Tension Infiltrometry Research Articles

K in an Urban World: New Contexts for Hydraulic Conductivity.

Hydraulic conductivity (K) is a key hydrologic parameter widely recognized to be difficult to estimate and constrain, with little consistent assessment in disturbed, urbanized soils. To estimate K, it is either measured, or simulated by pedotransfer functions, which relate K to easily measured soil properties. We measured K in urbanized soils by double-ring infiltrometer (K dring), near-saturated tension infiltrometry (K minidisk), and constant head borehole permeametry (K borehole), along with other soil properties across the major soil orders in 12 United States cities. We compared measured K with that predicted from the pedotransfer function, ROSETTA. We found that regardless of soil texture, K dring was consistently larger than K minidisk; with the latter having slightly less sample variance. K borehole was dependent upon specific subsurface conditions, and contrary to common expectations, did not always decrease with depth. Based on either soil textural class, or percent textural separates (sand, silt clay), ROSETTA did not accurately predict measured K for surface nor subsurface soils. We go on to discuss how K varies in urban landscapes, the role of measurement methods and artifacts in the perception of this metric, and implications for hydrologic modeling. Overall, we aim to inspire consistency and coherence when addressing K-related challenges in sustainable urban water management.

Assessment of hydraulic properties of technosols using Beerkan and multiple tension disc infiltration methods

The increasing global urban sprawl requires large amounts of materials, putting huge pressure on numerous natural resources. In particular, vast quantities of soils are used to create infrastructures or green spaces associated with new developments. Alternative solutions aimed at alleviating soil consumption are thus being encouraged. Creating urban soils by recycling waste from industrial and construction activities is feasible, but apart from their support function the resulting technosols should also be able to provide some ecosystem services such as the capacity to infiltrate water and filter contaminants. Various methods are routinely used for in situ characterization of the hydraulic behaviour of natural soils, but their ability to assess the hydraulic properties of technosols remains unclear. Indeed, technosols formed from recycled waste differ markedly from natural soil because they often contain a considerable proportion of coarse artefacts that affect their structure. In this study, results obtained by two distinct methods (ponding and tension infiltrometry), associated with two data processing methods (Beerkan estimation soil transfer (BEST) and numerical inversion), on a set of infiltration data measured on experimental plots made of technosols have been compared with each other. Both methods provided similar results and thus proved to be reliable when applied to technosols.Highlights Reuse of by‐products from anthropogenic activities is crucial to alleviate the consumption of natural soil. Hydraulic properties of technosols must be monitored to assess some of the ecosystem services they can provide. BEST and numerical inversion of multiple tension disc infiltration data gave consistent results. Reliability of the hydraulic characterization methods used for technosols deserves further inquiry.

Impacts of land use on hydrodynamic properties and pore architecture of volcanic soils from the Mexican Highlands

Volcanic soils are important resources because of their unique mineralogical and physical characteristics, and allophanic Andosols represent some of the world’s most fertile soils. However, their unique properties can be lost when cultivated. Most soils in the Central Valley, Mexico, are derived from volcanic materials. This valley encompasses one of the largest water supply systems in the world by volume, but is affected by soil degradation and deforestation. Sustainably managing volcanic soils requires understanding how land use affects their hydrodynamic properties. Gas adsorption and mercury intrusion porosimetry, water retention curves, tension infiltrometry and X-ray tomography were used to describe pore structure characteristics. Two volcanic soils (one Andosol and one derived from indurated tuff – Tepetates), three land uses (maize monoculture, maize–wheat rotation and fallow) and two horizons (Ap and A2 for maize monoculture and maize–wheat rotation) were studied. Tillage affected topsoil by increasing the sand fraction by 38% and decreasing total porosity and macroporosity by 23% and 40% respectively. Macropore size was reduced and the number of isolated macropores was higher in the tilled layer under maize, compared with untilled subsoil. The plot under maize–wheat rotation had lower allophane content, and saturated hydraulic conductivity was reduced by nearly an order of magnitude and water retention by half, compared with maize and fallow plots. Compared with Andosols, Tepetates showed differences in mineralogical composition with lower contents of amorphous compounds and in its porous network characteristics with twice the total and percolating macroporosity compared with the maize plot. Its high content of organic carbon (3.5%) seemed beneficial for its hydrodynamic properties. Sustainable agricultural management of these volcanic soils requires reducing mechanised tillage, avoiding periods when soil is bare, not applying maize–wheat rotation and applying maize–fallow rotation allowing natural vegetation growth.

