Mean Soil Research Articles

Fragmentation of soil-root complexes in sloping landscapes during tillage and soil translocation

It is well known that roots play a significant role in reducing water erosion in soil, yet few studies have reported the influence of crop roots on soil translocation induced by tillage in sloping fields. To examine the relationship between soil-root complexes (i.e., complexes of wheat roots and soil) and soil redistribution caused by tillage, a series of tillage experiments were carried out on bare soil and areas of wheat sown by drilling ( DS ) and nesting ( NS) using nine slopes with gradients varying from 0.19 to 0.32 m m −1 . The magnetic tracing technique was used to determine soil translocation rates under hoeing tillage in sloping landscapes in response to soil-root complexes and bare soil. The results indicated that mean displacement distance for DS and NS in the downslope direction was 0.15 m and 0.16 m, respectively. This was much shorter than that of bare soil which was 0.26 m. Mean tillage erosion rates ranged from 14.58 to 19.15 Mg ha −1 per tillage pass for DS and 13.90 –21.10 Mg ha −1 per tillage pass for NS , while reached 31.23–36.31 Mg ha −1 per tillage pass for bare soil. Tillage transport coefficients ( k 3 and k 4 ) were 6.31 and 106.46 kg m −1 per tillage pass for DS , 6.58 and 118.68 kg m −1 per tillage pass for NS , and 28.12 and 151.07 kg m −1 per tillage pass for bare soil, respectively. A significant difference in cohesive force ( C ) was found between DS ( NS ) and bare soil ( P < 0.05), thereby resulting in an increase in the soil shear strength of soil-root complexes. Compared with those of bare soil, the soil fractal dimension of soil-root complexes decreased significantly due to an increase in the percentage of coarse clods (>100 and 100–80 mm) and a decrease in the percentage of fine clods (50–20 and < 20 mm). Mean soil displacement distance caused by tillage displayed a negative relationship with C and wheat root traits (the root density, the root length density, and the root area ratio) within the hilly landscape of soil-root complexes ( P < 0.05), implying that wheat roots played a crucial part in soil translocation and soil fragmentation during hoeing tillage. Our study revealed that soil-root complexes markedly reduce the soil downslope transfer process during tillage and prevent the break-up of large clods by tillage implements on sloping farmland. • Wheat root attenuated the mechanical breakage of clods during tillage operation. • Root systems increase soil shear strength and reduce fragmentation of soil clods. • Displacement distance for soil-root complexes was smaller than that for bare soil. • Tillage erosion decreased with increasing structure stability and cohesive force.

Effects of Conservation Tillage on Soil Properties and Maize Yield in Karst Regions, Southwest China

Karst rocky desertification associated with human disturbance is one of the most serious eco-environmental problems, threatening the sustainable development of agriculture in southwestern China. In the current study, the practice of conservation tillage as one of the best ways of reducing the constraints is addressed. During a two-year trial (2014–2015), the effects of no tillage with straw cover (NT) and traditional tillage (TT) on soil properties and maize yields were investigated in karst regions, Southwest China. The results showed that the trial with NT increased soil moisture content by 3%, while decreasing soil bulk density by 7% in the top 30 cm compared with TT. In 2014, within 0–30 cm of soil depth, total nitrogen under NT treatment was 5% higher than that under TT treatment. In 2015, the mean soil organic matter (SOM) and available P were enhanced to 12% and 13% in 0–30 cm soil depth more than that under TT, respectively. The trial with NT significantly (p &lt; 0.05) increased available N in the top 20 cm by 9% as compared to TT. This improvement in soil physical and chemical properties might have increased the crop yield. After the two-year trial with NT, the mean maize yields increased by 11% compared with the TT trial. Therefore, conservation tillage is the better option considering long-term environmental sustainability in karst regions.

Use of high-resolution ground conductivity measurements for denitrifying conservation practice placement.

Accurate field-scale maps of soil properties including features such as texture, soil organic matter (SOM) content, and hydraulic conductivity are essential for proper placement of conservation practices that utilize anoxic soil environments for denitrification. However, in many cases, soil maps inaccurately represent subsoil properties and can mislead managers about where to install new practices. Non-invasive methods of subsoil property analysis including electromagnetic induction techniques are a potentially efficient method for improving existing field-scale soil maps. In this study, we quantified the accuracy of existing soil maps in an agricultural field in north-central Iowa. Of 60 soil cores collected and reclassified, 19 were identified as taxadjunct at the soil series level primarily due to hydrologic indicators and soil particle size. We assessed the correlation among physical and chemical soil properties measured in-lab and geophysical responses measured in-field. We identified significant correlation of SOM and sand to electrical conductivity for individual core and mean soil series data. From this analysis, we developed a conservation practice suitability map and evaluated the potential for field-scale geophysical investigations to serve as a new tool for agricultural conservation planning and placement of site-specific denitrifying conservation practices. Study results suggest that incorporating a geophysical conductivity investigation into conservation planning may improve understanding of critical soil properties beyond those ascertained with limited soil borings.

