Field-saturated Hydraulic Conductivity Research Articles

Improving stormwater infiltration and retention in compacted urban soils at impervious/pervious surface disconnections with biochar

Urban development often results in compacted soils, impairing soil structure and reducing the infiltration and retention of stormwater runoff from impervious features. Biochar is a promising organic soil amendment to improve infiltration and retention of stormwater runoff. Soil at the disconnection between impervious and pervious surfaces represents a critical biochar application point for stormwater management from urban impervious features. This study tested the hypothesis that biochar would significantly improve water retention and transmission at four sites, where varying percentages (0%, 2%, and 4% w/w) of biochar were amended to soils between impervious pavement, and pervious grassed slopes. Field-saturated hydraulic conductivity (Ksat) and easily drainable water storage capacity were monitored at these sites for five months (two sites) and 15 months (two sites). At the end of the monitoring periods, the physical, chemical, and biological properties of each site's soil were assessed to understand the impact of biochar on soil aggregation, which is critical for improved soil structure and water infiltration. Results indicated that the field Ksat, drainable water storage capacity, and plant available water content (AWC) were 7.1 ± 3.6 SE, 2.0 ± 0.3 SE, and 2.1 ± 0.3 SE times higher in soils amended with 4% biochar, respectively, compared to the undisturbed soil. Factor analysis elucidated that biochar amendment increased the organic matter content, aggregate mean weight diameter, organo-mineral content, and fungal hyphal length while decreasing the bulk density. Across the 12 biochar/soil combinations, the multiple linear regression models derived from factor analysis described the changes in Ksat and AWC reasonably well with R2 values of 0.51 and 0.71, respectively. Using soil and biochar properties measured before biochar addition, two recent models, developed from laboratory investigations, were found helpful as screening tools to predict biochar's effect on Ksat and AWC at the four field sites. Overall, the findings illustrate that biochar amendment to compacted urban soils can significantly improve soil structure and hydraulic function at impervious/pervious surface disconnections, and screening models help to predict biochar's effectiveness in this context.

Hydraulic characterization of Pwales aquifer in Malta Island preparatory for planning managed aquifer recharge (MAR) pilot plant

Whitin the aim to reduce the water demand by increasing water use efficiency and providing alternative water resources, and mainly to meet the demand of good quality irrigation water for agriculture, the Energy and Water Agency of Malta is planning to develop a Managed Aquifer Recharge pilot plant in Pwales Valley to improve the quantitative and qualitative status of the groundwater body. For this reason a detailed hydraulic characterization of the valley was carried out. Specifically, hydraulic properties of the rocks that constitute strata atop of the Pwales aquifer were determined by means of both laboratory measurements on samples and field test carried out in the studied area. The water retention and hydraulic conductivity functions, which relate the matric potential, ψ, and hydraulic conductivity, K, to the water content, θ, respectively, were measured using three experimental methods because each of them allows to obtain data points in a specific wet range. The water retention and hydraulic conductivity functions were measured on samples extracted from blocks of Upper Coralline Limestone formation, that hosts the aquifer, collected in three different quarries: Ghian Tuffieha, Mellieha and San Martin areas. The measured water retention and hydraulic conductivity data were fitted with LABROS SoilView Analysis software that allows to describe the functions and obtain the parameters which are crucial for modelling the water flow and transport processes in the critical zone. In addition, large ring infiltrometer test was carried out to determine the field saturated hydraulic conductivity, Kfs, and the average infiltration rate. Knowledge of the hydraulic characteristics of the Upper Coralline Limestone, completely missing in the scientific literature, allows developing a local groundwater-flow numerical model in order to better describe and understand how the water flows from the soil to the groundwater of the valley and visualize different environmental scenarios such as the potential effects of Managed Aquifer Recharge plant in the Pwales Coastal Groundwater Body.

