Physicochemical and morphological properties of termite (Macrotermes bellicosus) mounds and surrounding pedons on a toposequence of an inland valley in the southern Guinea savanna zone of Nigeria

Termites play a significant role in soil-forming processes of the tropics. The influence of termites on pedogenesis as affected by the toposequence, however, has rarely been explored. We investigated the soil physicochemical and morphological characteristics of epigeal mounds constructed by Macrotermes bellicosus (Smethman) compared with those of surrounding pedons along a toposequence (bottom, fringe and upland sites) of an inland valley in central Nigeria. The physicochemical and morphological properties of the mound soils varied according to structural units but were generally different from those of the adjacent pedons. The differences included finer texture, higher electrical conductivity, total N, exchangeable bases (Ca, Mg and K) and effective cation exchange capacity and lower C/N ratio and exchange acidity in the mound than the pedon at each toposequence position. This tendency to modify the soil properties was more prominent in the nest body where the termites actually live, that is, in the hives, royal cell and base-plate, than in the soils below the nest and the other mound parts, that is, the external wall, internal wall and pillars. We found this trend to a greater or lesser degree at all toposequence positions. Our findings suggest that: (1) M. bellicosus can manipulate the mound soils according to functional applications of structure units or environmental requirements for its livelihood, regardless of local soils; (2) M. bellicosus makes ecological patches (hot spots) at all toposequence positions in the same measure; (3) the influence of M. bellicosus on the pedogenesis is reduced in the lowlands compared with the uplands because the number and volume of the mounds were substantially lower in the bottom and fringe sites compared with the upland site.     

Physicochemical and morphological properties of termite (Macrotermes bellicosus) mounds and surrounding pedons on a toposequence of an inland valley in the southern Guinea savanna zone of Nigeria

Abstract

Termites play a significant role in soil-forming processes of the tropics. The influence of termites on pedogenesis as affected by the toposequence, however, has rarely been explored. We investigated the soil physicochemical and morphological characteristics of epigeal mounds constructed by Macrotermes bellicosus (Smethman) compared with those of surrounding pedons along a toposequence (bottom, fringe and upland sites) of an inland valley in central Nigeria. The physicochemical and morphological properties of the mound soils varied according to structural units but were generally different from those of the adjacent pedons. The differences included finer texture, higher electrical conductivity, total N, exchangeable bases (Ca, Mg and K) and effective cation exchange capacity and lower C/N ratio and exchange acidity in the mound than the pedon at each toposequence position. This tendency to modify the soil properties was more prominent in the nest body where the termites actually live, that is, in the hives, royal cell and base-plate, than in the soils below the nest and the other mound parts, that is, the external wall, internal wall and pillars. We found this trend to a greater or lesser degree at all toposequence positions. Our findings suggest that: (1) M.?bellicosus can manipulate the mound soils according to functional applications of structure units or environmental requirements for its livelihood, regardless of local soils; (2) M.?bellicosus makes ecological patches (hot spots) at all toposequence positions in the same measure; (3) the influence of M.?bellicosus on the pedogenesis is reduced in the lowlands compared with the uplands because the number and volume of the mounds were substantially lower in the bottom and fringe sites compared with the upland site.     

BASALTIC SOILS OF SOUTH-WEST ICELAND. II

Data for mechanical and chemical analyses are presented with tabulated mean and median values based on fifty-five freely drained and ten poorly drained soils. The soils are relatively coarsed textured. The sand content of the mineral fraction is about 70 per cent (mean value) for freely drained and about 45 per cent (mean value) for poorly drained soils. Organic C is generally high in freely drained soils but relatively low in poorly drained soils, because of accumulating aeolian matter in the latter group, mean values are 8.2 in freely drained and 16.5 per cent in poorly drained soils. The C/N ratio is about 15 for each soil group. The cation exchange properties including pH seem to be dominated by organic matter, which may contribute to the total CEC of the soils about 165–300 me/100 g C. CEC of soils is usually 40–50 me/100 g. For some selected soils CEC of the separated mineral fractions was confirmed experimentally through ammonia retention. The pH level, especially of the freely drained soils, is relatively high (mostly 5.4–6.3) in spite of low degree of base saturation (mostly 10–30 per cent), a characteristic probably derived from the parent material. A highly significant correlation exists between pH and organic C. Proportionally exchangeable Ca seems low, while Mg and Na may be abundant. In some soils exchangeable Mg may exceed Ca.     

