Soil Hydrological Properties Research Articles

Effects of Different Land Uses (Abandoned Farmland, Intensive Agriculture and Forest) on Soil Hydrological Properties in Southern Spain

A detailed knowledge of soil water repellency (SWR) and water infiltration capacity of soils under different land uses is of fundamental importance in Mediterranean areas, since these areas are prone to soil degradation risks (e.g., erosion, runoff of polluting compounds) as a response to different hydrological processes. The present study evaluates the effects of land uses on SWR and soil hydraulic conductivity (SHC) by direct measurements at the plot scale in three areas representing (1) intensive agricultural use, (2) abandoned farmland, and (3) a forest ecosystem in Southern Spain under Mediterranean climatic conditions. The physico-chemical properties and water content of the experimental soils were also measured. Significant SWR and SHC differences were found among the analyzed land uses. Forest soils showed high SWR and low SHC, while the reverse effects (that is, low SWR and high SHC) were detected in soils subjected to intensive agriculture. Organic matter and bulk density were important soil properties influencing SWR and SHC. The study, demonstrating how land uses can have important effects on the hydrological characteristics of soils, give land managers insights into the choice of the most suitable land use planning strategies in view of facing the high runoff and erosion rates typical of the Mediterranean areas.

Topsoil reinforcement of sandy slope for preventing erosion using water-based polyurethane soil stabilizer

The topsoil of sandy slope suffers from serious erosion due to its weak internal cohesion. Most of the efforts have been made to improve the stability of topsoil by recovering the inter-particle cohesion without due concern to environmental and ecological aspects. Thus, water-based polyurethane (PU) soil stabilizer is introduced to reinforce the topsoil of sandy slope for erosion control purpose. This study aims at understanding its reinforcement effect and proving the feasibility of polyurethane treatment in practice. A series of laboratory tests were performed on treated specimens with different PU concentrations and also compared to a fallow one by which the effect of this stabilizer on soil mechanical and hydrological properties, vegetation growth and erosion resistance were investigated. The results indicated that PU treatment can significantly increase the shear strength, unconfined compressive and tensile strength of natural sand. An increasing amount of PU resulted in marked improvements in cohesion, but slight changes in internal friction angle. On the other hand, the presence of PU conferred low permeability and good water stability to the natural sand. Even with a relatively small amount of PU treatment, a positive potential is observed in promoting the anti-erodibility of topsoil by enhancing its inter-particle cohesion due to the unique network membrane structure. Moreover, PU treatment also improved soil water retention characteristics and can provide a suitable environment for vegetation growth. Under the synergistic action of vegetation and polymer treatment, stronger erosion resistance of topsoil was observed. Thus, PU treatment can be used as an ecological and effective alternative method with regard to topsoil stabilization on sandy slope.

Does biocrust successional stage determine the degradation of vascular vegetation via alterations in its hydrological roles in semi‐arid ecosystem?

AbstractBiocrusts may influence soil moisture by changing soil hydrological properties and thus affect the growth of vascular vegetation. However, their effects on soil moisture and vascular vegetation have not been sufficiently evaluated. In this study, five treatments, including bare land with sporadic cyanobacterial biocrusts (BL), lichen‐dominated biocrusts, Artemisia ordosica (AO), A. ordosica with moss biocrusts, and old‐aged A. ordosica with moss biocrusts (OAMB), were established to evaluate the effects of biocrusts on soil hydrological properties and shrub growth. Our results showed that the field capacity (θf) and saturated soil moisture (θs) for the OAMB treatment was higher than that for the BL treatment, although the difference between the five treatments was insignificant. The OAMB treatment deceased soil moisture 8.7% on average due to their significant lower saturated hydraulic conductivity (Ks) (82.9%), compared with the BL treatment. The OAMB treatment protected against soil water loss during the beginning stages of evaporation and facilitated soil evaporation during the late stages. Interestingly, the soil water condition underneath the OAMB treatment was not improved after the degradation of AO. The A. ordosica with moss biocrusts treatment had 12.7% lower aboveground biomass and 46.0% lower twig biomass than that for the AO treatment, suggesting the negative effects of biocrusts on the growth of artificially planted shrubs. The findings have important implications for the competitive relationships between biocrusts and vascular vegetation and managing artificial planted shrubs.

