Top Soil Layer Research Articles

Patterns and drivers of soil carbon change (1980s-2010s) in the northeastern Qinghai-Tibet Plateau

Rapid climate warming, permafrost degradation and widespread vegetation improvement on the Qinghai-Tibet Plateau (QTP) have caused carbon input via photosynthesis and carbon output through soil respiration to significantly increase in recent decades; thus, its role as a carbon sink/source is unclear and highly disputed, especially at different soil depths. In this study, we took the Qinghai Plateau (northeastern QTP), with an area of 7.2 × 105 km2 (permafrost accounts for 52% of the land) and an elevation ranging from 1669 m to 6548 m, as the study region and estimated its spatial pattern of soil organic carbon (SOC) stock changes at different soil depths from the 1980s to 2010s. The paired site observations of the SOC stocks in the 1980s from the second national soil survey and in the 2010s from a field survey and the literature were compiled and then combined with 77 related environmental factors to drive multiple machine learning models (random forest, gradient-boosting machine, and Cubist), from which the spatial patterns of SOC stock changes at different soil depths (0–30, 30–50, and 50–100 cm) were revealed. The results indicated that the SOC stock increased in the soil at 0–100 cm over the past three decades, with a mean net accumulation rate of 7.36 g C m−2 yr−1 or a total of 0.153 Pg C. Compared with seasonally frozen soil, more significant increases in the SOC stock were observed in permafrost at the 0–100 cm depth (9.71 vs. 4.81 g C m−2 yr−1). However, the SOC stock changes in different soil layers showed significant differences. Specifically, the SOC stock substantially increased in the topsoil layer (0–30 cm), with a carbon increase of 7.82 g C m−2 yr−1; the SOC stock in the middle layer (30–50 cm) had a slight increase, with a carbon increase of 1.69 g C m−2 yr−1; and the SOC stock decreased in the bottom layer (50–100 cm), with a net carbon loss rate of 2.15 g C m−2 yr−1. We found that vegetation change was the key driver of SOC stock change in the topsoil layer. With the increase in soil depth, the importance of climate change on SOC stock change increased. We concluded that climate-driven carbon losses in the deep soil layer were offset by an increase in vegetation-driven carbon inputs at the top and middle soil layers, triggering plant-dominated negative soil carbon feedback to climate warming. With the temperature continuing to increase, however, we must pay more attention to the risk of carbon release in the middle and bottom soil layers.

Soil compaction in skid trails still affects topsoil recovery 28 years after logging in Central Amazonia

The use of heavy machinery in logging operations leads to soil compaction, especially in highly used skid trails. In Amazonia, recovery of topsoil physical properties has been reported in skid trails. So, the present study sought to determine if this was a full recovery by investigating additional attributes, such as soil chemical properties and fine root biomass (FRB). In addition, forest floor litter was investigated to present a more complete view of soil recovery dynamics. To accomplish this, litter above sampling locations was collected, as well as soil samples below this in two depths. These depths represented the recovered topsoil layer (0–5 cm) and the still compacted soil layer (5–10 cm) below. Three areas were compared: control, middle of the skid trails, and skid trail ruts. Dry mass, C%, N% were determined for litter and FRB. Foliar nutrients (P, K, Ca, Mg, Fe, Zn, Mn) were also determined. Soil chemical properties such as pH, cation exchange capacity, base saturation, aluminum saturation, soil organic C and nutrients (total N, available P, exchangeable Ca, Mg, K, Na, Fe, Zn, Mn) were also assessed. The primary objective was to determine if there was a full recovery of properties evaluated in the topsoil, but also to determine if the compacted soil below acted as an effective hardpan that potentially exerted influence on the recovered topsoil. In the skid trail ruts, results revealed no significant differences with the controls in the recovered topsoil for FRB and all but one soil nutrient, Mn which was elevated. Additionally, the base saturation and volumetric water content of the ruts topsoil was significantly higher than the controls indicating a potential hardpan condition below. So, even though a topsoil may be considered fully recovered, the compacted soil below may still exert influence in the form of increased soil moisture and nutrient accumulation. Therefore, the key finding of this research is that for the first time a recovered topsoil in skid trails was demonstrated to be affected and influenced by the compacted soil below. This influence in the very clayey soils of Amazonia was observed after nearly-three decades.

