Topsoil Water Content Research Articles

Soil evaporation under different types of land use in southern African savanna ecosystems

AbstractFor dryland ecosystems, soil evaporation is a major factor of the soil water balance. Often handled in one term with transpiration, little is known quantitatively about evaporation and impacts of soil and vegetation on it. On 12 plots at three sites in Angola, Namibia, and Botswana, potential and actual evaporation was measured using microlysimeters and parameterized. Dependencies on micrometeorological, soil, and site properties were statistically examined. In simulation runs with SWAP, the microlysimeter measurements were tried to be reproduced. Measured potential evaporation rates varied from 3.0 mm d–1 to 8.6 mm d–1. The evaporational parameter β ranged between 0.9 mm1/2 and 4.3 mm1/2. Evaporation was found to be strongly impacted by vegetation and land use, increasing from homogeneous bush areas over heterogeneous, more open woodlands to sparsely covered dryland agricultures. Correlations of evaporation variables with temperature, humidity, shading, topsoil water content, pF, bulk density, texture, and C content were found. Relationships were non‐explicit, which could be achieved by combining different factors. The simulation showed satisfying results with small deviations, confirming the model's general ability to depict the process. The application of the Boesten‐Stroosnijder‐model in combination with the used methods showed to be very useful to express evaporational properties, yet further research is necessary to improve consistency. A basis for evaporation prediction from known plot and soil characteristics and temporal and spatial up‐scaling could be given.

소형 풍동을 이용한 토양의 풍식 가능 입경 분석

The purpose of this study was to investigate maximum and minimum grain size which eroded by wind according to soil and wind conditions, such as top soil water content, roughness, land slope, wind velocity and proportion of grain size under 0.84mm. For performing this study, portable wind erosion tunnel was designed and utilized during field test, which facilitated measuring actual wind erosions under artificially controlled wind conditions. In the result, maximum, minimum grain size had strong negative correlation with roughness while weak positive correlation with wind velocity. Also, Slope which means the effect of gravity also influence grain size erodible by winds. Based on these results, regression equations were suggested for predicting maximum and minimum grain sizes by using multiple linear regression analysis from SPSS 20.0. The equation for maximum grain size erodible by winds showed a good agreement with the observed data with <TEX>$R^2$</TEX>=0.896. Other equation for minimum grain size had <TEX>$R^2$</TEX>=0.777.

Soil Water Dynamic Modeling Using the Physical and Support Vector Machine Methods

Comparison of long‐term daily prediction of soil water content at different depths of soil coming from two models, one physically based (HYDRUS‐1D) and the other being soft‐computing technique (Support Vector Machine), has been done. The models used provide quite accurate prediction for soil moisture content, especially in the most important layers for crop growth—those close to the surface. The RMSE of estimations of the volumetric soil water content in topsoil made by the Support Vector Machine (ν‐SVM) based model was 0.035, 0.030, and 0.021 cm3 cm−3 for depths of 5, 10, and 25 cm, respectively, while the physically based model had RMSE values of 0.042, 0.049, and 0.045 cm3 cm−3 for the same depths. Our results showed that the ν‐SVM modeling approach can be used for estimations of soil water content changes in time with the accuracy comparable of to the one of the physically based models.

Scaling Erica arborea transpiration from trees up to the stand using auxiliary micrometeorological information in a wax myrtle-tree heath cloud forest (La Gomera, Canary Islands)

We investigate evapotranspiration, sap flow and top soil water content variations in a wax myrtle-tree heath ('fayal-brezal' in Spanish) cloud forest in the Garajonay National Park (La Gomera, Canary Islands) over a 1-year period. We provide transpiration estimates for one of the representative species, the shrubby needle-like Erica arborea L., present in this relict subtropical forest. An ad hoc tree up to the stand scaling method that combines the sap flow and auxiliary reference evapotranspiration data is illustrated, showing to be useful when sap flow in a limited number of trees has been monitored. Individual daily-based scaling curves of the Gompertz type were necessary to explain the observed sap flow variability in E. arborea during the 1-year period investigated (r(2) ≥ 0.953 with mode of r(2) = 0.9999). The mean daily sap flow of an E. arborea individual amounted to 8.37 ± 5.65 kg day(-1) tree(-1), with a maximum of 20.48 kg day(-1) tree(-1), yielding an annual total of 3052.89 kg tree(-1). A comparison of the computed daily transpiration with the continuous micrometeorological time series monitored in the studied plot suggested that solar radiation was the main driving force of transpiration in E. arborea (cross correlation index = 0.94). Fog may also affect tree transpiration via its reduction of radiation and temperature, such that during foggy periods the mean daily water loss estimate of E. arborea was 5.35 ± 4.30 kg day(-1) tree(-1), which sharply contrasted with the 2.4-fold average transpiration values obtained for fog-free days, i.e., 12.81 ± 4.33 kg day(-1) tree(-1). The annual water balance rendered a 288 mm year(-1) water input to the forest and evidenced the need for accurately quantifying the contribution of fog water dripping from the canopy.

