Increasing Soil Depth Research Articles

Effect of waste dumpsites on some soil chemical properties and performance of okra (Abelmoschus esculentus) in Obio/Akpor Rivers State, Nigeria

Study was conducted at the screen house of department of crop and soil science, University of Port Harcourt to investigate the influence of two waste dumpsites on soil chemical properties and performance of okra in Obio/Akpor. A composite soil samples was randomly collected at two depths (0-15 and 15-30) cm from two dumpsites from Choba and Rumunduru at a distance of (0-1) and 100 meters (control) away from the dumpsites. The soil was placed on 10kg perforated bucket; three seeds of okra were planted per bucket and later thinned to two after germination. It was left for eight weeks. The experiment was on complete randomized design. Results showed significant (P<0.05) increase in soil chemical properties (%TOC, available P, TN, Ca, Mg and K) in impacted zone (0-1)meter over control (100) meter away in the two dumpsites. The soil chemical properties were significantly higher in Rumunduru dumpsite than Choba. There was no significant (P>0.05) difference in soil depths in the two locations, however, the concentration of soil chemical properties slightly decrease with increase in soil depth. There was a decrease in the concentration of heavy metals (Ni, Pb , Fe and Zn) along the main dumpsites away from the control in the two locations studied. Significant increase was observed in concentration of heavy metals in Rumunduru dumpsite over that of Choba. Concentration of the four metals decreased with increase in soil depth. All the metals were above the permissible limits with the exception of nickel. There was a significant (P<0.05) reduction in plant height on the impacted zone (0-1) m in distance over the reference point (control) in the two dumpsites. Significant difference was not noticed between the two soil depths, though the height was slightly higher at 0-15 depth than 15-30cm. Waste dumpsites affected negatively the plant performance especially at the impacted zone as there was retardation of growth and an increase in concentration of heavy metals.

Patterns and drivers of soil carbon change (1980s-2010s) in the northeastern Qinghai-Tibet Plateau

Rapid climate warming, permafrost degradation and widespread vegetation improvement on the Qinghai-Tibet Plateau (QTP) have caused carbon input via photosynthesis and carbon output through soil respiration to significantly increase in recent decades; thus, its role as a carbon sink/source is unclear and highly disputed, especially at different soil depths. In this study, we took the Qinghai Plateau (northeastern QTP), with an area of 7.2 × 105 km2 (permafrost accounts for 52% of the land) and an elevation ranging from 1669 m to 6548 m, as the study region and estimated its spatial pattern of soil organic carbon (SOC) stock changes at different soil depths from the 1980s to 2010s. The paired site observations of the SOC stocks in the 1980s from the second national soil survey and in the 2010s from a field survey and the literature were compiled and then combined with 77 related environmental factors to drive multiple machine learning models (random forest, gradient-boosting machine, and Cubist), from which the spatial patterns of SOC stock changes at different soil depths (0–30, 30–50, and 50–100 cm) were revealed. The results indicated that the SOC stock increased in the soil at 0–100 cm over the past three decades, with a mean net accumulation rate of 7.36 g C m−2 yr−1 or a total of 0.153 Pg C. Compared with seasonally frozen soil, more significant increases in the SOC stock were observed in permafrost at the 0–100 cm depth (9.71 vs. 4.81 g C m−2 yr−1). However, the SOC stock changes in different soil layers showed significant differences. Specifically, the SOC stock substantially increased in the topsoil layer (0–30 cm), with a carbon increase of 7.82 g C m−2 yr−1; the SOC stock in the middle layer (30–50 cm) had a slight increase, with a carbon increase of 1.69 g C m−2 yr−1; and the SOC stock decreased in the bottom layer (50–100 cm), with a net carbon loss rate of 2.15 g C m−2 yr−1. We found that vegetation change was the key driver of SOC stock change in the topsoil layer. With the increase in soil depth, the importance of climate change on SOC stock change increased. We concluded that climate-driven carbon losses in the deep soil layer were offset by an increase in vegetation-driven carbon inputs at the top and middle soil layers, triggering plant-dominated negative soil carbon feedback to climate warming. With the temperature continuing to increase, however, we must pay more attention to the risk of carbon release in the middle and bottom soil layers.

