Soil Cation Exchange Research Articles

Soil-mediated effects of acidification as the major driver of species loss following N enrichment in a semi-arid grassland

The semi-arid Inner Mongolia grassland ecosystem is experiencing dramatic decreases in plant diversity as global N deposition increases. However, a comprehensive understanding of the mechanisms for this loss in diversity is lacking. We collected biotic and abiotic properties on plant community and soils in a 6-year field study with six levels (ranging between 0 to 25.14 g N m−2 yr.−1) of N addition rate in this ecosystem. The decrease in plant diversity was primarily driven by the loss of forb species. We developed a comprehensive assessment of the mechanisms contributing to this forb loss, and demonstrated the pivotal role of soil-mediated effects of acidification in reducing forbs richness. Soil acidification was associated with altered status of soil exchangeable cations and reduced soil arbuscular mycorrhizal fungi (AMF) biomass. This led to reduced nutrient cations uptake, the accumulation of phytotoxic metals, and reduced P acquisition by plants. The acidification effects notably overwhelmed other operating mechanisms, such as light limitation, and increased N availability. Our results provide a comprehensive mechanistic understanding of diversity loss under N enrichment in this semi-arid ecosystem, and suggest that soil acidification is a major threat to biodiversity under future scenarios of N deposition.

誘導結合プラズマ(ICP)発光分光分析法による土壌の交換性陽イオンの定量

誘導結合プラズマ(ICP)発光分光分析法による土壌の交換性陽イオンの定量

Quantifying the effects of soil and climate on aboveground biomass production of Salix miyabeana SX67 in Quebec

Soil and climatic conditions for optimizing aboveground biomass yields of bioenergy short rotation coppices (SRCs) of Salix are not well elucidated. The objective of this study was to identify and quantify the limitations induced by soil and climate, and compare the magnitude of their effects, on annual aboveground yields across ten SRCs of Salix miyabeana SX67 in Quebec, Canada. The effects of weather variation between years on yields were also tested within locations. In five plots per SRC, soil bulk density, particle size, exchangeable cations and bulk composition were analysed, and moisture deficits were estimated using leaf δ13C. For each location, numerous weather variables were simulated for spring, summer and the whole growing season. Climate was calculated by averaging weather variables for growing seasons for which annual yields were available. Annual aboveground biomass yields were modelled using linear regression, partitioning of the variance and mixed models with soil, weather and climate variables as predictors. Across SRCs, silt content, soil organic matter, pH, exchangeable Ca and Mg, and total N and Zn were significantly and positively related to aboveground yields (adj. R 2 ranging from 0.38 to 0.79). Generally, annual yields were negatively related to summer temperature within SRCs (adj. R 2 = 0.92) and drought across SRCs (adj. R 2 = 0.54). Partitioning of the variance revealed that soil variables (~80%) had a greater effect on productivity than did climate variables (~10%). In fact, soil properties buffered or exacerbated water shortages and, thus, had a preponderant effect on yield.

Intrinsic Relationship between Matric Potential and Cation Hydration

Core Ideas Exchangeable cations are important in water sorption, hydraulic conductivity, swelling, flocculation–deflocculation, and fertility. Intrinsic relationship exists between matric potential and cation hydration at very low water contents. Proposed model predicts soil water content at low matric potentials for different exchangeable cations in soil. Model is applicable for soil water retention models and quantification of different types of exchangeable cations. The origin of matric potential in the tightly adsorbed soil water retention (SWR) regime, where matric potentials are generally less than −150 MPa, remains unsettled. Surface tension in soil pores and van der Waals attraction (VDW) near particle surfaces are known, respectively, as the sources of matric potential for capillary and adsorbed film water. However, theories based on VDW fail to predict the SWR for matric potentials less than −150 MPa. Recent studies show that cation hydration occurs at matric potentials much lower than those predicted by considering a particle surface hydration originating from the VDW forces. With this basis, a theoretical soil water retention curve (SWRC) model for drying path is proposed to quantify matric potential and its retained water by accounting for all water sorption mechanisms on or within soil particles, particularly the cation–water molecule or charge–dipole interaction. It is found that clays at very low soil water content, typically less than a few percentage gravimetric, charge–dipole interaction energy, dominate matric potential. Experimental SWR data for various cation‐exchanged soils confirms the validity of the theoretical SWRC model and its accuracy, indicating that cation hydration is mainly responsible for SWR for matric potentials less than −150 MPa. Furthermore, the predicted lowest matric potentials at zero water content for various soils agree well with experimental data. The lowest matric potential of a soil depends mainly on the type of exchangeable cations and thus is not a universal constant for all soils. These results have potential applications in using SWRC for the determination of cation exchange capacity and types of exchangeable cations in soils.