Variation in soil hydrological properties on shady and sunny slopes in the permafrost region, Qinghai–Tibetan Plateau

Soil hydrological properties not only directly influenced soil water content, evapotranspiration, infiltration, and runoff, but also made these factors of concern in arid and semi-arid regions. Prior research has focused on the temporal and spatial variation in soil hydrological properties and the impacts of climate change, ecosystem changes over time or human activities on soil hydrological properties. However, studies conducted on the differences in soil hydrological properties between shady and sunny slopes have seldom been conducted, especially in the permafrost region of the Qinghai–Tibetan Plateau. To investigate the variation in soil hydrological properties on shady and sunny slopes, we chose the Zuomaokongqu watershed of Fenghuo Mountain, which is located on the Qinghai–Tibetan Plateau, as the study area. Three experimental sites were selected in the study area, and the distance between experimental sites was 100 m. Based on the differences in altitude and vegetation coverage, five sunny slope sample points and three shady slope sample points were selected in each experimental site. At each of these sample points, the soil water content, soil-saturated conductivity, soil water-retention curve, soil physico-chemical properties, aboveground biomass, and underground biomass were examined in the top 0–50 cm of the active layer. The results showed that the soil hydrological properties of shady slopes differed significantly from those of sunny slopes. The soil water content of sunny slopes was 20.9% less than that of shady slopes. The soil-saturated water content of sunny slopes was 12.2% less than that of shady slopes. The soil water content of sunny slopes at − 0.3 Mpa and − 0.7 Mpa matric potential was 23.5% and 21.4% less than that of shady slopes, respectively. It was indicated that the soil water-retention capacity of sunny slopes was lower than that of shady slopes. However, the soil-saturated conductivity of sunny slopes was 84.5% larger than that of shady slopes and exceeded the range of soil-saturated conductivity, which was useful for plant growth. Meanwhile, the vegetation coverage on sunny slopes was lower than that on shady slopes, but the soil sand content showed the opposite relationship. Pearson’s coefficient analysis results showed that vegetation coverage and soil desertification, which are affected by permafrost degradation, were the main factors influencing soil hydrological properties on shady and sunny slopes. These results will help determine appropriate hydraulic parameters for hydrological models in mountain areas.

Soil physical properties following conversion of a reclaimed minesoil to bioenergy crop production

Land use, soil management and vegetation play important roles in restoration of reclaimed minesoils (RMS). There is a growing interest in converting marginal lands to bioenergy crop production instead of using highly fertile soils, which could jeopardize food security and soil quality. The objective of this study was to assess short-term changes of soil physical and hydrological properties after converting a RMS that was under meadow to miscanthus (Miscanthus giganteus) and corn (Zea mays L.) land-uses in Southeast Ohio. The study site was surface-mined for coal and lime, reclaimed and seeded with cool season grass and legume species mixture in 1986. The site remained under meadow land use until the establishment of this study in 2013. The results showed that bulk density (ρb) of the 0–10 cm soil depth (soil surface) under miscanthus and corn (1.28 and 1.25 Mg m−3) increased on average by 9% following conversion of meadow to miscanthus and corn land-uses, compared to the antecedent meadow (1.16 Mg m−3). There were no significant differences in ρb of soil below 20 cm depth, which was >1.5 Mg m−3. Decrease in soil aggregation was also observed at the soil surface after land-use change. The mean weight diameter (MWD) of water stable aggregates was 2.00 mm under the meadow land use, which was significantly lower under the corn (1.45 mm) and miscanthus (0.96 mm) land uses. Subsequently, water infiltration rate decreased by 50% in the miscanthus and corn land-uses compared to the meadow (0.23 cm min−1). Additionally, plant-available water capacity (P-AWC) also decreased by 28% in the miscanthus and corn land-uses compared to the meadow (2.5 cm) at the top 10 cm depth. The data show significant changes in some sensitive soil physical properties within a short period of one year upon converting from reclaimed meadow to miscanthus and corn land-uses, suggesting that disturbances associated with land use change have negative impact on soil properties and soil quality.