Combined effects of snow depth and nitrogen addition on ephemeral growth at the southern edge of the Gurbantunggut Desert, China

Water and nitrogen (N) inputs are considered as the two main limiting factors affecting plant growth. Changes in these inputs are expected to alter the structure and composition of the plant community, thereby influencing biodiversity and ecosystem function. Snowfall is a form of precipitation in winter, and snow melting can recharge soil water and result in a flourish of ephemerals during springtime in the Gurbantunggut Desert, China. A bi-factor experiment was designed and deployed during the snow-covering season from 2009 to 2010. The experiment aimed to explore the effects of different snow-covering depths and N addition levels on ephemerals. Findings indicated that deeper snow cover led to the increases in water content in topsoil as well as density and coverage of ephemeral plants in the same N treatment; by contrast, N addition sharply decreased the density of ephemerals in the same snow treatment. Meanwhile, N addition exhibited a different effect on the growth of ephemeral plants: in the 50% snow treatment, N addition limited the growth of ephemeral plants, showing that the height and the aboveground biomass of the ephemeral plants were lower than in those without N addition; while with the increases in snow depth (100% and 150% snow treatments), N addition benefited the growth of the dominant individual plants. Species richness was not significantly affected by snow in the same N treatment. However, N addition significantly decreased the species richness in the same snow-covering depth. The primary productivity of ephemerals in the N addition increased with the increase of snow depth. These variations indicated that the effect of N on the growth of ephemerals was restricted by water supply. With plenty of water (100% and 150% snow treatments), N addition contributed to the growth of ephemeral plants; while with less water (50% snow treatment), N addition restricted the growth of ephemeral plants.

Soil Moisture Deficit as a predictor of the trend in soil water status of grass fields

AbstractNutrient loss from agricultural land following organic fertilizer spreading can lead to eutrophication and poor water quality. The risk of pollution is partly related to the soil water status during and after spreading. In response to these issues, a decision support system (DSS) for nutrient management has been developed to predict when soil and weather conditions are suitable for slurry spreading. At the core of the DSS, the Hybrid Soil Moisture Deficit (HSMD) model estimates soil water status relative to field capacity (FC) for three soil classes (well, moderately and poorly drained) and has potential to predict the occurrence of a transport vector when the soil is wetter than FC. Three years of field observation of volumetric water content was used to validate HSMD model predictions of water status and to ensure correct use and interpretation of the drainage classes. Point HSMD model predictions were validated with respect to the temporal and spatial variations in volumetric water content and soil strength properties. It was found that the HSMD model predictions were well related to topsoil water content through time, but a new class intermediate between poor and moderate, perhaps ‘imperfectly drained’, was needed. With correct allocations of a field into a drainage class, the HSMD model predictions reflect field scale trends in water status and therefore the model is suitable for use at the core of a DSS.

