Shallow Soil Depths Research Articles

MINERALOGICAL AND CHEMICAL CHARACTERISTICS OF SPODOSOLS IN TOBA HIGHLAND, NORTH SUMATRA

Spodosols are problem soils due to coarse texture, acid soil reaction, low nutrient status, and low soil moisture retention. About 2.16 million ha of Spodosols (1.1% of the Indonesian<br />land areas) distributed in lowland and highland areas in Kalimantan, Sumatra, Sulawesi, and Papua. Spodosols of the Toba highland areas require special attention because these<br />forested lands are gradually cleared, but then abandoned because they are not suitable for agricultural development, causing land degradation. This study aimed to evaluate mineralogical and chemical characteristics of Toba highland Spodosols, North Sumatra, and their implication on agricultural development. Three pedons of the Toba highland Spodosols from Humbang Hasundutan regency were studied, consisted of soils developed from volcanic sand overlying liparite tuff under the influence of low temperature and high rainfall. Field observation was conducted in January 2008. Fifteen soil samples were collected from the three pedons based on the depth of soil horizon. Results indicated that the formation of these Spodosols were influenced by parent material, high elevation (1676-1821 m) above sea level), and by high amount of rainfall (2167 mm). The Spodosols in Toba highland were still in the early stage of development as characterized by shallow effective soil depth<br />(22-23 cm), domination of weatherable minerals (39-81%) in the sand fraction and dominated by amorphous mineral as shown by sum of A1 + 1/2 Fe extracted by ammonium oxalate as much as 0.6-12.8%. The Spodosols were also characterized by coarse texture (66-95% sand fraction in E and B horizons), high organic-C content (1.4-37.7%), acid soil reaction (pH 3.7- 5.3), very high K2O in Oa horizon (552-933 mg kg-1) and B spodic or C horizon (812-2028 mg kg-1), and low base saturation (< 5%). The existence of biological processes in the surface layer was indicated by accumulation of exchangeable bases<br />(0.88-1.14 cmolc kg-1 in Oa horizon and 0.09-0.25 cmolc kg-1 in B horizon), P2O5 (181-298 mg kg-1 in Oa horizon and 3-24 mg kg-1 in E horizon), and K2O (552-933 mg kg-1 in Oa horizon and 13- 30 mg kg-1 in E horizon). However, these nutrients were easily<br />leached after deforestation. With the sandy texture, loose structure, and no vegetation cover, the erosion hazard is high in the deforested areas. Therefore, lands with Spodosols of the Toba highland, especially are not recommended for agricultural development, rather they should be kept as forest lands.

Soil erosion risk associated with climate change at Mantaro River basin, Peruvian Andes

Soil degradation by water erosion has been accelerated by human activities. This process is aggravated in the Andes region due to steep slopes, sparse vegetation cover, and sporadic but high intensity rainfall, which together with a shallow soil depth, increases soil erosion risk. The objective of this study was to analyze the soil erosion risk, associated with A1B climate change scenario over the twenty-first century, for the Mantaro River basin (MRB), Peruvian Andes. The temporal analyses revealed maintenance of current soil erosion risk along the twenty-first century in almost all the MRB, whose current risk is either “very severe” or “extremely severe”. At the sub-basin level, for those located in the center and northern MRB, progressive increases were observed in the average erosion rate by the end of this century, increasing the soil erosion risk. In sub-basins under greater influence of the Andes, this risk was classified as “moderate” and remained this way throughout the century, despite the increase in rainfall erosive potential simulated for these. In annual terms, there was a significant trend of decreasing rainfall erosivity and increasing the concentration of rainfall simulated based on A1B climate change scenario. Because the A1B scenario affects rainfall erosivity mainly during the rainy season, this causes a risk to the environmental sustainability and future agricultural activities.

