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Soil Diversity in the Tropics
Abstract
Given that 40% of the terrestrial surface lies between the tropics, it should not be surprising that soils across the tropics are diverse. Soils in the tropics are also relatively unexplored and are poorly documented. Continued overgeneralization about so-called "tropical soils" initiated this paper's research, which documents that not only do the tropics contain all soil orders but that they are remarkably diverse. Much is to be learned from this perspective, not only about soil diversity in the tropics but about how science itself comes to grips with Earth's remarkable realities.
... Tropical rainforests host the most diverse plant communities on Earth and are of key importance in regulating the global carbon and water cycles (Hawkins et al. 2003, Richter et al. 2009). Tropical soils are usually more weathered than soils in temperate regions and contain less nutrients (Cardoso & Kuyper 2006, Jobbágy & Jackson 2001, Moreno-Jiménez et al. 2023, Richter & Babbar 1991, which can have a positive effect of increasing biodiversity through niche separation and species specialisation (Nadeau & Sullivan 2015, Richter et al. 2009). Biodiversity levels can be further enhanced in mountainous areas with diverse topography and microclimates, which are likely present in the study area in Eastern Ecuador (Graae et al. 2018, Maclean et al. 2015. ...
... The high water inputs from precipitation in the Amazon basin can increase the elution of nutrients from soil by leaching (Richter & Babbar 1991, Stallard & Edmond 1983, which can lead to soil acidification when extended amounts of bases are swamped out. This manifests in low soil pH, for example, the case for the plots on Cerro Copales (WIS9 and WIS10). ...
Ferns (Polypodiophyta) are an abundant floral element of the tropics with high sensitivity to environmental conditions and good indicators of overall biodiversity. Here, we set out to identify which geochemical factors determine fern diversity in a low-montane tropical rainforest in Eastern Ecuador. We conducted a field survey of high-spatial resolution completing a comprehensive fern inventory across two elevational ranges, combined with biochemical characterisation of the underlying soils. While α-diversity was negatively correlated with cation exchange capacity (CEC) and with elevation, β-diversity increased with elevation and with geographic
distance, as predicted. Our results confirm that ferns have a high sensitivity to both elevational and environmental gradients, where the latter in this study was derived from enhanced aluminium, iron and calcium contents in some of the studied soils. Further monitoring of fern communities could therefore help to better understand and predict how environmental change may impact biodiversity, with a particular focus on threats potentially arising from toxic elements being released in tropical soils through modified soil CEC.
... A full accounting of the factors affecting soil moisture also requires consideration of soil properties, especially soil texture (Quesada et al., 2012;Richter & Babbar, 1991). In general, the ecological effects of the soil water regime will depend on the degree of soil saturation in the wet months, the degree and frequency of water deficit periods, the water-holding capacity of the soil and the root distribution in the soil (Franco & Dezzeo, 1994). ...
... In general, the ecological effects of the soil water regime will depend on the degree of soil saturation in the wet months, the degree and frequency of water deficit periods, the water-holding capacity of the soil and the root distribution in the soil (Franco & Dezzeo, 1994). By having higheraggregation particles, clayey soils have better water-holding capacity (Richter & Babbar, 1991); therefore, clay soils should increase the time interval between precipitation inputs and groundwater recharge, whereas predominantly sandy soils should have faster groundwater level responses to precipitation. Our results suggest a contribution of clayey texture in increasing productivity in dry climates with a shallow water table (Figure 5c). ...
Aim
Water availability is the major driver of tropical forest structure and dynamics. Most research has focused on the impacts of climatic water availability, whereas remarkably little is known about the influence of water table depth and excess soil water on forest processes. Nevertheless, given that plants take up water from the soil, the impacts of climatic water supply on plants are likely to be modulated by soil water conditions.
Location
Lowland Amazonian forests.
Time period
1971–2019.
Methods
We used 344 long‐term inventory plots distributed across Amazonia to analyse the effects of long‐term climatic and edaphic water supply on forest functioning. We modelled forest structure and dynamics as a function of climatic, soil‐water and edaphic properties.
Results
Water supplied by both precipitation and groundwater affects forest structure and dynamics, but in different ways. Forests with a shallow water table (depth <5 m) had 18% less above‐ground woody productivity and 23% less biomass stock than forests with a deep water table. Forests in drier climates (maximum cumulative water deficit < −160 mm) had 21% less productivity and 24% less biomass than those in wetter climates. Productivity was affected by the interaction between climatic water deficit and water table depth. On average, in drier climates the forests with a shallow water table had lower productivity than those with a deep water table, with this difference decreasing within wet climates, where lower productivity was confined to a very shallow water table.
Main conclusions
We show that the two extremes of water availability (excess and deficit) both reduce productivity in Amazon upland ( terra‐firme ) forests. Biomass and productivity across Amazonia respond not simply to regional climate, but rather to its interaction with water table conditions, exhibiting high local differentiation. Our study disentangles the relative contribution of those factors, helping to improve understanding of the functioning of tropical ecosystems and how they are likely to respond to climate change.
... Yet, little is known about the patterns and controls on fine-root morphological traits in the tropical forest biome, despite the fact that these forests generally have similar or higher levels of fineroot production and turnover compared to other forest biomes (Finér et al. 2011). Given the substantial heterogeneity in climate, particularly MAP, as well as in soil types and soil biota in tropical forests (Davis et al. 2003;Richter and Babbar 1991), fine-root morphology may be expected to vary widely among tropical forests. For instance, there is considerable heterogeneity in soil orders (such as Ultisols, Oxisols, Inceptisols, Entisols, Andisols, Aridisols and so on), and their physical and chemical properties, including P availability within and among tropical regions (Richter and Babbar 1991;Dalling et al. 2016;Fujii et al. 2018), and this may eventually reflect in the alterations of the morphology of plant roots (Kochsiek et al. 2013;Lugli et al. 2019). ...
... Given the substantial heterogeneity in climate, particularly MAP, as well as in soil types and soil biota in tropical forests (Davis et al. 2003;Richter and Babbar 1991), fine-root morphology may be expected to vary widely among tropical forests. For instance, there is considerable heterogeneity in soil orders (such as Ultisols, Oxisols, Inceptisols, Entisols, Andisols, Aridisols and so on), and their physical and chemical properties, including P availability within and among tropical regions (Richter and Babbar 1991;Dalling et al. 2016;Fujii et al. 2018), and this may eventually reflect in the alterations of the morphology of plant roots (Kochsiek et al. 2013;Lugli et al. 2019). Furthermore, the high variability in floristic and structural composition as well as mycorrhizal fungal associations in different tropical regions could be mirrored in morphological traits of roots (Banin et al. 2012;Brundrett and Tedersoo 2018;Fujii et al. 2018). ...
Key functions of fine roots are often related to their morphological traits, yet little is known about the patterns and controls on fine-root morphological traits in the tropical forest biome. In this study, we consolidated data on key root morphological traits to describe patterns of root trait variation among different tropical regions and examined the relationships among root traits and climate and soil properties. We synthesized root traits (root diameter, specific root length (SRL), specific root area (SRA) and root tissue density (RTD)) from 59 site observations from nine countries in Africa, Asia, and Central and South America to determine the patterns and variation in root traits among different tropical regions. We also examined relationships among fine-root morphological traits, climate (mean annual precipitation, MAP; mean annual temperature, MAT) and soil properties (including available phosphorus (P), base saturation and clay content) using linear mixed-effects modelling. Plant fine-root morphological traits showed systematic variation among tropical regions—Africa, Asia and the Neotropics. Across the tropical biome, SRL was positively related to MAT, suggesting that in warmer tropical sites, plants tended to produce thinner roots with high SRL. Specific root length and SRA were positively related to base saturation, while soil available P explained some of the variation in SRL. This study demonstrates that soil properties, and to a lesser extent MAT, partially explain variation in key fine-root morphological traits across tropical forests. Importantly, we also identified wide variation in fine-root morphological trait values in the tropical biome that encompasses much of the variation seen worldwide. Consequently, attempts to predict tropical forest ecosystem functioning could improve significantly if regional differences in root traits are incorporated into process-based models.
... In humid tropical lowlands, high temperatures acting in concert with low activity minerals are believed to limit SOC stabilization by driving rapid rates of carbon mineralization and recycling (Malhi et al., 1999). However, this high temperature -low SOC idea overlooks the potential of subsoil horizons storing high proportions of SOC stocks at depth (Richter and Babbar, 1991). Deeper SOC stocks have slower turnover times due to soil mineralogical and chemical factors, the mechanisms behind which remain unclear (Jackson et al., 2017;Rumpel and Kögel-Knabner, 2011). ...
... The strong control by precipitation reflects Gabon's climatic gradient, which varies threefold from the wet northwest to the arid southeast. Precipitation has direct control on promoting or inhibiting microbial respiration and decomposition, a regulator of soil carbon storage (Richter and Babbar, 1991). Greater annual precipitation is associated with increased soil carbon stores, as wetter climates slow down decomposition and promote leaching of SOC to subsoil layers (Jenny, 1980;Post et al., 1982). ...
... There are commonly highly weathering soils distributed in tropical region, with extremely intensive leaching, low organic carbon content, and low nutrient retention (Richter and Babbar 1991). Such soils have high concentrations of Fe/Al oxides that fix strongly with phosphate, leading a large proportion of P occurs in occluded forms associated with secondary minerals (He and Zhu 1997;Tiessen 1998;Li et al. 2016). ...
Purpose
The turnover of organic phosphorus (Po) may be an important way to maintain P supply for plant growth under the phosphorus (P) deficiency in highly weathered tropical soils. However, there is limited information on Po change pattern and how abiotic and biotic factors influence Po transformation in tropical region. Thus, this study was aimed to the characteristics and controls of Po transformation towards the advanced stage of tropical soil evolution.
Methods
A well-establish tropical soil chronosequence (0.09, 0.146, 0.64, 1.12, 1.81, and 2.30 million years) derived from basalt in northern Hainan Island, China, was selected and the Po compounds in all soils determined by solution ³¹P nuclear magnetic resonance spectroscopy.
Results
Phosphate monoester showed a rapid increase in the earlier stage of pedogenesis (< 0.15 million year), thereafter declined to the minimum in the 1.12-million-year site and fluctuated in older soils. Meanwhile, the proportion of labile Po (including phosphate diester and its degradation products) increased continuously across the chronosequence, suggesting that long-term tropical soil evolution promoted labile Po accumulation that was vital to maintain P supply in highly weathered and P-deficient soil. Redundancy analysis revealed that Po transformation was jointly affected by soil total nitrogen, total organic carbon, phytase, and amorphous iron, accounting for 37.5% (p < 0.01), 29.5% (p < 0.01), 20.7% (p < 0.05), and 14.8% (p < 0.05) of explanation in the variations of Po compounds, respectively.
Conclusion
Our study has supplemented the blank of Po transformation during tropical soil evolution over a 2.30-million-year time scale and emphasizes the important role of soil C, N in regulating Po changes.
