Soil Hydrological Properties Research Articles

An improved distributed sensing method for monitoring soil moisture profile using heated carbon fibers

Soil moisture variation with respect to depth directly affects the engineering properties of soil and the health state of plants. At the present, there are few techniques that can satisfactorily quantify the vertical moisture profile within the soil medium. In this paper, a fiber optic sensor-based distributed temperature sensing (DTS) technique is introduced for soil moisture profile mapping. In this technique, a carbon fiber heated sensing-tube (CFHST) is integrated into conventional fiber optic sensing cable to improve the sensitivity, accuracy and spatial resolution of the measurement of soil moisture profile. The CFHST consists of three parts: the inner tubing, the carbon fiber heated cable (CFHC) tightly wrapped on inner tubing, and the interface screws installed on both ends of the inner tubing. The length of a unit CFHST is adjustable according to the actual demand of a specified application. The power supply model and installation method in field are introduced. Laboratory tests were conducted to establish the relationship between soil moisture and thermal response of CFHST. A foundation pit dewatering test was also carried out to validate the field performance of this monitoring technique. The test results show that the borehole-embedded sensor monitored and recorded the continuous change of soil moisture profile accurately (RMSE = 0.046 m3/m3). This technique can effectively capture the distribution profile of soil moisture along the depth direction, which provides a new approach to investigate the physical and hydrological properties of soils.

Dynamic effects of biochar concentration and particle size on hydraulic properties of sand

AbstractLarge‐scale application of biochar has been promoted as a strategy for improving soil quality in agricultural and contaminated lands, as biochar has the potential to alter soil physical and biogeochemical properties. Biochar at different concentrations has been shown to have inconsistent effects on soil hydrological properties, yet the cause of the inconsistency is not well understood. To investigate the relative roles of biochar size and concentration, we mixed pure sand with a commercially available biochar varying its concentrations and particle sizes and measured saturated (Ksat) and unsaturated hydraulic conductivity and water‐retention characteristics. An increase in the concentration of fine biochar (<2 mm) consistently decreased Ksat and increased saturated moisture content. In contrast, an increase in the concentration of unsieved (mixture of coarse and fine) biochar up to 5% (by volume) increased Ksat, whereas any further increases in unsieved biochar concentration decreased Ksat. Increase in biochar concentration, irrespective of particle size, consistently decreased the unsaturated hydraulic conductivity. Measuring the changes in the characteristics of water‐retention curves of biochar–sand mixtures with biochar particle size, we showed that added biochar can either decrease (clog) or increase pore spaces in the mixture on the basis of the quantity of fine biochar fraction, which in turn could decrease or increase the hydraulic conductivity of the mixture. Thus, biochar concentration and particle size must be taken into consideration to maximize the intended hydrological benefits of biochar amendment.

Human influences on streamflow drought characteristics in England and Wales

Abstract. Human influences can affect streamflow drought characteristics and propagation. The question is where, when and why? To answer these questions, the impact of different human influences on streamflow droughts were assessed in England and Wales, across a broad range of climate and catchments conditions. We used a dataset consisting of catchments with near-natural flow as well as catchments for which different human influences have been indicated in the metadata (“Factors Affecting Runoff”) of the UK National River Flow Archive (NRFA). A screening approach was applied on the streamflow records to identify human-influenced records with drought characteristics that deviated from those found for catchments with near-natural flow. Three different deviations were considered, specifically deviations in (1) the relationship between streamflow drought duration and the base flow index, BFI (specifically, BFIHOST, the BFI predicted from the hydrological properties of soils), (2) the correlation between streamflow and precipitation and (3) the temporal occurrence of streamflow droughts compared to precipitation droughts, i.e. an increase or decrease in streamflow drought months relative to precipitation drought months over the period of record. The identified deviations were then related to the indicated human influences. Results showed that the majority of catchments for which human influences were indicated did not show streamflow drought characteristics that deviated from those expected under near-natural conditions. For the catchments that did show deviating streamflow drought characteristics, prolonged streamflow drought durations were found in some of the catchments affected by groundwater abstractions. Weaker correlations between streamflow and precipitation were found for some of the catchments with reservoirs, water transfers or groundwater augmentation schemes. An increase in streamflow drought occurrence towards the end of their records was found for some of the catchments affected by groundwater abstractions and a decrease in streamflow drought occurrence for some of the catchments with either reservoirs or groundwater abstractions. In conclusion, the proposed screening approaches were sometimes successful in identifying streamflow records with deviating drought characteristics that are likely related to different human influences. However, a quantitative attribution of the impact of human influences on streamflow drought characteristics requires more detailed case-by-case information about the type and degree of all different human influences. Given that, in many countries, such information is often not readily accessible, the approaches adopted here could provide useful in targeting future efforts. In England and Wales specifically, the catchments with deviating streamflow drought characteristics identified in this study could serve as the starting point of detailed case study research.

