Soil Sand Content Research Articles

Soil chemical properties and their relationship with phytonematode populations inside and outside patches of soybean fields

Phytonematodes cause great losses to agricultural production. The magnitude of their economic impact is directly related to management practices, with the hypothesis that high nematode populations can also be found inside and outside symptomatic patches, and that they correlate with soil properties. This study examined the relationship of soil chemical properties and texture with phytonematode populations inside and outside patches with symptoms of nematode damage in soybean fields. Soil and root samples were collected from commercial fields in Paraguay. A total of 9 nematode parameters and 12 soil variables were evaluated. Statistical analyses were performed initially between nematode parameters and then between nematode parameters and soil properties. Pratylenchus spp. were identified in 95% of root samples. Principal component analysis showed that Pratylenchus spp., nematode eggs, and Meloidogyne spp. were more strongly correlated with roots from inside patches. Helicotylenchus spp., Heterodera glycines, and cysts were more abundant in soil samples, both from inside and outside patches. Pratylenchus spp. was positively correlated with soil sand content and potential acidity and negatively with sum of bases, micronutrients, and potassium, confirming the greater activity of this nematode in low-fertility sandy soils. No significant correlations were found between soil properties and patch type (inside or outside). It concludes that the soil properties interfere in the nematode population, especially in the Pratylenchus.

Assessment of potential ecological risk index based on heavy metal elements for organic farming in micro catchments under humid ecological condition

Soil pollution, influenced by both the natural and anthropogenic factors, significantly reduces environmental quality. This research was carried out in some micro catchments located on Ordu province of Black Sea Region-Turkey in order to determine potential ecological risk index based on heavy metal elements (HMs) for organic farming. For this purpose, 166 soil samples (0-20 cm) were taken from the study area and some physical and chemical and HM concentrations (Cd, Cu, Cr, Ni, Pb and Zn) analysis were done. In this study, it was determined; i-) some physical and chemical properties of catchments’ soils, ii-) HM contents and the correlation relation between physico-chemical properties of soil and HM concentrations and iii-) potential ecological risk index (PERI). PERI was calculated using the data obtained to evaluate the environmental risks of HMs in the region. The results showed that Cu concentration in 3%, Cr in 0.6% and Ni in 4.8% of the soil samples exceeded the threshold levels whereas, the concentrations of other HMs were lower than the critical values. Statistically, it was also found significantly positive relationships between sand content and Cu of soils whereas, it was determined significantly negative relationships between EC and Cu. In addition, according to the obtained PERI results, while 54% of total soil samples were low while, 42% of them were moderate class. Only 4% of them were classified as significant ecological risk level. Moreover, according to mean potential ecological risk index of these HMs, it can be ordered as Cd>Pb>Cu>Ni> Zn>Cr.

Global convergence in correlations among soil properties.

The correlations among major soil properties at a global scale are essential for explaining the global convergence of ecological processes in terrestrial ecosystems but have never been assessed. In this study, a global soil database was analyzed to determine whether correlations among soil properties were consistent and how such correlations varied among continents and land use types. Across the entire dataset, the electrical conductivity of soils increased significantly with increasing pH; additionally, the total nitrogen and cation exchange capacity increased significantly with increasing organic carbon content, while the organic carbon content and cation exchange capacity decreased significantly with increasing sand content in soil. The correlations between paired soil properties were consistent among continents and land use types. The slopes of the relationships, however, varied significantly by continent and land use type. The results indicated a global convergence of correlations among soil properties and variation in the slopes of specific relationships between paired soil properties among continents and land use types. Such consistent global correlations and different slopes of specific correlations can have important implications in explaining the global patterns of biogeochemical processes and can provide some basis for linking soil resources with ecological processes on a global scale. Keywords: continent, land use, organic carbon, electricity, pH, CEC DOI: 10.25165/j.ijabe.20201303.4547 Citation: Xie B C, Zhang C X, Wang G D, Xie Y G. Global convergence in correlations among soil properties. Int J Agric & Biol Eng, 2020; 13(3): 108–116.