Some effects of mound-building termites on the soils of a semi-arid area of Kenya

The nutrient status of soils from Macrotermes termite mounds, in and around Kajiado District, reflects that of the subsoils more closely than in some other studies, notably Watson (1977). Consequently the growth of vegetation on and around mounds was not noticeably enhanced, except in grasslands and in higher rainfall areas. There was no evidence that mounds acted as wicks. Mound soils contained greater concentrations of calcium, magnesium and potassium than subsoils in almost all cases where subsoil values were low, suggesting that the termites’ activities enhanced the nutrient status of mound soils. The nutrients were probably derived from their food, and the effects increased in some cases by their selection of clay on clay-poor soils. Nevertheless, the overall effects of Macrotermes on rangeland soils are probably small. The distribution of Macrotermes is remarkably unaffected by soil types; they construct mounds on almost all soils except those consisting largely of montmorillonite.     

Nutrient storage in termite (Macrotermes bellicosus) mounds and the implications for nutrient dynamics in a tropical savanna Ultisol

The role of mounds of the fungus-growing termite Macrotermes bellicosus (Smeathman) in nutrient recycling in a highly weathered and nutrient-depleted tropical red earth (Ultisol) of the Nigerian savanna was examined by measuring stored amounts of selected nutrients and estimating their rates of turnover via the mounds. A study plot (4?ha) with a representative termite population density (1.5?mounds?ha^?1) and size (3.7?±?0.4?m in height, 2.4?±?0.2?m in basal diameter) of M. bellicosus mounds was selected. The mounds were found to contain soil mass of 9249?±?2371?kg?ha^?1, composed of 7502?±?1934?kg?ha^?1 of mound wall and 1747?±?440?kg?ha^?1 of nest body. Significant nutrient enrichment, compared to the neighboring topmost soil (Ap1 horizon: 0–16?cm), was observed in the nest body for total nitrogen (N) and exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and in the mound wall for exchangeable K only. In contrast, available (Bray-1) phosphorus (P) content was found to be lower in both the mound wall and the nest body than in the adjacent topmost soil horizon. Consequently, the mounds formed by M. bellicosus contained 1.71?±?0.62?kg?ha^?1 of total N, 0.004?±?0.003?kg?ha^?1 of available P, 3.23?±?0.81?kg?ha^?1 of exchangeable Ca, 1.11?±?0.22?kg?ha^?1 of exchangeable Mg and 0.79?±?0.21?kg?ha^?1 of exchangeable K. However, with the exception of exchangeable K (1.2%), these nutrients amounted to less than 0.5% of those found in the topmost soil horizon. The soil nutrient turnover rate via M. bellicosus mounds was indeed limited, being estimated at 1.72?kg?ha^?1 for organic carbon (C), 0.15?kg?ha^?1 for total N, 0.0004?kg?ha^?1 for available P, 0.15?kg?ha^?1 for exchangeable Ca, 0.05?kg?ha^?1 for exchangeable Mg, and 0.06?kg?ha^?1 for exchangeable K per annum. These findings suggest that the mounds of M. bellicosus, while being enriched with some nutrients to create hot spots of soil nutrients in the vicinity of the mounds, are not a significant reservoir of soil nutrients and are therefore of minor importance for nutrient cycling at the ecosystem scale in the tropical savanna.     

Effect of different termite feeding groups on P sorption and P availability in African and South American savannas

Nest structures of six termite species, four with epigeous (above-ground) and two with subterranean nests were analysed to find out how their building and feeding habits could be related to their nests phosphorus status compared with control soils. Termite nest structure was found to affect significantly the P status in savanna soils: mounds of the African Trinervitermes geminatus and the South American Nasutitermes ephratae (both grass-feeders) displayed a greater amount of available P, especially in the inner part of the nest, than the surrounding soil. The abundant quantities of dead grass material stored in the mound can explain the available soil P increase. A similar increase in P availability was also found for the soil-feeder Cubitermes severus. In mounds of Macrotermes bellicosus, on the other hand, there was a drastic increase in P sorption (and a corresponding decrease in available P) compared to adjacent soils, which was attributed to the building strategy of this species. M. bellicosus selected clay from subsoil to build its nest structure. The data obtained for the subterranean species Ancistrotermes cavithorax and Microtermes toumodiensis indicated also that there is an increase in P sorption in mounds when compared with associated topsoils. Consequently, the nest structures of only certain termite species should be considered, and utilised, as a soil amendment in place of fertilisers. This impact on the P cycle in savannas seems to be related to the termite feeding status and to the type of material utilised in nest building. This should be taken into account before using termite nest material in soil fertility status improvement.     

