Soil Technology最新文献

The Penedès and Anoia regions in NE Spain are important areas for the cultivation of grapes used in the production of high quality wines. The Mediterranean climatic conditions define a xeric soil moisture regime. Rainfall are concentrated in spring and autumn while the summer is warm and dry. The climate is characterized by high rainfall intensities, being one of the main factors responsible for soil erosion in the area. Since grape quality depends on the availability of water for the vineyards and since soil erosion is an important parameter dictating the sustainability of vineyards, soil and water conservation can not be forgotten in the area. The most widely used measure for soil conservation in the area is terracing (hillside ditches, local name rases). Local technical solutions have been studied and in this paper different types of terraces are described and analysed in terms of its effectiveness for runoff control. Mean potential soil losses are evaluated according to the USLE and compared with field measurements in experimental plots. The distances between terraces have been calculated using the criteria proposed by several authors. Owing to the wide diversity of results, an acceptable value for ‘soil loss tolerance’ (T-value) has been used in order to establish some criteria to make recommendations, taking the values of soil loss measures in the field as a reference. According to these preliminary results based on measurements taken over a period of two years, some advisable distance between terraces (rases) in vineyards can be proposed in view to improve local criteria. With a slope of 6%, a distance of is 28 m would be advisable, and in fields with a slope of 8% the distance should be 20 m. Bennett's criteria to calculate distances between terraces are the more advisable being closely related with experimental results in the area.

Soil and groundwater resources in many parts of the world are threatened by spilled petroleum products. These products generally consist of complex mixtures of volatile hydrocarbons with different vapor pressures. The volatilization of light hydrocarbon fractions leads to changes in viscosity and density of the residual nonaqueous liquid. This may cause changes in the transport characteristics of the porous matrix and of the residual liquid. Differing volatilization and solubility characteristics result in differential distribution of released hydrocarbon components in air, soil, and water environmental compartments. Soil frequently serves as the site of petroleum spills and hence the capacity of the soil to filter, retain, or release hydrocarbons is fundamental in determining the type and extent of environmental contamination. Retention, volatilization, and transport of hydrocarbons as affected by soil physical and chemical properties is reviewed.

Pulverised fuel ash (PFA) applied at an application rate of 8.3% by weight, incorporated by ploughing to a badly compacted minespoil was shown to reduce bulk density significantly over a one year period. A second ameliorative treatment with 4.8% PFA, and a third treatment with ploughing alone both reduced bulk density after four months, but by twelve months displayed no statistically significant differences in bulk density compared to an untreated control.

Cylindrical soil samples of varying moisture contents (13.1 to 21.7% dry basis) were subjected to sinusoidal excitations of seven frequencies (300 to 2000 Hz). Wave propagation theory was extended to three-dimensional in situ testing. In situ experimentation involved recording accelerations from an input source and measuring the output response on a plane perpendicular to the input for both horizontal and vertical directions. Moisture content did not have a significant effect on soil deformation within the range of moisture contents examined. Soil deformation was dependent upon excitation frequency. The relative deformation of soil in situ was measured for three different input excitation and output response orientations. Poisson's ratios for three dimensions varied by input-output orientation due to anisotropy of the soil.

The measurement of fall-cone penetration on air-dried and slowly rewetted subsamples (< 1 mm) at different water contents characterizes hardsetting and non-hardsetting soils by differences in their maximum resistance to penetration (RP_max), the water content (WC_max) at RP_max, and the amount of water adsorbed between the two values of 0.5 × RP_max, called ‘insensitivity’ I. The insensitivity I is strongly correlated with the contents of organic matter and iron oxides which are considered as soil components improving aggregation. The insensitivity may be used to identify hardsetting soils. These have I-values < 7, whereas non-hardsetting soils have I-values > 10.

The authors study clay mineral and main nutrient element losses in runoff water generated by rainfall events in 1990–1991 from five field plots on a Petric Calcisol or Xerollic Paleorthid. Illite is the main layer silicate in the clay Ap horizon, with a smaller proportion of kaolinite and a minor amount of chlorite and smectite. Soil samples taken in different seasons show that plots under shrub vegetation are very much alike and, with the exception of available Fe, Cu, Mn and Zn, they are markedly different from arable soil plots, being much richer in organic C, total N and available K, but poorer in available P. Annual and seasonal losses of the main nutrient elements are small, with the highest amounts in the plots cultivated for barley and with cut shrub; losses are extremely low for the plot with shrub cover.

Surface microrelief substantially affects surface sealing, runoff, and soil erosion processes on bare soils. Yet, the stability of microrelief for different antecedent soil water contents and rainstorms is not well understood. This study investigates the effect of surface microrelief and antecedent water content on the decay of microrelief under different rainstorm regimes. Two different rainstorm regimes were studied in laboratory experiments: continuous rainfall for a total amount of 60 mm applied at 30 mm/h intensity, and intermittent rainfall consisting of five successive rainstorms of 12 mm each, again with an intensity of 30 mm/h and separated by one week drying cycles. Rough, medium, and fine microrelief surface conditions representing different degrees of seedbed preparation were studied for three soils at antecedent soil water contents of 2–4% and 14–20%. Before and after rainfall, digital elevation models determining the surface microrelief were developed using a laser scanner with 2 mm grid spacing. The specific surface area calculated from microrelief data was used as an index to characterize microrelief. Microrelief stability increased with increasing initial roughness and was much higher for the antecedent wet soils than for the dry soils. Microrelief stability for the continuous rainstorm regime was higher than for intermittent rainfall. Differences in microrelief stability were mostly attributed to different aggregate stabilities. Additionally, the higher stability for the rougher microrelief surfaces was attributed to the lower drop impact density and splash density on the surfaces with larger specific surface area. Aggregate slaking due to air escape and rapid wetting was found to be responsible for the low microrelief stability at initially dry conditions.

The erosivity of soils under a given rainfall energy appears to vary greatly among soil orders, probably reflecting differences in clay composition and organic matter content. This study was conducted to quantify microrelief, infiltration, and sediment yield changes during three consecutive simulated rain events on a Udic Haploboroll and a Typic Hapludalf from Minnesota, and a Mollic Kandiudalf, and Typic Palehumult from Uganda. Air dry aggregates (< 5 mm) were packed in 19 1 containers tilted to a 5% slope and were subjected to three consecutive high energy rain storms (63 mm h⁻¹) for a duration of 1 h. Runoff and sediment were continuously monitored during a storm. Infiltration was measured by continued weighing of the soil and containers. An automated non-contact laser relief meter was used to measure changes in soil roughness initially and after each storm. Soil surface roughness decreased during the rain events indicating that aggregate breakdown was the dominant process in seal formation. For example, random roughness decreased form 5.9 to 4.0 mm on Barnes loam and from 9.7 to 6.9 mm on Renova silt loam with cumulative rainfall of 0 and 126 mm. These infiltration rates indicated that the Barnes Loam (Haploboroll) and Kabanyolo clay (Kandiudalf) were unstable soils while Kachwekano clay (Palehumult) and Renova silt loam (Hapludalf) were quite stable. Final infiltration rates after 3 consecutive rainfalls on Kachwekano clay (15 mm h⁻¹) and Renova silt loam (13 mm h⁻¹) [the stable aggregate soils] were significantly higher than those of Barnes loam (4 mm h⁻¹) and Kabanyolo clay (3 mm h⁻¹). For the two stable soils a high infiltration rate on a rough surface was maintained until aggregate breakdown occurred and runoff began. Sediment yield from Barnes loam (29 kg m⁻²) and Kabanyolo clay (28 kg m⁻²) was significantly greater than soil loss from Kachwekano clay (0 kg m⁻²) and Renova silt loam (6 kg m⁻²). The microrelief method to quantify aggregate stability is an improvement over wet sieving and other related measurements because of its rapidity and because the statistical quantification can be linked to physical processes.

Ten 25 m² runoff plots at the Hilton experimental site, east Shropshire, UK, have been used to compare the physicochemical properties of loamy sand plot soils and sediment eroded from the plots over one year. Sediment contained more sand (2 mm–60 μm) and less clay (< 2 μm), silt (2–60 μm) and coarse fraction (> 2 mm) than soil. Erosion rates increased with slope and proportionally more silt and particularly clay were eroded on steeper slopes. Selective clay depletion has serious implications for soil structure and fertility. Correlations existed between the organic matter contents and particle size distributions of soil and sediment, but the sediment had less organic matter and lower pH values than soil. Sediment also contained lower concentrations of calcium, iron, potassium, magnesium, manganese and phosphorus than soil. Relationships between erosion and soil textural change appear to be partly technique-dependent, which suggests more uniformity in approach would be beneficial in studies on the effects of erosion on soil fertility.