Total Soil Profile Research Articles

Controls on vertical distribution of organic carbon in the intermontane valley soils (Barak, Northeast India)

The Intermontane valleys interspersed with rugged landscapes represent a unique ecosystem and are the barn of the eastern Himalayas (EH). Soil organic carbon (SOC) plays an important role in controlling cropland productivity in these valleys. Despite this, very little is known about SOC inventories (content and stocks) and their complex interplay with some of the major control factors such as climate, elevation, land use, parent materials, and soil properties. Therefore, the objective of this study was to assess the relative influence of heterogeneous control factors (PL: Parent materials and land use) on the vertical distribution of SOC inventories at a homogeneous climate and altitude. For the study, I choose one of the largest but largely unexplored intermontane valleys (Barak) of the eastern Himalayas. By exposing a total of 72 profiles to the C horizon or water table, a thorough analysis of the influence of PL on SOC inventories (Dichromate oxidizable) and key soil parameters controlling vertical distribution of SOC in valley soils were determined The measured SOC content in the surface soil (0.15–0.24 m deep) varied from 0.91% to 1.42%, while in the soil profile (up to a depth from 1.19 to 1.56 m), the SOC content (PWA: profile weighted average) ranged from 0.60% to 0.97%. The surface layer represented only 15% soil profile depth, while contributing 33% of the SOC content (Dichromate oxidizable). The variation in SOC content (PWA) was higher among soil parent materials (e.g. Alluvium, pebble bedded-sandstone, sandstone intercalated with shale, and pure shale, CV> 16.0%) than in land use systems (e.g. Paddy agriculture, forest, and plantation, CV <3.0%). The SOC stock on the soil profile (PWA) ranged from 19.4 to 36.0 Mg ha−1. The total (soil profile) SOC stock varied from 67.5 to 161.1 Mg ha−1. In general, the SOC inventories increased relative to the clay content (correlation, r = 0.38–0.75, p < 0.05) and parent materials controlled the variation in surface and subsurface soils while the effect of land use was mostly limited to surface soils only. Deep soils (>1.55 m) developed on shale with higher clay content had higher SOC inventories (p < 0.05) than coarse-textured sandstone soils. Parent materials contributed to greater heterogeneity (R2adj = 77.1%) in SOC inventories compared to land use systems (R2adj = 61.7%). Therefore, in addition to land use, parent materials should be considered an important control factor in the estimation of SOC inventories and future research on C- sequestration in the intermontane valleys.

Influence of cover crop on water and nitrogen balances and cash crop yield in a temperate climate: A modelling approach using the STICS soil-crop model

Cover crops are crucial to diversify cropping systems into more agroecological systems by providing ecosystem services, such as reduction of nitrate leaching, provision of a green manure effect, and soil carbon storage. However, they can influence water drainage and nitrogen (N) or water availability for the succeeding crop, depending on their management and the climate. In this simulation study, we used the STICS model to predict the influence of cover crop species, date of sowing and termination, and cover crop residue management on N and water balances, and the yield and stress of the succeeding cash crop. We performed 25-year simulations for five contrasting sites in south-western France, which is a temperate region of Europe with dry summers. As expected, cover crops decreased nitrate leaching effectively but also decreased drainage by a mean of 5–40 mm. This decrease depended mainly on the sowing and termination dates, while the decrease in nitrate leaching varied greatly among sites and depended most on sowing date, followed by cover crop species and then termination date. Cover crops had little influence on soil water content in the upper 0.1 m of soil at sowing of the succeeding cash crop, but decreased soil water content of the total soil profile by 0–30 mm. Soil water content depended most on termination date, followed by species and then site. Total soil mineral N content (SNC) also decreased, by 5–40 kg N.ha−1, at the three driest sites and up to 10 kg N.ha−1 at the rainiest site. Termination date, the second-most influential factor on SNC, indicated that later termination resulted in lower SNC than that after bare soil. N uptake by the succeeding cash crop depended on species and termination date, and a legume cover crop and earlier termination date resulted in higher N uptake. The decrease in maize and sunflower yield was due mainly to changes in the N stress index during the vegetative phase for maize, and both vegetative and reproductive phases for sunflower. No water stress or increase in irrigation volumes was predicted or was correlated with yield changes, except at dry sites for the few years that experienced a severe drought in spring. While cover crops decreased nitrate leaching effectively, they decreased drainage and could induce N stress for the succeeding crop, particularly in dry regions. Including legumes in mixtures and adapting the termination date to local climate conditions could decrease or avoid these negative effects.