The Patitapu Soil Moisture Network (PTSMN) dataset and its deployment in New Zealand’s hill country

A significant portion of New Zealand’s beef and sheep pastoral farming systems are located in the East Coast hill country of the North Island. In these landscapes, one of the main drivers of pasture growth is the highly variable soil water content. Decision making about fertiliser applications, stock and feed budgeting are guided by pasture growth models which rely on soil water information. However, due to the difficulties related to conventional soil moisture data collection, soil water dynamics are still poorly understood in hill country. To capture spatial and temporal soil moisture variability on diverse terrain positions, a soil moisture monitoring network was established at the field scale. The Patitapu Soil Moisture Network (PTSMN) is composed of twenty multi-sensor probes, collecting data from four consecutive depths at 0.1 m intervals. The paper describes the PTSMN deployment and the strategic selection of sensor locations through an extensive spatial analysis and discusses the challenges associated with the network deployment in an operating hill country farm. Additionally, we demonstrate the non-normal nature of soil moisture distribution and that Year 1 and Year 2 showed similarly shaped density curves in the 0.2 − 0.4 m soil depths indicating temporal stability. Similar magnitudes of temporal stability suggested the PTMSN is a temporally stable network although stability changed with depth. Results indicated that soil moisture variability decreased with depth and that higher mean soil moisture content was associated with low variability. Descending and ascending transition stages, i.e., drying, and rewetting periods resulted in the highest spatial variability. As PTSMN is a member of the International Soil Moisture Network, the calibrated, quality checked 2-year dataset has been made accessible online. The presented soil moisture dataset is expected to contribute to the research of near-surface and root-zone soil water dynamics and to assist with the establishment of future networks.

Artificial neural network modeling of soil gas radon concentration on different lithologies for Southwest Nigeria

Radon is a radioactive gas and a leading cause of lung cancer among non-smokers. An indicator of the level of risk associated with radon inhalation is the Geogenic Radon Potential (GRP) - a function of the soil gas radon concentration and the soil air permeability. Data is scarce on the variation of soil gas radon and GRP across different geological formations in southwest Nigeria. This study was designed to measure and develop a generalized predictive model for soil gas radon concentration and hence GRP on different bedrocks in southwest Nigeria. Soil gas radon was measured with a RAD 7 radon detector in 150 sites randomly selected over 20 major bedrocks. Soil air permeability was derived from soil saturated hydraulic conductivity measured using a constant head permeameter on undisturbed soil samples from the same sites. The GRP was obtained using Neznal relation. A 2 × 8 x 1 Artificial Neural Network (ANN) configuration culminated in the generation of a tested and validated predictive model for soil gas radon in southwest Nigeria. For the 150 sites, the range of values for soil gas radon concentration was 0.28–47.59 kBqm−3 and a mean of 10.39 ± 12.59 kBqm−3; soils on granitic bedrocks had the highest mean soil gas radon concentration (16.89 kBqm−3) and highest mean GRP (13.71). Sediments had the highest mean soil air permeability of 39.84 × 10−12 m2. Using Neznal classification, 75.30% of the sites were of low radon hazard rating. The developed predictive ANN model had a Goodness-of-Prediction (G) of 73.53%, Average Validation Error (AVE) of 0.073, Mean Bias Error (MBE) of 0.42, and Root Mean Square Error (RMSE) of 4.62kBqm−3, respectively. The model, validated using standard procedure had G, MBE, AVE, and RMSE of 86.49%, 0.61, 0.17, and 1.65kBqm−3, respectively which is an indication of good model performance.