... This enables them to minimise the loss of growth-constraining nutrients and to be less dependent on nutrient uptake from the soil (van Heerwaarden et al., 2003). From the leaf economic perspective, P resorption is assumed to be higher in P-limited tropical soils (Aerts & Chapin, 1999), although such relationship may vary due to strong heterogeneity in tropical soils (Richter & Babbar, 1991). ...
Soil nutrients can limit productivity on highly weathered soils, but vegetation can adopt a range of strategies to maintain productivity under low nutrient supply. Using a full nutrient flux approach, we examine nutrient use strategies across nine old-growth and logged lowland moist tropical forests in Malaysian Borneo. Soil nutrient availability was a weak predictor of productivity. We explored the reasons for this by examining the vegetation biogeochemical cycles of five key macro- and micronutrients. For nitrogen (N), we found very little evidence of nutrient limitation. Four nutrients showed evidence of shifting strategies under limitation, with clear evidence for quantifiable thresholds below which compensation strategies were invoked and contrasting resource optimization strategies employed for each nutrient. For potassium (K), enhanced leaf resorption was the primary strategy for coping with supply limitation. For calcium, shifting stoichiometry was the primary strategy. For phosphorus (P), a combination of both enhanced resorption and shifting stoichiometry was observed. The strongest relationships were found for P and K, with old-growth forests at this site showing some limitation and logged forests having sufficient nutrient supply. This study reveals the potential of nutrient flux approaches to describe the multifaceted and non-linear relationship between soil nutrient supply and uptake, and biomass productivity.
... This regional differences in the soil physical and chemical properties, probably suggests that there were variations in soil forming factors across the regions (Ceddia et al. 2009;Homann et al. 2007). According to Richter et al. 1985 cited in Richter and Babbar (1991) consequently in uence plant growth and development but also predisposes plants to diseases amongst others. Severity of race 1 strains on Fusarium wilt disease appeared to be related to a number of individual soil properties. ...
Background and Aims
If there is no effective control for a plant disease it is essential to look for other solutions. This study analyzed the interactions between soil conditions and the severity of race 1 strains of Fusarium wilt disease in different banana cropping systems in Uganda.
Methods
A survey was conducted in three regions of Uganda. The severity of race 1 Fusarium wilt on susceptible bananas was studied in various banana cropping systems. Soil samples were collected in each of the cropping systems from the different regions for both laboratory soil analyses and pot experiments.
Results
There were considerable differences in the soil chemical and physical status at regional level. Cropping systems also exhibited significant differences in potassium, calcium, magnesium, phosphorus and manganese contents in the soil. Soil properties were clearly correlated to the severity of race 1 strains of Fusarium wilt varied at different levels of the individual soil properties. Also soil types exhibited significant differences in their individual soil properties and severity of race 1 strains of Fusarium wilt disease. Similar results were also found in a pot experiment under controlled conditions.
Conclusion
Soil types with a high pH, high in potassium, calcium, available phosphorus and low in manganese and clay contents appear to be suppressive to race 1strain of Fusarium wilt in bananas.
... Farms are heterogeneous, characterized by important spatial variation in growing conditions, natural capital endowments, and market access (Richter and Babbar, 1991;Rosenzweig and Udry, 2020;Porteous, 2020). Such across-farm heterogeneity affects returns to technology adoption and, consequently, input adoption and use (Marenya and Barrett, 2009;Suri, 2011;Zingore et al., 2007;Suri and Udry, 2022;McCullough, Quinn and Simons, 2022). ...
... In Amazonia, soils are heterogeneous (Richter and Babbar, 1991) and shape the distribution and dynamics of the exceptional rainforest biodiversity (Cámara-Leret et al., 2017;Figueiredo et al., 2018;Schaefer et al., 2008;Tuomisto et al., 2003aTuomisto et al., , 2003b. One of the first attempts to document the spatial patterns in Amazonian geochemistry was done by Fittkau et al. (1975), who distinguished western Amazonia with young nutrient-rich soils of Andean origin, central Amazonia with nutrientpoor highly weathered soils, and peripheral northern and southern regions with intermediate soils derived from cratonic rocks. ...
... The greatest number of studies on ADEs have been of the anthropological type and little is known about their genesis (Woods and Mann, 2000). About 70 percent of the Amazon basin is composed of mainly very acid, highly weathered natural soils with poor availability of the most important plant nutrients (Richter and Babbar, 1991). There are, however, small patches of anthropogenic soils known as ADEs with completely different characteristics: ADEs are usually less acid with better cation exchange capacity and base saturation than natural soils (Glaser et al., 2001). ...
Black soils are carbon-rich and highly fertile soils known as the world's food basket due to the variability of crops they sustain. For decades, these fertile soils have been widely cultivated and have played a key role in global agricultural production of cereals, tuber crops, oilseed, pastures, and forage systems. In addition, black soils play an important role on climate change mitigation and adaptation. However, this black treasure is under threat. Because of land use change from natural grasslands to cropping systems, unsustainable management practices and excessive use of agrochemicals, most of the black soils have lost half of their soil organic carbon stocks and suffer from moderate to severe erosion processes, as well as nutrient imbalances, acidification, compaction and soil biodiversity loss.
FAO and its Global Soil Partnership are committed to the conservation and sustainable management of black soils and established the International Network of Black Soils. This report provides strategic information about the distribution, state and management of black soils and can guide decision-making regarding the sustainable management and conservation of black soils. One of the main recommendation of this report is the establishment of a global agreement for the sustainable management (for conservation, protection and production) of black soils. Sustainable management of black soils contributes to the Sustainable Development Goals (SDGs), particularly the SDG 1 (No poverty), SDG 2 (Zero hunger), along with other SDGs such as SDG 13 (Climate Action), SDG 15 (Land degradation neutrality), and SDG 17 (Partnerships for the Goals). It is also aligned with the four betters of the FAO Strategic Framework 2022-2031: better production, better nutrition, better environment, and a better life, leaving no one behind.
... Plants can only take up P from the soil in its anionic forms (H 2 PO 4 − or HPO 4 2− ). However, only 0.1% of the total P in soil solution is in the form of available P, and plant P uptake ability differs between cultivars (Richter and Babbar 1991). There are two types of P-deficient soils: soils with a low total P content overall, and soils with high total P content but low levels of available P (Driessen et al. 2001). ...
Soybean growth is frequently hampered by a lack of phosphorus (P). This study aimed to screen soybean cultivars for low P tolerance using cultivars from the Japanese core collection. Eighty-one soybean cultivars were grown in soil cultures for 25 days after transplanting. The plants were subjected to P treatment (− P treatment: 0 g P2O5 kg−1 soil; and + P treatment: 1 g P2O5 kg−1 soil). Shoot dry weight, root length, P concentration, and P uptake were measured at 25 days after transplanting. Low P-tolerant and low P-sensitive cultivars were selected based on multiple criteria, including shoot dry weight, P utilization efficiency, and low P tolerance (LPT) value. The shoot dry weight of 30 soybean cultivars was lower in − P than in + P. The root length showed a significant and positive correlation with P uptake, P utilization efficiency, and dry weight in the − P and + P treatments. The LPT values of soybean cultivars ranged from 8 to 160%. The low P-tolerant and -sensitive soybean cultivars can be used as study materials in future studies to elucidate the mechanism of low P tolerance in soybeans.
... The greatest number of studies on ADEs have been of the anthropological type and little is known about their genesis (Woods and Mann, 2000). About 70 percent of the Amazon basin is composed of mainly very acid, highly weathered natural soils with poor availability of the most important plant nutrients (Richter and Babbar, 1991). There are, however, small patches of anthropogenic soils known as ADEs with completely different characteristics: ADEs are usually less acid with better cation exchange capacity and base saturation than natural soils (Glaser et al., 2001). ...
Black soils are carbon-rich and highly fertile soils known as the world's food basket due to the variability of crops they sustain. For decades, these fertile soils have been widely cultivated and have played a key role in global agricultural production of cereals, tuber crops, oilseed, pastures, and forage systems. In addition, black soils play an important role on climate change mitigation and adaptation. However, this black treasure is under threat. Because of land use change from natural grasslands to cropping systems, unsustainable management practices and excessive use of agrochemicals, most of the black soils have lost half of their soil organic carbon stocks and suffer from moderate to severe erosion processes, as well as nutrient imbalances, acidification, compaction and soil biodiversity loss.
FAO and its Global Soil Partnership are committed to the conservation and sustainable management of black soils and established the International Network of Black Soils. This report provides strategic information about the distribution, state and management of black soils and can guide decision-making regarding the sustainable management and conservation of black soils. One of the main recommendation of this report is the establishment of a global agreement for the sustainable management (for conservation, protection and production) of black soils. Sustainable management of black soils contributes to the Sustainable Development Goals (SDGs), particularly the SDG 1 (No poverty), SDG 2 (Zero hunger), along with other SDGs such as SDG 13 (Climate Action), SDG 15 (Land degradation neutrality), and SDG 17 (Partnerships for the Goals). It is also aligned with the four betters of the FAO Strategic Framework 2022-2031: better production, better nutrition, better environment, and a better life, leaving no one behind.
... This characteristic has been used to support the assumption that deep SOC sequestration is negligible or resistant to surface environment change (Chabbi et al., 2009;Li et al., 2021). However, this assumption is likely to overlook the potential of deep soil horizons in storing high proportions of SOC stocks at depth (Richter and Babbar, 1991). Moreover, deep SOC may have a significantly different response to global change than surface soil layers (Bernal et al., 2016). ...
Soil organic carbon is one of the most commonly used indicators of soil health, as it plays a vital role in maintaining fertility and combating global warming. Understanding the vertical distribution and controlling factors of organic carbon in the entire regolith, rather than just the routinely defined upper 1 m portion of the soil, is crucial for assessing soil health in a holistic perspective. In this study, 21 boreholes in four different land uses were drilled from the land surface down to the bedrock in a typical subtropical agricultural watershed. The total organic carbon stock in the regolith ranged from 77.8 Mg C ha⁻¹ to 311.8 Mg C ha⁻¹ and the organic carbon content showed a progressive decline from land surface to bedrock. However, on average, only 19.0% of total organic carbon was stored at the depth 0–30 cm and 17.7% between 30 and 100 cm, whereas 63.3% was stored below 100 cm. Total organic carbon stock was significantly higher under paddy fields than under cropland, orchard or woodland in the upper 100 cm (p < 0.05) possibly due to straw incorporation, flooding of the paddy soils and their position on the lower slopes where eroded soil was deposited. However, there was no significant difference in total organic carbon stock below 200 cm (p > 0.05). According to the boosted regression tree analysis, soil texture outperformed the other edaphic factors and was the primary edaphic factor controlling TOC content of the different soils. The results show that there is a large carbon reservoir in the deep regolith. Land use strongly affects the distribution of carbon in the top 100 cm soil layers but has little effect on deep soil organic carbon. Deep TOC were closely linked to soil texture. This study highlights the importance of deep soil organic carbon for soil health and understanding the factors controlling its content for improved estimates of soil carbon storage.
