Upslope Positions Research Articles

Spatio‐temporal analysis of snow depth and snow water equivalent in a mountainous catchment: Insights from in‐situ observations and statistical modelling

AbstractThis research, conducted in the mountainous catchment near Abant Lake in the Western Black Sea region of Türkiye, aimed to investigate the spatiotemporal variations of snow depth (SD) and snow water equivalent (SWE) throughout the snow season from December 2019 to March 2020, encompassing both accumulation and melting periods. In total, 14 snow surveys were conducted, covering 58 permanent snow measurement points (PSMP) marked with snow poles. The classification and regression tree (CART) method was employed to statistically analyse their relationships with eight variables: snow period, forest canopy, aspect, slope, elevation, slope position, plan and profile curvature. The root mean square error (RMSE) for SD and SWE was determined to be 0.15 m and 46 mm, respectively. The study findings revealed that mean SD and SWE values were higher in forest gaps compared with under‐forest and open areas. Although the snow cover disappeared earliest in under‐forest areas, the melting rate was observed to be 43% and 17% slower compared with forest gaps and open areas, respectively. Wind redistribution resulted in minimum snow accumulation on western aspects, upper slope positions and ridges, while maximum accumulation was observed on southern aspects, valleys and lower slope positions. Higher elevations (>1580 meters) experienced faster snow melting rates, leading to earlier disappearance of snow cover. PSMPs located on slopes with lower degrees (<15°) exhibited lesser accumulation and earlier snow disappearance. The CART model identified the snow period as the most significant factor in predicting SD and SWE, based on variations in snowfall and air temperature. Other significant variables included forest canopy, aspect and elevation. The study suggests that the CART method is well‐suited for modelling complex snow dynamics, providing valuable insights into spatiotemporal variations in SD and SWE in mountainous regions.

Assessment of Soil Structural Quality Under Area Closure and Open Grazing Land in Hidabu Abote District, North Shewa Zone, Oromia Regional State, Ethiopia

The experiment was conducted at Sire Morise kebele, Hidabu Abote district, to assess soil structural quality of different land management system (area closure and open grazing land). In this study, area closure land management practice was compared with open grazing land management practice in similar slope positions for soil structural quality build up. Soil samples were collected from both land management system at three slope position with three times replication. Totally 36 undisturbed soil blocks were collected from both land management system at 10 and 20 cm sampling depths. The finding of the study showed that the average value of volumetric moisture content and saturated hydraulic conductivity of soil were greater at area closure than open grazing land management system and also higher at bottom slope position than middle and upper slope position. The mean value of air-filled porosity and bulk density were lower at both area closure management practices and bottom slope position. Bulk density, volumetric soil moisture content and saturated hydraulic conductivity at 20 cm sampling depth were shows significantly different with respect to management practices. According to visual assessment in the field, soil physical quality was unfavourable in open grazing land management system and upper part of landscape position soils and the visual assessment scores showed that the soils under area closure had a good soil structural quality. There were strong relations among the three visual field assessment methods and also between visual assessment methods and laboratory determined soil properties of both land management system. In general, the result of the study showed that physical and structural quality of soil in area closure was improved due to good land management system. Based on the result of study it can be conclude that area closure improves soil physical and soil structural qualities and from the technical point of view, open grazing lands in hilly area should be changed to area closure before soil properties and soil nutrient contents are exhausted more.

Reclamation of an eroded lakeshore slope using small vegetation islands and terraces

Bioengineering approaches to slope stabilization involve biological and mechanical methods with low impact on the environment and landscape. Slope stabilization using vegetation patches or islands can greatly decrease runoff and soil erosion on an eroded lake shore. While vegetation islands showed promise for forest and grassland reclamation, they have rarely been used on eroded lake shores. A study was conducted to determine whether bioengineering using native vegetation islands and terraces could successfully revegetate and stabilize a severely eroded lake shore slope in the central aspen parkland, Alberta, Canada. Three gullies and three slopes were terraced using pressure treated planks, then transplanted with non-dormant (mid-August) and dormant (mid-October) 20 cm diameter vegetation islands in a soil amended with 25% (by volume) compost. Volumetric water content was significantly less in lower slope positions than upper slope positions, and sediment transport to lower slope positions was much reduced. After one year, both non-dormant and dormant transplanted islands survived and established on the terraced slope, under relatively inhospitable growing conditions. Although non-dormant islands had significantly lower vegetation mortality (10% or less) than dormant islands on both slopes and gullies, no differences in health and vigour were found by the end of the study. Overall plant species number on the site increased during the study. Graminoid species densities increased, while those of forbs, shrub and tree species declined in the transplanted vegetation islands. Non-dormant islands had greater graminoid density than dormant islands, where Poa pratensis was the dominant species in the islands. Bioengineering with vegetation islands and terraces can assist in trapping runoff and sediment, and accelerate establishment of a diversity of plant species and groups relative to traditional revegetation methods.