Underneath it All: Soil Differences May Explain Contrasting Outcomes of Adjacent Prairie Restorations in Madison, Wisconsin

The evaluation of prairie restorations tends to focus on aboveground properties such as changes in plant diversity and the encroachment of non-native species. As a result, knowledge gaps persist concerning belowground controls of restoration success. To address these gaps at a 13-year-old prairie restoration site in Madison, Wisconsin, we spatially compared soil chemical, physical, and hydrological properties in two adjacent parcels that differed markedly in response to a tallgrass prairie restoration. We hypothesized that soil properties and their heterogeneity would differ significantly between the two parcels and that these differences would help explain the divergent response. In support of this hypothesis, soil organic matter, pH, and total nitrogen were significantly lower (p = 0.007, p < 0.001, and p = 0.006, respectively) in the restored parcel compared to the parcel that has yet to respond to any restoration efforts. Moreover, despite no significant difference in soil average bulk density between the two parcels, the restored parcel had significantly lower sand and silt fractions overall (p = 0.039 and p = 0.040, respectively). In contrast, except for total nitrogen, there were no apparent differences in the spatial heterogeneity of the measured soil properties between the restored and unrestored parcels, which did not support the second hypothesis of this study. These results demonstrate the utility of measuring belowground properties when assessing unexpected outcomes of prairie restorations as well as inform future hypothesis-driven experiments to determine which soil properties impede restoration and under what circumstances. KEYWORDS: Prairie Restoration; Bulk Density; Soil Organic Matter; Soil Properties; Soil Texture; Spatial Heterogeneity

Changes in soil physical and chemical properties after short drought stress in semi-humid forests

The Loess Plateau region of China is under increasing water shortage due to declining soil water content after reforestation. Thus, assessing the changes in soils properties in reforested lands is critical for sustainable restoration of vegetation. We conducted a continuous rainfall manipulation experiment from June 2015 to November 2016 using mature black locust (Robinia pseudoacacia) on southern Loess Plateau of China. The soil hydrological properties, aggregate distribution and aggregate organic carbon (OC) and total nitrogen (N) concentrations were measured. Two years of drought stress caused a significant decline in saturated hydraulic conductivity and total porosity, but an increase bulk density in the 0–10 cm soil layer. The short drought stress significantly decreased soil aggregate stability due to a decline in macro-aggregate mass. Drought stress significantly decreased total soil OC concentration and macro- and micro-OC or N concentrations, but had no significant effect on total N concentration after two years of drought. Furthermore, the influence of short drought on soil hydrological properties, aggregate distribution and aggregate OC and total N concentrations was mainly evident at the depth of 10 cm. Our results indicated that short drought has the potential to damage soil properties. The results of this study could provide more insight into the sustainability of afforestation in semi-humid areas of China's Loess Plateau.

Soil sedimentation and quality within the roadside ditches of an agricultural watershed

Roadside ditches are an integral component to the >6.3 million km of roadsides in the U.S. and act as drainageways for millions of hectares of watershed runoff. Our study of six roadside ditches in Lime Creek watershed characterized soil nutrients and heavy metal patterns as well as quantified the physical and hydrological properties of ditch soils. At all ditch sites, we identified significant sedimentation of silt-sized particles, total nitrogen, and soil carbon in shallow roadside ditch soils. A post-settlement surface soil horizon significantly higher in silt content was observed compared to the underlying subsoil and parent material. Although accumulation of several heavy metals was measured in ditch soils, significant variability was not observed within the ditch environment. Most of the heavy metal concentrations were found to be either similar to or lower than state-wide averages. Higher levels of calcium near the roads were likely due to annual use of road deicers. Overall, we estimated that 42 Mg/ha of total carbon and 5 Mg/ha of total nitrogen are being stored in agricultural ditch soils, which is similar to that of surrounding agricultural land in terms of total carbon storage, but much higher than estimates of total nitrogen storage. Our study of six roadside ditches in an eastern Iowa watershed documented the soil chemistry, morphology, and sediment accumulation that occurred since ditch construction. Further research is needed to develop a better understanding of how the soil and water conditions in the ditches related to the watershed areas that feed them.