Impacts of termites on selected soil physicochemical characteristics in the highlands of Southwest Ethiopia

Termites are reported to improve soil physicochemical properties thereby enhance soil fertility of their mound and foraging areas. Empirical study pertaining to these effects is missing in Southwest Ethiopia. For this study, soil samples affected by termite activities were collected at 1 m interval within 0–3 m distance from the base of six termite mounds on gently sloping and sloping land and analyzed for physicochemical parameters. The result of the analysis depicted that soil bulk density (1.38–1.15 g cm^?3) and moisture content (21.1–9.9%) decreased with increased distance from the mound base. While clay content decreased with increased distance from the mound base from72.0% to 45.5%, sand and silt contents increased from 8.0% to 21.3% and 19.3% to 28.5%, respectively. PH (6.23), organic carbon (3.85%), total nitrogen (0.4%), cation exchange capacity CEC (30.43 cmol kg^?1), exchangeable Ca (13.73 cmol kg^?1), Mg (3.15 cmol kg^?1), and PBS (56.8%) were higher on termite mounds. While, electrical conductivity (0.03 dS m^?1–0.06 dS m^?1), exchangeable K (0.52–0.93 cmol kg^?1) and Na (0.02–0.03 cmol kg^?1) showed increasing trend with the distance from the mound base. Our results indicated that termite mounds are important sinks of organic matter and mineral nutrients, and hence contribute to the enhancement of soil fertility. Thus, for subsistent farmers the uses of termite mounds as a fertilizer present an opportunity to improve agricultural production.     

Effects of termites on the physical and chemical properties of the acid sandy soils of southern Nigeria

Abstract

This study was aimed at characterizing the effects of the activity of termites of the genus Nasutitermes on the physico‐chemical properties of the acid sandy soils of southern Nigeria. Selected morphological properties of the termite mounds were measured in the field. Outside portions of the termite mound and surface (0–15 cm) soil were collected and analyzed for some physical and chemical properties. Results obtained showed a density of 112 mounds ha^‐1 with average height of 0.85 m. There were significantly higher proportions of clay, silt, and organic carbon, and higher pH, exchangeable potassium (K), calcium (Ca), magnesium (Mg), available phosphorus (P), effective cation exchange capacity and base saturation in the mounds of the Nasutitermes than in the surrounding topsoil. Mounds of Nasutitermes termites, if returned to the soil, could improve the properties of the soil in areas where termites occur in large numbers.     

THE POTASSIUM STATUS OF MALAWI SOILS

Twenty surface soils from four main Soil Groups in Malawi and their sub-soils were divided into three groups based on cation exchange capacity (group I, CEC < 50; group II, 50–100; and group III > 100μeq g^–1). In each soil group the maximum amounts of K removed by successive extraction with 0.005 M CaCl₂ solution were well related to the potassium potential pK–0.5p(Ca + Mg), exchangeable K, ‘step K’, and the quotient ‘step K’/CR.K, where CR.K is ‘constant-rate’potassium. In Group III soils only, ‘step K’/CR.K values were significantly correlated with pH, clay, and CEC, and this suggested that the soils were relatively rich in K⁺ specific binding sites. In 27 soils from an NPK factorial experiment on tea, the rate of depletion of extractable K reserve increased with ammonium sulphate treatment, whereas K fertilizers tended to off-set significantly (P= 0.001) the depletion of K reserve. The values for the change in free energy ΔG =RT In a_K/ (a_(Ca+Mg)) ^½, ranged from –12 to –16 kJ mol^–1, and field observations showed that tea plants growing on soils having ΔG values less than –15 kJ mol^–1 responded to K fertilizers. The investigation has indicated that heavily cropped soils are likely to show crop responses if the intensive cropping system does not include supplementation of K.     

