Soil Texture Type Research Articles

Ultrasonic acoustical assessment of molecular interaction in different soil texture and moisture absorbent growing media

The objective of the study is to measure the ultrasonic velocity, density, and viscosity of the plant-growing media prepared with different combinations of soil texture and moisture absorbent growing media. Four groups of soil texture (S1: loamy; S2: clay; S3: sand; and S4: pure sand/quartz) along with five moisture absorbent growing media (G1: coco peat; G2: vermiculite; G3: vermicompost; G4: sawdust; G5: hydrogel; and G6: control—soil alone) were used. Results showed that these acoustic detection technologies showed significant difference in soil physical properties. Ultrasonic studies described the nonlinear variations in the acoustical parameters among the different soil texture types and growing media tested. Moreover, the values of the acoustical parameters indicated the soil texture when added with any of the moisture absorbent media; water-holding properties of the soils are significantly varied and it suggests that even sand with less water-holding property can be used as a plant-growing medium, with the support of any of these moisture absorbent media (especially hydrogel). The lowest velocity was observed in pure sand alone. However, as the plasticity and the clay content of the soil increases, the porosity also increases and resulting in a decrease in the densities and increase in water content of the soil. Similarly, in heavy-textured soils (high clay content), addition of moisture absorbent media was negative. The comparative study of acoustical properties was made to elucidate the inter-ionic interactions in solutions of soil texture, and growing media and which help to choose the right combination of soil texture and moisture absorbent growing media. The results confirmed that the ultrasonic technique was a powerful and effective tool to investigate the molecular interaction between soil texture and moisture absorbent growing media and helpful for irrigation management.

Stability of Aggregates Made by Earthworms in Soils with Organic Additives

Earthworm activity is a key factor in creating soil aggregates, but introduced organic matter and abiotic factors are also equally important. The purpose of this study was to investigate the stability of aggregates made by earthworms in soils with organic additives. Additionally, the two aggregate stability measurement methods were compared: (i) the wet-sieve method and (ii) the laser diffraction method. A six-month container experiment containing sixteen treatments and controls were made. Each treatment included one of four types of soil texture: sand, loam, silty loam and clay, and one of four additives: straw, peat, compost and compost with added microorganisms. To each treatment, six earthworms were added, two each of species commonly occurring in Polish soils: Dendrodrilus rubidus, Aporrectodea caliginosa and A. rosea. This study confirmed that earthworm activity was the factor favoring aggregate formation. In terms of the investigated organic additives, the efficiency of aggregate creation was as follows: compost with active bacteria, compost, peat and straw. Nevertheless, earthworms alone, without the addition of an organic additive, did not form permanent aggregates. The wet sieving and laser diffractometry methods of measuring aggregate stability were comparable for silty, clayey and loamy soils.

The effect of organic fertilizers and inorganic fertilizer on mustard growth in Bahway village, Balik Bukit district, West Lampung regency

Soil fertility is the relationship between the physical, chemical and biological properties needed by plants to grow and develop. The land used as a medium for growing mustard greens is taken from Bahway Village. The soil is treated with organic and inorganic fertilizers to test its fertility. The data analysis used was one way ANOVA and the least significant difference test and a randomized block design with three treatments and two replications. The treatments were: P1=100% organic fertilizer, P2=100% inorganic fertilizer, P3=50% organic fertilizer + 50% inorganic fertilizer and control. Based on the research results, it is known that the type of soil texture in P1 and P2 has a clay-sand texture, while P3 and C have a sandy loam texture. In terms of chemical properties, the pH at P1, P2, P3 and C are 5.53, 5.79, 5.50 and 6.20. For available P values, P1 = 188.31 ppm, P2 = 7.44 ppm, P3 = 113.62 ppm, and C = 2.48. Availability of Cation Exchange Capacity P1 = 22.56me/100g, P2 = 21.80me/100g, P3 = 23.19me/100g, and C = 23.75me/100g. From these results, what showed that the growth of mustard plants increased was the P3 treatment.