Effect of Land Use on Soil Physical and Hydrological Properties on Sandstones Parent material in Akwa Ibom State, Nigeria

Knowledge of soil physical and hydrological properties is used by soil scien- tists, agronomists, hydrologists, irrigation engineers and environmental scientists for developing best management practices for efficient and economical manage- ment of soil and water for optimum crop production and designing liquid waste disposal systems. A study was conducted on the sandstone parent material in northern Akwa Ibom State to evaluate the effects of forest (FO), fallow (FA), and cultivated (CU) land use types on soil physical and hydrological properties. The effects of the three land use practices on soil properties were generally, sta- tistically non-significant; however, there were remarkable differences among the land uses. It was observed that bulk density (BD), water stable aggregates (WSA), soil organic carbon (SOC), saturated water content (SWC), field capaci- ty water content (FC), and sorptivity (S) were higher in CU than in FO and FA, indicating that forest soils may not always have improved soil physical and hy- drological properties than cultivated soil. However, since the soils are coarse- textured (with low clay content), conservation tillage involving the application of plant materials on the surface or ploughed into the soil and occasional fallow- ing to replenish the organic matter content, are needed to bind the primary parti- cles, stabilize soil structure, and improve water intake and storage, important indices for the optimum edaphological functions of the soils in the study area.

Changes in connectivity and hydrological efficiency following wildland fires in Sierra Madre Oriental, Mexico

Fire modifies soil surface, and hence soil hydrological properties change after wildland fires. High fire severity causes partial or total removal of vegetation, reduction of soil aggregate stability and increased water repellency, which are associated with high runoff and erosion. The spatial connection among these runoff sources is an important factor to consider when evaluating fire-induced changes on hillslope and catchment hydrology, as fire generates connected areas of bare soil, which may increase hydrological connectivity and hence post-fire runoff and erosion. The aim of this study was to quantify changes in hydrological connectivity and efficiency in two burned areas in central Mexico. By integrating rainfall simulation and spatial analysis, an index of connectivity (IC) and the lateral hydrological efficiency index (LHEI) were computed based on land/cover use, fire severity and topography within 287 burned sub-basins. Post-fire IC and LHEI were compared with the pre-fire scenario, and the relationship between LHEI and the proportion of burned area was assessed at the sub-basin level. Thresholds of the burned area per fire severity needed to increase LHEI were determined by a classification tree. The index of connectivity and LHEI were higher after wildland fires. The burned area was positively related with LHEI, and at least 43.3% of area burned with high severity is sufficient to produce the highest LHEI. The results are evidence of the effect of fire on hydrological connectivity and efficiency which adds to the understanding of fire–hydrology relations and can be used for integrated catchment management, ecological restoration and risk assessment.

Soil ecosystem functions in a high-density olive orchard managed by different soil conservation practices

The long-term effects of two different soil management practices, natural grass cover (NC) and conservation tillage (CT), on soil functions (carbon sequestration, habitat for organisms, and water movement and retention) were determined in a high-density, mature olive orchard (Olea europaea L. cv. Frantoio) growing in a sandy loam soil (Typic Haploxeralf) in a Mediterranean environment. Ten years after the beginning of the different soil management, soil samples were collected at 0–10 and 10–20 cm depth and at two distances from the trunk, underneath the olive canopy (UC) and in the inter-row (IR). There were no differences in fruit yield, oil yield, and yield efficiency between the two soil management systems during the 2011–2013 period. CT negatively affected soil organic carbon pools (total and humified), but only at the IR position. The distance from the plant did not significantly influence soil structure and hydrological properties, while NC treatment increased water movement and retention. Tillage reduced the microarthropod abundance, in particular Collembola and eu-edaphic forms, which were the most sensitive groups to soil perturbation. We conclude that natural grass cover was more effective than conservation tillage in maintaining or improving elements of soil functionality.

Comparison of Measured and Simulated Urban Soil Hydrologic Properties.

Urban communities use hydrologic models to plan for and assess the effectiveness of stormwater control measures. Although emphasis is placed on soils as permeable surfaces that regulate the rainfall-runoff process, representative soil hydrologic parameters for urban areas are rare. The extent to which measured and commonly simulated hydrologic data may differ is also largely uncharacterized. As part of the US EPA urban soil assessment, infiltration and drainage rates were measured in 12 cities, and the authors compared these measured data to estimates generated from the EPA National Stormwater Calculator (NSWC), United States Department of Agriculture (USDA) Soil Survey Geographic Database (SSURGO), and USDA Rosetta. The analysis highlights the overall lack of soil hydrologic data for many cities in the NSWC and SSURGO and show that common prediction algorithms for infiltration and drainage poorly represent urban soil hydraulics. Paired comparison of field-measured values and model-estimated values resulted in root-mean-square errors ranging from 23 to 173 mm=h. These findings are presented in the context of planning for effective stormwater and wastewater management practices, and the need for confirming simulation results with site-specific field data.