The manipulation of organic residues affects tree growth and heterotrophic CO2 efflux in a tropical Eucalyptus plantation

Fast-growing plantations are increasingly being established on tropical soils, where fertility is largely supported by soil organic matter (SOM) and where different management options of harvest organic residues is thought to impact the long-term sustainability of these plantations. The objectives of this study were: (1) to quantify the effect of contrasting methods of organic residue management on tree growth and soil CO2 effluxes in the first 2years after planting and (2) to evaluate the impact of organic residue manipulations on the mineralization of soil organic matter over the length of the experiment. Three treatments were setup in 0.125ha plots and replicated in three blocks at the harvesting of a Congolese Eucalyptus stand, resulting in an aboveground organic residue mass ranging from 0 to 6.3kgm−2. The mineralization of SOM was deduced in each treatment by partitioning sources of soil CO2 effluxes using decomposition experiments and by upscaling specific root respiration. Soil CO2 effluxes were greatly affected by seasons and organic residue manipulation, although there were no significant changes in topsoil water content and topsoil temperature over most of the study period. Aboveground organic residue was the first contributor to soil CO2 efflux in the two treatments with a litter layer. Organic residue management did not significantly influence the mineralization of SOM in our study, probably due to the low quality of Eucalyptus litter, or to the hypothetical lack of dissolved organic carbon transfers from litter to soil. A strong relationship was found between cumulative heterotrophic CO2 efflux and tree growth, supporting the hypothesis that the early growth of Eucalyptus trees in a sandy tropical soil is largely dependent on the nutrients released by the decomposition of organic residues.

Shrubs affect soil nutrients availability with contrasting consequences for pasture understory and tree overstory production and nutrient status in Mediterranean grazed open woodlands

Increases of woody plant cover in former savannas and managed savanna-like systems are currently considered one of the major components of global environmental change. Besides, shrub encroachment is frequently recommended as a practical tool to ensure tree regeneration. However, there is little evidence that this process affects neighboring plants—tree and pasture—production and nutrient status in Mediterranean open woodlands through the modification of soil properties. The effect of two contrasting, in terms relevant to nutrient cycling, shrub species, Cistus ladanifer and Retama sphaerocarpa, were investigated. Cistus, a shallow rooted shrub, reduced top-soil water content and enhanced P and K but depleted N and Mg availability under its canopy. It worsened consistently both tree overstory and pasture understory production and nutrient content. By contrast, Retama, a deep-rooted, N2-fixing shrub, increased top-soil water content and N and Mg availability, but diminished P availability. In addition, it affected distinctively to pasture (facilitation) and trees (competition) biomass production. Overall, pasture production, irrespective of the habitat, was mainly limited by P, whereas trees growing with Cistus were limited by Ca and N and those trees growing with Retama by P availability. Our results showed that shrubs are capable to affect consistently both pasture and tree production and nutrient status through the modification of soil nutrient availability. However, these effects depended on specific shrub-understory and shrub-overstory combinations, which have implications for managing grazed open woodlands.

Fractal Description of the Spatial and Temporal Variability of Soil Water Content Across an Agricultural Field

There is an increasing interest in quantifying the space-time variation of soil properties. This issue offers a unique set of problems that have been addressed using various methods. Here, the spatial and temporal scaling behavior of topsoil water content at the field scale was explored using the fractal approach. Results from fractal analysis were compared with those from other methods describing either spatial variability or temporal trends and stability of soil moisture. Time domain reflectometry probes were installed at the 0- to 20-cm depth in a clay loam soil under natural pasture in Ottawa, Ontario, Canada. Soil water content was measured 34 times at 164 points on a square grid with 10-m spacing. Mean soil water content and coefficients of variation showed significant negative linear relationship for both sampling dates (r2 = 0.783) and sampling points (r2 = 0.804). Both spatial and temporal data sets were characterized by a self-affine fractal Brownian motion model that requires two parameters, fractal dimension, D, and crossover length, l. For spatially sampled data sets at different times, D ranged from 2.589 to 2.910 and l ranged from 0.95 to 6.97 m. For temporal data sets measured on 10-m grid nodes, D was between 1.145 and 1.919 and l was from 0.069 to 9.40 days. Fractal analysis added information on the scale dependence of spatially and temporally sampled data sets, which is not taken into account by classical statistics. Also, interpretation of fractal parameters provided further insight when contrasted with temporal stability analysis. Fractal dimension and crossover length of temporal series showed spatial dependence, and ordinary kriging was used to map these two fractal parameters.