Estimation of runoff mitigation by morphologically different cover crop root systems

Summary Hydrology is a major driver of biogeochemical processes underlying the distinct productivity of different biomes, including agricultural plantations. Understanding factors governing water fluxes in soil is therefore a key target for hydrological management. Our aim was to investigate changes in soil hydraulic conductivity driven by morphologically different root systems of cover crops and their impact on surface runoff. Root systems of twelve cover crop species were characterized and the corresponding hydraulic conductivity was measured by tension infiltrometry. Relations of root traits to Gardner’s hydraulic conductivity function were determined and the impact on surface runoff was estimated using HYDRUS 2D. The species differed in both rooting density and root axes thickness, with legumes distinguished by coarser axes. Soil hydraulic conductivity was changed particularly in the plant row where roots are concentrated. Specific root length and median root radius were the best predictors for hydraulic conductivity changes. For an intensive rainfall simulation scenario up to 17% less rainfall was lost by surface runoff in case of the coarsely rooted legumes Melilotus officinalis and Lathyrus sativus , and the densely rooted Linum usitatissimum . Cover crops with coarse root axes and high rooting density enhance soil hydraulic conductivity and effectively reduce surface runoff. An appropriate functional root description can contribute to targeted cover crop selection for efficient runoff mitigation.

A modified hood infiltrometer to estimate the soil hydraulic properties from the transient water flow measurements

Summary In-situ measurements of soil hydraulic properties on covered soil surfaces (i.e. vegetated or residue covered surfaces) are of paramount importance in many agronomic or hydrological researches. These soil parameters are commonly estimated with the tension infiltrometry technique. This paper presents a portable and modified design of the hood infiltrometer (MHI) that, unlike to the original hood infiltrometer, allows estimating the soil hydraulic properties from the transient cumulative infiltration curve. The MHI consists of a water-supply reservoir attaches to a hat-shaped base placed on the soil surface. The base of the hat is closed by a system of sticks and a malleable material ring. To test the viability of this new design, the hydraulic conductivity (Ks) estimated with MHI in a loam soil using the multiple head approach was compared to the corresponding values calculated from the transient infiltration curve analysis. Next, the MHI was tested on three different soils at saturated conditions, and the sorptivity (S) and Ks estimated by the transient infiltration curve analysis were compared to the corresponding values obtained with a disc infiltrometer (DI). An additional field experiment was performed to compare the hydraulic properties measured with MHI on a bare soil and a soil covered with plants. Results demonstrated that this design allows hermetically closing the base of the hat without disturbing the soil surface. The Ks estimated with the multiple head approach was not statistically different (p = 0.61) to that obtained with the transient infiltration curve analysis. No significant differences between the Ks (p = 0.66) and S (p = 0.50) values estimated with DI and MHI were observed. The S values measured with MHI on the covered soil surface were significantly higher than that measured on the adjacent bare soil. These results indicate that MHI can be a viable alternative to estimate the hydraulic properties of covered soils from the measured transient infiltration curve.