An environmental cost-benefit analysis of alternative green roofing strategies

Green roofs and cool roofs are alternative roofing strategies that mitigate urban heat island effects and improve building energy performance. Green roofs consist of soil and vegetation layers that provide runoff reduction, thermal insulation, and potential natural habitat, but can require regular maintenance. Cool roofs involve a reflective layer that reflects more sunlight than traditional roofing materials, but require additional insulation during winter months. This study evaluates several roofing strategies in terms of energy performance, urban heat island mitigation, water consumption, and economic cost. We use MLCan, a multi-layer canopy model, to simulate irrigated and non-irrigated green roof cases with shallow and deep soil depths during the spring and early summer of 2012, a drought period in central Illinois. Due to the dry conditions studied, periodic irrigation is implemented in the model to evaluate its effect on evapotranspiration. Traditional and cool roof scenarios are also simulated by altering surface albedo and omitting vegetation and soil layers. We find that both green roofs and cool roofs significantly reduce surface temperature compared to the traditional roof simulation. Cool roof temperatures always remain below air temperature and, similar to traditional roofs, require low maintenance. Green roofs remain close to air temperature and also provide thermal insulation, runoff reduction, and carbon uptake, but might require irrigation during dry periods. Due to the longer lifetime of a green roof compared to cool and traditional roofs, we find that green roofs realize the highest long term cost savings under simulated conditions. However, using longer-life traditional roof materials (which have a higher upfront cost) can help decrease this price differential, making cool roofs the most affordable option due to the higher maintenance costs associated with green roofs.

Temporal persistence and stability of soil water storage after rainfall on terrace land

The “Grain for Green” Project on the Loess Plateau of China has converted a large area of cultivated slope farmland to terraces to reduce soil erosion and improve the ecological environment. The area of terraced land on the Loess Plateau was 32,600 km2 in 2010. Knowledge of the behavior of soil water storage (SWS) and its spatiotemporal distribution provides essential information concerning hydrological and ecological processes. This study aimed to analyze the temporal stability of SWS after rainfall for different time periods on terraces planted with jujube trees (Ziziphus jujuba Mill.). The SWS of 21 locations was obtained from July 19 to September 3 in 2014 and from August 01 to August 31 in 2015. Relative difference analysis and the nonparametric Spearman rank correlation test were used to check the temporal stability of SWS. The SWS on terraces was normally distributed and demonstrated moderate spatial variability. The SWS at three soil depths all showed strong temporal stability with stability in the order of 0–0.6 < 0–1.0 < 0–1.6 m. Rainfall significantly affected the temporal stability of SWS in the depth of 0–0.6 m. The number of representative locations of SWS was not constant. The best representative locations were not identical for different soil depths; however, a common representative location did exist for the different depths and periods. Moreover, the mean SWS generally increased from the upper to lower slope. The temporal stability of SWS was not significantly affected by rainfall but was significantly negatively correlated with sand content. The total root length and soil organic carbon content did not show any obvious correlations with mean SWS. It was feasible to use the representative locations of SWS to represent the mean SWS over a period of time. However, the cumulative absolute error increased with cumulative days. In conclusion, SWS in the deeper soil depths indicated greater temporal stability than that in shallow soil depth during wet period. The best representative locations for SWS were depth and time dependent.

Developmental Plasticity of Rice Root System Grown under Mild Drought Stress Condition with Shallow Soil Depth; Comparison between Nodal and Lateral roots

:The plasticity in root system development (RSD) is a key trait for the adaptation of rice to mild drought. However, the enhanced RSD due to the plasticity may not be always a sole function of promoted lateral root (LR) production, but also of the integrated responses of nodal root (NR) development. In this study, we aimed to evaluate the effects of mild drought intensities on the development of the NR and LR, and their contribution to the entire RSD. We used six genotypes including KDML105 (indica, lowland adapted), a high lateral rooting ability genotype. The plants were grown up to heading or maturity stage for two years under soil with limited soil depth (20 cm) assuming the presence of the hardpan and at different moisture gradients generated by the line source sprinkler system. The effects of drought intensities generally differed between the development of NR and LR. In both years, all genotypes showed highest LR development under mild drought stress intensities. However, in some genotypes including KDML105, NR development was maintained in a limited soil moisture range only, which was narrower and wetter than that in which LR plasticity was expressed. Furthermore, the entire RSD was maintained only when both the NR and LR were simultaneously promoted or maintained. These results suggest that the NR have less plasticity than the LR in response to drought and the contribution of the plasticity in LR development to the entire RSD is dependent on both the soil moisture and nodal rooting ability.