Taking the Pulse of Soil

Heat pulse methods for measuring thermal, hydrologic, and other properties of soils have advanced our understanding of soil characteristics.

Seasonal Wetness, Soil Organic Carbon, and Fire Influence Soil Hydrological Properties and Water Repellency in a Sagebrush‐Steppe Ecosystem

AbstractPrescribed fire is an important tool for rangeland management in sage‐steppe ecosystems, yet the long‐term effects of this practice on soil hydraulic properties are not well known. We explore interactions among site geomorphology, soil organic carbon (SOC) soil N, soil water repellency (SWR), and plant community type on infiltration properties before fire and 8 years thereafter in a semiarid research watershed. The objective was to assess the sustainability of rangeland burning in sage‐steppe ecosystems. Many types of measurements were made in three plant communities to identify how differences in soil hydraulic properties are related to differences in plant cover and soil texture and to determine relationships among SOC, SWR, soil water contact angle, and infiltration properties. Measurements were made on transects in burned and unburned catchments. We found that severity and occurrence of surface SWR were substantially reduced 8 years after a fire within the area originally covered with mountain big sagebrush, where the fire intensity was greatest. Surface SWR was lowest in the sparsely vegetated low sagebrush, where SOC was also lowest. Unsaturated hydraulic conductivity (Kh) increased in each vegetation type over the 8‐year period after burning and was not directly related to SWR. Spatial variability in Kh was primarily controlled by soil texture, whereas differences in sorptivity (S) were controlled by SWR and aridity. SOC is not well correlated to soil surface SWR. The decadal scale changes in Kh and associations between S and site characteristics indicate forms of resilience to fire across a moisture gradient.

Change of hydraulic conductivity of cohesive soils due to consolidation treatments with expanding resins

Settlements of ground subjected to foundation load are often due to both natural and/or anthropogenic causes, such as differential consolidation, seepage, periods of drought alternating with heavy rainfalls, growth of tree roots, sewer leaks, vibrations induced by vehicle traffic, excavations, or construction defects. Techniques of soil consolidation and stabilization by means of injection of polyurethane expanding resins have been efficiently used to mitigate or even solve this issue. The efficiency of the resin injection treatment has been well documented also thanks to the develop of a procedure of planning and monitoring which combines traditional geotechnical tests with the application of electrical resistivity tomography, which is strongly sensitive to the presence of water or voids. The combination of these survey methodologies allows to recognize the effect of injection in terms of soil compaction and water migration, a key factor for understanding the phenomenon and planning of resolutive interventions. The present study follows a previous work aimed at evaluating the increase in the geotechnical performance of cohesive soils treated by injection of expanding resins (same soil, resin, at the same site) and integrates it by focusing on the quantification of the effects of consolidation treatments, by means of expanding resins injection, on hydrologic properties of cohesive soils, focusing on saturated hydraulic conductivity measurements. Laboratory permeability test, performed in triaxial cell at different stress conditions and hydraulic gradients, were performed on undisturbed samples collected on “natural (non-treated)” and “treated soils”, before and after the injection of resin (MAXIMA ® by GEOSEC ® ) in a full-scale test site characterized by the presence of continuous and homogeneous cohesive soils, (clay and silts). The investigated soil is classified as CH or CL soil, very firm and apparently overconsolidated. The study shows how the treatment is able to modify the characteristics of hydraulic conductivity of the soil. The injected resins partly follow pre-existing weaknesses and partly impregnate homogeneous and continuous masses of soil in a capillary way, giving it, in addition to the already documented greater mechanical strength, a lower hydraulic conductivity. The electrical resistivity investigations allow to appreciate the volumes affected by the treatment to which the variations of the measured properties can be attributed.