Environmental and management influences on temporal variability of near saturated soil hydraulic properties

Structural porosity is a decisive property for soil productivity and soil environmental functions. Hydraulic properties in the structural range vary over time in response to management and environmental influences. Although this is widely recognized, there are few field studies that determine dominant driving forces underlying hydraulic property dynamics. During a three year field experiment we measured temporal variability of soil hydraulic properties by tension infiltrometry. Soil properties were characterized by hydraulic conductivity, effective macroporosity and Kosugi's lognormal pore size distribution model. Management related influences comprised three soil cover treatment (mustard and rye vs. fallow) and an initial mechanical soil disturbance with a rotary harrow. Environmental driving forces were derived from meteorological and soil moisture data. Soil hydraulic parameters varied over time by around one order of magnitude. The coefficient of variation of soil hydraulic conductivity K(h) decreased from 69.5% at saturation to 42.1% in the more unsaturated range (−10cm pressure head). A slight increase in the Kosugi parameter showing pore heterogeneity was observed under the rye cover crop, reflecting an enhanced structural porosity. The other hydraulic parameters were not significantly influenced by the soil cover treatments. Seedbed preparation with a rotary harrow resulted in a fourfold increase in macroporosity and hydraulic conductivity next to saturation, and homogenized the pore radius distribution. Re-consolidation after mechanical loosening lasted over 18months until the soil returned to its initial state. The post-tillage trend of soil settlement could be approximated by an exponential decay function. Among environmental factors, wetting-drying cycles were identified as dominant driving force explaining short term hydraulic property changes within the season (r2=0.43 to 0.59). Our results suggested that beside considering average management induced changes in soil properties (e.g. cover crop introduction), a dynamic approach to hydrological modeling is required to capture over-seasonal (tillage driven) and short term (environmental driven) variability in hydraulic parameters.

Malleable disc base for direct infiltration measurements using the tension infiltrometry technique

AbstractThe correct use of the tension disc infiltrometer requires the membrane of the disc base to be completely in contact with the soil surface. To achieve this contact, a thick layer of sand is commonly placed between the soil surface and the disc base. This paper presents an alternative disc (MDB), which, by incorporating a malleable membrane, allows direct infiltration measurements without using a contact sand layer. Infiltration curves obtained with this new design in a soil under three different tillage management treatments were compared with the corresponding curves obtained with a conventional disc (CDB) that uses a contact sand layer. The cumulative infiltration curves measured with CDB were analysed by the differentiated linearization (DL) method, and the corresponding curves obtained with MDB were analysed using both the DL and the cumulative linearization (CL) models. The values of hydraulic conductivity (K0) and sorptivity (S0) estimated with CDB were also compared with those obtained with MDB. Finally, the cumulative infiltration curves measured with CDB and MDB were compared with the corresponding modelled function for the respective K0 and S0 values calculated with the CL and DL models. The results show that, compared with CDB without a contact sand layer, MDB allows complete soil surface wetting even when non‐smoothed soil surfaces are used. The CDB, which yielded average K0 values 18% lower than those estimated with MDB, gave the highest values of standard error for the hydraulic parameters calculated. Furthermore, the subjective method employed in the CDB‐DL technique, which requires the first points of the differential infiltration line corresponding to the sand layer to be manually removed, introduces additional uncertainties in estimating S0 and K0. Comparison between the modelled and measured infiltration curves demonstrates that the DL or CL methods applied to MDB gave excellent estimates of S0 and K0. Copyright © 2012 John Wiley & Sons, Ltd.

Development of an Automated Tension Infiltrometer for Field Use

Tension infiltrometry is a useful in situ technique that is commonly used to determine hydraulic conductivity of the soil near saturation; however, the measurements are time consuming and costly. The aim of this study was to develop a fully automated tension infiltrometer for field use based on already existing designs. Differential pressure transducers were used to automate water level measurements, and the tension settings were automated by a set of solenoid valves. The effects of different design parameters on water level measurement fluctuations created by bubble disturbances (noise) were studied in the laboratory. The differential transducer provided less noisy measurements than the single transducer. The measurement noise was significantly smaller when a large‐diameter reservoir was used. The measurement noise was further reduced by using a reservoir system made of two tubes of different diameters slotted into each other. The effect of an increasing flow rate on the water level fluctuations was also investigated. Based on the design parameters tested, three identical tension infiltrometers connected to a single Mariotte bottle were built and tested under laboratory and field conditions. The pressure‐dependent hydraulic conductivity, K(h), values for all three replicates applied in the laboratory did not significantly differ from each other. In the field, the infiltration experiments were performed on a sandy loam soil on sites with and without wheel tracks. A significant reduction of K(h) values for most of the applied pressure heads was observed in the wheel track. The improved automated tension infiltrometer requires only a little operator intervention.