Plant roots and GHG mitigation in native perennial bioenergy cropping systems

AbstractNative perennial bioenergy crops can mitigate greenhouse gases (GHG) by displacing fossil fuels with renewable energy and sequestering atmospheric carbon (C) in soil and roots. The relative contribution of root C to net GHG mitigation potential has not been compared in perennial bioenergy crops ranging in species diversity and N fertility. We measured root biomass, C, nitrogen (N), and soil organic carbon (SOC) in the upper 90 cm of soil for five native perennial bioenergy crops managed with and without N fertilizer. Bioenergy crops ranged in species composition and were annually harvested for 6 (one location) and 7 years (three locations) following the seeding year. Total root biomass was 84% greater in switchgrass (Panicum virgatum L.) and a four‐species grass polyculture compared to high‐diversity polycultures; the difference was driven by more biomass at shallow soil depth (0–30 cm). Total root C (0–90 cm) ranged from 3.7 Mg C ha−1 for a 12‐species mixture to 7.6 Mg C ha−1 for switchgrass. On average, standing root C accounted for 41% of net GHG mitigation potential. After accounting for farm and ethanol production emissions, net GHG mitigation potential from fossil fuel offsets and root C was greatest for switchgrass (−8.4 Mg CO2e ha−1 yr−1) and lowest for high‐diversity mixtures (−4.5 Mg CO2e ha−1 yr−1). Nitrogen fertilizer did not affect net GHG mitigation potential or the contribution of roots to GHG mitigation for any bioenergy crop. SOC did not change and therefore did not contribute to GHG mitigation potential. However, associations among SOC, root biomass, and root C : N ratio suggest greater long‐term C storage in diverse polycultures vs. switchgrass. Carbon pools in roots have a greater effect on net GHG mitigation than SOC in the short‐term, yet variation in root characteristics may alter patterns in long‐term C storage among bioenergy crops.

지반조건 상호작용을 고려한 풍력발전타워의 공진회피 진동수 산정을 위한 고유진동수 해석 연구

Abstract Global warming and the depletion of fossil fuels have been caused by decades of reckless development.Wind energy is one form of renewable energy and is considered a future energy source. The wind tower is designedwith a fundamental frequency in the soft-stiff design between the 1P and 3P range to avoid resonance. Usually, toperform natural frequency analysis of a wind tower, the boundary condition is set to the Fixed-End, and soil-pile interaction is not considered. In this study, consideration of the effect of soil-pile interaction on the wind tower wasincluded and the difference in the natural frequency was studied. The fixed boundary condition was not affected bythe soil condition and depth of the pile and the coupled spring boundary condition was unaffected by the depth of pile but affected by the depth of the pile, and the Winkler spring boundary condition is affected by both the soilcondition and the depth of the pile. Therefore, the coupled spring boundary condition should be used in shallow depth soil conditions because the soil condition does not take the shallow depth soil into consideration.

The Interplay Between Bioenergy Grass Production and Water Resources in the United States of America

We apply a land surface model to evaluate the interplay between potential bioenergy grass (Miscanthus, Cave-in-Rock, and Alamo) production, water quantity, and nitrogen leaching (NL) in the Central and Eastern U.S. Water use intensity tends to be lower where grass yields are modeled to be high, for example in the Midwest for Miscanthus and Cave-in-Rock and the upper southeastern U.S. for Alamo. However, most of these regions are already occupied by crops and forests and substitution of these biome types for ethanol production implies trade-offs. In general, growing Miscanthus consumes more water, Alamo consumes less water, and Cave-in-Rock consumes approximately the same amount of water as existing vegetation. Bioenergy grasses can maintain high productivity over time, even in water limited regions, because their roots can grow deeper and extract the water from the deep, moist soil layers. However, this may not hold where there are frequent and intense drought events, particularly in regions with shallow soil depths. One advantage of bioenergy grasses is that they mitigate nitrogen leaching relative to row crops and herbaceous plants when grown without applying N fertilizer; and bioenergy grasses, especially Miscanthus, generally require less N fertilizer application than row crops and herbaceous plants.