Effects of three morphometric features of roots on soil water flow behavior in three sites in China

Soil physical properties, infiltrability, and water flow behavior are closely associated with root morphology. In this study, dye tracer experiments were conducted in the field to assess the effects of roots with various morphometric features on soil water flow behavior and soil infiltrability. Preferential flow is the dominant type of water flow in the three study sites (Minqin, Dongtai, and Mengla). The presence of roots caused noncapillary porosity and saturated hydraulic conductivity to increase by 26% and 252% in the Minqin, 92% and 93% in the Dongtai, and 234% and 96% in the Mengla, respectively, relative to that in in soils without roots. The various morphometric features of roots affect water flow behavior in soil. The fibrous roots of maize induced water to flow and distribute evenly throughout the plough layer of the study site in Minqin. Furrows and ridges in this site exhibited different soil physical and hydrological properties. Furrows could store higher amounts of water than ridges, thereby increasing the likelihood of water absorption by plants. In Dongtai, ponding and surface runoff occurred when water infiltration was inhibited by the mud layer, which exhibited a high soil bulk density value of 1.43 g cm−3 and a low saturated hydraulic conductivity value of 1.67 × 10−5 cm s−1. These phenomena were not observed in plots the smooth roots of Spartina alterniflora penetrated the mud layer. In this site, preferential flow and lateral flow, which is triggered by the sandy loam layer, are important for water discharge from the beach to the ocean. In Mengla, water flowed evenly on hard soil, which exhibited a high bulk density value of 1.43 g cm−3. The fine roots of rubber could guide water infiltration into deep soil layers (73.54 cm), thereby redistributing water to the root zones of rubber trees. Therefore, our findings indicated that water infiltration behavior, which is crucial for water distribution, is affected by the various morphometric features of roots.

Flash Flood Risk Assessment for Kyushu Island, Japan

Using advanced geospatial analysis technologies, flash flood risk is assessed for the island of Kyushu, Japan. In this study, the flash flood risk is redefined in terms of the flash flood potential index (FFPI) and the flash flood residential hazard (FFRH). The island experiences rainy weather, especially in the summer (June–August), when catastrophic flash flood events have historically occurred. Studies of the surface hydrological properties of the island are very rare and localized; hence, geospatial techniques are most appropriate for the assessment process. The Soil Conservation Service rainfall-runoff model was used to estimate hydrological responses on the island. Four factors were included in the flash flood assessment. A multi-criteria analysis was carried out to map the FFPI and FFRH from the evaluation factors. The results show that the highest flash flood risk occurs in the northern parts of the island, where the soil displays relatively low infiltration rates and relatively high curve numbers, despite the comparatively low precipitation rates that occur there. The results indicate that soil hydrological properties are the main driving forces of flash floods, especially in regions with low precipitation rates. The results of this research are consistent with previous in situ measurements of runoff made at several sites on the island. The results also show a strong geographic correlation with historical flash flood events on the island. This research validates the use of geospatial analysis for large geographic regions where in situ measurements cannot be taken due to time or cost constraints. The results of this study provide decision makers with the information needed to select a management strategy to address possible future flash flood events that considers safety and water harvesting.

