Effects of Nitrogen Fertilization on Soil Microbial Biomass and Community Functional Diversity in Temperate Grassland in Inner Mongolia,China

Nitrogen (N) fertilization may profoundly affect soil microbial communities. In this study, a field fertilization experiment was conducted in temperate grassland in Inner Mongolia, China to examine the effect of N fertilization on soil microbial properties and the main factors related to the characteristics of soil microbial community. Soil microbial biomass carbon (MBC) and microbial functional diversity along an N gradient were measured over three months (June to August). The result showed that N fertilization significantly decreased MBC under high N treatment (N200, 200 kg N ha^?1 y^?1) compared with the control (N0, 0 kg N ha^?1 y^?1) in the three months. Microbial functional diversity in July and August were significantly increased by low N treatment (N50, 50 kg N ha^?1 y^?1). Among the three fertilization treatments, microbial functional diversity under N200 in the three months was significantly lower than that of N50. The decrease of MBC and functional diversity under N200 were mainly due to the significant decline of plant belowground biomass under high N treatment. The increase of functional diversity under N50 treatment was due to the higher plant aboveground biomass as a result of the higher soil moisture availability. This finding highlighted that the higher N fertilization (N200) was not suitable for the growth and improvement of functional diversity of the soil microbial community, and that site and plant community play an important role in regulating the characteristics of soil microbial community.     

Dynamic Changes of Stipa bungeana Steppe Species Diversity as Better Indicators for Soil Quality and Sustainable Utilization Mode in Yunwu Mountain Nature Reserve,Ningxia, China

Due to serious degradation of typical Stipa bungeana steppe community on the Loess Plateau, a 26‐year (1982–2007) experiment has been carried out by methods of forbidden grazing, cutting, and rotational grazing. Our results show that the process of succession of long‐term enclosed S. bungeana community can be divided into two stages: 1980–1996, the forward succession stage, when the species diversity and biomass reach the peak (33.7 species/m² and 1349.41 g/m², respectively); 1997–2007, the slow succession stage, when the gradually thickening of litter layer (litter depth reaches 3–5 cm) directly causes the reduction of species diversity and biomass to 19.1 species/m² and 863.19 g/m², respectively. While under the cutting and rotational grazing methods, grassland succession can be divided into four stages: 1st–5th year, the continuing growth stage; 6th–9th year, the vigorous competing stage; 10th–15th year, the aggregation growth stage of constructive species with biomass reaching the peak (1444.19 g/m²); and 16th–23rd year, stable growth stage of constructive species, which form sub‐climax and are eventually dominated by S. bungeana, with the species diversity and biomass of 25–27 species/m² and 956.76–1165.35 g/m², respectively. The constructive species suddenly change in the 24th year, and the population of S. grandis increases rapidly to 21 m^?2 accounting for 25% of the total plant population. Long‐term enclosure leads to decreased species diversity and biomass and is not beneficial for grassland renewing. The species diversity and biomass of degraded grassland continuously decrease to 10 species/m² and 392.1 g/m² due to long‐term artificial failure and transitionally grazing, leading to harden soil with slow rainfall infiltration, where plants can only sustain life under the drought condition. Therefore, reasonable cutting and rotational grazing are the methods of choice for the gradual increase of species diversity and promotion of the natural renewal and forward succession of the grassland on Loess Plateau. These results provide reliable information for the diversity dynamic change as better indictors of soil quality and sustainable utilization mode.     

Depletion and recharge of soil water in two stands of norway spruce (picea abies (l.) karst)

Depletion and recharge dynamics of soil water were studied at two forest sites in Northern and Southern Sweden during three growing seasons. At each site, having a stand of Norway spruce (Picea abies (L.) Karst), soil water potential was measured with 90 gypsum blocks in 30 profiles at depths of 6, 20, and 50 cm from the soil surface. The size of the rectangular plots was 250 m². The large variation in soil water potential during desiccation periods extended throughout the measuring range of the gypsum blocks. The soil water potentials, at different times and depths, were log-normally distributed during only parts of the desiccation periods. Due to the large variation and skewed distribution of soil water potentials the nonparametric Spearman rank correlation statistics was used to analyse the pattern of desiccation and rewetting of the soil. In the beginning of a dry period the topsoil was more efficiently desiccated than the subsoil at both sites. This difference lasted throughout all droughts at the southern site and was explained by a higher root density in the topsoil. At the northern site, however, there was no difference in the degree of desiccation at different soil depths during an extended desiccation period. While certain microsites tended to be more depleted than others during desiccation periods, this did not prove to be significantly correlated to the rewetting of the soil after the different droughts. There was a vertical relationship in soil water desiccation in which an accentuated water depletion at the 6 cm soil depth was followed by a similar strong depletion 14 cm lower in the same observation profile. Strongly desiccated observation profiles were not necessarily situated close to each other but seemed randomly spread over the site. There was no relationship between extracted water at any of the three soil depths in the different observation profiles and proximity to trees or tree size.     