... The concept of edaphic factors as associated with plant species distribution is not new (Grubb 1989;Richter and Babbar 1991). However, ecological studies have long been interested in a mechanistic understanding underpinning species distribution patterns in terms of physiological processes. ...
Background
The Cerrado of central Brazil—the world’s largest Neotropical savanna – is comprised of a mosaic of highly heterogeneous vegetation growing on an extremely diverse geologic and geomorphologic background. Geomorphic processes under stable tectonic and climatic conditions facilitated the development of diverse edaphic properties, which interact with disturbance events to form unique vegetation types.
Scope
In this review, we detail how the geophysical environment affects soil formation and evaluate the mechanisms through which edaphic conditions control vegetation structure, floristic diversity and functional diversity.
Conclusion
The influence of geomorphic processes on edaphic properties has a marked impact on the ecology and evolution of plant communities. Species exhibit morphological and physiological adaptations that optimise their successful establishment in particular soil conditions. Furthermore, fire disturbance alters these soil-vegetation associations further regulating the structural nature of these communities. Therefore, we propose an integrative view where edaphic, chemical and physical properties act as modulators of vegetation stands, and these conditions interact with the fire regime. The knowledge of plant edaphic niches, their functional traits related to resource acquisition and use, as well as the interaction of edaphic properties and disturbance regimes is paramount to research planning, conservation, and successful restoration of the full diversity of Cerrado vegetation types.
... Tropical landscapes are characterized by enormously high edaphic diversity, with soils ranging from pedologically young Entisols and Inceptisols to pedologically old Ultisols and Oxisols [1][2][3]. This edaphic variation exerts strong control over ecosystem functioning and dynamics [4], including in the tropical dry forest (TDF) biome, which exhibits high soil heterogeneity. ...
Pantropical variation in soils of the tropical dry forest (TDF) biome is enormously high but has been poorly characterized. To quantify variation in the global distribution of TDF soil physical and chemical properties in relation to climate and geology, we produced a synthesis using 7500 points of data with gridded fields representing lithologic, edaphic, and climatic characteristics. Our analyses reveal that 75 TDF ecoregions across five biogeographic domains (Afrotropical, Australasian, Indo-Malayan, Neotropical, and Oceanian) varied strongly with respect to parent material: sediment (57%), metamorphic (22%), volcanic (13%), and plutonic (7%). TDF ecoregions support remarkably high variability in soil suborders (32), with the Neotropical and Oceanian realms being especially diverse. As a whole, TDF soils trend strongly toward low fertility with strong variation across biogeographic domains. Similarly, the exhibited soil properties marked heterogeneity across biogeographic domains, with soil depth varying by an order of magnitude and total organic C, N, and P pools varying threefold. Organic C and N pool sizes were negatively correlated with mean annual temperature (MAT) and positively correlated with mean annual precipitation (MAP). By contrast, the distribution of soil P pools was positively influenced by both MAT and MAP and likely by soil geochemistry, due to high variations in soil parent material across the biogeographic domains. The results summarized here raise important questions as to how climate and parent material control soil biogeochemical processes in TDFs
... In addition, soil type is another important sub-layer of the environmental condition criterion. This study used the soil type classification map based on the US soil taxonomy system (Richter & Babbar, 1991) to extract the soil raster layer Fig. 7. shows the GIS processed environmental impact layers in the study area. ...
The growing problem of urban water shortage and its sustainable management methods is one of today’s critical research needs globally. This paper applies an integration of the Geographic Information System (GIS) and Multi-Criteria Decision-Making (MCDM) with the help of triangular fuzzy sets to manage urban water supply priorities in a semi-arid region. Hence, a group decision-making approach was proposed by combining the Fuzzy AHP (FAHP) and the Fuzzy TOPSIS (FTOPSIS) models based on quantitative and qualitative criteria. Therefore, a hierarchical model-based GIS and AHP was developed to classify the effective criteria and determine the Importance Weights (IWs) of criteria according to the experts’ opinions and using data layers based on spatial criteria. The priority ranking of scenarios was obtained using the FTOPSIS method. Different criteria such as environmental, geographical, geological, economic, climatic, and social conditions were considered in this study. Furthermore, to assess the water supply scenarios under the essential water demands of the basin cities and suburbs, a hydrologic model utilizing WEAP software was designed. Among the considered criteria, total expense, climatic conditions, and geographic conditions with the IWs values of 0.9, 0.85, and 0.83 were determined as the most effective criteria for evaluating the scenarios' ranking, respectively.
... The mineral release is also inhibited by the acidic nature of many tropical soils. The soil types derived from the bedrock underlying tropical forests are mainly soils called oxisols and ultisols (Richter and Babbar, 1991). ...
Disturbed subgrade soil samples were collected from five (5) different erosion sites in Anambra State, Nigeria. In-situ and laboratory tests were conducted to ascertain the biochemical, physicochemical, and geotechnical properties of these samples. The topsoil characteristics were studied differently from the subsoil characteristics. All the samples considered were non plastic (from Atterberg limit tests). The result of relative size of soil particles in Anambra state reveals a higher mean values of sand when compared to silt and clay. The maximum dry density of the soil averaged (1858.19 ± 52.257) kg/m 3 and (1866.986 ± 50.298) kg/m 3 for the topsoil and subsoil respectively indicating high compaction values. The sodicity (Sodium Absorption Ratio and Exchangeable Sodium Percentage) of the soil was used to measure the dispersiveness of the soil, and the results show that Anambra state soils are highly dispersive, especially the topsoil. Hence, it is highly related to the erodibility of the soils in the zone considered. Furthermore, correlation analysis showed that there is a considerable correlation between geotechnical, physicochemical and biochemical properties of the soils in the state with the presence of sodium playing a major role in determining the influential properties.
... The tropics contain hyperdiverse wet forests, arid deserts, alpine ecosystems, dry forests, wetlands and peat lands, and many other ecosystem types. In this way, there is no representative tropical ecosystem or tropical soil (Hilgard 1906;Sanchez and Buol 1975;Richter and Babbar 1991) nor any singular tropical P cycle. Beyond the variations in climate, soil diversity in the tropics is driven by an extremely wide variety of parent materials, biota, landforms, geomorphic characteristics, and soil ages-the variation in these factors, each of which affects soils, is greater in the tropics than in the temperate zone (Sanchez 1976;Vitousek 1984;Richter et al. 1985;McGroddy et al. 2004;Porder et al. 2007;Townsend et al. 2008). ...
... However, according to Sanchez and Buol (1974), soil temperature, which is higher in the tropics than in other areas is the major difference between soils of tropical and extratropical areas. Other than that, soils in tropical areas are as variable as in any other region of the globe, encompassing soils of different ages with a wide range of weathering states (Richter and Babbar 1991;Sanchez and Logan 1992). ...
By analyzing 6,480 tree leaf samples from 57 sites within Brazilian biomes, we considered whether vegetation types in terrestrial ecosystems reflect biogeochemical diversity and whether they fit into a leaf economics spectrum (LES). To achieve this, we investigated the relations among leaf carbon (C) and nitrogen (N) concentrations, their isotope natural abundance and C:N ratio. In addition, we tested their correlations with mean annual temperature (MAT) and precipitation (MAP), as climatic factors. We found consistent differences in the C and N concentrations and their isotopic composition among the vegetation types. MAP is the main climatic driver of changes in N, C:N ratio, d 15 N, and d 13 C, correlating negatively with N and positively with C:N ratio. These relations show that these biomes follow an LES. The Caatinga had the highest d 15 N values, suggesting that N residence time in soil is longer due to low leaching and plant uptake. We observed that MAP is not the only factor influencing d 13 C values in different biomes; instead canopy effect probably explains the highest values observed in the Cerrado. Our results reinforce earlier findings that life diversity in the tropics reflects biogeochemistry diversity and leaf d 15 N opens the possibility for investigating plant().,-volV) (01234567 89().,-volV) trade-offs dictated by the LES. Finally, we expect our findings to contribute to a better understanding of the tropics in global climate models.
... Although the idea that edaphic factors control plant distributions is not new (see Grubb, 1989;Richter & Babbar, 1991), a growing body of research over the last two decades suggests that edaphic factors play a larger role in plant community assembly and plant diversity gradients than previously considered and warrant deeper consideration. For example, microbial biogeography is controlled primarily by edaphic variables (Fierer & Jackson, 2006) which, in turn, have cascading effects on plant diversity and productivity (Bever et al., 2010;Van Der Heijden, Bardgett, & Van Straalen, 2008). ...
Background
The central thesis of plant ecology is that climate determines the global distribution of vegetation. Within a vegetation type, however, finer‐scale environmental features, such as the physical and chemical properties of soil (edaphic variation), control patterns of plant diversity and distributions.
Aims
Here, we review the literature to provide a mechanistic framework for the edaphic control of plant diversity. First, we review three examples where soils have known, prevalent effects on plant diversity: during soil formation, on unusual soils and in regions with high edaphic heterogeneity. Second, we synthesize how edaphic factors mediate the relative importance of the four key processes of community assembly (speciation, ecological drift, dispersal and niche selection). Third, we review the potential effects of climate change in edaphically heterogeneous regions. Finally, we outline key knowledge gaps for understanding the edaphic control of plant diversity. In our review, we emphasize floras of unusual edaphic areas (i.e., serpentine, limestone, granite), because these areas contribute disproportionately to the biodiversity hotspots of the world.
Taxa
Terrestrial plants.
Location
Global.
Conclusion
Edaphic variation is a key driver of biodiversity patterns and influences the relative importance of speciation, dispersal, ecological drift, niche selection and interactions among these processes. Research is still needed to gain a better understanding of the underlying mechanisms by which edaphic variation influences these community assembly processes, and unusual soils provide excellent natural systems for such tests. Furthermore, the incorporation of edaphic variation into climate change research will help to increase the predictive power of species distribution models, identify potential climate refugia and identify species with adaptations that buffer them from climate change.
... Nevertheless, it also needs to be remembered that the Amazon Basin has a complex mosaic of soils, with ca. 40 % having young and intermediate pedogenetic development levels (Quesada et al., 2011;Richter and Babbar, 1991;Sanchez, 1976). Most of these less weathered soils occur in the west of the basin and were influenced by the uprising of the Andean Cordillera (Hoorn et al., 2010), thus having much younger geological ages. ...
We investigate the edaphic, mineralogical and climatic controls of soil
organic carbon (SOC) concentration utilising data from 147 primary forest
soils (0–30 cm depth) sampled in eight different countries across the Amazon
Basin. Sampled across 14 different World Reference Base soil groups, our
data suggest that stabilisation mechanism varies with pedogenetic level.
Specifically, although SOC concentrations in Ferralsols and Acrisols were
best explained by simple variations in clay content – this presumably being
due to their relatively uniform kaolinitic mineralogy – this was not the
case for less weathered soils such as Alisols, Cambisols and Plinthosols for
which interactions between Al species, soil pH and litter quality are argued
to be much more important. Although for more strongly weathered soils the
majority of SOC is located within the aggregate fraction, for the less
weathered soils most of the SOC is located within the silt and clay
fractions. It thus seems that for highly weathered soils SOC storage is
mostly influenced by surface area variations arising from clay content, with
physical protection inside aggregates rendering an additional level of
protection against decomposition. On the other hand, most of the SOC in less
weathered soils is associated with the precipitation of aluminium–carbon
complexes within the fine soil fraction, with this mechanism enhanced by the
presence of high levels of aromatic, carboxyl-rich organic matter compounds.
