Distribution In Soil Profile Research Articles

Elevated temperature reduces survival of peak populations of root-lesion nematodes (Pratylenchus thornei) after wheat growth in a vertisol

Elevated temperature was investigated to understand why there is a faster decline in Pratylenchus thornei population abundances in the topsoil than in deeper layers of vertisols after wheat matures in the subtropical grain region of eastern Australia. Soil containing a large population abundance of P. thornei (after wheat growth) was incubated in a replicated experiment for various periods up to 16 weeks at eight temperatures ranging from 10 to 45 °C in 5 °C intervals, with three moisture treatments, namely (a) field capacity maintained during incubation, (b) field capacity allowed to dry during incubation and (c) air-dried before incubation. After incubation, live nematodes were extracted from the soil samples by the Whitehead tray method for 2 and 7 days and P. thornei was counted in four life-stage categories. Temperatures ≥ 35 °C resulted in rapid death of P. thornei independent of any effects due to soil desiccation. At lower temperatures, survival over a 16-week period was better in soil maintained at field capacity than in soil allowed to dry. Death of P. thornei in soil that was air-dried before incubation was rapid during incubation at all temperatures tested. Elevated temperature of itself plus faster soil desiccation with increasing temperature are the likely causes of the faster decline in P. thornei population abundances in the topsoil than in the subsoil. These effects can contribute to soil profile distributions of P. thornei recorded in some fields in this subtropical grain region after clean fallow periods where greater population abundances of P. thornei occur in the subsoil layers than in the topsoil.

Coupled effects of mulching and nitrogen fertilization on crop yield, residual soil nitrate, and water use efficiency of summer maize in the Chinese Loess Plateau.

Appropriate water-saving and nitrogen management strategies are critical for achieving sustainable agricultural development in dry sub-humid areas of the Chinese Loess Plateau. The present study was conducted in 2004, 2005, 2008, and 2012 based on a long-term field experiment and aimed to investigate the coupled impacts of mulching and N fertilization on maize yield, water use efficiency (WUE), and residual soil nitrate (RSN) accumulated in the soil profile (0-200cm). The results demonstrated that mulch is conducive to increasing summer maize yield. The plastic film-mulched ridge and straw-mulched furrow (RF) treatment significantly increased maize yield across the studied period, while the straw mulch (SM) treatment did not significantly increase maize yield until the third experimental year. Compared with SM, the RF treatment showed more significant and positive effects on maize yield, WUE, and RSN accumulated in the 0-200cm soil depth. N fertilization significantly increased maize yield and WUE, but no significant differences were observed when 120 and 240kg N ha-1 were applied. The N240 treatment was characterized by relatively high NO3--N accumulation in 0-200cm soil depth and low ratios of soil nitrate in the upper to the lower soil layers, indicating a considerable potential for NO3--N leaching. Averaged across years, economic optimum N fertilizer rates (Nops) were 154, 148, and 150kg N ha-1 for the no mulch, RF, and SM treatments, respectively. This suggested that 25.8-51.2% of N rate can be reduced while maintaining an acceptably high maize yield. Additionally, understanding NO3--N depth distribution in 0-100cm soil profile can adequately predict and represent the characteristics of NO3--N accumulated in the 100-200cm and 0-200cm soil layers because of their significant correlations, thus saving time and money. In conclusion, the practice of RF combined with properly reduced farmers' N rate (~150kg N ha-1) is the preferred option for maize production in the Chinese Loess Plateau, and further research is required to investigate the effects of mulching on summer maize under Nop conditions.

Quantitative description of vertical organic matter distribution in real soil profiles by means a simple continuous model

Previously we have proposed a continuous model of soil organic matter (SOM) transformation which was based on describing only the most general notions of this process – a gradual increase in SOM stability toward transformation, occurring concurrently with partial decomposition of SOM. The model provided qualitative description of vertical SOM distributions in different soils. In the present study this model has been modified to make the description more realistic. The study demonstrates quantitative correspondence between the calculated and averaged observed vertical distributions of SOM for different biomes.

