Short-term tillage effects on soil cone index and plant development in a poorly drained, heavy clay soil

Soil compaction is a big challenge in managing poorly drained clay soils. An on-farm field study was conducted over 2 years in a poorly drained, heavy clay soil, Red River Valley, Manitoba, Canada, where soil compaction, crop growth and root development were perceived as serious concerns. To address these concerns, no-tillage and sub-soiling tillage were proposed and compared with the traditional tillage system in which light-duty field cultivators were used at tillage depths ranging from 50 to 75 mm. Measurements of soil cone index indicated that a hardpan existed at approximately 175 mm soil depth in each fall as a result of wheel traffic during the growing season. It may not be necessary to break the hardpan with fall tillage operations in the studied region, as the hardpan was naturally removed over winter. Effects of tillage practices were evaluated using seeding performance and plant development. No-tillage resulted in the similar speed of emergence, plant population and crop yield, but more uniform seeding depth and more roots in the topsoil layer (0–75 mm), when compared with the conventional tillage. Sub-soiling promoted much faster crop emergence, higher plant populations and crop yield as well as deeper root penetration than the conventional tillage. However, the draft force required for sub-soiling was four times that of the conventional tillage.     

Genesis,Classification, and Management Requirements of Soils Formed in Windblown Material in the Guinea Savanna Area of Nigeria

Abstract

Eight pedons representing the major soils found within the Guinea Savanna region of northern Nigeria were studied with respect to their important morphological, physical, chemical, and other characteristics, and their suitability for sustainable agricultural production was evaluated. The most important soil characteristics observed for separating the soils into mapping units include presence or absence of petroferric contact, effective soil depth especially to hardpan layer, gravel and subsoil clay content. Dominant pedogenic processes, which influence the rate of soil development in the area, include plinthization, clay eluviation‐illuviation, iron (Fe)‐oxyhydroxide release (lateral movement and enrichment), eolian deposition, and leaching. According to the USDA system of classification, the soils (MU‐EDA) in the summit to upper slope are classified as Lithic Haplustepts, those (MU‐EDB) at the midslope are Typic Haplustepts, the MU‐EDC (lower slope soils) as Dystric Haplustepts, and the MU‐EDD (soils at the valley floors) as Oxyaquic Haplustepts. In the FAO/UNESCO system, a typical toposequence in the area consists of Dystric Cambisols (CMd) petroferric phase (MU–EDA and EDB), Dystric Cambisols (MU‐EDC), and Gleyic Cambisols (CMg) for the MU‐EDD mapping unit. The land capability and fertility capability classes of the soils were also established. The MU‐EDA, EDB, EDC, and EDD soil units were grouped into land capability class IVes, IIIes, IIs, and Vw and fertility capability class L”Rdk (6–8%), Ldehk (3–5%), Ldh, and Lgehk, respectively.     

Benefits of site-specific subsoiling for cotton production in Coastal Plain soils

The negative impacts of soil compaction on crop yields can often be alleviated by subsoiling. However, this subsoiling operation is often conducted at unnecessarily deep depths wasting energy and excessively disturbing surface residue necessary for erosion control and improved soil quality. A corn (Zea mays L.)–cotton (Gossypium hirsutum L.) rotation experiment was conducted over 4 years on a Coastal Plain soil with a hardpan in east-central Alabama to evaluate the potential for site-specific subsoiling (tilling just deep enough to eliminate the hardpan layer) to improve crop yields while conserving energy. Seed cotton yield showed benefits of subsoiling (2342 kg/ha) compared to the no-subsoiling treatment (2059 kg/ha). Averaging over all years of the study, site-specific subsoiling produced cotton yields (2274 kg/ha) statistically equivalent to uniform deep subsoiling at a 45 cm depth (2410 kg/ha) while not excessively disturbing surface soil and residues. Significant reductions in draft force were found for site-specific subsoiling (59% and 35%) as compared to uniform deep subsoiling at a 45 cm depth in shallow depth hardpan plots (25 cm) and medium depth hardpan plots (35 cm), respectively. Calculated fuel use for site-specific subsoiling was found to be reduced by 43% and 27% in the shallow and medium depth hardpan plots, respectively, as compared to uniform deep subsoiling in these same plots. Producers in the Coastal Plains who can determine (or who know) the depth of their root-impeding layer and perform site-specific subsoiling can have comparable cotton yields to traditional uniform depth subsoiling with reduced energy requirements.     