Shelterbelt effects on soil redistribution on an arable slope by wind and water

Soil erosion is the most severe form of land degradation globally. Farmland shelterbelts are important for reducing erosion, especially erosion caused by the co-occurrence of water and wind. However, few studies have focused on how the distance from the shelterbelt associated with farmland topography affects the redistribution of soil quality indicators. The aims of this study is to reveal the relative importance of these two factors to soil quality under typical wind and water erosion conditions concurrent with the Songnen Plain, China. Topsoils (0–10 cm) were sampled at seven distances from the shelterbelt with three replicates, where topography heterogeneity was also considered. We found that the silt/clay content and soil nutrients at sites farther from the shelterbelt were significantly greater than those at sites closer to the shelterbelt (P < 0.05). Similarly, deposition was dominant at sites farther from the shelterbelt and downslope positions, while erosion was dominant at sites closer to the shelterbelt and upslope positions. Moreover, we discovered that the relative influence of distance from the shelterbelt and farmland elevation varied with individual soil quality indicators. Soil nutrients increased through the deposition of more fine-textured soil (silt/clay) positions farther from the shelterbelt. The downslope region responds to soil deposition by enhancing the plough pan thickness and lowering the bulk density and pH. Overall, distance from the shelterbelt and farmland elevation had interactive effects on soil quality, and erosion was primarily affected by distance from the shelterbelt (63.4 %), followed by elevation (22.7 %). Furthermore, the sites closer to the shelterbelt (i.e., 20 to 420 m) warrant particular attention due to the deposition of coarse-texture materials here. This work is crucial for an improved understanding of the synergistic effects of long-term water and wind co-occurrence on soil quality evolution.

Soil Fertility Assessment and Mapping under Different Land Use Types along Toposequence at Danka Watershed in Dinsho Districts of Bale Highland Oromia, Southeastern Ethiopia

Soil fertility assessment and mapping bases, to increase fertilizer usage efficiency, decision-makers, planners, and soil management in undulating slopes farming of Ethiopian highlands like Bale Highland. The study aimed to assess and map soil fertility status along toposequence under different land use types at the Danka watershed of Dinsho District Bale Highland, Southeastern Ethiopia. Following the initial reconnaissance field survey, 54 composite soil samples were prepared from the three land use types (natural forest, grazing, and cultivated) at three slope positions lower (0 - 10%), middle (10 - 15%), and upper (15 - 30%) at a soil depth of 0 to 20 cm. Finally, the laboratory results were interpolated using the IDW interpolation technique in ArcGIS software 10.5 for the soil fertility status map and further analyzed using R software 4.1.1 Version for mean separation. The study findings indicate that the soil texture class of the study was loam to clay loam, clay loam, and clay to clay loam at the upper, middle, and lower slope positions, respectively. The finding revealed that the values varied from 5.81 – 6.66, 2.07 – 6.25%, 0.13 – 0.71%, 2.83 – 17.56 gm/kg, and 14.04 -38.80 cmol (+)/kg) for the soil pH, organic matter, total nitrogen, available phosphorus, and CEC, respectively. In this study, most of the soil fertility status of the Danka watershed was as follows: natural forest &gt; grassland &gt; cultivated land use types and lower slope &gt; middle slope &gt; upper slope positions. In conclusion, the main factors contributing to the area's declining soil fertility status were monocropping, total crop residue removal, soil erosion, nutrient leaching, and inadequate soil management. The results of the current study offer the basis for the work of farmers, planners, decision-makers, and other agriculture-related stakeholders. Integrated soil fertility management with biophysical soil conservation measures is advisable for cultivated land at all slope positions. Further, a study on slope position-based crop response fertilizer rating for agricultural precision and ensuring food security is recommended in undulating fields of the Danka watershed.

