Soil Column Experiments Research Articles

Evaporation Through a Dry Soil Layer: Column Experiments

AbstractModeling of water vapor transport through a dry soil layer (DSL), typically formed in the top soil during dry seasons in arid and semi‐arid areas, is still problematic. Previous laboratory experiments in controlled environments showed that the only vapor transport process through the DSL is by Fick's law of diffusion. However, field experiments exhibited consistently higher evaporation rates than predicted by diffusion flow only. Some proposed reasons for the mismatch were: (a) daily cycles of condensation and evaporation in the DSL due to changes in solar radiation; (b) wind effects on air movement in the DSL; (c) atmospheric pressure fluctuations; (d) nonlinear influence of the DSL thickness on the evaporation process. To link the laboratory experiments with field observations, we performed soil column experiments in the laboratory with thick (>50 cm) DSL, and with different wind speeds, two radiative lamp schedules (continuous and 12 h daily cycles) and different thicknesses of DSL. Atmospheric pressure, air temperature and humidity were measured continuously. The results show that the evaporation rates observed are larger than those predicted by diffusion flow only. We found that it was possible to model the evaporation rates as a function of atmospheric pressure fluctuations. In conclusion, atmospheric pressure fluctuations can induce evaporation rates in DSL larger than estimated by diffusion flow only, possibly explaining the discrepancy between laboratory and field evaporation rates.

Effects of Wheat Straw Hydrochar and Its Modified Product on Rice Yield and Ammonia Volatilization from Paddy Fields

Hydrochar can mitigate ammonia volatilization when applied in paddy fields due to its acidity and adsorption property. To realize the recycling of agricultural biowaste as well as the control of nutrient loss from paddy fields, a simulation soil-column experiment with wheat straw hydrochar (WHC) and water-washed hydrochar (W-WHC) was conducted to evaluate the performance of rice yield and ammonia volatilization from paddy fields. The results showed that WHC and W-WHC applied in paddy fields both increased the rice yield and the increased effect at low application rate (0.5%) was higher than that at high application rate (1.5%). In comparison with the control treatment (CKU), the rice yields achieved from low application rate treatments for WHC and W-WHC increased by 17.16% and 20.20% respectively. Except for the equal emission rate between W-WHC with low application rate and CKU treatments, hydrochar (WHC, W-WHC) addition reduced the ammonia volatilization from paddy fields when compared with the CKU. Among them, the ammonia volatilization levels from low-application WHC and high-application W-WHC treatments were significantly lower than that from the CKU treatment, reduced by 31.01% and 17.40%, respectively. Based on the analysis of ammonia volatilization during different fertilization stages, the control effect of hydrochar addition on ammonia volatilization was mainly benefited from tillering and panicle fertilizer stages. The change in the nitrogen concentration of surface water at the tillering fertilizer stage and in pH at the panicle fertilizer stage with the addition of hydrochar was the main driving factor for the reduction in ammonia volatilization. The results show that sufficient amounts of hydrochar derived from wheat straw application can increase crop yield while reducing ammonia volatilization from paddy fields. This method provides an effective route for recycling agricultural biowastes.

Experiments and simulation of co-migration of copper-resistant microorganisms and copper ions in saturated porous media

Heavy metal (HV) pollutants may migrate to the groundwater environment through leaching, causing groundwater pollution. Compared with surface water pollution, groundwater pollution is complex and hidden. Existing methods for treating HV pollution in the vadose zone have had limited application owing to various problems. In recent years, microorganisms have been used in the field of pollution control and remediation owing to their outstanding adsorption and degradation properties and low cost, but their environmental safety and behavior in porous media are still poorly understood. This study aimed to investigate the migration behavior and mechanisms of copper ions in saturated porous media under the action of copper-resistant microorganisms and to establish a corresponding numerical model to simulate the results. The key parameters of adsorption and migration were determined through batch adsorption and soil column experiments. A one-dimensional soil column was used to conduct a co-migration experiment using copper-resistant microorganisms and Cu2+ in water-saturated quartz sand, and a co-migration mathematical model was constructed. It was found that the existence of microorganisms had an inhibitory effect on the migration of Cu2+ in quartz sand, and Cu2+ promoted the migration of microorganisms, reduced their adsorption, and increased their concentration in the column experiment effluent. The selected solute transport mathematical model had a good fitting effect on the breakthrough curves of copper ion and copper-resistant microorganisms during their co-migration. The results can provide parameters and a theoretical basis for the risk assessment and prevention of HV pollution in the saturated zone or aquifers.