Discussion on the Method of Measuring Sand Content

The determination of sand content is related to the accuracy of soil and water loss measurement. With the development of science and technology, there are many advanced sediment content measurement technologies. However, due to the differences and complexity of soil conditions in various regions, The applicability of this method for sand content measurement needs to be verified. This article explores the method for measuring sand content in red soil on the conditions of simulated rainfall and runoff experiments, and verifies the measurement accuracy of water samples with different sediment contents using the gravimetric method. The results show that when the sediment content is small, the error of the specific gravity method is large, and its accuracy increases with the increase of the sediment content, and the accuracy is the highest when the sediment content is about 40g/L. In addition, the fitting curve is used in this paper. The sediment content is measured and compared with the drying method. The experimental results show that the measurement accuracy is higher than the specific gravity method, but the results are different from the drying method.

Soil reconstruction after mining fails to restore soil function in an Australian arid woodland

The biogeochemical properties of soils drive ecosystem function and vegetation dynamics, and hence soil restoration after mining should aim to reinstate the soil properties and hydrological dynamics of remnant ecosystems. The aim of this study is to assess soil structure in two vegetation types in an arid ecosystem, and to understand how these soil properties compare to a reconstructed soil profile after mining. In an arid ecosystem in southeast Australia, soil samples were collected at five depths (to 105 cm) from remnant woodland and shrubland sites, and sites either disturbed or totally reconstructed after mining. We assessed soil physico‐chemical properties and microbial activity. Soils in the remnant arid ecosystem had coarse‐textured topsoils that overlay clay horizons, which allows water to infiltrate and avoid evaporation, but also slows drainage to deeper horizons. Conversely, reconstructed soils had high sand content at subsoil horizons and high bulk density and compaction at surface layers (0–20 cm). Reconstructed soils had topsoils with higher pH and electrical conductivity. The reconstructed soils did not show increased microbial activity with time since restoration. Overall, the reconstructed soil horizons were not organized in a way that allowed rainfall infiltration and water storage, as is imperative to arid‐zone ecosystem function. Future restoration efforts in arid ecosystems should focus on increasing sand content of soils near the surface, to reduce evaporative water loss and improve soil quality and plant health.

The wind erodibility in the newly emerged surfaces of Urmia Playa Lake and adjacent agricultural lands and its determining factors

Despite the great extent of Urmia Playa Lake (UPL), researchers have rarely ever studied the development of playa surfaces and their vulnerability to dust emission. Therefore, we aimed the current research to study the formation of UPL surfaces and how their physicochemical, mineralogical and geomorphological characteristics affect their susceptibility to wind erosion. An area of 41 km2 was chosen including lands from UPL and adjacent Agricultural Lands (AL). Different playa surfaces were identified on different geomorphic surfaces and mapped using Landsat images. Later, 75 soil samples from depth of 0–5 cm of different map units were collected and subjected to physicochemical analysis. Soil Erodible Fraction (EF) was also measured as an index for the wind erodibility of the examined soil surfaces. X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) analysis of soil samples from three playa surfaces with significantly different EF values were also conducted. Major reasons for the development of different playa surfaces were found to be basically related to geomorphic surfaces on which they have developed, size and mineralogical composition of the sediments as well as the landscape position and depth to the groundwater. Statistical analysis of EF of different playa surfaces and AL showed that Salt Crusts (SC) had the lowest mean EF value due to the formation of a thin layer of salt on its surface as it has developed on low stand geomorphic surface being fine-textured by nature and rich in Na, Mg and Cl ions. Abandoned Agricultural lands (AA) and AL had the highest mean EF values. High sand content of soils with anthropogenic origin along with conventional tillage practices resulting in soil organic matter loss and over grazing were the major reasons of their high EF. Therefore, these surfaces need to be monitored carefully and to be of high priority of conservation and dust control programs in the region.