Cenozoic paleosols San Diego area,California

Ancient weathering profiles provide mute evidence of the major climatic regimes that operated in the southern California area during the Cenozoic Era. A tropical climate during part of the Paleocene and Early Eocene caused severe weathering of Jurassic andesitic rocks, Cretaceous granitic rocks and Late Cretaceous and Early Eocene terrigenous rocks. Erosional remnants of this paleosol exist as buried soils up to 30 meters thick and as exhumed soils on some modern hills. The main weathering horizon is overwhelmingly composed of kaolinite with residual quartz grains and minor amounts of iron oxides. This tropical climate was in effect at 35° to 40° north latitude.Late Eocene sedimentary rocks were deposited under a semi-arid climate with 50 to 60 cm of annual rainfall that was concentrated during one season. This interpretation is based on: 1) the dominance of conglomerate and immature sandstone in the Upper Eocene section compared to the relative scarcity of claystone, 2) the immaturity of the clay mineral suite which is dominated by smectite and vermiculite, 3) the presence of fractured clasts presumably split by growth and differential expansion of salts, 4) the multiple caliche beds that individually are up to one meter thick, and 5) the paleohydrology of the fluvial deposits which transported rhyolite gravels over 300 km distance from an eastern bedrock source about 4,000 m high in a river of 1.3 sinuosity with 100 year flood discharges up to 30,000 m³/sec.The extensive marine terraces in San Diego are mantled by relict soils that record composite weathering characteristics from glacial and interglacial climates from Late Pliocene to present. Maximal development of the paleosol includes an ironstone concretion layer (B_ir horizon) above an illuvial clay layer (B_t horizon) which rests on an iron- and silicacemented hardpan (C_m horizon).     

Cenozoic paleosols San Diego area,California

Ancient weathering profiles provide mute evidence of the major climatic regimes that operated in the southern California area during the Cenozoic Era. A tropical climate during part of the Paleocene and Early Eocene caused severe weathering of Jurassic andesitic rocks, Cretaceous granitic rocks and Late Cretaceous and Early Eocene terrigenous rocks. Erosional remnants of this paleosol exist as buried soils up to 30 meters thick and as exhumed soils on some modern hills. The main weathering horizon is overwhelmingly composed of kaolinite with residual quartz grains and minor amounts of iron oxides. This tropical climate was in effect at 35° to 40° north latitude.Late Eocene sedimentary rocks were deposited under a semi-arid climate with 50 to 60 cm of annual rainfall that was concentrated during one season. This interpretation is based on: 1) the dominance of conglomerate and immature sandstone in the Upper Eocene section compared to the relative scarcity of claystone, 2) the immaturity of the clay mineral suite which is dominated by smectite and vermiculite, 3) the presence of fractured clasts presumably split by growth and differential expansion of salts, 4) the multiple caliche beds that individually are up to one meter thick, and 5) the paleohydrology of the fluvial deposits which transported rhyolite gravels over 300 km distance from an eastern bedrock source about 4,000 m high in a river of 1.3 sinuosity with 100 year flood discharges up to 30,000 m³/sec.The extensive marine terraces in San Diego are mantled by relict soils that record composite weathering characteristics from glacial and interglacial climates from Late Pliocene to present. Maximal development of the paleosol includes an ironstone concretion layer (B_ir horizon) above an illuvial clay layer (B_t horizon) which rests on an iron- and silicacemented hardpan (C_m horizon).     

农地耕层与犁底层土壤入渗性能的连续测量方法

研究农田土壤入渗性能对于了解铧式犁耕作对土壤水力性能的影响、指导农地耕作方式决策、农田灌溉、改善农地生态环境具有重要意义。该文提出了一种农耕地耕层与犁底层土壤入渗能力连续测量方法以及相应的计算模型。采用恒定流量向地表供水,由供水在地表湿润面积随时间的变化过程估计地表耕层土壤初期很高的入渗性能,由产流后供水流量与产流流量之差计算相对较低的土壤入渗性能及犁底层土壤入渗性能。并进行了室内模拟试验,结果表明该方法可连续测量农地耕层与犁底层的入渗过程。采用入渗量和供水量对比的方法进行误差分析,相对误差为5.75%,说明该方法具有较高精度。该方法省时、省水便于野外应用,为今后的进一步研究提供手段。     

