A new approach to calculate the particle density of soils considering properties of the soil organic matter and the mineral matrix

The particle density of soil (ρ_S) represents one of the soil's basic physical properties and it depends on the composition of both the mineral and the organic soil components. It therefore varies for different soils, e.g. within the group of mineral soils, and ranges from 2.4–2.9 g cm⁻³. Hence, awareness of this variability is important for properties estimated by a calculation involving particle density. Because ρ_S depends on both the soil's solid mineral particles and soil organic matter composition, we derived a function based on the mixture ratio of these two soil components. This approach represents a further development of earlier investigations dealing with the influence of organic carbon (C_org) on ρ_S. To parameterise this function, two data sets were used: (1) data from soils with C_org contents between 0% and 54.88% and corresponding values of ρ_S between 1.49 and 2.72 g cm⁻³; and (2) data from soils of 17 German long-term experiments contrasting in soil texture and in soil mineral inventory. Data set 1 was used to quantify the influence of soil organic matter on ρ_S, and data set 2 was used to calculate the influence of mineral matrix on ρ_S. The soil organic matter has two major influences on ρ_S: (1) via a mass effect (expressed as a mixture ratio between organic and mineral soil components); and (2) via a quality effect (expressed as calculated changes in particle density of organic soil components). Here, we calculated that with increasing content of soil organic matter (0–100%), the particle density of organic soil components rose from about 1.10 to 1.50 g cm⁻³, and present possible reasons for this phenomenon. Additionally, we demonstrate that the mineral matrix of the soil affects ρ_S especially via variations in the mineral inventory, but conclude that differences in particle size distribution of soils were to a lesser extent suitable for describing the influence of the mineral matrix on ρ_S. Overall, using our approach should generate more realistic values of ρ_S, and consequently of all calculated parameters which are sensitive to ρ_S.     

农田土壤速效钾含量的空间变异研究

论文以高产潮土区2007年104个土壤采样点耕层速效钾含量为基础,基于地统计学原理,结合GIS空间分析技术,探讨了土壤速效钾含量的空间变异特征,建立了土壤速效钾含量的空间变异模型,形成了土壤速效钾含量的空间分布图,阐明了影响高产农田土壤速效钾含量分布不均衡的原因。研究结果表明,高产潮土区土壤速效钾含量平均为287．476gkg^-1,最高为483．433gkg^-1,最低为119．435gkg^-1,球状模型是土壤速效钾连续性空间分布的最佳模型,其块金值,基台值为0．399,说明土壤速效钾在变程为57．691米的范围内具有中等强度的空间变异性,含量高低的区域分布比较明显,在地块东南部和中部为其含量较高的区域,含量较低的两个突出区域呈典型的圈层分布,由内向外含量递增,具有较强的渐变性分布规律。总的来看,土壤速效钾约有60．1％的空间变异来自于土壤母质、地形地貌、气候等非人为的结构性因素,39．9％的变异来自于随机性因素如施肥、灌溉、管理水平等因素的影响。     

Spatial and temporal variability of soil hydraulic conductivity in relation to soil water distribution, using an exponential model.

An internal drainage experiment was conducted to examine soil water content variability in space and in time. It is shown that the flux-gradient model used to describe water flow in field soil profiles, based on the Darcy–Buckingham equation, yielded results of extreme variability and questionable validity. The problem lies in the representativeness of a site due to soil variability, horizontally and vertically in time, which added to the character of the hydraulic conductivity versus soil water content relation, which in many cases can be approximated by exponential functions, leads to coefficients of variation up to 170% in the estimation of soil hydraulic conductivity values.     

