Soil hydrology and CO2 release of peat soils

A simple model to predict soil water components and the CO₂ release for peat soils is presented. It can be used to determine plant water uptake and the CO₂ release as a result of peat mineralization for different types of peat soils, various climate conditions, and groundwater levels. The model considers the thickness of the root zone, its hydraulic characteristics (pF, Ku), the groundwater depth and a soil‐specific function to predict the CO₂ release as a result of peat mineralization. The latter is a mathematical function considering soil temperature and soil matric potential. It is based on measurements from soil cores at varying temperatures and soil water contents using a respiricond equipment. Data was analyzed using nonlinear multiple regression analysis. As a result, CO₂ release equations were gained and incorporated into a soil water simulation model. Groundwater lysimeter measurements were used for model calibration of soil water components, CO₂ release was adapted according long‐term lysimeter data of Mundel (1976). Peat soils have a negative water balance for groundwater depth conditions up to 80—100 cm below surface. Results demonstrate the necessity of a high soil water content i.e. shallow groundwater to avoid peat mineralization and soil degradation. CO₂ losses increase with the thickness of the rooted soil zone and decreases with the degree of soil degradation. Especially the combination of deep groundwater level and high water balance deficits during the vegetation period leads to tremendous CO₂ losses.     

Bulk density by Proctor test as a function of texture for agricultural soils in Maputo province of Mozambique

Soil degradation processes may be of various kinds, including soil compaction. The present study was carried out with the objective of assessing the sensitivity of agricultural or recently abandoned soils in Maputo province of Mozambique to compaction. The assessment is based on the maximum of bulk density attained using the Proctor test (MBD).

In this study the soil texture is expressed by silt plus clay (S + C) or clay (C). The relations between the soil texture and MBD, and between soil texture and critical water content (CWC—soil water at which MBD is attained) were determined. Selected soils range from 10 to 74% of S + C and 9 to 60% of C.

The results suggest there is a relationship between the considered parameters, being that between S + C and MBD or CWC, the best. For MBD the relationship is represented by two quadratic equations with the boundary in between these being a S + C value of 25% and C value of 20%.

Based on the obtained results, one can conclude that the selected parameters may be a useful basis for estimation of the sensitivity to compaction of the Maputo province's soils. It is recommended that similar studies be carried out for soils under forest land and for soil of other provinces to establish the national physical degradation hazard as a function of soil parameters determined routinely and at low cost. The suggested parameters are texture and soil organic matter (SOM).     

Predicting soil workability and fragmentation in tillage: a review

Soil workability and friability are required parameters to consider when creating suitable seedbeds for crop establishment and growth. Knowledge of soil workability is important for scheduling tillage operations and for reducing the risk of tillage‐induced structural degradation of soils. A reliable evaluation of soil workability implies a distinctive definition of the critical water content (wet and dry limits) for tillage. In this review, we provide a comprehensive assessment of the methods for determining soil workability, and the effects of soil properties and tillage systems on soil workability and fragmentation. The strengths and limitations of the different methods for evaluating the water content for soil workability, such as the plastic limit, soil water retention curve (SWRC), standard Proctor compaction test, field assessment, moisture‐pressure‐volume diagram, air permeability and drop‐shatter tests are discussed. Our review reveals that there is limited information on the dry limit and the range of water content for soil workability for different textured soils. We identify the need for further research to evaluate soil workability on undisturbed soils using a combination of SWRC and the drop‐shatter tests or tensile strength; (i) to quantify the effects of soil texture, organic matter and compaction on soil workability; and (ii) to compare soil water content for workability in the field with theoretical soil workability, thereby improving the prediction of soil workability as part of a decision support system for tillage operations.     