Also examined as part of this study were a relatively small number of arenic
soils (viz. Arenosols and Podzols) for which there was a small but significant
influence of clay and silt content variations on SOM storage, with
fractionation studies showing that particulate organic matter may account
for up to 0.60 of arenic soil SOC. In contrast to what were in all cases
strong influences of soil and/or litter quality properties, after accounting
for these effects neither wood productivity, above-ground biomass nor
precipitation/temperature variations were found to exert any significant
influence on SOC stocks. These results have important implications for our
understanding of how Amazon forest soils are likely to respond to ongoing
and future climate changes.
... Similarly, attainable yields, that is the upper boundary what is biophysically possible, depend on soil and climatic conditions. Especially in the tropics soil spatial variability can be large within small distances and substantially affect yields (Pittelkow et al., 2015;Richter & Babbar, 1991). ...
Climate‐smart agriculture (CSA) and sustainable intensification (SI) are widely claimed to be high‐potential solutions to address the interlinked challenges of food security and climate change. Operationalization of these promising concepts is still lacking and potential trade‐offs are often not considered in current continental‐ to global‐scale assessments. Here, we discuss the effect of spatial variability in the context of the implementation of climate‐smart practices on two central indicators, namely yield development and carbon sequestration, considering biophysical limitations of suggested benefits, socioeconomic and institutional barriers to adoption, and feedback mechanisms across scales. We substantiate our arguments by an illustrative analysis using the example of a hypothetical large‐scale adoption of conservation agriculture in sub‐Saharan Africa. We argue that, up to now, large‐scale assessments widely neglect the spatially variable effects of climate‐smart practices, leading to inflated statements about co‐benefits of agricultural production and climate change mitigation potentials. There is an urgent need to account for spatial variability in assessments of climate‐smart practices and target those locations where synergies in land functions can be maximized in order to meet the global targets. Therefore, we call for more attention towards spatial planning and landscape optimization approaches in the operationalization of CSA and SI to navigate potential trade‐offs.
... Leptosols and Podzol Cs estimates are also much higher than those of Batjes (1996 Richter and Babbar, 1991;Sanchez, 1976). Most of these less weathered soils occur in the west of the 631 Basin and were influenced by the uprising of the Andean Cordillera ( Hoorn et al., 2010) and thus having 632 much younger geological ages. ...
We investigate the edaphic, mineralogical and climatic controls of soil organic carbon (SOC) concentration utilising data from 147 pristine forest soils sampled in eight different countries across the Amazon Basin. Sampling across 14 different World Reference Base soil groups our data suggest that stabilisation mechanism varies with pedogenetic level. Specifically, although SOC concentrations in Ferralsols and Acrisols were best explained by simple variations in clay content – this presumably being due to their relatively uniform kaolinitic mineralogy – this was not the case for less weathered soils such as Alisols, Cambisols and Plinthosols for which interactions between Al species, soil pH and litter quality seem to be much more important. SOC fractionation studies further showed that, although for more strongly weathered soils the majority of SOC is located within the aggregate fraction, for the less weathered soils most of the SOC is located within the silt and clay fractions. It thus seems that for highly weathered soils SOC storage is mostly influenced by surface area variations arising from clay content, with physical protection inside aggregates rendering an additional level of protection against decomposition. On the other hand, most of SOC in less weathered soils is associated with the precipitation of aluminium-carbon complexes within the fine soil fraction and with this mechanism enhanced by the presence of high levels of aromatic, carboxyl-rich organic matter compounds. Also examined as part of this study were a relatively small number of arenic soils (viz. Arenosols and Podzols) for which there was a small but significant influence of clay and silt content variations on SOM storage and with fractionation studies showing that particulate organic matter may accounting for up to 0.60 of arenic soil SOC. In contrast to what were in all cases strong influences of soil and/or litter quality properties, after accounting for these effects neither wood productivity, above ground biomass nor precipitation/temperature variations were found to exert any significant influence on SOC stocks at all. These results have important implications for our understanding of how Amazon forest soils are likely to respond to ongoing and future climate changes.
... Extraction and purification of natural tropical humic substances Humic soil (peat) was obtained from the banks of the Mogi River in the Municipality of Luiz Antonio, Sao Paulo state, Brazil (21°33′20"S 47°55′08″W). This soil was previously classified as a red podzolic soil, which is characteristic of humid tropical environments (Andriesse 1975;Richter and Babbar 1991), and its HS had already previously been analyzed and characterized by Vaz et al. (2015). Samples were collected from the 10-cm topsoil layer and extracted with potassium hydroxide (0.5 M for 4 h) in accordance to the procedure described by the International Humic Substances Society (IHSS) as excerpted from Swift (1996). ...
Few studies have been conducted so far into the effects of humic substances (HS) on aquatic organisms and their influence on the toxicity of chemical pollutants in the tropics. The aim of the present study was therefore to evaluate the direct effects of locally-derived tropical natural HS on the cladoceran Daphnia similis, the midge Chironomus xanthus and the fish Danio rerio. The influence of a HS concentration series on the acute toxicity of copper to these organisms was also assessed through laboratory toxicity testing. The HS did not exert direct acute effects on the test organisms, but long-term exposure to higher HS concentrations provoked a stress response (increase in feces production) to D. rerio and exerted effects on chironomid adult emergence and sex ratio. The biotic ligand model proved to be a useful tool in converting total copper concentrations to the appropriate bio-available fraction to which tropical aquatic organisms are exposed.
... Ao longo da Bacia Amazônia há uma grande variedade de tipos de solo, predominando, de uma forma geral, solos altamente intemperizados, principalmente na porção central e leste da Bacia (Quesada et al., 2010). Ainda que esta seja a predominância geral observada, em áreas menores, existe uma variedade maior nos tipos de solos associada a características geomorfológicas destas localidades (Quesada et al., 2009;Richter e Babbar, 1991;Sanchez e Buol, 1975;Sanchez, 1976), acarretando uma grande variação nas propriedades químicas e físicas dos mesmos (Quesada et al., 2010). Enquanto que os solos mais intemperizados e inférteis encontram-se associados aos Escudos Brasileiro e das Guianas e ao longo das paleovárzeas localizadas ao longo dos principais rios da região (Quesada et al., 2009;Richter e Babar, 1991;Irion, 1978;Sombroek, 1966), solos ligeiramente mais férteis geralmente ocupam níveis pedogênicos intermediários que ocorrem exclusivamente nas vizinhanças dos Escudos ou próximos às calhas dos Rios Juruá, Purus e Madeira (Quesada et al. 2009(Quesada et al. , 2010a. ...
No Brasil são esperadas mudanças profundas e variáveis no clima conforme a região do país, afetando tanto os ecossistemas aquáticos como os terrestres. Neste quesito, o país é um dos mais ricos do mundo, tendo seis biomas terrestres (Amazônia, Mata Atlântica, Pantanal, Pampa, Cerrado e Caatinga), que englobam alguns dos maiores rios do mundo – como os Rios Amazonas, Paraná e São Francisco, além de possuir uma costa com cerca de 8.000 km, contendo pelo menos sete grandes zonas estuari¬nas e toda a plataforma continental. O foco principal deste capítulo será investigar como os principais processos biogeoquímicos seriam afetados pelas mudanças climáticas nos principais biomas e bacias brasileiras. Devido à falta de informações espaciais compatíveis com as escalas dos biomas brasileiros, as análises realizadas neste capítulo concentram-se nas regiões de cada bioma onde há informações dispo¬níveis. Ao mesmo tempo em que esse tipo de limitação nos impede de fazer uma generalização para um determinado bioma, ela também serve como um alerta sobre a carência destas informações em escalas compatíveis com as grandes áreas de nossos biomas. Observa-se uma crítica carência de informações para determinados biomas – como o Pampa, o Pantanal e a Caatinga, contrastando com o volume maior de informações observado para a Amazônia e, secundariamente, o Cerrado. Somente recentemente estudos têm sido desenvolvidos na Mata Atlântica, mas ainda mostram-se concentrados em algumas poucas áreas. Os maiores estoques de carbono e nitrogênio do solo foram encontrados na Mata Atlânti¬ca, seguindo-se a Amazônia e o Cerrado. Quanto aos estoques de carbono e nitrogênio acima do solo, destacam-se a Mata Atlântica e, especialmente, a Amazônia como os biomas que possuem os maiores estoques. Interessantemente, somente na Amazônia e no Pantanal os estoques de carbono e nitrogênio são mais elevados na biomassa acima do solo em relação aos estoques do solo, divergindo dos outros biomas em que os maiores estoques se concentram efetivamente nos solos. O retorno de carbono ao solo via queda das folhas teve uma variação muito menos acentuada entre os biomas. Os sistemas florestais tendem a ter uma transferência ligeiramente maior em relação aos sistemas herbáceos-arbustivos, mas não tão mais elevado, se levarmos em consideração a maior biomassa acima do solo observada nos sistemas florestais. Por outro lado, a transferência de nitrogênio é significativamente maior nos sistemas florestados da Amazônia e Mata Atlântica em relação aos sistemas herbáceos-arbustivos como o Cerrado e a Caatinga. A despeito das grandes diferenças nos estoques de carbono do solo, as variações nos fluxos de CO2 para a atmosfera não foram elevadas entre os biomas, principalmente se excluirmos a Amazônia, onde os fluxos de CO2 foram claramente maiores. O fluxo de N2O do solo para a atmosfera é também considerado uma perda de nitrogênio do sistema. Neste caso as diferenças são mais acentuadas entre os biomas, tendo a Amazônia os maiores fluxos, seguindo-se a Mata Atlântica; enquanto fluxos muito baixos foram detectados para o Cerrado. No caso da fixação biológica de nitrogênio (FBN), as maiores entradas estão associadas aos sistemas florestais da Amazônia e Mata Atlântica, seguindo-se o Cerrado e, finalmente, o Pantanal e a Caatinga, com uma quantidade de nitrogênio fixada anualmente significa¬tivamente menor que os três biomas citados acima. Quanto à deposição atmosférica de nitrogênio, os valores foram semelhantes entre biomas, sendo, na maioria dos casos, abaixo dos valores que entram via FBN e ligeiramente mais elevados em relação aos fluxos de N2O para a atmosfera. A combinação de mudanças climáticas globais com alterações dramáticas na cobertura do solo, com desmatamento em larga escala, pode determinar alterações no regime climático local na região Amazônica e conse¬quentemente na estrutura e composição da vegetação nativa presente. O processo de “savanização” da Floresta Amazônica, surgiu como importante alerta à uma possível alteração estrutural da cobertura vegetal da região. Entretanto, estudos recentes, utilizando uma compilação maior de modelos climáticos globais, não reproduzem as condições ambientais e de resposta da floresta para que este processo seja estabelecido. No entanto deve-se salientar que uma profunda mudança na estrutura e funcionamento dos ecossistemas Amazônicos acarretaria perdas significativas nos estoques de carbono tanto do solo como da vegetação. Além das perdas de carbono, haveria outras mudanças fisiológicas e fenológicas similares àquelas descritas mais adiante para o Cerrado brasileiro. Tais mudanças se refletiriam não so¬mente no ciclo do carbono, mas também no ciclo do nitrogênio. A Mata Atlântica estoca quantidades apreciáveis de carbono e nitrogênio em seus solos, principalmente em maiores altitudes. Os aumentos previstos para a temperatura do ar na Região Sudeste do Brasil levariam a um aumento nos processos de respiração e decomposição, gerando um aumento nas perdas de carbono e nitrogênio para a atmosfera.