SOME EFFECTS OF MOUND-BUILDING TERMITES ON SOILS IN UGANDA

Most large mounds in Uganda are built by termites of the genus Macrotermes. Except for those in valley bottoms they are composed of subsoil which is thought to be collected mainly from depths of 0.5 to 1.0 m, although the evidence is inconclusive. Mounds of both M. bellicosus and M. subhyalinus contain less sand than the subsoil when this is sandy, but only M. subhyalinus mounds contain less clay when the subsoil has a high clay content. In general both species tend to produce a stone-free topsoil whose physical properties are closer to a loam than the average subsoil. Mounds of both species in valley bottoms appear to be built from topsoil. The amounts of organic matter, nitrogen, calcium, phosphorus, and potassium in mounds were estimated together with their rates of turnover. In terms of the demands of two typical crop plants the quantities held in mounds and their rate of release to the surrounding topsoil were small. Only calcium was likely to be cycled in significant amounts. It seems that termites only slightly affect the physical and chemical properties of Ugandan soils, even where mounds are comparatively abundant.     

A rapid method to determine cation exchange capacity and exchangeable bases in calcareous,gypsiferous, saline and sodic soils

Summary

A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO₃ or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant.

In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite.

In gypsiferous soils gypsum is transformed into insoluble BaSO₄ and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na₄EDTA is used as for calcareous soils.

In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO₄ in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations.

This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.     

Possible influence of termites (Macrotermes bellicosus) on forms and composition of free sesquioxides in tropical soils

There has been less concern about soil mineralogical alteration than about soil physical, chemical and biological changes induced by termite nest-building activity. Furthermore, much less attention has been paid to free sesquioxides than to phyllosilicate minerals. In the present study, we conducted field morphological observations and selective dissolution analysis to characterize free sesquioxides in termite (Macrotermes bellicosus) mounds as compared with surrounding pedons in different toposequence positions, i.e., seasonally flooded valley bottom, hydromorphic fringe and well-drained upland sites. Distinctive redoximorphic features, such as surface yellowish layers on mound structures from the fringe site, indicate possible alteration of iron sesquioxide forms in the mounds due to the transportation of soil from reductive (aquic subsoil) to oxidative (epigeal mound) environments by the nest-building activity of M. bellicosus. On the other hand, the iron-soluble content in the dithionite-citrate-bicarbonate (DCB) system (Fe_d) was generally higher in the mound structures than at the adjacent sub-surface (Ap2) horizon at each toposequence position, while there was less difference in the content of acid ammonium oxalate (AAO) extractable iron (Fe_o) as compared to Fe_d. As a consequence, the iron activity index (Fe_d/Fe_o ratio) was found for the most part to be lower in the mound structures than in the neighboring Ap2 horizon. In addition, the content of Fe_d, AAO-soluble Al (Al_o) and DCB-extractable Al (Al_d) was significantly correlated with clay content in these soils. These findings suggest that M. bellicosus preferentially collects clay particles, probably from the clay-rich subsoils, such as the argillic horizon, which has been formed by the co-migration of phyllosilicate minerals and relatively crystalline sesquioxides. The species then likely incorporates them into the mounds, which induces an increase in the Fe_d content relative to that of Fe_o, resulting in a decreased iron activity index in the mound structures.     

Aggregate formation in salt-affected soils of the Baer mounds

Particle-size and microaggregate-size distributions and the morphology of aggregates <1 mm have been studied in soils of the Baer mounds. It is shown that the soil aggregates contain specific clayey-salt microaggregates and coatings. The type of the clayey-salt pedofeatures (microaggregates and/or coatings) depends on the clay content in the soils, and the size and shape of the clayey-salt microaggregates depends on the concentration and chemistry of salts participating in their formation. The clayey material of the micro-aggregates is mainly represented by smectitic minerals. Calcareous (calcitic, dolomitic, and iron-bearing) clayey-salt microaggregates have been found in all the horizons of investigated soils, except for the Ap horizon of the soil of the former rice paddy in the hollow between the Baer mounds. Clayey-salt microaggregates with simultaneous participation of several different salts (chlorides and sulfates of Na, Mg, and Ca) have been detected in the solonchakous soil at the foot of the Baer mound. For the first time, quasicrystalline formations—pentagonal NaCl crystals of up to 3 μm in size with participation of phyllosilicates and sulfates of Na and Mg—have been described under native conditions in the B2 horizon of the solonchak. It is argued that the formation of clayey-salt aggregates contributes to the good microaggregation of the soils and to the stability of the Baer mounds under conditions of the arid climate.     