Deep tillage management for high strength southeastern USA Coastal Plain soils

Southeastern USA production is limited in Acrisols (Paleudults and Kandiudults) because they have high strengths and low water holding capacities. Production systems with crop rotations or deep tillage before planting were compared with less intensive management. Production systems included double-crop wheat (Triticum aestivum L.) and soybean (Glycine max L. Merr.) that were drilled in 0.19 m-row widths and grown in 15 m wide, 150 m long plots with soils of varying hardpan depths. Treatments included surface tillage (disked or none), deep tillage (paratilled or none), deep tillage with winter fallow and maize (Zea mays L.) in rotation, and disked/deep tillage with an in-row subsoiler where soybean was planted in conventional 0.76 m-wide rows. Cone indices were measured near the ends of each plot (120 m apart) to assess soil strength differences among soil types and among treatments. Cone indices were 1.50 MPa higher for non-deep tilled treatments than for deep tilled treatments and 0.44 MPa higher in wheel-track mid rows than in non-wheel-track mid rows. Cone indices were also 0.28 MPa higher for soils with shallower Bt horizons. Cone indices were not significantly different for subsoiled treatments and paratilled treatments. Rainfall was erratic throughout the 5-year experiment with dry periods lasting more than 2 weeks at a time and with annual totals ranging from 520 to 1110 mm. Wheat yields were 0.67 Mg ha⁻¹ greater for deep-tilled soils (subsoiled and paratilled) than for non-deep-tilled soils. Soybean yields were 0.36 Mg ha⁻¹ greater for paratilled than for subsoiled or non-deep-tilled treatments partly as a result of the more complete disruption of the paratill and partly because paratilled treatments were managed with narrow rows. Yields did not vary significantly among the soil types despite the fact that they had different cone indices. Tillage was a more dominant factor than soil type. For wheat, lower cone indices from tillage led to higher yields. For soybean, management of uniform loosening from deep tillage and narrow rows led to higher yields.     

Pedogenic and palaeoclimatic evidence from an Eemian calcrete in north‐western Sardinia (Italy)

A multidisciplinary approach was followed to study the pedogenic and palaeoclimatic information preserved in a buried palaeosol belonging to a Late Quaternary succession located along the bay of Alghero (north‐western Sardinia). The bay is dominated by a 5‐km long sandy beach‐ridge system backing an N‐S oriented lagoon system (Calich). The succession studied is characterized by basal shallow marine deposits, followed by clayey lagoon sediments and colluvial strata and capped by a relatively thick aeolianite. The research was based on pedological and sedimentological analyses, supported by optically stimulated luminescence (OSL) dating and by an in‐depth micro‐morphological study. Three main climatic pulses were highlighted during the Eemian. A wet period, with intense carbonate leaching occurred at the very beginning of the Eemian interglacial followed by very dry climatic conditions. This dry phase was long and arid enough to allow the formation of a thick calcrete hardpan, a typical feature of semi‐arid environments. The hardpan is dated at about 120 ka (kilo annum) and this dry event is tentatively associated with the late Eemian arid pulse (LEAP). The last phase of the Eemian recorded the restoration of a wetter climate. Finally, the succession indicated that even in a cooler environment, the central Mediterranean most probably maintained temperate conditions at least until the end of the MIS 5c (about 95 ka; early Würm).     

Improved root penetration of soil hard layers by a selected genotype

Abstract

Crops can be effectively grown on hardpan soils and water effectively used from deep in the profile if hard layers in soils can be penetrated or if they are broken up by tillage. Addition of gypsum to the soil or exploitation of genetic differences in root penetrability may help improve root penetration through hard layers with less need to depend on the energy requirements of deep tillage. To test this theory, a single‐grained Ap horizon of Norfolk loamy sand soil was compacted into soil columns to compare root penetrability of soybean [Glycine max (L.) Merr.] genotypes Essex and PI 416937 in the presence and absence of gypsum and at two soil compaction levels (columns with uniform compaction at 1.4 g cm^‐1 and columns with increasing compaction with depth from 1.4 to 1.75 g cm^‐1). Compaction treatments were imposed by constructing soil columns composed of 2.5‐cm‐deep, 7.5‐cm‐diameter cylindrical cores compacted to predetermined bulk densities (1.40,1.55,1.65,and 1.75 g cm^.3). Soil penetration resistances were measured on duplicate cores using a 3‐mm‐diameter cone‐tipped penetrometer. Columns were not watered during the study; soybean genotypes were grown in the columns until they died. Both genotypes lived one day longer in columns with lower bulk density and penetration resistance. Although root growth was more abundant for Essex than for PI 416937, root growth of PI 416937 was not decreased by compaction as much as it was for Essex. These results suggest that PI 416937 may possess the genetic capability to produce more root growth in soils with high penetration resistance. This study suggests that genetic improvement for root growth in soils with hard or acidic layers may potentially reduce our dependence on tillage. Gypsum did not affect root growth in this study.     