Drivers of field-saturated soil hydraulic conductivity: Implications for restoring degraded tropical landscapes

Water security represents a major challenge in East Africa, affecting the livelihoods of millions of people and hindering sustainable development. Predicted increases in rainfall intensity and variability are expected to exacerbate water insecurity and land degradation. Improving soil infiltrability is an effective strategy for addressing water insecurity and land degradation. Research on soil infiltrability is often highly localized; therefore, scientific understanding of the drivers of infiltrability on larger spatial scales is limited. The aim of this study was to understand the main drivers of infiltrability across five contrasting landscapes in Kenya. We measured field-saturated hydraulic conductivity (Kfs) in 257 plots and collected data for variables representing soil properties (sand content, soil organic carbon (SOC) and pH), land degradation (grazing pressure and presence of erosion), vegetation quantity (woody aboveground biomass), and vegetation quality (functional properties and diversity). We used generalized mixed-effects models to test for the effects of these variables on Kfs. Median Kfs for the five sites ranged between 23.8 and 101.8 mm h−1. We found that Kfs was positively associated with sand content (standardized effect 0.39), SOC content (0.15), and functional diversity of woody vegetation (0.09), while it had a negative relationship with the presence of erosion (−0.24) and grazing pressure (−0.09). Subsequently, we conclude that infiltrability can be enhanced through using land restoration strategies which specifically target parameters that affect Kfs. The results further support that Kfs is not solely dictated by inherent soil properties, and that management interventions which boost SOC, reduce erosion, and minimize unsustainable grazing can help address water scarcity by restoring soil hydrological function.

Ground Fire Legacy Effects on Water-Dynamics of Volcanic Tropical Soils

The forest floor is a critical component in maintaining the life cycles of forest ecosystems. It normally includes organic soil horizons, known as duff and litter, which are prone to be rapidly consumed after flaming and smoldering fires. This work aims to understand the legacy effects of surface and ground fires on the infiltration capacity of a volcanic forest soil. We studied five sites with fires recorded in the last 20 years. All of them are located in pine-oak forests of the volcanic mountain region in central Mexico with a temperate climate and Andic soil properties. Tension-infiltration tests were carried out to determine hydraulic conductivity and the number of active macropores. After each test, cores were taken to evaluate in a laboratory setting, where soil water repellency at different moisture concentrations and the integrative dynamic repellency index were determined. Field-saturated hydraulic conductivity was moderately high in all sites, with mean values of 13 and 42 mm·h−1 for burned and control plots, respectively. A non-linear relationship was found between recurrence and type of fires with the concentration of active pores and several dynamic water repellency parameters. This work confirmed the presence of latent combustion in these temperate neotropical forests. The changes in soil water repellency and hydraulic conductivity detected do not necessarily imply an exceeded soil infiltration capacity. However, many of the fires in this region are associated with increasing agricultural activities, so further studies are needed to determine if higher fire frequencies could exceed the resilience capacity of the soils triggering land degradation.

Influence of landscape position and climatic seasonality on soil water and gas conductivity properties in agricultural soils

Agricultural landscape management and climate seasonality can influence soil structure, hydraulic conductivity, and air permeability within the context of soil water and soil gas mobility. To investigate this, in situ and laboratory-based data were collected from three agricultural landscape positions within a watershed in eastern Ontario, Canada during a growing season. Macropore classification, water infiltration tests, and air permeability measurements were conducted in situ and standard soil characterizations were carried out on soil samples. Hydraulic conductivity of the soil matrix, based on grain size data, indicated that the highest values were consistently measured in the B horizon at each landscape setting. Macropores were found to be more abundant within uncultivated drainage ditch bank soils, compared to the adjacent cropped fields. Macropores in the ditch bank soils were exclusively consisted of circular biopores, while both circular and linear macropores were observed in the cultivated field soils. Air permeability, vertical hydraulic conductivity, and horizontal hydraulic conductivity were also greater in the uncultivated soils, relative to the cultivated soils. Field saturated hydraulic conductivity measurements offered evidence of anisotropy, likely due to the vertical nature of the macropore features. Macropore disposition and extent varied over the growing season, especially in the cultivated field soils where tillage and field trafficking are physically disruptive. Seasonality of macropore development will influence temporal changes in advection-based mass exchange of gas and water in the vadose zone. Modeling of mass exchange in agricultural soils should consider time variability in macroporosity to more realistically characterize infiltration and soil gas emissions.