Fine root dynamics in a tropical integrated crop-livestock-forestry system

Integrated crop-livestock-forestry (ICLF) systems explore synergistic interactions between soil, plant, and animals, maximizing land-use efficiency and sustainability. However, belowground dynamics under ICLF have not been investigated deeply, particularly the role of incorporating dead root material, a forefront strategy for releasing nutrients and storing carbon. To better understand belowground interactions, we conducted a 21-month assessment of fine-root growth and decomposition in an ICLF system, starting when Eucalyptus urograndis trees were three years old. Eucalyptus rows were spaced 15 m apart and integrated with annual crops and pasture. Distances of 1.9, 4.3, and 7.5 m from the trees were evaluated under two successional periods: (i) annual crop, when corn was interspaced with palisade grass (Urochloa brizantha); and (ii) pasture, when palisade grass was grazed. We used the minirhizotron technique to track fine-root production and decomposition down to a depth of 70 cm, capturing 2400 images. Root longevity was estimated per root diameter class (0-0.5-, 0.5–1.0-, and 1.0–2.0-mm) and phenotypical groups (e.g., grasses [corn + palisade grass] and Eucalyptus). Our data showed that root decomposition rate and necromass inputs into the soil were reduced at the closest distance from the Eucalyptus rows (i.e., 1.9 m). The incorporation of decomposed roots was higher in the topsoil (0–28 cm) and declined with increasing soil depths. The total decomposed root incorporation was 101 m m−2 of soil image for 7.5 and 4.3 m inter-row positions, almost twice as high as the recorded at 1.9 m (54 m m−2) from the trees. Daily root decomposition rates increased during the last rainy season, benefited from numerous dead corn roots, and facilitated by higher soil moisture and temperature. Grasses and Eucalyptus roots at 7.5 m from the tree rows had shorter longevity than those at 1.9 m, remaining 88 and 152 days less, respectively. Root diameter influenced the decomposition rate as thicker roots (diameter between 1.0 and 2.0 mm) of grasses and Eucalyptus stood in the soil for 243 and 261 days longer than the finest roots (diameter <0.5 mm). Our results highlight that root necromass accretion and decomposition are heterogeneous in ICLF systems. Furthermore, 3-to-5-year-old Eucalyptus trees drive the interactions, creating microclimate conditions that impair corn and palisade grass root production and reduce root turnover close to the trees. These findings provide a scientific base for managing the ICLF system (spatial and temporal arrangements) and developing models of soil carbon addition via roots in such complex and heterogeneous systems.

Manganese indicates root decomposition rates across soil layer, root order, and tree species: Evidence from a subtropical forest

Different spatial locations provide different external conditions for root decomposition, while species and root order cause obvious differences in root substrate quality. Both differences in internal and external conditions may determine root decomposition rate. We explored the effects of decomposition position, root order, and species differences on root decomposition, and determined the role of manganese (Mn) in root decomposition. We conducted a fine root decomposition experiment using roots from Schima superba, Cleyera japonica, and Eurya loquaiana (separated into orders 1−3, 4−5, and 6) in the litter layer, and at 0−10 cm, 20−30 cm, and 40−50 cm soil depth in a subtropical forest. Root mass and concentration of C, N, P, Mn, condensed tannins and total phenolics were measured during two years of decomposition. Root decomposition rates decreased with increasing soil depth for all root samples. Compared to decomposition at 0−10 cm soil depth, remaining mass (% of initial) declined by 7%–34% in the litter layer and increased by 17%–37% at 40−50 cm soil depth. Lower-order roots had a higher decomposition rate than higher-order roots in the litter layer, but at 40−50 cm soil depth, we observed the opposite. Root litter Mn concentration and remaining mass were negatively correlated during the whole decomposition period including the early, middle, and late stages. Initial root Mn content was negatively correlated with remaining mass after two years of decomposition in the litter layer, and at 20−30 cm, 40−50 cm soil depth. However, no significant relationship between mass remaining and initial root N, P, condensed tannins and total phenolics were observed in the subsoil. Variance partitioning showed that the soil layer contributes significantly to the variance in remaining root mass, C, and Mn, whereas root order group contributed more than the soil layer to remaining root N and P. Our results indicate that soil depth is more important than root order for fine root decomposition rate at a site scale. Relative root decomposition rate between lower- and higher-order roots depends on the decomposition environment. Overall, this study strongly suggests that root Mn concentration (whether in initial or other decomposition stages) was much more consistently correlated with mass remaining than traditional predictors of N, P, condensed tannins, or total phenolics. Root Mn concentration greatly indicates root decomposition rates across soil layers, root orders, and species. Initial root Mn concentration and Mn supply capacity of the decomposition environment jointly control root decomposition rates throughout the decomposition process.