Numerical Simulation of Solute Transport in Saturated Porous Media with Bounded Domains.

This work presents the first attempt to develop unconditionally stable, implicit finite difference solutions of one-sided spatial fractional advection-dispersion equation (s-FADE) by imposing the nonzero Dirichlet boundary condition (ND BC) or the nonzero fractional Robin boundary condition (NFR BC) at inlet boundary and the zero fractional Neumann boundary condition (ZFN BC) at outlet boundary. The results of the numerical studies performed using artificial solute transport parameters demonstrated that the numerical solution with the NFR BC as the inlet boundary produced much more realistic concentration values. The numerical solution with the NFR BC at the inlet boundary was capable of correctly describing the Fickian and non-Fickian behaviors of the solute transport at different α values, and it had the relatively same accuracy at different numbers of the spatial nodes. Also, the practical application of the numerical solution with the NFR BC as the inlet boundary was investigated by conducting tracer experiments in homogeneous and heterogeneous soil columns. According to the obtained results, this numerical solution described well solute transport in the homogenous and heterogeneous soils. The α values of the homogeneous and heterogeneous soils were obtained in the ranges of 1.849-1.999 and 1.248-1.570, respectively, which were in excellent agreement with the physical properties of the soils. In a nutshell, the numerical solution of the s-FADE with the NFR BC as the inlet boundary can be successfully applied to describe the solute transport in the homogeneous and heterogeneous soils with bounded spatial domains.

Modeling the vertical transport of antibiotic resistance genes in agricultural soils following manure application

Antibiotic resistance genes (ARGs) may be introduced to agricultural soil through the land application of cattle manure. During a rainfall event, manure-borne ARGs may infiltrate into subsurface soil and leach into groundwater. The objective of this study was to characterize and model the vertical transport of manure-borne ARGs through soil following the land application of beef cattle manure on soil surface. In this study, soil column experiments were conducted to evaluate the influence of manure application on subsurface transport of four ARGs: erm(C), erm(F), tet(O) and tet(Q). An attachment-detachment model with the decay of ARGs in the soil was used to simulate the breakthrough of ARGs in leachates from the control column (without manure) and treatment (with manure) soil columns. Results showed that the first-order attachment coefficient (ka) was five to six orders of magnitude higher in the treatment column than in the control column. Conversely, the first-order detachment and decay coefficients (kd and μs) were not significantly changed due to manure application. These findings suggest that in areas where manure is land-applied, some manure-borne bacteria-associated ARGs will be attached to the soil, instead of leaching to groundwater in near terms.

Experimental Study on Impermeability Law of Aquiclude Reconstructed by Mudstone of External Dump in Arid Zone

In order to achieve the goal of ecological restoration, plant irrigation, and water retention in the external dump of open-pit coal mine in the arid desert area, it is proposed to use the mudstone in the stripped material to reconstruct the surface aquiclude and improve the water holding capacity of the topsoil. By taking the Hongshaquan Open-Pit Coal Mine as the study object, the red mudstone of mining level +650 was selected as the topsoil aquiclude material through the geological survey. XRD diffraction experiments are used to determine the composition of red mudstone including kaolinite mineral, quartz, potash feldspar, albite, and illite. The moisture content of the red mudstone is 4.16% as measured by the indoor drying experiment. And the particle size of 0.5 mm, 1 mm, and 2 mm and the thickness of 5 cm, 10 cm, and 20 cm rock samples were selected to conduct the indoor soil column experiment. Three indicators of initial infiltration rate, stable infiltration rate, and average infiltration rate were obtained according to the analysis and calculation of the water column drop rate, wet peak drop rate, and cumulative infiltration rate so that the permeability law and coefficient of each group of tests can be known. The finite element transient analysis theory and numerical simulation method were adopted to verify the results of physical experiments. The research results show that +650 level red mudstone has a strong antiseepage ability, and the smaller the particle size, the better the antiseepage performance. For 0.5 mm and 2 mm particle sizes, as the paving height increases, the water-proof effect is better. The laying height of 1 mm particle size has no obvious influence on the water barrier effect. The physical simulation was confirmed to have the same result trend as the numerical simulation, both of which are quadratic functions with the error within a reasonable range.