Use of inverse modelling and Bayesian optimization for investigating the effect of biochar on soil hydrological properties

Physical properties of biochar such as small particle size and high porosity can modify soil properties and help to improve soil water dynamics. However, there has been no consistent long-term measurements of change in soil physical properties due to biochar application under real field conditions. In this study, we use a unique dataset of soil water content measurements in a corn-soybean cropping system (with biochar and no-biochar) for two years. Soil water content was measured every 30 min at 4 different depths and with 3 replications in corn plots. The effect of biochar was expected to be the difference between the physical soil properties of the two treatments. The APSIM model, a process-oriented crop model, was employed in order to find the physical properties of biochar and no-biochar treatments by using inverse modeling. First, a global sensitivity analysis was carried out to find the most sensitive inputs for the APSIM model for soil water simulation. Then the Metropolis-Hasting algorithm was used to inversely estimate the APSIM soil input properties using the soil moisture measurements. Results of the sensitivity analysis showed that the drainage upper limit (DUL) was the most sensitive soil property followed by saturated hydraulic conductivity (KS), saturated water content (SAT), maximum rate of plant water uptake (KL), maximum depth of surface storage (MAXPOND), lower limit volumetric water content (LL15) and lower limit for plant water uptake (LL). The difference between the posterior distributions (with and without biochar) showed an increase in DUL by approximately 10%. No considerable change was noted in LL15, MAXPOND and KS whereas SAT and LL showed a slight increase and decrease in biochar treatment respectively compared to no-biochar.

Adaptability of global olive cultivars to water availability under future Mediterranean climate

Adaptation to climate change is a major challenge facing the agricultural sector worldwide. Olive (Olea europaea L.) is a global, high value crop currently cultivated in 28 countries worldwide. Global data to assess the vulnerability of the crop to climate variability are scarce, and in some notable cases, such the United Nations Food and Agricutlure Organization database (FAO, 2006), qualitative assessments rather than quantitative indicators are provided. The aim of this study is to demonstrate a new approach to help overcome these constraints toward a globally applicable method to assess the adaptability of olive cultivars. The adaptability of 11 cultivars, widely used in 11 countries worldwide, was studied using a new generic approach based on the evaluation of soil hydrological regime against cultivar-specific hydrological requirements. The approach requires local data, notably on soil hydrological properties, but it is easily transferable to other countries and regions. We applied an agrohydrological model in 60 soil units to determine hydrological indicators both in a reference (1961–1990) and a future (2021–2050) climate case. We compared indicators with cultivar-specific requirements to achieve the target yield; requirements were established using experimental yield response curves. We estimated the probability of adaptation, i.e., the probability that a given cultivar attains the target yield, and we used it to evaluate the cultivar potential distribution in the study area. At the locations where soil hydrological conditions were favorable, the probabilities of adaptation of the cultivars were high in both climate cases. The results show that the area with suitable conditions for the target yield (area of adaptability) decreased under future climate for all the cultivars, with higher reduction for Frantoio and Maiatica and smaller reduction for Itrana, Nocellara, Ascolana, and Kalamata. These cultivars are currently grown in Argentina, United States (US), Australia, France, Greece, and Italy. Our results indicate also that these cultivars require higher available soil water to attain the target yield, i.e., we may expect similar vulnerability in other parts of the world. Based on these findings, we provide some specific recommendations for enrichment of global databases and for further developments of our approach, to increase its potential for global application.

Bulk density effects on soil hydrologic and thermal characteristics: A numerical investigation

AbstractSoil bulk density (ρb) is commonly treated as static in studies of land surface dynamics. Magnitudes of errors associated with this assumption are largely unknown. Our objectives were to (a) quantify ρb effects on soil hydrologic and thermal properties and (b) evaluate effects of ρb on surface energy balance and heat and water transfer. We evaluated 6 soil properties, volumetric heat capacity, thermal conductivity, soil thermal diffusivity, water retention characteristics, hydraulic conductivity, and vapour diffusivity, over a range of ρb, using a combination of 6 models. Thermal conductivity, water retention, hydraulic conductivity, and vapour diffusivity were most sensitive to ρb, each changing by fractions greater than the associated fractional changes in ρb. A 10% change in ρb led to 10–11% change in thermal conductivity, 6–11% change in saturated and residual water content, 49–54% change in saturated hydraulic conductivity, and 80% change in vapour diffusivity. Subsequently, 3 field seasons were simulated with a numerical model (HYDRUS‐1D) for a range of ρb values. When ρb increased 25% (from 1.2 to 1.5 Mg m−3), soil temperature variation decreased by 2.1 °C in shallow layers and increased by 1 °C in subsurface layers. Surface water content differed by 0.02 m3 m−3 for various ρb values during drying events but differences mostly disappeared in the subsurface. Matric potential varied by >100 m of water. Surface energy balance showed clear trends with ρb. Latent heat flux decreased 6%, sensible heat flux increased 9%, and magnitude of ground heat flux varied by 18% (with a 25% ρb increase). Transient ρb impacted surface conditions and fluxes, and clearly, it warrants consideration in field and modelling investigations.