Effect of Continuous Rice–Wheat Rotation on Soil Properties from Four Agro‐ecosystems of Indian Punjab

In Indian Punjab, rice–wheat is a dominant cropping system in four agro‐ecosystems, namely undulating subregion (zone 1), Piedmont alluvial plains (zone 2), central alluvial plains (zone 3), and southwestern alluvial plains (zone 4), varying in rainfall and temperature. Static and temporal variabilities in soil physical and chemical properties prevail because of alluvial parent material, management/tillage operations, and duration of rice–wheat rotation. A detailed survey was undertaken to study the long‐term effect of rice–wheat rotation on soil physical (soil separates, bulk density, modulus of rupture, saturated and unsaturated hydraulic conductivities, soil water content, and suction relations) and chemical (organic carbon, pH, electrical conductivity) properties of different textured soils (sandy clay loam, loam, clay loam, and silty clay loam) in these four zones of Punjab. Soil samples (of 0‐ to 30‐cm depth) from 45 sites were collected during 2006 and were analyzed for physical and chemical properties. The results showed that sand content and pH increased whereas silt and organic carbon decreased significantly from zones 1 to 4. Compared to other textures, significantly greater organic carbon, modulus of rupture, and pH in silty clay loam; greater bulk density in clay loam, and greater saturated hydraulic conductivity in sandy clay loam were observed. Irrespective of zone and soil texture, in the subsurface soil, there was a hard pan at 15–22.5 cm deep, which had high soil bulk density, modulus of rupture, more silt and clay contents (by 3–5%) and less organic carbon and hydraulic conductivity than the surface (0–15 cm) layer. These properties deteriorated with fineness of the soil texture and less organic carbon content. Continuous rice–wheat cropping had a deleterious effect on many soil properties. Many of these soils would benefit from the addition of organic matter, and crop yields may also be affected by the distinct hardpan that exists between 15 and 22.5 cm deep.     

Cotton management in a compacted subsurface microirrigated coastal plain soil of the southeastern US

A loamy sand Acrisol (Aquic Hapludult) that had been microirrigated for 6 years became so severely compacted that it had root limiting values of soil cone index in the Ap horizon and a genetic hardpan below it. Deep and surface tillage systems were evaluated for their ability to alleviate compaction. Deep tillage included subsoiling or none. Both deep tillage treatments were also surface tilled by disking, chiseling, or not tilling. Subsoiling was located in row or between rows to avoid microirrigation tubes (laterals) that were buried under every other mid row or every row. Cotton (Gossypium hirsutum) was planted in 0.96-m wide rows. Cotton yield was improved by irrigation from 485 to 1022 kg ha⁻¹ because both 2001 and 2002 were dry years. Tillage loosened the soil by an average of 0.5–1.3 MPa; but compacted zones remained outside tilled areas. Subsoiling improved yield by 131 kg ha⁻¹ when performed in row where laterals were placed in the mid rows; but subsoiling did not improve yield when it was performed in mid rows. For subsurface irrigation management in these soils, the treatment with laterals buried under every other mid row was able to accommodate in-row subsoiling which improved yield; and this treatment was just as productive as and had been shown to be less expensive to install than burying laterals under every row.     

东北几种耕作土壤的微形态特征

黑土、白浆土、苏打盐土是我国东北地区的主要耕作土壤。为了培育高肥沃度土壤,不仅需要了解它们的保肥量、供肥量、供肥速度和土壤的水、热、气状况等。也要摸清其结构性态,即土壤颗粒间的团聚垒结程度、团聚体的大小、排列状况和所形成团聚体的稳定性和孔隙性。以便揭示土壤肥力形成的机理,为进一步调节控制土壤肥力提供依据。     

Forms and profile distribution of potassium in typical soils of the lower Benue Valley of Nigeria