Assessment of PFAS in collocated soil and porewater samples at an AFFF-impacted source zone: Field-scale validation of suction lysimeters

Per- and polyfluoroalkyl substances (PFAS) measurable in soil porewater authoritatively represent the mobile mass fraction critical to accurate assessment of leaching from source zones. This study evaluated PFAS occurrence in lysimeter-collected porewater samples for two depth intervals at a decades-old aqueous film-forming foam (AFFF)-impacted field site quarterly for a year. Notably, site-wide Log10 (∑PFAS) concentrations did not significantly differ among sampling events despite highly variable sample yields due to a heterogeneous and dynamic soil moisture regime. However, Log10 (∑PFAS) concentrations were significantly higher in the shallow interval concordant with higher mean soil concentrations and higher total organic carbon (TOC) reflecting net retention, which is supported by soil-to-groundwater annual mass discharge estimates less than 0.2% of the total source mass for any given PFAS. Interestingly, PFAS-specific Log10 (soil-to-porewater ratios) significantly increased with soil concentration in both depth intervals contrary to concentration dependence resulting from the saturation of sorption sites potentially implicating self-assembly as an additional operative retention mechanism. Overall, these data validate the use of suction lysimeters for short-term site characterization deployments and emphasize the importance of in situ porewater samples for interrogating PFAS transport within source zones.

Simulation and evaluation of soil water and salt transport under controlled subsurface drainage using HYDRUS-2D model

Controlled drainage is an important measure to improve salinized soil in arid and semi-arid areas. However, free drainage during the growth period leads to excessive water loss, and crops lack water in the later growth period, resulting in crop yield reduction. Therefore, in arid and semi-arid areas, soil salts should be leached during the non-growing period, and drainage should be controlled during the growing period to ensure that crops have adequate water absorption and utilization, improve soil water availability for optimal water supply and salinity control. In this study, through field trials in 2020 and 2021, 3 treatments were set up. The depth of free drainage (FD) is common subsurface pipe drainage and the controlled drainage in the growth period were 40 cm (CWT1) and 70 cm (CWT2), respectively, and the drainage depth in the non-growing period was 100 cm. Using the HYDRUS-2D model to simulate the dynamic changes of soil water and salts in the 0–100 cm range, the calibration and validation of the HYDRUS-2D model were performed using the measured soil water and salt content values of 2020 and 2021. The results showed that the simulated soil water and salt contents agreed well with the measured contents. Controlled Drainage (CD) is a new agricultural drainage management practice that involves periodically increasing the outlet elevation of subsurface drainage pipes, CD significantly increased the water content of the 0–100 cm soil layer—especially at 0–40 cm depth—after growth stage irrigation. Under FD, CWT1, and CWT2, the 2-year mean soil water content of the 0–40 cm soil layer after growth stage irrigation in 2020 and 2021 was respectively 0.263, 0.278, and 0.267 cm3 cm−3, with the latter two values being higher by 5.70 % and 1.52 % than the former value, respectively. Soil water uptake by sunflower after irrigation mainly occurred in the 0–40 cm soil layer, which contributed 55.88–78.51 % of the total soil water uptake. Soil re-salinization occurred in the late growth stage (the flowering stage) under different treatments, with a mean re-salinization rate (relative to the period before spring irrigation) of 29.29 %, 33.48 %, and 30.34 % under FD, CWT1, and CWT2, respectively. Although the re-salinization rate was relatively high under CWT1 and CWT2, it had a low effect on crop growth as well as crop yield. HYDRUS-2D simulation was performed to compare different drain depths in the growth stage in order to determine the optimal drain depth for sunflower in moderately saline soils. To this end, the following metrics were considered for the main root zone (0–40 cm): soil water content, soil salt content, soil de-salination rate during spring irrigation, and soil re-salination rate in the late growth stage. Reduce soil salt content during spring irrigation, increase soil water content after irrigation during growth period, and minimize soil salt return rate in late growth stage, that is, to provide suitable water conditions for crop growth and minimize salt stress. The optimal drain depth during the growth stage was ultimately determined to be 50 cm.

Sensitivity of Land Surface Processes and Its Variation during Contrasting Seasons over India