On the influence of coarse fragments on soil water retention

The classical determination of the soil water retention curve (SWRC) by measuring soil water content θ at different matric potentials ψ using undisturbed soil samples is time consuming and expensive. Furthermore, undisturbed soil sampling can be an intricate task when coarse soil fragments (>2 mm) are present. The objective of this study was to test whether tension infiltrometry could be used to estimate the SWRC of stony soils and to investigate to what extent the coarse fragments affected the SWRC. Tension infiltrometer measurements were conducted at 44 sites with stony soils in arid Chile. Soil water retention curves obtained through inverse modeling were compared with laboratory‐determined water retention (θ, ψ) data pairs. Differences were found to be small, confirming the applicability of the inverse modeling method. Rock fragments had a significant indirect influence on water retention for matric potentials higher than −0.30 kPa, which could be attributed to their direct influence on pore size distribution.

Evaluating climatic and soil water controls on evapotranspiration at two Amazonian rainforest sites

Interactions between the biosphere and the atmosphere have profound impacts on the functioning of the Earth system. One of the most important areas of biosphere–atmosphere interaction is the Amazon basin, which plays a key role in the global cycles of carbon, water and energy. The Amazon is vulnerable to climatic change, with increasingly hot and dry conditions expected over the next 50–100 years in some models. The resulting loss of carbon from the Amazon basin has been suggested as a potentially large positive feedback in the climate system . We investigated the differences in atmospheric demand and soil water availability between two sites; Manaus, in central Amazonia, where evapotranspiration was limited in the dry season, and Caxiuanã in eastern Amazonia, where it was not. New soil hydraulic data including water release and unsaturated hydraulic conductivity curves were collected at Caxiaunã using the instantaneous profile method (IPM), pressure plate analysis and tension infiltrometry. These data were compared to existing data from Manaus. The plant available soil water at the Caxiuanã site was 2.1–3.4 times larger than the Manaus site. The hydraulic conductivity curves indicated the existence of a secondary macropore structure at very low tensions (−0.05 kPa to −1 kPa), potentially caused by biogenic macropores, but did not vary with respect to soil water potential between sites. In addition, differences in the climatic severity of the dry season were estimated. The maximum soil water deficit, projected using a simple model of forest water use, was similar between the sites. No difference in climatic severity between sites was found and we conclude that below-ground supply of water, rather than climatic differences, were likely to have caused the contrasting dry season behaviour at the two sites. These findings indicate that, in combination with other factors, heterogeneity in soil water retention capacity may exert strong controls on the spatial variation in forest responses to climatic change.

Characterizing Soil Water‐Conducting Macro and Mesoporosity as Influenced by Tillage Using Tension Infiltrometry

Knowledge of soil water conductive porosity is of paramount importance for understanding the water and solute movement in soil. The objective of this study was to describe and evaluate an alternative pore index, i.e., the representative mean pore radius for two consecutive soil water tensions (λΔΨ), for characterizing the water‐transmitting macro‐ and mesoporosity of soil. The hydraulic conductivity (K) and related hydraulic parameters were measured using a tension disk infiltrometer at −14, −4, −1, and 0 cm water pressure heads at a soil depth of 2 cm on a long‐term conservation tillage experiment (after 9 yr of trial) under conventional tillage (CT), reduced tillage (RT), and no‐tillage (NT) treatments. The soil was loam (Xerollic Calciorthid). The measurements were performed within the first half of a 16‐ to 18‐mo‐long fallow period. Unlike the model based on the classical capillary rise theory, which assumes no differences between measurement sites (e.g., tillage treatments) for the corresponding equivalent pore radius (C0) for macro‐ and mesopores, significant differences in λΔΨ values for macro‐ and mesopores were found between the three tillage systems tested. The number of water‐transmitting macro‐ and mesopores per unit area estimated by means of the capillary rise approach was significantly greater than that calculated using the λΔΨ pore index. Although significantly higher values of λΔΨ for both macro‐ and mesopores were observed under NT, a significantly lower near‐saturation K was found under NT than CT and RT treatments due to the lower density of water‐transmitting macro‐ and mesopores.