Identification of nitrate pollution sources of groundwater and analysis of potential pollution paths in loess regions: a case study in Tongchuan region, China

Groundwater is the essential and predominant source of drinking and irrigation water supplies in most arid and semiarid regions, particularly in Loess Plateau of China. The threat to groundwater quality by nitrate pollution has always been of considerable concern in loess regions. In this paper, correspondence analysis, stoichiometric analysis, ratios of major ions and some qualitative analysis are employed to discuss the spatial variability of nitrate (NO3 −), identification of NO3 − pollution sources and its potential pollution paths based on 112 water samples in Tongchuan region on the middle edge of Loess Plateau of China. Results indicate that the NO3 − concentrations ranged from 0.25 to 173 mg/L, 20.54% of water samples exceeded the Standards for Drinking Water Quality from China (≤44 mg/L), and 15.18% of samples exceeded the Guidelines for Drinking Water Quality from World Health Organization (≤50 mg/L); the water samples with high NO3 − concentrations primarily concentrated in river valleys, and the types were mainly pore waters and individual surface waters. Sewage or manure from livestock effluent was the primary sources of NO3 − in some surface waters, pore water samples with high NO3 − were closely related to agricultural input or a mixing process. Groundwater recharges from surface water and vertical infiltration in river valleys with shallow groundwater depth were considered as the potential pollution paths for NO3 − ions in the study area based on nitrate nitrogen distribution in soil profile. Driven by concentration difference and local seepage system, these NO3 − ions diffused around and groundwater buried in great depth was consequently polluted. Therefore, river valleys should be listed as the prior protection areas in loess regions; in addition, the time lag between land use changes and groundwater quality response should also be paid attention to in nitrate pollution prevention, particularly in the thick unsaturated zones.

Lead isotope distribution and enrichment factors in soil profiles around an abandoned Pb-smelter plant

Todos os Santos (all Saints) Bay area on Brazil’s east coast is known for one of the most significant cases of lead contamination in the country owing to the past activities of a Pb-smelter plant. This work was carried out to assess the concentration and sources of Pb based on Pb isotopes and enrichment factor of soil profiles surrounding Todos os Santos Bay in order to understand the expansion of contamination and to help the establishment of Pb regulatory standards for the region. Forty-four samples were collected from soil genetic horizons of six pedons that represent the range of dominant soil properties and geologic materials in the region. Concentrations of Pb and the isotopes 204Pb, 206Pb, 207Pb, and 208Pb were determined on an inductively coupled plasma (quadrupole) mass spectrometry. The soil enrichment factor was calculated using Al and Fe as conservative index elements. Average Pb concentration (15.87 mg kg−1) in uppermost horizons (from all six pedons) is slightly higher than soil background concentrations commonly reported in Brazil. Samples feature a wide range of Pb isotope ratios, ranging from 36.71 to 47.38 for 208Pb/204Pb, 15.00 to 15.65 for 207Pb/204Pb, 16.86 to 20.59 for 206Pb/204Pb, and 1.10 to 1.31 for 206Pb/207Pb. For the enrichment factor calculations, only Fe demonstrated a good agreement with Pb isotopic ratios. Both Pb isotopic composition and enrichment factor were useful tools to distinguishing natural and anthropogenic influence on the Pb soil concentrations.

Sulphur Forms Distribution in Soil Profiles of Different Locations of Southwestern Nigeria

Sulphur Forms Distribution in Soil Profiles of Different Locations of Southwestern Nigeria

Application of magnetic susceptibility in assessment of heavy metal contamination of Saxonian soil (Germany) caused by industrial dust deposition

Magnetic susceptibility is used worldwide as a measure of concentration of (ferri)magnetic minerals in soil, sediment and dust. In soils, these minerals are of various origins: air-derived particulate pollution, parent rocks or pedogenesis. Human activity causes different changes in the content of magnetic minerals as well as their spatial and vertical distribution in soil profiles. Magnetic minerals are characterised by an affinity to other elements occurring in the soil, e.g. heavy metals. Therefore magnetic susceptibility has been widely applied as approximation of soil contamination by heavy metals.The archival soil samples collected from different soil horizons in the territory of the Free State of Saxony (Germany) were subjected to magnetic susceptibility measurements using Bartington MS2B. Additionally, samples were chemically analysed in order to determine the content of Fe, Mn, Ni, Cu, Zn, Cd, Pb and As using a method of atomic absorption spectroscopy (AAS). The contamination factor (CF) and geoaccumulation index (Igeo) were applied for assessment of soil contamination with particular potentially toxic elements (PTE), while the more general pollution load index (PLI) was used for comparison between different geographic sites.Values of magnetic susceptibility varied from 16.6 to 1382×10−8m3kg−1 in organic soil horizons and from 0.1 to 1580×10−8m3kg−1 in deeper layers. Significant and relatively high correlation coefficients between soil magnetic susceptibility and the content of some heavy metals indicated that they were of the similar origin as (ferri)magnetic minerals occurring in soil (viz. industrial pollution, parent rocks or pedogenic processes). PLI distribution over the entire area of Saxony corresponds well with the magnetic susceptibility distribution, especially in the organic soil horizon. The indices qualify the northeastern part of Saxony as extremely or heavily polluted in the organic soil horizon (under forests) with decreasing contamination in deeper layers, being classified as non-polluted to moderately polluted. However, the prevailing Saxony area is characterised by low and moderate contamination by potentially toxic elements, such as heavy metals.