Impact of Deferred Versus Continuous Sheep Grazing on Soil Compaction in the Mediterranean Montado Ecosystem

Deferred grazing (DG) consists in adapting the number of animals and the number of days grazed to the availability of pasture. Compared to continuous grazing (CG), which is based on a permanent and low stocking rate, DG is a management strategy that aims at optimizing the use of the resources available in the Mediterranean Montado ecosystem. This study with sheep grazing, carried out between 2019 and 2021 on a 4 ha pasture in Alentejo region of the Southern of Portugal, assesses the impact of these two grazing management systems on soil compaction as a result of animal trampling. This area of native natural grassland (a dryland pasture, mixture of grasses, legumes, and composite species) was divided into four grazing parks of 1 ha each, two under DG management and two under CG management. At the end of the study, the cone index (CI, in kPa) was measured in the topsoil layer (0–30 cm) with an electronic cone penetrometer at 48 georeferenced areas (12 in each park). The results of CI measurement showed no significant differences between treatments in all depths measured (0–10, 10–20, and 20–30 cm). These findings are encouraging from the point of view of soil conservation and sustainability, revealing good prospects for the intensification of extensive livestock production. Future work should evaluate the long-term impact and consider, at the same time, other ecosystem services and system productivity indicators.

How a photovoltaic panel impacts rainfall-runoff and soil erosion processes on slopes at the plot scale

Photovoltaic (PV) power plants are fast growing worldwide due to the environmental benefit of solar power generation and the development of photovoltaic technology. However, the impacts of PV panels on rainfall-runoff and soil erosion processes in hillslope are not well understood. This study quantitatively investigated these impacts on a plot-scale slope through rainfall simulation experiments. A bare plot with in-situ loess soil in the Chinese Loess Plateau was divided to two 4 m × 1 m slopes (i.e., a test slope with a PV panel above its middle and a control slope without cover) as the study site in which 1-hr artificial rainfall with varying intensities (30 mm hr-1 to 100 mm hr-1) were conducted. The result showed that runoff volume, peak flow discharge rate and overland flow velocity were not remarkably different between the panel slope and the control slope, although the soil surface under the PV panel was rougher than the surface of the control slope. However, the slope with the PV panel produced 27 %–63 % less sediment flux at the outlet than the control slope, especially under heavy rainfall. This was attributed to the weakened splash erosion on the slope section under the PV panel due to the rainfall interception by the panel, which indicated that the key impact of the PV panel was preventing soil detachment by raindrop impacts. The PV panel delayed runoff start time under rainfall with heavy rainfall intensities (80 and 100 mm hr-1) due to the overland flow attenuation of the depression beneath the lower edge of the PV panel. These findings implied that PV panels on hillslopes may have the potential to retain soil organic matter in top soil layers and to improve soil structure (e.g., soil sealing control and soil aggregate protection), which may benefit to hillslope soil conservation and vegetation restoration in long term.

Afforestation of semi-arid regions of Mongolia: carbon sequestration in trees and increase of soil organic carbon

This work examines the variation of carbon sequestration (considered as the sum of above- and below-ground plant biomass production added to soil organic carbon) occurring in two sites (named respectively BN and ER) characterized by a semi-arid climate after planting three tree species (Populus sibirica, Ulmus pumila, and Hippophae rhamnoides). Soil organic carbon (SOC) was analyzed at four different depths (from 0–60 cm). In these two sites, the three tree species contributed differently to carbon sequestration. We found that above-ground plant biomass (leaf, branch, stem) was higher at the BN site whereas at the ER site prevailed below-ground biomass. That is probably due to the low tree density in BN site and the higher soil moisture content present in ER site. Among the three tree species considered, P. sibirica showed the highest biomass value. The SOC values were highest in the topsoil layer (0-40 cm) and decreased with depth. This works clearly shows that in semi-arid lands carbon sequestration depends on the environmental factors that characterize the site, the tree density, and the tree species selected.

Effects of the construction of fertile and cultivated soil layer on soil fertility and maize yield in Albic soil.

