas. In order to test the utility of geophysical survey for K recommendations, the spatial association between the maps of the estimates of plant available soil K content and γ-K counts was demonstrated by using different agreement coefficients and a regression model with correlated errors was estimated between the two variables. [Copyright &y& Elsevier]

Summary: This study was conducted to assess the role of the regeneration of soil structure by physical weathering of soils in columns on the transport of Nalidixic acid-resistant Escherichia coli strain (E. coli NAR) and also Bromide (Br). Leaching experiments were carried out at steady-state flow conditions, under a suction head of 5cm, through columns of repacked and weathered clay loam (CL) and sandy loam (SL) soils. A pulse-type boundary condition was used and breakthrough curves for bacteria and Br were obtained at three depths during a 24h leaching experiment. Observed data were analyzed employing the mobile–immobile water (MIM) models for repacked or weathered soil columns using HYDRUS-1D code. Both models described well the effluent concentrations. Calibration of the models to match the observed breakthrough curves of Br and E. coli NAR resulted in a smaller value of dispersivity for the later. For bacteria, the fitted attachment and straining coefficients increased with the clay content of the soil. Earlier peaks in the breakthrough curves were observed for the weathered soil columns. This was attributed to increased pore connectivity associated with weathering. In contrast the balanced and symmetrical shape of the breakthrough curves from the repacked soil columns indicates that leaching occurred mainly through matrix flow. [ABSTRACT FROM AUTHOR]

Abstract: Mixtures of organic and inorganic pollutants are frequently found in the environment. Because these pollutants can possess vastly different properties and compositions, their removal using conventional techniques is often difficult. In this work, electrokinetic remediation was studied to remediate clay soils and sandy soils that were contaminated with lead and phenanthrene. During electrokinetic remediation, an electric field is applied to mobilise and extract contaminants from the solid matrix. In order to improve this process, a suitable processing fluid must be selected. Surfactants and complexing agents are commonly used to increase the desorption and solubility of organic and metal pollutants, respectively. In the first stage of this study, different extraction agents, including citric acid, lactic acid, KI and EDTA, were tested for heavy metals. The agents tested for polyaromatic hydrocarbons (PAHs), including Tween 80, Tween 20 and Brij 35, were evaluated alone and in various combinations to solubilise both pollutants. The most effective combination, 1% Tween 80 and 0.1M EDTA, was used as a processing fluid in the electrokinetic treatment of kaolin and sandy soil that was polluted with lead and phenanthrene. In addition, the influence of the pH in this system was evaluated. Under the optimal operating conditions, more than 90% and 70% of pollutants were removed after 30days from the kaolin clay and the sandy soil, respectively. [Copyright &y& Elsevier]

Abstract: There is considerable disagreement on the effects of different soil conditions on the growth of Jatropha curcas L., although different reports agree on some factors, such as a preference for sandy soils over clay soils. This paper presents results on the growth of seedlings of a low-toxic Mexican cultivar in three different soils from the SE of Mexico. The Mexican seeds were sown in soils of different textures: sandy, sandy-loam and clay-loam. The germinated seedlings were monitored during a period of one month. Then, they were uprooted to record below and above ground morphological parameters and dry matter weight. Stem lengths, root collar diameter, length and diameter of the five main roots, number of true leaves and dry matter were analyzed using one-way ANOVA. The soils used were subjected to a chemical analysis to determine soil nutrient contents, which revealed that clay-loam soil had the highest nutrient content, followed by the sandy-loam, while sandy soil presented the lowest values. It was found that seedlings grown in sandy-loam soil were significantly taller than those in clay-loam and sandy substrates (P ≤ 0.05). Root collar diameter, root diameter, number of true leaves and dry matter weight did not present significant differences between plants grown in sandy-loam and clay-loam soils, however they showed significant differences when compared with plants grown in sandy soil. Therefore it can be concluded that development of seedlings in sandy-loam soils was greater, followed by those in clay-loam, while the poorest performance of the seedlings was recorded in sandy soil. [Copyright &y& Elsevier]

