Reduction In Saturated Hydraulic Conductivity Research Articles

Assessment of the yield and yield attributing characters of oat (Avena sativa L.) grown under different tillage methods and NPK fertilizer rates in semi-arid conditions

Field experiments were conducted to determine the effect of tillage practices and inorganic sources of different combinations of nitrogen, phosphorus, and potassium fertilizers on some physical properties of soil and the yield of oats. The main plots were tillage techniques of no-till (T1), tillage with a cultivator (T2), twice-disc harrow (T3), and moldboard plowing (T4). Split-plots were fertilizer treatments of F1 control without fertilizer, 70:45:50 kg ha−1 NPK (F2), 140:90:100 kg ha−1 NPK (F3), 210:135:150 kg ha−1 NPK (F4), and 280:180:200 kg ha−1 NPK (F5). Soil density, acidity, electrical conductivity, and soil organic carbon increased under T1, while saturated hydraulic conductivity decreased compared with other tillage practices. Soil bulk density and pH increased with increasing sampling depth, while electrical conductivity and soil organic carbon declined with depth. Results from this study indicated a reduction in saturated hydraulic conductivity with time. The highest grain yield was found in the T4 and T3. In contrast, the highest grain yield was observed under F4 and F5 fertilization treatments at location 1 and F5 and F4 treatments at location 2. There were significant differences in growth characteristics and yield components due to the influence of tillage practices and fertilization levels in both experiment locations.

Hydraulic and volume change behaviors of compacted highly expansive soil under cyclic wetting and drying

The wide engineered application of compacted expansive soils necessitates understanding their behavior under field conditions. The results of this study demonstrate how seasonal climatic variation and stress and boundary conditions individually or collectively influence the hydraulic and volume change behavior of compacted highly expansive soils. The cyclic wetting and drying (CWD) process was applied for two boundary conditions, i.e. constant stress (CS) and constant volume (CV), and for a wide range of axial stress states. The adopted CWD process affected the hydraulic and volume change behaviors of expansive soils, with the first cycle of wetting and drying being the most effective. The CWD process under CS conditions resulted in shrinkage accumulation and reduction in saturated hydraulic conductivity ( k sat ). On the other hand, CWD under CV conditions caused a reduction of swell pressure while has almost no impact on k sat . An elastic response to CWD was achieved after the third cycle for saturated hydraulic conductivity ( k sat ), the third to fourth cycle for the volume change potential under the CV conditions, and the fourth to fifth cycle for the volume change potential under the CS conditions. Finally, both swell pressure ( σ s ) and saturated hydraulic conductivity ( k sat ) are not fundamental parameters of the expansive soil but rather depend on stress, boundary and wetting conditions.

Effect of biochar particle size on water retention and availability in a sandy loam soil

The ability of biochar to enhance the physical and hydrological properties of light textured soils is highly dependent on the characteristics of biochar including its particle size. To investigate the effect of biochar particle size on water characteristics and soil structure of a sandy loam soil, date palm biochar prepared at a pyrolysis temperature of 450–500 °C was fractioned by dry sieving into four sizes: 2–1, 1–0.5, 0.5–0.1, and <0.1 mm, and mixed in soil pots with a sandy loam soil at an application rate of 4%. The soil pots were incubated in a greenhouse for 120 days, and water content was kept at field capacity throughout the experiment. Water retention, hydraulic conductivity, and soil structure parameters were measured. Results showed that the largest increase in both water content at field capacity and available water content was observed with the smallest biochar particle size due to increased microporosity as a result to the larger internal surfaces and the porous structure of the biochar particles. Condense particle packing and increased tortuosity due to increased microporosity resulted in a reduction in saturated hydraulic conductivity and bulk density of the soil and biochar mixtures. Soil structure was improved in the soil and biochar mixtures at all biochar particle sizes, nevertheless, no significant increase in soil structures was observed among biochar particle sizes < 1 mm. The application of biochar with particle sizes < 1 mm can enhance the physical and hydrological properties of light textured soils and increase water conservation in the soil, which will help to reduce the amount of water required for irrigation. However, assessment under field conditions is required to assess the long-term effect of biochar on water characteristics and soil structure.