Characteristics and controls of solute transport under different conditions of soil texture and vegetation type in the water–wind erosion crisscross region of China’s Loess Plateau

The analysis of solute transport characteristics in soil is of great significance in understanding nutrient cycling and pollutant migration in the Earth’s Critical Zone. The objective of this study was to investigate the transport characteristics and the influencing factors of Cl− in soils with different textures (sandy-S and loamy-L), and covered by different vegetation types (arbor-AR, shrub-SH and grass-GR) in the water–wind erosion crisscross region of the northern Loess Plateau of China. Results showed that the initial penetration time (TS: 12–80 min), entire penetration time (TE: 75–480 min), average flow velocity in the pore (V: 0.52–1.98 cm h−1) and the hydrodynamic diffusion coefficient (D: 0.75–2.55 cm2 h−1) of Cl− varied with different soil textures and vegetation types, and at different soil depths. The V and D associated with Cl− transport were highest in the 0–20 cm soil layer and decreased with increasing depth, while the opposite trend was observed for TS and TE. For the 0–1 m soil profile of the same texture but covered by different vegetation types, the average V and D followed the order of S-AR > S-GR > S-SH and L-AR > L-SH > L-GR, while the average TS and TE exhibited the exact opposite order. This behavior is caused by the varying distributions of root biomass under different vegetation types that affect the number of macropores, the connectivity density and the preferential flow paths in the soil. For the 0–1 m soil profiles of different textures covered by the same vegetation type, the average V and D followed the order of S-AR > L-AR; S-SH > L-SH; and S-GR > L-GR, while the average TS and TE showed the opposite trend. This is because the pore size and distribution in soil are significantly affected by soil mechanical composition. There are significant correlations between soil properties (e.g., bulk density, number of macropores, pore connectivity density, saturated hydraulic conductivity, soil organic carbon content and particle composition) and the transport parameters (e.g., V, TS, and TE). The pedotransfer functions using readily available soil properties can adequately predict V of Cl− transport under different conditions of soil texture and vegetation type. These results provide guidance for the rational configuration of artificial vegetation in different textural soils with respect to reduce nutrient loss and improve ecosystem functions in the northern Loess Plateau of China.

Forensic taphonomy: Characterization of the gravesoil chemistry using a multivariate approach combining chemical and volatile analyses

Soil thanatochemistry, defined as the study of the chemical changes occurring during the decomposition of buried corpses, is a young and inadequately documented field of research. In this study, we aim to determine the effects of decomposition on soil physico-chemical properties by combining pedological, chemical, and volatile analyses of soils surrounding buried animals. We examined chemical and volatile changes over time occurring throughout the soil column in two common soil-texture types (sandy loam and loam). We buried dead rats and let them decompose for two months. During their excavations, we characterized the physico-chemical conditions of three soil layers above the rats and one layer below, including (1) pH, dry matter, and electrical conductivity, (2) organic carbon and total nitrogen, (3) bioavailable nutrients (K, Na, Mg, Ca, and P), and (4) volatile organic compounds. Multivariate analyses (permMANOVA) revealed that a decaying rat is associated with changes in soil chemical characteristics in both soil types. However, the observed changes were not homogenous throughout the soil columns. Conditions in soil layers nearest the cadavers changed most during decomposition. We generated a predictive model by combining chemical and volatile analyses (10 % error rate), allowing us to identify key gravesoil indicators that could be used to reveal the former existence of a buried corpse in loam and sandy loam (indicators in order of importance): organic carbon, calcium, pH, conductivity, dimethyl-disulfide, and nitrogen.

Impact of climate, soil properties and grassland cover on soil water repellency

Numerous soil water repellency (SWR) studies have investigated the possible causes of this temporal phenomenon, yet there remains a lack of knowledge on the order of importance of the main driving forces of SWR in the context of changing environmental conditions under grassland ecosystems. To study the separate and combined effects of soil texture, climate, and grassland cover type on inducing or altering SWR, four sites from different climatic and soil regions were selected: Ciavolo (CI, IT), Csólyospálos (CSP, HU), Pwllpeiran (PW, UK), Sekule (SE, SK). The investigated parameters were the extent (determined by repellency indices RI, RIc and RIm) and persistence (determined by water drop penetration time (WDPT) and water repellency cessation time, WRCT) of SWR, as well as field water (Sw) and ethanol (Se) sorptivity, water sorptivity of hydrophobic soil state (Swh) water sorptivity of nearly wettable soil state (Sww) and field hydraulic conductivity (K). Our findings showed an area of land has a greater likelihood of being water repellent if it has a sandy soil texture and/or a high frequency of prolonged drought events. Water infiltration was positively correlated with all the sorptivities (r = 0.32–0.88), but was mostly negatively correlated with RI (r = – 0.54 at CI), WDPT (r = – 0.47 at CI) and WRCT (r = – 0.58 at CI). The importance of natural and synanthropized vegetation covers with regards to SWR was not coherent; moving to regions having coarser texture or moving to drier climatic zones led to higher risk of SWR conditions. Climate change has been predicted to lead to more frequent extreme weather events and prolonged dry periods across Europe, which will most likely increase the extent of SWR-affected areas and increase the role of SWR in water management of grassland ecosystems. Therefore, there is a need to determine SWR risk zones to prevent decreases in soil moisture content, soil fertility, carbon and nitrogen sink potentials, as well as biomass production of the related agro-ecosystems.

