Deep Soil Profiles Research Articles

Relationships between leaf water potential and soil water potential in grasses subjected to water stress

For grasses and other crops in general, soil water potential has been widely studied to determine if there is a deficit or excess of water content in the soil. However, the plant water absorption process is not only modulated by soil water potential but also by the combination of meteorological, soil depth, and crop canopy factors, which could be elucidated through water relations responses. The objective of this work was to compare the water relations of grass species established in different soil depths and subjected to water stress. Santo Agostinho (Stenotaphrum secundatum), Esmeralda (Zoysia japonica), Tanzania (Panicum maximum) and Tifton 85 (Cynodon spp.) were used in this trial. The four species of grasses were tested in four different soil rooting depths: 10, 20, 30 and 40 cm. The grasses were irrigated at soil moisture field capacity level, until the time of imposing the water stress period. Soil depth had a direct influence on leaf water potential and soil water potential. Moreover, correlation coefficients are higher in deeper soil profiles. The strongest correlations between leaf water potential and soil water potential were found in the deeper soil depth treatments. Therefore, for the soil depth treatment of 40 cm, the average R² for the four species was 0.55, the highest being 0.70 in Tanzania grass. It is possible to relate leaf water potential and soil water potential independently of the grass species used or the depth of soil available to the roots, which would allow the creation of new irrigation management strategies.

Causes and implications of the seasonal dissolution and precipitation of pedogenic carbonates in soils of karst regions – A thermodynamic model approach

Red Mediterranean Soils developed over carbonate rocks can precipitate pedogenic carbonates at the base of their profiles, forming an evolutionary stage of calcretes. We studied a 0.6 m deep soil profile in Dalmatia (Croatia) where the lowest section of the soil is a calcic horizon formed by diffuse calcite particles and small nodules. These nodules record different events of dissolution and precipitation. Using a 3-month period of soil environmental monitoring, where soil temperature, soil water content, soil bulk electrical conductivity and soil air CO2 were measured, we implemented a thermodynamic model for dissolution and precipitation of calcite in the soil. The simulation shows a stage dominated by calcite dissolution during spring and early summer followed by a stage dominated by calcite precipitation. Soil air CO2 is the main control of the calcite reactions, with concentration of solutes also being of some importance during the stage of calcite precipitation. Soil water content and temperature, both affect soil air CO2. Precipitation events also have high-frequency impact on soil air CO2, but the response is complex. The model enables soil water solutions to be supersaturated in relation to calcite without precipitation of that mineral. Simulated soil water reached variable values of supersaturation in relation to calcite before its precipitation was triggered, suggesting that there is no fixed threshold value for the precipitation of calcite in a particular soil. During the 3-month simulated period, 83% of the calcite dissolved was reprecipitated as pedogenic carbonate. Most of the initially dissolved calcite, was expected to be diffuse pedogenic carbonate particles, although nodules and bedrock at the base of the soil should also have contributed to the solutes dissolved. Therefore, karst landscapes where soils have pedogenic carbonates are expected to record less denudation rates than those regions without calcretes.

Distribution of Burkholderia pseudomallei within a 300-cm deep soil profile: implications for environmental sampling

The environmental distribution of Burkholderia pseudomallei, the causative agent of melioidosis, remains poorly understood. B. pseudomallei is known to have the ability to occupy a variety of environmental niches, particularly in soil. This paper provides novel information about a putative association of soil biogeochemical heterogeneity and the vertical distribution of B. pseudomallei. We investigated (1) the distribution of B. pseudomallei along a 300-cm deep soil profile together with the variation of a range of soil physico-chemical properties; (2) whether correlations between the distribution of B. pseudomallei and soil physico-chemical properties exist and (3) when they exist, what such correlations indicate with regards to the environmental conditions conducive to the occurrence of B. pseudomallei in soils. Unexpectedly, the highest concentrations of B. pseudomallei were observed between 100 and 200 cm below the soil surface. Our results indicate that unravelling the environmental conditions favorable to B. pseudomallei entails considering many aspects of the actual complexity of soil. Important recommendations regarding environmental sampling for B. pseudomallei can be drawn from this work, in particular that collecting samples down to the water table is of foremost importance, as groundwater persistence appears to be a controlling factor of the occurrence of B. pseudomallei in soil.

Variations and influencing factors of nitrate accumulation in the deep soil profiles of apple orchards on the Loess Plateau

Nitrate accumulation in the soil profile of uplands is an important fate of surplus nitrogen (N) fertilizer in intensive agricultural regions. A comprehensive understanding of the spatial variation in nitrate accumulation characteristics in the deep (>2 m) soil profile and identification of the key driving factors are important for mitigating N loss and associated environmental problems. We sampled the deep soil profiles (to 8–13 m) in four regions (i.e., R1, R2, R3 and R4) from north to south of the apple-planting region on the Loess Plateau (LP), spanning a highly spatial variation of climates, soils, orchard standing ages, and N fertilizer rates. Regression analysis and random forest analysis were used to identify the characteristics of nitrate accumulation in the vadose zones at the regional scale. The results showed that nitrate accumulation characteristics (represented by four indices: peaks of nitrate content, peak depths, nitrate accumulation depths and nitrate accumulation amounts) were significantly positively correlated with the stand ages of orchards. Nitrate stock in the soil profiles (0–8 m) increased from north to south and averaged 4149 and 13,633 kg N ha−1 in the 25-yr-old orchards for R1 and R4, respectively. Nitrate stock in the soil profiles (0–13 m) of 30-yr-old orchards in R4 averaged 19,283 kg N ha−1, ranging from 12,859 to 25,900 kg N ha−1. The nitrate accumulation depths in the orchards in the R1 and R4 regions were deeper due to the high soil sand content and high water input, respectively. It highlights that the water input rate and soil sand content were key controlling factors for peak depth and nitrate accumulation depth, while stand age and N fertilization rate mainly controlled the peak of nitrate content and nitrate accumulation amount. The southern apple-planting region with a shallow vadose zone and high irrigation is suggested to be designated as the nitrate vulnerable zone.

Soil Aggregate Stability in Salt-Affected Vineyards: Depth-Wise Variability Analysis

Soil aggregate stability is an ideal integrative soil quality indicator, but little is known about the relevance of such an indicator with soil depth for salt-affected soils. The objective of this study was to determine soil aggregate stability and identify preponderant aggregation factors, both in topsoil and subsoil horizons in salt-affected conditions. We conducted field investigations by describing soil profiles in pedological pits and by collecting soil samples from different field units. Soils were sampled within different soil horizon types, from superficial tilled organo-mineral horizons to mineral horizons. For all soil samples, we determined the mean weight diameter (MWD) as an indicator of soil aggregate stability and also determined associated physical and chemical properties in some samples. The measured MWD value from 0.28 mm to 1.10 mm could be categorised as unstable, with MWD values and variability decreasing drastically from the topsoil to the deepest mineral horizons. Analysis of MWD in relation to physical and chemical properties suggested that the variability in the MWD value of A-horizons was influenced by both clay fraction abundance and soil organic carbon (SOC) content and the nature of the agricultural practices, while at deeper B-horizons, the decrease in SOC content and the variability in other soil properties with soil depth could be used to explain the overall low aggregate stability. In this study, investigations of soil pits coupled with measurements of soil aggregate stability indicated that it could be possible to restore soil structure quality by limiting deep soil profile compaction in order to improve salt leaching and exportation.

Low-disturbance farming regenerates healthy deep soil toward sustainable agriculture - Evidence from long-term no-tillage with stover mulching in Mollisols

Currently, global agricultural development is in a critical period, as it contends with a growing population, degraded farmland, and serious environmental issues. Although low-disturbance practices are recommended to improve soil health, it is unclear whether such practices benefit critical deep soil functioning. Here, we compared the soil bacterial communities and physicochemical parameters across 3-m deep soil profiles in a Mollisol of Northeast China at the end of the dormant season after 10 years of farming under conventional tillage without stover mulching (CT), no-tillage without stover mulching (NTNS), and no-tillage with stover mulching (NTSM). We found that low-disturbance practices (NTNS and NTSM), compared with CT, evidently promoted soil bacterial species richness and diversity and enriched potential metabolic diversity. When compared to the bacterial communities in CT, the vertical dissimilarity of bacterial communities in NTNS decreased, while that in NTSM increased, indicating that no-tillage alone homogenized the composition of the bacterial community through soil depth profiles, but straw mulching enhanced the uniqueness of community composition at each layer. In comparison to CT, no-tillage with stover mulching significantly increased the soil water content and root-associated organic carbon (SEOC), and decreased soil pH. Mineral nitrogen declined with depth to 60 cm and then increased to its maximum at 250–300 cm under CT and at 120–150 cm under NTNS and NTSM. More mineral nitrogen at 0–150 cm under low-disturbance practices would provide more available nitrogen for crops in the coming growing season, while the accumulated nitrogen at 150–300 cm under CT may leach into the groundwater. Taken together, our results show that low-disturbance practices can regenerate whole-soil bacterial diversity and potential function, and promote water retention and nitrogen holding capacity within the root zone, thus reducing the dose of nitrogen fertilizer and mitigating nitrogen contamination to deep groundwater, ultimately contributing to agricultural sustainability in Mollisol regions.

Dynamics of organic carbon and nitrogen in deep soil profile and crop yields under long-term fertilization in wheat-maize cropping system

Soil organic carbon (SOC) and nitrogen (N) are two of the most important indicators for agricultural productivity. The primary objective of this study was to investigate the changes in SOC and N in the deep soil profile (up to 100 cm) and their relationships with crop productivity under the influence of long-term (since 1990) fertilization in the wheat-maize cropping system. Treatments included CK (control), NP (inorganic N and phosphorus (P) fertilizers), NPK (inorganic N, P and potassium fertilizers), NPKM (NPK plus manure), and M (manure). Crop yield and the properties of topsoil were measured yearly from 2001 to 2009. C and N contents were measured at five different depths in 2001 and 2009. The results showed that wheat and maize yields decreased between 2001 and 2009 under the inorganic fertilizer (NP and NPK) treatments. The average yield between 2001 and 2009 under the NP, NPK, NPKM, and M treatments (compared with the CK treatment) increased by 38, 115, 383, and 381%, respectively, for wheat and 348, 891, 2 738, and 1 845%, respectively, for maize. Different long-term fertilization treatments significantly changed coarse free particulate (cfPOC), fine free particulate (ffPOC), intramicroaggregate particulate (iPOC), and mineral-associated (mSOC) organic carbon fractions. In the experimental years of 2001 and 2009, soil fractions occurred in the following order for all treatments: mSOC>cfPOC>iPOC>ffPOC. All fractions were higher under the manure application treatments than under the inorganic fertilization treatments. Compared to the inorganic fertilization treatments, manure input enhanced the stocks of SOC and total N in the surface layer (0–20 cm) but decreased SOC and N in the deep soil layer (80–100 cm). This reveals the efficiency of manure in increasing yield productivity and decreasing risk of vertical loss of nutrients, especially N, compared to inorganic fertilization treatments. The findings provide opportunities for understanding deep soil C and N dynamics, which could help mitigate climate change impact on agricultural production and maintain soil health.

Drought response of 10 bermudagrass genotypes under field and controlled environment conditions

AbstractFresh water scarcity is increasingly affecting urban landscapes, and the best strategy for sustaining the turfgrass industry would be to create, select, and use drought‐resistant genotypes. Bermudagrasses (Cynodon spp.) have different mechanisms to survive drought stress either by growing long roots, stomatal regulation, or accumulating biochemical solutes in the leaf. The drought response of 10 bermudagrasses was evaluated under two environments: (a) unrestricted root zone in the field and (b) restricted 17‐cm root zone in a greenhouse. Each study consisted of four commercially available (‘Latitude 36’, ‘Tifway’, ‘TifTuf’, and ‘Celebration’) and six experimental genotypes (OSU1337, OSU1403, OSU1439, TifB16101, TifB16113, and TifB16120). In the field study, all the genotypes survived the 60‐ and 49‐d dry‐down periods in 2017 and 2018, respectively, without completely browning off. Results showed a range of drought performance among genotypes, with TifTuf and Latitude 36 being the best‐ and worst‐performing industry standards, respectively. TifB16101, TifB16120, and TifB16113 were consistently the top performers with a leaf firing (LF) and turf quality (TQ) above 6, lower canopy temperature (CT), and greater normalized difference vegetation index (NDVI) values in the field. However, when grown in 17‐cm pots, TifTuf, TifB16113, and TifB16120 demonstrated a TQ below 6 within 6 and 9 days of drought (DOD) in 2019 and 2020, respectively. The discrepancy between studies suggests that these genotypes may have the ability to extract water from deeper soil profiles when root zones are unrestricted. Furthermore, these findings reinforce the importance of soil depth in maintaining turfgrasses without supplemental irrigation.