Effects of organic carbon and clay contents on structure‐related properties of arable soils with high clay content

AbstractUnderstanding of factors governing soil structural features is necessary for managing key processes affecting crop productivity and environmental impacts of agriculture, for example, soil water balance, aeration, and root penetration. Organic matter is known to act as a major binding agent in soil aggregation and thus constitutes a central pillar in soil structure formation. However, knowledge of the structural role of organic matter or carbon (OC) in soils highly rich in clay‐sized particles (<0.002 mm) is limited. In this study, the effects of clay and OC contents on aggregate stability, water holding capacity, near‐saturated hydraulic conductivity, total porosity, and pore size distribution were assessed in cultivated fields with high clay content located in private crop production farms in southern Finland. Significant positive correlations were found between OC content and proportion of water stable aggregates and specific pore sizes from the range of 30 μm up to 1 mm diameter determined by image analysis. Porosities on a smaller size range derived from water retention measurements likewise showed a positive correlation with OC in <0.2 μm sizes. On the range of 0.2–1 μm, a negative relationship was observed, which induced a negative effect of OC on soil plant available water reserves. In line with the positive correlation between OC and larger soil pores, free water, representing the amount of water that can be drained by gravity, exhibited a positive relationship with OC suggesting that OC content can enhance aeration of soils with high clay content. Compared to OC, clay content tended to have an adverse effect on soil structural properties. Clay correlated negatively with pores larger than 30 μm, free water content, and extrapolated field saturated hydraulic conductivity. Further, our imaging results showed how saturated hydraulic conductivity was controlled by pore morphology, and there was a power law relationship between the conductivity and critical pore diameter. in agreement with the percolation theory. Overall, the structural impacts and hydrological implications of OC and clay in heavy clay soils vary by pore size ranges and their emergent practical impacts are thus not straightforward.

Ecohydrological influences of biocrusts and their pathways in a desert steppe ecosystem

AbstractBiological soil crusts (biocrusts) are a prevalent form of organic cover in drylands across the world, and they play a crucial role in shaping the ecohydrological processes and functioning of dryland ecosystems. However, in desert steppe ecosystems, the ecohydrological influences of biocrusts and their pathways have not yet been thoroughly understood. Here, we examined the influences of three types of biocrusts (cyanobacterial, cyanobacterial‐moss mixed, and moss biocrusts) on soil water retention and infiltration in a typical desert steppe of northwestern China, and we also analysed the possible pathways through which biocrusts affect them. Accordingly, the field capacity (θf, indicating soil water‐holding capacity) and saturated hydraulic conductivity (Ks, indicating soil infiltrability) of each biocrust‐covered soil and bare soil were measured both at 0–5 and 5–10 cm depths, on Arenosols (loamy sand texture) and Calcisols (silty loamy texture), respectively. Our results showed that the presence of biocrusts increased surface soil (0–5 cm) water‐holding capacity while decreased soil infiltrability, creating a remarkable impact on soil water retention and infiltration. As compared to bare soil, the θf of cyanobacterial, cyanobacterial‐moss mixed, and moss biocrusts were increased by 16.5%, 21.4%, and 21.7% on Arenosols and by 9.6%, 18.9%, and 22.8% on Calcisols, while their Ks were reduced by 43.2%, 56.2%, and 38.2% on Arenosols, and by 49.0%, 68.7%, and 36.0% on Calcisols, respectively. The development of biocrusts on sandy textured soil had a more pronounced impact on both soil water retention and infiltration than loamy textured soil. We found that biocrusts mainly changed soil water retention and infiltration by increasing the contents of clay and organic matter. More specifically, the increase in clay content led to a more significant effect compared to the increase in organic matter content on Arenosols, while the opposite influence was observed on Calcisols. Among the three types of biocrusts, the soil infiltrability of the mixed biocrusts was the lowest, perhaps due to the interaction between the accumulation of clay particles by moss and the secretion of extracellular polymeric substances by cyanobacteria. Our study highlights the remarkable ecohydrological impacts of biocrusts on desert steppe ecosystems, and the results imply that it is of great necessary to integrate biocrusts and their influences into our understanding of ecohydrological processes in global drylands.

Influence of Rangeland Land Cover on Infiltration Rates, Field-Saturated Hydraulic Conductivity, and Soil Water Repellency in Southern Patagonia

This study investigated the influence of rangeland land cover on infiltration rates (IRs), field-saturated hydraulic conductivity (Kfs), and soil water repellency in Patagonia. Four land cover types (shrubs, dwarf heath shrubs, bare soil, and Inter tussock) were examined to assess their effects on hydrological processes. IR was measured using the single-ring method, and soil water repellency was evaluated using the Beerkan method. We hypothesized that land cover type affects IR, Kfs, and soil water repellency. The results showed significant variations in IRs among land covers, with Tsf displaying lower rates than the other covers. Soil water repellency was prevalent in shrub and dwarf heath shrub−covered soils. Lateral flow was observed, indicating limited water infiltration. The obtained Kfs values were higher than the calculated hydraulic conductivity values (Ks). However, further investigation is required to assess the impact of capillarity (i.e., α*) on Kfs determination. This study enhances our understanding of hydrological processes in rangeland ecosystems and provides valuable insight into land management practices. By elucidating the relationships among land cover, IR, Kfs, and soil water repellency, this study contributes to sustainable water resource management in arid and semiarid regions.