Analysis of Temperature Effects on Tension Infiltrometry of Low Permeability Materials

Tension infiltrometers have become popular for in situ measurement of the near‐saturated hydraulic conductivity as a function of the soil water pressure head. Unfortunately, fluctuating ambient temperatures can cause dramatic pressure variations due to the presence of confined air inside the infiltrometer, thereby affecting the intended pressure head to be applied to the soil surface and hence also the measured infiltration rate. This is especially true for low infiltration rates and long equilibration times typical of low permeability materials, including unsaturated fractured rock. We developed a model to analyze the effects of temperature changes on the static pressure of the confined air volume within tension infiltrometers. The model was tested using several prototype infiltrometer designs in a computer‐controlled variable‐temperature room. Experimental results confirmed the model simulations. For example, predicted and measured changes in the pressure head in one experiment were 11.2 and 12.5 cm following a change of 18.5°C in the temperature. Using the model, we were able to optimize several infiltrometer designs that significantly reduced the undesired effects of temperature on tension infiltration results.

Estimating hydraulic conductivity of a fine-textured soil using tension infiltrometry

Tension infiltrometry has become quite popular to determine near saturated hydraulic properties of soils and to examine the effects of macropores on infiltration. The unsaturated hydraulic conductivity has traditionally been determined from steady-state tension infiltrometer data using Wooding's analytical solution. Recently, hydraulic parameters are increasingly being estimated from transient data using a numerical solution of the flow problem and nonlinear parameter optimisation. This inverse approach is convenient but its accuracy will vary with soil type. In this study, tension-disc infiltration data obtained on a tilled clay soil, located in the Basilicata region in Southern Italy, were analysed using both the traditional analytical and the numerical inversion approach. Three different parametric models were used for the unsaturated hydraulic conductivity for Wooding's solution; the two-line exponential and the bimodal piecewise-continuous models yielded similar results while the Mualem-van Genuchten (MvG) model provided a somewhat poorer description of the cumulative infiltration. The estimates for K s were one to two orders larger than those reported for core samples in soil databases. The optimised hydraulic functions revealed the presence of a bimodal pore system with a break-point in pressure head at −30 mm. Excellent agreement between measured and fitted infiltration curves was obtained for the numerical inversion procedure. The hydraulic conductivities obtained with Wooding's solution were systematically higher than those obtained from the inverse solution. The difference is presumably due to a lack of steady-state conditions and was greater than found in previous studies on coarser soils; the greatest difference (about 50%) occurred at lower pressure heads. The inverse solution may produce better results if another parametric model is used for the hydraulic properties instead of the Mualem-van Genuchten function.

Effects of conventional and conservation tillage on soil hydraulic properties of a silty-loamy soil

