Soil Technology最新文献

The Arya and Paris model for predicting soil water retention curves from particle-size distribution data is a commonly accepted method for rigid soils with medium grain size but limitations to its application for fine textured soils occur, due to the dominant role of internal structure in such soils. Moving from the consideration that simplified models for determining soil hydraulic characteristics may be usefully adopted to reduce laboratory investigation costs, in this study an attempt is made to extend the Arya-Paris formulation to clay-loamy soils by means of an experimental calibration function which takes into account the effective soil water retention behaviour. The methodology is based on an inversion procedure of the Arya-Paris model from observed values of water retention and potential during evaporation processes on undisturbed soil columns. It has been found that the resulting calibration function is typical for each soil and it substantially improves the prediction of the soil water retention curve from textural information.

Accurate measurements of soil heat flux are important for energy balance studies on bare soils. Measurements are usually made with passive transducers that transform the vertical soil heat flux into an e.m.f.. Measurement errors or bias result from differences between the calibration coefficients provided by the manufacturer and those determined in the field. These differences result from bad thermal contact between the soil and the fluxmeter and/or changes in soil thermal conductivity. New printed circuit heat fluxmeters are very thin (0.2 mm) and they provide a better thermal contact with the soil because they have an external copper layer instead of an insulating resin. We carried out a theoretical analysis to identify properties of the transducers (geometrical, thermal or electrical) most important for reducing the calibration variability. The transducer thickness was found to reduce the calibration variability due to large soil thermal conductivity variations. Transducer thermal conductivity is also important when the soil thermal conductivity is accurately known. The printed circuit transducers and classical soil heat flux transducers (thermopiles) where then compared in three different soils, a sandy loam, a loamy and a chalky soil under changing climatic conditions in spring. The outputs of both transducers were compared to reference soil heat flux measurements obtained by the heat storage method. The thermopile transducers were more sensitive (4.1 μV W⁻¹ m²) than the printed circuit transducers (1.6 μV W⁻¹ m²). Both transducers gave similar responses when the soil thermal conductivity varied over a narrow range. The total variation of the calibration coefficients of the printed circuit transducer was smaller for all three soils and for days where the soil thermal conductivity varied widely. We conclude that the printed circuit transducers should be used when field calibration is not possible, or when the calibration is not stable following large soil thermal conductivity variations. The experiment also showed that the theory does not completely describe the interaction between calibration coefficients and soil properties. We have therefore developed a new interpretation of the experimental data that takes into account the thermal contact between the soil and the transducer.

The effects of five types of geomembranes, placed at the soil surface, on runoff and erosion on steep earth slopes were studied under laboratory and field conditions. In the laboratory, the soil samples were packed in boxes held at a 50% slope and subjected to three consecutive simulated rainstorms of 120 mm each. The membranes dissipated the drops' impact and reduced runoff significantly compared with the control. There was no significant difference among the membranes regarding their effect on the runoff. In the field, the membranes lined earth dikes of 33–60% slope and 12–20 m length, during 2 years. There was no runoff and erosion from the lined plots compared with 80–125 tonne ha⁻¹ of erosion in the control plots. No considerable wear and tear of the membranes was observed.

Soils that pose high risk of erosion require amendment with either natural or synthetic soil conditioners to reduce soil loss hazards. The objective of this study was to evaluate the potential of using coal-derived humic substances (as soil conditioners) to reduce runoff erosion on erosion-susceptible soils. Surface (0–20 cm) samples of severely degraded soils from Principina in Tuscany (Orthic Xerofluvent) and Bovolone in Venice (Udic Ustochrept) in Italy were used to assess the effects of five rates (0, 0.05, 0.10, 0.50 and 1.00 g/kg) of humic acids (HA) on soil loss and other hydrological parameters. A rainfall simulator was used to apply approximately 40 mm/h intensity rain for 1 h on soil beds of dimensions 2 m × 0.5 m × 0.01 m, packed at a bulk density of 1.20 Mg/m³ and inclined at a slope of 15%. The amount of soil eroded (E) and the time to initiate runoff (Rt) and drainage (Dt) were related to changes in the water-holding capacity and aggregate stability of the soils following the HA treatments. In the control treatments, the values of E, Rt and Dt were higher in the Principina than Bovolone soil. Increasing HA rates generally delayed Rt, accelerated Dt and reduced E substantially on both soils. On the Principina soil a reduction of about 36% in soil loss was obtained by adding only 0.05 g/kg of HA (equivalent to 100 kg/ha). On the sandier Bovolone soil, the same magnitude of reduction was achieved with 0.10 g/kg (200 kg/ha) of HA. Improvements in Rt and Dt from the HA amendments explained between 58 and 81% of the variation in E from both soils. Furthermore, improvements in the water retention capacity more than in the aggregate stability of these soils accounted for the reduced runoff erosion. These results show that amending erosion-susceptible soils with low rates of coal-derived humic substances is a potentially effective soil management practice for reducing erosion rates.