Soil property changes following conversion of acacia woodland into grazing and farmlands in the Rift Valley area of Ethiopia

Continued conversion of woodlands into grazing and farmland is seriously undermining the natural ecosystem of the dry and fragile Rift Valley areas of Ethiopia. This study investigated the effects of land‐use change on soil organic carbon (SOC), total nitrogen (N), pH, exchangeable bases, cation exchange capacity (CEC) and base saturation (per cent) in three adjacent land‐use types: controlled grazing, open‐grazing and farmland. A total of 81 soil samples were collected and analysed. Contents of SOC and total N decreased drastically in open‐grazing and farmland (p < 0·001), and were significantly higher in the top 0·2 m than in the subsurface soil layer. Compared with the controlled grazing, reductions in the contents of SOC and total N in the top 1 m soil layer were 22–30 and 19 per cent, respectively, due possibly to the decrease in plant biomass input into the soil and the fast decomposition of organic materials. Long‐term cultivation had significantly increased the concentration of exchangeable K. Exchangeable Na was high in the lower layers, while Mg was higher in the top surface soil. CEC also varied with soil depth (p = 0·016); it was higher in the topsoil than in the subsurface soil, which may be, among others, due to the differences in soil organic matter distribution with depth. Although these semi‐arid soils are known to have low organic carbon and CEC levels, the values from the current study area are critically low, and may indicate the further impoverishment of the soils under high agricultural and grazing pressures. Copyright © 2010 John Wiley & Sons, Ltd.     

Termite mounds in relation to the surrounding soils in the forest and derived savanna zones of southeastern Nigeria

Some physical and chemical properties of the two common termite mounds in southeastern Nigeria, Macrotermes (MM) and Cubitermes (CM) mounds, were compared and their relationships with the surrounding top and subsoils investigated. Percentage sand, silt, pH, calcium, magnesium, potassium, sodium, iron, and organic carbon were higher and clay and penetrometer resistance lower in the CM than the MM. Sand, silt, organic carbon, and calcium decreased and clay increased from the forest to the derived savanna in the CM, but no clear trend was shown with the other properties in both the CM and the MM. Most of the nutrients were higher in the CM than in the adjacent top or subsoil but the reverse was the case with the MM. More nutrients are associated with the inorganic fractions of the soil than with the organic carbon in the mounds and the soils surrounding them. The Ca:Mg ratio in the mounds and the top and subsoils adjacent to them was low for most crops but the K:Mg ratio was mostly adequate. Because of these differences in properties and sizes of the mounds, different management strategies are recommended for them and the soils around them.     

Die Böden von Wallhecken in Schleswig-Holstein I. Klassifikation und Genese

Soils of Mound Hedges in Schleswig-Holstein I. Classification and Genesis In typical landscapes of Schleswig-Holstein soils of mound hedges were investigated (FAO (1989): Cumulic Anthrosol). New soils have been developed from the deposit of the mound hedge in less than 250 years. A classification with regard to the German classification of natural soils is suggested. The soil genesis from sandy deposits has reached the step of Dystric Regosols, groundwater has induced gleyic features. Soil genesis could be described chronologically, if time of deposition of these mound hedges is known. Some of the natural soils are conserved below the deposit. Pedogenesis in an area, changed by man, could be reconstructed. This is why systematic, scientific soil investigations of mound hedges may be very interesting.     

Seasonal and diurnal CO2 efflux from red wood ant (Formica aquilonia) mounds in boreal coniferous forests

Organic mounds of the red wood ants (Formica rufa group; RWA) have been shown to be “hot spots” of carbon dioxide (CO₂) efflux from the European forest soils. However, little information is available on the variability of CO₂ effluxes from RWA mounds and on the factors regulating CO₂ efflux. We assessed the seasonal and diurnal changes in CO₂ effluxes, temperatures and volumetric water contents from mounds of Formica aquilona, the important RWA of the boreal forests in Finland. The daily average CO₂ efflux from RWA mounds ranged 1.1-6.9 g CO₂ m⁻² h⁻¹ during the active ant season (May-September), and from 0.2 to 1.1 g CO₂ m⁻² h⁻¹ during their dormant period (October-April). Mound CO₂ efflux from May to September was 3.6-6.0 times higher than from the surrounding forest floors, and most likely came from RWA respiration. Seasonal changes in mound CO₂ effluxes were significantly correlated with mound temperature, but not with volumetric water content (7% on average). The high CO₂ efflux associated with increased volumetric water content (up to 34%) after a RWA mound was abandoned indicated that these dry mound conditions restrict microbial decomposition of mound organic matter. CO₂ effluxes were highest at night and lowest during the day, which is likely due to an increased ant activity or numbers in the mound at night. Diurnal changes in mound CO₂ efflux were negatively correlated with air temperature, and positively correlated with the difference between the mound and air temperature. This suggests that thermal convection of warmer mound air to the colder outside air at night might be also a cause of the diurnal changes. We conclude that seasonal and diurnal variations in mound CO₂ effluxes are dependent on RWA activities and fluctuation in RWA mound and outside temperatures.     