Organic Inputs and Chemical Fertilizer on Carbon Mineralization From Two Ultisols

There are challenges that limit the use of organic inputs for soil fertility management. Amongst them is the limited knowledge of factors that affect rates of decomposition and nutrient release from different organic inputs. A study was conducted on surface soil samples of two Ultisols to determine factors affecting carbon (C) mineralization from selected organic inputs. A loamy sand (LS) from a Kandiustult and a sandy clay loam (SCL) from a Paleustult were used. Fine earth fractions of the soils mixed with organic inputs with and without chemical fertilizer were incubated for 13 weeks and the CO2 evolved was measured. Organic inputs used were biomasses of Cajanus cajan, Tephrosia vogelii, Crotalaria juncea, Mucuna pruriens, a mixture of native grasses and shrubs and composted cattle manure. The latter two inputs are traditionally used by farmers, while the leguminous plants were recommended by scientists. Treatments with chemical fertilizer only, representing the conventional farming practice, and a control with soil alone were included. Addition of organic inputs with or without fertilizer increased total CO2 emissions by 81 to 129% on the LS and by 18 to 34% on the SCL. Adding chemical fertilizer significantly (p < 0.05) increased C mineralization rate constant (k) by 116% on the LS and 48% on the SCL. The mean residence time of organic carbon from treatments grouped by input type followed the order: Control > Traditional > Legumes > Conventional on both soils. In general, the k on the LS was double that on the SCL. The type of organic input, soil texture and application of chemical fertilizer significantly affected C mineralization rates from the soils.

Carbon stocks in riparian buffer systems at sites differing in soil texture, vegetation type and age compared to adjacent agricultural fields in southern Ontario, Canada

In any given watershed, riparian buffer systems (RBSs) can influence terrestrial carbon (C) sequestration and potentially enhance terrestrial C sinks. This study looked at the effects of soil texture, vegetation type and age on C stock sequestration in eight RBSs located within the Grand River Watershed (GRW), southern Ontario, Canada and compared the C stock with adjacent agricultural fields. Soil organic carbon (SOC) stocks on an equivalent mass basis were significantly higher (p<0.05) in mature buffers (192.7 Mg C ha-1) compared to adjacent agricultural fields (corn [Zea mays] –soybean [Glycine max] –wheat [Triticum aestivum] rotation), at 0-30 cm soil depth (88.2 Mg C ha-1), irrespective of soil texture and vegetation type of RBS. Sixty-year old deciduous tree buffers on clayey soils had the highest SOC concentration (5.94 %, p<0.05) at 0-30 cm soil depth while the young six-year old coniferous tree buffers on loamy soil had the lowest SOC concentration (2.87%). In mature deciduous [major species; sugar maple (Acer saccharum) and ash (Fraxinus excelsior)] buffers, biomass C stocks were 247 Mg C ha-1, which is up to two and half times greater than mature coniferous [major species; eastern white cedar (Thuja occidentalis) and white pine (Pinus strobus)] buffers (100 Mg C ha-1). Overall results support that increasing RBS within Ontario watershed areas can enhance C stocks and may contribute to Canada’s climate change mitigation efforts. In the context of riparian areas, deciduous species should be promoted over coniferous species to obtain higher terrestrial C sequestration within Ontario watersheds.