Long‐term effects of revegetation on soil hydrological processes in vegetation‐stabilized desert ecosystems

Planting of sand‐binding vegetation in the Shapotou region on the southeastern edge of the Tengger Desert began in 1956. The revegetation programme successfully stabilized formerly mobile dunes in northern China, permitting the operation of the Baotou‐Lanzhou railway. Long‐term monitoring has shown that the revegetation programme produced various ecological changes, including the formation of biological soil crusts (BSCs). To gain insight into the role of BSCs in both past ecological change and current ecological evolution at the revegetation sites, we used field measurements and HYDRUS‐1D model simulations to investigate the effects of BSCs on soil hydrological processes at revegetated sites planted in 1956 and 1964 and at an unplanted mobile dune site. The results demonstrate that the formation of BSCs has altered patterns of soil water storage, increasing the moisture content near the surface (0–5 cm) while decreasing the moisture content in deeper layers (5–120 cm). Soil evaporation at BSC sites is elevated relative to unplanted sites during periods when canopy coverage is low. Rainfall infiltration was not affected by BSCs during the very dry period that was studied (30 April to 30 September 2005); during periods with higher rainfall intensity, differences in infiltration may be expected due to runoff at BSC sites. The simulated changes in soil moisture storage and hydrological processes are consistent with ongoing plant community succession at the revegetated sites, from deep‐rooted shrubs to more shallow‐rooted herbaceous species. Copyright © 2009 John Wiley & Sons, Ltd.     

洞庭湖湿地土壤种子库特征及其与地表植被的相关性

本文研究洞庭湖三种分布于不同水位的主要群落(荻、苔草、虉草)土壤种子库大小组成、垂直分布特征及其地表植被的相关性.结果表明:荻群落土壤种子库密度最高,为44656粒/m2,苔草群落的最低,为15146粒/m2,虉草群落的居中,为31725粒/m2.种子主要分布于土壤表层(0～5 cm),且随土壤剖面深度的增加而迅速递减.三种群落湿地种子库由53种植物组成,分属18科39属,其中多年生物种20种,一或二年生物种33种.在荻、苔草和虉草三种群落中,种子库的多年生物种分别占29.9%、35.2%和38.0%,物种多样性指数分别为0.76、0.70和0.72;地表植被物种多样性指数分别为0.53、0.17和0.45,土壤种子库与相应地表植被相似性系数分别为0.40、0.28和0.52.可见,在洞庭湖这一通江湖泊湿地,多年生地表植被所产生的种子对土壤种子库大小贡献相对有限,种子库可能主要通过其它途径(如水的流动作用)输入.     

Daily variation characteristics of CO_2 emission fluxes and contributions of environmental factors in semiarid grassland of Inner Mongolia, China

Soil respiration refers to the process of soil gener-ating and emitting CO2to the atmosphere under the synthetic effect of different environmental factors,which includes mineralization of soil organic matter involved by microorganism and respiration of plant root system and soil animals.The emission of CO2to the atmosphere through soil respiration is the most important link of carbon cycle process of grassland ecosystem,and also the key ecological process of grassland ecosystem exerting effec…     