Soil Related Factors Controlling Erosion And Landslides In Malaysia

The high temperature and rainfall in Malaysia results in intensive tropical weathering and depending on the parent material, the resultant soil can have deep or shallow soil profiles. Thus, a variety of soils can form with different textures (clay content), structure and porosity. With the high rainfall, soils in steep terrain are subjected to surface erosion when exposed or landslides if the rainwater percolates into the soil profile. Key soil-related factors controlling soil erosion and landslides include local climate, parent material of soils and depth of the weathered profile. Slope and geomorphology, vegetation and land use as well as land management practices also influence erosion and landslides. Measures used to control soil erosion and stabilize slopes require improved understanding of soil weathering, erosion, landslide and their linkages in steep terrain.

Cultivation models and mulching strategies to improve root-bleeding sap, nutrients uptake and wheat production in semi-arid regions

The application of mulching materials has significantly improved the production of wheat in semi-arid regions. However, various mulching applications under different tillage practices, whether it can improve the root growth, spatial distribution of root, nutrients uptake and grain yield of wheat is not clear. Therefore, a two years field study was carried out during 2016–17 and 2017–18 to evaluate root growth, nutrients uptake, and wheat production under six treatments: CT: conventional planting; SM: wheat stalk mulching; FM: plastic mulching; RT: without plastic mulching with furrow and ridge planting; RP: plastic mulching with furrow and ridge planting; RPS: plastic mulching on ridges and stalk mulching on furrows. Under the RPS treatment, root biomass, soil moisture, soil enzymatic activity, and microbial abundance can be significantly improved, thus promoting root growth, nutrient absorption, and wheat production. The RPS treatment significantly improved the rooting system in the upper soil profile of 50 cm, which helped increase the yield of wheat. At various wheat growth stages, the RPS and RT treatment at the depth of 10–50 cm significantly increased root bleeding saps, and RLD, and reached up to the highest value at 125 DAP. However, there were no differences in RLD between the six different treatment methods in deeper soil profiles below 60 cm. In addition, during 2016–17 and 2017–18, the NH4+ and NO3- delivery rates under the RPS were significantly higher than that of FM and RT, while the delivery rates of NH4+ and NO3- under the RP treatment were maximum compared with FM practice. Under the RPS and RT treatments, the Fe, Ca, P, Zn, K, and Mg delivery rates were significantly maximum. In summary, RPS farming practices have been great potential to improve the rhizosphere environment, root biomass, and wheat yield in semi-arid regions.

SOIL-WATERGRIDS, mapping dynamic changes in soil moisture and depth of water table from 1970 to 2014

We introduce here SOIL-WATERGRIDS, a new dataset of dynamic changes in soil moisture and depth of water table over 45 years from 1970 to 2014 globally resolved at 0.25 × 0.25 degree resolution (about 30 × 30 km at the equator) along a 56 m deep soil profile. SOIL-WATERGRIDS estimates were obtained using the BRTSim model instructed with globally gridded soil physical and hydraulic properties, land cover and use characteristics, and hydrometeorological variables to account for precipitation, ecosystem-specific evapotranspiration, snowmelt, surface runoff, and irrigation. We validate our estimates against independent observations and re-analyses of the soil moisture, water table depth, wetland occurrence, and runoff. SOIL-WATERGRIDS brings into a single product the monthly mean water saturation at three depths in the root zone and the depth of the highest and lowest water tables throughout the reference period, their long-term monthly averages, and data quality. SOIL-WATERGRIDS can therefore be used to analyse trends in water availability for agricultural abstraction, assess the water balance under historical weather patterns, and identify water stress in sensitive managed and unmanaged ecosystems.