Vertical and lateral subsurface preferential flow along an agricultural catena

Despite all efforts, agricultural contaminants remain at alarming concentrations in Quebec surface waters. Preferential flow (PF) of soluble contaminants has been suggested as a contributing factor but has not been specifically studied in the humid climate of eastern Canadian soils. Three tracers were surface applied on plots along a catena on a loamy sand under intensive agricultural production in Beauce, Quebec. Tracer distribution in soil profiles was monitored three times over a 12-month period. At the summit, finger flow rapidly transported tracers into the subsurface. The subsurface preferential lateral flow rapidly brought the tracers downslope. Narrow points of preferential seepage and discharge and underground lateral PF were observed at the footslope. The summit and the backslope of the catena showed strong vertical and lateral subsurface PF, which made their contribution to subsurface tracer movement toward surface water equal to or greater than that of the footslope, in part because of the hydrological connectivity between summit, backslope, and surface water. PF and matrix flow were both significant in all parts of the catena. Therefore, all parts of a catena, even those far from surface water, should be considered when evaluating potential belowground contaminant transport toward surface water.

Spatial and seasonal distributions of soil sulfur in two marsh wetlands with different flooding frequencies of the Yellow River Delta, China

Soil samples from 0 to 100cm depth were collected in eight sampling sites (Sites A1, B1, C1 and D1; Sites A2, B2, C2 and D2) respectively along two 250-m length of sampling zones (Zone N and Zone S) from the Yellow River channel to a tidal creek in the short-term flooding and seasonal flooding wetland of the Yellow River Delta of China in fall of 2007 and spring of 2008 to investigate spatial and seasonal distribution patterns of total sulfur (TS) and their influencing factors. Our results showed that TS contents in both seasons in surface soil in Zone N increased with increasing distances away from the Yellow River channel except for Site D1 in fall. However, TS contents in both seasons in surface soil in Zone S showed a tendency of increasing and then decreasing with increasing distances away from the Yellow River channel. Relative to spring, the mean TS contents in surface soils were slightly higher in fall in Zone N, whereas an opposite tendency was observed in Zone S. The mean TS stocks were obviously higher in fall with 934.36g/m2 and 877.77g/m2 compared to those in spring with 729.85g/m2 and 696.78g/m2 in Zone N and Zone S, respectively. TS contents and stock generally declined with depth along soil profiles with one accumulation peaks at a soil increment of 40–60cm. Topsoil concentration factors also indicated that TS had shallower distribution in soil profiles. Soil total carbon (TC), total nitrogen (TN), soil organic matter (SOM), salinity and silt exerted positive loadings on TS, while soil pH and depth exhibited a negative correlation with TS content.

Long-term tillage impacts on soil organic matter components and related properties on a Typic Argiudoll