Seed Burial Depth and Soil Water Content Affect Seedling Emergence and Growth of Ulmus pumila var. sabulosa in the Horqin Sandy Land

We investigated the effects of seed burial depth and soil water content on seedling emergence and growth of Ulmus pumila var. sabulosa (sandy elm), an important native tree species distributed over the European-Asian steppe. Experimental sand burial depths in the soil were 0.5, 1.0, 1.5, 2.0 and 2.5 cm, and soil water contents were 4%, 8%, 12% and 16% of field capacity. All two-way ANOVA (five sand burial depths and four soil water contents) results showed that seed burial depths, soil water content and their interactions significantly affected all the studied plant variables. Most of the times, seedling emergence conditions were greater at the lower sand burial depths (less than 1.0 cm) than at the higher (more than 1.0 cm) seed burial depths, and at the lower water content (less than 12%) than at the higher soil water content. However, high seed burial depths (more than 1.5 cm) or low soil water content (less than 12%) reduced seedling growth or change in the root/shoot biomass ratios. In conclusion, the most suitable range of sand burial was from 0.5 to 1.0 cm soil depth and soil water content was about 12%, respectively, for the processes of seedling emergence and growth. These findings indicate that seeds of the sandy elm should be kept at rather shallow soil depths, and water should be added up to 12% of soil capacity when conducting elm planting and management. Our findings could help to create a more appropriate sandy elm cultivation and understand sparse elm woodland recruitment failures in arid and semi-arid regions.

Effects of land-use types on the vertical distribution of fractions of oxidizable organic carbon on the Loess Plateau, China

The oxidizability of soil organic carbon (SOC) influences soil quality and carbon sequestration. Four fractions of oxidizable organic carbon (very labile (C1), labile (C2), less labile (C3) and non-labile (C4)) reflect the status and composition of SOC and have implications for the change and retention of SOC. Studies of the fractions of oxidizable organic carbon (OC) have been limited to shallow soil depths and agroecosystems. How these fractions respond at deep soil depths and in other types of land-use is not clear. In this study, we evaluated the vertical distributions of the fractions of oxidizable organic carbon to a soil depth of 5.0 m in 10 land-use types in the Zhifanggou Watershed on the Loess Plateau, China. Along the soil profile, C1 contents were highly variable in the natural grassland and shrubland I (Caragana microphylla), C2 and C4 contents were highly variable in the natural grassland and two terraced croplands, respectively, and C3 contents varied little. Among the land-use types, natural grassland had the highest C1 and C2 contents in the 0–0.4 m layers, followed by shrubland I in the 0–0.1 m layer. Natural grassland had the highest C4 contents in the 1.0–4.5 m layers. Natural grassland and shrubland I thus contributed to improve the oxidizability of SOC in shallow soil, and the deep soil of natural grassland has a large potential to sequester SOC on the Loess Plateau.

Soil-Site Suitability Evaluation for Wheat in Calcareous Basaltic Soils of Girnar Toposequence in Southern Saurashtra Region of Gujarat

The five representative pedons were evaluated for their suitability to wheat in the soils of different land slopes of Girnar toposequence of Southern Saurashtra region of Gujarat. The soils of pedon P3 belonging to Typic Haplustert are suitable for wheat cultivation, whereas the soils of pedon P4 belonging to Typic Haplustepts and pedon P5 belonging to Typic Ustifluvents are currently not suitable for wheat cultivation. The soils of pedon P1 and P2 belonging to Lithic Ustorthents and Lithic Haplustepts are not suitable for wheat cultivation. Topography, texture, shallow soil depth, high CaCO3, drainage and salinity are major limitations in the soils of Girnar toposequence of Southern Saurashtra. Results showed that the suitability classes can be improved if the correctable limitations (soil fertility characteristics) are altered through soil amelioration measures.