... However, such perception is surprising because most the highly-diversified forest ecosystems in the world, such as the Amazon rainforest, grow well in nutrient-poor soils (Sanchez 1976). This perception has been challenged recently (Sanchez and Logan 1992), based on the premise that because of its diversity and complexity, tropical rainforest soils could range from young fertile soils to more highly weathered infertile soils (Sanchez 1976;Richter and Babbar 1991;Sanchez and Logan 1992). ...
Over the last 2 decades, the Philippine government has devoted a considerable amount of resources to the rehabilitation and reforestation of degraded forest land. However, deforestation and forest degradation have continued to be a major environmental problem in the Philippines as vast forest cover is lost annually. While large-scale reforestation projects have been initiated, most have been far from successful. This chapter argues that soil is the single most important factor affecting survival, growth, and development of trees and thus, influence the success of reforestation programs. Within the context of the Philippines, it analyzes soil factors that limits the success of reforestation projects and discusses the use of exotic and native tree species in reforestation. Finally, it presents current research and development efforts to reforest degraded forest land, particularly the National Greening Program, and the role of the reforestation program on soil carbon sequestration.
... ultisol, oxisols and arenosols). This has led to a decline in soil organic matter (SOM) and the leaching of soils, which become minerally deficient (Richter & Babbar, 1991;Liang et al., 2006;Steiner et al., 2007). It is, however, important to note that the constituents of these terra preta soils are far more complex than just sites of high charcoal/biochar addition (Kampf et al., 2003;Lehmann et al., 2003b). ...
Biochar application to soil is suggested as a way of enhancing soil fertility by increasing the availability of nutrients and water. The former is perhaps better documented while the latter has less experimental support. This review critically investigates the recent literature which focuses on determining whether biochar induces increases in plant available water and that this provides part of the explanation for possible increases in crop yield. A number of studies suggest that biochar increases crop yields, and this is linked to the enhancement of soil water content and increased crop growth. However, many of these studies fail to fully consider if the measured biochar increases of 10–30% in soil water content were actually responsible for an increase in plant available water for crop growth. There is also limited evidence of increased crop yields when biochar is used in field experiments. While biochar soil application may increase soil water content, this appears to most likely occur with free draining coarsely textured sandy soils. As yet there is limited evidence that biochar improves soil water content in temperate soils and even less that it facilitates plant tolerance to drought stress. More recent literature shows the use of methods which quantify soil biochar changes with respect to plant water availability. However, despite some advances in our understanding of biochar's mode of action, there are still only a few studies which link increases in plant available water with increased crop yields, and particularly with respect to the longer term use and functionality of soil‐applied biochar.
... The median values of pH, CEC, and V% in Amazonian rainforest were lower than the mean values for other Brazilian biomes (Marques et al., 2004a;Oliveira and Costa, 2004;Dalmolin et al., 2006;Maia et al., 2015;Souza et al., 2015), for rainforest in Ghana (Bowell, 1993), and for rainforest in southeastern Asia (Richter and Babbar, 1991). In Amazonia, median values were up to 17 % lower in pH, 50 % in CEC, and 78 % in V% (Table 2). ...
Evaluating soil geochemical diversity in the Amazon Basin has been a challenge largely because most study sites have been at the edge of the basin and it is difficult to get samples in such a region. Here we show that even among the most weathered soils, physicochemical soil properties express lithology. Our results are based on topsoil samples collected from different locations in minimally disturbed areas in the state of Amazonas, Brazil. Soil properties were measured using methods which are suitable for highly developed soils. The Chemical Index Alteration and Weathering Index of Parker was calculated based on the content of metal(loid)s in soils determined by X-ray fluorescence. Descriptive statistics, Pearson correlation, and Principal Component Analysis (PCA) were performed on data. In general, Amazon rainforest soils are more deeply weathered than soils in other Brazilian biomes and tropical rainforests in Asia and Africa. The high coefficient of variation of metal(loid) contents express pedogenesis and parent material diversity. Correlation analysis indicated that the tri-pentavalent elements are strongly associated with Al and Fe contents in the topsoil. In contrast, mono-divalent elements are correlated with sand and silt fractions. According to PCA, five soil groups with defined geochemical compositions and degrees of weathering could be identified: i) acidic sandy podzolized soils; ii) acidic loamy ferralitic soils with the highest content of tri-pentavalent ions; iii) acidic clayey kaolinitic soils with low metal(loid) contents; iv) acidic loamy kaolinitic soils with low metal(loid) contents; and v) silty neutral 2:1 clay soils. This study is the first effort to analyze the geochemical diversity in Amazon rainforest soils. These data are extremely valuable in determining the geochemical background for these soil types and this region. Geochemical variability can be predicted to some extent by lithology and pedogenesis, which can be applied to define the sampling required in future studies.
... L ow soil P availability is an important limiting factor to crop production in highly weathered and typically P poor tropical soils (Juo and Franzluebbers, 2003). Tropical regions comprise more than 30% of the earth's land surface, and Oxisols and Ultisols are present in more than two-thirds of this area (Richter and Babbar, 1991). The main processes controlling inorganic P (P i ) availability in these soils are the interactions with Fe and Al amorphous and crystalline oxides, and organic P (P o ) mineralization. ...
Core Ideas
There have been suggestions that ruzigrass increases soil P availability.
Ruzigrass was grown in rotation with soybean from 2012 to 2016.
The observed effect was opposite from the expected under long‐term field conditions.
Crop rotation with ruzigrass resulted in a lower soybean grain yield than fallow.
Under no‐till farming systems, the use of crop rotations with species adapted to low P soils may enhance soil P availability through P cycling. Growing ruzigrass [ Urochloa ruziziensis (R. Germ. and C.M. Evrard) Morrone and Zuloaga] as a cover crop has shown to increase resin extractable P in soils. However, it is not clear how the next crop responds to ruzigrass in the long term. The objective of this study was to evaluate the long‐term effect of growing ruzigrass on soil P availability to soybean [ Glycine max (L.) Merr.]. The evaluations were performed over 5 yr on a ruzigrass–soybean crop rotation, in Botucatu, Brazil. The treatments were P rates (0, 13, and 26 kg ha ⁻ ) applied to soybean seed furrows, and ruzigrass or fallow during the off‐season. Soil samples were taken after ruzigrass desiccation, and soil P was extracted with resin (P resin ). The use of ruzigrass increased soil organic matter (SOM) by approximately 20% compared with fallow, regardless of P rates, and increased P resin concentration in the 0‐ to 10‐cm soil depth by approximately 10% with 26 kg ha ⁻ of P. Surprisingly, grain yield and soybean leaf P concentration were lower after ruzigrass compared with fallow. Resin seemed to be unsuitable to compare P availability in different cropping systems. In the long‐term, growing ruzigrass as a cover crop in the off‐season decreases P and N availability to soybean, eventually decreasing soybean grain yield. Further studies are needed to understand the mechanisms involved in this unexpected soybean response when cropped in rotation with ruzigrass.
... Changes in tropical-forest SOC, particularly in the deeper soil layers, could strongly impact the total forest C stocks and net C balance of this biome. A second issue in tropical forests is that SOC shows marked spatial variation on all scales: from one square meter to the next (Powers, 2006) and across the major edaphic changes (topography, soil types; see Richter and Babbar, 1991) within a forest. An example of this within-forest heterogeneity is the significant difference in cumulative SOC content between two major soil types at the LS site (Table 6). ...
For more accurate projections of both the global carbon (C) cycle and the
changing climate, a critical current need is to improve the representation of
tropical forests in Earth system models. Tropical forests exchange more C,
energy, and water with the atmosphere than any other class of land
ecosystems. Further, tropical-forest C cycling is likely responding to
the rapid global warming, intensifying water stress, and increasing
atmospheric CO2 levels. Projections of the future C balance
of the tropics vary widely among global models. A current effort of the
modeling community, the ILAMB (International Land Model Benchmarking) project, is to compile robust observations that can be used to improve the
accuracy and realism of the land models for all major biomes. Our goal with
this paper is to identify field observations of tropical-forest ecosystem
C stocks and fluxes, and of their long-term trends and
climatic and CO2 sensitivities, that can serve this effort. We propose
criteria for reference-level field data from this biome and present a set of
documented examples from old-growth lowland tropical forests. We offer these
as a starting point towards the goal of a regularly updated consensus set of
benchmark field observations of C cycling in tropical forests.
... The myth that soils in the tropics are uniformly low in soil fertility was put to rest decades ago (Richter & Babbar 1991, Sanchez & Logan 1992, and it is widely acknowledged that ecosystem state factors such as parent material, weathering ages, topography, and landscape dynamics are as varied in the tropics as in the temperate and boreal zones, if not more so (Townsend et al. 2008). This variation can affect the magnitude-and in some cases even the direction-of changes in ecosystem processes and properties with land use change. ...
Secondary tropical forests that are in a state of regeneration following clearing for agriculture are now more abundant than primary forests. Yet, despite their large spatial extent and important role in the global carbon (C) cycle, secondary tropical forests are understudied, which challenges our ability to predict how tropical landscapes will respond to future disturbance and global change. We summarize research advances on alterations to C and nutrient dynamics during reforestation and how these are influenced by ecosystem state factors. During forest succession, aboveground biomass stocks and litter fluxes increase in a predictable way, but patterns in soil C dynamics are highly variable. The heterogeneous response of nutrients to reforestation is influenced by multiple factors, including losses incurred during prior land use and management. In contrast to primary tropical forests, where productivity is often limited by rock-derived nutrients, secondary forest growth may be more limited by nutrients from the atmosphere. Future research should identify which nutrients constrain forest regrowth.
Understanding the formation of tropical yellow to red earth (TYRE) is essential for preserving soil multifunctionality
in well-drained tropical landscapes. Weathering and bioturbation mutually interact in TYRE evolution,
whereas allochthonous materials appear restricted to distinct (paleo)landscapes. A layered appearance of
TYRE can result from quasi-constant deposition of invertebrate mound debris, outcompeting diffusional mixing.