Effects of Slope Position on Soil Physicochemical Properties of Cultivated Land Use Type in Danka Watershed of Dinsho District, Bale Highland, Oromia, Southeast Ethiopia

Quantify and understand soil nutrient loss under different undulating topography farming bases for site-specific management and targeted fertilizer application rates. The study aimed to assess the effect of slope positions on soil physicochemical properties at the Danka watershed of Dinsho District Bale Highland, Southeastern Ethiopia. Consequent to the reconnaissance survey, soil samples were taken from the cultivated land use type in three replications at three different soil depths (0-0, 20-40, and 40-60 cm) and three slope positions (upper, middle, and lower), analyzed follow standard laboratory procedure and further analyzed using R software 4.1.1 version. The results showed soil physicochemical properties were significantly (P ≤ 0.05) influenced by the interaction between slope positions and soil depth. The results of soil physical properties varied from 1.29 -1.73 g cm-3, 2.47 – 2.74 g cm-3, 47.80 - 36.75%, 10.78 – 15.11%, 12.76 – 18.16%, and 4.06 – 8.16% bulk density, particle density, total porosity, FC, PWP, and AWHC, respectively. Selected soil chemical properties varied from 5.91 - 6.45, 0.64 - 3.20%, 0.04 - 0.25%, 1.14 - 5.60 gm/kg, and 10.24 - 37.24 cmol (+)/kg) soil pH, organic matter, total nitrogen, available phosphorus, and CEC, respectively. The values of exchangeable bases were concentration increased from the upper slope position toward the lower slope position and with increased soil depth. Soil micronutrients were increased with increased slope and decreased with increased soil depth. The lowest slope position had relatively better soil nutrient contents than other slope positions. It is advised that integrated soil fertility management, biophysical soil and water conservation, and slope-based, site-specific fertilizer rating for advance agricultural precision and ensure food security.

Effects of erosion on macroaggregation, aggregate associated organic carbon sources and compositions in a Mollisol agricultural landscape

Macroaggregation is widely recognized as an important soil carbon (C) stabilization mechanism. However, in eroding landscapes, the relationships among soil aggregation, organic carbon (OC) sources, and chemical composition are poorly understood. In this study, we aimed to explore the effects of erosion and deposition on macroaggregation, OC sources, and chemical compositions in topsoil (0–20 cm) versus subsoil (80–100 cm) in a Mollisol agricultural landscape. The bulk soil was fractionated into macroaggregates (0.25–2 mm), microaggregates (0.053–0.25 mm), and clay and silt (<0.053 mm) using a wet sieving procedure. The plant sources of soil OC were quantified based on the stable isotope 13C (δ13C), and the chemical composition of macroaggregate associated OC (MaOC) was determined by solid-state nuclear magnetic resonance techniques. The results indicated that macroaggregates and MaOC comprised 45–72% of soil mass and 50–66% of soil OC, respectively. There was a reduction in macroaggregate-associated C3-derived C (C3-C) in the eroding position compared to that in the non-eroding position. However, similar amounts of C4-derived C (C4-C) were detected among three topographical areas, indicating the re-macroaggregation of eroded materials in the depositional position and preferential protection of C3-C. In the up-slope positions, topsoil MaOC was composed primarily of O-alkyl C (52%). Compared with the up-slope position, there was a considerable increase in the amount of aromatic C in the erosional macroaggregate fraction. However, at the eroding position, there was a marked increase in the proportion of substituted alkyl-C in the topsoil material, and deposition resulted in an increase in aromatic C in the subsoil. Overall, erosion and deposition change soil aggregation, and sources and composition of OC in different functional pools have important implications for the stabilization of organic matter along an eroding Mollisol hillslope.

Identification, Prioritization and Mapping of Major Constraints and Potentials in the Medo Watershed the Case of West Arsi District in Central Rift Valley Area of Ethiopia

The concentration to characterize the biophysical and socio-economic features in the integrated watersheds is to identify and prioritize production constraints for designing appropriate research and development interventions. The objective of this study was to assess the current biophysical of characteristics of Medo watershed, West Arsi Zone of Oromia, Ethiopia. To do so relevant data and tools were used; ArcGIS, Microsoft Excel sheet and fundamental formulae were applied for the analysis are some. The results of the study indicated that the major land use types in the watershed are agricultural land covering 50%, vegetation (shrubs, forests and, plantations) covering 24% and settlement covering 16% out of the total land use. Slope gradient of Medo watershed ranges from zero to more than 20 and the slope gradient of 2-5 and 5-10 cover the greatest in area coverage representing 201 ha and 170 ha respectively. We can also observe that about 8% out of the total area is subjected to severe erosion. Sandy clay loam was the dominant soil textural classes in the surface soils and Phaeozems, Retinols and Andosols are the dominant soil types, which cover 57%, 36% and 7% of the sub-watershed area for lower, middle, and upper slope positions, respectively. Mean annual rainfall of the area ranges from 960.09 mm at lower part of the watershed to the 1304.93 mm at upper part of the watershed. Accordingly, Medo sub-watershed is laid in majority of at sub humid agro ecological zone. An assessment of the trees within the landscape of watershed showed some remnant natural forests and a wide variety of shrubby vegetation is encountered at all landscapes. About 40 percent of the watershed, is under high to extremely severe soil loss values (&gt;45 ton per hectare per year). The baseline study also identified that those natural resources degradation such as land, and or/ soil fertility, reduction, and recent changes in the areas’ weather condition in line of climate change prevailing in current years are few of the many factors that are contributing to the land and crop productivity reductions in the area. Therefore, prioritizing the identified problem and preparing intervention of different technologies and development plans to solve the problems by taking into consideration the existing opportunities of the watershed.