Calculation of Steady State Capillary Rise from the Groundwater Table in Multi-Layered Soil Profiles

A computer program CRISP is presented to calculate steady state capillary rise from the groundwater table in single- and multi-layered soil profiles. The calculation is based on an integration of Darcy's equation and uses k-v functions, described with a modified formula of Brooks and Corey (1964). The three constants in this formula can be evaluated from texture and organic matter content, accounting for hysteresis (Bloemen, 1980). Application of the program CRISP shows that the heights of capillary rise from the groundwater table in single-layered soil profiles may be largely different. Of more interest for practical matters is capillary rise in multi-layered soil profiles, which may be strongly influenced by the depth of the groundwater table. The deepest admissable level of the groundwater table that guarantees a certain water supply to the root zone appears to vary widely for different soil profiles. This can be the starting point for a classification of soil profiles on the basis of their potentialities for capillary water supply. Characteristic textures and humus contents of upper soils and subsoils of different geo-genetical groups may thus become distinctive features. Possibly a subdivision of these groups is necessary. The depths of changes between distinguished layers are significant. The actual range of variations of the depth of the groundwater table should play part in a soil classification.     

Salt-Water Transport in Unsaturated Soils Under Crop Planting： Dynamics and Numerical Simulation

A laboratory salt-water dynamics experiment using unsaturated soils in packed silt loam and clay soil columns with different soil texture profiles and groundwater levels under crops were conducted to study the changes of salt-water dynamics induced by water uptake of crops and to propose the theoretical basis for the regulation and control of saltwater dynamics as well as to predict salinity levels. The HYDRUS 1D model was applied to simulate the one-dimensional movement of water and salt transport in the soil columns. The results showed that the salts mainly accumulated in the plow layer in the soil columns under crops. Soil water and salt both moved towards the plow layer due to soil water absorption by the crop root system. The salt contents in the column with lower groundwater were mostly greater than those with high groundwater. The water contents in the soil columns increased from top to the bottom due to plant root water uptake. The changes in groundwater level had little influence on water content of the root zone in the soil columns with crop planting. Comparison between the simulated and the determined values showed that model simulation results were ideal, so it is practicable to do numerical simulation of soil salt and water transport by the HYDRUS 1D model. Furthermore, if the actual movement of salt and water in fields is to be described in detail, much work needs to be done. The most important thing is to refine the parameters and select precise boundary conditions.     

种植作物条件下非饱和土壤中水盐的动态实验和数值模拟研究

A laboratory salt-water dynamics experiment using unsaturated soils in packed silt loam and clay soil columns with different soil texture profiles and groundwater levels under crops were conducted to study the changes of salt-water dynamics induced by water uptake of crops and to propose the theoretical basis for the regulation and control of salt-water dynamics as well as to predict salinity levels. The HYDRUS 1D model was applied to simulate the one-dimensional movement of water and salt transport in the soil columns. The results showed that the salts mainly accumulated in the plow layer in the soil columns under crops. Soil water and salt both moved towards the plow layer due to soil water absorption by the crop root system. The salt contents in the column with lower groundwater were mostly greater than those with high groundwater. The water contents in the soil columns increased from top to the bottom due to plant root water uptake. The changes in groundwater level had little influence on water content of the root zone in the soil columns with crop planting. Comparison between the simulated and the determined values showed that model simulation results were ideal, so it is practicable to do numerical simulation of soil salt and water transport by the HYDRUS 1D model. Furthermore, if the actual movement of salt and water in fields is to be described in detail, much work needs to be done. The most important thing is to refine the parameters and select precise boundary conditions.     

适宜水分和养分提高土壤中磺酸二甲嘧啶降解率

医疗和养殖过程中抗生素的广泛使用导致了土壤环境中抗生素的污染。为了解进入农田土壤中抗生素的降解规律,该文以养殖业广泛使用的磺胺二甲嘧啶和2种不同养分水平的土壤为试验材料,采用盆栽方法研究了肥料种类(有机肥、NPK肥、N肥、PK肥等)、耕作强度(翻耕、免耕)、水分条件(长期干燥、长期湿润、干湿交替、长期潮湿)及种植作物(种植蔬菜、不种蔬菜)对土壤中磺胺二甲嘧啶降解的影响。结果表明,与不施肥处理比较,施用有机肥、NPK肥、N肥可促进土壤中磺胺二甲嘧啶在土壤中的降解,并以施用有机肥的效果最为明显;但施用PK肥对土壤中磺胺二甲嘧啶的降解影响不明显。翻耕可促进土壤中磺胺二甲嘧啶的降解,干湿交替、长期湿润比长期干燥和长期潮湿土壤环境下更有利于磺胺二甲嘧啶的降解。种植蔬菜比不种蔬菜土壤的磺胺二甲嘧啶的降解率高,根际土壤中磺胺二甲嘧啶的降解高于总体土壤。高养分土壤中磺胺二甲嘧啶的降解一般高于低养分土壤。分析认为,施肥、土壤养分水平、种植蔬菜对土壤中磺胺二甲嘧啶的降解的影响可能主要与这些因素改变了土壤微生物活性有关;翻耕可促进土壤中抗生素的光降解强度。研究认为,施肥、耕作和水分管理可以在一定程度上加速土壤中磺胺二甲嘧啶的降解。     