Parthenium hysterophorus Weed Fecundity and Seed Survival at Different Soil pH and Burial Conditions

Parthenium hysterophorus L. is regarded as one of the most invasive weed species. This study evaluated the effect of soil pH on P. hyterophorus weed growth and fecundity, as well as the effect of burial depths on P. hyterophorus seed survival and emergence. The first study evaluated five soil pH levels (acidic, sub-acidic, neutral, sub-basic, and basic) in a randomised complete block design. Seed germinability and subsequent seedling growth (height, leaf area, biomass, and seed number/plant) were evaluated. This study showed that P. hysterophorus seeds have a similar germination capacity under varying soil pH conditions. However, acidic soil indicated accelerated growth (25% higher biomass with 15.2% more leaf area) and fecundity (13.4% faster to enter the flowering stage at 74 days after sowing). In the second study, two factors were tested; burial depths (0.5, 5, 10, and 20 cm) being nested into seven burial durations (0, 2, 4, 6, 8, 10, and 12 months). Seed viability (final germination percentage and germination rate index), electrical conductance, and emergence percentage were assessed with the burial conditions. The results showed that only seed buried at 0.5 cm depth indicated emergence (81.3% of cumulative emergence). Forty per cent of the seeds remained viable after exhumation at 0.5–5 cm depth, while only 19–27% survived as the burial depth increased beyond 10 cm depth within 12 months. The seed remained viable for more than 12 months as a seed bank, despite faster deterioration at increasing soil depth.

Response spectra for transient pore-pressure in a sandy seabed under random waves: Frequency-filtering effect

The real state of ocean waves is random in nature with various monochromatic components. Transient pore pressures in a sandy seabed under the action of the random-waves with JONSWAP spectrum and the regular-waves were physically modeled, respectively. The surface elevations and the corresponding transient pore pressures in the fine-sand were measured simultaneously in a wave flume. The frequency-filtering phenomenon was observed by Fourier analysis for random-wave induced pore pressure responses. In the Fourier energy spectra, both a primary-peak (high-frequency) and a secondary-peak (low-frequency) were identified within the relatively shallow soil layer. But the primary-peak kept declining rapidly, meanwhile the secondary-peak attenuated much more slowly with increasing soil depth, which can eventually lead to a shift between the high-frequency peak and the low-frequency one. As a consequence, the upgraded primary-peak frequencies of the dual-peaked spectra at the deeper soil layer would become smaller than the original significant frequencies, indicating that the pore pressure induced by long-wave components is of vital significance there. Furthermore, a filtering-depth parameter is introduced to characterize the frequency-filtering effect. Given the pore pressure at a certain soil depth, the quantitative relationship between the primary-peak and the secondary-peak can be predicted for an arbitrary soil depth.

Spatiotemporal variability of extreme precipitation events and their impacts on soil moisture and water table depth in Argentina’s core crop region

ABSTRACT This study reassesses the spatiotemporal variability of and changes in extreme precipitation events (EPEs) and examines the response of soil moisture and water table depth to EPEs in Argentina’s core crop region. Standardized nonparametric indices are applied to precipitation, soil moisture, and groundwater. The temporal variability of EPEs exhibits a decadal cycle and inter-annual modes with dominant frequencies between 2.5 and 4 years related to El Niño Southern Oscillation periodicities. The soil moisture and water table depth respond to precipitation variability replicating both decadal and inter-annual EPE variability. The response of soil moisture to EPEs attenuates in time as soil depth increases. Water table depth responds to EPEs with an average delay of 10 months. In recent decades, soil moisture increases (water table depth becomes shallower) rapidly when reacting to excess precipitation, while soil moisture decreases (water table depth deepens) slowly during and after drought events.