Soil moisture dynamics with hydro-climatological parameters at different soil depths

The soil–water interaction is crucial for effective hydrological processes determination. The soil moisture (SM) is an important parameter to provide priori information for the interactions imparting and affecting the energy fluxes response for such kind of processes. This work investigated the effects of climatic, geophysical and hydrological parameters on SM at 9 stations within Utah State, USA, for daily data recorded between 2010 and 2012 at 5 different soil depths (approximately 5, 10, 20, 50, and 100 cm). A high correlation was found for soil temperature, evapotranspiration (ET), and surface temperature, respectively, in most of the stations at either α = 5 % or 1 %. All stations exhibited a downward trend in SM for the top three soil depths, whereas, for other depths some stations depicted an upward trend. From time series analysis, it was found that surface average temperature, ET and soil temperature varied on seasonal basis with maximum in June and minimum in January of each year. In addition, SM availability in the top 5 cm of soil depth showed more significance for having strong correlation with hydroclimatic variables and were essential in interpreting many hydrological processes. From analyses at shallow soil depths (5 and 10 cm), the spatial SM variability across the stations was consistent during winter and spring whereas inconsistent during summer and autumn. In addition, the SM exhibited a temporal cyclic variability for almost all stations.

Depth of Seed Burial and Gender Influence Weed Seed Predation by Three Species of Ground Beetle (Coleoptera: Carabidae)

Ground beetles are postdispersal weed seed predators, yet their role in consuming buried seeds is not well studied. We conducted greenhouse experiments to investigate how seed burial affects consumption of weed seeds (volunteer canola) by adult ground beetles (Coleoptera: Carabidae). Seed burial depth influenced seed consumption rates as demonstrated by a significant interaction between seed burial depth, carabid species, and gender of the carabid tested. We observed higher seed consumption by females of all species, and greater consumption of seeds scattered on the soil surface compared with seeds buried at any depth. However, there was evidence of seed consumption at all depths. Adults ofPterostichus melanarius(Illiger) andHarpalus affinis(Schrank) consumed more buried seeds than did those ofAmara littoralisMannerheim. Agricultural practices, such as tillage, bury seeds at different depths and based on the results of this study, these practices may reduce seed consumption by carabids. Soil conservation practices that reduce tillage (conservation or zero tillage) will favor greater weed seed predation due, in part, to the high availability of seeds at the soil surface or at shallow soil depths.

인천국제공항 식재기반 구조 및 토양특성 연구

This study aims to suggest adequate soil management through the analysis of physicochemical properties of soil in the planting grounds of Incheon International Airport, which was constructed on a massive land reclamation site. Study areas were 5 sites at the international business complex, the passenger terminal, the airport support complex, the free trade zone, and the access road. Soil profile analysis showed that 9 plots out of the 27 plots were hardpan and heterospere within 80cm from the soil surface. The earth laid on the ground was categorized as gravel based soil(4 plots), dredged soil from the sea bottom and mixed reclamation materials(2 plots), clay with poor permeability(3 plots) and waste construction material(1 plot). Average soil hardness was and soil textures were sandy soil, sandy loam and loamy sand. Average soil pH was 6.7 and average organic matter content was 0.7%. Electrical conductivity was 0.0dS/m and exchangeable cation concentrations were 3.4cmol/kg, 1.5cmol/kg, 0.3cmol/kg and 1.0cmol/kg. Average cation exchange capacity was 11.0cmol/kg. Although average figures in Solum mostly meet the landscape design criteria, properties of each soil layer showed various values sometimes over the limit. Base saturations were 29.9%, 13.3% and 3.7% for lower soil, 33.3%, 17.0% and 2.7% for mid-soil and 32.6%, 12.2% and 1.9% for upper soil. Exchangeable sodium percentages were 16.4% for lower soil, 7.5% for mid-soil and 4.7% upper soil. Sodium adsorption rates were 0.8 for lower soil, 0.3 for mid-soil and 0.2 for upper soil. Factors affecting to the vegetation growth were heterogeneity and poorness of solum, disturbance of dredged soils, high soil hardness including hardpan in the subsurface soil layer and shallow effective soil depth, high soil acidity, imbalance of base contents, low organic matter content and low available phosphate levels in the soil.