Soil sealing by algae: An alternative to plastic pond liners for outdoor algal cultivation

Commercial production of algal biofuels is currently limited by high capital costs, particularly costs of synthetic pond liners that minimize seepage of cultivation fluids, salts, and nutrients into the subsurface beneath outdoor algae cultivation facilities. Even some profitable nutraceutical companies bear the high costs of pond liners. However, studies of animal waste holding ponds and aquaculture facilities have shown that underlying soils can effectively “self-seal”, potentially eliminating the need for plastic liners. Here, we explored the potential for self-sealing with algae to provide an alternative to synthetic pond liners in unlined algae cultivation ponds. Laboratory-scale soil column experiments were used to investigate soil clogging by algae, a topic rarely discussed in the literature. Columns composed of fine sand, loamy sand, and loam soil displayed reductions in saturated hydraulic conductivity of the entire soil column of up to two orders of magnitude in response to infiltration by the alga Scenedesmus dimorphus suspended in algal culture nutrient solution at a density of 5 × 108 cells L−1. Scanning electron microscope imaging showed a dense algal layer on the surface of each soil column, thickly coating mineral grains with algal material and filling pore spaces. The algal coating was absent in samples at >3 cm depth in the soil columns, and measurements of chlorophyll content also confirmed that algal cells were mostly confined to the soil surface. In this study, the application of an algal suspension contributed significantly to soil sealing. This new application of biological sealing technology should be studied further to determine its utility and durability as an alternative to plastic liners, perhaps in conjunction with soil compaction to achieve hydraulic conductivities beneath algal production ponds that are protective of groundwater quality.

Towards predicting the soil-specific threshold electrolyte concentration of soil as a reduction in saturated hydraulic conductivity: The role of clay net negative charge

The use of marginal quality water with saline and dispersive properties is set to become more prevalent in agricultural production given demands on freshwater resources. The threshold electrolyte concentration (CTH) is often used to define the suitability of such water, with irrigation practitioners seeking a general predictive model based on soil order. Recent work supports that the CTH absolute value is soil-specific, although there remains a requirement to identify the contribution of predictive factors in an effort to create a predictive function for the CTH. This work used 58 soils to explore the variability of the CTH within and between soil orders, subsequently comparing saturated hydraulic conductivity to leachate turbidity as a means to investigate CTH existing prior to the point of spontaneous dispersion. The role of clay net negative charge was investigated in terms of its relation to the CTH in an effort to move towards a predictive capacity for this soil-specific characteristic. Subsequently, it was demonstrated that the CTH was apparently described by net negative charge of clay particles, suggesting that surface interactions between clay particles and the bulk solution are important in governing soil stability from a soil-specific point of view The CTH occurred prior to the aggregate–dispersion threshold and was clearly soil-specific, even within a soil order. Future work is required to incorporate the ionisation potential and clay domain pressure models of soil stability to move towards a CTH predictive function based on quantified differences in soil mineralogy and charge characteristics, which is discussed.

Quantifying the aggregation-dispersion boundary condition in terms of saturated hydraulic conductivity reduction and the threshold electrolyte concentration

Marginal quality saline sodic water will be important for agricultural production in water limited environments, and has been demonstrated as suitable for irrigation on a soil-specific basis. Suitability is usually demonstrated as the threshold electrolyte concentration (CTH), defined as a 10–20% reduction in saturated hydraulic conductivity. Others have suggested that the aggregate-dispersion boundary may be used as this threshold, which is also known as the threshold turbidity concentration (CTU). Using a saturated hydraulic conductivity approach, this work sought to quantify the extent of reduction at the CTU and compare this to traditional CTH approaches to define the practicality of the thresholds. The CTU was determined as the point where dispersed clay was detected, and subsequently compared to the CTH with the difference between these compared within the measured domain. The reduction in saturated hydraulic conductivity from a Ca dominant stable condition was determined at each threshold value. It was found that saturated hydraulic conductivity at the CTU reduced by between 44 and 78% for the five Vertisol soils investigated, demonstrating that the CTU varied between soils and was substantially more than the 10–20% reduction in hydraulic conductivity at the CTH. Discussion on application of these thresholds to practical irrigation is provided, and suggests that irrigation water quality application can be optimised on a soil-specific basis. Results reinforce that management guidelines should not be based on the CTU, or at the aggregation-dispersion boundary.

