Hood Infiltrometer Research Articles

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.

Can a Change in Agriculture Management Practice Improve Soil Physical Properties

Soil conventional tillage has been associated with deterioration of its characteristics, while organic farming has been promoted as an approach to conserve a favorable soil environment. With the interest in nominating the tillage strategies without ploughing for maintaining long-term soil quality and subsequently increasing yields, this study set to identify if and how conservation tillage practices in organic management (OM) do improve soil physical properties compared to conventional management (CM). This study was conducted on matched field pairs in Baden-Württemberg, Germany. The conservation tillage treatment effects of OM (superficial tillage using chisel at 10 cm depth) was compared with conventional tillage practices CM (mouldboard ploughing at 30 cm depth). The field pairs were homogenous in most respects that would reflect tillage impacts. Measurements included soil infiltration capacity, saturated hydraulic conductivity, penetration resistance, and effective bulk density. Infiltration rate, measured using a hood infiltrometer at 10 parcels, was computed using Wooding’s analytical method, while Gardner’s equation was used to calculate the saturated hydraulic conductivity (Ks). The steady infiltration rate qs (h) was two times higher under OM than under CM with an average of 624 mm/h and 303 mm/h, respectively. Penetration resistances of OM were lower than under CM irrespective of the clay content. The degree of compactness (effective bulk density) was greater under CM than OM. That small change in soil compactness affects the water infiltration rate and the hydraulic properties rather than intrinsic soil matrix such as texture. Numerical model Hydrus-1D results were more representative for simulating the soil water transfer and hydraulic parameters under tillage changes.

Impact of land use reformation on soil hydraulic properties and recovery potential of conservation tillage in India's North-West Himalayan region

Degradation of soil hydro-physical properties resulted from inappropriate land management, require a resilient management system to check further degradation. Hence, understanding soil hydraulic properties (SHPs) of various land-use regimes may aid in the long-term management of ecologically sensitive and vulnerable agroecosystems. The study looked at influence of land-use conversion from native forest land to subsequent agricultural practices on SHPs in India's N-W Himalayan area, one of the world's most susceptible agroecosystems. Moreover, the water-conducting porosity at different pressure heads and the contribution of macro and mesopores to saturation flow were quantified. For this purpose, the infiltration rate and soil hydraulic conductivity of surface soil were investigated for sal forest, conventional tillage (CT), reduced tillage (RT), and zero tillage (ZT) using the hood infiltrometer at three pressure heads. The forest land use showed the highest value followed by ZT, RT, and CT respectively for soil hydraulic conductivity, tension and residual flux potential, flow-weighted mean pore radius, and hydraulically active porosity. Additionally, the macropores contributed 61.99–73.44 % of total water flow, while the meso-micropores contributed 26.56-38.01 % of total flow across the land uses. In the water-conducting process in all land use systems, macropore's contribution was relatively higher, which comprised only small space of total soil volume, signifies its importance. Further, scatter plot matrix depicted that, mean weighted diameter (MWD), and soil organic carbon (SOC) are dominating factors controlling hydraulic conductivity. The findings strongly suggest that, while conversion of native forest land to conventional agriculture degrades soil hydraulic characteristics, SHPs may be progressively recovered in the Himalayan region by adopting conservation agriculture strategies.

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.

Assessing the Effects of Anthropogenic Land Use on Soil Infiltration Rate in a Tropical West African Watershed (Ouriyori, Benin)