Soil structure and nutrient contents in underground fissures in a rock-mantled slope in the karst rocky desertification area

Near-surface karst fissures are filled with soils. These soils are often derived from the erosion and transport of surface soil but have different properties than the surface soil in karst rocky desertification regions. This study was undertaken to determine the soil structure and nutrient contents in underground fissures with different grades of rocky desertification (no, potential, mild, moderate and severe). Based on field surveys, near-surface karst fissures were selected in a typical karst plateau area. Soil particle compositions, particularly nutrient characteristics, were determined through field sampling and laboratory experiments. The results indicated that the higher the rock desertification grade was, the higher the soil sand (0.02–2 mm) content and the lower the clay (< 0.002 mm) content. The soil in both limestone and dolomite fissures was basically neutral to weakly alkaline. The surface soil in dolomite fissures presented a higher soil organic matter content than that in limestone fissures, but the opposite was true for the subsurface soil. From the surface to the lower layer, the total nitrogen content generally decreased, and the total phosphorus content generally decreased in dolomite fissures but exhibited a more complex pattern in limestone fissures. The total phosphorus content of the surface soil was higher than that of the subsurface soil, but the total potassium content was lower. There was no significant difference among different soil layers. Near-surface fissures are a good place to promote vegetation restoration projects, because they provide good soil structure and nutritional conditions for plant growth.

A modified calculation model for the saturation-dependent thermal conductivity of fine-textured soils

Thermal conductivity of soils is an important parameter in heat and water transfer analysis of soils. Here, a modified model was proposed to calculate the saturation-dependent thermal conductivity of fine-textured soils from the completely dry condition to the full water saturation. In the study, we developed a new parallel-series model for calculating the thermal conductivity of soils at the completely dry condition with a weighting parameter. The weighting parameter can be calculated using the ratio of the thermal conductivity of air to the thermal conductivity of solid grains. We also proposed a simplified equation to calculate the parameter a of the model proposed by Bi et al. using sand content and thermal conductivity of soils at the full water saturation. Substituting the new parallel-series model and the simplified equation for the parameter a into the model proposed by Bi et al., yielding the modified model. The modified model was evaluated with 14 soil samples. Results show that the modified model could well estimate the thermal conductivity from the completely dry condition to the full water saturation.

Modeling Experiments for Evaluating the Effects of Trees, Increasing Temperature, and Soil Texture on Carbon Stocks in Agroforestry Systems in Kerala, India

Research Highlights: Agroforestry systems in the humid tropics have the potential for high rates of production and large accumulations of carbon in plant biomass and soils and, thus, may play an important role in the global C cycle. Multiple factors can influence C sequestration, making it difficult to discern the effect of a single factor. We used a modeling approach to evaluate the relative effects of individual factors on C stocks in three agricultural systems in Kerala, India. Background and Objectives: Factors such as plant growth form, management, climate warming, and soil texture can drive differences in C storage among cropping systems, but the relationships among these factors and their effects are complex. Our objective was to use CENTURY, a process-based model of plant–soil nutrient cycling, in an experimental mode to evaluate the effects of individual factors on C stocks in soil and biomass in monocultures (annuals or trees) and agroforestry systems. Materials and Methods: We parameterized the model for this region, then conducted simulations to investigate the effects on C stocks of four experimental scenarios: (1) change in growth form; (2) change in tree species; (3) increase in temperature above 20-year means; and (4) differences in soil texture. We compared the models with measured changes in soil C after eight years. Results: Simulated soil C stocks were influenced by all factors: growth form; lignin in tree tissues; increasing temperature; and soil texture. However, increasing temperature and soil sand content had relatively small effects on biomass C. Conclusions: Inclusion of trees with traits that promoted C sequestration such as lignin content, along with the use of best management practices, resulted in the greatest C storage among the simulated agricultural systems. Greater use and better management of trees with high C-storage potential can thus provide a low-cost means for mitigation of climate warming.