Early Holocene pollen record of vegetation and climate history in response to the monsoonal activity in East Garo Hills, Meghalaya, India

This study presents a palynological analysis in 2.0 m deep sedimentary soil profile procured from Rongre Swamp of East Garo Hills to document changes in vegetation and climate in response to the monsoonal activity since 10,640 cal. BP. Four palaeovegetation and climate zones were recorded based on the frequencies of major pollen taxa in the region. The first phase was around 10,640–7,540 cal. BP broadly shows the existence of tropical forest in the region under the onset of warm and humid climatic condition. Subsequently, between 7,540–5,490 cal. BP, the forest got enriched with increased values of tropical mixed deciduous and evergreen elements. The vegetation scenario as marked by both deciduous and evergreen elements in increased values support the warm and humid climate in response to the relatively high monsoonal activity. Accordingly, in the third phase between 5,490–1,120 cal. BP, the values of major arboreal pollen taxa, Shorea, Mesua, Elaeocarpus and Duabanga have declined as compared to the preceding phase in relation to the relatively less warm and humid climate than the preceding phase in the region. In the last phase around 1,120 cal. BP to present, the forest got deteriorated as evidenced by the decreased values of arboreal pollen taxa. This phase clearly depicts the high anthropogenic activity as evidenced by the abundance of cultural pollen like cereal and Brassica.

PEDOLOGICAL STUDIES ON SOILS IRRIGATED FROM DIFFERENT WATER SOURCES IN THE AREA NORTH EAST TANTA CITY, GHARBIA GOVERNORATE, EGYPT

The current work was performed aiming to study the morphological, physiochemical characteristics as well as classification and capability evaluation for soils irrigated fromdifferent water sources in the area north east Tanta city, Gharbia governorate, Egypt.The study area is located in the Middle of Nile Delta between latitudes 30⁰ 45′ to 30⁰ 50′ N and longitudes 31⁰ 00′ to 31⁰ 05′ E, covering an area of about 78.97 km2 (18802.30 fed.). The area has many different irrigation water sources namely, Nile water, agricultural drainage water, waste and sewage water canals. Many industrial factories discharge their waste fluids and remnants into these different canals which intermixed with their waters and could be used for irrigation of the surrounded agricultural land in the area. Ten soil profiles were chosen including: three representing the soils use the fresh Nile water, five representing the soils use the agricultural drainage water and two representing the soils use sewage water for irrigation. The land and site features are observed and registered. The soil profiles were dug, morphologically described, and then samples were collected representing the subsequent layers in each profile for integrated physical and chemical analyses. Also, water samples were collected from the different irrigation water resources for chemical analyses. The studied area has almost flat topography with deep soil profiles and freely well drained. These soils have swelling clay loam to clay texture with moderate medium to coarse angular blocky structure and mostly grayish brown color.There are no clear differences in the morphological characteristics of the studied soils irrigated with different kinds of irrigation waters. The physiochemical properties revealed that, the studied soils are moderately alkaline and non- to slightly saline. All of the soils using Nile water haven’t sodicity effect. While, most of those using drainage or sewage water have moderate sodicity effect. Organic matter (OM) is almost lowand decreases with depth.The soils are slightly to moderately calcareous. Some soils from those irrigated with drainage or sewage water have relatively moderate OM and CaCO3 contents especially in the surface layers besides relatively high ESP. This could be ascribed to the interaction of factorial waste fluids and remnants in the irrigation water used for these soils. Most of the studied soil profiles haven't any diagnostic horizons, therefore they were classified under Entisols order.Some soils from those irrigated with agricultural drainage water or sewage water seem to have Natric horizons and classified under Aridisols up to sub great group level. The land capability evaluation using ASLE model indicated that, all of the studied soils are considered as a good class (C2). The quality evaluation of irrigation water samples indicates that, there is a slight restriction upon using the drainage and sewage waters for sensitive crops.