Legacy of plaggen agriculture: High soil organic carbon stocks as result from high carbon input and volume increase

Plaggic Anthrosols are anthropogenic soils formed by former plaggen agriculture in north-western continental Europe. Here, we present an inventory of organic carbon (OC) concentrations and stocks of Plaggic Anthrosols and of reference soils in the vicinity without plaggen fertilization history from eight sites in northwest Germany (Lower Saxony, North Rhine-Westphalia) and the eastern parts of The Netherlands (North Brabant, Overijssel). To evaluate the enrichment of Plaggic Anthrosols with OC and the implications for OC stocks, soils were analysed for basic soil properties (bulk density, pH, OC − and nitrogen (N) concentrations), texture, and acid oxalate-(FeOX) and dithionite-citrate-bicarbonate-extractable iron (FeDCB) concentrations. Organic C stocks and plant-available water capacity (PAWC) were calculated. The plaggic topsoils are characterized by high OC concentrations (6.5–36.9 mg g−1) and a thickness of 53–124 cm, in contrast to the modern cultivated ∼30 cm thick topsoils of the reference soils with 10.6–24.0 mg g−1 OC concentration. The plaggen agriculture formed a soil with improved properties and conditions for plant growth. The addition of plaggen material to the topsoils induced a volume increase as well as higher OC concentrations in the Ap horizons, resulting in significantly higher OC stocks in the Plaggic Anthrosols (6.3–14.5 kg m−2) compared to the reference soils (4.9–10.5 kg m−2). The additional soil volume amounted to 30–56% to the total soil profile depth (1.0 to 1.6 m) and comprised 25–62% of the total OC stocks. Compared to the reference soils, the volume increase of the plaggic topsoil increased the PAWC in the effective rooting zone by 1.6 to 3.4 times. Plaggic Anthrosols represent a relic of historical farming with preserved high OC concentrations and improved storage capacity for plant-available water, causing higher nutrient availability and an increase in yields, which in turn result in higher in-situ OM input, additionally contributing to high OC stocks. The results of this study demonstrate the potential of soil melioration practices similar to the former plaggen management to induce high OC concentrations and increase OC stocks in sandy agricultural soils.

Impact of European Beech Forest Diversification on Soil Organic Carbon and Total Nitrogen Stocks–A Meta-Analysis

Drought-sensitive European beech forests are increasingly challenged by climate change. Admixing other, preferably more deep-rooting, tree species has been proposed to increase the resilience of beech forests to drought. This diversification of beech forests might also affect soil organic carbon (SOC) and total nitrogen (TN) stocks that are relevant for a wide range of soil functions and ecosystem services, such as water and nutrient retention, filter functions and erosion control. Since information of these effects is scattered, our aim was to synthesize results from studies that compared SOC/TN stocks of beech monocultures with those of beech stands mixed with other tree species as well as monocultures of other tree species. We conducted a meta-analysis including 38 studies with 203, 220, and 160 observations for forest floor (i.e., the organic surface layer), mineral soil (0.5 m depth) and the total soil profile, respectively. Monoculture conifer stands had higher SOC stocks compared to monoculture beech in general, especially in the forest floor (up to 200% in larch forests). In contrast, other broadleaved tree species (oak, ash, lime, maple, hornbeam) showed lower SOC stocks in the forest floor compared to beech, with little impact on total SOC stocks. Comparing mixed beech-conifer stands (average mixing ratio with regard to number of trees 50:50) with beech monocultures revealed significantly higher total SOC stocks of around 9% and a smaller increase in TN stocks of around 4%. This equaled a SOC accrual of 0.1 Mg ha−1 yr−1. In contrast, mixed beech-broadleaved stands did not show significant differences in total SOC stocks. Conifer admixture effects on beech forest SOC were of additive nature. Admixing other tree species to beech monoculture stands was most effective to increase SOC stocks on low carbon soils with a sandy texture and nitrogen limitation (i.e., a high C/N ratio and low nitrogen deposition). We conclude that, with targeted admixture measures of coniferous species, an increase in SOC stocks in beech forests can be achieved as part of the necessary adaptation of beech forests to climate change.

Productivity, economic performance, and soil quality of conventional, mixed, and organic dryland farming systems in eastern Washington State