Abstract

Six profiles, derived from Precambrian Basement Complex rocks (mainly gneiss), Cretaceous sediments (mainly shale and sandstone), and Quaternary alluvium, and which are typical of the major agricultural soils in the Lower Benue Valley (Nigeria) were studied with the objective to determine their overall potassium (K) reserves and any relationship between these and other soil properties including their parent materials. Total K in the soils varies from 0.13–27.1 g kg^‐1 with average 6.64 g kg‐¹. This correlates positively with the clay, and negatively with the sand contents of the soils and is also influenced by their parent materials. The order of abundance according to parent material is: alluvium‐ > Basement Complex (gneiss)‐ ≈ shale‐ > sandstone‐derived soils. The concentrations of readily available K (RAK) in the soils are quite low, accounting for only between 0.30 and 7.8% of the total K in the soils and less than 4.0% of their exchange capacities. Based on critical limits established for many Nigerian soils, the soils derived from sandstone are clearly deficient in RAK, while soils developed from gneiss, shale and alluvium parent materials have moderate to sufficient levels for a wide range of crops. Non‐exchangeable or moderately available K (MAK) in the soils is also relatively low (0.020–8.59 mmol_c kg^‐1); while the sandstone‐derived soils have the least MAK, the alluvial soils have the most levels. However, the potassium supplying power (KSP) of the soils may be considered to be generally high. Although this bears no particular relationship to soil parent materials, the sandstone‐derived soils have the lowest KSP. The bulk of the total K reserves in the soils (55–88%) exists as difficultly available or structural K (DAK). The alluvial soils first, then the gneiss‐ and shale‐derived soils next have the highest contents of DAK, while the highly weathered sandstone soils have the lowest. Simple correlation analysis shows that, irrespective of parent material and K form, clay content and CEC are the most important soil properties influencing the overall K supplying status of these soils. It is concluded that in major agricultural soils of the Lower Benue Valley of Nigeria K exists mostly in the lattice structures of K‐bearing minerals, with accumulations in the subsurface horizons. Its plant‐available or supplying status is low on sandstone‐derived soils and moderate to sufficient on soils derived from Basement Complex rocks, shales and alluvium.     

Biological properties of soils in the Moscow State University Botanical Garden: The branch on Prospekt Mira

Among the urban soils of Moscow, the soils of botanical gardens remain poorly studied. In this connection, the investigation of the soils in the Botanical Garden of Moscow State University (the branch on Prospekt Mira) founded 300 years ago is of great interest. The morphological, microbiological, chemical, and physical properties of these soils classified by Stroganova as culturozems or recreazems are described in detail. These soils (including the buried horizons) have a neutral reaction, 3–4% organic carbon, and an elevated heavy metal concentration. The soils are enriched with Azotobacter (indicating their high fertility) and yeasts (lipomycetes, which are characteristic inhabitants of the soils under forest plantations). These organisms also inhabit the buried horizons. All the soils studied were not toxic with respect to Azotobacter.     

Soils of Low-Mountain Landscapes of North Karelia

Soils of low-mountain landscapes in the northwest of Karelia have been studied. The soil cover of the studied area is mainly represented by Al–Fe-humus soils (Podzols); thin soils (Leptosols) are widespread. Characteristic morphological features of all the studied soils are relatively shallow profiles, high stone content, and underlying by hard bedrock with fine earth material in crevices between large boulders. The studied soils have the high carbon and low nitrogen content, which points to unfavorable conditions of organic matter transformation. The content of most macro- and microelements is not high, which is typical for soils of the region; the content of copper and zinc exceeds the regional background two–three times. Regularities of the vertical zonality in the properties of soils of mountain ecosystems manifest themselves in decreasing thickness of the soil profile at higher altitude above sea level in parallel to decreasing thickness of the layer of loose rocks, while the stone content increases. In soils of the forest-tundra zone, the organomineral horizon with the high organic matter content is formed immediately under the forest litter. The litter horizon is the soils of this zone is characterized by increased concentrations of calcium, magnesium, phosphorus, and zinc.     

The importance of andic soils in mountain ecosystems: a pedological investigation in Italy

Andic soils have unique morphological, physical and chemical properties that induce both considerable soil fertility and great vulnerability to land degradation. In recent years there have been many reports of soils with andic properties in Non‐Volcanic Mountain Ecosystems (NVME) in different parts of the world. This paper attempts to assess the importance of andic soils in mountain ecosystems of Italy. We used the criteria of altitude (> 700 m above sea level), slope (< 12°) and active green biomass (maximum Normalized Difference Vegetation Index (NVDI) value > 0.5) for identifying sites where andic soil processes may occur in the NVME of Italy. We characterized in detail 42 soils in the areas thus identified. According to WRB (2006) the main soils are Andosols, Cambisols, Phaeozems, Umbrisols and Podzols. Despite the taxonomic diversity, the morphological, micromorphological and chemical properties indicate considerable pedological homogeneity in these soils. The most striking features are the large values of Al_o + 0.5Fe_o (as %), which is a standard index for andic soil properties ( USDA, 2006; WRB, 2006 ), but it occurs at the wrong depths for many of our soils to qualify as true Andosol/Andisols and there is little evidence of podzolization. We therefore suggest that (i) andic soils must be recognized more clearly in soil classification, particularly with respect to the depths at which andic properties are developed, and (ii) the importance of andic soils in Italian NVMEs (and possibly elsewhere in the world) has been underestimated. These soils warrant further investigation because of their agricultural potential and ecological importance.     