The study investigates the influence of near-surface atmospheric parameters on land surface processes at the land–atmosphere interface through the offline simulation of the 2D Noah Land Surface Model-based High-Resolution Land Data Assimilation System (HRLDAS). The HRLDAS is used to conduct sensitive experiments by introducing perturbation in the atmospheric parameters, and the experiments were conducted for the period 2011–2013 in India. In each sensitive experiment, a single parameter is perturbed at a time, keeping the rest of the forcing parameters unchanged, and the procedure is followed for all the forcing parameters. The results revealed that the downward longwave radiation and T2 are highly sensitive to land surface processes, while wind speed is the least sensitive. The land surface process sensitivity varies with soil moisture content. The annual mean soil moisture at the surface layer is increased (decreased) by 8% when long wave radiation is decreased (increased) by 20%. Similarly, the annual mean soil temperature increased (decreased) by 2.2 °C when T2 increased (decreased) by 1%. The latent heat flux is highly sensitive to longwave radiation over the wetter soil, while its sensitivity to rainfall is higher over the drier soil. This is attributed to evapotranspiration’s sensitivity to the preferred soil moisture state. Further, the land surface sensitivity varies with contrasting seasons. The sensitivity of soil moisture and latent heat flux is high in OND and JJA seasons, respectively, and are least sensitive in the MAM season. In contrast, the sensible heat flux is highly sensitive to solar radiation in the MAM season and comparatively less sensitive in the JJA season. The study suggests that the antecedent soil moisture state plays a critical role in modulating land surface process sensitivity, and, therefore, a realistic soil moisture state is important for land surface feedback processes.

Optimizing irrigation for winter wheat to maximize yield and maintain high-efficient water use in a semi-arid environment

Optimizing irrigation scheduling is vital in maintaining high crop yield and sustainable water use in water-limited regions worldwide. In this study, a 4-year field experiment (2016–2020) was conducted to evaluate the effect of six irrigation schedules on the grain yield performance, soil water content, plant evapotranspiration, and irrigation water use efficiency of typical winter wheat production system in the North China Plain. The six irrigation schedules involved irrigation at different growth stages, including one critical growth stage (60 mm per stage, I60), two stages (I120), three stages (I180), four stages (I240), and five stages (I300). No irrigation was performed in the control field (I0). The results showed that the plant height and yield components of winter wheat (spike number per hectare, kernels per spike, thousand-kernel weight) increased with the increase in annual irrigation amount. The grain yield in each study year increased quadratically (P < 0.05) with the annual irrigation amount. The soil water content in the 0–90 cm soil layer (where the wheat roots are mainly distributed) increased significantly during the growing season with the increase in annual irrigation amount. In I240, the mean soil water content (0–90 cm) during the growing seasons (17.3–22.6 %) was 61.7–80.8 % of the field water holding capacity, sufficiently favoring wheat growth. The average soil water storage (0–90 cm) during the wheat growing season ranged from 241.1 to 283.2 mm in the irrigation applied treatments, which were 21.7–63.8 mm (9.9–29.1 %) higher than in no irrigation treatment (I0, 219.4 mm). The 4-year averages of wheat grain yield did not differ significantly between I240 (7909.1 kg ha-1) and I300 (7868.6 kg ha-1); however, the average irrigation water use efficiency decreased from 33.0 kg ha-1 mm-1 in I240 to 26.2 kg ha-1 mm-1 in I300. Therefore, we recommend an irrigation scheduling at the regreening, jointing, flowering, and filling stages (I240, 60 mm per stage, 240 mm in total) to maintain high grain yield and sustainable soil water use for winter wheat production in the North China Plain and similar semi-arid regions.

Assessment of Soil Fertility and Creation of Thematic Mapping in the Coastal Soils of Ramanathapuram Block, Ramanathapuram District in Tamil Nadu, India

Aims: A view of the current analysis used GPS and GIS techniques to evaluate and map the soil fertility status of the Ramanathapuram block in the Ramanathapuram district of Tamil Nadu, India.&#x0D; Study Design: In this study, a systematic set of 100 georeferenced soil samples were collected from 100 selected villages and analyzed for 10 chemical parameters and the data along with GPS readings were used for the preparation of soil fertility maps using GIS.&#x0D; Methodology: Hundred soil samples were collected from the sixteen revenue villages of Ramanathapuram block, Ramanathapuram district, Tamil Nadu during the pre-monsoon season with lat-long coordinates by using GPS to evaluate the soil fertility. Ramanathapuram block is the middle- coastal block of Ramanathapuram district of Tamil Nadu. &#x0D; Results: In the present study, the mean soil values of pH (8.16), EC (0.74 dSm-1), organic carbon content (2.52 g/kg), Available N (159.36kgha-1), Available P (30.83 kgha-1), Available K (355.39kgha-1) and (Di- Ethylene Triamine Penta Acidic Acid DTPA) extractable micronutrients viz., Fe (7.21), Zn (0.16), Mn (6.46) and Cu (1.36) ppm were recorded respectively in Ramanathapuram block of Ramanathapuram district. Thematic maps pertaining to soil fertility were prepared using Arc GIS software 10.1.&#x0D; Conclusion: The georeferenced sampling sites can be revisited with the help of GPS, which helps in monitoring the soil fertility changes over long run. Further, it will be useful to the researchers, planners, policymakers, extension workers of the State Department of Agriculture, fertilizer industries, and farmers.

