Physical and chemical weathering rates and CO2 consumption in a tropical lateritic environment: the upper Niger basin

The chemical composition of Niger river water measured bimonthly at Bamako Mali. during the period 1990–1992 provides an estimate of present weathering rates in the upper Niger basin. The dominant weathering process is kaolinite formation ‘monosiallitization’.. However, seasonal variations promote gibbsite formation in the rainy season September. and smectite development in the dry season May. The results show that lateritic profiles continue to develop even during very dry episodes. The rate of profile development, calculated as the difference between the chemical weathering rate at the base of the soil profile and mechanical erosion rate at the soil surface, is about 1.3 to 3.7 mrMyr. A comparison between 43 river basins of the world shows that, for similar runoff, the CO2 flux consumed by silicate weathering is about two times lower in lateritic areas than in nonlateritic zones

Effect of land use changes in eastern amazonia on soil chemical, physical, and biological attributes

Land use change in rural settlements of the Amazon influences the abundance, diversity, and survival of soil fauna, especially earthworms, affecting the supply of ecosystem services. This study evaluated the effects of forest conversion to pasture on soil attributes and how the changes on the earthworm community affect soil porosity. Soil samples were collected from two toposequences (forest and pasture) at the summit (T1), midslope (T2) and footslope (T3) positions in July 2012 (dry season) and January and March 2013 (wet season). Samples were taken in five replicates at the depths of 0 to 10, 10 to 20, and 20 to 30 cm for determination of moisture, bulk density, total porosity, micromorphometry of pores, surface litter dry matter, chemical properties, and abundance and richness of earthworms. The numbers of macropores andmicropores and S index (S) were calculated. The change on land use increased soil organic matter, pH, and calcium and reduced dry matter, moisture, and S index in pasture, as well as the loss of earthworm morphospecies highly related to themaintenance and formation of soil macroporosity, especially large rounded pores and, secondarily, large complex pores. This resulted in a loss of soil physical quality.Fil: de Pierri Castilho, Selene Cristina. Universidade Do Estado de Mato Grosso (unemat);Fil: Cooper, Miguel. Universidade Do Estado de Mato Grosso (unemat);Fil: Domínguez, Anahí. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente; ArgentinaFil: Bedano, José Camilo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentin

Topographic Gradients in Bulk Soil Properties in Central Kentucky Karst Sinkholes

The Bluegrass physiographic region of Kentucky is underlain by the late Ordovician Lexington Limestone formation. This area has many identifiable karst features, including sinkholes. Karst sinkholes and associated soils coevolve, which may influence the distribution of bulk soil properties and storage of carbon across karst landscapes. Two sinkholes on the University of Kentucky’s C. Oran Little Animal Research Center in Woodford County, central Kentucky, were selected for analysis. We described and sampled nine pedons at the dominant landscape positions (e.g., summit, shoulder, backslope, footslope, and toeslope) within the two sinkholes; we characterized the physical, chemical, and mineralogical soil properties across the hillslope gradient (i.e., toposequence). As a general trend, total carbon content decreased with sampling depth, and the toeslope and footslope positions contained higher carbon stocks relative to other landscape positions. Total carbon and silt tended to accumulate in the base of sinkholes, whereas summit positions exhibited higher clay contents and iron and aluminum oxide concentrations. The relationship between silt and carbon, and negative relationships between carbon and clay content, exchangeable Ca, and dithionite-extractable Fe and Al may suggest that the carbon in the base of these features is less likely to be minerally associated. An estimated 20% of the world’s land surface is underlain by lithologies favorable for karst terrain formation making the characterization of the soil in these landscapes applicable outside of Kentucky’s Inner Bluegrass. Measuring the properties of soils in karst sinkholes will allow for a better understanding of their place in karst landscapes, as well as their role in carbon cycling