Pedological characteristics and classification of soils along landscape at highlands of Tsegede, Western Zone of Tigray, Ethiopia

Dynamics and distribution of soil characteristics as influenced by landscape /topographic features in acidic soils of Tsegede area in Northern Ethiopia has limited information. This study was conducted to characterize soil properties and classify major soil types. Four representative profiles along top sequence from varying slope positions crest at (Chegarkudo), upper slope and middle slope at (Endassilassie) and lower slope at (Intabela) were opened and described in-situ for morphological properties of soils and sampled horizon-wise for physico-chemical soil properties’ analysis. The results showed that soils at crest and upper-slope position were characterized by shallow depth, whereas those at middle and lower-slope positions exhibited relatively deep. The soil consistence ranges from slightly hard to hard (dry), friable to very friable (moist), yellowish red to dark red brown (dry) in color, moderate medium sub-angular to strong thick angular blocky in structure. The pH of surface soil ranged from 5.14 to 5.74 which was strongly acidic to slightly acidic and varied from clay loam to clay in texture, organic carbon, exchangeable bases and cation exchange capacity varied with profile depth. Based on the world reference base legend, the soils were classified as Skeletic Leptosols about 3756 ha, Cambic Leptosols about 1926 ha, Dystric Cambisols about 1883 ha and Leptic Cambisols about 1966 ha.

Tree growth as an effect indicator of silvopastoral systems in the low hilly area of western Henan province, China

The low hilly area is a major landform in the west of Henan province, China, and it is suffering soil and water loss because of human activities. The silvopastoral system that combines trees and grasses has been widely used to restore this fragile area. We conducted in situ field experiments in 2011 in the low hilly area of Henan province involving pure forests of Populus simonii (PS; Salicaceae), Platycladus orientalis (PO; Cupressaceae), Quercusvariabilis (QV; Fagaceae), and Robinia pseudoacacia (RP; Fabaceae), and also with each forest tree species being combined with Medicago sativa (MS; Fabaceae) as silvopastoral systems, i.e., PS-MS, PO-MS, QV-MS, and RP-MS, respectively. We recorded tree diameter at breast height (DBH) and tree height (TH) in the years 2014–2016, 2018, 2020, and 2022 for all the different vegetation types. Tree biomass load (TBL, i.e., tree biomass per unit area) was estimated based on DBH and TH using allometric equations for each tree species. Generally, the results showed that the DBH, TH, and TBL were promoted in the silvopastoral systems PS-MS, PO-MS, and QV-MS. Specially, the DBH and TBL of PS-MS and PO-MS tended to be higher and were significantly higher than the pure forests of PS and MS, respectively, in 2014–2016; the silvopastoral systems were not significantly different from the pure forests for DBH in 2018 and 2022, and for TBL in 2018 and 2020. TH was lower in PS-MS and PO-MS than that in PS and PO in 2014–2016, while there was no difference of TH between PS-MS and PS in 2018 and 2022, and TH was higher in PO-MS than that in PO in 2018, 2020 and 2022. The DBH, TH, and TBL were all higher in QV-MS than QV. The TBL in RP-MS was non-significant or lower compared to that in RP. Moreover, TBL tended to be lower in upslope positions than downslope in the pure forests, while there was no difference in most silvopastoral systems. In summary, PS and PO may be suggested as the tree species selection in vegetation restoration processes for about five years, QV may be a better alternative for a long term, while RP is not recommended.