The global trends of shortening crop rotations, simplifying cropping systems, and segregating livestock from cropping enterprises have generated high yields while creating high environmental costs. Diversification, including integrated crop/livestock systems and the use of cover, forage, and perennial crops, can be used to improve soil health, reduce financial risk, increase yields, and reduce many negative environmental externalities. With such diversification in mind, we conducted a 5-year study examining four contrasting farming systems in dryland eastern Washington State in terms of their impacts on total productivity, economic performance, and soil quality. The four systems were a conventional (CONV) winter wheat/spring wheat/spring pea rotation, typical for the area; a mixed crop-livestock (MIX) winter wheat/spring wheat/grazed winter pea forage rotation; an organic mixed crop-livestock (ORGcrop) rotation of 3 yr perennial alfalfa and grass/grazed pea forage/winter wheat; and an organic hay (ORGhay) continuous perennial alfalfa and grass system. Soft white winter wheat (SWWW) yields were higher following grazed pea forage in MIX (6.2 Mg ha−1) than following harvested pea crop in CONV (5.9 Mg ha−1) despite lower N fertilizer rates in MIX. Following 3 yr of alfalfa and grass hay and no N fertilizer, SWWW yields in ORGcrop (6.2 Mg ha−1) were similar to CONV and MIX yields but averaged 15.5% lower protein concentration. Over the 5-yr rotation, average net returns were ORGhay ($616 yr−1) > ORGcrop (216 yr−1) > MIX (−1 yr−1) = CONV (−13 yr−1), in part due to high hay prices and average grain prices during this period compared to long-term averages. Over the course of the study, total soil profile SOC showed significant negative trends in CONV (−3.1 Mg C ha−1 yr−1) and MIX (−4.1 Mg C ha−1 yr−1) but not in ORGcrop and ORGhay. In surface (0–15 cm) soil, microbial biomass carbon and nitrogen and beta-glucosidase activity were greater in ORGcrop and ORGhay than in CONV and MIX. The landscape position of this study site is of relatively poorer soil quality and results may differ across the heterogeneity of a whole farm field. Overall, ORGhay, ORGcrop, MIX, and CONV in this order produced a gradation of forage production relative to cereal production from greatest to least, and also a gradation of economic and soil sustainability metrics from greatest to least. This study found that integrating perennial crops, such as alfalfa and forage grasses, into organic farming systems can build soil quality, be profitable, and supply nitrogen to succeeding grain crops.

晋西黄土区人工林细根与土壤水碳的耦合关系

PDF HTML阅读 XML下载 导出引用 引用提醒 晋西黄土区人工林细根与土壤水碳的耦合关系 DOI: 10.5846/stxb201901120101 作者: 作者单位: 山西师范大学生命科学学院,山西师范大学生命科学学院,山西师范大学生命科学学院,山西师范大学生命科学学院,山西师范大学生命科学学院,山西师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 山西省自然科学基金（201601D021103）；国家自然科学基金项目（41401242） Coupling fine roots with soil moisture and organic carbon in artificial forests in loess region of western Shanxi Province Author: Affiliation: College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以晋西黄土区山西离石典型人工林刺槐、侧柏、核桃为研究对象，研究其深剖面（0-500 cm）细根参数、土壤水分和有机碳的分布特征，并以农地为对照，评价各人工林土壤水分亏缺和有机碳积累效应，在此基础上探讨三者的耦合关系。结果表明：（1）3种人工林土壤浅层（0-70 cm）细根累计生物量占整个土层的56%-71%，具有明显表聚性。（2）3种人工林土壤深层（70-500 cm）土壤水分亏缺效应均显著高于浅层（P < 0.05），与农地相比，其亏缺值表现为：侧柏 > 核桃 > 刺槐。（3）3种人工林深层土壤有机碳密度占整个土层的77%-86%；与农地相比，侧柏和核桃土壤有机碳积累效应总体为正向积累作用，刺槐则相反。（4）在土壤浅层，细根参数与土壤水分和有机碳密度均有显著相关性，而在深层，细根主要与有机碳密度显著相关，与土壤水分的相关性仅在刺槐样地显著。晋西黄土区不同人工林深层细根分布有很大差异，且已对其深层土壤水分和有机碳的分布产生影响。综合来看，刺槐的细根分布已造成深层土壤水分亏缺，同时也不利于深层有机碳的积累。 Abstract:In this study, the relationship between fine roots, soil moisture, and soil organic carbon in artificial forests was analyzed. Three tree species, Robinia pseudoacacia, Platycladus orientalis, and Juglans regia were selected in the loess region of western Shanxi Province, China. Soil and root samples were taken from 0-500 cm depths to analyze the distribution pattern of fine root parameters, soil moisture content (SMC), and soil organic carbon density (SOCD). Soil moisture deficit (SMD) and organic carbon accumulation (SOCA) in artificial forests were evaluated with long-term cropland as a control. The results showed that:(1) the cumulative proportion of fine root biomass in shallow soil layers (0-70 cm) ranged from 56% to 71%, which showed obvious surface aggregation in all three forests. (2) The SMD in deep soil layers (70-500 cm) was significantly higher than that in shallow soil layers of all forests (P < 0.05). Compared with the control, the SMD in deep soil layers of artificial forests ranked as P. orientalis > J. regia > R. pseudoacacia. (3) The SOCD in deep soil layers accounted for 77%-86% of total soil profile SOCD across different forests. Compared with the control, the SOCA in P. orientalis and J. regia plots was generally positive, while the SOCA in R. pseudoacacia plot was negative. (4) The fine root parameters were positively correlated with both SMC and SOCD in shallow soil layers. However, in deep soil layers, the positive correlation was observed mainly with SOCD. The significant correlation with SMC was found only in R. pseudoacacia plot. The deep distribution of fine roots considerably differed among three artificial forests in the loess region of western Shanxi, which had an obvious influence on the deep SMC and SOCD distribution. Overall, the fine root distribution of R. pseudoacacia contributed to SMD while negatively affecting SOCA in the deep soil. 参考文献 相似文献 引证文献