Prediction of surface runoff and soil loss in southeastern Norway using the WEPP Hillslope model

Yearly and daily surface runoff and soil loss simulated by the WEPP Hillslope model v. 2002.7 were compared with measurements from two different soil erosion plot sites in southeastern Norway. The soil at Bjørnebekk (Bj) was a levelled silty clay loam (2% organic matter) and the soil at Syverud (Sy) was a loam (5% organic matter). The plots at Bj were 21 m long and 8 m wide, while the plots at Sy were 30 m long and 7 m wide. Slope at both sites was 13%. Four management systems for grain production were used: autumn ploughing (AP), winter crop rotation (WCR), autumn harrowing (AH) and spring ploughing (SP). Hydraulic conductivity and soil erosion parameters were determined using WEPP-recommended equations based on measured soil parameters. In general, the WEPP Hillslope model simulated fewer runoff events than measured for all management systems during 1990–1998. Runoff events in winter were seldom predicted and small events (<5 mm) were mostly missed. To use the WEPP Hillslope model on Norwegian soils, where major soil loss events from arable land occur during late autumn, winter and early spring, improvements in winter hydrology calculations are needed. In particular calculations of soil frost development and infiltration into frozen soil need to be improved. The WEPP-recommended soil erosion parameter equations were unsuitable for these two Norwegian soils, especially for levelled soil.     

The spectral quality of light influences the temporal development of the microbial phenotype at the arable soil surface

The uppermost zone of soil represents the primary interface between the above- and below-ground compartments of terrestrial ecosystems and is functionally important since it affects water infiltration, gaseous exchange, erosion processes and the habitat for surface and near-surface dwelling fauna. Two microcosm-scale experiments were conducted to investigate the development of microbial communities in the uppermost centimetre of an arable soil surface following a physical disturbance event, and to determine the effects of the spectral wavebands of light upon such development. Following establishment of freshly disturbed surfaces, subsequently exposed in the field, phenotypically distinct communities determined by PLFA analysis were apparent after eight weeks. Community structure subsequently diverged with respect to depth and time over a further 24 weeks, following consistent trajectories in principal component ordinations. Microbial biomass concentrations increased over time and were greater in the uppermost surface layer (c. 1 mm) compared to deeper layers (up to 11 mm), hypothesised to be driven by the development of photoautotrophs in the extreme surface, where chlorophyll a concentrations increased by an order-of-magnitude over the experimental period. The waveband of light reaching the soil surface, controlled experimentally by the use of selective filters, had a profound effect upon these microbiological properties. In the absence of either light or photosynthetically active radiation (PAR), chlorophyll a concentrations were negligible. Restricting admission of UV-A to the surface resulted in a fourfold increase in chlorophyll a concentration at the extreme surface, and significantly greater concentration in the sub-surface layer compared to the +UV-A treatment. In the surface and sub-surface layers, biomass C concentrations were greatest where UV-A was restricted, and least where PAR was restricted. Biomass C decreased significantly with depth where UV-A was restricted, but increased with depth where PAR was restricted. The waveband of light reaching the soil surface did not affect biomass in the deeper layers. The phenotypic community structure was affected by both the admission and restriction of UV-A, but only in the community present in the extreme surface layers, and principally in relation to the relative proportions of the PLFAs 16:0, 14:0 and 16:1ω7c. Otherwise, the community phenotype was relatively insensitive to the waveband of light reaching the soil surface. This research demonstrates that it is effectively the uppermost 1 mm that is the biotically distinct phase of the arable soil surface, with the presence and waveband of light being an important governing factor that influences its development and phenotypic properties.     

Impact of soil compaction upon soil water balance and maize yield estimated by the SIMWASER model

The capability of the soil water balance model SIMWASER to predict the impact of soil compaction upon the yield of maize (Zea mays L.) is tested, using the results of a field experiment on the influence of soil compaction by wheel pressure upon soil structure, water regime and plant growth. The experimental site was located on an Eutric Cambisol with loamy silt soil texture at an elevation of 260 m in the northern, semi-humid sub-alpine zone of Austria. Within the experimental field a 7 m wide strip was compacted by a tractor driven trailer just before planting maize in May 1988. Compression effects due to trailer traffic resulted in distinct differences of physical and mechanical soil parameters in comparison with the uncompressed experimental plots down to a depth of about 30 cm: bulk density and penetration resistance at field capacity were increased from 1.45 to 1.85 g/cm³, and from 0.8 to 1.5 MPa, respectively, while air-filled pore space as well as infiltration rate were appreciable lowered from about 0.08–0.02 cm³/cm³ and from 50 to 0.5 cm per day, respectively. The overall effect was a clear depression of the dry matter grain yield from 7184 kg/ha of the non-compacted plot to 5272 kg/ha in the compacted field strip. The deterministic and functional model SIMWASER simulates the water balance and the crop yield for any number of crop rotations and years, provided that daily weather records (air temperature, humidity of air, global radiation, wind and precipitation) are available. Crop growth and soil water regime are coupled together by the physiological processes of transpiration and assimilation, which take place at the same time through the stomata of the plant leaves and are both reacting in the same direction to changes in the soil water availability within the rooting zone. The water availability during rainless seasons depends on the hydraulic properties of the soil profile within the rooting depth and on rooting density. Rooting depth and density are affected by both the type of the crop and the penetration resistance of the soil, which depends on the soil moisture status and may be strongly increased by soil compaction. The model SIMWASER was able to simulate these effects as shown by the calculated grain yields, which amounted in the non-compacted plot to 7512 and to 5558 kg dry matter/ha in the compacted plot.     