Effects of soil grading and sand content on soil-cement properties

The effect of soil-cement characteristics, unconfined compressive strength (UCS), dry density, and water absorption on the soil grading and sand content of six groups (natural soil, ≤ 2 mm, ≤ 1 mm, ≤ 0.5 mm, ≤ 0.25 mm, and ≤ 0.075 mm) of soil-cement block was studied. The results showed that the characteristics of soil-cement mixed with sand were influenced by soil grading. Better characteristics of soil-cement soil were obtained when the soil particle sizes of soil-cement were less than 0.075 mm of mixed sand. Every soil particle size has optimal sand content. Results showed that the optimal sand content of natural soil is 40%, whereas those of other soil particle sizes are all 55%. The results also showed that the UCS of 28-day ages is 1.79 times that of natural soil for soil-cement mixed with sand of ≤ 0.075 mm particle group, whose water absorption is 50% that of natural soil as the optimal sand content. Finally, the study of clay content showed that there exists an optimal clay content for various size groups, namely, 9.12%, 7.06%, 8.08%, 9.05%, 11.36%, and 13.60% for natural soil, ≤ 2 mm, ≤ 1 mm, ≤ 0.5 mm, ≤ 0.25 mm, and ≤ 0.075 mm, respectively.

Distribution of phosphorus fractions with different plant availability in German forest soils and their relationship with common soil properties and foliar P contents

Abstract. Repeated, grid-based forest soil inventories such as the National Forest Soil Inventory of Germany (NFSI) aim, among other things, at detecting changes in soil properties and plant nutrition. In these types of inventories, the only information on soil phosphorus (P) is commonly the total P content. However, total P content in mineral soils of forests is usually not a meaningful variable with respect to predicting the availability of P to trees. Here we tested a modified sequential P extraction according to Hedley (1982) to determine the distribution of different plant-available P fractions in soil samples (at depths of 0–5 and 10–30 cm) from 146 NFSI sites, encompassing a wide variety of soil conditions. In addition, we analyzed relationships between these P fractions and common soil properties such as pH, texture, and soil organic carbon content (SOC). The total P content among our samples ranged from approximately 60 to 2800 mg kg−1. The labile, moderately labile, and stable P fractions contributed to 27 %, 51 %, and 22 % of the total P content, respectively, at a depth of 0–5 cm. At a depth of 10–30 cm, the labile P fractions decreased to 15 %, whereas the stable P fractions increased to 30 %. These changes with depth were accompanied by a decrease in the organic P fractions. High P contents were related to high pH values. While the labile Hedley P pool increased with decreasing pH in absolute and relative terms, the stable Hedley P pool decreased in absolute and relative terms. Increasing SOC in soils led to significant increases in all Hedley P pools and in total P. In sandy soils, the P content across all fractions was lower than in other soil texture types. Multiple linear regression models indicated that Hedley P pools and P fractions were moderately well related to soil properties (with r2 values that were mostly above 0.5), and that the sand content of soils had the strongest influence. Foliar P contents in Pinus sylvestris were reasonably well explained by the labile and moderately labile P pool (r2 = 0.67) but not so for Picea abies and Fagus sylvatica. Foliar P contents in all three species could not be related to specific Hedley P pools. Our study indicates that soil properties such as pH, SOC content, and soil texture may be used to predict certain soil Hedley P pools with different plant availability on the basis of large soil inventories. However, the foliar P contents of tree species cannot be sufficiently well predicted by the soil variables considered here.

Productivity does not correlate with species and functional diversity in Australian reforestation plantings across a wide climate gradient