Soil C:N ratio is the main driver of soil δ15N in cold and N-limited eastern Canadian forests

Significant relationships have been observed between soil N isotopic natural abundance (δ15N) and both climate and soil characteristics across a large range of ecosystems over the globe, suggesting strong and consistent effects of these variables on N cycling. However, whether the strength and the nature of these relationships vary at regional scales and with soil depth is less documented, especially in northern cold and N-limited forest ecosystems. In this study, we analyzed δ15N in soil horizons at 21 forest sites in eastern Quebec along a gradient of concomitant decreasing N deposition and temperature (MAAT) and increasing precipitation (MAP). We hypothesized that both soil δ15N and the magnitude of increase in soil δ15N would decrease along this gradient, in accordance with relationships reported at a global scale. The data show an increase in δ15N with soil depth, although it remained constant or sharply decreased between the B- and the C-horizon at most sites. The natural abundance of 15N in the forest floor (FF), in the B-horizon and in the C-horizon averaged 2.2 ± 0.9‰, 6.2 ± 1.2‰ and 4.9 ± 2.0‰, respectively while total soil profile δ15N ranged from 3.8‰ to 7.4‰. Contrary to our hypothesis, soil δ15N was poorly correlated with climate, vegetation and most soil metrics. As a consequence, there was no spatial gradient in soil δ15N values and in the magnitude of increase in δ15N with soil depth across the study area. Soil C:N ratio was the only variable significantly correlated with soil δ15N. Multivariate models including the C:N ratio explained 47%, 60% and 36% of the inter-sites δ15N variation in B-horizon, C-horizon and total soil, respectively. In contrast with global scale studies, which have reported higher soil δ15N at sites with low soil C:N ratio, the relationship between these two variables was positive across the study area. The possible influence of ecto-myccorhizal association on this pattern is discussed. Overall, our data show that soil δ15N is controlled by complex mechanisms influenced by several variables with potential antagonist effects. Climate and most soil metrics appear to have no direct influence in the cold and N-limited forest ecosystems studied here and soil C:N ratio can affect soil δ15N in an opposite manner to what has been commonly observed.

Effects of long‐term irrigation on soil phosphorus under temperate grazed pasture

SummaryThe effect of 62 years of different irrigation regimes on the amounts, forms and distribution of phosphorus (P) in the soil profile to 100 cm under grazed pasture was determined. Irrigation treatments included nil irrigation (base average rainfall of 740 mm year−1; control), together with flood irrigation applied when gravimetric moisture (GM) in the topsoil decreased below 10 or 20% (i.e. rainfall +260 mm year−1 of supplemental irrigation [irrigation10%GM] and rainfall +770 mm year−1 [irrigation20%GM], respectively). Phosphorus fertilizer in the form of single superphosphate was applied annually at the rate of 23 kg P ha−1 to all treatments. Total soil profile P was smallest under the large rate of irrigation (5054 kg P ha−1) compared with the small rate (5908 kg P ha−1) and the control (6423 kg P ha−1), which was attributed mainly to changes in inorganic P. These data indicated that markedly more P was removed, transferred or lost under irrigation. Substantial increases in pasture production and animal grazing capacity occurred in response to irrigation, which in turn resulted in increased removal and transfer of P in animal products, animal excreta (stock camp transfer and irrigation outwash) and by leaching. Thus, combined annual removal of P in animal products, internal dung transfer and loss in irrigation outwash were directly related to irrigation frequency and increased from 8 to 18.6 kg P ha−1 for the irrigation10%GM and irrigation20%GM treatments, respectively.Highlights Examined effect of 62 years of irrigation on phosphorus in the soil profile to 100 cm. Phosphorus fertilizer was applied annually at the same rate to all treatments. Total soil profile P decreased with irrigation and was smallest under the large rate of irrigation. P removal and transfer or loss increased with irrigation frequency.