氮肥和秸秆施用对稻麦轮作体系下土壤剖面N_2O时空分布的影响

通过气体原位采集系统对稻麦轮作体系下土壤剖面不同层次N2O浓度动态变化进行了两年田间原位监测。共设4个处理:对照(N0S0)、施氮无秸秆(N1S0)、配施低量秸秆(N1S1)以及配施高量秸秆(N1S2)。结果表明,土壤剖面N2O浓度具有明显的时空分布特征:各处理在小麦和水稻生长前期均出现明显的浓度峰值,施加氮肥加大峰值,添加高量秸秆降低峰值。水稻生长季N2O主要产生在近表层土壤(7 cm和15 cm),N2O浓度两年均为15 cm≥7 cm≥30 cm≥50 cm;小麦生长季N2O主要产生在下层土壤(30 cm和50 cm)。与N0S0相比,施加氮肥3个处理均显著增加土壤剖面各层次的N2O浓度(p0.05),其中N1S0处理各土层N2O浓度是N0S0处理对应土层的2倍~3倍。配施高量秸秆(N1S2)能显著减少近表层土壤N2O浓度。     

黑土有机碳变化的DNDC模拟预测

为探讨黑土有机碳的长期变化规律及DNDC模型在土壤有机碳预测方面的适用性,本文利用吉林省公主岭地区黑土不同施肥措施下的长期定位试验数据,选取不施肥(CK)、单施化肥(NPK)、配施有机肥(NPKM)和增施有机肥(M2+NPK)4个处理进行土壤有机碳分析,并将数据用作DNDC模型验证。验证结果表明:各处理DNDC验证中RMSE值均小于10%(分别为5.09%、6.11%、9.38%、8.36%),说明模拟值与观测值一致性良好,模型可用于该地区土壤有机碳模拟。选取了化肥施用、有机肥施用、秸秆还田比率、温度及降水5个因子进行模型的敏感性分析,结果表明:有机肥的施用对土壤有机碳含量的影响最显著,且这种影响具有持久性。最后模拟了4种施肥情境下未来(至2100年)的土壤有机碳变化情况。结果表明:对照不施肥处理(CK)土壤有机碳含量略有下降,至2100年土壤有机碳含量为11.55 g·kg-1,较试验前土壤初始有机碳(13.2 g·kg-1)下降约12.5%。单施化肥处理(NPK)土壤有机碳含量较为稳定,并未出现土壤有机碳含量下降。配施有机肥(NPKM)和增施有机肥(M2+NPK)处理土壤有机碳含量增加明显,至2100年土壤有机碳含量为24.4 g·kg-1和27.6 g·kg-1,分别较初始有机碳含量上升84.8%和109.1%。     

The application of remote-sensing data to monitoring and modelling of soil erosion

This paper gives a brief synthesis of the information obtainable from remote-sensing data and how it can be related to two significant functions of catchment hydrology, namely, the processes of production and transfer. After presenting examples of the type of information that can be derived from remote sensing (characterisation of soil surface by different wavelengths, temporal changes of surface states, incision and geometry of possible water pathways on the surface, etc.), we examine how this information can provide parameters for input into runoff and erosion models. Finally, we assess the progress in assimilating remote-sensing data into deterministic models of storm runoff.     