Effects of subsoil compaction on hydraulic properties and preferential flow in a Swedish clay soil

Soil compaction by vehicular traffic modifies the pore structure and soil hydraulic properties. These changes potentially influence the occurrence of preferential flow, which so far has been little studied. Our aim was to study the effect of compaction on soil hydraulic and transport properties in subsoil. A randomized block design trial at two sites on a well-structured clay soil in central Sweden was established. Plots with two levels of compaction were created at both sites, in the following referred to as trafficked and control. The trafficked treatment was created by 4 passes track-by-track with a three-axle dumper with a maximum wheel load of 5.8Mg. After one year, undisturbed soil columns (20cm height×20cm diameter) from both trafficked and control plots at a depth of 30–50cm were sampled. The columns were analyzed using X-ray CT imaging, together with measures of the degree of preferential transport derived from non-reactive tracer breakthrough curves and measurements of saturated hydraulic conductivity (Ks) and air permeability at the field moisture content (Ka).Although the traffic treatment did not cause any compaction effects at one of the two sites, it did result in significant reductions in saturated hydraulic conductivity, air permeability and number of macropores at the second site. At this site, the traffic also significantly reduced the strength of preferential flow, presumably due to compaction-induced disruption of macropore continuity. In apparent contrast, some previous studies have shown increases in the strength of preferential flow as a result of compaction. We propose a conceptual model to explain these apparently contradictory results, which suggests that preferential flow should be strongest at some intermediate level of compaction.

Influence of Super Absorbent Polymers on Infiltration Characteristics of Alfisols in Semi-Arid Region

Infiltration characteristics of the soil are important to understand the water dynamics in the root zone of a soil-plant system. A laboratory experiment was conducted to study the infiltration characteristics of sandy loam soil under different application rates of super absorbent polymers (SAPs). Four polymer products (P1, P2, P3 and P4) of the commercial value with different concentrations (0.25%, 0.75%, 1.25% and 1.75%) were used and compared with control (soil without polymer). Among four polymer products tested, SAP P3 showed maximum reduction (90%) in the steady state infiltration rate as compared to P1, P2 and P4 tested over different concentrations. The steady infiltration rate was decreased by 3.6 to 1.75, 4.1 to 0.4, 1.4 to 0.52 and 1.6 to 0.76 cm/hr under P1, P2, P3 and P4, respectively in the polymer concentrations of 0.25, 0.75, 1.25 and 1.75%. The infiltration data were fitted to Philip model and model parameters had the best description of the relationship between infiltration rate and application rate of super absorbent polymers in the sandy loam soil with significant reduction in saturated hydraulic conductivity (A) varying from 12.4 to 84.75%. Out of four polymers tested, P3 had more reduction capacity in the infiltration rates of sandy loam soils as compared to other SAPs.

Influences of environmental factors on bacterial extracellular polymeric substances production in porous media

Summary Bioclogging of natural porous media occurs frequently under a wide range of conditions. It may influence the performance of permeable reactive barrier and constructed wetland. It is also one of the factors that determine the effect of artificial groundwater recharge and in situ bioremediation process. In this study, a series of percolation column experiments were conducted to simulate bioclogging process in porous media. The predominant bacteria in porous media which induced clogging were identified to be Methylobacterium, Janthinobacterium, Yersinia, Staphylococcus and Acidovorax, most of which had been shown to effectively produce viscous extracellular polymeric substances (EPS). The column in which EPS production was maximized also coincided with the largest reduction in saturated hydraulic conductivity of porous media. In addition, carbon concentration was the most significant factor to affect polysaccharide, protein and EPS secretion, followed by phosphorus concentration and temperature. The coupled effect of carbon and phosphorus concentration was also very important to stimulate polysaccharide and EPS production.

Modification of the McNeal Clay Swelling Model Improves Prediction of Saturated Hydraulic Conductivity as a Function of Applied Water Quality

A review of the McNeal clay swelling model, including its underpinning assumptions and the method for determining its parameters, was undertaken. Limitations of the model include model parameter identification, the fixed threshold exchangeable sodium percentage level at which hydraulic conductivity begins to decline, and the assumption that the expanding clay will always be 10% of the soil. To overcome these problems, an improved form of the model that accommodates a range of clay content is proposed. The modified model was used to estimate the reduction in saturated hydraulic conductivity in the three McNeal groups of soils containing different percentages of expanding clay. The model produced good agreement between the observed and estimated saturated hydraulic conductivities over the entire range of irrigation salinity (3–200 mmolc/L) and sodicity used for the original swelling model. The modified model was also successfully validated against three new sets of relative hydraulic conductivity data. The generalization of interlayer clay swelling in the modified model is more appropriately described as determining the dispersive potential of a given solution, rather than physical interlayer swelling. Consequently, this modified model more accurately predicts the reduction in saturated hydraulic conductivity as a function of the sodicity and salinity of the applied water.