Abstract: Subsoil compaction is a recognised threat in the European Soil Strategy and knowledge concerning the vulnerability of subsoils to compaction in Europe and the Netherlands is information required for the determination of priority areas (or risk areas) in the future European Soil Framework Directive. In Europe two risk assessment methods (RAM) are used in more than one country to determine the subsoil compaction risk. The first one (RAM-A) initially determines the susceptibility of soils to compaction as a function of texture and packing density. In the second step the vulnerability to compaction is determined as a function of susceptibility and climate. The second RAM (RAM-B) is a mechanistic model in which the soil mechanical strength determines whether a subsoil is susceptible to compaction. The RAMs are used to produce maps presenting the susceptibility and vulnerability to compaction of Dutch subsoils (RAM-A) and maps with the compression strength and maximal allowable wheel load of a Terra Tire to prevent compaction of Dutch subsoils (RAM-B). Both RAMs have weaknesses. RAM-A is an expert model and can be rather arbitrarily with results that are not in agreement with our experience. RAM-B suffers from lack of good data and probably underestimates subsoil strengths. Results of both RAMs are compared to each other and to a map showing the probability that the subsoil is already overcompacted. This probability map is based on bulk density data in the Dutch Soil Database (BIS). There is a good match between the results of both RAMs, however, the match with the probability map (presumed to be “reality”) is not good. In both RAMs sand and loamy sand soils are indicated as more vulnerable than clay soils, while in the probability map sand subsoils suffer less of subsoil compaction than clay soils. Of concern is that, according to the probability map, about 50% of the most productive and fertile soils of The Netherlands have overcompacted subsoils. [Copyright &y& Elsevier]

Abstract: Aggregation and stabilization of soil organic C (SOC) and N are highly dependent on soil texture and addition of organic resources (ORs). While OR quality may influence SOC and N stabilization within aggregates, the simultaneous addition of N-fertilizers may enhance OR decomposition resulting in loss of SOC. A mesocosm study was conducted on a clayey soil at Embu and a sandy soil at Machanga in central Kenya to determine the influence of soil texture, OR quality and N-fertilizer on aggregation, SOC and N. Tithonia diversifolia (high quality), Calliandra calothyrsus (medium quality) and Zea mays (maize; low quality) residues, natural abundance or labeled with 15N, were applied to soil at an equivalent rate of 4MgCha−1 compared to no input control. Each treatment was fertilized with 120kg 14N or 15Nha−1 as (NH2)2CO, or not fertilized. Soil samples were collected at installation of the mesocosms (start), and 8 months after installation (end). Soils were separated into different aggregate size fractions by wet sieving and macroaggregates were further fractionated to isolate microaggregates-within-macroaggregates. Total soil and aggregate fractions were analyzed for SOC and N. On average, 20% and 70% of SOC and N was in the macroaggregates in the sandy and clayey soils, respectively. There were no differences among OR quality in both soils but in the clayey soil all ORs resulted in greater SOC and N than in the control. However, proportions of OR-derived N in the macroaggregates, mostly in the microaggregates-within-macroaggregates were greater with sole applied maize in the clayey soil. The addition of N-fertilizer together with maize stover reduced soil N, macroaggregate N, and OR-derived N in the microaggregate and silt and clay fractions within macroaggregates compared to when maize was applied alone. In the sandy soil, Calliandra resulted in greater OR-derived N than Tithonia in the coarse particulate organic matter (cPOM; i.e., 5% compared to 2% of N applied). Thus, the greater polyphenol concentration in Calliandra likely slowed its decomposition compared to that of Tithonia. In addition, greater proportions of N and residue-derived N in the macroaggregates were observed in the coarse POM in the sandy soil whereas in the clayey soil it was in the microaggregates-within-macroaggregates. We conclude that the preservation of OR-derived N is affected by the chemical recalcitrance of the residues in sandy soils, whereas macroaggregate protection, and not OR quality, is the major factor in clayey soils. [Copyright &y& Elsevier]

Abstract: Effects of leachate addition on ammonia volatilization and N2O and CO2 emissions from two different soils were investigated using the 10-day laboratory incubation method at two levels of moisture content. Ammonia volatilization was dominated by soil pH and only occurred in alkaline clay soil, where 0.26–0.32% of soil ammonia could be lost. The N2O emission from the alkaline clay soil was one order of magnitude greater than that from the acidic sandy soil, when either water or leachate was irrigated. Increasing the moisture content from 46% water-filled pore space (WFPS) to 70% WFPS in the alkaline clay soil or the acidic sandy soil by either water or leachate irrigation increased the N2O emission by over twofold. The CO2 emission from each soil sample at the two WFPSs was almost the same. The CO2 emission from the alkaline clay soil with leachate addition was 72% lower than that from the acidic sandy soil with leachate addition, and 6.7 times higher than that from the alkaline clay soil with distilled water addition. Ammonia volatilization and N2O emission under leachate irrigation could be minimized by avoiding the excessively wet condition and by selecting the acidic sandy soil with low organic carbon and total nitrogen content. [Copyright &y& Elsevier]