Impact of soil hydrological properties on the 7Be depth distribution and the spatial variation of 7Be inventories across a small catchment

The natural fallout radionuclide 7Be is used as a tracer allowing estimates of soil redistribution on an event-based time scale. The observed 7Be inventory in the soil is converted to soil redistribution by comparing the 7Be inventory at a stable reference site to the location of interest and taking the 7Be depth distribution in the surface soil into account. The relaxation mass depth (h0), describing this depth distribution, is assumed to be uniform across the study area, whereas the 7Be inventory at the reference site represents the balance of atmospheric 7Be input and radioactive decay. The 7Be reference inventory should, therefore, not be influenced by soil redistribution or by any variation in physico-chemical characteristics of the soil within the entire study area. Most studies to date use 7Be to monitor soil redistribution on the spatial scale of a hillslope. However, if the assumptions of spatially uniform fallout and rapid and irreversible sorption of 7Be to soil particles can be extended over a larger area, 7Be could be used to monitor soil redistribution at the catchment scale. In this paper, the variability in 7Be distribution in the soil at hillslope and catchment scales is explored and possible sources of this variability are identified. To assess the impact of variability in soil hydraulic conductivity on the depth penetration of 7Be in surface soil, a rainfall simulation experiment with 9Be spiked rainfall was performed on artificially compacted soil cores. These rainfall simulation experiments indicated a significant positive correlation between the saturated hydraulic conductivity (Ksat) and the relaxation mass depth and, thus, demonstrated that the assumption of a spatially constant relaxation mass depth is likely to be invalid. An empirical correction factor is proposed to circumvent this problem. This work demonstrates the importance of assessing variability in soil hydrological properties across a study area and is also relevant to studies concerning the vertical transport of fallout contaminants in surface soil. To assess spatial variability in fallout across a catchment and across soil types, soil trays containing different soil types were placed at three reference locations in a small catchment of 8km2 across a nine month period. The spatial variation in 7Be reference inventory between the sites in the catchment was not larger than the variation within one reference site (37% and 36% respectively), indicating that the uncertainty on the reference inventory will be similar over the small catchment. However, the different soil types displayed diverse 7Be depth profiles and total 7Be inventories, suggesting that a clear understanding of sorption behavior across the soil types present in a catchment is needed prior to the use of 7Be as a catchment-scale sediment tracer.

The Effects of Timing of Inundation on Soil Physical Quality in the Water-Level Fluctuation Zone of the Three Gorges Reservoir Region, China

Core Ideas The soil pore network was analyzed by micro-CT images of intact soil core samples. The VESS method using the mass fractal dimension was applied to evaluate soil structural quality. Inundation decreases the number of soil pores and total porosity. Drainable micropores shift to non-drainable micropores after inundation in the reservoir zone. With the completion of the Three Gorges Dam, soils between the elevations of 145 and 175 m are exposed or submerged seasonally. Soil hydrological and physical properties are changed. A detailed investigation was performed to examine the influence of the timing of inundation on soil physical quality. Samples were collected in the water level fluctuation (WLF) zone and non-WLF zone in Zhongxian County, Chongqing. Soil samples were taken from depths of 0 to 10, 10 to 20, 20 to 30, and 30 to 40 cm. Soil structural quality was assessed by the visual evaluation of soil structure (VESS) method in situ; mean weight diameter (MWD) and mass fractal dimension (Dm) were measured to represent soil aggregate stability; and the soil water retention curve and computed microtomography (micro-CT) images were used to show soil pore networks. Our findings show a deterioration of soil structure indicated by a high structural quality (Sq) score in VESS (the higher the Sq score, the worse the soil structural quality) and a decline in soil aggregate stability indicated by low MWD and low Dm in the WLF zone. The data from both the soil water retention curve and micro-CT images demonstrate a deterioration of soil physical quality through decreased porosity and a shift of drainable micropores (0.1 < radii < 125 μm) to non-drainable micropores (radii < 0.1 μm) in the WLF zone of the Three Gorges Reservoir. The potential of environmental hazards of soil in WLF zone was also investigated.