Changes in selected soil physical properties caused by sodicity of soil and irrigation water

Sodic water and spring water percolated through clay, clay loam, and sandy loam (SL) soils with exchangeable sodium percentages (ESPs) of 0, 10, 30, and 50. Reduction in saturated hydraulic conductivity and water stable aggregates recorded at higher ESPs. At ESP ≈30, application of sodic and spring water to clay soil (C) reduced saturated hydraulic conductivity from 1.2 to 3 mm hr−1, whereas in SL soil, the values were 2.8 and 6.2 mm hr−1, respectively. Results indicated that at any ESP and water source, the highest free swelling obtained was in the C soil. This study has practical importance to the management of irrigation water quality with respect to soil deterioration.

Chemical and Physical Properties of Chihuahuan Desert Soils Irrigated with Industrial Effluent

Land application of secondary industrial effluent to Chihuahuan Desert upland near Las Cruces, New Mexico, was designed to meet the water demand of creosote and mesquite shrubs. The major objective of this study was to assess changes in chemical and physical properties of desert soils after 4 years (2002–2005) of irrigation with secondary industrial effluent. Soil texture and bulk density (pb) did not differ between irrigated and control plots, but did so between bare ground and mesquite sites in the control and irrigated plots. Reductions in saturated hydraulic conductivity (K s ), drainable porosity (θd), and effective porosity (θe) in the upper 0–15 cm of irrigated plot soils were attributed to decline of soil structure and dispersion of clays resulting from the addition of highly sodic and alkaline effluent to irrigated plots. Although rarely significant, consistently higher electrical conductivity, sodium adsorption ratio, chloride, exchangeable sodium percentage, and Na+ in the soil profile (between 30 cm and 210 cm) at creosote and mesquite sites compared to the bare ground site suggested deeper leaching of wastewater constituents at shrub sites. Deeper leaching of wastewater constituents beneath shrubs compared to bare ground areas may be attributed to higher water inputs caused by sprinkler spray interception, and higher Ks, θd, and θe of soils beneath creosote and mesquite canopies. Continued application of industrial effluent to a Chihuahuan Desert ecosystem over the long term should consider the relative importance of canopy and intercanopy areas.

Tillage effects on soil physical properties and performance of rice–wheat-cropping system under shallow water table conditions of Tarai, Northern India

This study was conducted for 3 years in silty clay loam (Aquic hapludoll) associated with water tables fluctuating between 0.05 and 0.96 m depths from the surface. Tillage treatments for rice ( Oryza sativa L.) were puddling by four passes of rotary puddler (PR), reduced puddling (ReP) for two passes of rotary puddler, conventional puddling (CP) and direct seeding without puddling (DSWP) in four replications. Tillage treatments for wheat ( Triticum aestivum L.) were zero tillage (ZT) and conventional tillage (CT) superimposed over the plots of rice tillage treatments. Puddling caused a significant reduction in saturated hydraulic conductivity (Ks), infiltration rate (IR), and specific volume (Rv). The reduction in Ks in the PR plot at 30 days after transplanting was 27 and 46% (3-year average) higher than in the ReP and DSWP plots, respectively, but was statistically at par with that in the CP plot in the surface tilled layer. This indicates that puddling by four passes of rotary puddler and that by conventional method adopted by farmers in those conditions gives the same level of control on percolation rate. Highest rice yield (5607 kg ha −1) was obtained in the PR plot, which was statistically equal to that in the ReP plot. Wheat yield was highest (4020 kg ha −1) in the DSWP plot of rice under CT condition. Total average grain production (rice + wheat) was highest under ReP–CT treatment combination. Results thus show that quality of soil puddle obtained by half the efforts in conventional puddling was sufficient for a significantly high yield of rice with minimum deterioration of soil properties. Similarly, wheat sowing by conventional tillage in such a reduced puddling plots of rice was sufficient for a significantly high yield of wheat.

Soil puddling for rice production under glasshouse conditions—its quantification and effect on soil physical properties

The effect of soil puddling on soil physical properties of 3 different textured soils (clay, loam, and silty loam) and growth of rice (Oryza sativa) on these soils was investigated under glasshouse conditions. Puddling intensity was expressed as the ratio of soil volume subjected to the puddling implement and the total soil volume in the puddled layer, thus integrating the effects of speed and time of the puddling operation. This parameter was well related to soil dispersion, bulk density, and saturated hydraulic conductivity. However, following prolonged periods of submerged conditions during rice growth, saturated hydraulic conductivity decreased with a decrease in soil dispersion, in contrast to an expected reduction in saturated hydraulic conductivity with increased dispersion. There was indication that continuous waterlogging reduced the effect of soil puddling, in particular on heavy-textured soils.