Sulfidated zero valent iron as a persulfate activator for oxidizing organophosphorus pesticides (OPPs) in aqueous solution and aged contaminated soil columns

Sulfidation treatment is an effective method of improving the catalytic performance of zero-valent iron (ZVI). Here, we prepared sulfidated, micro-sized ZVI (S-mZVI) using ball milling technology to activate persulfate (PS) with the goal of oxidizing organophosphorus pesticides (OPPs) in aqueous solution and aged OPP-contaminated soil columns. Energy dispersive spectroscopy (EDS), X-ray powder diffraction (XRD) and X-ray photoelectron spectrometry (XPS) analyses uncovered the formation of Fe2O3, FeOOH, FeS and FeS2 in the S-mZVI prepared by ball milling with different proportions of elemental S powder to make micro-sized ZVI particles. The presence of sulfur can regulate the morphology of S-mZVI with a dispersed and spherical shape, and it can improve the activation performance of PS. In aqueous solution, 11.2 mg of S-mZVI activated 2.5 mM PS (S-mZVI-PS) with an S/Fe molar ratio of 0.100, and it was the best at activating PS, leading to oxidation-rate constants of 0.030 s−1 for 10 mg/L phorate and 0.026 s−1 for 10 mg/L terbufos, which were much greater than those of the other S-mZVI and mZVI. The results of the soil column experiment showed that the PS, which had a low consumption for the total dosage, achieved higher degradation percentages among the three OPPs in the S-mZVI-PS treatment than those in the mZVI-PS treatment over 120 h, with the best performance achieved by oxidizing 69.7% phorate, 48.0% terbufos and 60.6% aminoparathion. The effluent concentrations of the three OPPs in the S-mZVI-PS treatment were significantly lower than those in the mZVI-PS treatment, while dissolved total iron and Fe(II) displayed the opposite results. These results indicate that S-mZVI prepared by ball milling can effectively activate PS and be applied to remediate OPP-contaminated soil.

Simulation study on the migration of F− in soil around Chagan Lake, China

Chagan Lake is located in the high-fluorine area of western Jilin, with high fluoride content in surface water, soil, and groundwater around it. Due to its unique topography and hydrogeological conditions, Chagan Lake collects surrounding water and is closely connected with groundwater. The complex surrounding water not only affects the groundwater quality through Chagan Lake, but also affects groundwater through the infiltration of vadose zone. In order to further study the characteristics of the migration of F- in the soil around Chagan Lake along with water flow in the vadose zone and its impact on groundwater, soil column experiments were carried out using soil collected in the field, combined with HYDRUS-1D to simulate the migration characteristics of F-. The model was verified by measured data, the sensitivity of each parameter was analyzed by the single-factor disturbance method, and the effect of F- on groundwater was simulated and predicted. The results showed that (1) the soil column experiment was carried out using transport solutions of different pH value. The time required for F- to penetrate the soil column under alkaline conditions was shorter, and the HYDRUS model used has a high degree of fitting. (2) The single-factor disturbance method is used to analyze the sensitivity of the parameters. The parameters that have a greater impact on the migration of fluoride ions in the soil are saturated hydraulic conductivity, adsorption coefficient, and soil bulk density. (3) In the prediction scenario, due to the adsorption and interception of the vadose zone, as the depth increases, the time it takes for F- to accumulate is also longer. The groundwater around Chagan Lake is relatively shallow, and surface F- in alkaline environment reaches the underground aquifer within 2 days. The F- concentration in the groundwater reaches its maximum before the end of the irrigation period. In neutral environment, the F- concentration in groundwater did not reach the maximum before the end of the irrigation period.

Rare earth element migration and impact of Dicranopteris dichotoma at mines in south China

The migration of rare earth elements (REEs) has a major influence on the environment. However, little is known about REEs migration control by Dicranopteris dichotoma at REEs mines. Therefore, this study examined the horizontal and vertical migration of REEs using artificial rainfall and naive soil column experiments, respectively, and the REEs migration control of Dicranopteris dichotoma at REEs mines in south China. The REEs contents in the runoff and sediment were found to be 32.42 μg and 3.39 mg, respectively, in the artificial rainfall experiment. The mean REEs content and amount in the leaching liquor were 0.23 μg L−1 and 7.75 μg, respectively. The REEs content after leaching was significantly lower than that before leaching in the 0–5 cm layer, was significantly higher than that before leaching in the 5–10 cm layer. However, the REEs content of the Fe–Mn oxide form showed significant variation among the sites with different Dicranopteris dichotoma covers. Moreover, the runoff reducing rate rose with increasing Dicranopteris dichotoma cover, and the sediment reducing rate increased to the relatively stable stage when Dicranopteris dichotoma cover was equal or greater than 70%. Thus, REEs migration by sediment is the dominant migration method, and the risk of REEs vertical migration in the soil is low and might have been overestimated. Further, Dicranopteris dichotoma does not control REEs migration by altering the REEs forms, and Dicranopteris dichotoma cover should reach and be maintained at ≥ 70% in order to control REEs migration at REEs mines in south China.

Artificial Macropores with Sandy Fillings Enhance Desalinization and Increase Plant Biomass in Two Contrasting Salt-Affected Soils

Salt accumulation in topsoil is a widespread restricting factor that limits agricultural production and threatens food security in arid and semi-arid regions. However, whether this upward enrichment was suppressed by macropores was less documented. Therefore, artificial macropores with sandy fillings (AMSF) method was proposed in this study. Soil column experiments showed a significant improvement of saturated hydraulic conductivity (Ks) by more than 260% under artificial macropore treatment. Freshwater irrigation was conducted to monitor the short-term water and salt movement. This research aimed at evaluating the potential benefit of AMSF method on soil desalinization in coastal farmland of northern China. The results demonstrated that downward movement of soil water was stimulated in AMSF method, accordingly, washing more salt ions out of top rooting zone. Particularly, 10 cm or more macropore depth treatments of AMSF method enhanced total desalinization by 52.1% to 176.6% in 0–30 cm soil layer, in comparison to the control group without macropore. Subsequent observations for alfalfa showed higher biomass by 20.8% under 15 cm macropore depth. The results here provided an exploration demonstration to pursue these studies with the ultimate goal of optimizing application strategies for amendment in coastal salt-affected lands of northern China.

Removal of chlortetracycline and antibiotic resistance genes in soil by earthworms (epigeic Eisenia fetida and endogeic Metaphire guillelmi)

The impacts of two ecological earthworms on the removal of chlortetracycline (CTC, 0.5 and 15 mg kg−1) and antibiotic resistance genes (ARGs) in soil were explored through the soil column experiments. The findings showed that earthworm could significantly accelerate the degradation of CTC and its metabolites (ECTC) in soil (P < 0.05), with epigeic Eisenia fetida promoting degradation rapidly and endogeic Metaphire guillelmi exhibiting a slightly better elimination effect. Earthworms alleviated the abundances of tetR, tetD, tetPB, tetG, tetA, sul1, TnpA, ttgB and intI1 in soil, with the total relative abundances of ARGs decreasing by 35.0–44.2% in earthworm treatments at the 28th day of cultivation. High throughput sequencing results displayed that the structure of soil bacteria community was modified apparently with earthworm added, and some possible CTC degraders, Aeromonas, Flavobacterium and Luteolibacter, were promoted by two kinds of earthworms. Redundancy analysis demonstrated that the reduction of CTC residues, Actinobacteria, Acidobacteria and Gemmatimonadetes owing to earthworm stimulation was responsible for the removal of ARGs and intI1 in soil. Additionally, intI1 declined obviously in earthworm treatments, which could weaken the risk of horizontal transmission of ARGs. Therefore, earthworm could restore the CTC-contaminated soil via enhancing the removal of CTC, its metabolites and ARGs.

Hydraulic properties of co-seismic landslide deposits around the Wenchuan earthquake epicentre: Large-scale column experiments

The co-seismic landslides and rock avalanches caused by the 2008 Wenchuan earthquake generated numerous poorly consolidated deposits over a vast area. Rainfall-induced initiation and remobilization of these deposits have resulted in many post-earthquake disasters, such as rapid erosion, flow slides, and debris flows, threatening the local residents. The hydraulic properties of the deposits dominate the evolution of the soil moisture in the slope during rainfall, consequently affecting the initiation and failure types of these geo-disasters. Thus, laboratory tests and infiltration experiments were conducted with material from co-seismic landslide deposits in the Wenjia Gully near the Wenchuan earthquake epicentre. The soil-water characteristic curve (SWCC) of the co-seismic deposit material was determined by a pressure plate extractor and tensiometers. Then, a series of large-scale soil column experiments were conducted with the materials. The results of the experiments showed a relatively high permeability and low matric suction of the co-seismic deposit compared with other soils. The infiltration characteristics of the deposit material with different initial water contents, compactness, and fine particle contents were also analysed and compared. A linear solution of the Green and Ampt equation was employed to estimate the infiltration rate in the deposit during rainfall events, which fit the results of the experiments well. The influence of matric suction on the water absorption and retention capacity was obvious when the moisture content was less than 5%, resulting in a variable evaporation rate and a soil-water hysteresis phenomenon. The results of this study provide reliable experimental evidence with which to evaluate the distribution and evolution of soil moisture in landslide deposits, which is significant for geo-hazard assessments and mitigation works. • Large-scale soil column experiments were conducted to study the hydraulic properties of co-seismic landslide deposits. • The permeability of co-seismic landslide deposits is relatively high, which results in an infiltration rate of 0.174–2.4 m/h. • An algebraic solution of the Green and Ampt equation is used to estimate the evolution of the wetting front. • The evaporation rate is much lower than the infiltration rate due to the increase in matric suction, which results in a soil-water hysteresis.

Assessing the mobility of veterinary drugs with column experiments using different soils and under controlled flow conditions

Veterinary pharmaceuticals are pollutants that received much attention during the last 20 years. Macrocyclic lactones are a class of drugs globally used in animal and human health, as well as crops protection. Some of its members are key substances for global food security. In this research, the mobility of eprinomectin (EPM) in soil columns (25 cm soil height; 10 cm diameter) was assessed for the first time. Soil density in the columns was 1.1–1.2 g/cm3. Porosity was 0.54–0.60. Three different soil types were used (agricultural, pastoral, wetland). In the experiment, chloride was used as a non-reactive tracer to determine the hydrodynamic conditions in the columns. Therefore, water velocity (v) was 0.146–0.151 cm/h, dispersion coefficient (D) 0.011–0.017 cm2/h and dispersivity (D/v) was 0.072–0.121. Our results showed that the drug remained in the top layers of the columns, after applying an extreme irrigation scenario. The retardation factor for EPM was 43.4–54.5 while for chloride was 0.99–1. EPM fraction (% of applied mass) in 0–1 cm was 13.8–18.0% and in 1–5 cm was 53.3–73.0%. An amount 13–29% was irreversibly bound or degraded during this experiment. From a soil management perspective, the continuous application of EPM contaminated manure, could result in high concentrations in the top 10 cm of the soil profile. Soil column experiments, where hydrodynamic conditions are well defined, are useful for the environmental impact assessment of veterinary pharmaceuticals.

Tillage and irrigation increase wheat root systems at deep soil layer and grain yields in lime concretion black soil

In lime concretion black soil, a two-factor (tillage and irrigation) split block experiment from 2015 to 2017 was conducted to identify whether their combination is suitable for the improvement of winter wheat yield and water use efficiency. The main treatments were subsoiling (SS) and rotary tillage (RT), with secondary treatments of three irrigation regimes: no irrigation during the whole growth period (W0), irrigation at jointing stage (W1), and irrigation at both jointing and anthesis stages (W2). In combination with a soil column experiment, the contribution of the root system in different soil layers to yield was clarified. The results indicated that both tillage and irrigation significantly influenced the spatiotemporal distributions of the root systems and yield components, while tillage produced the strongest effect. Compared with RT, SS significantly promoted the root penetration and delayed root senescence in deep soil layers. With increasing soil depth, each root configuration parameter (dry root weight density, DRWD; root length density, RLD; root surface area per unit area, RSA; root volume per unit area, RV) gradually decreased, and the peak appearance times of each root parameter in RT and three parameters (RLD, RSA and RV) in SS were postponed from heading to anthesis and from anthesis to filling stage, respectively. The average post-peak attenuation values at soil layers from 60 to 100 cm in W1 were less than those in W0 and W2. SSW1 generated the highest grain yields, with an average increase of 31.88% compared with the yield in RTW0. Root systems at three soil layers (0–40 cm, 40–80 cm and below 80 cm) differentially contributed to grain yields with 78.32%, 12.09% and 9.59%, respectively. The growth peak of the deep root system in SSW1 was postponed to the filling stage, and the post-peak attenuation declining rates were also slowed. Therefore, SSW1 is an effective cultivation method improving grain yields and water use efficiency in lime concretion black soil.