Soil infiltration at a watershed scale is important for understanding and predicting the hydrological process in soil-water-plant systems. This study investigated the effects of land use (LU) conversion on the infiltration rate in the Ouriyori watershed. To that end, in situ infiltration was carried out over the watershed under thirty-six pairs of adjacent cropland-fallow plots using the hood infiltrometer. Saturated hydraulic conductivity (Ks), soil properties, and soil classes were further compared. Results showed a high variability of Ks following the LU classes with a coefficient of variation greater than 60%. After data log transformation, the mean values of Ks showed high infiltration and ranged between 2.59 and 2.42 cm d−1, respectively, for fallow land and cropland. Thus, Ks was relatively lower in cropland compared to fallow land. Hence, the low infiltration recorded in croplands indicated the degradative impacts of unceasing tillage operations for crop production without crop residue incorporation into the soil during tillage. There was no significant difference in bulk density and soil texture in both types of land use. Considering soil classes, the highest infiltration rate was found in Ferric Luvisol and the lowest rate in Dystric Gleysol, meaning that the high infiltration observed in Ferric Luvisol was due to the abundance of soil macropores. Change in natural vegetation to croplands induced a low infiltration rate and macropore connectivity. Moreover, fallow lands tend to provide water storage capacity through the improvement of mesopores, while soil compaction through agricultural activities reduces soil porosity and therefore soil infiltration. In addition, the paired Student’s t-test performed on the transformed data was statistically significant, indicating a difference between Ks under cropland and Ks under fallow land. To improve soil and water conservation for crop production as well as for sustainable rural populations’ livelihoods in the watershed, occasional fallowing may be observed to dampen infiltration hindering soil surface conditions.

Effects of environmental factors on the influence of tillage conversion on saturated soil hydraulic conductivity obtained with different methodologies: a global meta-analysis

Abstract. The saturated hydraulic conductivity (Ksat) is a key soil hydraulic property governing agricultural production. However, the influence of the conversion from the conventional tillage (CT) to conservation tillage (CS; including no tillage, NT, and reduced tillage, RT) on the Ksat of soils is not well understood and still debated. In this study, we applied a global meta-analysis method to synthesize 227 paired observations for soil Ksat from 69 published studies and investigated factors influencing the effects of conversion to CS on Ksat. Results showed that soil layer, conservation tillage type, soil texture type, and cropping system management did not have significant effects on the influence of conversion to CS on Ksat. When the Ksat was measured by the rainfall simulator, the conversion to CS significantly (p&lt;0.05) increased the surface and subsurface soil Ksat by 41.7 % and 36.9 %, respectively. In addition, the subsurface Ksat also tended to increase under CS practices when the Ksat was measured by a tension disc infiltrometer. However, when the Ksat was measured by a hood infiltrometer, ring infiltrometer, constant/falling head, and Guelph permeameter, the conversion to CS had no significant effects on the Ksat. It is observed that, when the conversion period was less than 15 years, the Ksat under CS showed a greater increase for a longer conversion period. Climatic and topographic factors, including the mean annual temperature (MAT) and the mean annual precipitation (MAP), were statistically related to the responses of Ksat to tillage conversion at the global scale. Quadratic polynomials can describe the relationships between them. These findings suggested that quantifying the effects of tillage conversion on soil Ksat needed to consider experimental conditions, especially the measurement technique and conversion period.

Land‐use intensity and biodiversity effects on infiltration capacity and hydraulic conductivity of grassland soils in southern Germany

AbstractEvidence from experimental and established grasslands indicates that plant biodiversity can modify the water cycle. One suspected mechanism behind this is a higher infiltration capacity (νB) and hydraulic conductivity (K) of the soil on species‐rich grasslands. However, in established and agriculturally managed grasslands, biodiversity effects cannot be studied independent of land‐use effects. Therefore, we investigated in established grassland systems how land‐use intensity and associated biodiversity of plants and soil animals affect νB and K at and close to saturation. On 50 grassland plots along a land‐use intensity gradient in the Biodiversity Exploratory Schwäbische Alb, Germany, we measured νB with a hood infiltrometer at several matrix potentials and calculated the saturated and unsaturated K. We statistically analysed the relationship between νB or K and land‐use information (e.g., fertilising intensity), abiotic (e.g., soil texture) and biotic data (e.g., plant species richness, earthworm abundance). Land‐use intensity decreased and plant species richness increased νB and K, while the direction of the effects of soil animals was inconsistent. The effect of land‐use intensity on νB and K was mainly attributable to its negative effect on plant species richness. Our results demonstrate that plant species richness was a better predictor of νB and K at and close to saturation than land‐use intensity or soil physical properties in the established grassland systems of the Schwäbische Alb.