Effect of Climate Change on the Growth of Endangered Scree Forests in Krkonoše National Park (Czech Republic)

Scree forests with large numbers of protected plants and wildlife are seriously threatened by climate change due to more frequent drought episodes, which cause challenges for very stony, shallow soils. The effect of environmental factors on the radial growth of five tree species—European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst.), sycamore maple (Acer pseudoplatanus L.), European ash (Fraxinus excelsior L.), and mountain elm (Ulmus glabra Huds.)—was studied in the mixed stands (105–157 years) in the western Krkonoše Mountains (Czech Republic) concerning climate change. These are communities of maple to fir beechwoods (association Aceri-Fagetum sylvaticae and Luzulo-Abietetum albae) on ranker soils at the altitude 590–700 m a.s.l. Production, structure, and biodiversity were evaluated in seven permanent research plots and the relationships of the radial growth (150 cores) to climatic parameters (precipitation, temperature, and extreme conditions) and air pollution (SO2, NOX, ozone exposure). The stand volume reached 557–814 m3 ha−1 with high production potential of spruce and ash. The radial growth of beech and spruce growing in relatively favorable habitat conditions (deeper soil profile and less skeletal soils) has increased by 16.6%–46.1% in the last 20 years. By contrast, for sycamore and ash growing in more extreme soil conditions, the radial growth decreased by 12.5%–14.6%. However, growth variability increased (12.7%–29.5%) for all tree species, as did the occurrence of negative pointer years (extremely low radial growth) in the last two decades. The most sensitive tree species to climate and air pollution were spruce and beech compared to the resilience of sycamore and ash. Spectral analysis recorded the largest cyclical fluctuations (especially the 12-year solar cycle) in spruce, while ash did not show any significant cycle processes. The limiting factors of growth were droughts with high temperatures in the vegetation period for spruce and late frosts for beech. According to the degree of extreme habitat conditions, individual tree species thus respond appropriately to advancing climate change, especially to an increase in the mean temperature (by 2.1 °C), unevenness in precipitation, and occurrence of extreme climate events in the last 60 years.

Multi-Proxy Study of a Holocene Soil Profile from Romania and Its Relevance for Speleothem Based Paleoenvironmental Reconstructions

In this study, we describe a sedimentary deposit situated above Ascunsă Cave (SW Romania) that should be in depositional connection with coeval stalagmites from the cave. We excavated a 2.5 m deep soil profile and took contiguous bulk samples every 5 cm. Soil samples were analyzed for clay mineralogy, grain size, chemical composition, magnetic susceptibility, and stable carbon isotopes. Radiocarbon dating revealed that the soil is of Holocene age, and presents a depositional hiatus between 5.4 and 2.3 thousand years before the present. Due to the open system behavior of soils and mobility of organic matter, a few hundred years of uncertainty should be considered for the duration of this hiatus. The fine fraction is dominated by silt, while the clay mineralogical association is made of illite, chlorite, kaolinite, vermiculite, and illite–vermiculite and illite–chlorite mixed layered minerals. The sediment source of this soil is represented by a nearby mélange complex, as well as by an underlying terra rossa-type soil. As this latter type of soil is widespread in our study area, we performed luminescence dating on two samples from a representative location close to our site and it appears that this type of Mediterranean soil was formed during the Last Interglacial period. δ13C variability in soil organic matter and a stalagmite from the cave are comparing well, and could help future studies identify modifications in isotopic fractionation processes within the cave.

Long-term vegetation restoration increases deep soil carbon storage in the Northern Loess Plateau