Age-depth profiles from optically stimulated luminescence (OSL) and charcoal radiocarbon (14Cchar) data of
TYRE sites in different tropical landscapes, both from the literature and the present study, all reveal quasiconstant
soil upbuilding, in accordance with our model. The rates of soil upbuilding are mostly in the range
of 100–200 mm*ka^-1, which conforms with published mounding rates of termites and ants. By comparison,
geochemical transformation of rock to saprolite proceeds at rates at least one order of magnitude smaller.
Termites mining saprolite, sometimes even below indurated subsoil, produce TYRE, thus linking the interconnected
subsystems of differing process rates. The work of the bioengineers appears essential for transforming
the deep-weathering products into well-structured TYRE. Future research may extend the provided database, the
spatial scale, and the use of geochronology, coupled with paleoenvironmental proxies, in order to further
enhance our understanding of tropical soil and landscape evolution, as one basis for advances in sustainable land
use.
Context Minerals and organic matter physically associate in many soils, yet the precise nature, either via a hierarchy of aggregate particles or by build-up of organo–mineral associations, remains obscure, especially in tropical forest environments. Aims We investigated physically protected organic matter by comparing soils with contrasting parent material, topography, and pedogenesis, but with similar tropical moist forest on Barro Colorado Island in the lowlands of Panama. Methods Bulk soil from 10 sites was separated by size into free-floating particles, macroaggregates (>250 μm), microaggregates (53–250 μm), and <53-μm particles. A subsample of macroaggregates was disintegrated and separated into coarse particles (>250 μm), occluded microaggregates, and occluded <53-μm particles. Concentrations and natural abundance of stable isotopes for carbon (C) and nitrogen (N) were determined for each fraction, and ratios (C:N, stable isotopes) were used to characterise organic matter for each fraction. Key results Macroaggregates were the largest fraction of bulk soil (71%) and were 15% greater in kaolinite- than smectite-dominated soils. Macroaggregates were composed of coarse particles (14%), occluded microaggregates (62%), and occluded <53-μm particles (24%). Concentrations of C and N widely varied among fractions but the variation was not related to clay mineralogy. The C:N ratio and stable N isotope ratio indicated more decomposed organic matter in kaolinite- than smectite-dominated soils. Conclusions and implications Macroaggregates composed of plant detritus and microaggregates in the Barro Colorado Island soils imply that the aggregate hierarchy route ultimately protects soil organic matter in this tropical forest environment.
Ferns (Polypodiophyta) are an abundant floral element of the tropics with high sensitivity to environmental conditions and good indicators of overall biodiversity. Here, we set out to identify which geochemical factors determine fern diversity in a low-montane tropical rainforest in Eastern Ecuador. We conducted a field survey of high spatial resolution completing a comprehensive fern inventory across two elevational ranges, combined with biochemical characterisation of the underlying soils. While α-diversity was negatively correlated with cation exchange capacity and with elevation, β-diversity increased with elevation and with geographic distance, as predicted. Our results confirm that ferns have a high sensitivity to both elevational and environmental gradients, where the latter in this study was derived from enhanced aluminium, iron and calcium contents in some of the studied soils. Further monitoring fern communities could therefore help to better understand and predict how environmental change may impact biodiversity, with a particular focus on threats potentially arising from toxic elements being released in tropical soils through modified soil cation exchange capacity.
The impact of anthropogenic activities on soil characteristic properties is a great concern worldwide. The human impact is putting pressure on land use due to increasing population and growing food demands. Removal of top fertile layer due to human interventions creates a major threat on soil fertility, crop productivity, green forest cover, environment balance, etc. There is tremendous damage to soil resources in recent years due to change in land use and land cover methods. Due to urbanization and industrialization, there is extensive land covering for making buildings, industrial setups, and construction of roads. The subsequent changes in soil–landscape pattern are altering soil structure and properties. The rate of soil weathering and formation has altered. There is increase in rate of podzolization, laterization, and acidity of soil. In this chapter, an attempt has been made to study the impact of anthropogenic activities on soil ecosystem integrity including global soil pattern, soil profile, and physicochemical and biological parameters.
Mineral weathering relative to soil has two parts: weathering happened previously where hard rocks have been broken down into clay which ultimately forms soil, loams, and unconsolidated sands both chemically and physically and other is soil and mineral weathering happening currently which acts as vital source of crop nutrients. This chapter discusses background of chemical weathering of minerals, sequence of weathering of minerals from soil, mainly throwing light on the factors which controls the rate of chemical weathering like temperature and time factor, biotic process, oxidation, reduction, water, leaching, acidity, and many more.
Abstract It has been suggested that some tropical grasses can acquire phosphorus (P) from hematite and gypsite by exuding organic acid anions (OAs). However, it remains to be determined exactly which OAs could be involved in each case. The objective of this study was to verify the exudation OAs by ruzigrass (Urochloa ruziziensis), palisade grass (U. brizantha), and Guinea grass (Megathyrsus maximus) as a response to P deficiency. The grasses were grown in leachate columns with adequate and deficient P nutrient solutions. The concentration of OAs in the leacheate and root surface, as well as shoot and root dry matter, and P uptake were determined. Citrate, isocitrate, and malate concentration in leachates and root surfaces increased with P starvation, mainly for the Urochloa grasses. Oxalate exudation was similar for the grasses under adequate P supply, but was lower in Guinea grass under P starvation. Palisade grass showed a higher concentration of total OAs in the root surface than the other species due to a great production of oxalate and isocitrate. Palisade grass showed greater dry matter yields regardless of P deficiency, and Guinea grass always had the higher shoot:root ratio. Urochloa grasses have a higher capacity to cope with low P availability by exuding OAs along with a lower shoot:root ratio than Guinea grass.
Rocks exposed at the surface of the Earth break down (weather) at rates determined by topography, climate, and plant growth, releasing elements important to plant nutrition. Carbonic acid, derived from the reaction of CO2 with rainwater, dominates the rate of chemical weathering in most circumstances. The weathering process also results in the formation of soils and characteristic soil horizons. Soil mineralogy controls the availability of certain ions, especially phosphorus, to plant roots and the losses of ions to runoff waters. Studies of chemical transport in streams and rivers allow the calculation of regional and global weathering rates and the transport of dissolved and particulate matter to the sea. Humans alter many of the natural processes of soil development through land clearing and exposure of soils to acid rain.
Current scientific and public attention on various aspects of global change has highlighted the complex relationship between climatic events and ecological function in terrestrial ecosystems. In this chapter, we examine the complex relationships between hydrologic and nutrient cycling in dry forests, which are found in dry tropical, subtropical, and Mediterranean forests globally (Fig. 17.1). Dry tropical forests, which cover the most area within dryland forests and are more suitable for human habitation than wet tropical forests, provide an excellent example of this interaction because they display structure and function that are closely linked to sporadic rainfall. There are 25 biodiversity hotspots around the world that contain high degrees of endemism and are undergoing exceptional loss of habitat, with 11 of these hotspots containing tropical dry forests (Myers et al. 2000). Moreover, the area of dryland forest is similar in extent to the area of tropical moist forest (Bastin et al. 2017), yet these forests are more vulnerable to climate change and pressures from land use change and thus, our need to understand the complexity of dryland forest ecosystems has become increasingly important.
Given the dimensions of the Amazon basin (7.5 million km²), its internal dynamics, increasing anthropogenic strain on this large biome, and its global role as one of two continental biospheric tipping elements, it appears crucial to have data-based knowledge on carbon and nitrogen concentrations and pools as well as on possible intra-annual dynamics. We quantified carbon (Ct, Corg), nitrogen (N) and sulfur (S) concentrations in litter (ORG) and mineral soil material (TOP 0–20 cm, BOT 30–50 cm) of upland (terra firme) oxisols across Amazonas state and present a first pool calculation. Data are based on triplicate seasonal sampling at 29 sites (forest and post-forest) within the binational project EcoRespira-Amazon (ERA). Repeated sampling increased data accuracy and allows for interpreting intra-annual (seasonal) and climate-change related dynamics. Extreme conditions between the dry season in 2016 and the subsequent wet season (ENSO-related) show differences more clearly. Median CNS in the Amazon basin TOP soils (Ct 1.9, Corg 1.6, N 0.15, S 0.03 wt-% under forest canopy) as well as Corg / N ratios show concentrations similar to European soils (FOREGS, GEMAS). TOP Ct concentrations ranged from 1.02 to 3.29 wt-% (medianForest 2.17 wt-%; medianPost-Forest 1.75 wt-%), N from 0.088 to 0.233 wt-% (medianForest 0.17 wt-%; medianPost-Forest 0.09 wt-%) and S from 0.012 to 0.051 wt.-% (medianForest 0.03 wt.-%; medianPost-Forest 0.02 wt-%). Corg / N ratios ranged from 6 to 14 (median 10). A first pool calculation (hectare-based) illustrates forest versus post-forest changes. The elements are unevenly distributed in the basin with generally higher CNS values in the central part (Amazonas graben) as compared to the southern part of the basin. Deforestation and drought conditions lead to C and N losses – within 50 years after deforestation, C and N losses average 10 to 15 %. Regional climate change with increased drought will likely speed up carbon and nitrogen losses.
O cultivo de braquiária ruziziensis (Urochloa ruziziensis) em sistemas de rotação de culturas tem sido sugerido como uma estratégia para aumentar a ciclagem e disponibilidade de fósforo no solo. Foi avaliado um experimento de longa duração em Botucatu/SP, Brasil, em que a braquiária tem sido cultivada na entressafra de soja (Glycine max) desde 2006, com a aplicação de 0, 30 e 60 kg ha-1 de P2O5. Inicialmente, foi testada a hipótese de que o cultivo de braquiária durante a entressafra pode aumentar a disponibilidade de fósforo no solo. A concentração de fósforo no solo extraído com resina foi maior no solo após a braquiária do que no solo com pousio. Surpreendentemente, o teor foliar de fósforo e a produtividade da soja foram menores após a braquiária do que após pousio. Em função dos resultados observados no primeiro capítulo deste estudo, foi conduzido um experimento com o objetivo de mensurar as frações de fósforo disponíveis para plantas de milho (Zea mays) cultivadas após a braquiária, e avaliar a adsorção e dessorção de fósforo no solo. Amostras de solo do experimento de campo foram coletadas para condução de um experimento em vaso, especialmente para possibilitar uma adequada amostragem de raízes de milho. Novamente, a concentração de fósforo extraído com resina não teve correlação com a resposta das plantas. Por meio da calorimetria de titulação isotérmica foi possível verificar uma menor dessorção e maior adsorção de fósforo no solo cultivado com braquiária do que no solo mantido em pousio, possivelmente devido ao acúmulo de fósforo orgânico e maior interação da matéria orgânica no solo com os óxidos de ferro e alumínio. Uma vez que o acúmulo de fósforo orgânico pode resultar em menor disponibilidade de fósforo no solo, um terceiro estudo foi conduzido com o objetivo de avaliar o fósforo orgânico no solo cultivado com braquiária, principalmente o mio-inositol hexafosfato, considerado uma das formas menos disponíveis de fósforo no solo. O mio-inositol hexafosfato foi separado com cromatografia líquida de alta performance após oxidação dos extratos de solo com hipobromito. A braquiária resultou em menor concentração de mio-inositol hexafosfato no solo do que o pousio; apesar disso, o menor acúmulo deste composto não é suficiente para evitar a menor disponibilidade de fósforo no solo. A falta de correlação do fósforo extraído com resina e a resposta das plantas em rotação com braquiária estimulou a condução de uma pesquisa, apresentada no Capítulo 4, com o objetivo de avaliar a cinética de dessorção do fósforo. Por meio do método de gradiente de difusão de fósforo em finas membranas, foi possível observar que o cultivo de braquiária resulta em menor disponibilidade de fósforo devido à redução da mobilidade e menor ressuprimento do fósforo da fase sólida para a solução do solo, o que por sua vez ajuda a explicar como é difícil estimar a disponibilidade de fósforo com os métodos usuais de extração de fósforo, que não levam em consideração estes fatores determinantes da disponibilidade de fósforo. A persistência destes resultados é um indicativo de que não é possível obter aumento da disponibilidade de fósforo no solo com o cultivo de braquiária ruziziensis.