AbstractAimUnderstanding biodiversity–ecosystem function (BEF) relationships in forest systems is crucial for effective forest management and restoration, yet testing these relationships is often limited by biased diversity patterns in forestry plantings (biased towards commercially valuable species) and uncontrollable diversity in mature natural forests. Multispecies reforestation plantings present a valuable opportunity to investigate BEF relationships in woody systems, especially across large environmental gradients.LocationReforestation plantings across the arable region of Australia.Time period1951–2012.Major taxa studiedThree hundred and sixty‐four woody plant species.MethodsWe examined relationships between productivity and diversity using inventory data from 977 plots in 386 multispecies reforestation plantings. Diversity was estimated using observed species richness and three functional diversity indices calculated from four functional traits: specific leaf area, wood density, seed mass and maximum attainable height. We modelled how plot‐level biomass accumulation (a productivity proxy) correlated with these diversity indices, as well as age since planting, plant density and three environmental variables: solar radiation, moisture availability and soil sand content. These models were fitted across Australia and, separately, within eight groups of plantings with similar environmental conditions.ResultsWe found no correlation between diversity and productivity, regardless of the diversity metric or spatial scale used (continent‐wide or within environment groups). Instead, productivity was best explained by local environmental conditions and plant density.Main conclusionsA positive relationship between diversity and productivity was not evident in planted forests across a wide range of Australian woodland and forest systems, at least in the first few decades of growth. Our findings suggest that the positive relationship between diversity and productivity commonly reported in experimental settings should not be assumed for all systems and conditions.

Moderate grazing increases the abundance of soil methane-oxidizing bacteria and CH4 uptake rate in a typical steppe of Inner Mongolia, China.

Microbial oxidation is the only biological sink of atmospheric methane (CH4). It is essential to understand the variation of CH4 fluxes among different grassland use types for developing low-emission management system. Here, we measured the CH4 flux and the soil methane-oxidizing bacteria abundance in a typical steppe under grazing, mowing and fencing management in central Inner Mongolia, with the aims to determine the effects of these grassland use types on CH4 flux, and to test the hypothesis that pmoA functional gene abundance regulates CH4 fluxes. The measurements were conducted on the experimental grassland that had experienced four grassland use treatments over five years. The treatments were whole growing season grazing from May to September (T1), spring and summer grazing (twice in May and July)(T2), autumn mowing (T3) and enclosure (T0). We measured CH4 flux using static chamber method, and quantified the abundance of pmoA functional genes using molecular techniques. Moreover, we measured plant biomass and soil physicochemical properties. The results showed that moderate grazing significantly enhanced CH4 uptake rate and the methane-oxidizing bacteria abundance (i.e., the pmoA gene copy number per gram of dry soil). The pmoA gene copy number ranged from 6.9×104 to 3.9×105 per gram of dry soil in growing season. The CH4 uptake rate was (68.21±3.01) μg·m-2·h-1 under T1, which was 22.1%, 37.5% and 30.9% higher than that under T2, T3 or T0 , respectively. The CH4 uptake rate was positively correlated with abundance of CH4 oxidizing bacteria and soil sand content, but negatively correlated with soil silt content, soil moisture, NH4+-N and NO3--N content, and plant biomass. These results suggested that the steppe ecosystem is a CH4 sink under all land-use types in central Inner Mongolia, and that moderate grazing would enhance methane-oxidizing bacteria abundance and CH4 uptake by improving soil sand content, reducing soil mineral nitrogen content and plant production in the typical steppe ecosystem. These results were of significance for the development of low-emission grassland management system.

Multifunctionality debt in global drylands linked to past biome and climate.

Past vegetation and climatic conditions are known to influence current biodiversity patterns. However, whether their legacy effects affect the provision of multiple ecosystem functions, that is, multifunctionality, remains largely unknown. Here we analyzed soil nutrient stocks and their transformation rates in 236 drylands from six continents to evaluate the associations between current levels of multifunctionality and legacy effects of theLast Glacial Maximum (LGM) desert biome distribution and climate. We found that past desert distribution and temperature legacy, defined as increasing temperature from LGM, were negatively correlated with contemporary multifunctionality even after accounting for predictors such as current climate, soil texture, plant species richness, and site topography. Ecosystems that have been deserts since the LGM had up to 30% lower contemporary multifunctionality compared with those that were nondeserts during the LGM. In addition, ecosystems that experienced higher warming rates since the LGM had lower contemporary multifunctionality than those suffering lower warming rates, with a ~9% reduction per extra degree Celsius. Past desert distribution and temperature legacies had direct negative effects, while temperature legacy also had indirect (via soil sand content) negative effects on multifunctionality. Our results indicate that past biome and climatic conditions have left a strong "functionality debt" in global drylands. They also suggest that ongoing warming and expansion of desert areas may leave a strong fingerprint in the future functioning of dryland ecosystems worldwide that needs to be considered when establishing management actions aiming to combat land degradation and desertification.