Infiltration into soils is strongly correlated with macroporosity. Under agricultural land use, the properties of the macropore network are governed by the applied management and tillage system. On an experimental site with a silt loam soil partly under conventional and conservation tillage, the methods of visual inventarization of stained and unstained macropores and infiltration measurements with an infiltrometer were applied to the macropore system. Dye tracer experiments with methylene blue as tracer agent yielded a penetration depth of 120 cm on the conservation tillage plot while a penetration depth of only 50 cm was recorded on the conventionally tilled plot. For both tillage treatments, infiltration rates were lower in the topsoil than in soil depths >30 cm. The conservation tillage plot showed higher infiltration rates at 50 and 90 cm soil depth than the conventional tilled plot. For both tillage systems, the visual recording of stained and unstained macropores ( d⩾1 mm) resulted in macropore densities ranging between 100 and 1,000 macropores/m 2, with the highest numbers in the topsoil and a gradual decrease with soil depth. At the conservation tillage plot, below 20 cm soil depth, macropore density was greater than at the conventionally tilled plot. Macroporosity obtained from the visual registering varied between 0.09% and 0.83% for the conventional tillage plot and between 0.08% and 0.6% for the conservation tillage plot. Macroporosity derived from tension infiltrometry, assuming a minimum macropore radius of 0.5 mm, range between 0.02% and 0.1%, about one order of magnitude lower than the figure obtained from visual inventarization. The results indicate a greater continuity and connectivity of the macropore system for silty soils with conservation tillage systems. Therefore, conservation tillage could possibly offer a means to reduce surface runoff and flood generation in agricultural landscapes dominated by silty-loamy soils.

Soil macroporosity and infiltration characteristics of a forest podzol

Spatial distribution of soil macroporosity was determined for a forest podzol from tension infiltrometer measurements at the soil surface. Surface-derived macroporosity values were compared with point infiltration characteristics obtained from soil water content and soil water chemistry measurements during an experimental irrigation, and with parameters of a kinematic wave model applied to soil water content data. Macroporosity estimated by the tension infiltrometer ranged from 0·00087 to 0·0219% of soil volume, and infiltration at these two sites was dominated by propagation of a well-defined wetting front through the soil profile and bypass flow via soil macropores, respectively. Infiltration at sites with intermediate macroporosities reflected a combination of these two processes, although results were inconclusive at one site owing to lateral flow at the base of the soil profile. There was no agreement between macroporosities estimated by the tension infiltrometer and the kinematic wave model. The maximum soil conductance parameter within the profile at a site, however, was related directly to the surface-derived macroporosity. The partial agreement between surface-derived macroporosity estimates and point infiltration characteristics shown here supports the use of tension infiltrometry as a rapid, non-destructive method of assessing spatial variations in the relative contribution of macropore flow to the infiltration process. Copyright © 2000 John Wiley & Sons, Ltd.

Foraging by deep-burrowing earthworms degrades surface soil structure of a fluventic Hapludoll in Ohio

The presence of deep-burrowing earthworms can affect soil structure and infiltration, therefore influencing agricultural productivity. We investigated the effects of deep-burrowing earthworm species on soil structure at the surface of chisel-plowed or ridge-tilled cropping systems in Pike County, OH, planted to corn ( Zea mays L.). Earthworm populations were experimentally manipulated in field enclosures by adding predominantly deep-burrowing Lumbricus terrestris L., or leaving enclosures unmodified in each tillage system. In 1995, after 2 years of bi-annual additions, we measured surface residue cover, dry sieved aggregates (DSA)- and water-stable aggregates (WSA), and carbon and nitrogen concentration of aggregates by size class, in each treatment combination. Also, in 1998, we used tension infiltrometry to examine crusting effects at the soil surface among earthworm treatments in the chisel-plow treatment. Earthworm additions yielded increased density and biomass of L. terrestris than ambient controls, and to a greater extent in the ridged corn–soybean ( Glycine max L. Mess.)–wheat ( Triticum aestivum L.) (CSW) than corn–soybean (CS) rotation. Percentage residue cover in CS cropping decreased with earthworm additions. Earthworm additions decreased the geometric mean weight diameter (GMWD) of DSA and WSA in chisel-plow treatment compared to no additions. Earthworm additions influenced carbon-to-nitrogen (C/N) ratios for smaller DSA and WSA. Water-stable aggregate C/N decreased with size class. The overall effect of earthworm additions was an increase in deep-burrowing earthworms, a decrease in surface residue cover, and more pronounced crusting, which decreased mesopore conductivity.

Variations in the hydrology of an underdrained clay hillslope

This paper presents evidence for the existence of the hydrological routes by which rainfall moves to the drainage system through clay soil at Wytham (in Oxfordshire, UK), focusing particularly on the hydrology of the A horizon. Tile drain discharge was continuously monitored at the site, and piezometer and tensiometer arrays were installed over the hillslope in order to study the spatial variations in hydrological response to rainfall. A combination of dye tracing, ring and tension infiltrometry was used to determine the variations in infiltration capacity over the hillslope and to characterise macropore flow. The study established that both lateral and vertical macropore flow through inter-pedal cracks are an important component of the hydrology of an underdrained site. Two regions of macropore discontinuity were identified in the soil profile; at the base of the rotovated layer and at the base of the A horizon. Saturated layers developed at both these locations during rainfall. Over the winter, a surface seal developed at the base of the hillslope. Tension infiltrometer measurements suggested that once the soil surface was sealed, earthworm burrows of >6mm diameter were responsible for up to 86% of the vertical infiltration into the A horizon.Temporal variations in hydrological characteristics were noted due to the swelling of the clay soil as it wetted up during the autumn and winter period. Lateral flow took place by a combination of macropore and preferential routes in saturated regions within the A horizon. During periods of winter drainflow lateral macropore flow in the top 10cm of the soil was the most important lateral route for water and was initiated by a critical pore water pressure of +0.3KPa. Deeper lateral flow was limited and occurred predominantly through the soil matrix. During autumn drainflow, however, inter-pedal cracks were well developed through the A horizon and lateral flow at the base of the A horizon was dominant.

Macroporosity and Hydraulic Properties of Earthworm‐Affected Soils as Influenced by Tillage and Residue Management

AbstractMacropores affect infiltration of water and solutes in soil. A field study was conducted to determine the effect of tillage‐residue management on earthworm development of macropore structure and the infiltration properties of a silt loam soil cropped in continuous corn. Tillage treatments included rototilled and nontilled soils, with or without residues, and innoculated with earthworms. Infiltration properties were measured with an instantaneous infiltration test of a 1.61 cm pulse of 0.5% methylene blue solution and by measuring steady‐state infiltration rates at +5, 0, −3, and −12 cm pressures. There were no significant tillage‐residue effects on steady‐state infiltration rates. The time required to reach steady state was 930 and 1020 s in treatments with residues, compared to 180 and 415 s in treatments without residue. Dye solution infiltrated in 22 and 217 s in no‐till and tillage‐with‐residue treatments, respectively, compared to >544 s in the remaining treatments. Estimates of effective porosity calculated using infiltration data and by counting stained macropores with depth were 0.85 and 1.3% in no‐till and 0.99 and 0.29% in tillage‐with‐residue treatments, respectively. In no‐till treatments, large quantities of dye solution, unaccounted for by steady‐state measurements, infiltrated rapidly and were stored in deep, surface‐connected earthworm macropores. In tillage‐with residue treatments, infiltration of dye solution, unaccounted for by macropore stained count measurements, occurred along partially incorporated residue pieces. Measurements of infiltration properties should include measurements of early infiltration and storage in macropore systems (ponded tests) and of steady‐state infiltration into the soil matrix (tension infiltrometry) once the macropore system has filled with water.

Field assessment of crusting on a tilled sandy clay loam

Abstract.Nine different techniques were used to record the initial change in the physical and hydrological properties of a freshly tilled soil surface following successive cycles of wetting and drying. The study was made in the field on a sandy clay loam soil ploughed and harrowed and then exposed to three simulated rainfall events of 76 mm/h for 15 minutes. Although the degradation of the soil surface increased with each successive rainfall, the most significant changes were observed after the first rainfall. Qualitative observations of clod size distribution and crust development provide a good indication of the early stages of soil surface degradation. Complementary physical data were quickly obtained using a hand held shear vane. These techniques are simple and robust enough that they can be used in on‐farm research programmes, where resources, both human and technical are at a premium. Tension infiltrometry provided hydrological information that complemented the physical information provided by the above techniques, but is not as simple.