Repeated falling-head method for in situ measurements of saturated hydraulic conductivity using a single cylinder

A simple, repeated falling-head (RFH) method, which uses an inexpensive portable cylinder to quickly determine field-saturated hydraulic conductivity (Kfs), is presented. A cylinder of radius r, inserted vertically from the soil surface to a depth d, is used as a water supply tank, through which water infiltrates into the soil. The falling-head test is repeated without allowing the cylinder to be drained entirely to eliminate the effects of the initial soil moisture conditions. Either change in the water level (H) in the water supply cylinder or strong linearity between the infiltration flux (qs) and H can be used to determine Kfs directly or by multiplying the slope with an empirical ring-installation scaling length, Lg; thus, no soil-dependent variable is necessary. To obtain the Lg value for various conditions, we carried out numerical experiments using HYDRUS (2D/3D) with a recently implemented reservoir boundary condition for six different soil textures, ranging from coarse soil (e.g., sand) to fine soil (e.g., silty clay loam), and two different ranges of water levels, 15 ≤ H ≤ 25 cm and 2 ≤ H ≤ 6 cm. Numerical results showed that the Lg has a strong linear dependence on d and r, where Lg increases as d and r increase. We propose a new linear model to determine Lg with optimized coefficients for each H range. Numerical results showed no significant differences in the estimated Kfs after the second repetition, confirming that repeating the falling head test twice is sufficient. The newly obtained Lg values were then applied to the experimental data obtained at multiple fields having different soil textures. The Kfs values determined using the RFH method agreed well with those measured using the field two-ponding depths steady-state method and/or the FH method in the lab. These results demonstrate the reliability of the proposed RFH method.

Hydraulic conductivity assessment of falling head percolation tests used for the design of on-site wastewater treatment systems

The suitability of a location for an on-site wastewater treatment process (for areas which lack access to centralised wastewater treatment systems) requires an assessment of the permeability of the soil into which the effluent will be discharged. In many jurisdictions this is determined using some type of in-situ percolation test. Falling head percolation tests, which give a value of percolation time (PT) that is empirically related to the notion of hydraulic conductivity, are widely used as they are relatively simple to carry out, but the test does not have a sound theoretical framework and test methods are not standardised internationally. In comparison, the saturated hydraulic conductivity of a soil obtained from a constant head well permeameter test is independent of test conditions, and so is a more suitable metric for design. A database of over 900 falling head tests carried out across a range of different subsoil types in Ireland has been collated, all with the inherent limitations of the existing regulative framework regarding the percolation test and soil texture assessment. These tests were then modelled using Hydrus 2-D numerical modelling simulations to determine equivalent field saturated hydraulic conductivity (Kfs) values and thereby provide a correlation with PT values across the range of subsoil conditions. In addition, falling head tests have been carried out in parallel to constant head permeameter tests in the field and compared against the relationship derived from the broad dataset of simulated results. This revealed an optimal solution by which to determine Kfs from the field permeameter test (using parameters recommended for most structured soils from clays to loams). The trendline based on Irish data was also compared against more generic formulations of the relationship between PT, and Kfs and shown to match closely, particularly the Reynolds (2016) ‘unified’ methodology. Finally, the Irish threshold PT limits for on-site wastewater treatment have been converted to Kfs values and compared against other international standards.