Afforestation plays an important role in soil carbon storage and water balance. However, there is a lack of information on deep soil carbon and water storage. The study investigates the effect of returning farmland to the forest on soil carbon accumulation and soil water consumption in 20-m deep soil profile in the hilly and gully region of the Chinese Loess Plateau. Four sampling sites were selected: Platycladus orientalis (Linn.) Franco forest (PO: oriental arborvitae), Pinus tabulaeformis Carr. Forest (PT: southern Chinese pine), apple orchard (AO) and farmland (FL, as a control). Soil organic carbon (SOC) and soil inorganic carbon (SIC) content were measured in 50-cm sampling intervals of 20-m soil profiles, as well as the associated factors (e.g. soil water content). The mean SOC content of PT was the highest in the 1–5 m layer and that of FL was the lowest (p < 0.05). Compared with FL, the SOC storages of PO, PT and AO increased by 2.20, 6.33 and 0.90 kg m−2 (p > 0.05), respectively, in the whole profile. The SIC content was relatively uniform throughout the profile at all land-use types and SIC storage was 9–10 times higher than SOC storage. The soil water storage of PO, PT and AO was significantly different from that of FL with a decrease of 1169.32, 1161.60 and 1139.63 mm, respectively. After the 36-yrs implementation of the “Grain for Green” Project, SOC in 20 m soil profiles increased as a water depletion cost compared with FL. Further investigation is still needed to understand the deep soil water and carbon interactions regarding ecological restoration sustainability in the Northern Loess Plateau.

Evaluation of Uncertainties in Site Response Analysis of Deep Soil Profiles in South Carolina Coastal Plain

ABSTRACTThe South Carolina Coastal Plain consists of deep soil sediments over basement bedrock. The depth of basement bedrock varies from being present at the surface to a depth of more than 1200 m at the southern tip of the state. A large variation exists in the thickness of the sediment, which impacts the seismic site response analyses of the Coastal Plain, particularly in areas where the availability of deep shear-wave velocity profiles is limited. This study evaluates the impact of variations in the shear-wave velocity profiles for two sites in the South Carolina Coastal Plain. The shear-wave velocity profiles were measured using different geophysical methods, including a combined multichannel analysis of surface waves and microtremor array measurement (MASW-MAM) method and P–S suspension logging. The equivalent-linear site response analyses were conducted by applying a synthetic earthquake motion at the depth of the B–C boundary (a depth of competent rock in which the shear-wave velocity is 760 m/s). The results are presented in terms of the amplification factor and its standard deviation. Results show that the average shear-wave velocity at the first 30 m (VS30), the shear-wave velocity contrast at the interface of the base layer and the B–C boundary, and the depth to the B–C boundary have a significant impact on the amplification factor and its variability, particularly for the amplification factor at periods higher than 0.1 s. The MASW-MAM method provided significantly lower VS30 values than the P–S suspension logging method at one of the two sites. Consequently, an additional peak in the amplification factor was observed for the site that had a low VS30, and the corresponding period was close to the resonant period of the loose, surface deposit.

Intensive vegetable production results in high nitrate accumulation in deep soil profiles in China

A comprehensive understanding of the patterns and controlling factors of nitrate accumulation in intensive vegetable production is essential to solve this problem. For the first time, the national patterns and controlling factors of nitrate accumulation in soil of vegetable systems in China were analysed by compiling 1262 observations from 117 published articles. The results revealed that the nitrate accumulation at 0–100 cm, 100–200 cm, 200–300 cm, and >300 cm were 504, 390, 349, and 244 kg N ha−1, with accumulation rates of 62, 54, 19, and 16 kg N ha−1 yr−1 for plastic greenhouse vegetables (PG); for open field vegetables (OF), they were 264, 217, 228, and 242 kg N ha−1 with accumulation rates of 26, 24, 18, and 10 kg N ha−1 yr−1, respectively. Nitrate accumulation at 0–100 cm, 0–200 cm, and 0–400 cm accounted for 5%, 11%, and 17% of accumulated nitrogen (N) inputs for PG, and represented 4%, 9%, and 13% of accumulated N inputs for OF. Nitrogen input rates and soil pH had positive effects and soil organic carbon, water input rate, and carbon to nitrogen ratio (C/N) had negative effects on nitrate accumulation in root zone (0–100 cm soil). Nitrate accumulation in deep vadose zone (>100 cm soil) was positively correlated with N and water input rates, and was negatively correlated with soil organic carbon, C/N, and the clay content. Thus, for a given vegetable soil with relatively stable soil pH and soil clay content, reducing N and water inputs, and increasing soil organic carbon and C/N are effective measures to control nitrate accumulation.