Revegetation with artificial plants improves topsoil hydrological properties but intensifies deep-soil drying in northern Loess Plateau, China

Knowledge about the effects of vegetation types on soil properties and on water dynamics in the soil profile is critical for revegetation strategies in water-scarce regions, especially the choice of vegetation type and human management measures. We focused on the analysis of the effects of vegetation type on soil hydrological properties and soil moisture variation in the 0–400 cm soil layer based on a long-term (2004―2016) experimental data in the northern Loess Plateau region, China. Soil bulk density (BD), saturated soil hydraulic conductivity (Ks), field capacity (FC) and soil organic carbon (SOC) in 2016, as well as the volumetric soil moisture content during 2004–2016, were measured in four vegetation types, i.e., shrubland (korshinsk peashrub), artificial grassland (alfalfa), fallow land and cropland (millet or potato). Compared with cropland, revegetation with peashrub and alfalfa significantly decreased BD and increased Ks, FC, and SOC in the 0–40 cm soil layer, and fallow land significantly increased FC and SOC in the 0–10 cm soil layer. Soil water storage (SWS) significantly declined in shrubland and grassland in the 40–400 cm soil layer, causing severe soil drought in the deep soil layers. The study suggested that converting cropland to grassland (alfalfa) and shrubland (peashrub) improved soil-hydrological properties, but worsened water conditions in the deep soil profile. However, natural restoration did not intensify deep-soil drying. The results imply that natural restoration could be better than revegetation with peashrub and alfalfa in terms of good soil hydrological processes in the semi-arid Loess Plateau region.

KARAKTERISTIK HIDROLOGI TANAH DI BAWAH TEGAKAN PINUS (Pinus merkusii), MERAWAN (Hopea odorata Roxb) DAN MAHONI UGANDA (Khaya anthoteca)

Kerusakan hutan dapat mempengaruhi fungsi hidrologi hutan sebagai pengatur tata air, menjaga waktu dan penyebaran aliran air sungai, menjaga iklim mikro, dan melindungi daerah di bawahnya dari berbagai bencana seperti banjir. Penanaman pohon kembali dinilai merupakan salah satu upaya untuk memperbaiki kondisi hutan dan lingkungan. Tujuan penelitian ini adalah untuk mengkaji karakteristik hidrologi tanah di bawah tegakan tanaman Pinus (Pinus merkusii), Mahoni Uganda (Khaya anthoteca), dan Merawan (Hopea odorata Roxb). Metoda yang digunakan adalah pengukuran sifat-sifat fisik tanah secara periodik. Hasil penelitian ini menunjukkan perbedaan karakterisitik kadar air, infiltrasi dan permeabilitas pada berbagai tegakan pohon. Perubahan kadar air tertinggi terjadi pada tanah di bawah Pinus sebesar 3.05%, Merawan sebesar 2.40%, dan terendah pada Mahoni Uganda sebesar 1.89% pada kedalaman tanah yang sama. Infiltrasi tertinggi sebesar 116.25 cm jam-1 di bawah tegakan Pinus, terendah 24 cm jam-1 di bawah tegakan Merawan. Permeabilitas tertinggi sebesar 13.27 cm jam-1 di bawah tegakan Pinus, terendah di bawah tegakan merawan sebesar 2.72 cm jam-1. Tekstur tanah relatif sama pada masing-masing tegakan yakni didominasi oleh liat. Tanah di bawah tegakan tanaman Pinus, Merawan dan Mahoni Uganda termasuk kelompok hidrologi tanah B.