Effects of wastewater pre-treatment on clogging of an intermittent sand filter

Intermittent sand filters (ISFs) are widely used in rural areas to treat domestic and dilute agricultural wastewater due to their simplicity, efficacy and relative low cost. However, filter clogging reduces their operational lifetime and sustainability. To reduce the potential of filter clogging, this study examined pre-treatment of dairy wastewater (DWW) by coagulation with ferric chloride (FeCl3) prior to treatment in replicated, pilot-scale ISFs. Over the study duration and at the end of the study, the extent of clogging across hybrid coagulation-ISFs was quantified, and the results were compared to ISFs treating raw DWW without a coagulation pre-treatment, but otherwise operated under the same conditions. During operation, ISFs receiving raw DWW recorded higher volumetric moisture content (θv) than ISFs treating pre-treated DWW, which indicated that biomass growth and clogging rate was higher in ISFs treating raw DWW, which were fully clogged after 280 days of operation. The hybrid coagulation-ISFs remained fully operational until the end of the study. Examination of the field-saturated hydraulic conductivity (Kfs) showed that ISFs treating raw DWW lost approximately 85 % of their infiltration capacity in the uppermost layer due to biomass build-up versus 40 % loss for hybrid coagulation-ISFs. Furthermore, loss on ignition (LOI) results indicated that conventional ISFs developed five times the organic matter (OM) in the uppermost layer compared to ISFs treating pre-treated DWW. Similar trends were observed for phosphorus, nitrogen and sulphur, where proportionally higher values were observed for raw DWW ISFs than pre-treated DWW ISFs, with values decreasing with depth. Scanning electron microscopy (SEM) showed a clogging biofilm layer on the surface of raw DWW ISFs, while pre-treated ISFs maintained distinguishable sand grains on the surface. Overall, hybrid coagulation-ISFs are likely to sustain infiltration capacity for a longer period than filters treating raw wastewater; therefore, requiring smaller surface area for treatment and minimal maintenance.

Influence of long-term tillage and diversified cropping systems on hydro-physical properties in a sandy loam soil of North-Western India

A study was conducted to determine the combined effects of three tillage practices and four maize (Zea mays L.)-based cropping systems on physical, saturated, and near-saturated hydraulic properties in a sandy loam soil of North-Western India. Split-plot experimental design was adopted with tillage [conventional tillage (CT), zero tillage (ZT), and permanent raised bed (PB)] as the main plot treatments and intensified crop rotations [Maize (Zea mays L.)-Wheat (Triticum aestivum)-Greengram (Vigna radiata L.) (MWGg), Maize-Chickpea (Cicer arietinum L.)-Sesbania (Sesbania aculeata) (MCpSb), Maize-Mustard (Brassica juncea) -Greengram (MMuGg) and Maize-Maize-Sesbania (MMSb)] as subplot treatments. The saturated and near-saturated soil hydraulic conductivity were derived from steady-state infiltration rates measured using a hood infiltrometer on the surface soil at 0, − 1, and − 3 cm pressure heads. The long-term (10 years) study revealed that the bulk density (BD) of the soil under conservation agriculture (CA) practices (PB and ZT) was significantly (P ≤ 0.05) lower than that in CT practices. The soil BD in the MCpSb cropping system was measured to be the lowest (1.24 g cm−3) among all the cropping systems. The soil aggregate mean weight diameter (MWD) under PB and ZT was determined to be 31% and 27% higher than in the CT treatments. In tillage × cropping systems interactions, the highest MWD was observed in the PB×MWGg. The saturated and near-saturated hydraulic conductivity (K(h)) were estimated to have higher values in CA practices (PB and ZT) than in the CT treatments. In the case of cropping systems, the soil's mean field saturated hydraulic conductivity was estimated to be significantly (P < 0.05) higher under the MWGg, MCpSb, and MMuGg than the MMSb. The present study indicates that conservation agriculture-based crop management with diversified maize-based rotation (MCpSb, MWGg, and MMuGg) could be promising alternatives to conventional tillage practices (CT). Among the cropping system choices, MWGg was more effective in improving the soil's hydro-physical properties in the study area.

Influence of the 2021 Brood X cicada emergence on near surface hydrology in forested and urban landscapes