Icelandic grasslands as long-term C sinks under elevated organic N inputs

About 10% of the anthropogenic CO2 emissions have been absorbed by northern terrestrial ecosystems during the past decades. It has been hypothesized that part of this increasing carbon (C) sink is caused by the alleviation of nitrogen (N) limitation by increasing anthropogenic N inputs. However, little is known about this N-dependent C sink. Here, we studied the effect of chronic seabird-derived N inputs (47–67 kg N ha−1 year−1) on the net soil organic C (SOC) storage rate of unmanaged Icelandic grasslands on the volcanic Vestmannaeyjar archipelago by using a stock change approach in combination with soil dating. We studied both early developmental (young) soils that had been receiving increased N inputs over a decadal timescale since an eruption in 1963, and well-developed soils, that had been receiving N inputs over a millennial timescale. For the latter, however, the effects on both decadal (topsoil; 40 years) and millennial (total soil profile; 1600 years) SOC storage could be studied, as the age of topsoil and the total soil profile could be determined from volcanic ash layers deposited in 1973 and 395 AD. We found that enhanced N availability—either from accumulation over time, or seabird derived—increased the net SOC storage rate. Under low N inputs, early developmental soils were weak decadal C sinks (0.018 ton SOC ha−1 year−1), but this increased quickly under ca. 30 years of elevated N inputs to 0.29 ton SOC ha−1 year−1, thereby equalling the decadal SOC storage rate of the unfertilized well-developed soils. Furthermore, for the well-developed soils, chronically elevated N inputs not only stimulated the decadal SOC storage rate in the topsoil, but also the total millennial SOC storage was consistently higher. Hence, our study suggests that Icelandic grasslands, if not disturbed, can remain C sinks for many centuries under current climatic conditions and that chronically elevated N inputs can induce a permanent strengthening of this sink.

Preferential flow characteristics of reclaimed mine soils in a surface coal mine dump

There are a large number of macropores/tubular channels of a few centimeters and plant roots in reclaimed dump soils, which are the main reasons for the formation of soil macropores and soil preferential flow. To systematically study the morphological characteristics and variation of soil preferential flow for different reclaimed vegetations in a dump, a dye-staining experiment and physical and chemical analysis were carried out to investigate the formation mechanism and influencing factors of soil preferential flow in the vegetation restoration process. The results indicate that there were differences in the soil water breakthrough curves for different plots. The macropore effluent rate generally increased at first and then tended to stabilize. The soil steady effluent rate decreased with increasing soil depth, which reached the maximum and minimum values at the depths of 0∼5cm (0.0193∼0.0315mms-1) and 50∼60cm (0.0028∼0.0035mms-1), respectively. Furthermore, the radius of soil macropores under different types of reclaimed vegetation ranged from 0.03 to 4.71mm, most of which ranged from 0.11 to 2.36mm. The soil macroporosity of different reclaimed vegetation types ranged from 0.03 to 16.58%, which was significantly greater than 5%. The soil macroporosity determined 65% of the variation in the steady effluent rate and 42% of the variation in the saturated hydraulic conductivity. Furthermore, the dye coverage ratio decreased as the soil layer depth increased in different plots, and there were some differences in each plot. The maximum dye coverage ratio occurred in the 0∼5cm soil layer, which reached 90.37%. The dye coverage ratio at a depth of 0∼60cm in six plots followed the order of Robinia pseudoacacia (26.48%)>Ulmus pumila (20.12%)>mixed forest (17.32%)>farmland (15.06%)>shrub (13.97%)>weeds (10.07%). The soil preferential flow mostly occurred in the 0∼40cm soil depth layer, which occupied more than 93% of the total soil profile (0∼60cm). Moreover, a Pearson correlation was used to analyze the relationship between environmental factors (soil, water, and plant factors) and the dye coverage ratio. The dye coverage ratio of soil preferential flow under different reclamation vegetations was very significantly or significantly positively correlated with the gravel content, mean radius of soil macropores, soil saturated hydraulic conductivity, root weight density, and root length density, which promoted the formation and development of soil preferential flow. This study will provide a scientific basis for understanding the formation mechanism and perfecting the research system of soil preferential flow, vegetation restoration, and reconstruction in a dump; furthermore, this research offers significance guidance in the construction of green mines and the development of regional economics.

Storage and spatial patterns of organic carbon of soil profiles in Guangdong Province, China

Regional soil organic carbon (SOC) investigations play an important role in building knowledge of the global soil C cycle system. The purpose of the present study was to estimate soil organic carbon (SOC) storage for different soil types and land uses in Guangdong Province, China. The results showed that the total SOC storage in the study area was 1.25 Pg, of which 0.41 Pg SOC was in A horizon soils (mean depth 17.0cm), 0.51 Pg SOC was in the B horizon (mean depth 29.5cm) and 0.33 Pg SOC was in the C horizon (mean depth 48.9cm). SOC storage in Ferrallisols was approximately 0.976 Pg for the total soil profile, accounting for 78.1% of total SOC storage. Forest soils were the main SOC pool by land use, accounting for approximately 80.3% of total SOC storage. Regardless of soil type and land use, subsoil was the primary SOC storage location in the study area. The SOC contents of the upper soil horizon were closely related to the SOC contents of the lower soil horizon, possibly suggesting that there is movement of SOC from the surface soil to lower horizons. Because of soil degradation and erosion, approximately 13.3 Tg SOC entered the surrounding water, accounting for 3.2% of the SOC storage of A horizon soils, and approximately 20.9 Tg SOC was redistributed in surface soils of the study area each year.