Geomorphic implications of Pre-Wisconsin soils on the White River Plateau erosion surface of northwestern Colorado

The White River Plateau erosion surface (Miocene-Pliocene) at an elevation of approximately 2850 m (9500 ft) is dominated by weakly developed Holocene soils which commonly possess simple A-C horizonation. However, Pre-Wisconsin soils occur on the surface in isolated areas at both high and low topographic sites, most notably in Triangle Park. These Pre-Wisconsin soils consist of composite, polygenetic profiles having truncated, clayey subsoils which are overlain by stone or pebble lines, colluvium, soil creep, and probable local eolian deposits Truncation of the paleosols preceded development of the Holocene soils, which have formed on bedrock surfaces and have been superposed on the truncated, buried paleosols Soil distribution and character, in relation to structure of bedrock on the erosion surface, indicate that the surface as it now exists is structurally controlled and has a topography generated in late Tertiary to Pre-Wisconsin time.     

Injection of chemical amendments into compacted subsoils: Growth and nutrient uptake by wheat

Abstract

Some form of deep tillage is required in the coarse‐textured sandy soils of the Southeast in order to attain maximum yield of wheat. ‘Slit‐till’ is a tillage system that modifies plowpans and permits root penetration and proliferation into subsoil horizons. A greenhouse experiment was conducted to determine the effects of calcium nitrate, calcium phosphate, ammonium phosphate, ammonium nitrate, and dolomitic limestone slurry on wheat (Triticum aestivum sp.) root development through the slit of a compacted acid subsoil, and the effects of injection of chemical amendments on the soil chemical properties of acid subsoil. Soil cylinders were prepared using A and B horizons of Marvyn loamy sand (fine‐loamy, siliceous, thermic, Typic Hapludults) soil by placing 56‐cm of subsoil and 10‐cm of topsoil in PVC tubing. A 6‐cm‐thick hardpan was created at the top of the subsoil. Leaf and root concentrations of P were increased by chemical injections in the slit. All amendments increased plant height, but tillering was not affected by chemical amendments. Gypsum blocks placed at 10, 20, and 45 cm indicated a decrease in soil water at the 20‐cm depth 25 days after plant emergence with all amendments except ammonium phosphate. Soil pH was increased and KCl‐extractable aluminum was decreased by dolomitic limestone up to 3.0 cm from zone of injection.     

广东的海涂土壤

广东面临南海,岸线长而曲折,多港湾和岛屿,众多河流的来水来沙,形成沿岸大面积的海涂土壤。其土层深厚,质地不一,盐分和养分含量较高,气候条件优越,开垦利用价值很高,潮间带宜农垦面积以珠江口较大,是今后围垦种植的主要基地,适时围垦后可宜发展外向型农业;广阔的潮下带及不适宜农垦的潮间带,宜发展海水养殖业,这是今后海岸带开发利用的重要领域。并毗邻港澳、经济特区和沿海开放城市前缘,因此,积极开发利用丰富的海涂土壤资源,对促进沿海经济发展是有其重要的战略意义。     

A quaternary soil sequence in the Kennet Valley,central southern England

The field characteristics, texture, mineralogy and micromorphology of the soils of four chronologically separate river terraces of the River Kennet are described. The soils on the three uppermost terraces have illuvial (palaeoargillic) horizons, which have been intensely disturbed by periglacial activity. These horizons are overlain by similarly disrupted eluvial horizons mixed with aeolian silts derived from outside the Kennet catchment. The illuvial horizons most probably result from interglacial pedogenesis under climatic conditions warmer and wetter than at present, whilst the aeolian material was probably added to the soils during the last glacial period (Devensian). The lowest and youngest terrace is characterised by an undisturbed (normal argillic) soil developed in loams derived predominantly from the aeolian silts. Consequently, it is postulated that the soils of the lowest terrace owe their characteristics to a phase of postglacial pedogenesis.The results illustrate that several phases of pedogenesis can be recognised, which provide important information on the Quaternary development of the area. This is especially significant where floral, faunal, or archaeological evidence of environmental changes is unavailable.