Soil Organic Carbon Distribution and Components in Different Plant Communities Along a Water Table Gradient in the Huixian Karst Wetland in Guilin

In order to reveal the effect of vegetation type and soil physicochemical properties on the distribution of soil organic carbon and its components, a field survey was carried out on nine different plant communities along a water table gradient in the Huixian wetland with samples of soil at 0-10 cm, 10-20 cm, and 20-30 cm in depth. The soil organic carbon (SOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), easily oxidized organic carbon (EOC), dissolved organic carbon (DOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) were measured. The correlations among soil organic carbon components and soil physicochemical properties were also examined. The results showed that:① The average proportion of LFOC and HFOC to SOC at 0-30 cm soil depth was 11.10% and 88.90%, respectively. The distribution ratio of the heavy component was much higher than of the light component in soils. ② The content of SOC, DOC, EOC, POC, and MBC (except in the Panicum repens community) and the values of DOC/SOC, EOC/SOC, and POC/SOC all decreased with increase of the soil depth. ③ Among the nine different plant communities, the contents of SOC, LFOC, HFOC, MBC, DOC, EOC, and POC of Cladium chinense were significantly higher than for other communities in same soil layers. ④ There were significantly positive correlations among soil organic carbon components (SOC) and soil total nitrogen (TN). LFOC, HFOC, DOC, and POC were also positively correlated with soil pH. The soil bulk density was significantly negative correlated with LFOC, HFOC, DOC, EOC, and POC, and the content of clay was also negatively correlated with LFOC, HFOC, DOC, POC, and MBC. ⑤ Path analysis showed that TN, soil pH, soil sand content, and soil water content (SWC) has indirect effects on HFOC by influencing other soil factors. Soil TN had strong positive effects on EOC, DOC, and POC, and SWC also has the largest direct negative effect on MBC. This showed that there were close interactions between soil physicochemical properties and soil organic carbon components. This study may provide a reference base for sustainable development and scientific predictions regarding the Huixian Karst wetland.

Changes in soil organic matter and soil humic substances following the afforestation of former agricultural lands in the boreal-nemoral ecotone (Latvia)

Abandonment of agricultural land is a widespread process in Northern Europe, which is associated with changes in content and distribution of organic matter in soil, including C stocks. There is insufficient information on changes in soil organic matter properties during afforestation of these lands. The aim of the study was to determine and describe the influence of afforestation on organic carbon (CORG) content and properties of soil organic matter (SOM) in mineral topsoil in the boreo-nemoral ecotone in Latvia. We studied soils in 4 model territories that represented abandoned farmlands and territories where mixed or coniferous forests were established at different times on former agricultural lands. Soil samples from mineral topsoil (genetic A or AE horizons) were obtained during the summer period in two model territories (11 sampling sites) with loamy texture soil, and two model territories with higher sand content of soil (9 sampling sites). The soil samples were analysed for organic carbon (CORG) and total nitrogen (NTOT) content. Soil alkali (NaOH) extracts were used to determine properties of soil organic matter – alkali extractable carbon (CHS) content, composition and humification index (HIX) of soil humic substances (HS) and spectroscopic (UV–Vis, fluorescence emission spectra, FTIR) properties of the soil humic acid fraction (HA). CORG content gradually increased with forest land age. Gradual decrease in the humic acid (HA) to fulvic acid (FA) ratio (CHA/CFA) after land-use change indicated that SOM was transported to mineral topsoil mainly through leaching of the soluble FA fraction. FTIR spectra revealed that the HA fraction from all studied soils had relatively similar chemical structure and that SOM in mineral topsoil was degraded to relatively similar compounds. However, HAs extracted from forest soils had higher abundance of –OH groups, more aromatic CC structures, and relatively lower abundance of NH groups in amides. UV–Vis and fluorescence emission spectroscopic analysis of HA fraction along with PCA analysis showed that soil properties also may have affected chemical properties of soil organic matter during the afforestation. Molecular weight of the HA fraction gradually increased with age of the forest land in sandy soils while there were no significant changes in sandy loam soils. Fluorescence emission analysis also showed that HAs extracted from EAh horizons in Podzol and Anthrosol soils in old forest lands had the highest aromaticity.The results suggest that sandy soils have the most dynamic changes in SOM properties after afforestation. Therefore, further studies should focus on whether and how these changes affect SOM fate in soils, physical stabilisation with mineral soil and SOM leaching into subsoil.