Coupling effects of soil organic carbon and moisture under different land use types, seasons and slope positions in the Loess Plateau

Understanding the response of soil organic carbon (SOC) and moisture to different land-use types, slope positions, seasonal variations, and their interactions has great significance for land use and management. However, the coupling effects of SOC and soil moisture in typical hilly and gully regions are still elusive. Therefore, in this study, five different land-use types, including cropland, abandoned land, grassland, shrubland, and forestland were selected in a typical Chinese loess hilly-gully region, and soil samples were collected from 0 to 200 cm profiles at the upper, middle, and lower slope positions in four seasons. The results demonstrated that the distributions of SOC and soil moisture were jointly significantly affected by land-use types, seasons, and slope positions (P < 0.01). Average SOC content was found to be highest in the shrubland, followed by grassland, abandoned land, forestland, and cropland. SOC storage at the lower slope position was 10.97% higher than that at the upper slope position. SOC storage in winter was 45.47% higher than that in summer. SOC storages of abandoned land, grassland, shrubland, and forestland were 17.38%, 33.08%, 52.52% and 1.26% more than that of cropland, respectively. Soil moisture fluctuated greatly in 0–100 cm layers and was stable beneath the 100 cm layers, which was highest in autumn, and lowest in summer. Whereas, under different land-use types, the soil moisture of cropland was the highest, especially significantly higher than all revegetated treatments in the 60–200 cm soil layers. Compared with cropland, soil water storage at other land-use types was averagely 36.45 % lower in the entire 200 cm soil profile. SOC was positively correlated with soil moisture under different factors. Thus, we recommend planting shrub and grass in watersheds with serious soil erosion in the semi-arid hilly and gully region, because they can sequestrate more SOC and retain more soil water.

Drivers of vegetation and soil determine natural regeneration of a single plantation at different slope positions

Promoting natural regeneration in artificial forest ecosystems is crucial for sustainable management. Understanding the fundamental mechanisms and drivers of tree regeneration is the prerequisite for promoting it effectively. This study worked with Larix principis-rupprechtii, a species considered difficult to regenerate. Twenty-four sample plots measuring 30 m × 30 m were established, with eight plots at each of the lower, middle, and upper slope positions, respectively. Field investigation and multivariate analysis were performed to uncover the regeneration traits in the plantations with abundant seedlings on the continuous slope. The results revealed that ground diameter and height of the regeneration (RGD and RH) were larger at the lower slope, with significant positive correlations to available nitrogen (contribution rate, CR: 0.858) and slope (CR: 0.652). In contrast, regeneration density (RD), representing the quantity of regeneration, was greater at the middle slope. Its significant impact factors were slope position (CR: −0.648) and herb diversity, represented by Pielou index (CR: 0.961). Stand density had a significant negative effect on regeneration, particularly at the upper slope, with CRs of −0.842 and −0.764 to RGD/RH and RD, respectively. Common contribution was found among the factors, with the largest contribution groups being the topographical and soil factors (CR: 0.358). These findings provide valuable insights into the single species regeneration progress on northern mountainous slopes and offer essential information for developing facilitation methods for the natural regeneration in artificial forests.

Responses of molecular composition and biodegradation of dissolved organic matter to erosion in topsoil versus subsoil in a Mollisol agricultural ecosystem

Although dissolved organic matter (DOM) has a substantial influence on biogeochemical processes relevant to erosion in agricultural ecosystems, the mechanisms underlying the dynamics and biodegradation of DOM in eroding landscapes are yet to clarified. In this study, we examined the changes in dissolved organic carbon (DOC), profile distribution, biodegradation, and chemical characteristics associated with erosion in a Mollisol agricultural landscape. The results showed that DOC content in the mid-slope was significantly higher than that in the down-slope, particularly at depths of 40–100 cm. The higher humification index and low biological index indicated that the DOM in the depositional position was characterized by a higher humic content compared to the up-slope positions. The up-slope samples were found to contain larger amounts of protein-like substances, whereas the mid- and down-slope soils comprised a larger proportion of anthropogenic humic-like materials, indicating that DOM in the up-slope soil was primarily microbial-derived. For the topsoils, the activities of β-glucosidase and cellulase were highest in the down-slope both before and after incubation, thereby suggesting that the deposition was conducive to the secretion of these enzymes by soil microbes. Overall, our observations indicated that erosion and deposition had a significant effect on the chemical composition and biodegradation pathways of DOM in soil profiles. These findings provided detailed information on the heterogeneous DOM characteristics at the molecular level, as well as DOC effects on environmental behavior in agricultural eroding environments.