Application of a low-cost database to soil erosion and soil conservation studies in the Awash Basin,Ethiopia

In large-scale land resource planning exercises, Geographical Information Systems (GIS) form a valuable means of storing, retrieving, displaying, and analysing spatially-referenced data, as well as enabling the simulation of the consequences of various alternative development options. However, at this scale only generalized policies for the allocation of finance can be made, and the implementation of those policies will invariably require detailed evaluation at the local level. This suggests that expenditure on the central planning process itself should be limited, with funds reserved for later site studies. The form of GIS adopted centrally should also lend itself to easy use and interpretation by policymakers and planners. These requirements suggest that GIS development using proprietary off-the-shelf database management software may be preferable to high-technology GIS software. This paper outlines the development of such a GIS, based on dBase-III-plus and its internal programming language, in the analysis of problems of soil erosion and soil conservation in the large (110,000 km²) drainage basin of the Awash River in Ethiopia. The methodology employed involves the FAO modification of the Universal Soil Loss Equation, which clearly lacks a secure process basis, but is appropriate for the scale of planning involved and the quality of calibration data available. The GIS is used to map patterns of soil erosion, to identify target areas for conservation on the basis of criteria of sensitivity to land use change, and to assess the costs and benefits of conservation work in those areas. It is suggested that the simple form of GIS involved in this study has much to offer environmental managers in developing countries in the rapid development of plans for soil conservation.     

Responses of the bacterial and fungal biomass in a grassland soil to multi-year applications of dairy manure slurry and fertilizer

Plots of a tall fescue (Festuca arundinacea) sward in the south coastal region of BC, Canada, were treated with dairy manure slurry or fertilizer at 50 or 100 kg NH₄-N ha⁻¹ up to four times per year for six consecutive years; control plots received no manure or fertilizer. The length of fungal hyphae and abundance of bacterial cells were determined by direct counting at 19 sample dates during the fourth (1997), fifth (1998) and sixth (1999) application years. Bacterial abundance was significantly greater in manured soil than in fertilized and untreated soils. In contrast, hyphal length was significantly greater in untreated soil than in manured and fertilized soils. In subplots that ceased to receive manure in 1998, bacterial abundance remained greater through 1998 and 1999 than in previously fertilized plots, indicating that the 4 year cumulative effect of manure was detectable for at least two growing seasons after applications cease. The apparently negative effect of manure and fertilizer on fungal hyphae also appeared to persist through 2 years after applications ceased. Bacterial abundance increased after an initial application of manure for 1 year to previously untreated plots, but not to levels comparable to plots treated with manure continuously from 1994 to 1998.Increases in bacterial abundance, during the one to three week intervals immediately following individual applications of manure, were inconsistent and other factors, such as soil moisture, temperature and perhaps crop phenology appear to have had strong effects on the timing of these microbial responses. Annual means for bacterial abundance and total microbial biomass in the continuous manure treatment were similar for all 3 years. This suggested that the manure-induced increase in microbial biomass probably reached a plateau between one and 3 years after applications commenced. The large bacterial populations along with abundant carbon substrates in manured soil, relative to fertilized soil, were probably capable of immobilizing influxes of mineral N, explaining the observations that less leaching occured from manured than from fertilized soils.     

Contribution of phytoecological data to spatialize soil erosion: Application of the RUSLE model in the Algerian atlas

Among the models used to assess water erosion, the RUSLE model is commonly used. Policy makers can act on cover (C-factor) and conservation practice (P-factor) to reduce erosion, with less costly action on soil surface characteristics. However, the widespread use of vegetation indices such as NDVI does not allow for a proper assessment of the C-factor in drylands where stones, crusted surfaces and litter strongly influence soil protection. Two sub-factors of C, canopy cover (CC) and soil cover (SC), can be assessed from phytoecological measurements that include gravel-pebbles cover, physical mulch, annual and perennial vegetation. This paper introduces a method to calculate the C-factor from phytoecological data and, in combination with remote sensing and a geographic information system (GIS), to map it over large areas. A supervised classification, based on field phytoecological data, is applied to radiometric data from Landsat-8/OLI satellite images. Then, a C-factor value, whose SC and CC subfactors are directly derived from the phytoecological measurements, is assigned to each land cover unit. This method and RUSLE are implemented on a pilot region of 3828 km² of the Saharan Atlas, composed of rangelands and steppe formations, and intended to become an observatory. The protective effect against erosion by gravel-pebbles (50%) is more than twice that of vegetation (23%). The C-factor derived from NDVI (0.67) is higher and more evenly distributed than that combining these two contributions (0.37 on average). Finally, priorities are proposed to decision-makers by crossing the synthetic map of erosion sensitivity and a decision matrix of management priorities.     