Testing of Nickel Metal Quality Standard at Different Soil Textures With Rice as Indicator Plant

Fertilizers and pesticides application in the agricultural sector provide a significant benefit in agricultural production. However, the use of fertilizers and pesticides continuously can be a harmful effect on the condition of the agricultural environment and the living things around it. Heavy metal pollution from the use of fertilizers and pesticides can cause health problems in humans, animals, and soil. Nickel is a dangerous heavy metal. The purpose of this study was to obtain the value of nickel-metal quality standards in two types of soil texture with rice as an indicator plant. This nickel quality standard testing activity was carried out in 2018 at the Indonesian Agricultural Environment Research Institute. Light textured soil was obtained from Bantul and heavy textured soil from Lamongan and Ngawi. Soil samples were tested for the adsorption of heavy metals using the Langmuir approach. A pot experiment was conducted at the screen house for heavy metals calibration in the soil. The results of the regression of the nickel content in the soil and rice can be seen as the quality standard value. Estimated quality standards in light-textured soils (Bantul) was 1.388 mg kg -1 , heavy-textured soils (Lamongan and Ngawi) was 1.855 mg kg -1 and 1.697 mg kg -1 , respectively. The value of nickel-metal quality standards in the clayey soils are higher than those in the light-textured soils

Soil texture and straw type modulate the chemical structure of residues during four-year decomposition by regulating bacterial and fungal communities

The changes of chemical structure and decomposer community during straw degradation have been inconsistent in previous reports, showing either convergence or divergence of chemical structures or microbial communities among different straw types. Hence the strength of their relationship remains unclear. Here, we directly measured the chemical structures and bacterial and fungal communities of wheat (Triticum aestivum L.) and maize (Zea mays L.) residues after four-year decomposition in three Calcaric Fluvisols that varied in soil textures. Separation of the chemical structures among the six soil-straw combinations (two straw types × three soil textures) were generally coupled with trends in the communities of bacterial and fungal decomposers, but the nature of their coupling differed. In the sand soil, soil texture was the central feature that shaped bacterial and fungal communities for both straw types, driving in turn the convergence of chemical structures of both decomposing straws. In contrast, in the sandy loam and silty clay soils, straw type was the primary regulator of the colonizing bacterial and fungal communities, which resulted in the divergence of chemical structures according to straw type.

The impact of manure and soil texture on antimicrobial resistance gene levels in farmlands and adjacent ditches

Manure application can spread antimicrobial resistance (AMR) from manure to soil and surface water. This study evaluated the role of the soil texture on the dynamics of antimicrobial resistance genes (ARGs) in soils and surrounding surface waters. Six dairy farms with distinct soil textures (clay, sand, and peat) were sampled at different time points after the application of manure, and three representative ARGs sul1, erm(B), and tet(W) were quantified with qPCR. Manuring initially increased levels of erm(B) by 1.5 ± 0.5 log copies/kg of soil and tet(W) by 0.8 ± 0.4 log copies/kg across soil textures, after which levels gradually declined. In surface waters from clay environments, regardless of the ARG, the gene levels initially increased by 2.6 ± 1.6 log copies/L, after which levels gradually declined. The gene decay in soils was strongly dependent on the type of ARG (erm(B) < tet(W) < sul1; half-lives of 7, 11, and 75 days, respectively), while in water, the decay was primarily dependent on the soil texture adjacent to the sampled surface water (clay < peat < sand; half-lives of 2, 6, and 10 days, respectively). Finally, recovery of ARG levels was predicted after 29–42 days. The results thus showed that there was not a complete restoration of ARGs in soils between rounds of manure application. In conclusion, this study demonstrates that rather than showing similar dynamics of decay, factors such as the type of ARG and soil texture drive the ARG persistence in the environment.

Facing the 3rd national land survey (cultivated land quality): soil survey application for soil texture detection based on the high-definition field soil images by using perceptual hashing algorithm (pHash)