Variation in soil hydrological properties on shady and sunny slopes in the permafrost region, Qinghai–Tibetan Plateau

Soil hydrological properties not only directly influenced soil water content, evapotranspiration, infiltration, and runoff, but also made these factors of concern in arid and semi-arid regions. Prior research has focused on the temporal and spatial variation in soil hydrological properties and the impacts of climate change, ecosystem changes over time or human activities on soil hydrological properties. However, studies conducted on the differences in soil hydrological properties between shady and sunny slopes have seldom been conducted, especially in the permafrost region of the Qinghai–Tibetan Plateau. To investigate the variation in soil hydrological properties on shady and sunny slopes, we chose the Zuomaokongqu watershed of Fenghuo Mountain, which is located on the Qinghai–Tibetan Plateau, as the study area. Three experimental sites were selected in the study area, and the distance between experimental sites was 100 m. Based on the differences in altitude and vegetation coverage, five sunny slope sample points and three shady slope sample points were selected in each experimental site. At each of these sample points, the soil water content, soil-saturated conductivity, soil water-retention curve, soil physico-chemical properties, aboveground biomass, and underground biomass were examined in the top 0–50 cm of the active layer. The results showed that the soil hydrological properties of shady slopes differed significantly from those of sunny slopes. The soil water content of sunny slopes was 20.9% less than that of shady slopes. The soil-saturated water content of sunny slopes was 12.2% less than that of shady slopes. The soil water content of sunny slopes at − 0.3 Mpa and − 0.7 Mpa matric potential was 23.5% and 21.4% less than that of shady slopes, respectively. It was indicated that the soil water-retention capacity of sunny slopes was lower than that of shady slopes. However, the soil-saturated conductivity of sunny slopes was 84.5% larger than that of shady slopes and exceeded the range of soil-saturated conductivity, which was useful for plant growth. Meanwhile, the vegetation coverage on sunny slopes was lower than that on shady slopes, but the soil sand content showed the opposite relationship. Pearson’s coefficient analysis results showed that vegetation coverage and soil desertification, which are affected by permafrost degradation, were the main factors influencing soil hydrological properties on shady and sunny slopes. These results will help determine appropriate hydraulic parameters for hydrological models in mountain areas.

Analysis of Factors Influencing Stability of Overlying Soil Layer on Thin Bedrock Based on Crack Development‐Closure Test

The water‐blocking properties of the clay layer at the bottom of the Cenozoic overburden in China are an important factor influencing the safety of thin bedrock coal seam mining. Clay has remolding properties that are unlike the nonreversible characteristics of cracks in brittle rock, and failure cracks in clay can reclose or continue to expand under the influence of different external factors. In this work, the soil layer on top of thin bedrock is the research object, and the influences of the particle composition, water content, soil layer thickness, and crack width on the crack development‐closure state of soil layer are analyzed by the orthogonal test method. Visual analysis shows that the order of influence of each factor on the stability of soil layer is the crack width, particle composition, soil layer thickness, and water content. The stability of soil layer decreases with increasing crack width and sand content and decreasing soil layer thickness; in addition, soil layer stability decreases first and then increases with increasing water content. Further variance analysis shows that the crack width and particle composition are key factors that impact the stability of soil layer and that the soil layer thickness has some influence, while the water content has little effect on the stability of soil layer. In addition, the crack will reclose when the sand content in soil is less than 50% and the crack width is less than or equal to 1.0 mm, and the soil layer is prone to further failure when the sand content in soil is more than 50% and the crack width is greater than or equal to 3.0 mm; when the soil layer thickness is 15.0 cm, its stability is better than when the soil layer thickness is 10.0 cm or 5.0 cm.