AbstractThe 2021 emergence of the 17‐year Brood X cicadas (Magicicada septendecim, M. cassinii, and M. septendecula) saw billions of cicadas emerge from the soil throughout the midwestern and eastern United States. The emergence left connected burrows visible at the surface, which are hypothesized to affect near surface hydrologic processes. To investigate these processes, we used single‐ring, dual head infiltrometers to measure field saturated hydraulic conductivity (Kfs, n = 70) across patterns of emergence and land use in south‐central Indiana, USA. Our experimental design included locations with and without cicada burrows in forested (undisturbed) and urbanized (disturbed) areas. Across undisturbed sites, we found a significant 80.8% increase in Kfs between soils with (median = 14.1 cm/h; n = 20) and without (median = 7.8 cm/h; n = 20) cicada burrows. At disturbed sites, we found no significant difference in Kfs between sites with (median = 4.2 cm/h; n = 18) and without (median = 4.4 cm/h; n = 12) cicada burrows. We found a significant correlation between the number of burrows present at the surface and Kfs rates for undisturbed sites ( = 0.42; p = 0.008), while no correlation was found for the disturbed sites ( = −0.09; p = 0.62). Our measurements suggest that the effect of burrows on Kfs is minimized in urbanized areas, potentially due to compaction and other impacts from human disturbance that mitigate the presence of macropores left by cicadas. In contrast, surface‐connected macroporosity from Brood X cicada burrows in undisturbed areas act as a conduit for precipitation into the soil profile and bypass flow into deeper horizons and the shallow groundwater table, with implications for runoff dynamics, soil and groundwater recharge and quality, and nutrient cycling.

Mechanical Intervention in Compacted No-Till Soil in Southern Brazil: Soil Physical Quality and Maize Yield

The intense and successive use of mechanization in modern cropping systems has increased soil compaction under no-till areas. In this study, we aimed to assess the performance of a fixed shank coupled with a seeder for the mitigation of soil compaction induced by machinery traffic as an efficient alternative to replacing the chiseling and subsoiling operations in no-till areas. We evaluated a long-term experiment conducted in clay loam (Rhodic Haplustox) soil in southern Brazil. The experiment was conducted under a randomized block design, whose treatments consisted of three wheel-traffic intensities: 0 wheel-traffic (0 WT), 14 wheel-traffic (14 WT), and 28 wheel-traffic (28 WT), combined with four soil tillage mechanical interventions under a no-till field: no-till (NT), no-till with a fixed shank (NT + FS), soil chiseling (SC), and soil subsoiling (SS). The soil physical attributes evaluated were the soil penetration resistance (SPR), macroporosity (MaP), microporosity (MiP), total porosity (TP), bulk density (BD), field-saturated hydraulic conductivity (Kfs), S index, and plant-available water capacity (PAWC). In addition, three critical soil physical functions were evaluated by using a soil physical quality index (SPQI). The results showed that SPR was sensitive to soil compaction and captured differences among the mechanical intervention methods. Machinery traffic caused soil compaction, increasing SPR and reducing PAWC. Soil chiseling and subsoiling promoted lower BD, a higher TP, MaP, Kfs, and higher S index at the 0.05–0.15 m soil layer. Based on the SPQI, no changes were detected in the soil physical functions between NT and NT + FS. On the other hand, SC and SS enhanced soil physical functioning by 10%. We concluded that a 15-cm deep fixed shank could not mitigate the soil compaction induced by machinery traffic at the seeder operation. Therefore, this method is less effective in improving the soil’s physical environment than chiseling and subsoiling operations. Finally, we encourage monitoring the persistence of these benefits on the soil over the subsequent crop seasons and in years with an intense water deficit along with the crop cycle.

Contrasting effects of native and exotic vegetation on soil infiltrability in the Sonoran Desert

Invasion by exotic grasses is transforming drylands across the planet, but the ecohydrological feedbacks of such invasions are not fully understood. For example, in the Sonoran Desert, previous studies have shown that buffelgrass (Cenchrus ciliaris) alters the spatial patterns of soil moisture, leading researchers to hypothesize that such alterations are related to the plants' effects on soil infiltrability. To evaluate this hypothesis, we compared field-saturated hydraulic conductivity (Kfs) in a native shrubland with that in a neighboring savanna extensively dominated by exotic buffelgrass. We measured Kfs during the dormant and growing seasons in both canopy and intercanopy zones. We found that Kfs was generally lower during the dormant season than during the growing season. There were no significant differences between sites during the dormant season, and at both sites, Kfs was 6–7 times higher under shrubs than in the intercanopies. During the growing season, Kfs for the exotic intercanopy was comparable to that for shrub cluster edges (140 mm h−1) and was more than twice that for the native intercanopy. Both shrubs and buffelgrass improved Kfs by reducing soil bulk density (thus increasing porosity). Additionally, surface roughness in the exotic intercanopy was nearly 3 times higher than in the native intercanopy. The combination of greater surface roughness and higher infiltration rates during the growing season most likely alters hydrological connectivity in savannas invaded by exotic grasses such as buffelgrass. By capturing portions of the runoff generated in the intercanopy, these grasses reduce runon into shrub patches, with potentially substantial impacts on native vegetation dynamics and stability.