Impact of long‐term sub‐soiling tillage on soil porosity and soil physical properties in the soil profile

AbstractLong‐term conventional tillage leads to soil compaction and formation of a plough layer, which affects soil physical properties, transport of water, and growth of crop roots toward deeper soil, resulting in soil degradation and a decline in crop productivity. Long‐term sub‐soiling tillage has proven to be an effective measure for remediating the plough layer and improving the structure and physical properties of the soil. In this study, we experimentally investigated the effects of long‐term sub‐soiling tillage in an arid region of Henan Province, China, along a deep soil (0–100 cm) profile over 8 years of sub‐soiling tillage at a depth of 30 cm and compared the results against conventional tillage at a depth of 15 cm. We measured soil pore distributions of macropores (&gt; 1 mm in diameter), mesopores (0.16–1.0 mm), and total pores (&gt; 0.16 mm) measured by X‐ray computed tomography (CT), soil total porosity (ϕ) and &gt; 0.16 mm equivalent porosity measured by conventional methods, soil bulk density (ρs), soil organic carbon content (SOC), the proportion of macroaggregates (&gt; 0.25 mm) (PMA), soil field moisture capacity (fc), available moisture content, and saturated hydraulic conductivity (Ksat). The results indicate that long‐term sub‐soiling tillage increased soil pore numbers at 0–35 cm depth (macropores, mesopores, and total pores), improved pore shape, and significantly increased porosity at 0–20 cm depth (macropores, mesopores, and total pores; p &lt; 0.05) compared to conventional tillage. In addition, ϕ and &gt; 0.16 mm equivalent porosity were increased by 10.4 and 87.1% at depths of 0–60 cm under sub‐soiling tillage, respectively. SOC (0–55 cm depth), fc (0–45 cm depth), available moisture content (0–40 cm depth), Ksat (0–40 cm depth), and PMA (0–50 cm depth) were increased by 16.7, 14.3, 23.8, 471.5, and 98.3%, respectively, and ρs (0–60 cm depth) was reduced by 8.6%. Observed correlations between SOC, soil pore parameters, and soil physical properties suggest that soil pore parameters and soil physical properties can be improved by increasing SOC. These correlations are stronger under sub‐soiling than that under conventional tillage. Therefore, sub‐soiling is an effective technique for improving soil pore characteristics and physical properties while preventing soil degradation.

Tree species mixing reduces biomass but increases length of absorptive fine roots in European forests

Abstract Mixed‐species forests often enhance the provision of ecosystem functions, both above‐ and below‐ground. Several of these effects are mediated by the amount and spatial distribution of tree tissues. However, previous studies on tree diversity effects on fine‐root biomass (FRB) have returned inconsistent results and did not distinguish between absorptive and transport fine roots. Furthermore, owing to the lack of species‐specific data, it is not well understood whether complementarity or selection effects contribute more to these mixing effects. Here, we analysed tree species mixing effects on fine‐root traits while considering the respective tree species contributions and root functional types. Specifically, we tested whether tree species mixing increases FRB and root length density (RLD) and results in vertical root stratification. We quantified FRB and RLD in 30‐cm deep soil profiles for 13 tree species in mixed and pure stands across four widespread European forest types. The differentiation of different fine‐root species in mixtures allowed us to disentangle complementarity and selection effects. Across all sites, mixtures supported on average less FRB than pure stands, which was reflected in negative complementarity and selection effects. RLD of absorptive fine roots did not change across the soil profile and even increased in the topsoil, which was associated with positive complementarity effects. There was no evidence for vertical root stratification. Conifer proportion, which was mainly associated with selection effects, dampened net diversity effects. Root functional type further influenced tree species mixing effects. Synthesis. Despite the underyielding of FRB in mixtures, overall soil occupation by absorptive fine roots (RLD) did not decrease in mixtures, pointing to morphological root trait adaptations associated with higher resource‐use efficiency. Increased RLD in the most nutrient‐rich layer in mixtures further indicates complementary interactions among species and a greater resource uptake capacity. This work illustrates that considering only one aspect of trait‐functioning relationships, for example, root biomass, may not capture the full effect of plant diversity on ecosystem functioning. The integration of a larger range of relevant traits is required. Moreover, traditional classification of fine roots based on the 2‐mm diameter cut‐off may obscure responses of roots to environmental changes.