An insight to calculate soil conservation service

Quantifying soil conservation service is critical for sustainable land management. However, the traditional algorithm includes a gap between barren land and real soil erosion (BSERef), and its paradox is that a mass of barren land rarely exists in ecologically adaptable areas with fertile soils, which might overestimate soil conservation service. This study suggests a practical algorithm to effectively evaluate soil conservation service of different ecosystems. We propose a new algorithm based on the difference between cropland without control practices and real soil erosion (CSERef), which is compared with the BSERef algorithm. Our results show that: (1) a nearly five times smaller mean soil conservation amount of cropland occurred in the CSERef algorithm (3.76×106 t·yr–1) than in the BSERef algorithm (20.04×106 t·yr–1); (2) land use has higher explanatory power for the spatial differentiation of soil conservation rate in the CSERef algorithm (15.93% – 46.34%) than in the BSERef algorithm (5.95% – 44.49%). Our results demonstrate that the BSERef algorithm overestimates the soil conservation service of cropland in ecologically adaptable areas, whereas the CSERef algorithm can effectively assess the influence of land use change induced by anthropogenic activities on soil conservation service. Furthermore, we develop an assessment framework in terms of land use classification system following the Chinese Academy of Sciences. The framework considers that for water bodies, there is no soil conservation service; for non-ecologically adaptable areas (unused land) with vast barren lands and vegetation cover below 5%, the BSERef algorithm is recommended; the CSERef algorithm is suggested to use in ecologically adaptable areas (including woodland, grassland, cropland and construction land). This assessment framework can provide scientific assistance for decision-makers to formulate strategies for sustainable land management.

Investigating the Effects of Snow Cover and Vegetation on Soil Temperature Using Remote Sensing Indicators in the Three River Source Region, China

Soil temperature is an important physical variable that characterises geothermal conditions and influences geophysical, biological and chemical processes in the earth sciences. Soil temperature is not only affected by climatic and geographical factors; it is also modulated by local factors such as snow cover and vegetation. This paper investigates the relationship between snow cover and vegetation and soil temperature with the help of two classical remote sensing indicators, the Snow Cover Days (SCD) based Advanced Very High Resolution Radiometer and the Normalized Difference Vegetation Index (NDVI)-based Global Inventory Modelling and Mapping Studies, to analyse the influence of local factors on soil temperature in the Three River Source Region (TRSR). Combing multi-layer geothermal observations from 23 stations in the TRSR with meteorological dataset, soil properties datasets, snow cover and vegetation indices, a non-linear model, the Random Forest model, is used to establish a multi-layer soil temperature dataset to analyse the influence of surface cover factors in each depth. The results showed that the annual SCD had a decreasing trend during 1982–2015 and was negatively correlated with the annual mean soil temperature; the annual NDVI had no significant trend, but it was positively correlated with the annual mean soil temperature. Regionally, there was a significant decrease in SCD in the mountainous areas bordering the source areas of the three rivers, and there was a trend of increasing NDVI in the northwest and decreasing vegetation in the southwest in the TRSR. The stronger the correlation with soil temperature in areas with a larger SCD, the more the snow has a cooling effect on the shallower soil temperatures due to the high albedo of the accumulated snow and the repeated melting and heat absorption of the snow in the area. The snow has an insulating effect on the 40 cm soil layer by impeding the cooling effect of the atmosphere in winter. In sparsely vegetated areas, vegetation lowers ground albedo and warms the soil, but in July and August, in areas with more vegetation, NDVI is negatively correlated with soil temperature, with heavy vegetation intercepting summer radiant energy and having a cooling effect on the soil.