Longevity of Shallow Subsurface Drip Irrigation Tubing under Three Tillage Practices

Shallow Sub‐Surface drip irrigation (S3DI) has drip tubing buried about 2 inches below the soil surface. It is unknown how long drip tubing would be viable at this shallow soil depth using strip‐ or no‐tillage systems. The objectives were to determine drip tube longevity, resultant crop yield, and partial net revenue when using conventional, strip‐, and no‐tillage. Drip tubing (8, 10, and 15 mil) was buried 1.5 inches in 2006 and left in the field for five years under strip‐ and no‐till areas and removed and reinstalled in conventionally‐tilled areas. Crop rotation was cotton (Gossypium hirsutum L.) the first year, corn (Zea mays L.) the next three years, and peanut (Arachis hypogaea L.) in the final year. There was no difference in cotton lint yield by tillage treatment and irrigated lint yield was 2.4 times greater than nonirrigated. There was no difference in irrigated corn yield across year or tillage practice. Irrigated corn yield was 5.8 times greater than nonirrigated yield. Irrigated peanut yield was the same across tillage treatments but was 2.6 times greater compared with nonirrigated yield. For tube longevity, conventionally tilled areas had less tube repairs compared with strip‐ or no‐tilled practices. Thinner wall tubing (8 mil) had 3.5 times more holes compared with thicker wall tubing (15 mil). The “cost‐to‐repair” versus “cost‐to‐replace” tubing indicates average replacement time at about 5.4 years. There were less production expenses for strip‐ and no‐ till compared with conventional tillage. Both strip‐ and no‐tillage systems are recommended when installing S3DI.

Management considerations to minimize environmental impacts of arsenic following monosodium methylarsenate (MSMA) applications to turfgrass

Monosodium methylarsenate (MSMA) is an organic arsenical herbicide currently utilized in turfgrass and cotton systems. In recent years, concerns over adverse impacts of arsenic (As) from MSMA applications have emerged; however, little research has been conducted in controlled field experiments using typical management practices. To address this knowledge gap, a field lysimeter experiment was conducted during 2012–2013 to determine the fate of As following MSMA applications to a bareground and an established turfgrass system. Arsenic concentrations in soil, porewater, and aboveground vegetation, were measured through one yr after treatment. Aboveground vegetation As concentration was increased compared to nontreated through 120 d after initial treatment (DAIT). In both systems, increased soil As concentrations were observed at 0–4 cm at 30 and 120 DAIT and 0–8 cm at 60 and 365 DAIT, suggesting that As was bound in shallow soil depths. Porewater As concentrations in MSMA-treated lysimeters from a 30-cm depth (22.0–83.8 μg L−1) were greater than those at 76-cm depth (0.4–5.1 μg L−1). These results were combined with previous research to devise management considerations in systems where MSMA is utilized. MSMA should not be applied if rainfall is forecasted within 7 DAIT and/or in areas with shallow water tables. Further, disposing of MSMA-treated turfgrass aboveground vegetation in a confined area – a common management practice for turfgrass clippings – may be of concern due to As release to surface water or groundwater as the vegetation decomposes. Finally, long-term MSMA use may cause soil As accumulation and thus downward migration of As over time; therefore, MSMA should be used in rotation with other herbicides.

Influence of environmental factors on seed germination and emergence of Iresine diffusa

SummaryIresine diffusa has become more abundant under no‐till soyabean in Argentina. The influence of temperature, light, cold‐wet storage, osmotic potential, dry storage and depth of seed burial on germination and emergence of I. diffusa was examined in a growth chamber experiment. Iresine diffusa seeds germinated at the highest proportion (&gt;0.80) in all fluctuating day/night temperatures tested. Conversely, under a constant temperature regime, maximum germination rates occurred at 15 (0.78) and 20°C (0.82), and minimum germination rates occurred at 10 (0.19) and 30°C (0.36). Seed germination was not influenced by light exposure. However, germination decreased after 12 (0.76) and 16 (0.65) weeks in cold‐wet storage. To reduce germination significantly, −0.4 MPa of osmotic potential (induced by PEG‐6000) or 120 mmol L−1 of salt (NaCl) concentration was required. Seeds of I. diffusa showed high viability (0.85) after 720 days of dry storage. Low emergence was recorded for seeds buried at 2 cm, and seedling emergence was completely inhibited when seeds were buried at 5 and 10 cm. Iresine diffusa seeds had high viability and were capable of emerging in a broad range of environmental conditions. The thermal germination conditions, shallow soil depths and high moisture conditions in germination phase for I. diffusa are congruent with the conditions in Argentina no‐tillage soyabean. Thus, no‐tillage could provide better conditions for germination than conventional tillage systems. However, due to the fact that I. diffusa can reproduce by rhizomes, further research should be conducted to understand the relative importance of the vegetative reproductive strategy in relation to the presence and persistence of this weed in fields.