Cambridge Core - Natural Resource Management, Agriculture, Horticulture and forestry - Properties and Management of Soils in the Tropics - by Pedro A. Sanchez
Até a primeira metade do século XIX, investigadores consideravam os solos um manto alterado superficial sobre rochas capaz de sustentar plantas. Os países desenvolvidos já detinham avançados conhecimentos de suas geologias, climas, e recursos naturais. O russo V.V. Dokuchaev desenvolveu a concepção da formação de um solo a partir da interação dos fatores ambientais gerando processos internos. Esta evolução era evidenciada pelas diferentes “camadas” formadas – horizontes compondo um perfil de solo. Cada distinta interação dos fatores e processos resultaria um determinado tipo de solo. Surge, assim, uma nova ciência, em 1893 – a Pedologia, que rapidamente se expandiu mundialmente, inclusive em antigas colônias do ultramar. Procurou-se realizar no presente texto um histórico do conhecimento científico dos solos desde o século XVIII até meados do século XX. Nesse longo intervalo, países do terceiro mundo, como o Brasil, contaram inicialmente com investigadores estrangeiros no domínio desses conhecimentos. Aqui a ciência alcançou significativa evolução a partir da segunda metade do século XX, quando foram publicados os primeiros levantamentos de reconhecimento pedológico dos nossos estados federativos.
Nutrient resorption plays an important role in plant ecology because it plays a key role in nutrient conservation strategies of plants. However, our current knowledge about the patterns of nutrient resorption among herbaceous species at a global scale is still inadequate. Here, we present a meta-analysis using a global dataset of nitrogen (N) and phosphorus (P) resorption efficiency spanning 521 observations and 248 herbaceous species. This analysis shows that the N resorption efficiency (NRE) and P resorption efficiency (PRE) across all herbaceous plant groups are 54.7 % and 64.5 %, respectively. Across all species, NRE, PRE and N : P resorption ratios (NRE : PRE) vary statistically significantly at a global scale, i.e., NRE, PRE and NRE : PRE increase with increasing latitude but decrease with increasing mean annual temperature (MAT) and mean annual precipitation (MAP). For different functional groups, similar patterns of NRE, PRE and NRE : PRE with respect to latitude, MAT and MAP are observed. Our study are very important complementary to global-scale studies of nutrient resorption and also can inform attempts to model biogeochemical cycling at a global scale.
Three sources of soil acidity (bicarbonate leaching: base-cation accumulation in aboveground wood, roots, and forest floor;and acid atmospheric deposition) were evaluated in relation to exchangeable acidity of three forested Udults in Tennessee. The Udults have low effective CEC (CEC/sub e/), from 2.4 to 3.7 cmol/sub c/ kgâ»Â¹. In the three soils, H/sup +/ from bicarbonate leaching averaged 0.60 kmol/sub c/haâ»Â¹ yrâ»Â¹ over 2 yr. In five forest stands, 30 to 80 yr in age, H/sup +/ from accumulation of excess base cations in aboveground wood, roots, and forest floor averaged 1.11 kmol/sub c/ haâ»Â¹ yrâ»Â¹. Atmospheric H/sup +/ inputs, estimated from bulk precipitation, averaged 0.67 kmol/sub c/ haâ»Â¹ yrâ»Â¹. Total deposition of atmospheric acidity to these eastern Tennessee forests is on the order of 1 kmol/sub c/ haâ»Â¹ yrâ»Â¹. Variations in H/sup +/ inputs were caused by annual differences in the hydrologic cycle and by stand differences due to nutrient-cycling and soil-chemistry effects. In these forest ecosystems, sources of soil acidity from annual bicarbonate leaching and cation accumulation appeared to exceed atmospheric inputs. Exchangeable acidity in the forested Udults was large compared with annual fluxes of acidity. In the upper 60 cm of the three soils, KCl-exchangeable acidity ranged from 100 to 274 kmol/sub c/ haâ»Â¹, and BaClâ-TEA (triethanolamine) acidity ranged from 505 to 820 kmol/sub c/ haâ»Â¹. Despite low precipitation pH and low soil CEC/sub e/, the additional H+ from acid deposition has not caused significant alteration of soil acidity or base solution of these Udults.
Nine profiles representing the major soils in the Occidental Plateau of São Paulo State, Brazil, were characterized after detailed geomorphic and soil mapping were completed on a 70.8 km ² area. The stable upland geomorphic surface had Oxisols, surrounded by younger erosional surfaces with Ultisols, Alfisols, and Inceptisols. Mollisols formed where the erosional surfaces exposed calcareous sandstone. The argillic horizons of the Ultisols and Alfisols in these positions apparently have formed in material that would qualify as an oxic horizon before it was exposed. Laterally moving water at these sloping sites is believed to initiate free Fe removal and lessivage. Lateral water movement at the contact between the surficial deposits of oxic composition and the underlying calcareous sandstones appears to supply the bases for the Alfisols developed in the oxic material.
Kaolinite dominates the clay mineralogy of the soils formed in unconsolidated deposits, but attapulgite and smectite are present in the calcareous sandstone. In the soils shallow to calcareous sandstone the attapulgite apparently has weathered to smectite within a few centimeters of the rock.
Three sources of soil acidity (bicarbonate leaching; base‐cation accumulation in aboveground wood, roots, and forest floor; and acid atmospheric deposition) were evaluated in relation to exchangeable acidity of three forested Udults in Tennessee. The Udults have low effective CEC (CEC e ), from 2.4 to 3.7 cmol c kg ⁻¹ . In the three soils, H ⁺ from bicarbonate leaching averaged 0.60 kmol c ha ⁻¹ yr ⁻¹ over 2 yr. In five forest stands, 30 to 80 yr in age, H ⁺ from accumulation of excess base (EB) cations [EB = (Ca + Mg + K) − (P + S)] in aboveground wood, roots, and forest floor averaged 1.11 kmol c ha ⁻¹ yr ⁻¹ . Atmospheric H ⁺ inputs, estimated from bulk precipitation, averaged 0.67 kmol c ha ⁻¹ yr ⁻¹ . Total deposition of atmospheric acidity to these eastern Tennessee forests is on the order of 1 kmol c ha ⁻¹ yr ⁻¹ . Variations in H ⁺ inputs were caused by annual differences in the hydrologic cycle and by stand differences due to nutrientcycling and soil‐chemistry effects. In these forest ecosystems, sources of soil acidity from annual bicarbonate leaching and cation accumulation appeared to exceed atmospheric inputs. Exchangeable acidity in the forested Udults was large compared with annual fluxes of acidity. In the upper 60 cm of the three soils, KCl‐exchangeable acidity ranged from 100 to 274 kmol c ha ⁻¹ , and BaCl 2 ‐TEA (trieth‐anolamine) acidity ranged from 505 to 820 kmol c ha ⁻¹ . Despite low precipitation pH and low soil CEC e , the additional H ⁺ from acid deposition has not caused significant alteration of soil acidity or base solution of these Udults.
Several national and international institutions are updating the soil classification systems they use in their soil resource inventory programs. The Food and Agriculture Organization (FAO) of the United Nations (1988), the Soil Survey Staff (1987) of the United States Department of Agriculture (USDA) Soil Conservation Service (SCS), several institutions in France and French-speaking African countries, and EMBRAPA (Empresa Brasileira de Pesquisa Agropecuária) in Brazil, among others, are revising their systems.
Unesco's Man and Biosphere Programme has studied new methods for the integrated management of watersheds in such widespread places as the southern Andes, the Himalayas, the Alps of Switzerland and Austria, and in China. The International Hydrological programme, for its part, supports several projects related to run-off control and sediment transport. The authors they stress the need for information about conservation techniques suitable for steep slopes, and for 'adaptive research' that moulds management practices to local conditions. -from Authors
Describes the antecedents of the 7th Approximation since that system was strongly influenced by those classifications which had preceded it. Since 1938 classification broke down as survey progressed, it was necessary to develop a revised system but working from the bottom up no order could be introduced into the classification. The definitions used in the 7th Approximation are explored with the aid of examples, and there are sections on the genetic implications and the use of soil taxonomy. -K.Clayton
These were earlier termed latosols and are intensively weathered soils of tropical or subtropical regions. The oxic horizon is defined, and its properties are described. Its genesis is discussed with sections on plinthite and the oxisol profile. -K.Clayton
This chapter on soil-genesis models indicates that although there are no totally acceptable models, all do have conceptual value. While most models exhibit an awareness of systems concepts, there is a lack of continuity in their application. Most modelers recognize that soils are open systems, but there is no consistent pattern in the application of other systems properties. Several of the more popular models have been developed for general purposes. In doing so, the basic principle of hierarchies have been violated: hypotheses, laws, and principles that are developed and tested for one level are not necessarily applicable at another level. The mere fact that few models explicitly state the hierarchical level at which they are directed leads to a lack of well-defined hypotheses and objectives that can be tested. The problem of dealing with thermodynamics in soil-genesis models is even more difficult to address, particularly from the standpoint of validation. Yet this must not preclude the modeler from using thermodynamic terms in the classical sense nor defining the terms if used in a non-thermodynamic manner to prevent confusing semantic problems from arising.
It is surprising that many recent works on the geomorphology of low latitudes pay scant attention to the role of termites for their activities are obvious in the field. Their effectiveness is particularly evident in the savannas where they must influence processes as infiltration, soil creep, surface wash and rain splash detachment, as well as being responsible for soil horizons and stone lines. -K.Clayton
Explores the idea that tropical rain forests may strongly influence the inorganic landscape but this landscape and its associated climate have relatively little effect on the rain forest ecosystem. It is concluded that these relationships are true, and that only when native forest is cut and the conserving mechanisms are destroyed will its impact on the environment and the tropical ecosystem become apparent. -K.Clayton
Response to international distribution of Soil Taxonomy has ranged from acceptance as an official system to absolute rejection. The scheme is used as the primary classification for national soils programs in 12 countries. It is commonly used by soil scientists of 19 other countries for international communication though the national programs of these countries depend on other systems. The system addresses the world-wide range of soils. The impact of Soil Taxonomy on soil classification world-wide has been far greater than that of any other development in the discipline during the past 50 years. In addition to its use as a primary system in 12 countries, elements of its principles, concepts, and devices have been incorporated to varying extent in both general and national schemes used in many countries. More importantly, it has prompted a changed perspective of soils and the beginnings of transformation from a qualitative to a quantitative approach to soil classification in many countries.