Effect of ground water level on the release of carbon, nitrogen and phosphorus during decomposition of Carex. cinerascens Kükenth in the typical seasonal floodplain in dry season

From November 2016 to April 2017, the decomposition of Carex. cinerascens Kükenth litter along the natural gradients of groundwater level at Poyang Lake wetland beach were simulated using litterbag technique. The depth of the underground water table of the G-L was −25 to −50 cm, while those of G-ML, G-MH and G-H ranged from −15 to −25 cm, −5 to −15 cm, and −5 to 5, respectively. Additionally, the dry weight loss rate increased gradually with increasing days, with that of G-H being highest, followed by G-MH, G-ML and G-L. The decomposition rate of the four gradients increased rapidly to day 30, then decreased slowly until stabilizing. Additionally, the decomposition rate was highest in G-H, followed by G-MH, G-ML and G-L. The Olson negative exponential model could simulate the decomposition good and predicted the time required for 50% decomposition of the G-H, G-MH, G-ML and G-L gradients was about 166, 197, 205 and 247 days, respectively, while required for 95% was about 1.97, 2.23, 2.43 and 2.92 years, respectively. The overall trend in the relative return index of carbon, nitrogen and phosphorus increased with increasing decomposition days, and the order was G-H > G-MH > G-ML > G-L. Differences in soil pH, bulk density, soil total nitrogen, soil organic matter, microbial biomass carbon and soil sand content in the decomposed environment due to groundwater had a significant impact on decomposition and nutrient release. The relative return index of carbon was significantly positively correlated with soil pH, but significantly negatively correlated with soil bulk density, soil nitrogen content, microbial biomass nitrogen and soil organic matter. The above results show that groundwater is the key factor influencing litter decomposition in Poyang Lake wetland during the dry season, with higher groundwater levels promoting the decomposition.

Occurrence and distribution of vermiform plant-parasitic nematodes and the relationship with soil factors in field pea (Pisum sativum) in North Dakota, USA

Summary Plant-parasitic nematodes restrict crop growth and cause yield loss in field pea (dry edible pea). A 4-year survey of commercial pea fields was conducted in North Dakota, one of the leading producers of field pea in the USA, to investigate nematode distribution, prevalence, abundance and association with soil properties. Beginning in 2014, a total of 243 soil samples were collected from 16 counties, and soil properties of 115 samples were analysed to determine the association of nematodes with soil factors (texture, organic matter, nutrients). The plant-parasitic nematode genera, Paratylenchus (absolute frequency = 58-100%; mean density = 470-1550 (200 g soil)−1; greatest density = 7114 (200 g soil)−1) and Tylenchorhynchus (30-80%; 61-261; 1980, respectively), were the most frequent and widely distributed. Pratylenchus and Helicotylenchus were identified in one-third of the counties surveyed with mean densities ranging from 43 to 224 and 36 to 206 (200 g soil)−1, respectively. Xiphinema was found relatively frequently but at low densities. Hoplolaimus and Paratrichodorus were rarely detected at lower densities. Canonical correspondence analysis revealed that soil factors explained 19% of the total variance of nematode genera abundance. The relationship between nematode abundance and soil sand content and pH was significant, while clay, silt, organic matter and nutrients were not significantly related to nematode abundance. This is the first multi-year study investigating nematodes associated with field peas and their relationship with soil factors in a major field pea production region of the USA.