Soil Technology最新文献

Although it is widely recognised that gully and sheet erosion threaten sustained agricultural production in much of Swaziland, very little information is available about the current status of erosion and whether the situation is worsening. Since the country is very active geomorphologically, it is not clear whether an inherently erodible environment or human impact is the major causal factor explaining the severity and spatial distribution of erosion. Soil erosion is associated particularly with deeply weathered saprolite but few studies have been made on applied issues related to the physical and chemical properties of this material.

A knowledge of the physical properties influencing the quasi-steady infiltration rates (Ic) of soils is useful in the hydrological modelling of the infiltration process. In this study, the Ic of 18 highly permeable soils in the derived savannah zone of south-eastern Nigeria were characterized and related to land use, bulk density and pore size distribution. Unmulched soils with or without conventional tillage and soils in continuous pasture/grass cover had relatively slow to moderate Ic, whereas mulched soils, soils amended with plant residues or under secondary forests/legume cover had rapid to very rapid Ic. The saturated porosity and void ratio gave low correlation with Ic with correlation coefficients (r) of 0.388 and 0.217, respectively. Mesoporosity (i.e. pores with equivalent radius of 1.5–15 μm) and microporosity (i.e. pores with equivalent radius of 0.1–1.5 μm) had negative influence on Ic, with respective ’r’ values of −0.566 and −0.404. Preferential porosity (Pe) (i.e. pores with equivalent radius > 15 μm) and dry bulk density (ϱ_b) were the most important soil physical properties influencing Ic. Their correlation coefficients (r) with Ic were respectively, 0.852 and −0.806 (p = 0.001). This shows that soil management systems which increase the bulk density due to compaction with concomitant reduction in the proportion of the preferential pores will reduce Ic substantially on these soils. The Philip (1957) model, $\text{Ic}\text{=}\text{A + 1}\text{2St}{}^{\mathrm{<mtext>-1</mtext><mtext>2</mtext>}}$ (where A and S are the fitting parameters), could not predict the measured quasi-steady infiltration rates very satisfactorily.

We carried out a time domain reflectometry (TDR) calibration for 25 forest floor samples of five different forest stands. Linear regression was used to estimate the volumetric water content from the refraction index. Due to the presence of bound water, it was impossible to predict the calibration line parameters from theoretical values with a refractive mixing model. However, when the apparent dielectric constant of the water was considered, it was possible to predict the offset parameter because the low forest floor bulk density caused the calibration line slope and offset to be almost reversely proportional. Calibration parameters for different forest floor materials are presented. Allowing a somewhat higher margin of error we could also establish general calibration curves which were in close agreement with a published calibration curve (Malicki et al., 1994). An error analysis showed that decomposition of organic matter, residual water and temperature effects have negligible effects on the calibration parameters. Shrinkage of the organic material significantly influenced both the volumetric water content and the TDR reflection times. If not corrected, both effects yielded systematic errors of approximately 0.02 cm³ cm⁻³ for a strongly shrinking H horizon.

Dye-tracer studies in the field using Brilliant Blue FCF as tracer were performed to investigate the effect of irrigation intensity and soil heterogeneity on preferential flow. In two fields, both level and newly tilled in terms of seed bed preparation, to plots of 1.6 × 1.6 m were applied 50 mm of dye solution at rates of 10 and 50 mm h⁻¹. In the second year level, plots of grass of similar size were applied with 25 mm dye solution at a rate of 3.1, 6.2, 12.5, and 25 mm h⁻¹. For all plots the stained patterns were examined one or two days after application of dye solution by the excavation of 11 vertical cross sections of 100 × 100 cm and 10 cm apart from each other. Flow patterns were digitized and depth functions for the degree of dye coverage and the number of activated flow channels were calculated. Furthermore, the structural features of each cross section were examined visually. The results show that deep penetration of water into the soil profile took place as preferential flow through macropores, mainly earthworm channels, with much of the water thus bypassing the soil matrix. In the top 0–25 cm layer, the degree of dye coverage tended to be larger for the lower irrigation intensities indicating that water flow in the top soil took place through a relatively great proportion of the pores in the soil matrix. In the 35–100 cm subsoil layer the number of stained macropores tended to be larger for the higher irrigation intensities. Thus, at higher irrigation intensity a positive pressure potential apparently developed more extensively in the topsoil initiating preferential flow through a greater number of macropores in the subsoil. In the newly tilled soil, water flow took place through a relatively great part of the topsoil matrix. Deeply penetrating stained earthworm channels originated, predominantly, in the well defined transition zone between topsoil and subsoil. In the soil left untilled and grass covered for about one year the continuity of macropores was more pronounced, and stained channels could frequently be traced from the subsoil all the way to the soil surface, in particular at low irrigation intensity.