Plastic film mulch for half growing-season maximized WUE and yield of potato via moisture-temperature improvement in a semi-arid agroecosystem

Abstract Effects of plastic mulching in ridges and furrows for varying durations on yield and water use efficiency (WUE) in potato were investigated in rainfed areas of north-western China in 2009 and 2010. The experiment comprised four mulched treatments (M50, M65, M80/85, and Mw – indicating plastic film mulch for 50, 65, and 80/85 d after sowing, and whole growth season, respectively – after which mulch in furrows was removed) and a non-mulched control. The results showed that film mulching warmed topsoil and increased topsoil water content. The daily mean topsoil temperature in mulched plots was 2.5–3.2 °C higher than that in controls during the early growing season (sowing–emergence), the difference became less as the plant canopy grew; on some days later in the season, the difference was even negative (i.e. the topsoil temperature in mulched was lower than in control plots). Seedlings under mulching emerged 8.1–11.7 d earlier than those in controls due to the increased topsoil temperature and moisture in the early season. Mulching also prolonged the duration from seedling to maturity by 0.7–15.0 d and significantly increased plant height, leaf area index, and dry matter. Compared to non-mulched plots, yields in mulched plots increased by 33.9–92.5% and 62.9–77.8% in 2009 and 2010, respectively, and corresponding WUEs improved by 41.4–112.6% and 45.9–70.6%. Both tuber yield and WUE were highest in M65. The data indicate that mulching for about 65 d after sowing was ideal to optimize soil moisture and soil temperature and in turn to improve potato productivity and WUE in this semi-arid rainfed region.

Edaphic Characterization, Water and Salt Translocation in Saline Marsh at Local Scale in Songnein Plain, Northeast China

The degradation of saline marsh in Songnen plain was controlled by many factors. Based on in-situ observation and laboratory analysis, soil properties and matters translocation in Zhalong wetland at local scale as affected by freeze and thaw action was explored. Results show that within the study plot, 1500 m in distance, but varying only 80 cm in altitude, existed four types of soils i.e. Shallow-horizon Alkalic Halosols (SAH), Crust Alkalic Halosols (CAH) and Para-alkalic Dark-Aquic Cambosols (PDC) and Sodic Hapli-Orthic Gleyosols (SHG). High content total porosity with amounts to 62% in surface horizon in marsh would help to water conservation and wetland formation. In contrast, large rate of silt or clay in texture in alkali soil and meadow soil constrain the water content in topsoil, i.e. the saturated water content 0-30 cm horizon of meadow soil and alkali soil were merely 0.83 and 0.7 m3 m-3. Residues &amp; roots in surface layer of SHG expand the period of freezing phase as long as 9 months comparing to 7 months in SAH, and maximum freezing fringe in the former was 24 cm deeper than the latter (178 cm versus 154 cm). Seasonal freeze and thaw action has obvious influence on water storage in topsoil in saline marsh, leading different of soil succession therein. Soil moisture content in the surface layer of marsh increased from 2.05 to 2.62 m3 m-3(over-saturated), but no obvious change in PDC and Alkali soils. In contrast, electrical conductivity of saturated paste in SAH and CAH increased from 6.5 to above 10 dS m-1. Therefore, it did not accord with the practical situation of Northeast China as that of strong evaporation was the only cause that caused saline marsh alkalinization. Protecting the vegetation or restoring surface coverage by plant in saline land in spring may help land dealkalization in high latitude arid &amp; semiarid regions.

Spatial distribution of top soil water content in an experimental catchment of Southeast Brazil

Soil water content is essential to understand the hydrological cycle. It controls the surface runoff generation, water infiltration, soil evaporation and plant transpiration. This work aims to analyze the spatial distribution of top soil water content and to characterize the spatial mean and standard deviation of top soil water content over time in an experimental catchment located in the Mantiqueira Range region, state of Minas Gerais, Brazil. Measurements of top soil water content were carried out every 15 days, between May/2007 and May/2008. Using time-domain reflectometry (TDR) equipment, 69 points were sampled in the top 0.2 m of the soil profile. Geostatistical procedures were applied in all steps of the study. First, the spatial continuity was evaluated, and the experimental semi-variogram was modeled. For the development of top soil water content maps over time a co-kriging procedure was used having the slope as a secondary variable. Rainfall regime controlled the top soil water content during the wet season. Land use was also another fundamental local factor. The spatial standard deviation had low values under dry conditions, and high values under wet conditions. Thus, more variability occurs under wet conditions.