Spatial prediction of temporal soil moisture dynamics using HYDRUS‐1D

This article investigates the soil moisture dynamics within two catchments (Stanley and Krui) in the Goulburn River in NSW during a 3‐year period (2005–2007) using the HYDRUS‐1D soil water model. Sensitivity analyses indicated that soil type, and leaf area index were the key parameters affecting model performance. The model was satisfactorily calibrated on the Stanley microcatchment sites with a single point rainfall record from this microcatchment for both surface 30 cm and full‐profile soil moisture measurements. Good correlations were obtained between observed and simulated soil water storage when calibrations for one site were applied to the other sites. We extended the predictions of soil moisture to a larger spatial scale using the calibrated soil and vegetation parameters to the sites in the Krui catchment where soil moisture measurement sites were up to 30 km distant from Stanley. Similarly good results show that it is possible to use a calibrated soil moisture model with measurements at a single site to extrapolate the soil moisture to other sites for a catchment with an area of up to 1000 km² given similar soils and vegetation and local rainfall data. Site predictions were effectively improved by our simple data assimilation method using only a few sample data collected from the site. This article demonstrates the potential usefulness of continuous time, point‐scale soil moisture data (typical of that measured by permanently installed TDR probes) and simulations for predicting the soil wetness status over a catchment of significant size (up to 1000 km²). Copyright © 2012 John Wiley & Sons, Ltd.     

Towards the estimation root-zone soil moisture via the simultaneous assimilation of thermal and microwave soil moisture retrievals

The upcoming deployment of satellite-based microwave sensors designed specifically to retrieve surface soil moisture represents an important milestone in efforts to develop hydrologic applications for remote sensing observations. However, typical measurement depths of microwave-based soil moisture retrievals are generally considered too shallow (top 2–5 cm of the soil column) for many important water cycle and agricultural applications. Recent work has demonstrated that thermal remote sensing estimates of surface radiometric temperature provide a complementary source of land surface information that can be used to define a robust proxy for root-zone (top 1 m of the soil column) soil moisture availability. In this analysis, we examine the potential benefits of simultaneously assimilating both microwave-based surface soil moisture retrievals and thermal infrared-based root-zone soil moisture estimates into a soil water balance model using a series of synthetic twin data assimilation experiments conducted at the USDA Optimizing Production Inputs for Economic and Environmental Enhancements (OPE³) site. Results from these experiments illustrate that, relative to a baseline case of assimilating only surface soil moisture retrievals, the assimilation of both root- and surface-zone soil moisture estimates reduces the root-mean-square difference between estimated and true root-zone soil moisture by 50% to 35% (assuming instantaneous root-zone soil moisture retrievals are obtained at an accuracy of between 0.020 and 0.030 m³ m⁻³). Most significantly, improvements in root-zone soil moisture accuracy are seen even for cases in which root-zone soil moisture retrievals are assumed to be relatively inaccurate (i.e. retrievals errors of up to 0.070 m³ m⁻³) or limited to only very sparse sampling (i.e. one instantaneous measurement every eight days). Preliminary real data results demonstrate a clear increase in the R² correlation coefficient with ground-based root-zone observations (from 0.51 to 0.73) upon assimilation of actual surface soil moisture and tower-based thermal infrared temperature observations made at the OPE³ study site.     

Thresholds and relations for soil‐hydraulic and soil‐physical properties as a function of burn severity 4 years after the 2011 Las Conchas Fire,New Mexico,USA

Wildfire effects on soil‐physical and ‐hydraulic properties as a function of burn severity are poorly characterized, especially several years after wildfire. A stratified random sampling approach was used in 2015 to sample seven sites representing a spectrum of remotely sensed burn severity in the area impacted by the 2011 Las Conchas Fire in New Mexico, USA. Replicate samples from each site were analysed in the laboratory. Linear and linear indicator regression were used to assess thresholds in soil‐physical and ‐hydraulic properties and functional relations with remotely sensed burn severity. Significant thresholds were present for initial soil‐water content (θ_i) at 0–6 cm depth between the change in the Normalized Burn Ratio (dNBR) equal to 618–802, for bulk density (ρ_b) at 3–6 cm between dNBR equal to 416–533, for gravel fraction at 0–1 cm between dNBR equal to 416–533, for fines (the silt + clay fraction) at 0–1 cm for dNBR equal to 416–533, and for fines at 3–6 cm for dNBR equal to 293–416. Significant linear relations with dNBR were present between ρ_b at 0–1 cm, loss on ignition (LOI) at 0–1 cm, gravel fraction at 0–1 cm, and the large organic fraction at 1–3 cm. No thresholds or effects on soil‐hydraulic properties of field‐saturated hydraulic conductivity or sorptivity were observed. These results suggest that ρ_b and LOI at 0–1 cm have residual direct impacts from the wildfire heat impulse. The θ_i threshold is most likely from delayed groundcover/vegetation recovery that increases evaporation at the highest burn severity sites. Gravel and silt + clay thresholds at 0–1 cm at the transition to high burn severity suggest surface gravel lag development from hydraulic erosion. Thresholds in ρ_b from 3 to 6 cm and in silt + clay fraction from 3 to 6 cm appear to be the result of soil variability between sites rather than wildfire impacts. This work suggests that gravel‐rich soils may have increased resilience to sustained surface runoff generation and erosion following wildfire, with implications for assessments of postwildfire hydrologic and erosion recovery potential.     