We examined the effects of fertile soil layer construction technology on soil fertility and maize yield with a 3-year field experiment in Albic soil in Fujin, Heilongjiang Province. There were five treatments, including conventional tillage (T15, without organic matter return) and fertile soil layer construction methods [deep tillage (0-35 cm) with straw return, T35+S; deep tillage with organic manure, T35+M; deep tillage with straw and organic manure return, T35+S+M; deep tillage with straw, organic manure return and chemical fertilizer, T35+S+M+F]. The results showed that: 1) compared with the T15 treatment, maize yield was significantly increased by 15.4%-50.9% under fertile layer construction treatments. 2) There was no significant difference of soil pH among all treatments in the first two years, but fertile soil layer construction treatments significantly increased soil pH of topsoil (0-15 cm soil layer) in the third year. The pH of subsoil (15-35 cm soil layer) significantly increased under T35+S+M+F, T35+S+M, and T35+M treatments, while no significant difference was observed for T35+S treatment, compared with T15 treatment. 3) The fertile soil layer construction treatments could improve the nutrient contents of the topsoil and subsoil layer, especially in the subsoil layer, with the contents of organic matter, total nitrogen, available phosphorus, alkali-hydrolyzed nitrogen and available potassium being increased by 3.2%-46.6%, 9.1%-51.8%, 17.5%-130.1%, 4.4%-62.8%, 22.2%-68.7% under the subsoil layer, respectively. The fertility richness indices were increased in the subsoil layer, and nutrient contents of the subsoil layer were close to those of topsoil layer, indicating that 0-35 cm fertile soil layer had been constructed. 4) Soil organic matter contents in the 0-35 cm layer were increased by 8.8%-23.2% and 13.2%-30.1% in the second and third years of fertile soil layer construction, respectively. Soil organic carbon storage was also gradually increased under fertile soil layer construction treatments. 5) The carbon conversion rate of organic matter was 9.3%-20.9% under T35+S treatment, and 10.6%-24.6% under T35+M, T35+S+M, and T35+S+M+F treatments. The carbon sequestration rate was 815.7-3066.4 kg·hm-2·a-1 in fertile soil layer construction treatments. The carbon sequestration rate of T35+S treatment increased with experimental periods, and soil carbon content under T35+M, T35+S+M and T35+S+M+F treatments reached saturation point in the experimental second year. Construction of fertile soil layers could improve the fertility of topsoil and subsoil and maize yield. In term of economic benefits, combination application of maize straw, organic material and chemical fertilizer within 0-35 cm soil, cooperating with conservation tillage, is recommended for the Albic soil fertility improvement.

Forecast of the development of thermal erosion processes in the Yamalo-Nenets Autonomous Okrug under modern climate changes

The study of exogenous processes and their effects on natural and anthropogenic systems is a very important aspect for the development of Arctic territories. One of these processes is thermal erosion, which is widespread in the Yamalo-Nenets Autonomous District due to the presence of permafrost in the vast majority of its area. The main prerequisites for the manifestation of thermal erosion processes can be divided into several groups of factors. Firstly, the geomorphological characteristics of the territory play a key role: the lengths and slopes. Secondly, the lithological and granulometric composition of rocks, as well as ice content and temperature, determine the resistance of the soil to the thermal and mechanical effects of flowing water. Thirdly, the amount of precipitation is an important factor, especially precipitation in winter and heavy rainfall in summer. They contribute to a high concentration of runoff in short periods of time, which leads to rapid destruction of rocks and the removal of large volumes of loose material. Finally, the fixation of the top layer of soils by the root system can be considered the main reason that counteracts the development of thermal erosion. The purpose of this study is a prognostic assessment of the risks of the development of thermal erosion processes in the context of the observed climate warming. To assess the risks, data from climate modeling of the Yamalo-Nenets Autonomous District for the middle of the XXI century were used for an ensemble of climate models included in the CMIP6 project. The analysis of Google Earth satellite images and information about the geological and geomorphological features of the region are used for zoning the territory in terms of dynamics and dangers of thermal erosion. The result of the study was the compilation of a map of the Yamalo-Nenets Autonomous District by categories of risks associated with thermal erosion processes. It is shown that in the perspective of several decades, more than 50% of the region's area is subject to intensification of thermal erosion destruction of soils, which requires careful planning of economic development and design of protective structures. An attempt has been made to assess the impact of erosive and thermoerosive effects on the natural environment of the Yamalo-Nenets Autonomous Okrug due to climate change using the recommendations of this assessment by Order of the Ministry of Economic Development of the Russian Federation dated 05/13/2021 N 267. Climatic factors can seriously enhance the causes and negative consequences of the development of thermoerosion, while local manifestations should be assessed using field data based on the calculation methods.