Response Characteristics of Soil Organic Carbon Pool and Its Chemical Composition During Secondary Forest Succession in the Loess Plateau

In order to explore the characteristics of the soil organic carbon(SOC)pool and its chemical composition during the succession of secondary forests in the Loess Plateau, samples of the primary stage (Populus davidiana forest), transition stage (Populus davidiana and Quercus wutaishansea mixed forest), and top stage (Quercus wutaishansea forest) of secondary forest succession in the Huanglong Mountain forest area of the Loess Plateau in Northern Shaanxi were selected as the research object. The variation characteristics of SOC content, storage, and its chemical composition at different soil depths (0-10, 10-20, 20-30, 30-50, and 50-100 cm) were analyzed. The results showed that:① the contents and storage of SOC increased significantly with the secondary forest succession process (P<0.05). The content of SOC decreased significantly with the increase in soil depth, and the storage of SOC increased from 64.8 Mg·hm-2 in the primary stage to 129.2 Mg·hm-2 in the top stage, with an increase of 99%. ② During the succession of secondary forests, in the surface (0-30 cm) soil organic carbon, the relative content of aliphatic carbon components that have a simple structure and can be decomposed more easily decreased, and the relative content of aromatic carbon components that have a complex structure and cannot be decomposed easily increased, indicating that the chemical composition of organic carbon stability of surface-layer soil increased significantly with the process of secondary forest succession. However, the stability of the chemical composition of SOC in the deep layer (30-100 cm) first increased and then decreased, that is, the transition stage>the top stage>the primary stage. ③In the process of secondary forest succession, the stability of SOC chemical composition in the primary stage and transition stage increased significantly with the increase in soil depth. The top stage tended to be stable, and the deep soil carbon stability decreased slightly. ④ Pearson correlation analysis showed that during the secondary forest succession process, SOC storage and chemical composition stability were significantly negatively correlated with soil total phosphorus content. In general, the content and storage of SOC in the 0-100 cm soil increased significantly during the secondary forest succession, playing the role of a "carbon sink." The stability of the chemical composition of SOC in the surface layer (0-30 cm) increased significantly, but in the deep layer (30-100 cm), it increased first and then decreased.

Preliminary investigation of soil organic carbon distribution and turnover patterns, and potential pollution sources in and around a typical coking plant in North China

The variation characteristics of soil organic carbon (SOC) in and around the coking plant area are still unclear. In this work, the concentration and stable carbon isotope composition of SOC in coke plant soils were investigated to preliminarily identify the sources of SOC in and around the plant area, and to characterize soil carbon turnover. Meanwhile, the carbon isotopic technique was used to initially identify the soil pollution processes and sources in and around the coking plant area. The results demonstrate that the SOC content (12.76 mg g−1) of the surface soil in the coking plant is about 6 times higher than that outside the coking plant (2.05 mg g−1), and the variation range of δ13C value of the surface soil in the plant (−24.63～-18.55‰) is larger than that of the soil outside the plant (−24.92～-20.22‰). The SOC concentration decreases gradually from the center of the plant outward with increasing distance, and the δ13C in the middle and north of the plant tends to be positive compared with the δ13C in the west and southeast of the plant. As the increase of soil depth, the SOC content and δ13C value in the plant increases. On the contrary, δ13C value and SOC content outside the plant decreases, with a minor variation. Based on the carbon isotope method, the SOC in and around the coking plant area is mainly from industrial activities (e.g., coal burning and coking), and partly from C3 plants. Notably, organic waste gases containing heavy hydrocarbons, light oils, and organic compounds accumulated in the northern and northeastern areas outside the plant due to south and southwest winds, which may pose an environmental health risk.