The statistical power of post-fire soil-hydraulic property studies: Are we collecting sufficient infiltration measurements after wildland fires?

Infiltration and associated soil-hydraulic properties, such as field-saturated hydraulic conductivity (Kfs), sorptivity (S), or saturated soil–water content (θs) are measured after wildland fires to assess risks of water-related hazards and water supply impairment. Yet the statistical power of these data to distinguish between burned and unburned infiltration is seldom assessed, despite the typically small number of total measurements (N). Here, parametric and nonparametric statistical approaches are used to assess the primary influences on the statistical power and whether the N is sufficient to achieve a representative power of 0.9. About half of the studies examined did not achieve a power ≥0.9 at the as-sampled N, suggesting the need for post-fire infiltration studies to collect more measurements. Effect size was the primary control on power, and therefore the N needed to achieve a given power. Because effect size tends to decrease with time since fire, N generally needs to increase with time since fire in infiltration studies. Power estimates were similar for parametric and nonparametric analyses. Comparisons between infiltration methods suggested that steady state rainfall simulation produced a greater power for a given N, relative to both tension infiltrometers and constant or falling head permeameters. The greater power of the steady state rainfall simulation method was the result of smaller variability, compared to the tension infiltrometers and constant or falling head permeameters. The substantial variability of post-fire tension infiltrometer measurements may complicate using these data in meta-analyses. This work further suggests that synthesis or meta-analysis studies of post-fire soil-hydraulic properties may be more robust if data are weighted by statistical power. The differences in statistical power between infiltration measurement methods require further demonstration for a broader range of datasets before extrapolation beyond the datasets considered here.

Temporal variation of saturated and near‐saturated soil hydraulic conductivity and water‐conducting macroporosity in a maize‐wheat rotation under conventional and conservation tillage practices

AbstractKnowledge of temporal variation of soil hydraulic properties (SHPs) is crucial to understand soil physical behaviour under different tillage practices. The objective of this study was to assess the variation of saturated and near‐saturated soil hydraulic conductivity (NSHC) and water‐conducting macroporosity (Ɛ) under long‐term (09 years) tillage regimes viz. zero tillage (ZT), conventional tillage (CT), and minimum tillage (MT) in a rain‐fed maize‐wheat crop rotation (RMWC) in the North‐West Himalayas, India (NWHI). A hood infiltrometer (HI) was used to measure the steady‐state water flux (q) at 0, −10, and −30 mm pressure head (PH) after harvesting of maize and over two wheat cropping seasons for each treatment. The infiltration data were analyzed in terms of unsaturated hydraulic conductivity k(h), field saturated hydraulic conductivity (ks), water‐conducting macroporosity (Ɛ). The results showed that the seasonal effects on ks, k(h), and Ɛ values were significantly different (p ≤0.05) for tilled treatments (CT and MT). In contrast, no significant difference (p ≤0.05) was found for untilled treatment (ZT). Significantly higher (p ≤0.05) ks, k(h), and Ɛ values were observed in ZT than CT and MT, associated with higher SOC and lower ρb values. A multivariate analysis of variance of the ks showed a highly significant difference (p ≤0.01) with both time and tillage treatments. Overall, a significant improvement of hydraulic conductivity characteristics was observed during the wheat‐growing seasons compared with the maize harvest season. The temporal dynamics of SHPs under different tillage regimes indicate that ZT can be a suitable tillage practice for reducing runoff and soil loss in monsoon maize and winter wheat cropping system.