The Effects of Timing of Inundation on Soil Physical Quality in the Water‐Level Fluctuation Zone of the Three Gorges Reservoir Region, China

Core Ideas The soil pore network was analyzed by micro‐CT images of intact soil core samples. The VESS method using the mass fractal dimension was applied to evaluate soil structural quality. Inundation decreases the number of soil pores and total porosity. Drainable micropores shift to non‐drainable micropores after inundation in the reservoir zone. With the completion of the Three Gorges Dam, soils between the elevations of 145 and 175 m are exposed or submerged seasonally. Soil hydrological and physical properties are changed. A detailed investigation was performed to examine the influence of the timing of inundation on soil physical quality. Samples were collected in the water level fluctuation (WLF) zone and non‐WLF zone in Zhongxian County, Chongqing. Soil samples were taken from depths of 0 to 10, 10 to 20, 20 to 30, and 30 to 40 cm. Soil structural quality was assessed by the visual evaluation of soil structure (VESS) method in situ; mean weight diameter (MWD) and mass fractal dimension (Dm) were measured to represent soil aggregate stability; and the soil water retention curve and computed microtomography (micro‐CT) images were used to show soil pore networks. Our findings show a deterioration of soil structure indicated by a high structural quality (Sq) score in VESS (the higher the Sq score, the worse the soil structural quality) and a decline in soil aggregate stability indicated by low MWD and low Dm in the WLF zone. The data from both the soil water retention curve and micro‐CT images demonstrate a deterioration of soil physical quality through decreased porosity and a shift of drainable micropores (0.1 &lt; radii &lt; 125 μm) to non‐drainable micropores (radii &lt; 0.1 μm) in the WLF zone of the Three Gorges Reservoir. The potential of environmental hazards of soil in WLF zone was also investigated.

Heterogeneity in Event-Based Soil Hydrologic Response to Different Land Use Types in Upper River Njoro Catchment, Kenya

Soil hydrologic response depends on the soil characteristics such as infiltration capacity, porosity, organic matter content and bulk density. Knowledge on the dynamics of these soil parameters and soil hydrologic response as a result of different land use types is crucial for formulation and adoption of proper soil and water conservation techniques for increased agricultural production. In this research, soil hydrologic response to different land use types is evaluated. Four land use types were purposely selected. These included natural forest, deforested land, fallow agricultural land and grassland. Soil samples were collected and soil hydraulic and hydrological properties that included soil texture, bulk density, saturated hydraulic conductivity, porosity and organic matter content were determined in the soil laboratory. The evaluated soil hydrological response parameters included runoff coefficients, infiltration rate, water repellency and ponding time. The findings showed that the highest and lowest mean bulk density of 1.36 and 0.96 g/cm3 was recorded for deforested and natural forest land respectively. The highest mean saturated hydraulic conductivity (170.21cm/day), porosity (0.62) and organic matter content (4.63%) were observed in the natural forest while the lowest values (24.78cm/day, 0.47 and 0.75%) respectively were found in the deforested land. High water repellency (100.34 cm/hr) and runoff coefficient (0.0077) was recorded in the deforested areas. The findings of this indicate how different land use types affect on-site hydrologic response and generation of stream flow in the catchment hence providing baseline data for future soil and water relations research.

Spatial Distribution of Soil Hydrological Properties in the Kilombero Floodplain, Tanzania