PEDOLOGICAL STUDY OF HILLY SOILS DEVELOPED ON BASEMENT COMPLEX TERRAIN IN MINNA, NIGER STATE, NIGERIA

A pedological characterization of hilly soils developed on basement complex terrain was carried in Minna, Niger State, Nigeria. The site was delineated into three physiographic units (positions) and designated as summit, shoulder and foot slope. Two modal profile pits were excavated in each unit to permissible depths, giving a total of six (6) profiles. The soil samples were analysed in the laboratory following standard analytical procedures. Particle size analysis showed dominance of sand over other mineral fractions irrespective of the physiographic units. Silt was next to sand in dominance and clay particle was the least in particle size. Bulk density increased with increasing soil depth in all the physiographic positions while porosity decreased down the profiles. Soil reaction (pH) ranged from moderately acid to slightly acidic in all the terrains. Organic carbon, total nitrogen and available P decreased with the increased in soil depth in all the landforms. Calcium and Magnesium were moderate while Potassium rated high in the sampled soils. The mean Na in the sampled soils rated low to moderate. Cation Exchange Capacity (CEC) in the soils rated moderate while percentage base saturation (BS) rated high. The soils are non- sodic and the electrical conductivity (EC) values are low. Thesoils of summit and shoulder were classified as Typic Paleustalfs while the footslope soils were classified as Typic Paleudalfs. The soils were classified as Plinthosols when correlated with WRB for soil resource.

Soil C, N and P stoichiometry in different forest stand types in the middle and lower reaches of the Beijiang River, China.

We examined the vertical distribution characteristics of soil organic carbon (C), total nitrogen (N), total phosphorus (P) and their ecological stoichiometric ratios in 0-80 cm soil profile under three forest stand types in the middle and lower reaches of the Beijiang River, including broad-leaved forest, coniferous forest, and mixed coniferous and broad-leaved forest. The results showed that soil C, N and P contents of the three forest stand types were 12.17-14.25, 1.14-1.31, and 0.27-0.30 g·kg-1, respectively. The contents of C and N decreased with the increases of soil depth. The content of C and N in each soil layer showed that coniferous and broad-leaved mixed forest > coniferous forest > broad-leaved forest. There was no significant difference in P content among the three stand types, and there was no obvious variation in the vertical profile. The soil C/N, C/P, and N/P of the three forest types were 11.2-11.3, 49.0-60.3, and 4.5-5.7, respectively. There was no significant difference in soil C/N among the three stand types. The highest soil C/P and N/P were found in the mixed forest. There was no interaction between soil depth and stand type in affecting soil C, N, P contents and their stoichiometric ratios. There was significant positive correlation between C and N, and between N and C/P in each stand type and soil layer. Soil C/P and N/P had stronger ecological indicating effects on stand types. The coniferous and broad-leaved mixed forest was strongly limited by P availability.

Effects of microtopographic patterns on plant growth and soil improvement in coastal wetlands of the Yellow River Delta.

To clarify the effects of microtopography on plant growth and soil water, salt and nutrient characteristics of saline soils in mudflats within muddy coastal zones and explore suitable microtopographic modifications. Six microtopographic modification patterns, namely, S-shaped, stripe-shaped, pin-shaped, stepshaped, dense stripe-shaped and crescent-shaped patterns, were established in the coastal mudflats of the Yellow River Delta. The soil water, salt, ion, total carbon, total nitrogen, and total phosphorus contents and their ecological stoichiometric characteristics were measured and analyzed after theimplementation of different microtopographic modification patterns, with bare mudflats as the control. The results showed that microtopographic modification significantly changed the soil water and salt contents and the soil total carbon, total nitrogen and total phosphorus contents. Compared with the bare ground, microtopographic transformation significantly promoted the growth of the pioneer plant Suaeda salsa, significantly increased the soil water and nutrient contents, and significantly decreased the soil salinity. The soil salinity was mainly reduced by Na+ and Cl- ions. The soil salinity and nutrient contents gradually decreased with increasing soil depth, indicating the occurrence of surface aggregation. Compared to that of the bare ground, the soil C/N was significantly lower and the N/P was significantly higher in the microtopographic treatments, and the overall performance suggested soil N limitation. The ions contained in the saline soil were dominated by Na+ and Cl-, followed by Mg2+ and SO4 2-, with lower contents of K+, Ca2+ and HCO3 -. Among the six microtopography modification patterns, the crescent-shaped pattern best promoted vegetation restoration. This pattern was the most effective in reducing soil salinity, with a 98.53% reduction in soil salinity compared with that of bare ground, followed by the pin-shaped pattern. Compared with that in the bare ground samples, the nutrient content in the samples from the step-shaped modification increased by 23.27%; finally, the S-shaped, step-shaped and dense stripe-shaped patterns performed poorly in terms of plant restoration and soil improvement. It is suggested that a crescent-shaped pattern should be considered first when carrying out microtopographic transformation on the beaches of the Yellow River Delta, followed by stripe-shaped and pin-shaped patterns. The dense strip-shaped should not be adopted.