Canopy rainfall storage capacity as affected by sub‐alpine grassland degradation in the Qinghai–Tibetan Plateau,China

Grassland degradation resulting from global climate change, overgrazing, and rodent damage is expected to influence the magnitude of canopy hydrological fluxes because of reduced vegetation biomass and changed species composition. The objectives of this study were to estimate herbaceous canopy rainfall storage capacity (S) along three different stages of sub‐alpine grassland degradation (non‐degraded, lightly degraded and moderately degraded) in the Qinghai–Tibetan Plateau, China, and relate changes in S to canopy properties. An artificial wetting method and the water budget balance method, using rain simulations, were used for estimating S. Grassland degradation significantly reduced S. In non‐degraded, lightly degraded and moderately degraded grasslands, S estimated using the artificial wetting method were 0.612 ± 0.08 mm, 0.289 ± 0.04 mm, and 0.217 ± 0.01 mm, respectively; S estimated using the water budget balance method were 0.979 ± 0.32 mm, 0.493 ± 0.13 mm, and 0.419 ± 0.09 mm, respectively. These changes could be explained by accompanying changes in above‐ground biomass and leaf area index, as well as changes in species composition. Species‐specific rainfall storage capacity varied by a factor of 2.7 among the investigated species, with graminoids having the lowest values. Leaf area index was more correlated to S than was canopy coverage. Converting fresh weight of non‐leaf tissues into effective leaf area of the corresponding species and then introducing a coefficient of leaf area according to the specific storage capacity of leaves improved the linear relationship between S and leaf area index. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of plant roots on the soil erosion rate under simulated rainfall with high kinetic energy

ABSTRACT

This study examined the effects of herbaceous plant roots on interrill erosion using two herbaceous species: clover (Trifolium repens) and oats (Avena sativa). We developed a simple rainfall simulator with relatively high normalized kinetic energy (KE; 23.2 J m^?2 mm^?1). Under simulated rainfall, we measured eroded soil for 42 boxes with various amounts of aboveground and belowground biomass. Aboveground vegetation had a significant effect on the soil erosion rate (SER). We found a clear negative relationship between the percent vegetation cover (c) and the SER. In contrast, plant roots showed no effects on the SER. The SER was not significantly different between the boxes with and without plant roots under similar c conditions. Thus, plant roots could have less of an effect on the SER under higher KE conditions.

Editor M.C. Acreman Associate editor N. Verhoest     

Effects of rainfall intensity and slope gradient on the application of vetiver grass mulch in soil and water conservation

The objective of this study is to investigate the effect of rainfall intensity and slope gradient on the performance ofvetiver grass mulch (VGM) in soil and water conservation.The study involved field ...     

The impact of natural vegetation restoration on surface soil moisture of secondary forests and shrubs in the karst region of southwest China

Soil moisture is crucial to vegetation restoration in karst areas, and climate factors and vegetation restoration are key factors affecting changes in soil moisture. However, there is still much controversy over the long-term changes in soil moisture during vegetation restoration. In order to reveal the changes in soil moisture during vegetation restoration, we conducted long-term positioning monitoring of soil moisture at 0–10 and 10–20 cm on secondary forests sample plot (SF, tree land) and shrubs sample plot (SH, shrub land) in karst areas from 2013 to 2020. The results showed that the aboveground biomass of SF and SH increased by 50% and 240%, respectively, and the soil moisture of the SF and SH showed an increasing trend. When shrubs are restored to trees in karst areas, the soil moisture becomes more stable. However, the correlation coefficients (R²) between the annual rainfall and the annual average soil moisture of SF and SH are 0.84 and 0.55, respectively, indicating that soil moistures in tree land are more affected by rainfall. The soil moisture of shrubs and trees are relatively low during the months of alternating rainy and dry seasons. Rainfall has a very significant impact on the soil moisture of tree land, while air temperature and wind speed have a significant impact on the soil moisture of tree land, but the soil moistures of shrub land are very significantly affected by rainfall and relative humidity. Therefore, during the process of vegetation restoration from shrubs to trees, the main meteorological factors that affect soil moisture changes will change. The results are important for understanding the hydrological processes in the ecological restoration process of different vegetation types in karst areas.     