Near-saturated soil hydraulic conductivity and pore characteristics as influenced by conventional and conservation tillage practices in North-West Himalayan region, India

Tillage plays an important role in modifying soil hydraulic properties. The objective of the present study was to evaluate the effect of conservation tillage practices in a maize-wheat cropping system on near-saturated soil hydraulic properties and pore characteristics in the North-West Himalayan region, India. Three treatments viz. conventional tillage (CT), minimum tillage (MT), and zero tillage (ZT) were evaluated in terms of field saturated hydraulic conductivity (ks), unsaturated hydraulic conductivity k(h), the inverse of capillary length (α), flow-weighted mean pore radius (r0), numbers of pores per square meter (n0) and water-conducting macroporosity (Ɛ). The above hydraulic conductivity and pore characteristics were derived from steady-state water flux (q) measured using hood infiltrometer at 0, −1, and −3 cm pressure head for each treatment after seven years of establishment of this tillage experiment. Results revealed significantly (p < 0.05) higher values of ks, k(h), α, and Ɛ in ZT as compared with CT. MT had intermediate values. Higher α values suggested a greater gravity-dominated flow under ZT and MT as compared with CT. Analysis of r0 values indicated better connectivity of pores in ZT and MT as compared with CT. Macropore flow suggested that on average pore radii, > 0.50 mm conducted about 63.60, 68.01, and 75.97 % of total flow (at 0 cm pressure head) in the corresponding water-conducting macroporosity of 0.00030, 0.00044, and 0.00069 % of soil volume under CT, MT, and ZT, respectively. Overall, zero-tillage based agriculture system was found to improve near-saturated soil hydraulic properties.

Using Wastewater in Irrigation: The Effects on Infiltration Process in a Clayey Soil

Soil water infiltration is a critical process in the soil water cycle and agricultural practices, especially when wastewater is used for irrigation. Although research has been conducted to evaluate the changes in the physical and chemical characteristics of soils irrigated by treated wastewater, a quantitative analysis of the effects produced on the infiltration process is still lacking. The objective of this study is to address this issue. Field experiments previously conducted on three adjacent field plots characterized by the same clayey soil but subjected to three different irrigation treatments have been used. The three irrigation conditions were: non-irrigated (natural conditions) plot, irrigated plot with treated wastewater for two years, and irrigated plot with treated wastewater for five years. Infiltration measurements performed by the Hood infiltrometer have been used to estimate soil hydraulic properties useful to calibrate a simplified infiltration model widely used under ponding conditions, that were existing during the irrigation stage. Our simulations highlight the relevant effect of wastewater usage as an irrigation source in reducing cumulative infiltration and increasing overland flow as a result of modified hydraulic properties of soils characterized by a lower capacity of water drainage. These outcomes can provide important insights for the optimization of irrigation techniques in arid areas where the use of wastewater is often required due to the chronic shortage of freshwater.

Hydraulic Properties of a Cultivated Soil in Temperate Continental Climate Determined by Mini Disk Infiltrometer

Hydraulic conductivity at and near saturation (Ks and K(h)) are among the most important characteristics defining water behavior in soil. Characterization of possibilities, advantages and limitations of the Mini Disk infiltrometer (MDI) for Ks and K(h) determination in comparison with Hood infiltrometer (HI) was the main aim of this study. The MDI device was subjected to testing on a cultivated silty clay loam soil under three different tillage treatments; conventional, reduced and no-tillage plot. The results are based on 72 infiltration experiments carried out during four experimental phases within one year. