Original Soil Research Articles

On‐ and off‐site erosion impacts of restoration measures in a tropical karst watershed

AbstractKarst areas are vulnerable landscapes which, if unprotected, could be permanently degraded. To bridge the gap existing in the reduction of on‐ and off‐site impact of restored tropical karst areas, this study was carried out in a 3.5 ha karst watershed of the Brazilian savanna (Cerrado). Precipitation, surface runoff, and soil loss were measured in representative runoff plots (22.1 × 1.84 m), used to assess the watershed erosion and sediment yield to a downstream sinkhole. The study was carried out during three hydrologic years, between September 2018 and May 2020. The predominant soils in the watershed were Lithic entisol and Quartzsamment, and the original land covers were natural savanna, seasonal forest, and degraded pastureland (Andropogon gayanus). The latter was restored with native savanna species, in the lower part of the watershed, and with a reformed pastureland, in the upper part. The USLE rainfall erosivity (R), soil erodibility (K), and soil cover (C) factors, runoff, soil loss, and the original soil and sediment textures were obtained from the runoff plots. The watershed soil loss and sediment yield were obtained by the USLE and GIS. Precipitation and rainfall erosivity ranged from 936 to 1223 mm, and from 6694 to 7746 MJ mm ha−1 h−1, in the period, respectively. Although the ecological watershed restoration reduced mean soil loss from 11.6 to 5.8 Mg ha−1 year−1, and sediment yield from 29.2 to 14.6 Mg year−1, on‐ and off‐site soil loss tolerances were still exceeded in 29 and 61% of the basin area, respectively. Ecological restoration also reduced the sand and clay content of the sediment entering the underground caves and river downstream, contributing to their hydrologic sustainability.

Use of DMT and CPTU tests in the evaluation of shear modulus G 0 for soils of different origin

Use of DMT and CPTU tests in the evaluation of shear modulus G 0 for soils of different origin

Influence of Moisture Content and Dry Density on the Compressibility of Disturbed Loess: A Case Study in Yan’an City, China

Loess is a kind of soil that experiences a long period of deposition, and it is relatively stable under natural conditions. However, in the process of engineering construction in loess areas, the original soil structures of the loess are destroyed, inducing changes in the composition and water content in the loess. These changes may cause different environmental and engineering geologic problems. To reveal the engineering properties of disturbed losses in the Chinese Loess Plateau, the physical properties of 135 groups of disturbed loess samples in Yan’an City were analyzed statistically, and the compression properties of loess with different moisture contents and dry densities were studied by high-pressure consolidation experiments. We elucidate the compressive deformation law for perturbed solids at different moisture contents and dry densities. The experimental results show that the water content rate for the best compaction performance of the disturbed loess is 16%. The compressive deformation coefficient generally decreases with increasing dry density and water content. However, when the soil moisture is low, a small amount of water and salt is concentrated in the contact position of the powder, and the soluble salt is condensed into cement. The molecular forces between particles and the bonding forces of bound water and capillary water are larger. The soil forms a porous structure with coarse grains as the main skeleton, and the cement bonding strength is strong at the contact points of the coarse grains. As a result, the loess shows high intensity at low-water content. This results in a compression-deformation coefficient that increases with dryness density in the small load range.

Effectiveness and compatibility of fabricated hydraulic lime prepared with ultrafine pozzolanic materials in consolidating soil-matrix

In this experiment, fabricated hydraulic lime (FHL) was synthesized by blended hydrated lime and superfine pozzolanic components, and the solvent for preparing lime-suspension was optimized through a static bleeding test. A systematic comparison was conducted between a commercial natural hydraulic lime (NHL) and synthesized FHL in consolidating soil-matrix. Their effects were evaluated in terms of effectiveness (penetration depth and surface hardness) and compatibility (color difference and vapor transmission). Both consolidants were proved to be compatible, while FHL-suspension outperformed NHL in effectiveness, due to the filling effect and cementation with the original loose soil particles supplied by superfine pozzolanic components, and their quicker hydration products helped the formation of a spatial network in consolidated matrixes. In addition to the known widely available raw materials supply, this experiment confirmed the properties advantages of FHL, which supplied a potentially suitable material for the anti-weathering purpose of earthen relics.

Lalombi Tropical Peat Soil Improvement Using Iron Oxide admixture and Cement

Peat soil has a relatively high water content of up to 400%. With a high moisture content, peat soil can hinder construction work. For this reason, in construction planning, an investigation must be carried out on the characteristics and strength of the soil, especially the properties of the soil that affect the bearing capacity of the soil to withstand the load of the construction on it. This study aimed to determine the characteristics and changes in the bearing capacity of peat soil after mixing with cement and iron oxide admixture. The variation of mixing iron oxide is 0%, 4%, 8%, and 16%, while for variation of cement mixture is 5%. This research was conducted on the soil, including testing physical and mechanical properties. Engineering properties tests include direct shear and consolidation tests. This research conducted the elemental chemical content in peat soil and SEM (Scanning Electron Microscope) test. Based on the classification of peat soil at this location with an ash content-value of 29.41%, it can be classified as High Ash Peat (peat with ash content > 25%). In the direct shear test, the cohesion value and the shear angle continued to increase as the percentage of the iron oxide mixture increased to 16%, where the shear angle changed from 7.60º to 45°. In the consolidation test, the original soil Cc value of 0.00820 decreased with the addition of iron oxide to 16%; the Cc value decreased to 0.00277. The decrease in Cc indicates that the soil becomes easily compacted, and The value of the Coefficient of Consolidation (Cv) on peat soil was 0.00535 cm²/sec. The most significant increase in the original soil with a mixture of 16% iron oxide was 0.01463 cm²/sec. The Chemical results have been given a mixture of 16% iron oxide and 5% cement, the change of C (Carbon), Fe (Ferrum) and Ca (Calcium). The value of O (Oxygen) in peat soil was 48.05% and then decreased to 43.67%, this indicates that the pores in the peat soil are reduced, and when the pores are reduced, the peat soil becomes denser. The value of Si (Silica) also decreased from 30.01% to 21.21%. This occurred because silica reacted with lime. After all, silica is an adhesive that binds lime, making the granules denser. Peat soil’s Fe (Ferrum) value was 3.12%, then increased to 16.72%. This also helped the soil to become stronger because of the higher specific gravity of iron. Peat soil’s Al (aluminium) value was 12.15% after being given a mixture of iron oxide and cement increased to 12.16%.

Micromorphological soil assessment in abandoned quarry dumps of the Central Caucasus, Russia

This study compared the micromorphological and agrochemical metrics in soils from the quarry dumps and zonal soils, the Central Caucasus. Soil micromorphological investigations are important tool for evaluation of soil dynamics after anthropogenic impacts on terrestrial ecosystems. The results showed that the carbon content in the primary soil of the sand and gravel quarries was lower than that in the reference soil. The differences detected were statistically significant for both the Urvan plot soils (t = 11.95; p = 0.000) and the Progress plot soils (t = 18.73; p = 0.000). In contrast, in the quarry with clay bottom substrate (Gerpegezh), no significant difference was found between the reference and postmine soils. The reference soil around the sand and gravel quarries was slightly more acidic than the primary soil. In the clay quarry, the primary soil was more acidic with a strong acidic value, while the reference soil was neutral. The difference of nutrients (P, K, NH4+, NO3-) between the primary and reference soils were negligible. The only exception was the NO3- content in the reference soil of Progress settlement, where it was significantly higher (t = 4.19; p = 0.002) than in the original soil of the site. No difference was observed for the mineral component of the primary soil. Investigation of key zonal soils of the region. Zonal Caucasus soils: Phaeozem Gleiyc, Phaeozem and Umbric Retisol are different in terms of micro texture. Thus, Phaeozem Gleiyc characterizes by microstructure composed by primary angular mineral forms. Phaeozem and Retisol demonstrated formation of biogenic structure with alteration of mineral particles. Data obtained show that rapid self revegetation of the quarries results in initialization of primary soil formation and transformation of the soil microstructure and organization on the micro level.

Abundance, classification and genetic potential of Thaumarchaeota in metagenomes of European agricultural soils: a meta-analysis

BackgroundFor a sustainable production of food, research on agricultural soil microbial communities is inevitable. Due to its immense complexity, soil is still some kind of black box. Soil study designs for identifying microbiome members of relevance have various scopes and focus on particular environmental factors. To identify common features of soil microbiomes, data from multiple studies should be compiled and processed. Taxonomic compositions and functional capabilities of microbial communities associated with soils and plants have been identified and characterized in the past few decades. From a fertile Loess–Chernozem-type soil located in Germany, metagenomically assembled genomes (MAGs) classified as members of the phylum Thaumarchaeota/Thermoproteota were obtained. These possibly represent keystone agricultural soil community members encoding functions of relevance for soil fertility and plant health. Their importance for the analyzed microbiomes is corroborated by the fact that they were predicted to contribute to the cycling of nitrogen, feature the genetic potential to fix carbon dioxide and possess genes with predicted functions in plant-growth-promotion (PGP). To expand the knowledge on soil community members belonging to the phylum Thaumarchaeota, we conducted a meta-analysis integrating primary studies on European agricultural soil microbiomes.ResultsTaxonomic classification of the selected soil metagenomes revealed the shared agricultural soil core microbiome of European soils from 19 locations. Metadata reporting was heterogeneous between the different studies. According to the available metadata, we separated the data into 68 treatments. The phylum Thaumarchaeota is part of the core microbiome and represents a major constituent of the archaeal subcommunities in all European agricultural soils. At a higher taxonomic resolution, 2074 genera constituted the core microbiome. We observed that viral genera strongly contribute to variation in taxonomic profiles. By binning of metagenomically assembled contigs, Thaumarchaeota MAGs could be recovered from several European soil metagenomes. Notably, many of them were classified as members of the family Nitrososphaeraceae, highlighting the importance of this family for agricultural soils. The specific Loess-Chernozem Thaumarchaeota MAGs were most abundant in their original soil, but also seem to be of importance in other agricultural soil microbial communities. Metabolic reconstruction of Switzerland_1_MAG_2 revealed its genetic potential i.a. regarding carbon dioxide (CO_2) fixation, ammonia oxidation, exopolysaccharide production and a beneficial effect on plant growth. Similar genetic features were also present in other reconstructed MAGs. Three Nitrososphaeraceae MAGs are all most likely members of a so far unknown genus.ConclusionsOn a broad view, European agricultural soil microbiomes are similarly structured. Differences in community structure were observable, although analysis was complicated by heterogeneity in metadata recording. Our study highlights the need for standardized metadata reporting and the benefits of networking open data. Future soil sequencing studies should also consider high sequencing depths in order to enable reconstruction of genome bins. Intriguingly, the family Nitrososphaeraceae commonly seems to be of importance in agricultural microbiomes.

Novel Antibiotic Resistance Genes Identified by Functional Gene Library Screening in Stenotrophomonas maltophilia and Chryseobacterium spp. Bacteria of Soil Origin

As one of the most diverse habitats of microorganisms, soil has been recognised as a reservoir of both antibiotics and the antibiotic resistance genes (ARGs). Bacteria naturally inhabiting soil or water often possess innate ARGs to counteract the chemical compounds produced by competitors living in the same environment. When such bacteria are able to cause infections in immunocompromised patients, their strong innate antibiotic resistance mechanisms make treatment difficult. We generated functional gene libraries using antibiotic-resistant Stenotrophomonas maltophilia and Chryseobacterium spp. bacteria isolated from agricultural soils in Lithuania to select for the genetic determinants responsible for their resistance. We were able to find novel variants of aminoglycoside and β-lactam resistance genes, with β-lactamases isolated from the Chryseobacterium spp. functional gene library, one of which is a variant of IND-like metallo-β-lactamase (MBL) IND-17 and the other of which is a previously uncharacterised MBL we named CHM (Chryseobacterium metallo β-lactamase). Our results indicate that soil microorganisms possess a diversity of ARG variants, which could potentially be transferred to the clinical setting.

Assessing combined analysis of electrical resistivity tomography and multichannel analysis of surface waves for ground improvement assessment near by-pass road, Silchar, Assam

Soft clayey soils are generally improved by the consolidation process. The different improvement techniques which are in vogue include the use of stone columns, sand drains with and without preload and prefabricated vertical drains. Upon improvement, the soft soil attains a higher strength and better resistance to excessive settlement. The extent of this improvement of the soft soil is measured through different in-situ tests including Standard Penetration Test (SPT), Cone Penetration Test (CPT) and Pressuremeter Test. Most of these tests are invasive and require boreholes for the collection of soil samples. Geophysical tests can scan the entire area within a short time and can accurately interpret the extent of the improvement depending on the expertise of the investigators. Sometimes a combination of two or more geophysical tests is suitable for an accurate prediction of any change in soil properties. The present study is an attempt to measure the effect of ground treatment by implementing two types of geophysical tests, namely, Electrical Resistivity Tomography (ERT) and Multichannel Analysis of Surface Wave (MASW) near a by-pass road in Silchar, Assam. The tests were conducted on a newly constructed road embankment that had undergone excessive settlement and was subsequently treated with stone columns with a preload. Both the geophysical tests showed improvement in soil properties as well as in the bearing capacity of the original soft soil. A bore log survey was also carried out before the improvement work to validate the results of the geophysical tests. Existing correlations among geophysical properties and soil properties were used to obtain the effect of improvement. It has been observed that geophysical tests can easily be carried out to accurately calculate the effect of improvement of soil properties. A combination of two or more geophysical methods yields a better understanding of the post-treatment results.

Island volcanism predicts pheomelanin‐based plumage colouration in a cosmopolitan raptor

AbstractAimPheomelanin is a pigment responsible for yellowish‐to‐reddish colours of vertebrate teguments. Its biosynthesis is favoured under high concentration of intracellular thiols, which, in turn, can depend on the environmental exposure to sulphur. Thus, pheomelanin production should be more intense and frequent in environments characterized by high level of sulphur, such as volcanic regions. In this study, we aimed at addressing this hypothesis by investigating variation in plumage colour of insular populations of the cosmopolitan barn owl (Tyto alba species complex) according to the presence of soils of volcanic origin (i.e. andosols) and recent volcanic activity.LocationWorld.TaxonBarn owl species complex.MethodsWe measured plumage colouration of more than 2000 museum specimens from 50 islands and archipelagos worldwide. We then compared plumage colouration between populations living on volcanic (i.e. where andosols and/or recent volcanic activity are present) and non‐volcanic islands/archipelagos.ResultsConsistently with the prediction, plumage colouration is significantly darker (i.e. pheomelanic) on islands/archipelagos where andosols and/or recent volcanic activity are present than absent, although this environmental factor explains a small fraction of plumage colour variability across islands (<10%). Similar results were obtained when specimens' sex and climatic predictors were included in the analyses.Main ConclusionsBecause excessive intracellular levels of thiols can be toxic, pheomelanin synthesis may function as a mechanism keeping these compounds below the toxicity threshold and limiting their detrimental effects on physiology. Darker plumage may also be favoured because it promotes background matching against the dark environment typical of volcanic islands (dense vegetation cover and/or dark soil). Our results add to the little evidence that the environmental exposure of compounds that are involved in melanin biosynthesis can affect animal pigmentation and suggest that soil composition may be a factor that affects melanogenesis, possibly contributing to generate spatial variation in pheomelanin‐based traits in animals.

Compost-derived humic acid impacts on the biodechlorination of pentachlorophenol in high organic matter paddy soil

The long-term accumulation of pentachlorophenol (PCP) has adversely affected the paddy soil ecosystem. PCP reductive dechlorination under anaerobic conditions is an efficient pathway for PCP degradation. This process is affected by the content of organic matter and the iron mineral composition of the soil. Our previous study analyzed the effects of compost-derived Humic acids (HAs) on reductive dechlorination of PCP in a paddy soil system under Fe-reducing conditions. The effects and mechanisms of high organic matter and compost-derived HAs in promoting PCP dechlorination need further investigation. This study examined paddy soils with high organic matter content in Heilongjiang Province. PCP reductive dechlorination in this system was studied using HAs from three stages of municipal solid waste compost as soil supplements. The results showed that natural HA and microorganisms could promote the dechlorination and transformation of PCP in the paddy soil system. After removing humic acid, the detected concentrations of PCP in paddy soil and solid-liquid interface were 1.84 and 9.67 times of those in the original soil experiment, respectively. The concentration of low chlorine products decreased significantly in the sterilized group. Compost-derived HAs from different stage were also presented various effect on PCP reductive dichlorination. Furthermore, the synergistic effect between natural HA and compost-derived HAs would limit the electron donating capacity of compost-derived HAs in the paddy soil with high organic matter. Organic matter in soil has an important influence on pollutant fate. Late-stage HA were more effective in promoting PCP degradation than early-and middle-stage HAs. The research provided a comprehensive and meticulous analyses of the effects of compost-derived HAs on PCP bio-dechlorination in paddy soil with high organic matter.

DESIGN OF THE NEW RUNWAY AT SUPADIO INTERNATIONAL AIRPORT'S RIGID PAVEMENT THICKNESS USING FAA METHOD

Supadio International Airport in Pontianak is a gateway for many domestic and international tourists. In order to boost West Kalimantan's economy and tourism, PT. Angkasa Pura II (Persero) wants to expand the Supadio International Airport by adding a second runway. This article looks at how the FAA (Federal Aviation Administration) method was used to plan the thickness of the rigid pavement on the new runway at Supadio International Airport. The expected number of people and aircraft will be calculated using the double-moving average method. The anticipated time frame is 2035, with 12.763.479 passengers and 121.782 aircraft movements annually. The Airbus A330-300 requires the most considerable thickness of the concrete slab, consisting of dual tandem wheel types and a maximum take-off weight (MTOW) of 533.519 lbs. As the original soil is in poor condition, a 52.5-cm-thick embankment is required to achieve a CBR value of 6%. The rigid pavement thickness design result for the design life of 2035 is as follows: surface course = 56,39 cm, subbase course = 15,24 cm, stabilized subgrade/base soil = 52,5 cm for critical areas, and a surface course of 50,751 cm, subbase course = 13,716 cm, and stabilized subgrade/base soil = 52,5 cm for non-critical soil.

Combined Column Test for Characterization of Leaching and Transport of Trace Elements in Contaminated Soils

Environmental assessments are required prior to remediation and redevelopment of contaminated sites. To date, regulatory guidelines are commonly based on total concentrations. Occasionally, simple leaching procedures are included in environmental assessment. Despite being essential for quantification of contaminant transport, analysis of hydraulic conductivity is rarely considered. Cost-effective methods that reflect both contaminant leaching and hydrogeological properties of contaminated soils are needed to ensure proper soil management. The aim of this study was to simultaneously evaluate contaminant leaching and hydraulic conductivity in soil using a combined column test (CCT) and compare this to the leaching results from batch tests (BT) and transport estimates derived from the empirical Hazen equation. Two soils of different origin were characterized using the CCT. By including physical and chemical factors affecting the release and retention of contaminants, the CCT provides an integrated assessment of leaching and transport of trace elements from soils. Additionally, the effect of soil compaction was investigated as a physical treatment to reduce leaching and transport in contaminated soils. Soil compaction did not demonstrate reduced leaching, but a less extensive contaminant transport was observed due to reduced hydraulic conductivity in the soil.

Convolutional Neural Network-Based Soil Water Content and Density Prediction Model for Agricultural Land Using Soil Surface Images

For appropriate managing fields and crops, it is essential to understand soil properties. There are drawbacks to the conventional methods currently used for collecting a large amount of data from agricultural lands. Convolutional neural network is a deep learning algorithm that specializes in image classification, and developing soil property prediction techniques using this algorithm will be extremely beneficial to soil management. We present the convolution neural network models for estimating water content and dry density using soil surface images. Soil surface images were taken with a conventional digital camera. The range of water content and dry density were determined considering general upland soil conditions. Each image was divided into segmented images and used for model training and validation. The developed model confirmed that the model can learn soil features through appropriate image argumentation of few of original soil surface images. Additionally, it was possible to predict the soil water content in a situation where various soil dry density conditions were considered.

The Influence of Lablab Purpureus Growth on Nitrogen Availability and Mineral Composition Concentration in Nutrient Poor Savanna Soils

Low soil fertility in savanna soils has been linked to low crop yields, with nitrogen being the most limiting factor in crop yield. Soil used in this pot experiment was obtained from Motshephiri village with low total N, low NO3− and high NH4+. A pot experiment was conducted in a greenhouse laid in a Randomized Complete Block Design with four treatments (1) control, (2) Bradyrhizobium japonicum inoculant, (3) superphosphate and (4) Bradyrhizobium japonicum inoculant + superphosphate). The superphosphate was applied at three different levels (45, 60 and 75 kg/ha). Lablab was cultivated in each treatment and the results of the study indicated that lablab growth significantly increased total N and NO3−, and reduced concentration NH4+ relative to the original soil herein referred to as pre-lablab growth. However, the N forms (total N, NO3− and NH4+) did not differ significantly amongst different levels of superphosphate with or without Bradyrhizobium japonicum inoculant. Lablab growth, proved to have a significant impact on both the soil macro (P, K, Ca, Mg, and Na) and micronutrient level (Fe, Mn, Cu, B and Cl) with the exception of Zn. This study suggests that lablab’s ability to rapidly boost soil N content, overall soil fertility in a short period of time without the use of superphosphate fertilizers or Bradyrhizobium japonicum inoculants makes it ideal for intercropping or rotating with non-leguminous crops that have a short growing season.

Study of an Optimized Mechanical Oscillator for the Forced Vibration of the Soil Cutting Blade

In the nursery sector, the transport and planting of trees must occur with the roots wrapped in a ball of the original earth. The cutting of the original soil can be carried out with a semicircular vibrating blade moved by an oscillator mounted on a self-propelled machine. The oscillator produces an excitation torque supplied to the blade together with the soil cutting torque. The advantage of the vibrating blade is a reduction in the cutting torque of up to 70%. However, to correctly design the oscillator, we need to investigate the link between the maximum displacement of the blade, the maximum oscillation velocity, the cutting velocity, the dry friction, the excitation torque, the elastic torque, the cutting torque, the required power, the required energy, and the excitation frequency. The maximum displacement and velocity ratio need to have the right values to minimize the cutting torque and to avoid the springs reaching the end of stroke; otherwise, vibrations are transmitted to the machine and to the operator. Therefore, starting from the forced oscillation differential equation and using an approximate solution method developed by Den Hartog, along with some experimental data, a mathematical model was constructed to optimize the oscillator design. After construction, it was coupled to blades of various diameters (0.6, 0.9, and 1.2 m) to undergo experimental tests. The soil cutting tests highlighted the achievement of the above objectives and, at the same time, confirmed the validity of the Den Hartog equations used to calculate the phase lag and the maximum displacement, resulting in an average error of 4.4% and a maximum error of 6.4%.

Effect of shape-stable phase change materials on heat transfer characteristics of ground source heat pump backfill materials

Ground source heat pump (GSHP) systems can utilize shallow geothermal energy to realize low-carbon buildings. The backfill material used in GSHPs directly affects the heat exchange between the ground heat exchanger and soil. Phase change materials (PCMs) can utilize the phase change process to realize both the storage and release of energy. Applying PCMs to GSHP backfill materials may be beneficial towards improving efficiency and saving energy. In this study, decanoic acid and lauric acid were used as composite PCM and graphite powder was added to enhance thermal conductivity. Expanded perlite was used as absorbent and silica sol was used to shape and encapsulate PCM. A shape-stable phase change material (SSPCM) was prepared for GSHP backfilling. Basic characteristics including thermal conductivity of SSPCMs were assessed and analyzed, and one-dimensional heat transfer experiments were carried out. The results showed that at a decanoic acid to lauric acid mass ratio of 7:3, the phase change temperature of binary organic acids is 19.9 °C, and the latent heat of phase change is 124.03 kJ/kg. At a 60% mass content percentage of PCMs, the amount of added graphite powder was 4%, the thermal conductivity of the SSPCM encapsulated by silica sol was 0.1431 W/(m·K), and the mass loss rate of SSPCM was less than 5% after 25 high and low temperature cycles. Materials with the above parameters have suitable comprehensive properties and can be used as preferred phase change backfill material for GSHP. The thermal conductivity of the backfill material is negatively correlated with the mixing ratio of SSPCM, and positively correlated with water content. At an intermittent ratio of 10:14, after 10 h of heating, the temperature range of the phase change backfill sample was 0.38–7.45 °C lower than that of the original soil backfill sample; after 14 h of cooling, the temperature of the phase change backfill sample was closer to the initial temperature. Therefore, adding SSPCM to the backfill material is beneficial to the long-term intermittent operation of GSHPs.

Pengaruh Penambahan Abu Gergaji Kayu pada Tanah Fat Clay Ditinjau Dari Indeks Properties Tanah dan UCST (Unconfined Compressive Strength Test)

The soil is the base layer of the construction that must have good carrying capacity. To find out the magnitude of the carrying capacity of the soil, one of them is using UCST (Unconfined Compressive Strength Test) testing. This study was conducted by taking soil samples in Olak Kemang Seberang Jambi City which is classified as fat clay soil. The purpose of this study was to see the effect of addition saw ash wood towards soil properties index values and UCST (Unconfined Compressive Test). The percentage of addition of saw ash wood used is 8%, 10%, 12%, and 14%. Based on the test results, changes in the value of the soil properties index experienced a peak at a percentage of 14% for each test of moisture content, specific gravity, and atterberg. Based on the results of the UCST test conducted, the peak of the increase in the highest soil carrying capacity value at a percentage of 14% was 4.02 kg / cm2, an increase from the original soil UCST value of 2.15 kg / cm2.