Soil sealing and soil water content under no‐tillage and conventional tillage in irrigated corn: Effects on grain yield

The main objective of this research was to analyse the effect of soil management on soil sealing and on soil water content under contrasting tillage practices and its influence on corn yield. The experimental research was carried out in a field cultivated with irrigated corn differentiated into three zones representing a gradient of soil texture (Z1, Z2, and Z3, i.e., increasingly coarser). Two plots under different soil management practices (conventional intensive tillage, CT, and no‐tillage, NT) were selected in each zone. The susceptibility to sealing of each soil and the steady infiltration rates were evaluated in the laboratory subjecting the soils to rainfall simulation applied at an intensity of 25 mm h^?1. In addition, soil porosity under each treatment was quantified. Soil water content (0–90 cm depth) was determined gravimetrically at the beginning and the end of the growing cycle and at the surface (0–5 cm) during three growing seasons and continuously at two depths (5–15 and 50–60 cm) during the last growing cycle. Soil water content was simulated using the SIMPEL model, which was calibrated for the experimental conditions. Corn yield and above‐ground biomass were also analysed. Significant differences in soil sealing among zones, with decreasing soil sealing for coarser textures, and treatments were observed with infiltration rates that were near twice in NT than in CT, being the effect of soil cover significant in the reduction of soil detachment and soil losses. NT showed higher soil water content than CT, especially in the surface layers. Above‐ground biomass production was smaller in CT than in NT, and in the areas with higher sealing susceptibility was 30% to 45% smaller than in other zones, reaching the smallest values in Z1. A similar reduction in corn yield was observed between treatments being smaller in CT than in NT. No‐tillage has been confirmed as an effective technique that benefits soil physical properties as well as crop yields in relation to CT, being its impact greater in soils susceptible to sealing.     

Quantifying soil loss with in-situ cosmogenic 10Be and 14C depth-profiles

Conventional methods for the determination of past soil erosion provide only average rates of erosion of the sediment's source areas and are unable to determine the rate of at-a-site soil loss. In this study, we report in-situ produced cosmogenic ¹⁰Be, and ¹⁴C measurements from erratic boulders and two depth-profiles from Younger Dryas moraines in Scotland, and assess the extent to which these data allow the quantification of the amount and timing of site-specific Holocene soil erosion at these sites. The study focuses on two sites located on end moraines of the Loch Lomond Readvance (LLR): Wester Cameron and Inchie Farm, both near Glasgow. The site near Wester Cameron does not show any visible signs of soil disturbance and was selected in order to test (i) whether a cosmogenic nuclide depth profile in a sediment body of Holocene age can be reconstructed, and (ii) whether in situ ¹⁰Be and ¹⁴C yield concordant results. Field evidence suggests that the site at Inchie Farm has undergone soil erosion and this site was selected to explore whether the technique can be applied to determine the broad timing of soil loss. The results of the cosmogenic ¹⁰Be and ¹⁴C analyses at Wester Cameron confirm that the cosmogenic nuclide depth-profile to be expected from a sediment body of Holocene age can be reconstructed. Moreover, the agreement between the total cosmogenic ¹⁰Be inventories in the erratics and the Wester Cameron soil/till samples indicate that there has been no erosion at the sample site since the deposition of the till/moraine. Further, the Wester Cameron depth profiles show minimal signs of homogenisation, as a result of bioturbation, and minimal cosmogenic nuclide inheritance from previous exposure periods. The results of the cosmogenic ¹⁰Be and ¹⁴C analyses at Inchie Farm show a clear departure from the zero-erosion cosmogenic nuclide depth profiles, suggesting that the soil/till at this site has undergone erosion since its stabilisation. The LLR moraine at the Inchie Farm site is characterised by the presence of a sharp break in slope, suggesting that the missing soil material was removed instantaneously by an erosion event rather than slowly by continuous erosion. The results of numerical simulations carried out to constrain the magnitude and timing of this erosion event suggest that the event was relatively recent and relatively shallow, resulting in the removal of circa 20–50 cm of soil at a maximum of ∼2000 years BP. Our analyses also show that the predicted magnitude and timing of the Inchie Farm erosion event are highly sensitive to the assumptions that are made about the background rate of continuous soil erosion at the site, the stabilisation age of the till, and the density of the sedimentary deposit. All three parameters can be independently determined a priori and so do not impede future applications to other localities. The results of the sensitivity analyses further show that the predicted erosion event magnitude and timing is very sensitive to the ¹⁴C production rate used and to assumptions about the contribution of muons to the total production rate of this nuclide. Thus, advances in this regard need to be made for the method presented in this study to be applicable with confidence to scenarios similar to the one presented here.     