Fractionation of Manganese Compounds in the Topsoil Layer Affected by Coal Waste Heap (Central Russian Forest-Steppe)

Fractionation of Manganese Compounds in the Topsoil Layer Affected by Coal Waste Heap (Central Russian Forest-Steppe)

Dolomite and organic compost application for preventing acid mine drainage formation in a mesocosm system

Acid mine drainage (AMD) is one of most serious environmental problems facing mining industries. It results from oxidation of sulfide minerals contained in mining wastes, such as rock disposals in mine sites. This study was to investigate AMD formation from waste rocks containing potentially-acid forming (PAF) materials treated with dolomite and compost in a mesocosm system. The system comprised a plastic drum of 150-cm height and 50-cm diameter filled with 15-cm sand at the botom layer, over-laid by 50-cm mixture of PAF+10% of either dolomite or compost, and 35-cm top-soil layer on the top. The drum surface of the sand layer was equipped with a valve to drain leached water into a collecting container. The control was a similar constructed mesocosm without addition of either ameliorant. The drums were installed into the ground of the mined land so that their surfaces were as high as the surrounding soil surface and left under field condition. The leachate samples were taken two-weekly in the early two months and monthly until the day 487. The system demonstrated that both dolomite and compost significantly increased pH from around 3 to pH>6 and reduced dissolved Al and Fe concentrations. However, the dissolved Mn concentration was still high (>20 mg L−1) in all treatments even at the pH reached >6. .

Fractionation of Manganese Compounds in the Topsoil Layer Effected by a Coal Waste Heap (Central Russian Forest-Steppe)

In the Tula region, to analyze the fractionation of Mn in the soils effected by acid sulfate water, at 11 points (a total of 57 samples), we studied electrical conductivity of the water extract, the granulometric composition, pH, the concentration of total organic carbon and the three mobile fractions (exchangeable, complexed, and specifically sorbed) the metal. Technosols of a waste heap with a predominantly very acidic medium often have sulfate salinity. Acid sulfate water and solid-phase matter from the waste heap form talus, which bury highly productive Chernozems and Phaeozems. In terms of the fractionation of Mn, bared Regosols (Phytotoxic) at the talus are close to the toxic substrates of the waste heap, and plant-covered Regosols are close to the background Chernozems. In the transported material of plant-covered Regosols, the content of Mn mobile compounds increases. The input of acid sulfate water into the A-horizon of Chernozems increases the content of water-soluble \({\text{SO}}_{4}^{{2 - }}\) and Ca2+ and decreases the content of mobile compounds and the total content of Mn.

Soil microbial necromass regulation of long-term fertilizer N retention influenced by maize stover mulching

Microbial immobilization of nitrogen (N) fertilizer is critical for N retention in soils and is mainly influenced by agricultural management, including crop residue return. However, the underlying relationship between microbially mediated processes and long-term fertilizer N dynamics has not been characterized well in arable soil. Here, by tracing in situ the temporal changes of soil amino sugars initially synthesized from the 15N fertilizer applied in the 1st year, we investigated the dynamic contribution of microbial necromass to long-term fertilizer N retention in soil influenced by maize stove mulching. After the 1st year of fertilizer application, microbial necromass contributed to 36.3–43.9 % of the remaining fertilizer N in the topsoil (0–10 cm), but the remaining fertilizer N in the subsoil (10–20 cm) was predominantly attributed to microbial necromass accumulation, regardless of maize stover mulching. During the following 9 years, the fertilizer-derived microbial necromass N decreased at a slower rate (42.3–52.8 %) than the remaining fertilizer N (73.5–76.7 %) in the topsoil layer, while the former decreased synchronously with the latter in the subsoil layer, indicating that microbial necromass played a critical role in long-term fertilizer N stabilization though it could serve as a transitional N pool for N supply. For the microbial necromass of different origin, the residence time of fertilizer N in fungal necromass (34.7–48.7 y) was longer than that in the bacterial necromass pool (21.4–27.1 y) in the cultivated soil layer (0–20 cm), explicitly indicating that the retention of fungal necromass was inclined to contribute to long-term fertilizer N stabilization while bacterial necromass was associated with fertilizer N turnover. Compared with fertilizer application alone, maize stover mulching enhanced the initial fertilizer N retention by increasing microbial necromass accumulation but had no influence on the subsequent dynamics of both the remaining fertilizer N and fertilizer-derived microbial necromass N, thus improving long-term fertilizer N retention. Specifically, maize stover mulching increased the stability of microbial necromass N by enhancing the retention and prolonging the residence time of fungal necromass over bacterial necromass, thus improving the contribution of microbial necromass to the long-term stabilization of fertilizer N in the cultivated soil.