Effect of mulch and irrigation practices on soil water, soil temperature and the grain yield of maize (Zea mays L) in Loess Plateau, China

Agricultural management practices, such as mulching and irrigation can change the characteristics of the soil surface and hence influence the hydrothermal properties of the soil. A two-year field experiment was conducted at the Changwu agro-ecosystem research station to evaluate the effects of mulch and irrigation practices on moisture and temperature in the upper layers of the soil and on crop growth and yield performance in spring maize (Zea mays L) fields. Four mulching and irrigation treatments were examined: supplementary irrigation (SI), film mulching (FM), straw mulching (SM; in 2008 only) and a rain-fed (RF) control. The soil water (0 - 15 cm depth range) and soil temperature (0 - 5 cm depth range) were studied during the crop growing season and the treatments' yield performances were compared. Over the whole season, the average topsoil water content was significantly higher (P < 0.05) under the SM (23.3% in 2008), SI (21.4% in 2007, 22.5% in 2008) and FM (20.0% in 2007, 21.6% in 2008) treatments than under RF (17.1% in 2007, 19.6% in 2008). The seasonal trends in atmospheric and soil temperatures were similar under all treatments. The seasonally-averaged soil temperature at 07:00 and 14:00 h was highest under the FM treatment and lowest under the SM treatment. Plant height and leaf and stem biomass were significantly higher (P < 0.05) under the SI treatment than under the RF and FM treatments from silking to physiological maturity. Both the FM and SI treatments significantly improved (P < 0.05) the crop grain yield (GY) and yield components. Key words: Loess Plateau, soil water, soil temperature, spring maize.

Predicting plot-scale water infiltration using the correlation between soil apparent electrical resistivity and various soil properties

The identification of runoff source areas is essential for Integrated Water and Resources Management (IWRM). Although direct methods for the determination of steady-state water infiltration in soils (Inf) do exist, these are tedious and time-consuming. Geophysical techniques offer an alternative, however, geophysical data are often misinterpreted, especially in terms of the inter-relationships between soil apparent electrical resistivity (Rho) and Inf and several other soil physical or chemical properties. This paper evaluates the magnitude of the extend Rho measurements might allow prediction of Inf. This study was conducted in the Kwazulu-Natal province of South Africa where surface runoff arising from the steep slopes has a large impact in land degradation. Measurements of Rho with an RM-15 resistance meter were taken within a 10×30m plot showing similar sandy-loam Acrisols but different proportions of soil surface coverage by plants (from 0–5% to 75–100%), depth to the clayey Bw horizon (D2B), top-soil (0–0.1m) water content (θ) and bulk density (BD). There was a low correlation between Rho and Inf obtained under controlled conditions of rainfall (30mmh−1during 45min) at fifteen 1m2 micro-plots (r2=0.30). However, the correlation with the normalized Rho (Rhon) as if D2B, θ, and BD were constant over the study plot and equal to their average value, was much higher (r2=0.66), pointing out the need to consider the complex and multiple correlations between soil properties and Rho in an attempt to map the spatial variations of Inf. Finally, the use of Rhon as a co-kriging co-variate appeared to significantly improve the short range spatial prediction of water infiltration in soils and thus IWRM implementation.

Digital mapping of A-horizon thickness using the correlation between various soil properties and soil apparent electrical resistivity

Conventional soil science methods for the estimation of the spatial variations of soil properties within landscapes are destructive, time consuming, and do not allow the estimation of the short range variability. Recent advances in geomatic global positioning systems and sensors offer new possibilities for the mapping of spatially varying soil patterns. Although geophysical techniques offer an alternative to traditional soil sampling methods, the resulting data are still often misinterpreted, especially in terms of the inter-relationships between, for example, soil apparent electrical resistivity ( ρ) and several soil physical or chemical properties. Our main objective was to test the suitability of using ρ measurements for mapping the thickness of the organo-mineral A-horizon ( ThickA). ρ was mapped (0–0.5 m), using an RM15, in a highly water eroded field plot of 300 m² showing large variations in ThickA, but no significant variations in soil clay and nutrient content. The correlations between ρ and ThickA, the top-soil water content ( θ 0.1), and the bulk density ( BD 0.1) were determined at the nodes of a regular grid of 2 m ( n = 96). Principal Component Analysis (PCA) was used to identify the impact of the different soil properties on the ρ data. ThickA varied between 0.17 and 0.3 m, and ρ between 1046 and 3864 Ω m . There was a significant correlation between ρ and ThickA ( r = 0.56) and also between θ 0.1 ( r = 0.23) and BD 0.1 ( r = 0.22). If it was assumed that θ 0.1 and BD 0.1 were constant over the study plot then there was a correlation between ρ and ThickA with an r of 0.88, thus making possible the accurate mapping of ThickA (MAE = 0.017 m; i.e., 7% of the average value of ThickA). Prediction (MAE = 0.015 m) was only slightly improved through the use of regression kriging of ThickA with ρ recalculated as the covariate. This result showed that apparent soil electrical resistivity measurements could be very successful for estimating A-horizon thickness provided that limited information on top-soil characteristics is included in the mapping process.