Late Quaternary pedogenesis of lacustrine terraces in Gallocanta Lake, NE Spain

Transitional areas of lake margins are complex environments whose evolution is strongly controlled by flooding frequency and persistence. The edaphic development of lacustrine marginal environments can be reconstructed by combining detailed geomorphological analysis with a systematic edaphic study of toposequences. This approach has been applied to a set of recent lacustrine terraces in the downwind palustrine area of the Gallocanta saline lake, located in a semiarid area in NE Spain. Up to five terraces, from 1.6 to 4.5 m above the lake bottom, have been identified and mapped using stereo photointerpretation and airborne LiDAR data. Several cycles of water level fluctuations, as part of a general trend towards lake desiccation, have generated stepped terrace levels. The soils of these terraces have different morphological characteristics and provide evidences for the Gallocanta paleolake being larger than that of the present day. The soils have a sandy loam texture with variable clay content (1% to 46%) and a predominantly carbonate composition (mean = 26%). The soils are developed in a sequence of lacustrine carbonate-rich (mean = 37%) fine-grained gray layers overlaying detrital (mean = 51% gravels) and frequently erosive, carbonate-poor reddish layers. The pedogenesis of the downwind palustrine area is mainly characterized by poorly-developed carbonate accumulations and common redox mottles associated with water level fluctuations in the lake, which continuously rejuvenate or truncate the soils. Integrating pedological and geomorphological features provides insight into recent complex lacustrine and soil forming processes and facilitates management strategies and plans for this protected saline environment.This article has been funded by the Spanish Ministry of Economy and Competitiveness (MINECO) under projects AGL2012-40100 and PCIN-2014-106, by the Spanish Research Council (CSIC) under the project i-COOP-2016SU0015, and supported by the Andalusian PAI Research Group no. RNM-328. E. Luna was financed by the fellowship B087/13 from Aragón Government, Spain. Orthophotographs and LIDAR data were supplied by the Spanish National Geographic Institute (Instituto Geográfico Nacional). Rainfall data from Tornos were provided by the Spanish Meteorological Agency (AEMET) after contract no. L2 990130734

Mycorrhizae (VAM) of soybean in soil toposequences and mycorrhizal dependency of corn and soybean cultivars

A field survey investigated the effect of soil toposequences on vesicular-arbuscular mycorrhizal fungal (VAMF) spore counts in soil and VAMF colonization of soybean. VAMF spores were significantly different among locations, series, and series within a location. Colonization was negatively correlated with soil drainage;A second study determined whether soybean and corn cultivars varied in mycorrhizal dependency (MD) and, if so, whether this variability was explained by differences in plant morphological or physiological characteristics. Mycorrhizal dependency, nutrient uptake, phosphatase activities, and leaf areas of six corn and five soybean cultivars grown in low P soil were studied under greenhouse conditions. Soybean cultivars had higher MD than corn cultivars. Among soybean cultivars, unimproved cultivars had higher MD than improved cultivars. Shoot growth of Soja was 19 times greater and Mandarin four times greater with VAMF colonization than without colonization. Argentine pop, unimproved corn cultivar, was highly responsive to VAMF colonization whereas Reid yellow dent was unresponsive. Total uptake of P, N, K, Ca, Mg, and Zn was higher in mycorrhizal plants, but percentages of N, Mg, and Ca were lower. Acid phosphatase activity, shoot weights, leaf areas, and percentages of P were positively correlated with VAMF colonization;A further study evaluated three soybean cultivars, from high MD to low MD, for differences in root morphologies, P uptake, P use efficiencies, and root acid phosphatase activity at three P levels. This study showed significant cultivar-by-mycorrhizae and cultivar-by-P level interactions. Mycorrhizal dependency of Soja decreased from 70% in low P to 10% in high P soils. VAMF colonization of Swift at high P resulted in a 4.3% reduction in shoot weight. At low P, VAMF Soja plants had 564% greater total P than nonmycorrhizal plants. Comparable values for Mandarin and Swift were 242 and 165%, respectively. Soja roots had higher acid phosphatase activity than other cultivars and a higher relative increase in activity with VAMF colonization than without colonization. The root lengths of Soja were significantly shorter than those of Swift and Mandarin. The mean diameter of lateral roots of Soja was greater than that of Swift and Mandarin roots. Root lengths and surface areas were negatively correlated with MD. (Abstract shortened by UMI.

Comparison of physicochemical properties of soils under contrasting land use systems in Southwestern Nigeria

Soil physicochemical properties were determined for soils under cropland and forest at the headquarters of the International Institute of Tropical Agriculture in Ibadan, Southwestern Nigeria to examine the 30-year effects of different land use on the fertility of five soil series toposequences underlain by a Basement Complex. The cropland had been under cultivation for 30 years, during which mainly maize and yams had been cultivated in rotation with application of chemical fertilizer and intermittent fallow, while the forest had secondary vegetation that had been regenerated during a 30-year period under protection. The findings for cropland indicated an accumulation of available phosphorus and exchangeable potassium, soil compaction and slight depletion of topsoil organic carbon content; and the findings for forest indicated soil acidification and accumulation of exchangeable Ca at the surface soil horizon. These findings suggest the possibility of maintaining soil fertility with a long-term intensive and continuous crop farming system in kaolinitic Alfisol soil over the inland valley toposequences of tropical Africa