The Impact of Profile Genesis and Land Use of Histosol on Its Organic Substance Stability and Humic Acid Quality at the Molecular Level

This study is designed to evaluate soil organic matter (SOM) quality indicators: molecular indicators of dissolved organic matter (DOM) and hydrophobicity of humic acid (HA), distribution of quantity in humified and labile fractions of histosols during renaturalization. The aim is to determine the differences in the qualitative composition of humic acids at the molecular level, which are decided by the previous tillage and genesis, and to evaluate the impact of anthropogenization on the peat soil according to hydrophobicity, as well as to estimate the impact of soil genesis and removing peat layer. Soil samples were taken from the three Sapric Histosol (according to WRB2022) profiles and the 0–30 cm layer in three field replicates (Lithuania, Radviliskis mun.). Our study suggested that in the differently managed drained Sapric Histosol under renaturalization, the most significant changes occurred in the topsoil layer (0–30 cm), in which an increase in the content of SOM particles 106–2 µm in size. It is expedient to grow perennial grasses and legumes to maintain the soil organic carbon stability mobile humic acids to mobile fulvic acids ratio (MHA:MFA 0.83 to 0.86). An evaluation of the quality of HA (E4:E6) revealed their highest maturity in the unfertilized perennial grasses (3.88) and crop rotation (3.87) with grasses. The highest concentrations of hydrophilic groups (ratio of the C=O to O-H) were found in Sapric Histosol under deciduous hardwood forest (12.33). The lowest hydrophilicity (9.25 and 9.36) was of the crop rotation Sapric Histosol with removed peat layer. The most sustainable use of drained Sapric Histosol in the context of the sustainability and quality of its humus substances should be associated with the formation of perennial grass and clover grassland and the cultivation of deciduous hardwood. Therefore, the horizon forms on the top part of the profile, which protects deeper Histosolic material layers from its mineralization.

A Long-term Consistent Artificial Intelligence and Remote Sensing-based Soil Moisture Dataset

The Consistent Artificial Intelligence (AI)-based Soil Moisture (CASM) dataset is a global, consistent, and long-term, remote sensing soil moisture (SM) dataset created using machine learning. It is based on the NASA Soil Moisture Active Passive (SMAP) satellite mission SM data and is aimed at extrapolating SMAP-like quality SM back in time using previous satellite microwave platforms. CASM represents SM in the top soil layer, and it is defined on a global 25 km EASE-2 grid and for 2002–2020 with a 3-day temporal resolution. The seasonal cycle is removed for the neural network training to ensure its skill is targeted at predicting SM extremes. CASM comparison to 367 global in-situ SM monitoring sites shows a SMAP-like median correlation of 0.66. Additionally, the SM product uncertainty was assessed, and both aleatoric and epistemic uncertainties were estimated and included in the dataset. CASM dataset can be used to study a wide range of hydrological, carbon cycle, and energy processes since only a consistent long-term dataset allows assessing changes in water availability and water stress.

Microplastic Accumulation in Agricultural Soils with Different Mulching Histories in Xinjiang, China

Microplastics (MPs) in soils have been widely studied, yet very little is known about their distribution in agricultural soils and the impact of mulching history. In this study, soil samples were taken across 3 soil layers of 60 sites with varying years of mulching history (<5 years, 5–10 years, 10–20 years and >20 years) in agricultural film-mulched cotton fields of Xinjiang, China. Microplastics were obtained from the soils using oil separation combined with density separation. Stereomicroscopy and Fourier transform infrared spectroscopy (FTIR) were used for identification. The average microplastic abundance of the sites with different years of mulching history are 538, 1484, 5812 and 9708 pieces/kg, respectively. The microplastics with sizes 1000–5000 and 200–500 μm are dominant in soils with less than 10 years and over 10 years of continuous mulching history, respectively. The results show that the abundance of microplastics increases and the size of microplastics decreases gradually as the number of years of mulching history increases. In addition, the best polynomial fitting curves were found between microplastic abundance (y) and mulching years (x) in different soil layers, and the relationship in the topsoil layer can be fitted as the following equation: y = 20.6x2 = 41.39x + 198.65 (p < 0.01, R2 = 0.62). The results indicate that residual agricultural mulching film is the dominating source of microplastics in cotton fields. This study provides rationale for further research on microplastics prediction in agricultural film-mulched fields.