Black plastic mulch affects soil temperature and yield of sweet potato under short season temperate climates

ABSTRACT Temperature is critical for the plant growth and yield of sweet potato (Ipomoea batatas L.) in northern cool season climates. Few studies have quantified the effect of temperature using different crop systems to improve the growth of sweet potato (Ipomoea batatas L.). Our study examined the impact of black mulch on raised beds for sweet potato (Ipomoea batatas L.) production in open field conditions in Manitoba. Black mulched plots were compared with non-mulched plots over 3 years for effects on soil temperature and commercial yields. Three year mean soil temperatures (19.9°C) were significantly higher under mulched plots compared to non-mulched soil (19°C). Higher total, marketable and US#1 yields were harvested from mulched plots than non-mulched plots; however, no differences were recorded for US#2, jumbo and cull yields over 3 years. Marketable yield increases of 47, 39 and 30%, were recorded for mulched plots over non-mulched plots in years 2018, 2019 and 2020, respectively, with a 3-year average yield increase of 39%. Use of black mulch contributed to increased sweet potato commercial yields in short season-temperate climates.

Soil temperature variations between a Typic Fragiudults and a Typic Paleudults in the Ozark Highlands of Missouri

Soil temperature measurements from a Soil Climate Analysis Network (SCAN) monitoring site in the Ozark Highlands Major Land Resource Area (MLRA 116A) were evaluated on landscapes comprising Typic Fragiudults (Scholten series) and Typic Paleudults (Poynor series). The five soil forming factors were similarfor both soils, with the major difference between the adjacent soils being a fragipan in the Scholten series. Air and soil temperatures were collected from a weather station of the USDA-Natural Resources Conservation Service near the border of the mesic soil temperature regime and udic soil moisture regime zone. The mean annual soil temperature observed in the Scholten soil (13.5° C) was0.5° C cooler than the mean annual soil temperature in the Poynor soil (14.0° C). This study showed little difference in mean soil temperatures between soiltypes from January to April and from August to December. During the months of May, June and July, the Poynor mean soil temperature was higher (by 1.1° C, 1.4° C and 1.2° C, respectively) than the Scholten mean soil temperature.According to this study, it is possible that the mean annual soil temperature of fragipan soils is cooler than adjacent soils with no fragipan properties. Thegreatest differences between mean soil temperature and mean air temperature were observed during the months of November (5.1° C for Scholten soil and 5.3°C for Poynor soil); December (5.0° C for Scholten soil and 4.9° C for Poynor soil); and January (4.5° C for Scholten soil and 4.4° C for Poynor soil). The smallestdifference was during the month of March (0° C for Scholten soil and 0.3° C for Poynor soil). This study also indicated that the mean annual soil temperature in the Ozark Highlands can vary by soil series depending on soil properties affecting heat transfer within pedons.

What explains the year-to-year variation in growing season timing of boreal black spruce forests?

Amplified climate warming in high latitudes is expected to affect growing season timing of the vast boreal biome. It is unclear whether the presence of permafrost (perennially frozen ground) might have an influence on changes in growing season timing. This study examined how different environmental variables explained, either directly or indirectly, the variation in growing season timing of boreal forest stands with and without permafrost. We expected that environmental variables explaining the variation in growing season timing differed or had different explanatory power depending on permafrost presence or absence. The growing season was delineated from daily gross primary productivity (GPP) time series derived from 40 site-year data of net ecosystem carbon dioxide exchange measured with eddy covariance techniques over five black spruce (Picea mariana [Mill.])-dominated boreal forest stands in North America. In permafrost-free forest stands, a combination of start in canopy ‘green-up’ in spring and the timing of air and soil temperature increasing above freezing explained the start-of-season (SOSGPP). Results from commonality analysis and structural equation modeling suggest that canopy ‘green-up’ and air temperature directly affected SOSGPP in permafrost-free forest stands. In addition, soil temperature acted as mediator for an indirect effect of air temperature on SOSGPP. In contrast, none of the environmental variables, or their combination, explained the variation in SOSGPP in forest stands with permafrost. The explanatory power of environmental variables was more consistent regarding the end-of-season (EOSGPP). In both, forest stands with and without permafrost, EOSGPP was directly explained by mean soil water content in the fall and the first day of continuous snowpack formation. A better understanding how environmental variables control SOSGPP and EOSGPP in forest stands with and without permafrost will help to refine parameterizations of the boreal biome in Earth system models.