No shift to a deeper water uptake depth in response to summer drought of two lowland and sub-alpine C₃-grasslands in Switzerland.

Temperate C3-grasslands are of high agricultural and ecological importance in Central Europe. Plant growth and consequently grassland yields depend strongly on water supply during the growing season, which is projected to change in the future. We therefore investigated the effect of summer drought on the water uptake of an intensively managed lowland and an extensively managed sub-alpine grassland in Switzerland. Summer drought was simulated by using transparent shelters. Standing above- and belowground biomass was sampled during three growing seasons. Soil and plant xylem waters were analyzed for oxygen (and hydrogen) stable isotope ratios, and the depths of plant water uptake were estimated by two different approaches: (1) linear interpolation method and (2) Bayesian calibrated mixing model. Relative to the control, aboveground biomass was reduced under drought conditions. In contrast to our expectations, lowland grassland plants subjected to summer drought were more likely (43-68%) to rely on water in the topsoil (0-10 cm), whereas control plants relied less on the topsoil (4-37%) and shifted to deeper soil layers (20-35 cm) during the drought period (29-48%). Sub-alpine grassland plants did not differ significantly in uptake depth between drought and control plots during the drought period. Both approaches yielded similar results and showed that the drought treatment in the two grasslands did not induce a shift to deeper uptake depths, but rather continued or shifted water uptake to even more shallower soil depths. These findings illustrate the importance of shallow soil depths for plant performance under drought conditions.

Climate–growth relationships of relict Picea jezoensis at Mt. Gyebang, South Korea

A study was conducted to evaluate climatic variation at Mt. Gyebang, South Korea, and its influence on the modelled and observed growth of its relict Picea jezoensis population. Using the MT-CLIM and Biome-BGC models, year-to-year meteorological variation and subsequent changes in growing season, primary productivity and water balance were simulated. These were compared with the observed growth of sample P. jezoensis trees at the site. According to weather data and model calculations, the P. jezoensis stand at Mt. Gyebang was exposed to significant climate variations affecting growing season, carbon balance, and water balance. Although the length of growing season showed an increasing trend over time, the observed growth of P. jezoensis was unaffected by the length of growing season. Probably due to the site's shallow soil depths and species’ shallow rooting depth, the modelled increase in productivity caused by climate variation was not manifested in an increase in growth of P. jezoensis. These findings imply that the competitiveness of P. jezoensis at this site has declined over time and that an active approach to conservation planning for this species and site is warranted.

English

The experiment was conducted to assess land degradation in agrarian soils of Ebonyin State. Ten farmers’ fields were selected based on land use and landscape positions across the three zones in the state. Physical and socio- economic information were obtained from the farmers and extension agents. Surface and sub-surface soil samples were collected for physical and chemical analysis. The soils at the upland were clay loam and at lower slope to valley bottom were clay loam to clay in texture. The upland and low land soils were strongly acidic (4.1) to moderately acidic (5.5) with low P (3.36 - 5 mg/kg). The soils also were low in cation exchange capacity (CEC) (1.36 - 2.68). Soil degradation indicators include crop conditions, poor yield, low fertility level, shallow soil depth (50 cm), high gravel content (> 35%), compaction of exposed sub soils and soil erosion. The factors and causes of soil degradation include improper tillage system, continuous cultivation, nutrient mining due to many crops per heap under mixed cropping and improper crop combination. Conservation agriculture with minimum tillage and green manure are recommended for sustainable production while combination of organic and in-organic fertilizer is recommended to improve soil quality.