Dynamics of soil bio-physicochemical properties under different disturbance regimes in sal forests in western Himalaya, India

Disturbance is a key factor in controlling vegetation diversity, nutrient influx rate, and biochemical cycling in terrestrial forest ecosystems. Limited studies are available on changes in tree diversity, soil nutrients and enzyme activities in response to different intensities of land disturbances in the Himalayan forests. Present study investigated the impact of varying intensities of disturbances on tree diversity and their relationship with soil physical and bio-chemical properties in sal forests, Western Himalayas. Sites were categorized into four different classes of disturbances, namely, No disturbance (ND), Low disturbance (LD), Moderate disturbance (MD), and High disturbance (HD). Composite samples were collected at two depths (0–15 and 15–30 cm) in each plot to investigate soil physical and biochemical properties. Multivariate analyses were conducted to find relationship between tree vegetation and soil physical and biochemical properties. Soil organic carbon (Corg), total nitrogen (Nttl), available phosphorous (Pavl), microbial biomass carbon (Cmic), nitrogen (Nmic), phosphorous (Pmic), and enzymes (dehydrogenase (DHA), Urease, acid and alkaline phosphatase) followed the order: MD > ND > LD > HD. Across disturbances, soil physical and biochemical characteristics significantly (p < 0.05) decreased with increasing soil depths. Across the sites, positive correlation was observed among soil microbial biomass, enzymes, Corg, clay, and moisture. Redundancy analysis (RDA) results revealed that species distribution is essential regulator in the variation of prominent soil variables, viz., nutrients (Nttl and Pavl), Cmic, and DHA across disturbance categories and soil depths. Moreover, variance partitioning analysis (VPA) showed that changes in vegetation composition across disturbance levels explain 13.12 % of the variation in soil biochemical subset higher than soil physicochemical subset. The result illustrated that moderate disturbance increases species composition, soil nutrient properties and microbial activity. These findings would help understand microbial activity and its relationship with disturbances, suggesting site-specific measurements for soil nutrient availability and above-below ground interactions.

Soil organic carbon regulation from chemistry in top- but microbial community in subsoil in eastern coastal China poplar plantations

Although patterns in the vertical distribution of soil organic carbon (SOC) are key to assessing soil C sequestration potential, they remain poorly understood. We sampled 18 soil profiles at one meter depth at the Dongtai Forest Farm to investigate the vertical distribution of SOC, the stoichiometric relationship between SOC and total nitrogen (TN) and the controlling factors of SOC at different soil depths. We found that SOC content decreased significantly with increasing soil depth. Approximately 67% of SOC was stored in the top 30 cm. The N-C scaling slope (i.e., the slope of the relationship between log-transformed N and C not significantly different from 1.0) revealed significant differences between top- and subsoil with N and C scaled isometrically in topsoil (0–30 cm), but not in subsoil (30–100 cm). SOC content was co-regulated by soil physiochemical and microbial properties at the site level with soil chemical and microbial properties dominant in the top- and subsoil, respectively. Topsoil SOC increased with soil TN, available phosphorus (AP) and fungal abundance. Subsoil SOC increased with the fungal-to-bacterial ratio, fungal abundance and soil dissoluble organic carbon (DOC). Our study highlights the dominance of microbial community in regulating SOC in the subsoil and advances our understanding of the variation in mechanisms regulating SOC along the soil profile.