Cation exchange capacity (CEC) recoveries from a leaching procedure utilizing intact soil columns were compared to extracts from disturbed soil samples to determine the influence of macropores and preferential flow on ion exchange. Eleven soils representing eight soil series with a variety of morphological and physicochemical characteristics were used in the study. Leachate was introduced into duplicate undisturbed soil columns following the 1 M NH₄OAc, pH 7.0 procedure at a weight to volume ratio equivalent to that used for the disturbed soil samples. Effluents from disturbed and undisturbed samples were collected and analyzed for CEC and total extractable bases. Average CEC values for the intact columns were 49.1% lower than those measured by routine analysis. Regressional analysis indicated a significant difference between the two methods (p < 0.1). Particle size distribution was identified through multiple linear regression analysis as the most influential physicochemical property contributing to the difference between methods. Soil columns with sandier textures displayed high recovery rates attributable to uniform porosity and low CEC. As the silt fraction increased, the difference between methods increased due to formation of macropores and associated preferential flow through the soil matrix. However, increased clay levels allowed more thorough hydration of the matrix which apparently restricted flow, increased residence time and promoted exposure of more exchange sites, thus resulting in intermediate recovery rates. These results suggest that routine CEC measurements based on batch extractions of disturbed soil samples may overestimate ion exchange interactions, and therefore, overestimate true contaminant sorption capacities of soils.

The effect of conventional tillage, minimum tillage and no tillage on structure development and degradation in the Ap horizon of a Haploxeralf in central Spain was studied. Conservation tillage systems were found to favour restoration of soil structure degradation caused by conventional tillage, particularly in the 0–10 cm upper soil layer.

A rainfall simulator designed to perform experiments in rugged terrain is presented. The portability of the apparatus allows the researcher to work in remote areas and on steep slopes. Rainfall intensity and distribution within the plot (0.24 m²) and drop-size were measured under different water pressure. For the best simulated rainfall distribution (1.55 kg cm² of water pressure and 55 mm h⁻¹ of rain intensity) the drop velocity and the kinetic energy were measured.

The effects of termite activity and four mulch types on the water balance of crusted soil were studied on two soils (a lixisol and a cambisol) in northern Burkina Faso. A split plot design with three replications was used, with termite and non-termite as main factor and mulch treatments as second factor with three variables consisting of Pennisetum pedicellatum mulch (straw), woody material of Pterocarpus lucens mulch (woody material) and composite mulch (straw + woody material) applied at rates of 3, 6 and 4 t ha⁻¹, respectively. Dieldrin kept termites away from the non-termite plots during the experiment. Water balance terms were assessed during three rainy seasons (1993, 1994 and 1995). Termite activity resulted in a statistically significant increase of water infiltration, soil water storage and drainage. In 1993 the mean values for soil storage were higher (but not statistically significant) on mulched plots than on bare plots. During 1994 and 1995 the three mulch treatments formed a distinctive group that differed from bare treatments. Mulch treatment did not affect evapotranspiration and draimage in the two dry/normal years (1993 and 1995). Termite activity in mulch resulted in a statistically significant improvement in the humidification and water conservation of the crusted soil. Mulch without termites did not have a statistically significant effect on the water status of structurally crusted soil. This suggests that termite activity is a key element in the effectiveness of the mulching technique on crusted soil in the Sahel.

Non-irrigated and irrigated Ordinary Chernozems of Stavropol Upland, Central Precaucasus (Russia), were examined. A number of morphological and instrumental methods was used for detailed investigation of the carbonates in the soils. This approach allowed us to reveal the essential change of the carbonate status of the irrigated Chernozems as a result of changing the soil moisture regime and the predominance of leaching processes under 30 years irrigation by fresh water. The changes included distinct enhancement of spatial variability and instability of carbonate-illuvial horizon deposition, the highest data scatter on carbonate content within this horizon, the signs of increased mobility of carbonate material and the change of the mechanism of the carbonate accumulations. Carbonates moving with soil solutions and mobile migrational forms of carbonate accumulations as well as segregating forms and lithogenic concretions were transformed under the irrigation. Irrigation for 30 years resulted in unfavorable reclamative changes of the Ordinary Chernozems carbonate status: decalcification of the upper part of the solum, disappearance of the mobile carbonate accumulations from the upper horizons, the initial point of the compact carbonate-hardened horizon in the low part of profile and the increase of the calcium and magnesium content in the soil solution. The problem studied is complicated because of the inherent variability of carbonate parameters and the multitude of factors having an influence on carbonate status. Much more work is needed because of the importance of the topic for sustainability of agricultural production systems, for prediction and overcoming of unfavorable consequences of irrigation, for the up-to-date problem of the greenhouse effect and the response of carbonate reserves to climate changes.

In August of 1992 a wildfire affected 9498 ha of pine forest and shrub in Sierra Calderona (Valencia, Spain). The results obtained in six stations of erosion control located in the burned are since the end of the fire are reported. Topographical, edaphological and vegetation characteristics of each station are described. Seven episodes of erosive rain with production of runoff and sediments, between August 1992 and April 1993 were studied. The data suggest that the highest soil losses were produced in the period immediately after the fire. Runoff and sediments produced in each station have been quantified. It has been observed that under similar conditions, the taxonomical and textural characteristics are determinant factors in the production of runoff and so, of soil loss.