Spatial Variation in Soil Physico-Chemical Properties along Slope Position in a Small Agricultural Watershed Scale

Both cropland management and slop erosion are important factors influencing soil properties, but there are relatively few studies on their combined effects. Studies at the agricultural watershed scale can satisfy both of these conditions, and to reduce the effects of soil heterogeneity due to differences in spatial scale, it is better to select different slopes in the same small watershed. To understand how soil properties will respond to the variation of slope position and cropland management at an agricultural watershed, we present the distribution of soil bulk density (BD), saturated hydraulic conductivity (Ks), water-stable aggregates, soil organic carbon (OC), nitrogen (N), and phosphorus (P) at four slope positions in two cropland management systems of a small agricultural watershed in the black soil region of northeast China. The selected four slope positions include upper slope, middle slope, lower slope, and footslope positions. The two cropland management systems consist of a sustainable cropland system (i.e., contour ridge tillage at upper slope position, longitudinal ridge tillage at middle slope and lower slope positions, and grassland at footslope position) and a conventional cropland system (i.e., contour ridge tillage at upper slope position, longitudinal ridge tillage at middle slope, lower slope positions, and footslope positions). The results showed that soil bulk density and microaggregates decreased but the concentration of OC and nutrients, Ks, and small-macroaggregate increased from the upper slope position to the lower slope position in both the conventional and sustainable croplands, which was due to the interaction effect of cultivation with erosion. In comparison with conventional cropland, sustainable cropland has greater Ks, large-macroaggregate, small-macroaggregate, microaggregate, and concentrations and stocks of OC, N, and P, but showed lower bulk density and silt + clay fraction. However, the prominent differences in both croplands were presented in the footslope position, which is ascribed to the interaction of cultivation, erosion, and cropland management. These results highlighted that sustainable cropland management practice has the potential to improve soil structure and prevent soil and nutrient loss.

Characterization and Classification of Soils and Land Suitability Evaluation for the Production of Major Crops at Anzecha Watershed, Gurage Zone, Ethiopia

The study was conducted at Anzecha watershed in Gurage Zone, Ethiopia, to characterize and classify the soils and to evaluate the physical land suitability of the area for the production of major crops (maize, teff, and wheat). The soils were classified based on World Reference Base for soil resource. The physical land suitability was made following FAO guideline using maximum limitation method. Four profiles were opened along toposequence and designate as upper, middle, lower, and toe slope positions (pedons 1, 2, 3, and 4), respectively. Soils of the watershed had low level of available phosphorous, low electrical conductivity, no coarse fragments, low acidity, and great depth. The soils were classified as Acrisols, Nitisols, and Vertisols. The land suitability evaluation for production of major crops showed that upper slope position (20.8%) was currently not suitable (N1) for maize, teff, and wheat. Middle slope position (27.3%) was marginally suitable (S3) for maize, teff, and wheat. Lower slope position (32.5%) was moderately suitable (S2) for maize and marginally suitable (S3) for teff and wheat. Toe slope position (19.4%) was moderately suitable (S2) for maize and teff and marginally suitable (S3) for wheat. There is no topographic position that was classified as highly suitable (S1). Hence, farmers of the area should implement major land improvement practice to create optimum condition for production of major crops or should change a land utilization type. Moreover, the soils of the study area were acidic and, therefore, there has to be acid soils management strategy in the area.