Soil fertility and pomelo yield influenced by soil conservation practices

Abstract Exchangeable cations and soil nutrients leach out/lost in the raised bed soils system through irrigation water and rainwater. Cover crops or crop residue mulching are considered sustainable agricultural measures because they prevent soil degradation and compaction and increase the soil ecological diversity. However, the impact of these on soil quality in fruit orchards in the Vietnamese Mekong Delta is not well studied. The present work aimed to assess the effect of cover crops (grass, pinto peanut) and rice straw mulching on change in soil chemical properties and productivity of pomelo. The 3-year (2019–2021) field experiment was conducted at Phu Huu Commune, Chau Thanh District, Hau Giang Province, Vietnam. Four treatments, control (no-cover crop), grass cover crop, mulching with rice straw (MRS), and pinto peanut cover crop were used. Soil samples were collected from the depth of 0–20 and 20–40 cm for analyzing soil pH, total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), and soil organic matter (SOM). Results showed that MRS or cover crop by pinto peanut significantly decreased soil acidity in the topsoil layer. Soil fertility properties (TN, TP, AP, and SOM) at the depth 0–20 cm were greatly improved after the application of the mulched rice straw and cover crop by legume, thus improving pomelo yield. Further study is required to understand the effects of the cover crop with pinto peanut and rice straw mulching on the physical and biological properties of soil as well as nutrient uptake of pomelo orchards.

Combining Rock-Eval® thermal analysis and thermochemolysis to evaluate the influence of forest management on soil organic matter quality and stability

The effect of forest management practices on carbon quality is poorly documented. To assess changes in the quality and stability of soil organic carbon (SOC) of a temperate forest upon human activities, we investigated soil from forests (i) developed following natural regeneration after clearcutting 20 and 40 years ago, (ii) developed following afforestation on an abandoned crop area 40 years ago and (iii) in an area where regular clear-cut (with wood residues input) was conducted 40 years ago. Topsoil and subsoil layers were collected (0–20 cm and 50–80 cm). Soil organic matter (OM) was characterized by elemental analysis (total carbon and total nitrogen), thermal analysis (Rock-Eval®) and thermochemolysis (i.e., Py-GC/MS in the presence of tetramethylammonium hydroxide (TMAH)). In addition, a size fractionation to separate the labile coarse fraction (50–2000 μm) from the fine fraction (<50 µm) was performed. These fractions were analyzed by thermal analysis.Despite no measurable differences in carbon and nitrogen contents, the characterization of the OM by thermal analysis, and the relative quantification of OM compounds revealed differences in the composition in OM for the topsoil layers. The thermal analysis clearly distinguished sites with inputs of woody residues (higher HI) with a higher relative contribution of lignin and cutin/suberin compounds. However, the OM thermal stability seems mainly controlled by the organo-mineral interactions rather than chemical composition. Combination of Rock-Eval® thermal analysis and Py-GC/MS suggests that thermal stability cannot be used as an indicator of stability in specific contexts where pedogenetic processes are deeply modified by regular and extensive anthropogenic inputs of woody residues.

Discrete element modelling of soil pressure under varying number of tire passes

Pressure imposed on an arable farmland by farm machinery can lead to severe soil compaction. A model was developed with Discrete Element Method (DEM) to simulate soil – tire interaction. Virtual dead weight method was performed for the purpose of model calibration. Simulated soil pressure data were obtained from the topsoil layer under varying number of tractor tire passes (1P, 2P, 3P, 4P, 5P, 6P, 7P and 8P). Simulation results were validated with maximum soil pressure data from a field experiment in which soil pressure was measured at 0.1 m depth in sandy loam soil. Model results of maximum soil pressure increased from 137.7 to 242.5 kPa when the number of passes increased from 1P to 8P. Prediction of the maximum soil pressure was reasonably accurate for 1P and 2P with Relative Mean Errors (R.M.E) less than 9%. Predictions for 3P to 8P had higher R.M.E. In terms of model application, soil sinkage and rolling resistance ranged from 0.07 to 0.14 m and 225.3 to 517.8 N respectively between one to eight passes. The model developed in this study can be used in the simulation of soil pressure distribution and deformation in the topsoil layer induced by heavy farm machinery.