Soil pH and Exchangeable Cation Responses to Tillage and Fertilizer in Dryland Cropping Systems

ABSTRACTLong-term use of nitrogen (N) fertilizers can lead to fertility-lowering soil chemical changes. To examine this in geologically young soils in the northern Great Plains of North America, we present near-surface (0–7.6 cm) soil chemistry data from 16 years of two crop rotations: continuous crop (CC; spring wheat [Triticum aestivum L.]—winter wheat [T. aestivum]—sunflower [Helianthus annuus L.]) and crop-fallow (C-F; spring wheat—fallow) that underwent factorial tillage (none, minimum, conventional) and N rate (low, medium, high) treatments. For CC, the N rate (but not tillage) had a significant effect on pH, with the high N rate leading to the largest pH decline (−0.76). The nitrogen rate also had a significant effect on cation exchange capacity (CEC) for CC, whereby CEC increased with the N rate. Managers utilizing high N rates should be aware of the potential for soil acidification, even in the northern Great Plains of North America.

Climate‐driven thresholds for chemical weathering in postglacial soils of New Zealand

AbstractChemical weathering in soils dissolves and alters minerals, mobilizes metals, liberates nutrients to terrestrial and aquatic ecosystems, and may modulate Earth's climate over geologic time scales. Climate‐weathering relationships are often considered fundamental controls on the evolution of Earth's surface and biogeochemical cycles. However, surprisingly little consensus has emerged on if and how climate controls chemical weathering, and models and data from published literature often give contrasting correlations and predictions for how weathering rates and climate variables such as temperature or moisture are related. Here we combine insights gained from the different approaches, methods, and theory of the soil science, biogeochemistry, and geomorphology communities to tackle the fundamental question of how rainfall influences soil chemical properties. We explore climate‐driven variations in weathering and soil development in young, postglacial soils of New Zealand, measuring soil elemental geochemistry along a large precipitation gradient (400–4700 mm/yr) across the Waitaki basin on Te Waipounamu, the South Island. Our data show a strong climate imprint on chemical weathering in these young soils. This climate control is evidenced by rapid nonlinear changes along the gradient in total and exchangeable cations in soils and in the increased movement and redistribution of metals with rainfall. The nonlinear behavior provides insight into why climate‐weathering relationships may be elusive in some landscapes. These weathering thresholds also have significant implications for how climate may influence landscape evolution and the release of rock‐derived nutrients to ecosystems, as landscapes that transition to wetter climates across this threshold may weather and deplete rapidly.

English

Special liming materials have the potential to control soil acidity and constitute a source of nutrients for plant development. In this study, the efficiency of special liming materials was evaluated. Their effects in soil exchangeable cations and available P concentrations were compared with the ones of dolomitic limestone (DL). Samples of Typic Distrudept and Rhodic Hapludox were collected from 0 to 20 cm layer. Two experiments were conducted in a completely randomized block of 4x4x8 factorial design. Four liming materials were studied: DL, granulated micronized calcite (GMC), granulated micronized dolomite (GMD) and carbonated suspension (CS). The liming materials were added to the soils doses that increase the soil bases saturation (V) to 50, 70 and 90%; and a control treatment. The treated soil samples were incubated at 23 ± 2°C and 60% of soil water retention capacity for eight periods (0, 7, 15, 30, 45, 60, 75 and 90 days). Exchangeable Ca, Mg and K, and available P were determined. All liming materials increase exchangeable Ca and Mg, and available P. However, the most efficient source that increased exchangeable Ca in the studied soils were CS followed by GMC. Key words: Special liming materials, micronized limestone, carbonated suspension, availability of nutrients, Inceptisol, Oxisol.