Analysis and interpretation of soil properties dynamics is a keystone in understanding the hydrologic responses and yield potential of floodplain wetlands. This study characterizes the distribution and spatial trends of selected soil physical properties in the Kilombero floodplain, Tanzania. A total of 76 composite soil samples were taken from 0 to 20 cm and 20 to 40 cm depth in a regular grid design across three hydrological zones, related to flooding intensity defined as fringe, middle, and riparian during the rainy season of 2015. The samples were analyzed for soil texture, bulk density, organic carbon, and saturated hydraulic conductivity. Seasonal soil moisture content was monitored at depths of 10, 20, 30, and 40 cm, using 17 frequency domain reflectometry profile probes type PR2, installed at each hydrological zone for 18 months (March 2015–August 2016). Data were subjected to classical statistical and geostatistical analyses. Results showed significant (p &lt; 0.05) differences in bulk density, texture, soil organic carbon (SOC), and saturated hydraulic conductivity (Ksat) across the hydrological zones. Bulk density showed a clear increasing trend towards the fringe zone. Mean Ksat was highest at the riparian zone (69.15 cm·d−1), and clay was higher in the riparian (20.3%) and middle (28.7%) zones, whereas fringe had the highest percentage of sand (33.7–35.9%). Geostatistical spatial results indicated that bulk density, silt, and SOC at 0–20 cm had intermediate dependence, whereas other soil properties at both depths had high spatial dependence. Soil moisture content showed a significant (p &lt; 0.05) difference across the hydrological zones. The riparian zone retained the highest soil moisture content compared to the middle and fringe zone. The temporal soil moisture pattern corresponded to rainfall seasonality and at the riparian zone, soil moisture exhibited a convex shape of sloping curve, whereas a concave sloping curve for topsoil and for the middle zone at the subsoil was observed during the start of the dry season. Our results are seen to contribute to a better understanding of the spatial distribution of soil properties and as a reference for soil and water management planning in the floodplain.

Impact of multi-day rainfall events on surface roughness and physical crusting of very fine soils

Soil surface roughness (SSR), a description of the micro-relief of soils, affects the surface storage capacity of soils, influences the threshold flow for wind and water erosion and determines interactions and feedback processes between the terrestrial and atmospheric systems at a range of scales. Rainfall is an important determinant of SSR as it can cause the dislocation, reorientation and packing of soil particles and may result in the formation of physical soil crusts which can, in turn, affect the roughness and hydrological properties of soils. This paper describes an experiment to investigate the impact of a multi-day rainfall event on the SSR and physical crusting of very fine soils with low organic matter content, typical of a semi-arid environment. Changes in SSR are quantified using geostatistically-derived indicators calculated from semivariogram analysis of high resolution laser scans of the soil surface captured at a horizontal resolution of 78μm (0.078mm) and a vertical resolution of 12μm (0.012mm). Application of 2mm, 5mm and 2mm of rainfall each separated by a 24h drying period resulted in soils developing a structural two-layered ‘sieving’ crust characterised by a sandy micro-layer at the surface overlying a thin seal of finer particles. Analysis of the geostatistics and soil characteristics (e.g. texture, surface resistance, infiltration rate) suggests that at this scale of enquiry, and for low rainfall amounts, both the vertical and horizontal components of SSR are determined by raindrop impact rather than aggregate breakdown. This is likely due to the very fine nature of the soils and the low rainfall amounts applied.

TerraGIS – a web GIS for delivery of digital soil maps in cotton‐growing areas of Australia

AbstractEffective management of soil requires the spatial distribution of its various physical, chemical and hydrological properties. This is because properties, for example clay content, determine the ability of soil to hold cations and retain water. However, data acquisition is labour intensive and time‐consuming. To add value to the limited soil data, remote sensing (e.g. airborne gamma‐ray spectrometry) and proximal sensing, such as electromagnetic (EM) induction, are being used as ancillary data. Here, we provide examples of developing Digital Soil Maps (DSM) of soil physical, chemical and hydrological properties, for seven cotton‐growing areas of southeastern Australia, by coupling soil data with remote and proximal sensed ancillary data. A greater challenge is how to get these DSM to a stakeholder in a way that is useful for practical soil use and management. This study describes how we facilitate access to the DSMs, using a simple‐to‐use web GIS platform, called terraGIS. The platform is underpinned by Google Maps API, which is an open‐source development environment for building spatially enabled Internet applications. In conclusion, we consider that terraGIS and the supporting information, available on the sister web page (http://www.terragis.bees.unsw.edu.au/), allow easy access to explanation of DSM of soil properties, which are relevant to cotton growers, farm managers, consultants, extension staff, researchers, state and federal government agency personnel and policy analysts. Future work should be aimed at developing error budget maps to identify where additional soil and/or ancillary data is required to improve the accuracy of the DSMs.