Integrated Use of Phosphatic Fertilizer and Farm Manure on Soil Physical Properties and Maize Yield

Soil fertility, one of the important determinants of agricultural productivity, is generally thought to be supplemented through the application of nutrients mainly through inorganic fertilizers and organic amendments. The physical health of the soil creating suitable environment for the availability and uptake of these nutrients is generally ignored. The present study was aims to characterize the soil physical environment in relation to integrated application of farm manure (FM) and inorganic fertilizer in hybrid maize (Zea mays L.). A Field experiment was conducted at Research Area of Institute of Soil Environmental Sciences, University of Agriculture Faisalabad to evaluate the impact of different levels of DAP fertilizer @ 70:80:90 kg ha-1 in combination with FM @ 0, 5, 10 Mg ha-1 to check the soil physical properties as well as yield of hybrid maize. The experimental design was RCBD under factorial structure with 9 treatments replicated thrice. Crop was harvested at maturity and taking observations like physical parameters (Bulk density, porosity, infiltration rate, field saturated hydraulic conductivity, soil strength) and yield parameters (1000 grain weight, plant height, total grain yield) following standard procedures. Results showed that integrated use of farm manure and phosphorus rates significantly affect the plant height, grain yield of maize. Farm maure and phosphorus levels also increased soil porosity and soil hydraulic conductivity. But it reduced the soil bulk density and soil strength. So to improve soil physical properties, to gain substantial yield of maize phosphorus rates applied in a planned manner rather than excessive use and effects of farm manure should also be kept under consideration.

A perennial living mulch substantially increases infiltration in row crop systems

Poor infiltration in annual row crop systems can cause a range of problems, including sediment and nutrient loss in runoff, diminished trafficability, anaerobic soil conditions, and reduced precipitation use efficiency. Soils covered by perennial vegetation generally sustain much higher infiltration rates, and consequently are less prone to these problems. Kura clover (<i>Trifolium ambiguum</i> Bieb.) living mulch (KCLM) is a management system that seeks these environmental benefits of perenniality, while allowing continued production of annual row crops like maize (<i>Zea mays</i> L.) and soybean (<i>Glycine max</i> [L.] Merr.). This is done by planting them into tilled or killed strips within a perennial stand of kura clover. Our objective was to compare the hydrologic performance of long-term KCLM systems (in place for at least five years) against adjacent fields or plots in conventional row crop production on the same soil types. Measured variables included field-saturated hydraulic conductivity (K_fs), moisture release curves, and bulk density. K_fs was measured with a constant head single ring infiltrometer, and moisture release curves were determined with the evaporation method. Bulk density was measured on 5 cm diameter cores extracted from the surface horizon of each treatment. None of the long-term sites contained appreciable sloped land, so supporting runoff measurements were made on a third field in Minnesota where the KCLM had only been in place for two years, using lined plots with flumes and tipping buckets. Results revealed substantial and significant differences in K_fs at the long-term sites. At one site the mean value was 11 times greater in the living mulch than in the conventional fields, while at the other site it was 19 times greater. The runoff plots showed a 93% reduction in sediment loss for the KCLM relative to conventional production over the course of a year that included 10 runoff-inducing storms. These results suggest that KCLM may confer similar hydrologic benefits to prairie strips if strategically placed in fields or watersheds.

Assessing soil and land health across two landscapes in eastern Rwanda to inform restoration activities

Abstract. Land degradation negatively impacts water, food, and nutrition security and is leading to increased competition for resources. While landscape restoration has the potential to restore ecosystem function, understanding the drivers of degradation is critical for prioritizing and tracking interventions. We sampled 300–1000 m2 plots using the Land Degradation Surveillance Framework across Nyagatare and Kayonza districts in Rwanda to assess key soil and land health indicators, including soil organic carbon (SOC), erosion prevalence, vegetation structure and infiltration capacity, and their interactions. SOC content decreased with increasing sand content across both sites and sampling depths and was lowest in croplands and grasslands compared to shrublands and woodlands. Stable carbon isotope values (δ13C) ranged from −15.35 ‰ to −21.34 ‰, indicating a wide range of historic and current plant communities with both C3 and C4 photosynthetic pathways. Field-saturated hydraulic conductivity (Kfs) was modeled, with a median of 76 mm h−1 in Kayonza and 62 mm h−1 in Nyagatare, respectively. Topsoil OC had a positive effect on Kfs, whereas pH, sand, and erosion had negative effects. Soil erosion was highest in plots classified as woodland and shrubland. Maps of soil erosion and SOC at 30 m resolution were produced with high accuracy and showed strong variability across the study landscapes. These data demonstrate the importance of assessing multiple biophysical properties in order to assess land degradation, including the spatial patterns of soil and land health indicators across the landscape. By understanding the dynamics of land degradation and interactions between biophysical indicators, we can better prioritize interventions that result in multiple benefits as well as assess the impacts of restoration options.