Evaluation of Soil Chemical Properties under Paddy Production System in Central Kenya: Soil Exchangeable Cations

<p>Lowland irrigated schemes contribute the most rice produced in Kenya. However, production is low and highly variable due to management problems. Production could be increased with appropriate soil management which requires that baseline fertility status of the soils and how they vary be known. This study examined the variability of selected soil chemical properties in the Mwea Irrigation Scheme in Central Kenya. Soil samples were collected from the top 0-15 cm depth in August 2013 and 2014 and analysed for pH, electrical conductivity (EC) and the exchangeable cations potassium (K<sup>+</sup>), calcium (Ca<sup>2+</sup>), magnesium (Mg<sup>2+</sup>) and sodium (Na<sup>+</sup>). Significant variability in soil EC as well as soil cation concentration was observed among units. Overall results showed soil pH ranged from 4.56 (very strongly acidic) to 8.05 (moderately alkaline). Soil EC varied from 0.17 to 1.52 dS m<sup>-1</sup> with higher elevation areas recording lower values (< 0.50 dS m<sup>-1</sup>) and lower elevation areas recording higher EC values (> 0.50 dS m<sup>-1</sup>). On average, exchangeable Ca<sup>2+</sup> was 38.17 cmol<sub>c</sub> kg<sup>-1</sup>, Mg<sup>2+</sup> 23.80 cmol<sub>c</sub> kg<sup>-1</sup>, Na<sup>+</sup> 1.24 cmol<sub>c</sub> kg<sup>-1</sup> and K<sup>+</sup> 0.35 cmol<sub>c</sub> kg<sup>-1</sup>. The soil exchange complex was mainly dominated by Ca<sup>2+</sup> and Mg<sup>2+</sup> and cation concentration in the soil was in the order Ca<sup>2+</sup> > Mg<sup>2+</sup> > Na<sup>+</sup> > K<sup>+</sup>. Soil K is low and severe cation imbalances exist with regard to K<sup>+</sup> and other cations thus making K<sup>+</sup> deficient for plant uptake. Management practices and farming systems which enhance soil K status should be encouraged to help boost and sustain rice yield.</p>

Biogeographic Distribution Patterns of Bacteria in Typical Chinese Forest Soils.

Microbes are widely distributed in soils and play a very important role in nutrient cycling and ecosystem services. To understand the biogeographic distribution of forest soil bacteria, we collected 115 soil samples in typical forest ecosystems across eastern China to investigate their bacterial community compositions using Illumina MiSeq high throughput sequencing based on 16S rRNA. We obtained 4,667,656 sequences totally and more than 70% of these sequences were classified into five dominant groups, i.e., Actinobacteria, Acidobacteria, Alphaproteobacteria, Verrucomicrobia, and Planctomycetes (relative abundance >5%). The bacterial diversity showed a parabola shape along latitude and the maximum diversity appeared at latitudes between 33.50°N and 40°N, an area characterized by warm-temperate zones and moderate temperature, neutral soil pH and high substrate availability (soil C and N) from dominant deciduous broad-leaved forests. Pairwise dissimilarity matrix in bacterial community composition showed that bacterial community structure had regional similarity and the latitude of 30°N could be used as the dividing line between southern and northern forest soils. Soil properties and climate conditions (MAT and MAP) greatly accounted for the differences in the soil bacterial structure. Among all soil parameters determined, soil pH predominantly affected the diversity and composition of the bacterial community, and soil pH = 5 probably could be used as a threshold below which soil bacterial diversity might decline and soil bacterial community structure might change significantly. Moreover, soil exchangeable cations, especially Ca2+ (ECa2+) and some other soil variables were also closely related to bacterial community structure. The selected environmental variables (21.11%) explained more of the bacterial community variation than geographic distance (15.88%), indicating that the edaphic properties and environmental factors played a more important role than geographic dispersal limitation in determining the bacterial community structure in Chinese forest soils.