Chemistry of soil and foliage in declining sugar maple stands over 13 years of nitrogen addition

Cumulative effects of nitrogen (N) deposition are a matter of concern in temperate forests of northeastern North America. Increased N deposition may stimulate forest growth and carbon sequestration while also causing N saturation, which may lead to soil cation depletion, particularly in base-poor systems. We applied ammonium nitrate for 13 years in a sugar maple (Acer saccharum; SM) stand at the rates of 3 (Low N, LN) and 10 times (High N, HN) the ambient N deposition rate. N concentrations in soil layers were similar among treatments, except for a nitrate increase in the top B horizon in the HN treatment. Exchangeable Ca2+, Mg2+, and K+ were significantly lower than for the Control, at least in one of the top organic soil layers in the HN treatment. The temporal dynamics of foliar chemistry revealed that N:P ratio increased and both Ca and Mn decreased in the early years following treatment initiation, but that they did not change much thereafter. Foliar Ca values in the HN treatment are the lowest reported in the literature. This probably explains why the proportion of crown dieback steadily increased over time, reaching values as high as 80% in the HN treatment in 2017.

Water Infiltration into Soil under Oscillating Precipitation Regimes

An analytical study of the problem of water infiltration into a homogeneous unsaturated soil showed that, in the case of periodical water recharge through the soil surface, the character of the flow will tend to uniform with the depth. The stabilization of the flow was found to be due to the effect of two factors: capillary dissipation and nonlinearity. The role of each factor was studied by constructing appropriate exact solutions. An estimate was proposed for the depth at which flow variations become insignificant. This estimate takes into account the joint effect of both these factors. An explicit expression for it contains the hydraulic characteristics of the soil and the main characteristics of the surface recharge regime. The pumping effect was also studied and it was showed that, at some assumptions regarding the soil hydraulic characteristics, it manifests itself in that the time-averaged water content in the top soil layers is less than that at greater depth.

The community of soil fungi associated with the western red cedar (Thuja plicata Donn ex D. Don, 1824)

ABSTRACT The western red cedar (Thuja plicata Donn ex D. Don), an important forest-forming species in the Western part of the North American continent, is an alien species naturalised in Europe. It is popular and highly valued in horticulture. While considering the progressing climate change, it may also be a potential alternative to native species in European forests. The community of soil fungi associated with the western red cedar in forested areas of Europe has not been fully determined. Thus, this study is aimed to identify the community of soil fungi associated with the western red cedar. The experimental plots are located in the Kościan Forest District (51°98’87″ N; 16°23’54″ E). All soil samples were taken from the topsoil layer at a depth of 25 cm with a trowel, three from the centre of natural regeneration (1G, 2G, 5G) and three from the centre stand under the canopy of old-growth western red cedar (3G, 4G, 6G). Fungi were identified directly from the soil based on the ITS1 rDNA region. The derived product was sequenced using Illumina’s sequencing by synthesis (SBS) technology. Sequences were referred to the National Center for Biotechnology Information (NCBI) database applying the BLAST algorithm. The fungal counts were defined based on the number of operational taxonomic units (OTU) in the sample. The OTU number was 835 206, with fungal isolates accounting for 683 095 (81.79%). A total of 8 591 taxa belonging to the Kingdom Fungi were identified. The species with the greatest shares in the community included Mortierella spp. (10.5%), Russula spp. (5.6%), Hydnum spp. (3.44%), Solicoccozyma spp. (3.1%) and Penicillium spp. (2.2%). Results showed that saprotrophs and mycorrhizal fungi predominated in the community. The dominance of ectomycorrhizal fungi over arbuscular ones, quite impressive natural regeneration was shown in T. plicata stands in Kościan. Subsequent research should take into account tree stands in Poland in which natural regeneration does not occur or occurs sporadically.