鹅凰嶂山地雨林土壤阳离子交换量和交换性盐基离子分布特征

  目的  探究广东阳春鹅凰嶂山地雨林土壤阳离子交换量和交换性盐基离子的空间分布特征,了解该区域森林土壤的保肥能力及其影响因子。  方法  以鹅凰嶂山地雨林内不同位置、不同土层土壤作为研究对象,分析土壤阳离子交换量和交换性盐基离子空间分布格局、剖面垂直分布规律。  结果  鹅凰嶂山地雨林土壤阳离子交换量5.46 ± 0.97 cmol(+) kg?1,交换性阳离子呈现明显表聚现象;土壤交换性盐基总量在表层土（0 ~ 10 cm）中呈现阴坡 > 阳坡、下坡位 > 中坡位 > 上坡位的规律,土壤盐基离子含量基本呈现K+ > Mg2+ > Ca2+ > Na+的趋势,且Ca2+/Mg2+ < 1.6;土壤阳离子交换量、交换性盐基总量与土壤总有机碳含量呈极显著正相关。  结论  鹅凰嶂山地雨林土壤的保肥能力较差,且存在生理性缺钙的风险,阳坡尤为明显;同时存在土壤有机质稳定性不高导致阳离子交换量下降的潜在风险。     

Die Böden von Wallhecken in Schleswig-Holstein. II. Aufbau und Umsetzung der organischen Bodensubstanz

Soils of Mound Hedges in Schleswig-Holstein. II. Composition and Transformation of Soil Organic Matter Two Cumulic Anthrosols of mound hedges and the fossil A-horizons below the deposits, were investigated by means of wet chemistry and ¹³C-NMR spectroscopy in order to characterize soil organic matter (SOM) and to compare their SOM with natural and recent soils. The bulk humus of the Cumulic Anthrosols contains a high amount of easily soluble polysaccharides. Despite their high bioavailability sugars, starch and mobile fulvic acids are not completely consumed by microorganisms and translocated into the subsoil. The initial phase of podzolization is indicated due to this process and the very low pH-level of the soils. After deposition about 30 % of the soil carbon in the A-horizons is mineralized. Litter compounds are predominantly decomposed, whereas humic compounds are selectively preserved or newly synthesized. The significance of the humic compounds in the soil organic matter increases after deposition. This is why the potential cation exchange capacity of the fossil Ahorizons is similar to this of the recent ones.     

Chemical,physical and micromorphological properties of termite mounds and adjacent soils along a toposequence in Zona da Mata,Minas Gerais State,Brazil

Little is known about the effects of neotropical mound-building termites in soil chemical and physical properties. The influence of soil termite activity on soil characteristics was studied by assessing chemical, physical and micromorphological properties of a toposequence of Latosols (Oxisols). Soil samples were collected from the walls and inner parts of termite mounds and also from adjacent soil. A high diversity of termite genera was found in the mounds along the toposequence, together with the inquiline termites and other soil-dwelling arthropods. Chemical analyses showed that pH and the contents of organic C and N, P, Ca and Mg were significantly higher in termite mounds compared with adjacent areas, with an inverse trend for Al content. Significant differences in pH and exchangeable Al were observed between soil and mound across the slopes. The mound density across the landscape was higher at the upper slope segment, followed by the hill top, middle slope and lower slope segments. Considering a lifespan of 30 years and dimensions of termite mounds found in the toposequence we conclude that the textural and chemical uniformity of Latosols may be increased, following the pedobiological turnover during mound building, with local rates varying from 2.1 to 7.5 m³ ha^− 1.