Salt-Water Dynamics in Soils: Ⅰ. Salt-Water Dynamics in Unsaturated Soils Under Stable Evaporation Condition

A long term simulation test on salt-water dynamics in unsaturated soils with different groundwater depths and soil texture profiles under stable evaporation condition was conducted.Salinity sensors and tensiometers were used to monitor salt and water variation in soils.The experiment revealed that in the process of fresh groundwater moving upwards by capillary rise in the column,the salts in subsoil were brought upwards and accumulated in the surface soil,and consequently the salinization of surface soil took place.The rate of salt accumulation is determined mainly by the volume of capillary water flow and the conditions of salts contained in the soil profile.Water flux in soils decreased obviously when groundwater depths fell below 1.5m.When there was an interbedded clay layer 30cm in thickness in the silty loam soil profile or a clay layer 100cm in thickness at the top layer,the water flux was 3-5 times less than in the soil profile of homogeneous silty loam soil.Therefore,the rate of salt accumulation was decreased and the effect of variation of groundwater depth on the water flux in soils was weakened comparatively.If there was precipitation or irrigation supplying water to the soil,the groundwater could rarely take a direct part in the process of salt accumulation in surface soil,especially,in soil profiles with an interbedded stratum or a clayey surface soil layer.     

Salinization,alkalinization and sodification in Punjab (Pakistan): characterization of the geochemical and physical processes of degradation

Evidence of soil degradation impeding soil tillage and irrigation in cultivated soils in Pakistan is identified, described and represented in a general process of degradation. Based on a chemical analysis of soil characteristics, it is shown that a more general geochemical degradation process may occur in these soils. Two paths of salinization, i.e. neutral salinization and alkalinization inducing a process of sodification, are identified. The wide range of chemical properties of soils and corresponding geochemical processes can be explained by the great diversity of quality in irrigation water that is taken either from the canal or from the groundwater. The basic module of a geochemical model AQUA (Vallès and DeCockborne, 1992) is calibrated with the help of a study of the soil geochemical properties (identification of minerals, characterization of exchanges) and then used to assess the effect of four different water qualities on sandy and loamy soils. Based on these scenarios, the salinity, alkalinity and sodicity hazard of irrigation water is assessed by taking into account simultaneously the electrical conductivity and the residual alkalinity (calcite-residual alkalinity, residual sodium carbonates) or irrigation water and the soil cation exchange capacity: these three indicators appear the most relevant in the context of the study. Copyright © 1999 John Wiley & Sons, Ltd.     

黄土高原土壤水分性质及其分区

黄土高原土壤具有很好的调节作物供水的功能,这和土壤的水分性质有关。本文研究了土壤的持水性能、有效性能和移动性能等。影响黄土高原土壤水分性质的主要因素是土壤质地。文内绘制了包括五个质地带的土壤质地分区图。田间持水量在轻壤土、中壤土和重壤土范围内均为20%±2,未表现出明显相关。萎蔫湿度则几乎完全决定于土壤质地。文内绘制了田间持水量和萎蔫湿度的等值线图。土壤水物理蒸发影响深度可达2-3米。两米土层内物理蒸发失水量轻壤土和中壤土达田间持水量的25-35%;具有下伏粘化层的重壤土,60厘米以下矢水量不大于10%。后者为作物准备了较多的储水。文内列出了不同质地土壤的水分特征曲线的经验方程,所有资料汇总于土壤水分性质表中。本研究结果为合理利用土地提供了基础数据。     