Rainfall runoff and erosion in Napa Valley vineyards: effects of slope,cover and surface roughness

The effects of slope, cover and surface roughness on rainfall runoff, infiltration and erosion were determined at two sites on a hillside vineyard in Napa County, California, using a portable rainfall simulator. Rainfall simulation experiments were carried out at two sites, with five replications of three slope treatments (5%, 10% and 15%) in a randomized block design at each site (0%bsol;64 m² plots). Prior to initiation of the rainfall simulations, detailed assessments, not considered in previous vineyard studies, of soil slope, cover and surface roughness were conducted. Significant correlations (at the 95% confidence level) between the physical characteristics of slope, cover and surface roughness, with total infiltration, runoff, sediment discharge and average sediment concentration were obtained. The extent of soil cracking, a physical characteristic not directly measured, also affected analysis of the rainfall–runoff–erosion process. Average cumulative runoff and cumulative sediment discharge from site A was 87% and 242% greater, respectively, than at site B. This difference was linked to the greater cover, extent of soil cracking and bulk density at site B than at site A. The extent of soil cover was the dominant factor limiting soil loss when soil cracking was not present. Field slopes within the range of 4–16%, although a statistically significant factor affecting soil losses, had only a minor impact on the amount of soil loss. The Horton infiltration equation fit field data better than the modified Philip's equation. Owing to the variability in the ‘treatment’ parameters affecting the rainfall–runoff–erosion process, use of ANOVA methods were found to be inappropriate; multiple‐factor regression analysis was more useful for identifying significant parameters. Overall, we obtained similar values for soil erosion parameters as those obtained from vineyard erosion studies in Europe. In addition, it appears that results from the small plot studies may be adequately scaled up one to two orders of magnitude in terms of land areas considered. Copyright © 2000 John Wiley & Sons, Ltd.     

Carbon fluxes from eroding peatlands – the carbon benefit of revegetation following wildfire

Peatlands are among the largest long‐term soil carbon stores, but their degradation can lead to significant carbon losses. This study considers the carbon budget of peat‐covered sites after restoration, following degradation by past wildfires. The study measured the carbon budget of eight sites: four restored‐revegetated sites, two unrestored bare soil control sites, and two intact vegetated controls over two years (2006–2008). The study considered the following flux pathways: dissolved organic carbon (DOC); particulate organic carbon (POC); dissolved carbon dioxide (CO₂); primary productivity; net ecosystem respiration, and methane (CH₄). The study shows that unrestored, bare peat sites can have significant carbon losses as high as 522 ± 3 tonnes C/km²/yr. Most sites showed improved carbon budgets (decreased source and/or increased sink of carbon) after restoration; this improvement was mainly in the form of a reduction in the size of the net carbon source, but for one restored site the measured carbon budget after four years of restoration was greater than observed for vegetated controls. The carbon sequestration benefit of peatland restoration would range between 122 and 833 tonnes C/km²/yr. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of soil water-repellent layer depth on post-wildfire hydrological processes