Regional assessment of soil erosion using the distributed model SEMMED and remotely sensed data

The soil erosion model for Mediterranean regions (SEMMED) is presented and used to produce regional maps of simulated soil loss for two Mediterranean test sites: one in southern France and one in Sicily. The model demonstrates the integrated use of (1) multi-temporal Landsat Thematic Mapper (TM) images to account for vegetation properties, (2) a digital terrain model in a GIS to account for topographical properties and to assess the transport capacity of overland flow, (3) a digital soil map to assess the spatial distribution of soil properties, and (4) a limited amount of soil physical field data. The principle drawbacks of the model are that it does not account for soil particle detachment by overland flow nor for soil surface crusting. The model is most sensitive to the initial soil moisture storage capacity and the soil detachability index. The main advantages of SEMMED are that it simulates processes at a regional scale and, where possible, it uses available data sources such as remote sensing imagery, digital elevation models (DEM) and (digital) soil databases, which usually are not available for smaller catchment areas. Using SEMMED it is possible to produce regional maps of erosion assessments, which are of more practical use in land use planning and land management than simple extrapolations from small plot experiments.     

Depolymerization and mineralization rates at 12 Mediterranean sites with varying soil N availability. A test for the Schimel and Bennett model

It has been suggested that the relative abundance of soil nitrogen forms should change along an N availability gradient. This model was originally described at a biome scale, and few studies have tested it at other scales. Moreover, none of them has examined whether changes in the relative rates of ammonification, nitrification and depolymerization rates also occurs. Our goal was to test whether these N transformation rates change along an N availability gradient which is likely to exist between forest, shrubs and grasses. We used three N availability indexes (total K₂SO₄-extractable N, ion exchange membrane N and the sum of N mineralization and depolymerization rates). Depolymerization dominated over mineralization in the two poorest plant communities, while ammonification and nitrification rates dominated in intermediate and nutrient rich plant communities respectively. These results confirm that the Schimel and Bennett model can be applied at a regional scale, and that N availability may be modulating not only the dominant N form, but also the relative abundance of a particular N transformation rate.     

Derivation of site-related measures to minimise soil erosion on the watershed scale in the Saxonian loess belt using the model EROSION 3D

The Saxonian loess belt is one of the areas in Germany most endangered by water erosion. As consequence of extreme rainstorms, farmland and adjacent areas, e.g. villages, roads, biotopes and watercourses, are repeatedly damaged. Estimating soil loss is a crucial factor for sustainable land use planning in this region. Since soil erosion measurements are usually conducted at the scale of plots, thereby being both costly as well as time-consuming, erosion models are substantial tools for soil protection policies. This paper summarises and integrates the results of a research project aimed at assessing the present situation as well as that of future landscape planning alternatives, using the physically based EROSION 3D simulation model on a catchment scale. EROSION 3D can estimate the yields of sediment for small watersheds and enables environmental researchers and planners to locate the main areas of soil loss and deposition. Five different scenarios based on past and present land use information as well as future landscape 2 planning alternatives were simulated.The modelling results showed that scenarios based on only one option for minimising soil loss were not sufficiently effective in reducing sediment production. However, the combination of active soil protection measures such as conservation tillage with passive measures like grassed waterways or buffer strips resulted in an adequate soil protection. In contrast to passive protection measures, best management practices like non-tillage systems are commonly used in the Saxonian loess belt already. Thus, the implementation of passive measures is an important future task in land use planning. Simulation models like EROSION 3D can provide the information needed for the adequate localisation and the dimensioning of site-specific measures.     