Area representative soil water content estimations from limited measurements at time-stable locations or depths

Summary To minimize the number of soil water content ( SWC ) measurements for estimation of field- or watershed-scale soil water storage, we present an analysis of time-stable soil water data across both measurement locations and soil depth intervals. The proposed analysis applies the time stability concept to select area-representative measurement locations, and assesses the potential for identifying the most time-stable depth interval (MTSD) using a minimal number of selected time-stable locations (MTSLs). For that purpose, we used a time series of 21 SWC datasets, measured at 20 locations and 20 corresponding depth intervals down a 3-m soil profile, during a two-year period in the 38-ha study area of the Liudaogou watershed of the China Loess Plateau. After identifying the MTSLs, analysis of time stability of measurement depth intervals showed single soil water depth measurements at between 2 and 5 of the MTSLs were sufficient to determine the area-representative SWC . The MTSD was determined to be about mid-way in the soil profile, irrespective of total soil profile depth measured. Confirmation of the time-stability analyses was done by comparing the representative SWC estimations for the 38-ha sampling area with additional SWC measurements across the 6.9 km 2 watershed. The encouraging results of our analysis suggest that time stability analysis may be an effective way to assess large-scale soil water storage in arid and semi-arid regions.

Distribution of water loss via evapotranspiration in a pistachio tree orchard under drip irrigation and non-irrigation conditions

The present study aimed to measure the distribution of water loss via evapotranspiration (ET) in a pistachio tree orchard under drip irrigation and non-irrigation conditions at the experimental orchard of the Pistachio Research Institute, Gaziantep, Turkey. The experimental design consisted of a 10 × 10 m 2 grid system constructed of PVC pipes spaced 2 m apart (horizontally and vertically) that was placed around each tree for the drip irrigation condition (water applied every 7 days) and the non-irrigated condition. Moisture content was measured using the neutron scattering method for both treatments. Water loss via ET was estimated based on the soil water balance method, which included measurement of soil moisture, precipitation, and irrigation. Total water loss via ET under drip irrigation conditions was 518 mm vs 220 mm under non-irrigated conditions. Water loss via ET for the total soil profile and individual layers under non-irrigated conditions was higher at the four outer corners of each 10 × 10 m 2 grid than under irrigated conditions. Moreover, water loss via ET was the highest at the grid system pipes closest to the two laterals under irrigation conditions. In addition, the total percentage of water loss via ET was the highest at the 60-80-cm and 20-40-cm soil layers under drip irrigation and non-irrigation conditions, respectively, and the total percentage of water loss via ET was the lowest at the 40-60-cm and 0-20-cm soil layers under drip irrigation and non-irrigation conditions, respectively. Lastly, it could be considered that root density increased as water loss via ET increased.

Beryllium-10 concentrations in the hyper-arid soils in the Atacama Desert, Chile: Implications for arid soil formation rates and El Niño driven changes in Pliocene precipitation

Meteoric 10Be concentrations in soil were measured to understand the mechanism, timescale, and climatic dependence of soil formation in the hyper-arid Atacama Desert. The observed systematic decline of soil 10Be concentrations with depth has been reproduced using a simple model that assumes soil matrix, including 10Be, builds up as layers over time while 10Be decays in situ. This suggests a mechanism of soil accumulation via atmospheric deposition, which is in agreement with stable isotopic evidence. The model estimates an age of ∼6.6±0.4Ma for the total soil profile. Small discrepancies between the model and observations are likely mainly due to changes in precipitation rates that can impact 10Be delivery rates and 10Be movement within the profile. Interpreted in this way, the 10Be data suggest drying in the Atacama after ∼4.7Ma, and returning to an insignificant wet period at ∼1Ma, which was possibly connected to El Niño- or La Niña-like climate change.