Land and soil surveys are of significance to investigate the conditions of land or soil in certain regions. The determination of soil texture type relies on the fundamental laboratory measurement of soil physical granulometric composition. Traditional approaches cannot be used finely in the field. In this paper, the relationship between soil texture and high-resolution field soil images was established. The android application was developed based on the pHash to determine soil texture type in the field investigation. The whole experiment is divided into three sections—preparation of field and standardized soil samples, development of the android application, and the verification of the android application. A total of 37 arable soil samples from different geographical locations with various typical soil texture types were taken during the national land survey in China. Necessary pretreatment with soil samples was done before laboratory analysis. The standardized soil image database was established by uploading standardized soil images. The JAVA language is applied to realize the pHash of the application by IntelliJ IDEA. Physical particle clay and sand content are the chosen indicators to describe the soil granulometric composition quantificationally for the verification part—these two contents of each sample were measured by both the pipette method and the android application more than three times separately—then contrast the testing results to indicate the performance of the android application. Fitting performances of the pipette method and android application reached 89.23% in all group results. The statistical analysis of the difference between the two approaches is not significant (p > 0.05). It is believed that increasing the training number can improve this android application in subsequent studies. Our research changes the idea of determining the soil texture from direct measurements to intermediate comparison, which makes soil texture in-field detection feasible. This android application extends the measure tools by learning the thought of computerized algorithms. The measurement results of the application show accuracy and repeatability during the determination of soil granulometric composition, compared with the ones of the pipette method. Android application based on the perceptual hashing algorithm can be friendly used during land and soil surveys, as well as other field studies.

Characteristics of landsildes and mass wasting in south area of Lumajang District

The study aims to determine the types of landslides and mass wasting, characteristics of landslides and mass wasting, and the factors causing landslides and mass wasting in the southern region of Lumajang Regency. The method used in this study was carried out in three stages, namely determining the coordinates of landslide and mass wasting locations, determining landslide and mass wasting samples, determining landslide and mass wasting types, measuring slope slope, and measuring the dimensions of landslide and mass wasting infiltration. The results obtained were 8 landslide points and mass wasting impacts due to reduced land cover and soil texture type. Differences in soil types, infiltration rates, geology, vegetation, slope and rainfall have no impact on landslides and mass wasting.

Evaluation of Noah-MP Land-Model Uncertainties over Sparsely Vegetated Sites on the Tibet Plateau

The water budget and energy exchange over the Tibetan Plateau (TP) region play an important role on the Asian monsoon. However, it is not well presented in the current land surface models (LSMs). In this study, uncertainties in the Noah with multiparameterization (Noah-MP) LSM are assessed through physics ensemble simulations in three sparsely vegetated sites located in the central TP. The impact of soil organic matter on energy flux and water cycles, along with the influence of uncertainties in precipitation are explored using observations at those sites during the third Tibetan Plateau Experiment from 1August2014 to31July2015. The greatest uncertainties are in the subprocesses of the canopy resistance, soil moisture limiting factors for evaporation, runoff (RNF) and ground water, and surface-layer parameterization. These uncertain subprocesses do not change across the different precipitation datasets. More precipitation can increase the annual total net radiation (Rn), latent heat flux (LH) and RNF, but decrease sensible heat flux (SH). Soil organic matter enlarges the annual total LH by ~26% but lessens the annual total Rn, SH, and RNF by ~7%, 7%, and 39%, respectively. Its effect on the LH and RNF at the Nagqu site, which has a sand soil texture type, is greater than that at the other two sites with sandy loam. This study highlights the importance of precipitation uncertainties and the effect of soil organic matter on the Noah-MP land-model simulations. It provides a guidance to improve the Noah-MP LSM further and hence the land-atmosphere interactions simulated by weather and climate models over the TP region.

Effects of plot length and soil texture on runoff and sediment yield occurring on machine-trafficked soils in a mixed deciduous forest