Changes in soil organic carbon fractions in abandoned croplands of Nepal

Cropland abandonment in Nepal is an emerging land use change that has significant impacts on ecosystem functions, particularly soil organic carbon (SOC) pools and stocks. Information relating to SOC is limited for the mountainous terrain of Nepal that is subject to either SOC loss from erosion or SOC accumulation from secondary succession after cropland is abandoned. The rate of cropland abandonment is accelerating in Nepal but the impact of the abandoned duration on SOC, fractions, and SOC stock has not yet been investigated. We used a space-for-time substitution approach to assess the impacts of abandonment on SOC concentrations, stocks and associated pools of carbon across abandoned cropland (<5, 5–10, and > 10 years) compared with forest, pasture, and currently cropped land. Soil samples were collected at four depth increments (0–10, 10–20, 20–40, 40–60 cm). The change in SOC and stock was found to be significantly higher in the surface (0–20 cm) compared with sub-surface soil (20–60 cm) and consistently decreased with increasing soil depth under all land uses. Change in soil nitrogen concentration followed a similar pattern to that of SOC at all land uses and depths. Among the SOC fractions, particulate organic carbon increased significantly by a greater proportion compared to mineral-associated organic carbon and dissolved organic carbon after 10 years of cropland abandonment. Abandoned cropland >10 years had a higher SOC stock (64.19 Mg ha−1) in the soil profile (0–60 cm) compared with cropped land (58.76 Mg ha−1) although it remained lower than forest (66.56 Mg ha−1) and pasture (66.60 Mg ha−1) soils. Although there was a decrease in the first five years, there was a significant accumulation of SOC, associated fractions, and SOC stock after ten years of abandonment and colonisation by vegetation indicating the inception of ecosystem regeneration in abandoned croplands in the mountainous region of Nepal.

Maize Yield Response, Root Distribution and Soil Desiccation Crack Features as Affected by Row Spacing.

Plant density is among the most critical factors affecting plant yields and resource use efficiency since it drives the exploitation of the available resources per unit area, root distribution and soil water losses by direct evaporation from the soil. Consequently, in fine-textured soils, it can also affect the formation and development of desiccation cracks. The aim of this study, carried out on a sandy clay loam soil in a typical Mediterranean environment, was to investigate the effects of different row spacings of maize (Zea mais L.) on yield response, root distribution and the main features of desiccation cracks. The field experiment compared bare soil and soil cropped with maize using three plant densities (6, 4 and 3 plants m-2), obtained by keeping the number of plants in a row constant and varying the distance between the rows (0.5-0.75-1.0 m). The highest kernel yield (16.57 Mg ha-1) was obtained with the greatest planting density (6 plants m-2) with a row spacing of 0.5 m; significantly lower yields were recorded with spacings of 0.75 and 1 m, with a decrease of 8.09% and 18.24%, respectively. At the end of the growing season, soil moisture in the bare soil was on average 4% greater in comparison to the cropped soil and was also affected by row spacing, decreasing with the decrease in the inter-row distance. An inverse behaviour was observed between soil moisture and both root density and desiccation crack size. Root density decreased to the increase in soil depth and to the increase in distance from the row. The pluviometric regime occurred during the growing season (total rainfall of 343 mm)-resulted in the formation of cracks of reduced size and with an isotropic behaviour in the bare soil, whereas in the cultivated soil, the cracks were parallel to the maize rows and increased in size with decreasing inter-row distance. The total volume of the soil cracks reached a value of 135.65 m3 ha-1 in the soil cropped with a row distance of 0.5 m, and was about ten times greater in comparison to the bare soil and three times greater in comparison to a row spacing of 1 m. Such a volume would allow a recharge of 14 mm in the case of intense rainy events on soil characterised by low permeability.

Soil Nutrient Distribution and Preferential Flow Transport Patterns in Robinia Pseudoacacia Communities of Degraded Wetlands

The Yellow River Delta wetlands in the Yellow River Delta National Nature Reserve are facing serious degradation due to water scarcity and soil salinization. This study aims to investigate the mechanism of wetland degradation by analyzing the small-scale distribution of soil nutrients and preferential flow transport patterns in the Robinia Pseudoacacia community, which is a typical vegetation community in degraded wetlands. Soil physical and chemical properties based on field staining experiments were analyzed, and indoor solute penetration experiments were conducted to investigate the distribution of soil nutrients and hydrological characteristics. The results showed that the contents of soil organic carbon, organic matter, total nitrogen, and available phosphorus decreased with increasing soil depth, with higher contents in the preferential flow area than in the matrix flow area. Soil organic carbon, organic matter, total nitrogen, total phosphorus, and available phosphorus showed positive correlations with each other, while soil pH and conductivity exhibited negative correlations with the above nutrients. The efflux rate of the Acacia community exhibited a gradual decline as soil depth increased, and the relative concentration of the solution exhibited a non-monotonic pattern of decrease, increase, and subsequent decrease with increasing soil depth. The findings could provide valuable guidance for the restoration and management of degraded wetlands in the Yellow River Delta.