Evaluating the effects of temperature on soil hydraulic and mechanical properties in the collapsing gully areas of south China

The soil hydrologic and mechanical properties play an important role in the slope stability in the red soil hilly region of southern China. In this study, the red soil layers in a collapsing gully wall were used to investigate the effects of temperature on the soil water retention curve (SWRC) and shear strength. The results showed that the SWRCs of the red soil under different temperatures could be accurately described by the van Genuchten (VG) model (R2 > 0.95, root mean square error (RMSE) < 0.024). An increasing temperature significantly decreased the soil water holding capacity (WHC), especially in the intermediate range of the SWRCs of the red soil. The soil saturated hydraulic conductivity (Ks) increased linearly with temperature. The soil cohesion and soil friction angle decreased by approximately 44.13% and 30.40% respectively when the soil water content increased from 0.24 cm3 cm−3 to 0.42 cm3 cm−3. The mean soil cohesion and soil friction angle decreased approximately 8.56 kPa and 1.34° respectively when the soil temperature increased from 25 °C to 40 °C. Regression analysis showed that the soil cohesion increased as the power function with increasing matric suction (0–2000 kPa), and friction angle increased as the linear function with increasing matric suction. These results illustrated that an increase in temperature will decrease soil matric suction and shear strength but enhance the soil infiltration rate under certain soil moisture levels. Therefore, the stability of a collapsing gully wall will sharply decrease under the conditions of high temperature and heavy rain in summer.

Temperature effects on root exudation in mature beech (Fagus sylvatica L.) forests along an elevational gradient

AimsRoot exudation may have a large impact on soil biological activity and nutrient cycling. Recent advances in in situ-measurement techniques have enabled deeper insights into the impact of tree root exudation on rhizosphere processes, but the abiotic and biotic controls of exudation rate remain poorly understood. We explored the temperature dependence of root exudation in mature beech (Fagus sylvatica L.) trees.MethodsWe measured fine root exudation in seven beech forests along an elevational gradient (310–800 m a.s.l.) and related carbon (C)-flux rates to mean daily temperature, actual precipitation, mean summer temperature (MST) and precipitation (MAP), soil moisture (SWC), and stand structure.ResultsAverage mass-specific exudation (averaged over all sampling dates) ranged from 12.2 µg C g−1 h−1 to 21.6 µg C g−1 h−1 with lowest rates measured at highest elevations and peak rates at mid-elevation (490 m). Regression analyses showed a highly significant positive effect of site-specific daily air and soil temperature on exudation rates (p < 0.01) with an average increase by 2 µg C g−1 h−1 per 1 °C-temperature increase, while the relation to mean summer or annual temperature and mean temperature of the measuring year was less tight. Exudation decreased with increases in mean annual precipitation and soil moisture, but increased with increasing stem density.ConclusionsThe root exudation rate of beech trees roughly triples between 10 °C and 20 °C mean daily temperature, evidencing a large temperature influence on root-borne C flux to the soil.

Evaluation and Source Analysis of Heavy Metal Pollution in Sediments of the Yellow River Basin Based on Monte Carlo Simulation and PMF Model

As sediment is an essential component of rivers, the enrichment of heavy metals in sediment presents a serious threat to the aquatic environment. Many industrial cities are located along the Yellow River, and heavy metal pollution is a prominent problem in these areas. Thus, the study of heavy metal pollution in sediments of the Yellow River basin is of vital significance to the safety of the Yellow River basin ecosystem. In this study, we collected data on the concentrations of heavy metals (Pb, Cd, Cr, As, Zn, Cu, Ni, and Hg) in the sediments of the Yellow River basin from 2000 to 2020. We first analyzed the spatial distribution characteristics of heavy metals based on descriptive statistics and geostatistics and then used the Monte Carlo method to evaluate the probability of the ground accumulation index(Igeo), potential ecological risk, and toxicity units. Finally, the number of pollution sources and their contribution rates were determined by combining the positive definite matrix factor (PMF) decomposition model and Pearson correlation analysis. It was found that the mean values of ω(Pb), ω(As), ω(Zn), ω(Ni), ω(Cu), ω(Hg), ω(Cr), and ω(Cd) in the Yellow River basin sediments were 26.92, 11.78, 87.17, 31.13, 24.96, 0.07, 73.36, and 0.58 mg·kg-1, which exceeded the mean soil background values in the Yellow River basin provinces by 1.27, 1.08, 1.26, 1.05, 1.09, 2.32, 1.14, and 5.95 times, respectively, among which Cd exceeded the standard by the largest factor and should be taken seriously. The Igeo was ranked as Cd>Hg>Cr>Cu>Pb>Zn>As>Ni, and Cd and Hg showed medium-severe pollution. The proportions of heavy ecological risk in sediments in the upper, middle, and lower reaches of the Yellow River basin were 18.6%, 15.7%, and 7.1%, respectively, with a decreasing trend. Heavy metals in the sediments of the Yellow River basin were in a low-toxicity state. The PMF-Pearson correlation analysis showed that the four sources of heavy metals in the Yellow River basin sediments were mining sources (42.2%), natural activities (38.3%), agricultural activities (11.6%), and electroplating wastewater (7.9%). The results of this study can provide a basis for developing relevant pollution prevention and control measures in the Yellow River basin.