Experimental investigation on the effects of clay colloid-facilitated ammonium transport through saturated porous media under variable transport conditions

Ammonium contamination is one of the major environmental issues in subsurface contamination and groundwater which in turn poses risks to human health. Predicting and formulating desirable situations is necessary for the study of NH4+ ion adsorption and transport in the environment. The purpose of the present paper is to assess the influence of various factors, such as different colloidal concentration, different size of porous media and different flow rates on colloid-facilitated NH4+ ion transport. In order to understand the influence of colloid concentration on NH4+ ion transport in porous media, few soil column experiments were performed in laboratory scale. Different clay colloidal concentrations with NH4+ ion solution as contaminant were supplied to the soil column and the leached out solution was tested using UV–vis spectrophotometer to find the concentration of NH4+ ion; 500ppm clay colloidal concentration in fine sand medium at 5ml/min flow rate has been identified as most suitable condition for NH4+ ion subsurface adsorption with highest cumulative NH4+ ion adsorption of 1.9mg/g, whereas 200ppm clay colloidal solution had least cumulative NH4+ ion adsorbed values than other solutions. TherefoZhangre, 200ppm colloid solution was found to be most efficient for NH4+ ion transport. The efficiency of NH4+ ions transport in all the solutions in the study was doubled at a flow rate of 15ml/min than at 5ml/min. The outflow NH4+ ion concentration was lower for fine sand than medium sand in all the cases in the study. The results illustrated that variable factors in the study can either facilitate or retard ammonium ion adsorption.

Biowaste hydrothermal carbonization aqueous product application in rice paddy: Focus on rice growth and ammonia volatilization

Hydrothermal carbonization (HTC) is known as a green biomass conversion technology. However, it often suffers from the issue of disposing hydrothermal carbonization aqueous products (HCAP). Based on the characterization and composition of acidic HCAP, a rice paddy soil column experiment was conducted to observe the effects of HCAP on ammonia (NH3) volatilization form paddy soil and rice yield. The experiment was designed with five treatments. HCAPs were produced at 220 °C and (SHC220-L) and 260 °C (SHC260-L) derived from poplar sawdust, HCAP produced at 220 °C (WHC220-L) and 260 °C (WHC260-L) derived from wheat straw, and a control group without HCAP application (termed CKU hereafter). The results showed that HCAP treatments increased the rice yield by 4.30%–26.0% compared to CKU. HACPs prepared at lower temperatures (SHC220-L and WHC220-L) mitigated the cumulative NH3 volatilization by 11.2% and 7.6%, respectively, and mitigated yield-scale NH3 volatilization (cumulative NH3 volatilization/total yield) by 14.2% ∼ 22.4%. HCAP significantly improved the N use efficiency of rice. We found that the NH3 volatilization was related to NH4+-N concentration and pH of surface water, soil TOC and NH4+-N oxidation functional genes. This study implied that HCAP could be potentially used as a liquid fertilizer, which will be a potential substitute for chemical N fertilizers. There is still a long way before HCAP can be applied in full-scale for N fertilizer reduction and waste recycle.

Hydraulic redistribution by hybrid poplars (Populus nigra x Populus maximowiczii) in a greenhouse soil column experiment

AimsHydraulic redistribution (HR) enhances water resources for neighboring crops in silvopastoral agroforestry (AF). Here, we tested whether and to what extent water stressed shallow-rooted neighboring plants benefit from water redistributed by deep-rooted poplar plants.MethodsWe conducted trace experiments with deuterated water (2H2O) in greenhouse soil column experiments. We measured hydraulic lift (HL) by poplars grown at two levels of soil drying and estimated the amount of hydraulically lifted water. In a parallel experiment we grew poplars and barley (Hordeum vulgare) in two columns connected via a small cross-rooting segment.ResultsSoil moisture measurements and stable isotope signatures of soil and xylem water proved the occurrence of HL in poplar. Additionally, stable isotopes proved the transport of water from deep roots of poplars to shallow roots of barley.ConclusionsIn conclusion, the experiments showed that poplars are capable to redistribute water during drought spells and that this water can facilitate plant growth of shallow-rooted crops. This result implies evidence for an enhanced soil water supply of plants in agroforest systems under drought conditions.