Soil organic matter affects a number of soil processes and properties. A better understanding of soil-profile distribution of organic matter components and related soil properties under long-term tillage systems is thus needed. The objective of this study was to evaluate the impacts of 33 years no-till (NT), double disk (DD), chisel (CH), and plow tillage (PT) under corn (Zea mays L.)–soybean (Glycine max L.) rotation on soil organic C (SOC), particulate organic matter (POM), pH, and wet aggregate stability to 100cm soil depth on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls) in eastern NE. After 33 years, NT and DD management increased SOC by 1.2 times and mean weight diameter (MWD) of aggregates by 2 times compared with CH and PT at the 0–10cm depth. At the 0–20cm, NT had 1.1 times higher SOC concentration than CH and PT. When compared with data collected 24 years prior to this study, SOC at the 0–20cm increased by 12.5% across NT, DD, and CH and by 2.7% for PT. No-till had 5 times higher total POM concentration than PT, 4.7 times higher than CH, and 2.4 times higher than DD at the 0–10cm depth. However, at the 10–20cm, PT had higher POM than other tillage systems, which is most probably due to mixing and burial of residues at the bottom of the plow layer. Soil pH did not differ among tillage treatments at the 0–10cm, but it differed in this order: PT>CH>DD>NT at the 10–20cm and PT=CH=DD>NT at the 20–40cm depth. The lower pH under NT, DD, and CH in deeper soil depths may be due to the limited or no lime mixing in these systems compared with PT. When compared with data (pH 5) collected 33 years prior to this study, soil pH increased by 0.9 in NT, 1.4 in DD, 1.5 in CH, and 1.9 units in PT at 0–20cm depth, probably due to surface application and incorporation of lime. Overall, 33 years of NT increased near-surface soil organic matter components and soil aggregation compared with the PT.

Effects of slow-release fertilizers on nitrate leaching, its distribution in soil profile, N-use efficiency, and yield in potato crop

The purpose of the present study was to study the effect of slow-release fertilizers on nitrate leaching, its distribution in soil profile, N-use efficiency (NUE), and yield in potato cultivation in the years 2012 and 2013. The treatments included nano-nitrogen chelate (NNC), sulfur-coated nano-nitrogen chelate (SNNC), sulfur-coated urea (SCU), and urea (U) at three levels of nitrogen input (46, 92, and 138 kgN/ha). For this purpose, a factorial experiment in completely randomized designs (CRD) was designed and conducted with three replicates. The results of variance analysis showed that each treatment had significant effects on yield, leaching, and soil nitrate. Comparison of nitrate leaching values due to the treatments showed that NNC, SNNC, and SCU fertilizers led to reduced nitrate leaching levels by 35.72, 41.56, and 9.94 % compared to U fertilizer application. In contrast, potato yield increased by 56.10, 59.61, and 49.76 % with NNC, SNNC, and SCU fertilizers, respectively, compared to U fertilizer application. The highest NUE value in both years was observed in 46 kgN/ha of nitrogen input treatment. This value in the years 2012 and 2013 was 1056 and 793 kg/kg and belonged to the SNNC and SCU treatments, respectively. Moreover, the maximum tuber nitrate concentration (228 mg/kg) was recorded with the third nitrogen level of urea.

Nitrogen Distribution in Soil Profile under Sesame, Maize and Wheat Crops as Affected by Organic and Inorganic Nitrogen Fertilizers Using 15N Technique

Nitrogen Distribution in Soil Profile under Sesame, Maize and Wheat Crops as Affected by Organic and Inorganic Nitrogen Fertilizers Using 15N Technique

Novel approach for quantitatively estimating element retention and material balances in soil profiles of recharge basins used for wastewater reclamation

We investigated changes in element content and distribution in soil profiles in a study designed to monitor the geochemical changes accruing in soil due to long-term secondary effluent recharge, and its impact on the sustainability of the Soil Aquifer Treatment (SAT) system. Since the initial elemental contents of the soils at the studied site were not available, we reconstructed them using scandium (Sc) as a conservative tracer. By using this approach, we were able to produce a mass-balance for 18 elements and evaluate the geochemical changes resulting from 19years of effluent recharge. This approach also provides a better understanding of the role of soils as an adsorption filter for the heavy metals contained in the effluent. The soil mass balance suggests 19years of effluent recharge cause for a significant enrichment in Cu, Cr, Ni, Zn, Mg, K, Na, S and P contents in the upper 4m of the soil profile. Combining the elements lode record during the 19years suggest that Cr, Ni, and P inputs may not reach the groundwater (20m deep), whereas the other elements may. Conversely, we found that 58, 60, and 30% of the initial content of Mn, Ca and Co respectively leached from the upper 2-m of the soil profile. These high percentages of Mn and Ca depletion from the basin soils may reduce the soil's ability to buffer decreases in redox potential pe and pH, respectively, which could initiate a reduction in the soil's holding capacity for heavy metals.