Spatial Distribution and Fluorescence Properties of Soil Dissolved Organic Carbon Across a Riparian Buffer Wetland in Chongming Island, China

The migration of soil dissolved organic carbon (DOC) from terrestrial to aquatic environments has important impacts on the adjacent water quality and the transport of organic and inorganic contaminants. However, few studies have investigated the sources and properties of DOC in riparian zones. A total of 34 soil samples were collected across four riparian buffer zones (Zones A–D) on Chongming Island, China. The vertical distributions of soil organic carbon (SOC) and DOC, fluorescence excitation-emission matrix (EEM) spectra of DOC and the optical indices, including fluorescence index (FI), index of recent autochthonous contribution (BIX), and humification index (HIX), were measured across the riparian environment to investigate the sources and fluorescence properties of DOC. The results showed that SOC stored in the surface soil (0–30 cm) accounted for 40% of the total soil profile SOC. The DOC accumulated in Zones A–C, which accounted for 5% of the SOC. The fluorescence EEM spectra of DOC showed that DOC contained humic-like and protein-like substances, which were mainly derived from recent plant debris by microbes. A large amount of humic-like substances were sorbed to minerals in the surface soil (0–30 cm). In addition, the riparian topography and soil physico-chemical properties (pH, EC and moisture) dictated the transformation and transport of DOC. The results suggested that EEMs could reveal the source of DOC in riparian soil systems, and that optical indices were complementary tools that revealed the characteristics of soil DOC and provided supplemental evidence about DOC sources.

Changes of preferential flow path on different altitudinal zones in the Three Gorges Reservoir Area, China

Liu, M., Du, W. and Zhang, H. 2014. Changes of preferential flow path on different altitudinal zones in the Three Gorges Reservoir Area, China. Can. J. Soil Sci. 94: 177–188. Preferential flow in soil macropores plays an important role in runoff control and soil and water conservation. The aim of this study was to investigate the distribution of preferential flow paths in the soil profile of various altitudinal belts, analyze its variation among different soil horizons, and define the cause of soil macropores. A dye tracer method combined with photographic analysis was conducted for four hillslope sites in the Three Gorges Reservoir Area of China (TGRA). The results show that stained area proportion, as well as its vertical distribution in soil sections, presented varied patterns due to changes of forest vegetation and soil type with altitude. Stained area ratio of soil profiles increased, while stained depth decreased with increasing altitude. For soil sections in the subalpine belt, mid-mountain belt, and low-mountain belt of TGRA, stained area ratios were 62, 42, and 45%, and stained depths were 52.4, 56.4, and 69.5 cm, respectively. For brown earth covered with subalpine temperate deciduous broad-leaved forest, stained area ratios were the largest, but dyed patches were concentrated in the humus horizon. For yellow earth covered with low-mountain warm coniferous forest, stained depth reached 69.5 cm, and stained patches existed in the total soil profile. Compared with forest soil, stained depth and stained area ratio of abandoned farmland in low-mountain belt were lower, and the depth of dye infiltration was even shallower.

A comparison of Quaternary soil chronosequences from the Ionian and Tyrrhenian coasts of Calabria, southern Italy: Rates of soil development and geomorphic dynamics

Soil development during the Quaternary was investigated, by comparing and integrating analytical datasets of three soil chronosequences developed on different terrace staircases along the Tyrrhenian (western) and Ionian (eastern) coasts of northern Calabria, southern Italy. Two of these soil chronosequences developed on early to late Pleistocene marine terraces in two sectors of the Praia area (western coast), whereas the third one developed on fluvial terraces in the Rossano area (eastern coast) spanning from middle to late Pleistocene ages, respectively. We present and discuss both novel results and already published data related to selected morphological, physical, chemical, mineralogical and SEM analyses from the two coastal sectors. We explored the effects of time on soil development, trying to unravel the role of soil-forming processes, parent material and geomorphic dynamics on direction and rates of pedogenesis. A complex nature of parent materials was indicated by the geochemical signature, coupling certain similarities with some heterogeneity between the two study sectors but also across single soil profiles, as a response to morphodynamic processes (soil reworking, aggradation, burial and/or erosion), in turn promoting soil ageing and/or rejuvenation. These processes and lithological discontinuities were also responsible for some data scattering from calculated soil chronofunctions for peculiar soil properties and pedogenic indices plotted against estimated soil ages. Among the main outcomes, good positive correlations were obtained for the (Fed–Feo)/Fet and Fed/Fet indices, weighted on the basis of total soil profile and single horizon thicknesses to minimize the effects of soil truncation by erosion processes. Our results confirm the reliability of these indices as soil development indicators. Moreover, they suggest that: (i) rates of soil development did not change significantly over ca. 100–800 ka, despite the cyclical alternation of Pleistocene climate changes; (ii) dominant soil-forming processes tend to minimize original differences of pedogenic substrata and local (pedo)climatic conditions through time. In addition, soil chronofunctions permitted to estimate the unknown age (the time range of soil development before burial, about 200 ky) of a buried soil profile in the Rossano area, not correlated to any terrace surface of known age. The occurrence of etched quartz grains in soils of different ages for the two study sectors clearly indicates different rates of silica dissolution in the Tyrrhenian and Ionian coasts of Calabria, promoted by different climatic and pedoenvironmental conditions.