Temperature field of complex soilscapes (by the example of the Vladimir opolie region)

Problems of the assessment of soil temperature regime at the polypedon level have yet to be solved. An approach suggested by the authors consists of three stages: (1) the characterization and prediction of the soil water regime as a factor influencing the soil temperature regime, (2) the obtaining of thermophysical functions for the particular elements of complex soilscapes, and (3) the calculation and assessment of the temperature regime of complex soilscapes in the form of the functional fields of soil temperature isopleths. This approach has been applied to predict the soil temperature regime of an arable field in the Vladimir opolie region. The complex soilscape of the field consists of medium loamy agrogray soils, agrogray soils with the second humus horizon, and podzolized agrogray soils. At the beginning of the growing season, minimum temperatures are observed in the areas of agrogray soils with the second humus horizon; the difference in soil temperatures at a depth of 20 cm reaches 1°C, and the difference in the sum of active soil temperatures reaches 20°C. Then, this difference changes considerably, so that the agrogray soils with the second humus horizon become warmer than the agrogray soils. In general, the functional field of soil temperatures within the complex soilscape is highly dynamic and diverse, which is specified by the variability in the water-physical and thermophysical properties of particular soils.     

Effect of Fluctuating Hydrological Conditions on the Mobility of Heavy Metals in Soils of a Freshwater Estuary in the Netherlands

The objective of this study was to measure the mobility of heavy metals in freshwater estuary soils that are seasonally inundated and to characterize the distribution of sulfide precipitates in these soils. Precipitation and dissolution of labile sulfides may account for changing pore water concentrations of heavy metals in freshwater wetland soils that are subject to temporary flooding or fluctuating groundwater levels. The presence of authigenic zinc- and iron-(mono)sulfide in this type of soils during periods with a high groundwater level was demonstrated by electron microprobe analyses. Because sulfide precipitates are strongly associated with root remnants, fresh soil organic material may be an important intermediary in the sulfur cycling and, consequently, in the behavior of heavy metals in these freshwater soils. Oxidation of labile sulfides may be partly responsible for the increased zinc and sulfate concentrations in the pore water during periods with low groundwater levels. Heavy metals may also be mobilized by degradation of their host phase organic matter during periods with high biodegradation.     

Dynamics of Physical and Physicochemical Properties of Urban Soils under the Effect of Ice-Melting Salts

Physical (water content, density, and air and water regimes) and physicochemical (electrical conductivity, pH, and SAR) properties of urban soils were investigated on test plots of Moscow to evaluate their dynamics under anthropogenic impact. The wilting point and the dependence of the capillary-sorption and total water potentials of the soil water content were determined in laboratory experiments with natural and artificially saline soil samples to evaluate the effect of salt antifreeze substances on water availability for plants under conditions of active application of deicing reagents. Seasonal dynamics of these parameters were investigated. It was found that electrolytes display a steady tendency for the accumulation and redistribution in the root zone rather than for their deep leaching despite humid climatic conditions in Moscow megalopolis. In summer, regular droughts result in drying of the root zone to critical values and to the concentration of electrolytes up to the values that make the total water potential of soil unsuitable for water uptake by roots. The key factor of soil degradation under the impact of electrolytes is the soil dispersity: the finer the texture, the higher the soil salinization and solonetzicity and the stronger irreversible changes in the soil water retention capacity and physical properties.     

Dependence of Changes in Soils on Trails and their Impact Zones from a Level of Recreational Impact in Forest Parks in Moscow

Based on a case study of Moscow forest parks Losinyi Ostrov and Bitsevskii Les, the paper presents a quantitative assessment of changes in the physical, chemical, and biological properties of soils on trails in these parks and in linear trailside (pritropinochnye) zones depending on the recreation load level. It is shown that soil properties differ in their sensitivity to recreation. The widths of impact zones range from 20 to 100 cm from the edges of trails depending on the sensitivity of the soil property, recreation load, and type of biogeocenosis.     