Soil variability is no stranger to a pedologist. In fact, landscape variability is the very essence of the discipline and dates to antiquity. The development and implementation of Soil Taxonomy have furthered pedogenic quantification. The transfer of technology from laboratory models to field conditions presents serious difficulties. Models are material specific but soils as landscape bodies contain wide ranges of physical, chemical, morphological and mineralogical properties, laterally and vertically. In addition, many parameters are not single valued but vary with transient soil features. Many do not vary randomly in space and thus are not normally distributed. Inability to adequately cope with spatial variability remains a major obstacle to interpretations of field research. The chapter provides an overview to identify the magnitude and loci of spatial variability, its systematic versus random origin and the pedologist's role in communicating such information to users of soil surveys.
This chapter focuses on laterite. The term laterite is restricted to highly weathered material: rich in secondary forms of iron, aluminum, or both; poor in humus; depleted of bases and combined silica; with or without nondiagnostic substances, such as quartz, limited amounts of weatherable primary minerals or silicate clays; and either hard or subject to hardening upon exposure to alternate wetting and drying. The chapter covers issues, such as the nature of laterite, the environment of laterite, profiles containing laterite, the formation of laterite, geomorphic relationships, and the softening of laterite and explains them in detail.
The concept of the "Biological life of a soil," or the time span over which a soil will support trees, is proposed here and is essential to long-term land use planning. Ecologically sound management requires that we begin to measure the actual terrestrial nutrient losses resulting from various land treatments. A method for measuring nutrient input, storage, and loss for predictions of potential soil nutrient loss is described. The theoretical evolution of the depleted white sands in South America is used as an example of the "Life and Death" of a soil to illustrate the general trend of soil-plant coevolution which appears to occur in many areas. Accelerated nutrient decline and the problems of "nutrient shock" or temporary depletion in younger temperate soils are also discussed.
Africa's potential mineral wealth is still largely unknown, and the use of temperate-zone technology limits our knowledge of tropical agriculture. Transport costs and security constrain investment in these areas. A greater international research effort is needed, especially on soils and climate, to find out the true potential of tropical Africa. Individual countries must participate in adapting research results to their regions, however, while farmers must cooperate by applying the results. The myth of enormous and easily exploitable resources is maintained for political and economic reasons. The author suggests that it is no help to African nations to ignore the natural and man-made difficulties that will complicate exploitation. 5 references. (DCK)
Variability in data from morphologically matched pairs of pedons was assessed to establish operational norms in sampling and to consider alternative sampling procedures.
Coefficients of Variation (C.V.'s) were computed for the physical properties—percent sand, silt, clay, and 1,500 kPa moisture—and range from 9 to 40% for loess, 23 to 35% for glacial drift, 33 to 47% for alluvium and residuum, 18 to 32% for A and B horizons, and 33 to 51% for C horizons. C.V.'s were computed for the chemical properties—extractable acidity, sum of bases, cation exchange capacity (CEC), base saturation, pH, and organic carbon—and range from 12 to 50% for Alfisols, 4 to 71% for Aridisols, 6 to 61% for Entisols, 10 to 63% for Inceptisols, 9 to 46% for Mollisols, 16 to 132% for Spodosols, 10 to 100% for Ultisols, and 8 to 46% for Vertisols. Cation exchange C.V.'s are directly related to pH dependent charge.
On the average, clay content for central concepts of phases of series can be estimated within ± 5% clay (95% confidence level) by 1 to 4 samples in loess soils, 2 to 8 samples in glacial drift soils, and 4 to 24 samples in alluvial and residual soils.
Similar estimates of base saturation (sum of cations) within ± 10% (95% confidence level) require 2 samples for Aridisols and Vertisols; 5 for Mollisols; 10 for Alfisols, Ultisols, Entisols, and Inceptisols; and 16 for Spodosols.
Vertical distribution of properties and properties of important horizons are efficiently evaluated by sampling one complete pedon plus satellite samples of important horizons from other pedons. To assess a single horizons efficiently, sample only that horizon in several pedons. Sampling of paired pedons is a good first approach technique to study soils in an area.
Feldspar grains or their pseudomorphs from the different weathering zones are studied with the SEM. Weathering commences with dissolution to form voids in the grains. Close to the rock, the first product is allophanic material present as globules adhering to the voids in the grains. In the δ zone the product is halloysite with some amorphous silica spherules. The surface of the pseudomorph has a hummocky appearance suggesting an amorphous intermediary phase prior to halloysite formation. Kaolinite formation commences in the γ p zone and gibbsite in the γ m zone. Admixtures of kaolinite and halloysite may be found on the same pseudomorph, but admixture of gibbsite with another secondary mineral is not encountered.
Biotite follows a similar trend of alteration. It is concluded that irrespective of the primary weatherable mineral, the type of secondary mineral found is a function of the microenvironment.
To facilitate description and study, the deep profile is divided into several morphological zones, via., α, γ m , γ p and δ zones. Clay content progressively increases from the rock zone δ to the soil zone α. The silt/clay ratio increases from the δ to the upper part of the γ p zone and then decreases again. These changes are explained in terms of the fragmentation or aggregation of various minerals during the clay separation procedure. Estimates of the mineralogical composition in the fine earth shows differences in the zones, and the charge characteristics are related to these.
Changes in the microfabric are monitored with thin‐sections. Micrographs are presented showing fabric characteristics and some examples of pseudomorphic alteration. A brief discussion on the genesis of the profile is given.
Agriculture is becoming more intensive in central Brazil, but there is little information available on the fertility status of most of the soils. To determine this status a total of 518 topsoil samples were collected from a 600,000‐km ² area in central Brazil. Laboratory characterization included pH, exchangeable Al, cation exchange capacity, nutrient levels (including micronutrients), organic matter, texture, and color. The results, presented as frequency distributions, indicate the following general conditions: a pH of 4.8 to 5.2, an organic matter level of 1.5 to 3.0%, extremely low levels of effective CEC and extractable Ca, Mg, P, and Zn, a high level of Fe, a high degree of Al saturation, and a broad range in textural class. Organic matter was the most important soil fraction in relation to effective CEC in these soils. The data suggest that problems associated with fertilizer inputs needed to bring these soils under more intensive agriculture are generally similar, but may vary in degree.
The term Latosol was coined in 1947. The general concept resembles that of Oxisol in current taxonomy, but the two terms are far from equivalents.
Processes of soil formation have been related to prominent great soil groups by means of names such as podzolization, laterization, and solonization. A change from this point of view seems necessary when soils of the world are considered as a continuum with a number of properties in common. It is therefore proposed that soil genesis be considered as two overlapping steps; viz, the accumulation of parent materials and the differentiation of horizons in the profile. Of these two steps, the second is of more immediate concern to soil scientists.
Horizon differentiation is ascribed to additions, removals, transfers, and transformations within the soil system. Examples of important changes that contribute to development of horizons are additions of organic matter, removals of soluble salts and carbonates, transfers of humus and sesquioxides, and transformations of primary minerals into secondary minerals. It is postulated that these kinds of changes, as well as others, proceed simultaneously in all soils. It is further suggested that the balance within the combination of changes governs the ultimate nature of the soil profile. If this point of view is valid, the same kinds of changes occur in horizon differentiation in soils as unlike as Chernozems and Latosols, but the balance among the processes is not the same.
Research was conducted to establish the genetic relationship between soil color patterns and natural drainage characteristics in a hydrosequence of Oxisols formed in Tertiary/Quaternary sediments of the Cerrado (Savanna) Region of the Central Plateau of Brazil. Stratigraphic, geomorphic, and pedogenic evidence supports the hypothesis that soils having reddish hues and codominant hematite and goethite Fe mineralogy formed in a prior environment, then underwent changes in Fe oxide mineralogy in response to changes in hydrology brought about by landscape evolution and climate change. -from Authors
Effects of the stemflow component of the biohydrologic soil forming factor on chemical properties of a Miami soil were investigated. Chemical analyses were made on horizons from soil profiles sampled in radial trenches emanating from the stem of a large American beech tree, at four distances from the stem. Data were subjected to analysis of variance using a two‐way classification with four replications and means were tested with Duncan's Multiple Range Test.
A beech tree was selected for the study in order to maximize the intensity of the biohydrologic factor (because of the large amount of stemflow associated with this species). Stemflow water was collected periodically for volume measurements and chemical analyses.
Stemflow water from the beech tree had a very high content of organic C; moderately high quantities of Ca and K; small quantities of Na, Mg, and P; and very small quantities of Al, Fe, and Mn. Stemflow water created a much wetter environment, of highly enriched water, in soil contiguous to the stem than that prevailing in soil farther from the stem. This resulted in very pronounced effects on chemical properties of the soil under the tree. In A horizons there were progressive increases inward toward the stem in organic C, total N, exchangeable acidity, exchangeable K, CEC, and free Fe 2 O 3 ; and progressive inward decreases in pH, exchangeable Ca, exchangeable Mg, and base saturation. In B horizons there were progressive inward decreases in pH, exchangeable Ca, exchangeable Mg, exchangeable K, CEC, base saturation, and free Fe 2 O 3 .
A compilation of soil carbon and nitrogen storage data for more than 3500 soil profiles from under natural vegetation or relatively undisturbed sites is presented in this report. A summary table of the carbon and nitrogen storage in a pedon of surface cubic meter for each soil profile, as well as location, elevation, climate, parent material, and vegetation information, are presented. The data were used to determine average carbon and nitrogen storage on land surfaces of the world. Calculations were also made of storage related to climatic classifications, ecosystem clasifications, and latitudinal increments from the equator to 75/sup 0/. Carbon (kg.m/sup -3/) varies from 2 in hot dry climates, through 10 in many cold dry or seasonally moist (warm or hot) climates, to more than 30 in wet alpine or subpolar climates. Nitrogen storage, an order of magnitude smaller than carbon storage in soils, shows broad parallels but exceeds 1600 g.m/sup -3/ for subtropical/tropical premontane or lower montane soils, as well as alpine or subpolar wet soils. Such limiting conditions, defined by a balance of income and loss rates for mature soil profiles, also explain much of the variation among major ecosystem complexes whose soils are partly disturbed, incompletely recovered, or imperfectly known regarding their maturity and stability. Classifying profiles into Holdridge life zones and using appropriate life zone areas, we estimate 1309 x 10/sup 15/ g carbon and 92 x 10/sup 15/ g nitrogen in the world's soils. Alternatively, using average organic carbon and nitrogen densities from one degree latitude bands multiplied by the earth's surface area in the respective bands, we arrive at 1728 x 10/sup 15/ g of carbon and 117 x 10/sup 15/ g of nitrogen. Inadequacies that lead to the disparate estimates are discussed. 123 references, 5 figures, 7 tables.