Exchangeable cations in deep forest soils: Separating climate and chemical controls on spatial and vertical distribution and cycling

The vertical distribution of soil exchangeable cations (Ca2+, Mg2+, K+, and Na+) results from the integration of multiple processes: weathering of primary minerals, atmospheric input, leaching, and biological cycling. While weathering and atmospheric input affect the location of cation inputs to the soil system, leaching and biological cycling translocate cations in opposing directions within the profile. Little research has been conducted on deep soil relative to surface soil, and thus attempts to verify hypotheses about the drivers of exchangeable cation vertical distributions have not been possible on a broad scale. This study excavated soils down to 2.5 or 3m at 22 sites across the coastal Pacific Northwest ranging from northern Washington to southern Oregon. Samples were analyzed for soil carbon (C), nitrogen (N), and exchangeable cations. PERMANOVA was used to evaluate the effect of soil chemical (C, N, and pH), environmental (climate, parent material, elevation), physical (texture) and spatial (horizon, depth) gradients on the distribution of exchangeable cation contents and stocks. The majority of exchangeable cation stocks are located in deeper soil horizons. On average, 66% of Ca2+, 76% of Mg2+, 57% of K+, and 63% of Na+ stocks were below 1.0m. Master soil horizon was the most significant predictor of the distribution of cations within the soil profile with substantial separation between A horizon samples and B and C horizon samples. There was a significant interaction between horizon and soil C, with higher soil C concentrations and stocks corresponding with lower Ca2+ and Mg2+ contents and stocks in horizons of the same type. Between sites, climate and cumulative carbon stocks were the dominant controls over cation distribution, with high C stocks and wet, cool climate leading to low exchangeable Ca2+ and Mg2+. These results suggest that leaching with dissolved organic matter could be a driver of exchangeable Ca2+ and Mg2+ distributions in the Pacific Northwest. On the other hand, K+ and Na+ were largely uncorrelated with these environmental gradients. Biological uptake is a more important control over the distribution of exchangeable K+, while atmospheric deposition drives the relatively uniform distribution of Na+ both between sites and within profiles.

Root exudation of low-molecular-mass-organic acids by six tree species alters the dynamics of calcium and magnesium in soil

Soils in plantations of Cryptomeria japonica in Japan have ∼threefold more exchangeable Ca compared with soils in other types of forest vegetation even in a Ca-poor environment. To explain mechanisms underlying this phenomenon, we determined the effect of root exudation rate of low-molecular-mass organic acids (LMMOAs) on exchangeable cations in soil. We conducted a pot experiment using C. japonica and five dominant tree species in Japan, and measured the root exudation rates of LMMOAs and exchangeable nutrient concentrations in the soils. To estimate whether the root exudation rate of LMMOAs is elevated in response to Ca deficiency, we created variation in Ca availability by adding different amounts of crushed oyster shells. The root exudation rates of LMMOAs were two to five times higher for C. japonica than for other tree species, but did not differ significantly among the different quantities of oyster shell. Exchangeable Ca and Mg were significantly higher in the soils with C. japonica and significantly correlated with the root exudation rate of LMMOAs (R2 > 0.24) at high and moderate quantities of oyster shell. Therefore, variation among species, in terms of root exudation of organic acids, might be one important factor affecting the cation dynamics in soil.

Consistent effects of canopy vs. understory nitrogen addition on the soil exchangeable cations and microbial community in two contrasting forests

Anthropogenic N deposition has been well documented to cause substantial impacts on the chemical and biological properties of forest soils. In most studies, however, atmospheric N deposition has been simulated by directly adding N to the forest floor. Such studies thus ignored the potentially significant effect of some key processes occurring in forest canopy (i.e., nitrogen retention) and may therefore have incorrectly assessed the effects of N deposition on soils. Here, we conducted an experiment that included both understory addition of N (UAN) and canopy addition of N (CAN) in two contrasting forests (temperate deciduous forest vs. subtropical evergreen forest). The goal was to determine whether the effects on soil exchangeable cations and microbial biomass differed between CAN and UAN. We found that N addition reduced pH, BS (base saturation) and exchangeable Ca and increased exchangeable Al significantly only at the temperate JGS site, and reduced the biomass of most soil microbial groups only at the subtropical SMT site. Except for soil exchangeable Mn, however, effects on soil chemical properties and soil microbial community did not significantly differ between CAN and UAN. Although biotic and abiotic soil characteristics differ significantly and the responses of both soil exchangeable cations and microbial biomass were different between the two study sites, we found no significant interactive effects between study site and N treatment approach on almost all soil properties involved in this study. In addition, N addition rate (25 vs. 50kgNha−1yr−1) did not show different effects on soil properties under both N addition approaches. These findings did not support previous prediction which expected that, by bypassing canopy effects (i.e., canopy retention and foliage fertilization), understory addition of N would overestimate the effects of N deposition on forest soil properties, at least for short time scale.