Landscape characteristics influence the spatial pattern of soil water storage: Similarity over times and at depths

Similarity in the spatial patterns of soil water storage (SWS) over time and at depths at multiple scales and locations reflects the similarity in the underlying hydrological processes. The objective of this study was to examine the similarity in the spatial patterns of SWS and its characteristic landscape positions for variable soil depths and over time at a field scale. Soil water content (further converted to SWS by multiplying with depth) was measured for five years (2007–2011) along a transect of 128 points at a study site that has representative hummocky landscape of the North American Prairie Pothole region. Surface (0–20cm) and subsurface (20–140cm at 20cm interval) soil water contents were measured using time domain reflectometry and a neutron probe, respectively. High rank correlation coefficient between the measurements over time and at any depth layers (surface=0–20cm, root zone=0–60cm and total active soil profile=0–120cm) indicated strong similarity of the spatial patterns of SWS and thus the underlying hydrological processes. The spatial patterns at large scales (>72m) were contributed by alternating knolls and depressions (dominant macro-topographical variations in this type of landscape) and were very similar between any measurement times and depth layers. Similarity over time was changed at medium scales (18–72m) due to the changes in the landform elements. However, changes in the small-scale (<18m) spatial patterns were not associated with any landscape characteristics. Similarity was increased at different scales with increase in soil depth owing to strong buffering capacity. Information on the similarity of the spatial patterns at different scales and locations can be used to identify change in sampling domain as controlled by hydrological processes operating at different scales and locations and thus can deliver maximum information with minimum sampling efforts.

Season- and depth-dependent time stability for characterising representative monitoring locations of soil water storage in a hummocky landscape

Characterizing the inherent spatial variability of soil water is intensive in terms of sampling effort and therefore costly. The objectives of this study were to examine time stability of the spatial pattern of soil water storage (SWS) at different seasons and depths, to identify representative monitoring locations (RMLs) that consistently reflect field average SWS, and to recommend efficient ways to identify these locations. Soil water was measured down to 1.4m at 0.20-m vertical depth intervals using time domain reflectometry and neutron backscattering along a hummocky transect in semiarid central Canada. Strong Spearman rank correlation coefficients between SWS spatial series indicated similarity of spatial patterns, which showed strong seasonal dependence: intra-season time stability was stronger than inter-annual time stability, which was stronger than inter-season time stability. The observed time stability was used to identify an RML. The RML for the surface layer (0–0.20m) was different from the root zone (0–0.60m) and the total active soil profile (0–1.20m), the latter two having adjacent RMLs. The bias (~3%–10% maximum) associated with using an RML to predict field-averaged SWS was examined using regression. However, the prediction of field-averaged SWS using an RML was better compared to the prediction using field extreme locations in terms of error associated with the prediction. Predictions using more than one RML yielded better results than when a single RML was used. Successful and rapid identification of RMLs greatly reduced the number of observations needed to characterize the average soil water behaviour of a field. The measurement of SWS through representative monitoring location(s) may be used for environmental monitoring and modelling, irrigation scheduling, nutrient recommendations, and predicting greenhouse gas emissions.

Dual-chamber measurements of δ13C of soil-respired CO2 partitioned using a field-based three end-member model

The contribution of old soil C (SOM) to total soil respiration (RS) in forest has been a crucial topic in global change research, but remains uncertain. Isotopic methods, such as natural variations in carbon isotope composition (δ13C) of soil respiration, are more frequently being applied, and show promise in separating heterotrophic and autotrophic contributions to RS. However, natural and artificial modification of δ13CRs can cause isotopic disequilibria in the soil-atmosphere system generating a mismatch between what is usually measured and what process-based models will predict. Here we report the partitioning of the soil surface CO2 flux in a warm Mediterranean forest into components derived from root, litter/humus, and SOM sources using a new, three end-member mixing model, and compare this with the conventional partitioning into autotrophic and heterotrophic components. The three end-member mixing model takes into account both the discrimination during CO2 respiration/decomposition of the three components, as well as the fractions of their CO2 fluxes integrated over the total soil profile mass. In addition, we used a novel dual-chamber technique to ensure that δ13CRs was subjected to minimal artefacts during measurement.We observed that by using measured soil surface CO2 concentrations as a baseline level for the dual-chamber operation, it was possible to achieve and monitor the necessary conservation of the soil CO2 steady-state diffusion conditions during the measurements, without using permanent collars inserted deeply into the soil. When RS (8.64 g CO2 m2 d−1) was partitioned into two components, the mean autotrophic and heterotrophic respiration was 56 and 44%, respectively. When RS was partitioned using the three-way model, however, roots, litter/humus, and SOM contributed 30, 33, and 37% of the total flux. Our results confirm that to improve the estimates of the partitioning method, it is important to distinguish the fractional contribution of the long-term SOM-derived flux from younger and more labile sources.