ASSESSMENT OF SOIL MOISTURE AND NUTRIENTS ON TERRACE SLOPE OF HARD-SETTING SOILS IN SEMI-ARID EASTERN KEN

&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt; Terraces are structures consisting of ditches and embankments used to control erosion and increase land productivity. There is, however, little emphasis on the effects of the ditch dimensions on soil moisture and nutrient dynamics. &lt;strong&gt;Objective:&lt;/strong&gt; To determine the effect of varying ditch depths on soil moisture and nutrient quantities and their variability within the terrace slope on hard-setting soils. &lt;strong&gt;Methodology:&lt;/strong&gt; Soil samples were collected seasonally in 2014 and 2015 from terraces with different ditch depths (60, 30, and 0 [control] cm) for the determination of soil moisture content (SMC). The samples were collected from the upper, middle and lower slope positions of each terrace. Soil from the three slope positions of each terrace was also sampled at the end of the study and analyzed for total nitrogen (%TN), available phosphorous (Av. P), exchangeable potassium (K&lt;sup&gt;+&lt;/sup&gt;) and % organic carbon (OC) contents. Data were subjected to a two-way analysis of variance and differences in means determined at a 95% level of confidence. &lt;strong&gt;Results:&lt;/strong&gt; Significant interactions (P&amp;lt;0.001) in SMC were observed between seasons, ditch depths and slope positions. Higher SMC was found in treatments with 30 and 60 cm ditch depths in all the slope positions and seasons compared to the control. Soil moisture contents in the lower and upper slope positions were significantly different between the terraces with 30 and 60 cm ditch depths when rainfall was high and evenly distributed, but non-significant in poorly distributed rainfall seasons. Significant differences (P ≤ 0.05) in contents of total nitrogen and available phosphorous were found between the upper and lower slope positions of the terraces with ditches. &lt;strong&gt;Implications: &lt;/strong&gt;The effect of ditch depths on moisture, total nitrogen and available phosphorous contents and their variability within the slope depended on the amount and distribution of rainfall. &lt;strong&gt;Conclusion: &lt;/strong&gt;Construction of terraces with shallow ditch depths (of 30 cm) is recommended to conserve soil moisture and nutrients nitrogen and phosphorous on hard-setting soils in the marginal areas of semi-arid Eastern Kenya. &lt;/p&gt;

Soil organic carbon and its' stock potential in different land-use types along slope position in Coka watershed, Southern Ethiopia

Understanding organic carbon accumulations in soils is crucially essential concerning carbon sequestration, fighting climate change, increasing land productivity, improving soil properties, providing energy to the microbial community, enhancing ecological restoration, and reversing global environmental damage. This study was aimed at assessing the effects of land-use-cover change (LULC) on soil organic carbon (SOC), its' stock potential, and bulk-density (BD) along slope position in the Coka watershed. Replicated soil samples had been collected and composited from 30 cm depth topsoil of five major land use types and three slope positions. This result showed that significantly (P < 0.001) lowest and highest mean of soil organic carbon stock (SOCS) was observed under bare lands (37.835 Mg ha−1) and bushlands (144.582 Mg ha−1), respectively which was the same for SOC concentration. Barelands lose 3.82 times (3.82x) higher SOCS than bushland and 2.68x more SOCS than forestland. Both SOC-stock and SOC showed significant (P < 0.001) differences among slope positions, which were the highest in lower-slope followed by middle-slope, which had 1.8 and 2.6x higher than in middle-slope and upper-slope positions, respectively. Thus, the multivariate-test result divulges that LULC along slope positions has a strongly significant (P < 0.05) main and interaction effect on SOCS in the area. Therefore, the potential contribution of bushland and forestland uses should be improved for SOC sequestration, soil productivity improvement, and environmental protection.

Spatial Patterns of Infiltration on a Bench Terraced Hillslope in Kigezi Highlands, South-Western Uganda

The spatial patterns of infiltration on bench terraced hillslopes are not fully understood. Moreover, these patterns are pivotal for assessing hydrological processes affecting water distribution, surface flow and soil erosion, and groundwater recharge. Our objective was to determine the spatial patterns of steady-state infiltration rates on a bench terraced hillslope; and assess the influence of soil properties on the infiltration process. We employed Geo-Information Science (GIS) to stratify the terraced bench hillslope into three slope position sequences, namely, Upslope, Middle slope, and Downslope. Besides, in each slope position segment, a bench terrace was randomly selected; and later stratified into three plot segments, namely, Upper (A), Middle (B), and Bottom (C), for purposes of conducting infiltration experiments. At each plot segment, three infiltration experiments were replicated to ascertain the intra-bench and inter-bench terrace steady-state infiltration rates. The experimental field design consisted of three slope position sequences, three plot segments, and three replicates, hence, leading to a total of twenty-seven (27) experiments. The infiltration measurements were conducted using a standard double-ring infiltrometer. We sampled soil for two different depths, namely; 0-15 cm and 15-30 cm, at each infiltration experiment to establish its relationship to the infiltration process. Using a Spatial Autocorrelation tool embedded in ArcGIS 10.2, we analysed the spatial patterns of infiltration along the hillslope. Furthermore, a Two-Way analysis of variance (ANOVA) was used to determine differences between the means of the infiltration rates across the hillslope sequences. Descriptive Statistics were used to investigate the Degree of Variability in infiltration rates. Results showed that beyond 15 m, infiltration rates vary significantly (P&lt;0.018) from 5 cm hr-1 to 40 cm hr-1 between the bench terraced hillslope sequences, with a mean rate of 21 cm hr-1. Intra-bench steady-state infiltration rates varied higher in the Bottom (C) compared to Upper (A) and Middle (B) segments, especially in the Upslope sequence, where rates varied from 6 cm hr-1 to 20 cm hr-1 with a coefficient of variation (CV) of 45%. The clay content in the soil had a significant influence (P&lt;0.003) on infiltration in the study sites of the hillslope with a correlation coefficient (R, r2 = -0.5). We concluded that the spatial patterns of infiltration on a bench-terraced hillslope are influenced by slope position. Infiltration is higher at the Downslope and Middleslope bench terraces as compared to the Upslope bench terrace. Soil texture and the structural condition of the bench terraces themselves play a cardinal role in the variations in infiltration. Within the bench terraced land parcels, infiltration is higher on the downslope and lower in the upslope positions. Since percent clay content increased with slope, it was noted as a fundamental soil characteristic affecting infiltration within the bench terraces. Our recommendation was that in bench terraces where steady-state infiltration was high such as in downslope and middle slope positions, the terrace bunds should be strengthened with grass and stone embarkments to consolidate them coherently. This strategy may reduce terrace bund breakages and consequently counter surface flow on the bench terraced hillslope. Besides, in areas where low steady-state infiltration rates were recognised, such as the upslope position, agronomic practices should be enhanced.