Soil water repellency induced by wildfires can alter hydraulic properties and hydrologic processes; however, the persistence and vertical position (i.e., depth) of water-repellent layers can vary between systems and fires, with limited understanding of how those variations affect infiltration processes. This study occurred in two forested locations in the south-central Appalachian Mountains that experienced wildfires in late 2016: Mount Pleasant Wildfire Refuge, Virginia, and Chimney Rock State Park, North Carolina. In each location, sites were selected to represent unburned conditions and low to moderate burn intensities. At each site, we measured the soil water repellency at the surface (ash layer or O horizon) and ~2 cm below the surface (A horizon) using the water drop penetration time method (n = 10–14). Soil water content was also measured over the upper 10 cm of the soil (n = 10), and infiltration tests were conducted using a tension infiltrometer (n = 6–8). The results showed that soil repellency was highest in the surface layer at the Mount Pleasant location and was highest in the subsurface layer at the Chimney Rock location. Soil water content was lower in unburned soil than in burned soil, especially for measurements taken immediately postfire, with soil water content negatively correlated with water repellency. Water repellency in the surface layer significantly reduced relative infiltration rates (estimated as differences between initial and steady-state rates), whereas subsurface water repellency did not affect relative infiltration. As a result, water repellency persisted longer in sites with surface as opposed to subsurface water repellency. Finally, differences between burned and unburned sites showed that although the wildfires increased the occurrence of water repellency, they did not alter the underlying relationship between relative infiltration and water repellency of the surface soil.     

Estimation of soil erosion in the Xihanshui River Basin by using 137Cs technique

The Cesium-137 technique was used to estimate soil erosion in the Xihanshui River Basin.More than 100 samples were taken from 10 sites and 20 hillslopes with a 10cm diameter hand-operated core driller.Each sample was 60 cm long.The ¹³⁷Cs activity was analyzed by gamma spectrometry.The simplified mass balance model and the profile distribution model were used to calculate soil erosion and deposition rate.The local ¹³⁷Cs reference ranged from 1,600 to 2,402 Bq m^-2.The data shows an exponential decrease of mass concentration and amount with depth in an undisturbed soil profile.Soil erosion in the river basin is moderate or severe on cultivated land with annual erosion rates of 2,000-6,000 t km^-2yr^-1.In general,very severe or severe soil erosion occurred at the upper slope sections,moderate or severe soil erosion at the middle section,and moderate or slight soil erosion at the lower slope sections.On the slopes with natural vegetation,consisting of herbaceous and wood species,the erosion rate is much lower or not detectable.On the lower section of slopes with well-developed vegetation however,there was no soil loss,instead deposition occurred at a rate of more than 300 t km^-2 yr^-1.The slope gradient and vegetation cover affected soil erosion and deposition rates.In general,the rate of soil erosion was proportional to the slope gradient and inversely proportional to the degree of vegetative cover.     

Soil moisture dynamics in coastal savanna soils in the tropics under different soil management practices

Abstract

Soil moisture is important for crop cultivation and its adequacy to meet crop-water requirements is determined by the degree of soil management practised and the quantity of water applied to the soil. This study investigates soil moisture dynamics on three plots: Bare (clean, weeds removed), Weedy (kept weedy), and Mulched (cleared of weeds and fully covered with grass mulch) during rainy and dry periods at the Teaching and Research Farm at the University of Cape Coast, in the coastal savanna zone of Ghana. Soil moisture dynamics under different levels of soil compaction were also studied. A Massey Ferguson tractor (MF265) was used to compact the soil at various levels by making 0, 1, 5, 9 and 13 passes. During both the rainy and the dry periods, moisture retention in the soil under bare, weedy and mulched plots increased with depth. During the rainy period, the mean soil moisture retention was in the order: Mulched > Weedy > Bare at both 0–20 cm and 20–40 cm depths. Within a 7–day period, soil moisture measurements from a day after heavy rainfall (intensity > 7 mm h^?1) gave mean moisture losses of 2.7, 4.1 and 3.9% for the Bare, Weedy and Mulched plots, respectively. During the dry period, however, the mean soil moisture retention was of the order: Mulched > Bare > Weedy at both 0–20 cm and 20–40 cm depths. Mean moisture loss during a 7–day dry period was 4.5, 2.9 and 3.4% for the Bare, Weedy and Mulched plots, respectively. Under different levels of soil compaction, the mean moisture retention in the soil increased from 8.3% at 0 pass to 17.8% at 13 passes within the 0–20 cm depth, whilst it decreased from 13.3 to 5.9% from 0 to 13 passes, respectively, within the 20–40 cm depth. It was realized that at less than two passes, the mean soil moisture retention within the 0–20 cm depth was less than the mean moisture retention within the 20–40 cm depth, but the converse happened for more than two passes. The study showed that mulching the soil surface helped to retain enough soil moisture during both the rainy and the dry seasons. Also, soil with high sand content required some sort of soil compaction in order to retain enough moisture at the crop rooting zone.