Responses of absorptive root and mycorrhizal colonization of Chinese fir (Cunninghamia lanceolata) to varied environmental conditions

Root branching and mycorrhizal symbioses are two major mechanisms for soil resource acquisition by trees. Understanding the relationship between these two mechanisms and their responses to varied environmental conditions is crucial for predicting the responses of foraging strategies of roots to environmental changes. This study was conducted in 11 Chinese fir (Cunninghamia lanceolata) plantations distributed in different environmental conditions in Subtropical China to assess the relationship between root tip traits related to nutrient foraging (branching ratio of 1st-order roots to 2nd-order roots, arbuscular mycorrhizal (AM) colonization) and their environmental variables, including mean annual precipitation (MAP), mean annual temperature (MAT), soil C, soil N, soil P, and soil pH. Root branching was more sensitive to environmental conditions than mycorrhizal symbioses. The branching ratio and AM colonization of Chinese fir were significantly related to several environmental variables. The branching ratios were positively correlated with MAT, but negatively correlated with soil C, soil N, and soil pH (P < 0.05), suggesting that harsh environmental conditions can promote absorptive root branching. To our surprise, the AM colonization of absorptive roots was not as sensitive to environmental factors as branching ratio. However, the AM colonization of absorptive roots was positively correlated with soil pH (P < 0.1), indicating that soil acidity controls mycorrhizal symbioses. Moreover, the branching ratio was significantly negatively correlated with AM colonization (P < 0.05). Our results confirmed that environmental conditions significantly regulate fine root branching and its mycorrhizal symbioses, but with different controlling variables. The negatively correlated relationship of branching ratio and AM colonization shows that environmental factors regulate absorptive root traits in different ways.

Soil erosion risk assessment and treatment priority classification: A case study on guder watersheds, Abay river basin, Oromia, Ethiopia

Soil erosion is the most persistent environmental problem in the Upper Blue Nile River (UBNR) basin of Ethiopia. Guder River is one of thetributaries of UBNR basin which critically required soil conservation practices. The main objective of this particular research article was to appraise soil erosion hazard priority classification with an easy and uncomplicated erosion modelling tool, the universal soil loss equation (USLE) using GIS software and RS data. Remote Sensing data such as annual mean precipitation, land-use land-cover, and soil map, digital elevation model map were used to determine the USLE factor values. The average annual rainfall data was derived from the widely used climate dataset CRU TS (Climatic Research Unit gridded Time Series) and converted to rainfall erosivity factor. Soil Erodibility Factor Soil (K) was calculated from FAO soil data “Digital Soil Map of the World - ESRI shapefile format”. Topographic Factor (LS) was delineated from a 30m digital elevation model. Cover Factor (C) and Support Practice Factor (P) were estimated from a 20m Ethiopia Sentinel2 Land-use Land-cover year, 2016. The study classified the Guder watersheds into different kinds of severity classes for prioritization of soil and water management options and conservation strategy. The mean annual soil eroded for the whole sub-basin was estimated at 25.23 tha−1y−1. The study output outcomes demonstrated that about 0.1% (426ha) 6.9% (46764 ha), 8.9% (60055 ha), and 19.8 % (134320ha) have been under Catastrophic, very severe, severe, high erosion severity class respectively. About half of the Guder sub-basin has been underneath a very slight erosion. Nevertheless, the area covered by very severe erosion was 6.9%, and the annual percent of sum-total soil erosion accounted for was 46.86%. The second and third in magnitude soil lost annually from the sub-basin with regards to per cent of total soil loss were severe (26.53%), and high (21.53%) respectively. In only 7% of the area under investigation, soil erosion estimated was to go beyond 100 t/ha/yr. erosion rate. District wise erosion affected and hotspot areas were identified: Middle of Steep slopes Mountainous parts of Ginde Beret, Jeldu, Ifata, Ambo, parts Ababo and Horo Guduru located in the study area borderline, Toke Kutaye, along the boundary of Midakegn and Cheliya were found in severe to very severe erosion. Finally, the study proposed that the government, policymakers, and soil and water management agents plan and implement the conservation measures and give awareness to stakeholders for optimum use of limited precious resources.