阶段培养法测定稻田氮素矿化量的效果评价

传统原位培养法测定的氮素矿化量与无氮区水稻吸氮相关性不高。为此对传统培养方法进行改进,以期为准确测定土壤供氮提供方法。传统培养方法是在插秧前取土,按水土比约1:1装入自封袋中于田间原位连续培养,每隔约30 d取样测定土壤无机氮含量。改进培养方法则采取阶段培养的方法,在插秧前取土,同上法装入自封袋,再将自封袋放入装满水的离心管中于田间培养,在下次取土样(约30 d后)的同时取出上次培养的土袋,并测定土壤无机氮含量。2013—2015年的试验结果表明,随着培养时间的延长,传统培养方法测定的矿化氮先增加后降低,与最高值相比,矿化氮下降了6.7%~28.6%;而改进的阶段原位培养法测定矿化氮未出现下降情况,因此传统方法测定的矿化氮较改进方法降低了30.0%~67.7%(p0.05)。培养时间对矿化氮量影响显著,土样在田间连续培养约40 d就有抑制氮素矿化的风险,因此,每次培养时间不宜过长。改进培养方法测定的矿化氮量与田间无氮区水稻吸氮量之间具有正相关关系,决定系数R~2为0.621(p0.01)。在测定稻田土壤矿化氮时,应采用阶段培养法,每次培养时间不宜超过40 d。该方法测定矿化氮量可以作为评价土壤供氮能力的指标。     

The efficacy of three techniques to alleviate soil compaction at a restored sand and gravel quarry

Reinstated soil at restored sites often suffers from severe compaction which can significantly impede root development. Several methods, such as ripping and complete cultivation, are available to alleviate compaction that may occur as a result of soil reinstatement. This paper examines the effectiveness of the industry standard industrial ripper and a prototype modern ripper, the Mega‐Lift, in comparison with the recommended best practice method of complete cultivation. An investigation of the penetration resistance of the soil at a restored sand and gravel quarry was carried out using a cone penetrometer and a ‘lifting driving tool’ (dropping weight penetrometer) 3 years following cultivation. All the cultivation treatments reduced soil compaction to some degree compared with the untreated control. However, the penetration resistance values suggest that rooting would be restricted at relatively shallow depths in the plots cultivated using the industrial and Mega‐Lift ripper; penetration resistance exceeded 2 MPa within the first 0.33 m. Complete cultivation maintained penetration resistance values of less than 2 MPa within the depth limit of the penetrometer of 0.42 m. In addition, the results from the ‘lifting driving tool’ indicate that soils treated using complete cultivation remained significantly looser than those treated with the ripper to a depth of at least 0.80 m. The results demonstrate that complete cultivation remains the most effective method of alleviating soil compaction on restored sites, although it is recognized that its relatively high cost may restrict the uptake of the technique.     

空间插值方法在土壤养分评价中的应用——以滩小关水源地评价为例

以地理信息系统技术和传统技术相结合,定性与定量相结合,用系统论和对比分析的方法调查,分析,评价了滩小关水源地土壤养分质量状况,并针对其中存在的问题提出了建议。其中,利用GPS快速准确地测到带有坐标记录的采样点,利用ArcviewGIS对采样点进行空间插值获取土壤养分等级空间分布图并进行了科学的分析。结果表明:研究区土壤养分含量缺乏,尤其氮磷养分不足,有机质含量不高。     

CN-SIM—a model for the turnover of soil organic matter. I. Long-term carbon and radiocarbon development

A novel computer model is presented which describes the flow of C and N in the soil. It employs a structure with conceptual compartments. Organic matter is represented by seven different compartments, two for added matter, two for soil microbial biomass, one for microbial residues, one for native (‘humified’) organic matter, and one for inert organic matter. The latter pool represents both truly inert matter, and matter with negligible turnover in a time-span of decades to a century. This paper describes the parameterisation and performance of this model on selected long-term field carbon and radiocarbon data from United Kingdom, Sweden and Denmark. Previously unpublished radiocarbon data series from Denmark are included. Statistical methods were employed to estimate parameters, and obtain proximate confidence intervals for these parameters. Simulations in good agreement with measured values could be achieved, using the same set of parameters on all sites. It was demonstrated that the inert pool might constitute any amount between approx. 10 and 50% of total soil C, so that modelling cannot be used as a tool to obtain narrow estimates for this pool.