Monitoring rainfall intensity and moisture water content using soil column experiment

Indonesia is a tropical country that has two seasons, rainy season and dry season. The wetting and drying of soil due to changing of the seasons caused change on soil properties such as moisture soil water content, effective soil porosity, soil suction etc. During rainy season, rainfall infiltration caused increasing of moisture soil water content in a soil slope, tends to reduce soil shear strength and followed by slope instability. In this soil column experiment was set up with rain gauge station and YL-69 sensor and capacitive soil moisture sensor to monitor rainfall infiltration and soil moisture water content in red clay soil. A wireless sensor network with low power wide area network technology integrated with the cloud to observe rainfall intensity and soil water content in soil column with realtime monitoring. The focused on improving the accuracy of rainfall intensity and soil water content sensors readings using regression methods. The experiment results showed that rainfall intensity was observed accurately while for the YL-69 sensor, the error reading was 5.15% and the error reading capacitive soil moisture sensor was 2.99%.

Total and denitrifying bacterial communities associated with the interception of nitrate leaching by carbon amendment in the subsoil.

Nitrate leaching is severe in greenhouse where excessive nitrogen is often applied to maintain high crop productivities. In this study, we investigated the effects of carbon amendment in the subsoil on nitrate leaching and the emission of greenhouse gases (CH4 and N2O) using a soil column experiment. Carbon amendment resulted in over 39% reduction in nitrate leaching and 25.3% to 60.6% increase of total N content in the subsoil zone as compared to non-amended control. Strikingly, the abundance of nirS, nosZ, and 16S rRNA were higher in the treatment than the corresponding controls while no significant effect was detected for nirK. Carbon amendment explained 14%, 10%, and 4% of the variation in the community of nosZ, nirS, and nirK, respectively. It also considerably (more than 7 times) enriched genera such as Anaerovorax, Pseudobacteroides, Magnetospirillum, Prolixibacter, Sporobacter, Ignavibacterium, Syntrophobacter, Oxobacter, Hydrogenispora, Desulfosporomusa, Mangrovibacterium, and Sporomusa, as revealed by the analysis of 16S rRNA amplicon. Network analysis further uncovered that carbon amendment enriched three microbial hubs which mainly consists of positively correlated nirS, nosZ, and anaerobic bacterial populations. In summary, carbon amendment in the subsoil mitigated nitrate leaching and increased the nitrogen pool by possible activation of denitrifying and anaerobic bacterial populations. KEY POINTS: • Carbon amendment in subsoil reduced NO3- leaching by over 39% under high N input. • Carbon amendment increased the total N in subsoil from 25.3% to 60.6%. • Carbon amendment enriched nirS- and nosZ-type denitrifying bacteria in subsoil.

Quantification of the sources of soluble organic N (SON) from new litter or indigenous soil in a typical subtropical forest

AbstractDecomposition of forest litter plays a major role in nitrogen (N) dynamics in soil. However, the effect of new litter on indigenous soil N and its contribution to soil N in natural forest remains unknown. An in situ soil column experiment was conducted and 15N labelled litter was added to decompose for 14 months to examine the effect of litter retention on soil N dynamics in a typical subtropical forest. Litter removal in the soil column was used as a control. The results showed that litter removal caused a continuous decrease in concentration of soil soluble organic N (SON) in the first 5 months (August in 2018‐January in 2019), and SON concentration went up in the eighth month. Litter retention accelerated the reduction of soil SON concentration in the first 2 months, and SON concentration maintained a high value after that period. Soil NH4+‐N derived from litter was nitrified rapidly, and the newly formed NO3−‐N was quickly immobilized or lost. Only 1.8% of soil SON came from litter N and 98.2% from indigenous soil N under the decomposition of labelled litter. Litter provided N to form new soil SON continuously, however, only a small part of SON was relatively stable. Soil SON and total N (TN) are formed after long‐term litter accumulation and decomposition, and litter retention plays an important role in soil N dynamics.