Soil organic carbon distribution and factors affecting carbon accumulation in natural and plantation forests in tropical China

Tropical rainforests are the most complex forest ecosystem in the world, and play an important role in the global carbon cycle. To investigate the accumulation characteristics of soil organic carbon (SOC) in tropical rainforests of different origins, soil samples from plantation and natural forests of tropical mountain rainforests in Wuzhi Mountain (WM), Qixian Mountain (QM) and Diaoluo Mountain (DM) in eastern Hainan Island, China, were collected at various depths (0–10, 10–30 and 30–50 cm). SOC concentrations of different-forest-origin soils were analysed and compared, and the effects of soil physicochemical parameters on SOC concentration in natural and plantation forests were investigated. SOC concentrations in plantation forests in WM, QM and DM were higher than those in natural forests, although the difference was not statistically significant. In the 0–50 cm soil depth, the SOC concentrations of different-forest-origin soils decreased with increasing soil depth, with SOC concentrations in the surface layer (0–10 cm) of natural forests being significantly higher than those in the middle layer (10–30 cm) and bottom layer (30–50 cm) (P < 0.05). Natural forests have lower pH than plantation forests. Correlation analysis revealed significant negative correlation (P < 0.05) between SOC concentration in both forest origins and soil pH. The proportion of clay and silt is greater in natural forests than in plantation forests, but the proportion of sand is greater in plantation forests.

Characteristics of Soil Calcium Content Distribution in Karst Dry-Hot Valley and Its Influencing Factors

Calcium is an essential macronutrient in soils and plays an important role in the structure and function of an ecosystem. In this study, we selected the Huajiang dry-hot valley region in southwest China as our research object, aiming to comprehend the soil calcium distribution characteristics of different altitudes and vegetation types in this karst dry-hot valley region. The results showed that the mean value of total soil calcium content in the karst dry-hot valley was 13.00 ± 3.28 g·kg−1, and the mean value of the proportion of exchangeable calcium content to total calcium was 50.31%. In the vertical profile, total soil and exchangeable calcium contents decreased with increasing soil depth. With increasing altitude, total soil and exchangeable calcium contents increased. Among the different vegetation types, the total and exchangeable calcium contents of crops were higher than the three natural vegetation types of forest, scrub, and grassland, and the soil calcium content of forest was the lowest. Total soil and exchangeable calcium content in the karst dry-hot valley were affected by rock exposure rate, vegetation coverage, soil thickness, soil organic matter and soil pH. In addition, the unique environmental gradient characteristics at different elevations in the dry-hot valley area may redistribute soil calcium, and the positive vegetation succession may cause a gradual decrease of soil calcium content in the area.

Comparative assessment of selected micronutrients under three different land use systems in Odighi, Edo State, Nigeria

This study carried out a comparative assessment of selected micronutrients under mixed tree plantation, cassava and secondary forest land use systems in Odighi, Edo State, Nigeria. The objectives of the study were to determine the concentrations of selected micronutrients under each of the three land use systems; evaluate the distribution of these micronutrients among the three land use systems; and examine the impact of the three land use systems on the selected micronutrients. Using transect sampling design, 18 soil samples were collected from each of the three land use systems giving a total of 54 soil samples for the study. The cassava land use was 7-10-year-old, mixed tree plantation was 10-15-year-old, while secondary forest was 25-year-old and above. Results showed that the concentrations of the selected soil micronutrients (iron, copper, manganese, and zinc) increased with increasing soil depth in all the examined sites except for manganese under cassava land use. The status of iron and zinc were rated excess while copper and manganese were rated optimum for crop production. The study observed significant (p &lt; 0.05) variations for iron and manganese contents across the examined land uses and concluded that the direction and magnitude of changes in the status of micronutrients were a reflection of long-term impact of the different land uses and soil management measures. Liming of the soil and limited use of nitrogen-containing fertilizers are recommended to ameliorate zinc toxicity in the study area. Also, farmers in collaboration with agriculture extension workers should regulate the usage of organic and inorganic fertilizers as soil treatments to avoid excessive concentrations of iron and zinc in the study area.