Water-table management in lowland UK peat soils and its potential impact on CO2 emission

The rate of oxidation of peat soils is highly seasonal and varies with temperature and soil moisture content. Large variations in soil moisture content result in wet–dry cycles that can enhance peat degradation. Water‐table management plays a crucial role in controlling and damping the effect of these environmental factors. However, maintaining high ditch water levels in fields bounded by ditches does not guarantee a high field groundwater level. The effect of installing subsurface irrigation at different spacings on water table elevation was studied in a low‐lying peat grassland. The water table elevation data were compared against values predicted with a water balance model. In addition, greenhouse experiments were carried out on undisturbed soil core samples collected from the peat grassland as well as a low‐lying peatland under intensive arable faming to measure CO₂ evolution under different water regimes. The field data from the peat grassland suggest that sub‐irrigation spacing as low as 10 m is necessary during summer periods to maintain groundwater levels similar to those in the ditches. Over the same period of observation, the difference in water level between the ditches and the non‐irrigated fields is as high as 0.7 m. Modelled outputs are in good correlation with the field observations, and demonstrate that simple water balance models can provide an effective tool to study the effect of water management practices and potential changes in subsurface conditions, climate and land use on water‐table levels. The measurement of CO₂ emission from undisturbed peat soil columns shows that the rate of oxidation of soil organic matter from peat soils is highly seasonal and that drainage exacerbates the rate of peat mineralization.     

Degradation and persistence of rotenone in soils and influence of temperature variations

The persistence and degradation of rotenone and its primary degradation product 12a beta-hydroxyrotenone in soils were determined under standardized laboratory conditions in the dark at 20 or 10 degrees C and at 40% of water holding capacity. Degradation experiments were carried out on two types of soil collected in southern Italy, a silt clay loam (SCL) and a loamy soil (L). A kinetic model was developed to describe degradation rates of rotenone, taking into account the production, retention, and degradation of the main metabolites. The DT50 values of rotenone and 12a beta-hydroxyrotenone, were 8 and 52 days in SCL soil, and 5 and 23 days in L soil at 20 degrees C, respectively. However, at 10 degrees C a tendency for slower degradation of rotenone and 12a beta-hydroxyrotenone was observed (25 and 118 days in SCL and 21 and 35 days in L soils, respectively). The differences were significant for most data sets. Temperature had a strong effect on degradation; a 10 degrees C increase in temperature resulted in a decrease in the DT50 value by a factor of 3.1 and 2.2 in SCL and of 4.2 and 1.4 in L soils for both rotenone and 12a beta-hydroxyrotenone, respectively. Results show that the degradation rates of both rotenone and 12a beta-hydroxyrotenone were greatly affected by temperature changes and soil physicochemical properties. The degradation reaction fits the two compartment or the multiple compartment model pathways better, which clearly indicates a rather complex rotenone degradation process in soils. Results provide further insights on the rates and the mechanisms of rotenone degradation in soils, aiming to more clearly describe the degradation pathway of chemical residues in the environment.     

Colloid-chemical model for describing some soil processes

Arguments are presented for changing the approach to soil studies in order to consider the behavior of soils in terms of a colloid-chemical model rather than in terms of a physical model. Experimental studies of changes in the stickiness of an air-dry chernozem depending on the time elapsed since adding water, of the catalase activity of soils depending on the time elapsed since adding water and salt solutions, of the thermal diffusivity of soils depending on the time elapsed since adding water, and of the soil temperature showed that the soil solution is a structured colloidal system. Electron microscopic studies of soil solutions confirmed that colloidal particles of soil solutions interact with one another due to long-range aggregation to form periodic colloidal structures enclosing soil moisture. It was concluded that the colloidal structuring of the soil solution makes it similar to physiological fluids and makes the soils similar to biological systems; therefore, the consideration of soils in terms of a colloid-chemical model expands our knowledge of these systems and can be useful for soil scientists.     