Bioavailability of 2, 4, 6-Trinitrotoluene (TNT) to Earthworms in Three Different Types of Soils in China

ABSTRACTTo study the effects of aging time (the length of time when contaminants are sequestered in soil) and soil properties on TNT bioavailability in soil, earthworms (Eisenia fetida) were exposed to three types of soils (fluvo-aquic soil, loessal soil, and black soil) contaminated by TNT for 7, 14, 21, 28, 35, and 42 days. The Earthworm-Soil Accumulation Factor (ESAF) of TNT and soil properties were analyzed. The ESAFs in black soil were significantly lower than those in fluvo-aquic soil and loessal soil (P < 0.05). In loessal soils, the ESAF increased with aging time, while that in black soils decreased. The ESAF of TNT had a significantly negative correlation with soil organic matter content, clay contents, and cation exchange capacity, which were the main factors affecting the TNT bioavailability in soils (P < 0.01). There was more quartz and feldspar in black soil, as well as more particles and micropores on the surface, which resulted in the easy adsorption and lower bioavailability of TNT. In conclusion, TNT bioavailability in soils is affected by aging time, soil physical and chemical properties, and mineral and surface properties, which must be considered when biotreatment for TNT in soils is applied.

Long-term tobacco plantation induces soil acidification and soil base cation loss.

Changes in soil exchangeable cations relative to soil acidification are less studied particularly under long-term cash crop plantation. This study investigated soil acidification in an Ali-Periudic Argosols after 10-year (2002-2012) long-term continuous tobacco plantation. Soils were respectively sampled at 1933 and 2143 sites in 2002 and 2012 (also 647 tobacco plants), from seven tobacco plantation counties in the Chongqing Municipal City, southwest China. After 10-year continuous tobacco plantation, a substantial acidification was evidenced by an average decrease of 0.20 soil pH unit with a substantial increase of soil sites toward the acidic status, especially those pH ranging from 4.5 to 5.5, whereas 1.93 kmol H(+) production ha(-1) year(-1) was mostly derived from nitrogen (N) fertilizer input and plant N uptake output. After 1 decade, an average decrease of 27.6 % total exchangeable base cations or of 0.20 pH unit occurred in all seven tobacco plantation counties. Meanwhile, for one unit pH decrease, 40.3 and 28.3 mmol base cations kg(-1) soil were consumed in 2002 and 2012, respectively. Furthermore, the aboveground tobacco biomass harvest removed 339.23 kg base cations ha(-1) year(-1) from soil, which was 7.57 times higher than the anions removal, leading to a 12.52 kmol H(+) production ha(-1) year(-1) as the main reason inducing soil acidification. Overall, our results showed that long-term tobacco plantation not only stimulated soil acidification but also decreased soil acid-buffering capacity, resulting in negative effects on sustainable soil uses. On the other hand, our results addressed the importance of a continuous monitoring of soil pH changes in tobacco plantation sites, which would enhance our understanding of soil fertility of health in this region.

Physical, chemical, and biological properties of soil under soybean cultivation and at an adjacent rainforest in Amazonia

Land-use change in the Amazon basin has occurred at an accelerated pace during the last decade, and it is important that the effects induced by these changes on soil properties are better understood. This study investigated the chemical, physical, and biological properties of soil in a field under cultivation of soy and rice, and at an adjacent primary rain forest. Increases in soil bulk density, exchangeable cations and pH were observed in the soy field soil. In the primary forest, soil microbial biomass and basal respiration rates were higher, and the microbial community was metabolically more efficient. The sum of basal respiration across the A, AB and BA horizons on a mass per area basis ranged from 7.31 to 10.05 Mg CO2-C ha-1yr-1, thus yielding estimates for total soil respiration between 9.6 and 15.5 Mg CO2-C ha-1yr-1 across sites and seasons. These estimates are in good agreement with literature values for Amazonian ecosystems. The estimates of heterotrophic respiration made in this study help to further constrain the estimates of autotrophic soil respiration and will be useful for monitoring the effects of future land-use in Amazonian ecosystems.