The Impact of Vineyard Abandonment on Soil Properties and Hydrological Processes

Core Ideas A Guelph permeameter was used to quantify water movements. The active vineyard had higher permeability and saturated conductivity than the abandoned one. Vineyard soils showed a higher variability among seasons and slope positions. In the abandoned plot, there was a high correlation with gravel, OM, and clay content. In the vineyard, human impacts on the soil did not allow any key factor to be obtained. Soil and water resources are affected by land use changes such as land abandonment in vineyards. Changes in water resources and soil water dynamics can result in sudden alterations in erosion rates and trigger land degradation. In this study, we examined the impact of land abandonment on soil properties and hydrological processes in two paired plots: an active and an abandoned vineyard. Laboratory analyses were performed to assess texture, antecedent soil moisture, stoniness, soil water content, and organic matter (OM). A Guelph permeameter was used to quantify the permeability (Per) and saturated hydraulic conductivity (Kfs) at different slope positions and seasons (before and after harvest). Results showed that soil texture and OM were highly modified, and as consequence soil hydrology, after abandonment. We observed a significantly higher Per (26.8 mm h−1) and Kfs (8.4 mm h−1) in the active vineyard soil than in the abandoned one (Per of 14.2 mm h−1 and a Kfs of 5.4 mm h−1). The soils of the active vineyard showed a greater variability among seasons and slope positions. In the abandoned vineyard, the results showed a high correlation of Per and Kfs with gravel content and OM and a negative correlation with the clay fraction. Natural revegetation improved the soil water retention capacity. In the active vineyard, we could not find any relevant factor to explain the soil hydrological properties, and this may be attributed to the disturbance induced by human activities, such as machinery, trampling, and the use of herbicides.

The Impact of Continuous Living Cover on Soil Hydrologic Properties: A Meta‐Analysis

Core Ideas Meta‐analysis compared soil hydrology in perennial‐ and annual‐based crop systems. Continuous living cover practices significantly increased porosity, field capacity. There may be a greater effect in drier environments and sandier soils. Experiments in place longer than ten years also tended to increase the properties. Results suggest how continuous living cover can negate rainfall variability impacts. Increased rainfall variability due to climate change threatens the efficacy of critical soil ecosystem services. One strategy to negate effects of too much or not enough rainfall is to improve soil water properties. Practices that offer “continuous living cover” can enhance soil water storage and other soil hydrologic properties relative to annual crop systems, but to what extent such benefits can accrue, under different conditions, remains under‐quantified. To address these uncertainties, we conducted a meta‐analysis that included 27 studies representing 93 paired observations measuring two soil hydrologic properties: porosity and the water retained at field capacity. All experiments compared the impact of continuous living cover practices (cover crops, perennial grasses, agroforestry and managed forestry) to annual crop controls. Continuous living cover significantly increased total porosity (8.0 ± 2.2%) and the water retained at field capacity (9.3 ± 2.7%). There was some evidence indicating improved effects in relatively drier environments (&lt;900 mm annual rainfall) and in regions with sandier soils. There was no evidence of publication bias, and a sensitivity analysis indicated that overall effects were robust. The similar direction and magnitude of improvements in both properties could be evidence of similar physical and chemical processes impacted by the continuous presence of living roots. Overall, our findings suggest that continuous living cover practices may be a potential adaptation strategy to combat rainfall variability. Furthermore, properties such as porosity and field capacity may serve as proxies to determine how management influences soil water and heath more broadly.