Runoff decreased significantly in each soil texture group, as plot length increased (2–40 m), whereas sediment yield showed an increasing trend. Runoff and sediment yield were higher in the clayey soil than in the loamy soil texture. An important issue for decreasing the negative impact of ground-based skidding operations on the physical environment is the appropriate drainage of the surface flow away from the skid trail to decrease runoff and subsequent soil loss. Water diversion structures can be used to disperse the water from the trail to the stand but information on adequate spacing is lacking, especially when considering machine-trafficked forest soils. The objective of this study was to quantify the effects of plot length (2, 5, 10, 20, 30, and 40 m) and two soil texture types (clayey and loamy) on runoff and sediment yield in skid trails in a mixed deciduous forest in order to determine the ideal spacing between adjacent water diversion structures. Runoff and sediment yield were measured for 25 rainfall events occurring over a 6-month period. The Pearson correlation was applied to determine the relationship among runoff, sediment yield, selected soil properties, plot length, soil texture, and canopy cover. In each soil texture group, runoff and sediment were plotted with rainfall intensity and plot length by a Gaussian polynomial regression model. Results show that plot length and soil texture significantly affected the amount of runoff and sediment yield. Plot length was positively and significantly correlated with sediment yield and negatively correlated with runoff. The highest runoff was found on the plot length of 2 m under clay soil by 1.49 mm followed by plot length of 5 m with clay by 1.15 mm and plot length of 2 m with loamy soil by 1.03 mm. In both soil texture classes, the runoff decreased significantly, as plot length increased. Likewise, in each plot length tested, the values of runoff were higher in the clayey soil than in the loamy soil texture. Significantly higher values of sediment yield were found in the plot length of 40 m and 30 m under the clayey soil (8.63 g m−2 and 6.84 g m−2) followed by plot length of 40 m under loamy soil (6.15 g m−2). In each soil texture, sediment yield increased significantly, as plot length increased. Additionally, in each plot length, sediment yield was higher in the clayey soil than in the loamy soil texture. The results of this study can be applied to mitigate the environmental impacts of ground-based skidding operations on skid trails and to determine the optimal distance of water diversion structure.

Geoaccumulation and Ecological Risk Indexes in Papaya Cultivation Due to the Presence of Trace Metals

The aim of this research was to evaluate the impact of heavy metals on Maradol papaya cultivation soil, through the geoaccumulation index (Igeo) and the ecological potential risk index (RI). Soil samples from 15 locations in the Cotaxtla municipality of Veracruz, Mexico were tested for pH, soil texture, and concentrations of lead (Pb), chromium (Cr), cadmium (Cd), zinc (Zn), copper (Cu), and organic matter (MO). The pH varied between values of 5.5 ± 0.10 and 7.7 ± 0.22, while the MO varied from 1.57% ± 0.97% to 13.1% ± 1.342%. The type of soil texture represented 48% sandy loam, 40% loam, 8% clay loam, and 4% silt-loam. For heavy metals, average levels were found in the following order Cr (0.695 ± 0.018) &gt; Zn (0.615 ± 0.016) &gt; Pb (0.323 ± 0.012) &gt; Cu (0.983 ± 0.011) &gt; Cd (0.196 ± 0.011) mg kg−1. The Igeo values from 96% of the analyzed sampling points were below zero and were considered uncontaminated. The other 4% of samples, from the Potrerillo1 (PT) site, had Igeo values of 1.13, where the highest concentration of Cd was found, which indicates moderate contamination levels. The RI index at the PT site was in the category of moderate contamination, and the rest of the points correspond to the category of low pollution.

Comparison of interpolation methods for mapping layered soil particle-size fractions and texture in an arid oasis

Soil particle-size (clay, silt, and sand) fractions and texture maps are key inputs for soil physical, chemical, hydrological, agricultural, and ecological models. In the current study, ordinary kriging (OK), simple kriging (SK), and universal kriging (UK) combined with additive, centered, isometric and symmetry log-ratio (ALR, CLR, ILR and SLR) transformations and compositional kriging (CK) are used to map the layered soil texture and to interpolate the soil particle-size fractions based on soil surveys in the middle reaches of Heihe river basin in Northwest China. Results depicted that silt loam is the dominant soil texture in soil profiles of 0–140 cm, accounting for almost 50% in the study area. Layers 3–5 (soil depth of 40–100 cm) show the strongest spatial dependency of soil particle-size fractions as compared to other layers. The results revealed that soil particle-size fractions and soil texture interpolation are dependent on the proper selection of interpolation methods. SLR transformation are better than other log-ratio transformations when interpolating each soil particle-size fraction using different kriging methods. However, for interpolating soil texture types, ALR transformation is the best for OK and SK, and CLR for UK. UK-SLR is recommended to interpolate soil particle-size fractions for all soil layers, and UK-CLR to interpolate the layered soil texture of the study area. More than eighty soil samples should be taken to get a higher soil particle-size fractions/soil texture interpolation precision.