Thermal acclimation of leaf dark respiration of beech seedlings experiencing summer drought in high and low light environments

Little is known about how environmental factors shape the short- and long-term responses of leaf respiration to temperature under field conditions despite the importance of respiration for plant and stand carbon balances. Impacts of water availability and canopy cover on leaf dark respiration (R) and temperature sensitivity were assessed in beech (Fagus sylvatica L.) seedlings in a sub-Mediterranean population. We studied seedlings established within canopy gaps (39% global site factor; GSF) that were subject to either no watering (unwatered plants; UW) or regular watering (2-10% higher volumetric topsoil water content as summer progressed; W plants) and seedlings established beneath the adjacent understorey (12% GSF). Leaf R rose exponentially with diurnal increases in temperature; the same temperature sensitivity (Q(10): 2.2) was found for understorey and gap plants, irrespective of watering treatment. Respiration estimated at 25 degrees C (R(25)) was lower in the understorey than the gaps and was significantly lower in the unwatered than in the watered gap plants by the end of summer (0.65 versus 0.80 micromol m(-2) s(-1)). R(25) declined with increasing summer temperature in all plants; however, respiration estimated at the prevailing ambient temperature did not change through the summer. There were parallel declines in R(25) and concentrations of starch and soluble sugars with increasing summer temperature for gap plants. We conclude that seasonal shifts in temperature-response curves of beech leaf R occur in both low- and high-light environments; since leaf R decreased with increasing plant water deficit, such shifts are likely to be greater whenever plants experience summer drought compared to scenarios where plants experience high rainfall in summer.

Soil-plant hydrology of indigenous and exotic trees in an Ethiopian montane forest

Fast-growing exotic trees are widely planted in the tropics to counteract deforestation; however, their patterns of water use could be detrimental to overall ecosystem productivity through their impact on ecosystem water budget. In a comparative field study on seasonal soil-plant water dynamics of two exotic species (Cupressus lusitanica Mill. and Eucalyptus globulus Labill.) and the indigenous Podocarpus falcatus (Thunb.) Mirb. in south Ethiopia, we combined a 2.5-year record for climate and soil water availability, natural-abundance oxygen isotope ratios (delta(18)O) of soil and xylem water, destructive root sampling and transpiration measurements. Soil was generally driest under C. lusitanica with its dense canopy and shallow root system, particularly following a relatively low-rainfall wet season, with the wettest soil under E. globulus. Wet season transpiration of C. lusitanica was twice that of the other species. In the dry season, P. falcatus and C. lusitanica reduced transpiration by a factor of six and two, respectively, whereas E. globulus showed a fivefold increase. In all species, there was a shift in water uptake to deeper soil layers as the dry season progressed, accompanied by relocation of live fine root biomass (LFR) of C. lusitanica and P. falcatus to deeper layers. Under P. falcatus, variability in soil matric potential, narrow delta(18)O depth gradients and high LFR indicated fast water redistribution. Subsoil water uptake was important only for E. globulus, which had low topsoil LFR and tap roots exploiting deep water. Although P. falcatus appeared better adapted to varying soil water availability than the exotic species, both conifers decreased growth substantially during dry weather. Growth of E. globulus was largely independent of topsoil water content, giving it the potential to cause substantial dry-season groundwater depletion.