DETERMINATION OF HYDROLOGIC CHARACTERISTICS OF SİNOP DEMİRCİKÖY WATERSHED AND PRODUCTION OF MONTHLY SATURATION DEGREE MAPS

The aim of this study is to determine the hydrologic characteristics and to analyze the temporal saturation degree variations of Demirciköy Watershed which is located in Sinop City and subjected to rapidly increasing population. This study is important in terms of preventing the natural disasters such as fl ood, storm water, landslide and mitigation of damages within the frame of watershed planning concept. This study consists of fi eld, offi ce and laboratory stages. In context of fi eld studies, representative soil samples are taken from study area. Within the scope of laboratory studies, soil hydrologic properties are characterized with the determination of soil texture of the soil samples handled from study area. The results of the laboratory tests are utilized as part of offi ce studies with the use of the Soil Moisture Distribution and Routing (SMDR) model in Geographic Information Systems (GIS) environment considering the meteorological data such as precipitation, temperature and evapotranspiration. Spatial and temporal variation of saturation degree in Demirciköy Watershed is determined with SMDR model. The obtained monthly saturation degree maps show the variation of soil moisture in a year and allow determining the potential runoff generation zones. The results of the study show that soil moisture in South part of watershed is lower than in North part. 

Effects of compost amendment on the available soil water and grape yield in vineyards planted after land levelling

The aim of this research was to compare the effect of compost amendment on soil water and on the available water for vines planted in levelled soils in comparison to those planted in undisturbed soils. Two vineyards, one levelled before vineyard establishment and one planted in the original soil, were compared. In each of them, the effect of compost application on the surface was compared with a control (without compost application). Soil characteristics such as soil texture, organic matter content, hydraulic conductivity and soil sealing were evaluated in each area. In addition, soil water was monitored at different soil depths in each treatment. Available soil water was evaluated along the growing cycle in two years with different rainfall distributions. Soil hydrological properties improved with compost amendment, in particular soil water holding capacity at different pressures. Soil water distribution within the soil profile and available water varied between the years depending on rainfall characteristics. For a given year, it varied significantly between levelled and unlevelled plots and between treated and untreated areas. In dry years, the available soil water reached very low values within the growing cycle, being lower in the levelled plot and higher in compost-amended areas in both plots. Compost amendment increased yield to a lesser proportion in the levelled soils but more in the dry than in the wet years. The results indicate the need to use different management strategies within the plots to optimize the use of water due to the differences in the final soil characteristics after land levelling operations.

Does functional soil microbial diversity contribute to explain within-site plant β-diversity in an alpine grassland and adehesameadow in Spain?

SummaryQuestions Once that the effects of hydrological and chemical soil properties have been accounted for, does soil microbial diversity contribute to explain change in plant community structure (i.e. within-site beta-diversity)? If so, at which spatial scale does microbial diversity operate? Location: La Mina in Moscosa Farm, Salamanca, western Spain (dehesa community) and Laguna Larga in the Urbion Peaks, Soria, central-northern Spain (alpine grassland). Methods The abundance of vascular plant species, soil gram-negative microbial functional types and soil chemical properties (pH, available phosphorus, and extractable cations) were sampled at both sites, for which hydrological models were available. Redundancy analysis (RDA) was used to partition variation in plant community structure into hydrological, chemical and microbial components. Spatial filters, arranged in scalograms, were used to test for the spatial scales at which plant community structure change. Results In the case of the dehesa the diversity of soil gram-negative microbes, weakly driven by soil pH, contributed to a small extent (adj-R2 = 2%) and at a relative medium spatial scale to explain change in plant community structure. The abundance of a few dehesa species, both annual (Trifolium dubium, Vulpia bromoides) and perennial (Poa bulbosa, Festuca ampla), was associated with either increasing or decreasing soil microbial diversity. In the alpine meadow the contribution was negligible. Conclusions Microbial diversity can drive community structure, though in the hierarchy of environmental factors structuring communities it appears to rank lower than other soil factors. Still, microbial diversity appears to promote or restrain individual plant species. This paper aims to encourage future studies to use more comprehensive and insightful techniques to assess microbial diversity and to combine this with statistical approaches such as the one used here. This article is protected by copyright. All rights reserved.