Variation of soil hydraulic conductivity by anionic surfactants in soil column

Remediation techniques using surfactants to flush hydrophobic organic contaminants from soils have recently been investigated. However, less attention has been given to evaluating the effects of surfactants on the hydraulic properties of porous media. The objective of this study was to investigate the effects on saturated hydraulic conductivity of the interactions between soil type (sand, clay loam) and anionic surfactants (DOSL, SLS, TDCA). Saturated hydraulic conductivities of two Iowa soils, Fruitfield sand and Webster clay loam, were measured in constant-head laboratory columns. The two soils were leached with solution of 4% (v/v) sodium diphenyl oxide disulfonate (DOSL, trade name Dowfax 8390) or 4% (w/v) sodium lauryl sulfate (SLS, trade name SLS) or 4% (v/v) trideceth-19-carboxylic acid (TDCA, trade name Sandopan JA36). As controls, soils were also leached with deionized water. Reductions in hydraulic conductivity due to surfactant leaching ranged from 9% to 85% relative to the initial values measured with deionized water. The most severe reductions in saturated hydraulic conductivity occurred in Webster soil leached with solution of TDCA. For three surfactants, more clogging occurred in the Webster clay loam than the Fruitfield sand. For both soils, the least clogging occurred with DOSL. Doubling the DOSL concentration to 8.2% did not change its effect on hydraulic conductivity for either soil. Results of this study suggest that the surfactant DOSL is a good candidate for surfactant-assisted remediation based on its relatively small effects on soil hydraulic conductivity. These results indicate that potential surfactant-assisted hydraulic conductivity losses should be considered prior to in-situ surfactant remediation.

ENHANCED ANIMAL WASTE MANAGEMENT THROUGH APPLICATION OF SURFACTANTS TO SOIL MATERIAL: LABORATORY FEASIBILITY TESTING

Laboratory testing was conducted to determine the feasibility of using surfactants to enhance soil performancewith regard to animal waste management at feedlot and dairy sites. Three surfactants, one anionic (sodium dodecyl benzenesulfonate) and two cationic (polyoxypropylene methyl diethyl ammonium chloride and tetradecyl trimethyl ammoniumbromide), were tested on a sandy loam. The best surfactants are those capable of substantially reducing the amount of leachingunder saturated and unsaturated flow conditions. Maintaining acceptable mechanical compaction characteristics, and ifpossible, limiting nitrate mobility are also important. The experimental program therefore focused on three areas: (1)Surfactant influence on leaching as indicated by effects on soil hydraulic properties (saturated hydraulic conductivity, soilmoisture diffusivity, and unsaturated soil wetting front penetration); (2) Surfactant effects on mechanical compaction; and(3) Nitrate transport in surfactantmodified soil.Saturated hydraulic conductivity was measured using fallinghead permeability tests. Transient unsaturated horizontalcolumn experiments provided information concerning surfactant influence on soil moisture diffusivity and wetting frontpenetration. Standard Proctor methods were applied in the study of surfactant effects on mechanical compaction. Adsorptionbatch tests gauged nitrate mobility in surfactanttreated soilThe anionic surfactant (sodium dodecyl benzene sulfonate) and one of the two cationic surfactants (polyoxypropylenemethyl diethyl ammonium chloride) produced considerable reductions in saturated hydraulic conductivity, soil moisturediffusivity, and unsaturated soil wetting front penetration. With regard to mechanical compaction, the anionic surfactant andthe other cationic surfactant (tetradecyl trimethyl ammonium bromide) affected decreases in the optimum moisture contentcorresponding to maximum dry bulk density. The moisture content range between optimum and the wet value correspondingto 90% or 95% maximum dry bulk density is also much narrower for these two surfactants, thereby increasing the difficultyof field compaction. Interestingly, the cationic surfactant having the greatest influence on soil hydraulic properties was notthe same one having the most substantial effect on mechanical compaction. Adsorption batch tests indicate nitrate mobilityin the sandy loam is not significantly altered by soil treatment with any of the three surfactants. The polyoxypropylene methyldiethyl ammonium chloride test results (no adverse effects on mechanical compaction and reduced hydraulic conductivity,diffusivity, and wetting front penetration) are alone enough to suggest the feasibility of using surfactants to enhance soilperformance for animal waste management. However, more investigation is needed with a greater variety of surfactants ona number of different soils, particularly with regard to hydraulic property testing using leachate typically generated at animalfeedlot and dairy facilities.

Air entrapment and consolidation occurring with saturated hydraulic conductivity changes with intermittent wetting

A study was designed to measure air entrapment and consolidation as mechanisms that might contribute to reduced hydraulic conductivity with intermittent wetting similar to surge irrigation cycles. The changes in hydraulic conductivity with intermittent wetting would result in infiltration rate changes. Air entrapment and consolidation in a surface layer sample of 50 mm was the focus of the study. During drainage periods between successive wettings, pressure head gradients within the surface layer samples were controlled to simulate drainage in a field situation. Air entrapment was found to occur consistently with reduction in saturated hydraulic conductivity while consolidation was not as consistent in its response with changes in saturated hydraulic conductivity.

Factors affecting protozoan predation of bacteria clogging laboratory aquifer microcosms

Laboratory aquifer microcosms were used to test the ability of a protozoan predator(Acanthamoeba castellanii) to mitigate reductions in saturated hydraulic conductivity of a porous medium caused by its bacterial prey (Bacillus sp.). Predation was able to prevent clogging and reduced bacterial numbers in the short term in continuous‐flow sand columns inoculated with bacteria and protozoa used to simulate aquifer conditions. However, over the longer term, increased pressure in columns with bacteria and protozoa was similar to control columns inoculated with bacteria alone. Several factors allowed the bacteria to persist and clog the columns in spite of predation. Bacteria were able to migrate from the point of inoculation up a nutrient gradient against flow toward the column inlet, whereas amoebae were not able to migrate. The availability of the bacterial prey was limited by growth of the bacteria in crevices of the sand particles that were not accessible to the amoebae. The availability of bacterial prey was also limited by aggregation of the cells into masses that were too large for the amoebae to phagocytize. The growth of cells in crevices and the aggregation of cells were confirmed with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) on thin sections prepared from column samples. Bacteria were found growing among the sand particles predominantly as aggregates. Growth of bacteria as aggregates coupled with the large barren surfaces and lack of biofilms added evidence to arguments that a key mechanism of microbial clogging is blockage of pores by these aggregates.

Changes in physical properties of a soil associated with logging of Eucalyptus regnan forest in southeastern Australia

Logging operations can cause soil profile disturbance and compaction. Soil profile disturbance and compaction change soil physical properties, which may reduce site productivity, increase soil erosion and degrade catchment water quality. This study was undertaken to measure the effect of logging on physical properties of the 0–100 mm surface soil in the Victorian Central Highlands, southeastern Australia. Soil physical properties were measured in the snig tracks, log landings, general logging areas (disturbed areas which were not occupied by snig tracks or log landings) and undisturbed areas. Within the general logging areas, measurements were made for three levels of soil profile disturbance: litter disturbed, topsoil disturbed and subsoil disturbed. The results indicated that logging significantly increased bulk density and decreased organic carbon and organic matter content, total porosity and macroporosity on over 72% of the coupe area. However, on 35% of the coupe area, the snig tracks, log landings and subsoil disturbed areas of the general logging area, bulk densities and macroporosities reached critical levels where tree growth could be affected. On these areas, organic carbon decreased between 27 and 66%, bulk density increased between 39 and 65% and macroporosity decreased between 58 and 88%. Saturated hydraulic conductivities decreased to critical levels for runoff to occur on over 72% of the coupe area (topsoil and subsoil disturbed areas of the general logging area, snig tracks and log landings). On this area, the reduction in saturated hydraulic conductivity varied between 60 and 95%.

The residual effects of tracked vehicles on soil surface properties

Differences in soil surface properties were measured on soil cores collected from within tracks and adjacent undisturbed areas. The passage of tracks resulted in an increase in bulk density, a reduction in saturated hydraulic conductivity and an increase in cone penetrometer resistance. Laboratory direct-shear tests showed in-track soil was stronger than out-of-track samples. The saturated hydraulic conductivity of in-track soil cores increased with an increasing number of wetting and draining cycles, whereas out-of-track samples showed little change. Implications for erosion, vegetation regeneration and management strategies for off-road vehicle areas are discussed, with some speculation as to the rate of recovery of impacted areas.