Mineral Soil Texture–Land Cover Dependency on Microwave Dielectric Models in an Arid Environment

In this study, we measured and characterized the relative dielectric constant of mineral soils over the 0.3–3.0 frequency range, and compared our measurements with values of three dielectric constant simulation models (the Wang, Dobson, and Mironov models). The interrelationship between land cover and soil texture with respect to the dielectric constant was also investigated. Topsoil samples (0–10 cm) were collected from homogenous areas based on a land unit map of the study site, located in the Gamsar Plain in northern Iran. The field soil samples were then analyzed in the laboratory using a dielectric probe toolkit to measure the soil dielectric constant. In addition, we analyzed the behaviors of the dielectric constant of the soil samples under a variety of moisture content and soil fraction conditions (after oven-drying the field samples), with the goal of better understanding how these factors affect microwave remote sensing backscattering characteristics. Our laboratory dielectric constant measurements of the real part (ε′) of the frequency dependence between the factors showed the best agreement with the results obtained by the Mironov, Dobson, and Wang models, respectively, but our laboratory measurements of the imaginary part (ε″) did not respond well and showed a higher value in low frequency because of salinity impacts. All data were analyzed by integrating them with other geophysical data in GIS, such as land cover and soil textures. The result of the dielectric constant properties analysis showed that land cover influences the moisture condition, even within the same soil texture type.

Comparison of additive and isometric log-ratio transformations combined with machine learning and regression kriging models for mapping soil particle size fractions

Digital soil mapping approaches relating to the soil particle size fractions (psf) face the challenge around how to establish the statistical or geostatistical models from large sets of environmental variables, especially in a situation with sparse soil profile data. Recently, many machine learning (ML) models have sprung up with advantages over statistical models. However, few studies focused on the comprehensive comparative analyses between ML and geostatistical models in the soil psf mapping. And the exploration of optimal combination of data transformation and model simulation was even less. Therefore, two transformed methods such as additive log-ratio (ALR) and isometric log-ratio (ILR) transformations combine with two ML models such as boosted regression tree (BRT), random forest (RF) and a classic geostatistical model of regression kriging (RK) were implemented to map soil psf in the Heihe River basin, China. A total of 640 samples and thirteen scorpan factors were collected and used for the comprehensive comparative analysis. Results showed that the scorpan factors such as temperature, precipitation, elevation, soil type, soil organic carbon, vegetation types and normalized difference vegetation index had important impacts on the soil psf mapping. ILR transformation was better than ALR transformation with advantage of improving stability of data distributions and ML models could also improve the mapping performance in comparison with RK models for better handling candidate factors. For these ML models, the RF models had better accuracy performance than the BRT models. In contrast, ILR transformation combined with RF model (ILR_RF) had the best performance, with the lowest root mean square error values (sand, 15.35%; silt, 14.20%; and clay, 6.66%), Aitchison distance value (0.86), standardized residual sum of squares value (0.60), and the highest concordance correlation coefficient value (0.73) and coefficient of determination value (56.69%) for clay content. In addition, ILR_RF had a relatively higher right ratio of soil texture type (68.44%) and better predict performance for most soil texture types. The predicted maps generated from ILR_RF presented more reasonable and smoother transitions. In the future, more ML models should be explored and more variables related to soil psf should be introduced into the models to improve the predictive performance.

Arbuscular Mycorrhizal Fungi Colonization in the Rhizosphere of Aspilia pruliseta Schweif. ext Schweif in the Semiarid Eastern Kenya

The use of arbuscular mycorrhizal fungi (AMF) to enhance soil phosphate uptake is a biological technique considered to cure phosphate deficiency in soils. This study investigated association of Aspilia pruliseta Schweif shrub with AMF in Kenya. The study aims at profiling a tropical shrub with multiple ecological benefits that could reduce addition of chemical phosphatic fertilizer into the soil and reverse negative consequences of eutrophication. Sampling was purposive to have areas with or without Aspilia pruliseta vegetation growing. A small amount (10 g) of the soil from 27 composite samples was used for spore count determination and a similar amount for next generation sequencing. Spore counts varied significantly among soil textural types, sample locations, and soil depth. Sandy loam had the highest spore counts with a mean average of 404 spores. The spore count decreased significantly ( P &lt; .05) with the depth of soil from a mean of 514 spores to 185 along the rhizosphere. The intensity of spore morphotypes was significantly higher at P &lt; .05 for soils whose vegetation was covered with Aspilia pruliseta than those without. Aspilia pruliseta vegetation used together with sandy loam soil could culture commercial mycorrhiza fungi production for use in agrisystems.