Soil Fertility Status under Important Agroforestry Tree Species in Himachal Pradesh

A study was conducted to evaluate the soil fertility status under six different agroforestry species in Himachal Pradesh. Soil reaction was found to be nearly neutral under all the vegetations with lesser variability which showed pH stability. Bulk density was observed lower in the soils under different vegetations as compared to control in all the depths. Organic carbon and organic matter was higher in the soils under different vegetation as compared to control. Organic carbon was decreasing down the profile under all the vegetation and maximum in upper layers. Among the vegetations, maximum (1.38 %) organic carbon was observed in the soils under Bauhinia variegata followed by Morus alba (1.33 %), Grewia optiva (1.30 %), Toona ciliata (1.28 %), Albizia chinensis (1.22 %) and the least was under Celtris australis (1.20 %). The availability of nitrogen was higher in the surface soils under different vegetations in comparison to soils without any vegetation. The pattern of availability of phosphorous and its distribution in soil profile was therefore similar to that of organic carbon and nitrogen. Ex. potassium content varied from (97.17 kg/ha to 195.29 kg/ha) in all the depths under different vegetation, as compared to control (83.27 kg/ha to 139.87 kg/ha). pH and bulk density under barren land was statistically different at 0.05 level with the pH and bulk density under different plantations. Organic carbon in the soils under barren land showed statistically significant differences with the soils under different plantations.

Distribution and assessment of Pb in the supergene environment of the Huainan Coal Mining Area, Anhui, China.

Coal mining area is highly subject to lead (Pb) pollution from coal mining activities. Several decades of coal mining and processing practices in dozens of coal mines in the Huainan Coal Mining Area (HCMA) have led to the accumulation of massive amounts of coal gangue, which piled in dumps. In order to investigate the impacts of coal gangue dumps on Pb level in the supergene media of the HCMA, a systematic sampling campaign comprising coal gangue, soil, wheat, and earthworm samples was conducted. The average Pb content in the coal mining area soil is 24mg/kg, which is slightly higher than the associated coal gangues (23mg/kg) and markedly higher than reference region soil (12.6mg/kg). Soil in the HCMA present a slight to moderate Pb contamination, which might be related to the weathering and leaching of coal gangue dumps. Lateral distribution of Pb in HCMA soil differed among individual coal mines. The soil profile distribution of Pb depends on both natural and anthropogenic contributions. Average Pb content is higher in roots than in stems, leaves, and wheat husks, while the Pb level in seeds exceeded the maximum Pb allowance for foods (Maximum Levels of Contaminants in Foods of China, GB 2762-2012). Earthworms in the selected area are significantly enriched in Pb, suggesting higher bio-available Pb level in soil in the HCMA.

Geochemical fractions of chromium, copper, and zinc and their vertical distribution in floodplain soil profiles along the Central Elbe River, Germany

The determination of geochemical fractions of heavy metals (HM) in soils is a key issue when studying their mobility. Therefore, we have determined the geochemical fractions and the vertical distribution of chromium (Cr), copper (Cu), and zinc (Zn) in seven floodplain soil profiles in relation to flooding conditions and relevant soil properties. These soil profiles represent two different soil groups (Mollic Fluvisols and Eutric Gleysols) which differ significantly in flooding duration and soil properties. The metals were fractionated sequentially to seven fractions as follows: F1: soluble+exchangeable, F2: easily mobilizable, F3: bound to Mn oxides, F4: bound to soil organic matter (SOM) (might include sulphides), F5: bound to low crystalline (amorphous) Fe oxides, F6: bound by crystalline Fe oxides, and F7: residual fraction.The total Cr, Cu, and Zn concentrations ranged from 54.4 to 134.1, 165.2 to 215.7, and 128.5 to 1097.8mgkg−1, respectively, and exceeded the precautionary values of the BBodSchV (1999). Total metal concentrations correlated significantly to soil organic carbon (SOC), total sulphur (St), and cation exchange capacity (CEC), as well as crystalline and amorphous Fe- and Mn-oxides. The residual fraction was dominant for Cr, the organic bound for Cu, and crystalline Fe oxides for Zn. The potential mobile fraction (PMF=∑F1–F6) ranged from 38.4 to 71.4, 63.9 to 85.1, and 51.5 to 83.3% of the total Cr, Cu, and Zn, respectively. However, the mobile fraction (MF=∑F1–F2) ranged from 0.96 to 1.84, 2.1 to 4.1, and 9.1 to 28.7% of the total concentrations of Cr, Cu, and Zn, respectively. The order of the PMF in the studied soil profiles was Cu>Zn>Cr, while the order of the MF was Zn>Cu>Cr. The PMF of the three metals was positively correlated with SOC and Mn oxides. The PMF was positively correlated with CEC (Cr, Zn), St (Cr), and Fe oxides (Zn). The PMF of Cu and Zn correlated negatively with clay. The MF of the three metals was correlated negatively with soil pH. The MF of Zn was correlated positively with clay, SOC, and St. The MF of Cr was correlated positively with clay, while it correlated negatively with SOC, St, CEC, and Fe–Mn oxides. The Fluvisols revealed higher total concentrations and potential motilities of Cr, Cu, and Zn compared to the Gleysols. However, the Gleysols had a higher metal mobility compared to Fluvisols due to their longer flooding duration. The solubility of Cr below the average water level in the studied profiles was higher than above the water level, while the solubility of Cu and Zn above the water level was higher than below the water level in both soil groups. The potential mobility of the studied metals (especially of Cu followed by Zn), and thus the transfer of these metals into the grassland and food chain, should be high, which might be harmful to the floodplain ecosystem.

Spatial and seasonal distributions of soil phosphorus in a typical seasonal flooding wetland of the Yellow River Delta, China

Soil samples from 0 to 100 cm depth were collected in four sampling sites (Sites A, B, C and D) along a 250-m length of sampling zone from the Yellow River channel to a tidal creek in a seasonal flooding wetland of the Yellow River Delta of China in fall of 2007 and spring of 2008 to investigate spatial and seasonal distribution patterns of total phosphorous (TP) and available phosphorus (AP) and their influencing factors. Our results showed that TP contents in spring and AP contents in both seasons in surface soils increased with increasing distances away from the Yellow River channel. TP contents in surface soils (0–10 cm) followed the order Site A (698.6 mg/kg) > Site B (688.0 mg/kg) > Site C (638.8 mg/kg) > Site D (599.2 mg/kg) in fall, while Site C (699.6 mg/kg) > Site D (651.7 mg/kg) > Site B (593.6 mg/kg) > Site A (577.5 mg/kg) in spring. Generally, lower TP content (630.6 mg/kg) and higher AP level (6.2 mg/kg) in surface soils were observed in spring compared to fall (656.2 mg/kg for TP and 5.2 mg/kg for AP). Both TP and AP exhibited similar profile distribution patterns and decreased with depth along soil profiles with one or two accumulation peaks at the depth of 40–80 cm. Although the mean TP content in soil profiles was slightly higher in spring (635.7 mg/kg) than that in fall (628.0 mg/kg), the mean TP stock was obviously lower in spring (959.9 g/m2) with an obvious accumulation at the 60–80 cm soil depth compared to fall (1124.6 g/m2). Topsoil concentration factors also indicated that TP and AP had shallower distribution in soil profiles. Correlation analysis showed that AP had significant and positive correlation with these soil properties such as soil organic matter, salinity, total nitrogen and Al (p < 0.01), but TP was just significantly correlated with TN and Al (p < 0.05).

Soil layering and preferential flow impacts on seasonal changes of GPR signals in two contrasting soils

Experimental evidence has shown that soil layering can significantly alter water movement through soil profiles, especially in sloping landscapes. Detailed knowledge of soil layering and its position in the landscape is therefore necessary for determining dynamic subsurface flow. In this study, we used Ground Penetrating Radar (GPR) in combination with high resolution real-time soil water monitoring to investigate seasonal changes in GPR signals to identify soil horizon interfaces and their impacts on water flow in two contrasting soils. The results showed that 1) in the deep Rushtown soil located in a concave hillslope, GPR reflections in the Bw–BC and BC–C horizon interfaces became clearer as soil became wetter. Such increased contrast along interfaces was due to the presence of water associated with water-restricting BC horizon and lateral flow from upslope area; and 2) in the shallow Weikert soil located in a planar hillslope, GPR reflections in the soil–bedrock interface and the weathered–unweathered rock interface become intermittent as soil became wetter. This scattering of GPR reflection was due to the non-uniform distribution of water in fractured shale bedrock and possible tree root effects. While wet condition permitted the enhanced detection of water distribution in both soil profiles, optimal time for detecting soil layering was different for these two soils: wet condition was more suited for detecting water-restricting dense layer in the deep Rushtown soil, while dry season was optimal for identifying the soil–bedrock interface in the shallow Weikert soil. Overall, this study demonstrates the value of repeated GPR surveys in different seasons to capture subsurface hydrologic processes and the impacts of soil layering and preferential water distribution on seasonal changes of GPR signals. It also provides a useful reference for selecting optimal time for GPR survey in the field.