Effects of land‐use changes on soil organic nitrogen fractions in the black soil region of Northeast China

AbstractSoil organic nitrogen (SON) accounts for more than 90% of the total nitrogen (TN) in black soil and is one of the most important indicators of soil fertility. However, the effect of land‐use changes on SON fractions is still unclear in black soil. Hence, natural grassland (uncultivated), farmland (converted from natural grassland), and artificial forestland (grain plots converted into forests) in the black soil region of Northeast China were selected for research. TN, available nitrogen (AN) and SON fractions (ammonia nitrogen (AMN), amino acid nitrogen (AAN), hydrolysable unknown nitrogen (HUN), acid insoluble nitrogen (AIN)) in the topsoil (0–20 cm), and subsoil (20–40 cm) were analysed and compared with elucidate the effects of land‐use changes on SON fractions. The results showed that compared with natural grasslands, the contents of TN and AN in farmlands were 49.1%–67.4% and 48.0%–67.7% less, respectively, and the content of AAN decreased the most in SON fractions, by 52.2%–76.7%, followed by the content of AMN, which decreased by 46.9%–70.7%. The contents of TN and AN in the artificial forestland increased by 18.8% and 30.6%, respectively, compared with those in the farmland. Other than AAN, the content of the SON fractions in the artificial forestland soils was greater than that of the farmland, and the content of HUN increased the most in the SON fractions, by 29.6%, followed by the content of AIN, which increased by 25.8%. The proportions of AMN and AAN in the TN of the natural grassland were 1.2 and 1.7 times those of the artificial forestland, respectively. In conclusion, after natural grassland is converted to farmland, it will destroy the original soil structure, change the physical and chemical properties of the soil, significantly reduce the soil nitrogen supply potential, and significantly decrease nitrogen accumulation. The conversion of grain plots into forestland significantly improved the soil nitrogen storage capacity, but the potential nitrogen supply did not reach the levels of the uncultivated lands. Changes in land use types lead to changes in soil structure and vegetation cover, which in turn alter soil nitrogen cycling. These results provide a scientific basis for evaluating the nitrogen supply capacity of different land‐use types. The study suggests that the land use structure in the area should be properly matched to restore soil nitrogen reservoirs and maintain and improve soil fertility, taking into account local environmental conditions.

IMPROVING CLAY SOIL STABILITY WITH THE ADDITION OF RICE HUSKS THROUGH CHEMICAL METHODS

Soil stability is a mixture of soil with a certain material, the aim is to improve the technical properties of the soil so that it can technically meet certain requirements. Soil stability is a mixture of soil and other materials, for the purpose of achieving the correct gradation, so that the technical properties of the soil are better. Chemical stability is the addition of chemical elements to the clay with the addition of other ingredients, namely rice husk ash (ASP), so that a physical change is achieved and a change in the physical properties of the soil occurs, with an increase in the size of the soil load capacity (CBR). This study aims to obtain the appropriate variable for adding rice husk ash to the stability of clay as a stabilizer seen from the unconfined compressive strength test to obtain a capacity value of high load. The research method was carried out by testing the properties of soil index, soil compaction tests (standard proctor) and unconfined compression strength tests (Unconfined Compression Strength) in the laboratory. 200 with variations of 5%, 10% and 15%. Index property tests such as water content tests refer to ASTM D2216:2010, Sieve Analysis (ASTM D-422), Atterberg Limit, Liquid Limit (LL) (ASTM D-4318), and Specific Gravity (Gs) (ASTM D-854). Soil mechanical properties test (proctor standard) (ASTM D 698), free compression resistance test (ASTM D 2166). The conclusive results show that the free compressive strength value increased in the mass without hardening with a 10% husk ash percentage of 1.0005 kg/cm2 and a Cu value of 0.502 kg/cm3. While the results of the free compression strength test with curing for 24 hours, the highest bearing value occurred, in the original soil variation of 1.000 kg/cm3 and a Cu value of 0.500 kg/ cm3. For the value of the free compressive strength, there is a decrease, namely at variations of 5%, 10% and 15% with a time of 24 hours.