Reclamation is needed on three million ha of slowly permeable saline-sodic soils in the Indus Plain of Pakistan. Previous studies measured an increased field-saturated hydraulic conductivity (K_fs) in the soil under study with cropping and gypsum application. This field experiment was conducted on a low permeability, saline-sodic soil (a fine-loamy, mixed thermic Typic Natrustalf) to compare the leaching of sodium and soluble salts and changes in chemical properties after various treatments. Treatments were: (i) perennial alfalfa (Madicago sativa L.), (ii) a rotation of sesbania [Sesbania bispinosa (Jacq.)W.F. Wright]-wheat (Triticum aestivum L.)-sesbania, (iii) incorporated wheat straw at 7.5 Mg ha⁻¹ and (iv) a fallow control. These four treatments were each combined with and without 25 Mg ha⁻¹ of gypsum and open-ditch drainage. Electrical conductivity (EC), pH, Na⁺, Ca²⁺, Mg²⁺ and Cl⁻ of the soil in the saturated paste extract under each treatment were measured in each 20 cm increment to 120 cm after 6 month and 1 yr. Gypsum application increased the soluble Na⁺ in the top 20 cm soil. Poor internal drainage of the soil caused the exchanged Na⁺ to remain in the soil solution. However, one year after the treatments, the crop rotation with gypsum significantly decreased SAR, EC, pH and Cl⁻ in the top 20 cm of soil. Alfalfa decreased these same parameters when compared to fallow in the top 80 cm of soil in gypsum-treated plots. The open-ditch drainage was not helpful in reclamation of this soil. In general, for surface soil improvement, a combination of added gypsum plus crop rotation was the best. For improvement of the deeper soil profile, gypsum plus alfalfa was the most effective of the treatments used.

An interactive sampling procedure is proposed to optimize environmental risk assessment. Subsequent sampling stages were used as quantitative pre-information. With this pre-information probability maps were made using indicator kriging to direct subsequent sampling. In this way, optimal use of the remaining sampling stages was guaranteed. Interactive sampling was applied to a lead-pollution in the Dutch city of Schoonhoven. Environmental risks were quantified by the probability of exceeding the intervention level. The data and sampling schemes were stored in a GIS. Using six conditional simulations of stochastic fields, interactive sampling schemes were compared to conventional sampling schemes by calculating type I and type II errors. The interactive schemes had much lower type I errors than the conventional schemes, and comparable type II errors. Moreover, the interactive sampling schemes left a smaller fraction of the not-sanitated area polluted than the conventional ones did. They predicted almost 70% of the area correctly, as compared to 55% by conventional schemes.

Saturated hydraulic conductivity (K_S) is an important soil hydraulic parameter for it establishes a limit on the rate of water and solute transmission through soil. However, its determination in the laboratory has been shown to be much influenced by column size. We evaluated the spatial variability of laboratory K_S measurements using three different column sizes: firstly, sixty 5.1 cm long columns of 5 cm diameter were used (type-I), next, thirty 20 cm long and 20 cm diameter columns were considered (type-II), and finally, thirty columns 100 cm long and of 30 cm diameter (type-III) were studied. All columns were collected along a transect in a sandy loam soil with macropores. Estimates of macroporosity at three depths (2.5, 12.5, and 16.5 cm) for twenty-four of the type-II columns were calculated from stained dye patterns obtained during ponded infiltration. The geometric mean of K_S decreased with increasing column size, i.e., from 2.24, 1.68 to 0.56 cm/h for type-I, -II, and -III columns, respectively. The coefficient of variation (CV) based on a log-normal distribution showed a similar trend: 619% for type-I, 217% for type-II, and 105% for type-III. Type-II and type-III columns were large enough to encompass a representative elementary volume (REV). The percentage of dye-staining (macropore cross-sectional area) decreased from 3% at 2.5 cm to 1.7% and 1.6% at 12.5 and 16.5 cm, respectively. Percentage of depth-averaged macropore area was moderately variable with CV = 51%. A geostatistical analysis revealed that a weak spatial structure existed for type-I K_S measurements whereas type-II and type-III columns displayed better spatial correlation with a range of approximately 14 m and 11 m, respectively. Spatial correlation was also observed for depth-averaged macropore area with a range of 12 m. The cross-semivariogram calculated between type-II K_S values and depth-averaged macropore area obtained from the same columns indicated positive spatial cross-correlation for all lags.

Loamy soils of the northern European loess belt commonly are exposed to erosion caused by concentrated runoff. Such runoff generates mud flows that, when strong, may create major problems because of the damage they cause to infrastructure. Using multi-temporal SPOT data and GIS technologies, a method is proposed and tested for mapping surfaces affected by runoff, as well as for evaluating the effectiveness of such remotely sensed index to infer erosion. This work is part of a major research effort, jointly undertaken by BRGM and INRA, which develops a predictive approach for monitoring erosion at a regional scale. Results have shown that the method for estimating surfaces affected by runoff, is quite reliable for areas underlain by loamy soil. However, the correlation between such surfaces and effective erosion, i.e. soil loss quantitative measurements, remains low, even though it confirms the possibility of using statellite data rather than other sources of information. It became clear that the conditions of low erodibility during the period of our study were a handicap for this type of validation; another problem is caused by the choice of the optimum observation period, which can vary as a result of winter rainfall events.