TAU-OMEGA遥感辐射模型改进与参数化

大尺度地表土壤水分信息的获取对水资源管理、农业生产以及气候变化等相关研究具有重要意义。TAU-OMEGA（$ \tau -\omega $）模型是利用被动微波遥感技术进行大尺度土壤水分信息提取的常用模型。由于$ \tau -\omega $模型忽略了植被层的体散射作用,该模型仅适用于L波段,存在C波段适用性差及模型参数无法定量计算的问题。该研究在分析植被冠层对微波散射机制的基础上,通过增加反映冠层多次散射作用的辐射添加项对$ \tau -\omega $模型进行了改进,成功解决了模型在C波段的适用性问题;通过理论推导,得出了模型$ \omega $参数的理论计算方法,基于模拟数据集,实现了基于冠层叶面积指数的模型$ \omega $和$ \tau $参数的计算,解决了$ \tau -\omega $模型中$ \omega $参数无法根据遥感数据进行定量计算的问题。以玉米冠层为例,在C波段（6.6 GHz）,改进的$ \tau -\omega $模型对地表微波辐射亮温的模拟值与实测数据保持了较好的一致性,模拟误差较改进前有了极大的下降,V极化均方根误差为3.02 K,H极化均方根误差为3.94 K,结果表明了该研究提出的模型改进与参数化方案的合理性,研究结果为联合光学和被动微波遥感数据进行大尺度土壤水分反演奠定了基础。     

香港土壤研究 Ⅵ.基于改进层次分析法的土壤肥力质量综合评价

采用改进层次分析法（AHP），并结合覆盖整个香港地区的51个典型土壤剖面样品分析得到的pH（H2O）、有机质、质地等包含土壤物理和土壤化学的10项指标进行综合评价。评价结果表明：香港地区的土壤肥力质量总体不高，有1／2以上调查样点属中等以下水平。在不同生态景观类型中，农业土壤的肥力质量相对较高。土壤过酸和磷素水平（包括全磷和速效磷含量）过低是香港土壤肥力质量低下的主要原因。此外，山火焚烧和侵蚀在一定程度上加剧了土壤肥力的退化，因此需要加强地表植被和水土的保育工作。     

Soil matric potential and salt transport in response to different irrigated lands and soil heterogeneity in the North China Plain

Purpose

In the lowland area of the North China Plain (NCP), increasing utilization of brackish water could promote the transformation of precipitation into available water resources, and alleviate the conflict between increase food production and freshwater scarcity. However, the processes of soil water movement and salt migration might be altered, because utilization of brackish water results in frequent changes in groundwater depth and thickness of vadose zone. Thus, it was necessary to understand soil water movement and salt migration when using brackish water for irrigation.

Materials and methods

In this study, soil matric potential (SMP) and total dissolved solids (TDS) at multiple depths were measured in situ to investigate the mechanisms of soil water movement and salt migration at one grassland (site 1) and at three typical irrigated croplands (sites 2, 3, and 4) with different soil textures and groundwater depths in a lowland area of the NCP.

Results and discussion

The study showed that deep soil water and groundwater were recharged generally following heavy precipitation during rainy season. SMP values increased quickly at site 4 due to relatively homogeneous soils, followed by site 3?>?site 2?>?site 1 with an obvious hysteresis response of SMP at multiple depths to precipitation. Soil water mainly moved downward in piston flow, and preferential flow also existed in the soil above 100 cm in the percolation process at four sites. Generally, SMP values followed the order of site 4?>?site 1?>?site 2?>?site 3 and exhibited an inverse trend for TDS, which was mainly due to soil heterogeneity and soil texture in vertical profiles. The differences in SMP among the four sites were mainly due to land use and groundwater depth. There were significantly differences in spatiotemporal distribution of water and salts between homogenous and heterogeneous soils. The processes of infiltration and water redistribution ended quickly in relatively homogeneous soils after heavy rains. However, there was obvious hysteresis in SMP with an increase in soil depth in heterogeneous soils.

Conclusions

Homogenous soils favored water infiltration, salt leaching, and groundwater recharge, and the flow of soil water flow was blocked and salt accumulated significantly in layered soils. The soil water movement and the transformation relationship between water and salt in the vadose zone provided a basis for utilization of brackish water irrigation in lowland region of the NCP.