Soil-profile distribution of inorganic N during 6 years of integrated crop-livestock management

Excessive accumulation of soil nitrate-N can threaten water and air quality. How integrated crop-livestock systems might influence soil-profile nitrate-N accumulation has not been investigated. Therefore, we determined soil nitrate-N accumulation during 6 years of evaluation of diverse cropping systems on a Typic Kanhapludult in Georgia, USA. Of the total change in soil nitrate-N content that occurred during 6 years (i.e. increase of 14kgNha−1year−1), an average of 60% occurred in the primary rooting zone (0–90-cm depth) and 40% occurred in the zone below typical rooting (90–150-cm depth). Soil nitrate-N accumulation was greater in cropping systems with greater N fertilizer input, while it was surprisingly insensitive to differences in harvested N output. Soil nitrate-N accumulation was greater under conventional tillage than under no tillage at all soil depths (e.g. 5.1±4.2kgNha−1year−1 greater at a depth of 90–150cm), suggesting soil disturbance was a key factor in mobilizing N and keeping it more disassociated from the organic–inorganic cycling system. Grazing of cover crops had variable effects on soil nitrate-N content: greater soil nitrate-N content in the rooting zone at the end of 1 year (63 vs. 47kgNha−1), greater soil nitrate-N content in the zone below typical rooting at the end of 3 and 4 years (91 vs. 70kgNha−1), and lower soil nitrate-N content in the rooting zone at the end of 6 years (89 vs. 120kgNha−1). These results confirm the beneficial effect of no-tillage management on moderating nitrate-N accumulation in the soil profile and indicate a variable, but mostly neutral effect of cover crop grazing on soil nitrate-N accumulation.

Long-term effect of different soil management systems and winter crops on soil acidity and vertical distribution of nutrients in a Brazilian Oxisol

“Strategies” to sustain crop productivity by reducing the fertilizer and lime demands must be developed. The use of plant species that use more efficiently the soil nutrients and tillage systems that provide nutrients accumulation in more labile forms are prerequisites for sustainable agroecosystems. This study aimed to evaluate the long period effect of cultivating different winter species under different soil management systems on vertical distribution of soil nutrients and the soil acidity distribution in soil profile. The experiment was established in 1986 with six winter treatments (blue lupine, hairy vetch, oat, radish, wheat and fallow) under conventional tillage (CT) and no-tillage (NT) in a very clayey Rhodic Hapludox in Southern Brazil. As a result of 19 years of no soil disturbance, soil chemical attributes related to soil acidity and the availability of P and K were more favorable to crops growth up to 10cm in the soil under no-tillage than in the conventional tillage. On other hand, lime applications in low doses on the soil surface were not efficient in neutralizing the aluminum toxicity below 10cm depth. It shows that repeated use of lime on the soil surface under NT system can be a viable alternative strategy only when soil acidity and aluminum toxicity in subsurface has been previously eliminated using the adequate amount of lime and incorporating it into the arable layer. Moreover, in the conventional tillage system P and K availability were higher below 10cm depth compared to the no-tillage system. Even after 19 years of no soil disturbance in the NT system the available P content below 10cm soil layer was lower than the optimal content of available P recommended to cash crops. The reduced surface K application over time was sufficient to gain adequate crop yields and to maintain the optimal content of soil available K in both soil management systems. The effects of soil management systems were predominant on the soil acidity attributes, and no effects of winter cover crops were observed on soil acidity attributes. Black oat and blue lupine were more efficient in P cycling, increasing the soil available P content especially in the surface soil under NT. The lower amount of biomass produced over time when no cover crops were used in the winter period resulted in lower P and K availability in the soil, showing the important role of growing winter species to maintain soil fertility.