Clipped Cowpea (Vigna unguiculata (L.) Walp) Fodder Management: A Potential for Soil Organic Matter Enrichment in Degraded Savannah Soils of Nigeria

Severe nutrient depletion of the soils of the savannah tropics of Africa over the years has made it difficult to improve the productivity of varieties of crops using cultural practices alone. But interestingly, it has been observed that when a cowpea (Vigna unguiculata (L.) Walp) crop is cut (clipped) before senescence; it can regenerate after defoliation (provided there is enough soil moisture). And when the clipped organic fodder is added and/or ploughed back into the soil, it enriches the soil organic matter (SOM) content that in turn enhances crop productivity. Thus, this study was carried out with the objective of determining the influence of intra-row spacing, clipping height and time on the productivity of cowpea and SOM; at the Institute for Agricultural Research, Ahmadu Bello University, Samaru, Zaria, Nigeria; during the 2002-2005 wet seasons. The experimental lay out was a Randomized Complete Block Design (RCBD), replicated three times. The collected data was analyzed statistically using the analysis of variance test (ANOVA); and the means separation was done using the Duncan Multiple Range Test (DMRT). Results showed that the textural class of the experimental site soil was loam silt; with a conducive pH of (6.6 in 2002 and 5.5 in 2005), for crop growth. The soil organic carbon content (SOC), nitrogen (N) and cation exchange capacity (CEC) were very low (0.30 g kg-1, 0.88 g kg-1 and 4.90 respectively) in 2002. These increased to 10.37 g kg-1, 2.2 g kg-1 and 11.10 respectively in 2005. Total rainfall in 2002 was 1007.9mm and 871.5mm in 2005. Mean air temperature, relative humidity and sunshine hours in 2002 ranged between 21.0-31.5 °C, 16.0-90.6 and 4.5-8.5 respectively; while mean air temperature and relative humidity ranged between 24.7-32.0 °C and 40.5-85.3% respectively in 2005. Total harvested clipped fodder yield was 15t ha-1; and this was added to the soil; and it effectively increased SOM content by about 42%. Consequently, it was concluded that the adoption of this innovative clipping management technology, holds great potential of improving soil pH, increasing soil CEC, SOM and crop productivity generally, for the low technology, resource poor, and subsistence farmers in the region. Without doubt, overcoming SOM decline is a major component in the development of more sustainable agro-systems.

Ameliorating Effects of Fungus Chaff and Its Biochar on Soil Acidity

A biochar was generated from fungus chaff at 300 °C, and the ameliorating effects of fungus chaff and its biochar on an acidic Ultisol were compared using incubation experiments. Incorporation of fungus chaff and its biochar significantly increased soil pH and soil exchangeable base cations but decreased soil exchangeable acidity. The ameliorating effect was greater for the biochar than the fungus chaff, and thus the biochar was a better amendment for acidic soil than its feedstock of fungus chaff. The biochar ameliorated soil acidity mainly through the release of its contained alkaline substances, while fungus chaff increased pH of acidic soils through two mechanisms: release of alkaline substances and inhibition of soil nitrification. The incorporation of fungus chaff increased soil-available organic carbon and thus accelerated the microbial assimilation of inorganic nitrogen, while incorporation of fungus chaff biochar enhanced nitrification due to increased soil pH.

Structural, physiognomic and above-ground biomass variation in savanna–forest transition zones on three continents – how different are co-occurring savanna and forest formations?