Spatial Variations in Fine Root Turnover, Biomass, and Necromass of Two Vegetation Types in a Karst Ecosystem, Southwestern China

Revealing the patterns of fine root turnover traits can aid our understanding of the mechanisms of fine roots in adapting to soil nutrient changes. In a karst ecosystem of southwest China, the fine root turnover rate, production, biomass, necromass, biomass/necromass ratio, as well as the soil total and available nitrogen (N) and phosphorus (P) concentrations, and root carbon (C) and N concentrations were analyzed in upper, middle, and lower slope positions of two vegetation types (shrubland and forest). The results showed that the soil total and available N and P and fine root production, biomass, and necromass were significantly higher in upper slope positions than those in lower slope positions in both vegetation types. However, the fine root turnover rates were slightly higher in upper positions than those in lower positions. In addition, fine root necromass was significantly lower in shrubland than that in forest, while the biomass/necromass ratio was the opposite. Therefore, fine root production and biomass were significantly affected by slope position, while the fine root biomass/necromass ratio was significantly influenced by vegetation type. Additionally, fine root necromass was significantly influenced by the slope position and vegetation, but the turnover rate was slightly impacted by the two factors. It was also found that fine root production, biomass, and necromass had significant positive correlations with the soil total and available N and P and root C concentrations, and had significant negative correlations with root N concentrations. Moreover, the biomass/necromass ratio was positively and negatively related to the root N concentrations and C/N ratios, respectively. Thus, the variations in these five parameters of fine root turnover were mainly explained by fine root nutrients and the interactive effects between fine root and soil nutrients. The above results indicated that these variations in fine roots responding to soil and root nutrient changes might be an adaptive mechanism to enhance plant nutrient acquisition in nutrient-poor karst ecosystems.

Root exudation in a sloping Moso bamboo forest in relation to fine root biomass and traits.

Exudation by fine roots generally varies with their morphological traits, but the effect of belowground resource availability on the root exudation via root morphological traits and biomass remains unknown. We aimed to determine the effects of morphological and physiological traits on root exudation rates and to estimate stand-scale exudation (Estand) by measuring the mass, length, and surface area of fine roots in a Moso bamboo forest. We measured root exudation as well as morphological and physiological traits in upper and lower plots on a slope with different belowground resource availability. The mean (± S.D.) root exudation rates per mass in the upper and lower slope were 0.049 ± 0.047 and 0.040 ± 0.059 mg C g-1 h-1, respectively, which were in the range of exudation found in woody forest ecosystems. We observed significant relationships between root exudation per mass and root respiration, as well as specific root length and surface area. In contrast, exudation per length and area did not correlate with morphological traits. The morphological traits did not differ between slope positions, resulting in no significant difference in root exudation per mass. Fine root biomass, length, and surface area on a unit ground basis were much higher in the lower than those in the upper slope positions. Estand was higher when estimated by mass than by length and area because the morphological effect on exudation was ignored when scaled using mass. Estand was 1.4–2.0-fold higher in the lower than that in upper slope positions, suggesting that the scaling parameters of mass, length, and area determined the Estand estimate more than the exudation rate per mass, length, and area. Regardless of scaling, Estand was much higher in the Moso bamboo forest than in other forest ecosystems because of a large fine-root biomass.