Improving the estimation of complete field soil water characteristic curves through field monitoring data

In this work, Soil Water Characteristic Curves (SWCCs) were reconstructed through simultaneous field measurements of soil pore water pressure and water content. The objective was to evaluate whether field-based monitoring can allow for the improvement of the accuracy in SWCCs estimation with respect to the use of laboratory techniques. Moreover, field assessment of SWCCs allowed to: a) quantify the hydrological hysteresis affecting SWCCs through field data; b) analyze the effect of different temporal resolution of field measures; c) highlight the differences in SWCCs reconstructed for a particular soil during different hydrological years; d) evaluate the reliability of field reconstructed SWCCs, by the comparison between assessed and measured trends of a component of the soil water balance. These aspects were fundamental for assessing the reliability of the field reconstructed SWCCs. Field data at two Italian test-sites were measured. These test-sites were used to evaluate the goodness of field reconstructed SWCCs for soils characterized by different geomorphological, geological, physical and pedological features. Field measured or laboratory measured SWCCs data of 5 soil horizons (3 in a predominantly silty soil, 2 in a predominantly clayey one) were fitted by Van Genuchten model. Different field drying and wetting periods were identified, based on monthly meteorological conditions, in terms of rainfall and evapotranspiration amounts, of different cycles. This method allowed for a correct discrimination of the main drying and the main wetting paths from field data related and for a more reliable quantification of soil hydrological properties with respect to laboratory methodologies. Particular patterns of changes in SWCCs forms along depth could be also identified. Field SWCCs estimation is not affected by the temporal resolution of the acquisition (hours or days), as testified by similar values of Van Genuchten equation fitting parameters. Instead, hourly data may offer a clearer vision of the drying and wetting paths, due to the highest number of experimental data points. Moreover, in temperate climate situations as those of the test-sites, main drying curves and main wetting curves of a particular soil were substantially similar also for different hydrological cycles with peculiar meteorological conditions. SWCCs parameters were implemented in a numerical code (HYDRUS-1D) to simulate soil water storage for different soil horizons. Field reconstructed SWCCs allowed for simulating with a higher precision these trends, confirming the reliability of the reconstructed field curves by a quantitative point of view. Moreover, best results were obtained considering hysteresis in the modeling.

Tillage Erosion Effect on Soil Hydrological Properties in a Hilly Landscape

AbstractTwo or more processes of soil erosion simultaneously exist in a hillslope landscape, and those processes can interact with each other. Yet, how one process impacts another remains unresolve...

Impact of Three Types of Biochar on the Hydrological Properties of Eroded and Depositional Landscape Positions

The addition of biochar to improve soil hydrological properties has been evaluated by many researchers. However, most studies have been conducted in controlled laboratories or greenhouses. This study was conducted in the field with the objective of evaluating the impact of biochar on the hydrological properties of soils at eroded and depositional landscape positions. Three plant-based biochar materials, produced from C-optimized gasification of corn stover (Zea mays L.) (CS), ponderosa pine (Pinus ponderosa Lawson and C. Lawson) wood residue (PW), and switchgrass (Panicum virgatum L.) (SG); dairy manure (DM); and a mixture of manure and pinewood biochar (DMP), were applied at a rate of 10 Mg ha⁻¹. The data indicated that the biochar and manure treatments significantly impacted the soil hydrological properties at both landscape positions. Soil moisture content (kg kg⁻¹) at field capacity was 4, 16, 8, 12, and 24% higher with CS, PW, SG, DM, and DMP, respectively, than the control treatment after soybean [Glycine max (L.) Merr.] harvest in 2014. Biochar with manure showed a relatively larger improvement in soil hydrological properties than the other treatments. The effects of biochar varied for different years and soil types because of differences in the feedstocks used to produce the biochars. The biochar treatments were not effective for reducing soil penetration resistance (SPR); however, DM significantly decreased the SPR. Data from this short-term study suggest that biochar can be used to improve soil hydrological properties. Future studies with different rates and types of biochar under different climatic conditions are needed.