Abstract. Through interpretations of remote-sensing data and/or theoretical propositions, the idea that forest and savanna represent "alternative stable states" is gaining increasing acceptance. Filling an observational gap, we present detailed stratified floristic and structural analyses for forest and savanna stands located mostly within zones of transition (where both vegetation types occur in close proximity) in Africa, South America and Australia. Woody plant leaf area index variation was related to tree canopy cover in a similar way for both savanna and forest with substantial overlap between the two vegetation types. As total woody plant canopy cover increased, so did the relative contribution of middle and lower strata of woody vegetation. Herbaceous layer cover declined as woody cover increased. This pattern of understorey grasses and herbs progressively replaced by shrubs as the canopy closes over was found for both savanna and forests and on all continents. Thus, once subordinate woody canopy layers are taken into account, a less marked transition in woody plant cover across the savanna–forest-species discontinuum is observed compared to that inferred when trees of a basal diameter &gt; 0.1 m are considered in isolation. This is especially the case for shrub-dominated savannas and in taller savannas approaching canopy closure. An increased contribution of forest species to the total subordinate cover is also observed as savanna stand canopy closure occurs. Despite similarities in canopy-cover characteristics, woody vegetation in Africa and Australia attained greater heights and stored a greater amount of above-ground biomass than in South America. Up to three times as much above-ground biomass is stored in forests compared to savannas under equivalent climatic conditions. Savanna–forest transition zones were also found to typically occur at higher precipitation regimes for South America than for Africa. Nevertheless, consistent across all three continents coexistence was found to be confined to a well-defined edaphic–climate envelope with soil and climate the key determinants of the relative location of forest and savanna stands. Moreover, when considered in conjunction with the appropriate water availability metrics, it emerges that soil exchangeable cations exert considerable control on woody canopy-cover extent as measured in our pan-continental (forest + savanna) data set. Taken together these observations do not lend support to the notion of alternate stable states mediated through fire feedbacks as the prime force shaping the distribution of the two dominant vegetation types of the tropical lands.

English

The study of earthworm cast and anthill as plant-soil systems and the surrounding soil is helpful in the appraisal of soil and crop productivity. Therefore, this study was carried out in a tropical and subtropical area to determine the effect of plant-soil systems and the surrounding soil on the yield parameters (plant height, leave surface and dry matter weight) of maize (Oba Super 2) under greenhouse condition. Analyses of soil samples of earthworm cast, anthill (termite mound) collected by hand sampling and the surrounding soil collected with core samplers at 10 cm depth and auger samplers at 2 depths (surface, 0 to 15 cm; subsurface, 15 to 30 cm) were examined for chemical and physical properties. Three kilograms each of the soils from three locations (Nsukka, Ede Oballa and Orba) was used for testing maize. Earthworm species (Eudrilus eugeriae and Agrotoreutus nyongii) and termite species (Macrotermes and Odontotermes species) that produced the mounds and termite mounds were identified, respectively. The study results found that soil physical and chemical properties were significantly (P<0.05) affected by the plant-soil systems relative to control. Interaction of the plant-soil systems by location and by soil depth was significant (P<0.05) for the measured soil parameters such as soil pH, organic carbon, nitrogen, exchangeable cations (Ca+2, Mg+2, K+ except Na+), CEC and available P. Plant height, leaf surface and dry matter yield of maize were found significantly positively (P<0.05) increased. For better and sustainable improvement of soil productivity and yield of maize crop, combined use of earthworm cast and termite mound as plant-soil systems is recommended. Key words: Maize performance, mounds, termite, cast, earthworm, greenhouse, Nigeria.

Initial effects of thinning on soil carbon storage and base cations in a naturally regenerated Quercus spp. forest in Hongcheon, Korea

Thinning can affect soil carbon (C) and base cation balances by reducing tree density and altering microclimate and organic matter budget; however, the subsequent changes in soil C and base cation contents after thinning are not well elucidated. Thus, this study investigated the effects of thinning on C storages in soil (at 0–10 cm, 10–20 cm, and 20–30 cm depths) and forest floor and concentrations of soil exchangeable base cations (Ca2+, Mg2+, K+, and Na+). Thinning treatments of different intensities based on the removed basal area (no thinning: control, 15% thinning: T15, and 30% thinning: T30) were applied to a naturally regenerated 31 to 40-year-old Quercus spp. forest. Soil C concentrations at 10–20 cm and 20–30 cm depths were significantly higher in T15 and T30 than in the control after 39 months, but not after 4 months. T15 and T30 treatments seemed to increase soil C storage at 0–30 cm after 39 months, but did not significantly change forest floor C storage after 4 and 39 months. Concentrations of exchangeable K+ of T15 and exchangeable base cations except for Ca2+ of T30 depth were significantly lower than those of the control at 0–10 cm after 4 months, but not after 39 months. This study shows that thinning treatments on a naturally regenerated Quercus spp. forest could increase soil C concentration after a few years but temporally decrease concentrations of soil exchangeable base cations.