Spatial variation of soil water content in topsoil and subsoil of a Typic Ustifluvent

Water content is a fundamental property affecting plant growth, transport and transformation of soil nutrients, and water and energy budgets in the soil–plant system. Its spatial variation has important implications for all these processes. In this study, spatial variation in soil water contents was evaluated at pressures of −0.033 ( θ −0.033 MPa ), −0.10 ( θ −0.10 MPa ), and −1.50 MPa ( θ −1.50 MPa ) at the soil depth from surface to the lower and of a plow layer in a Typic Ustifluvent in an 8.5 ha level area (1–2% slope). Topsoil (0.0–0.30 m) and subsoil (0.31–0.60 m) were sampled based on a regular grid spacing of 25 m-by-25 m. Variables θ −0.033 MPa , θ −0.10 MPa , and θ −1.50 MPa were measured with a pressure plate apparatus. Results were evaluated and compared with conventional statistics and geostatistics. Coefficient of variation (CV) for soil water content increased as soil water pressure decreased in both topsoil and subsoil. Semivariance analysis and ordinary block kriging-produced surface maps for θ −0.033 MPa , θ −0.10 MPa , and θ −1.50 MPa showed that topsoil and subsoil were similar in spatial variation of water content at all three corresponding soil water pressures. The geostatistical range values were between 298 m ( θ −0.10 MPa in topsoil) and 486 m ( θ −0.10 MPa in subsoil), both indicating a strong spatial dependence of soil water content. The semivariograms for θ −0.033 MPa , θ −0.10 MPa , and θ −1.50 MPa were similar in shape in both topsoil and subsoil. Cross-dependence between sand content and soil water contents showed that soil texture controlled the spatial variation of water contents at the site, at all depths and pressures evaluated.

Transpiration dynamics of an Austrian Pine stand and its forest floor: identifying controlling conditions using artificial neural networks

In this study, artificial neural network analyses (ANN) were used to identify the forcing environmental variables that are most significant in governing the transpiration rates of an Austrian Pine stand and its forest floor. Latent heat flux densities (Lh) of the Austrian Pine stand and its forest floor were separately measured using the eddy covariance technique. To assess the sensitivity of the ANNs to input information on the soil water status, the site calibrated soil hydrological model SWIF was used to compute average volumetric soil water contents of different depth intervals. Results show that forest floor transpiration dynamics can be adequately modelled using the global radiation reaching the forest floor and the topsoil water content (0–50 cm). The response functions of the total forest and forest floor showed a clear difference in sensitivity of latent heat fluxes to global radiation, air temperature and soil water content. Most significantly, results demonstrate that the presented ANN analysis is suited for assessing effective rooting depths from measured transpiration rates and soil water contents.

Mapping field-scale hydromorphic horizons using Radio-MT electrical resistivity

Pedological soil surveys usually based on auger sampling encounter methodological and economic difficulties. Electrical resistivity (ER) techniques could be used as a simple and practical method to determine their spatial variability. However, attempts to map soils using ER techniques have very often limited success, especially in bottomland areas, due to large variations inherent in ground data. The aim of this study is to seek the interest of a geophysical method, the radio magnetotelluric-resistivity (Radio-MT), to map field-scale hydromorphic horizons for loamy pedological systems in bottomlands characterized by large variations of soil water content and depth to upper boundary of saprolite. The sampling survey was carried in the Armorican massif (western France). The electrical measurements were taken along transects on an agricultural field (80×150 m). The soil sampling was performed on a regular grid with a mesh of 10 m. On each point, some soil properties were measured (type and thickness of the loamy horizons, depth to the upper boundary of saprolite, soil water content at 10, 20, 40 and 60 cm depths). A direct relationship between apparent resistivity and horizon type distribution was not established. The best correlations were between the electrical conductivity and depth to the upper boundary of saprolite and topsoil water content. The correlation coefficients, r, are 0.51 and 0.34, respectively. To identify the soil types, we modeled the influence of these two soil properties by multiple regression technique. Deviations from the regression model were then interpreted by taking into account the succession of soil horizons. These results seem to indicate that the electrical method used in this study could not be directly used to evaluate spatial prediction of the hydromorphic soil distribution, but indirectly by taking into account soil properties such as the soil water content and the upper boundary of saprolite.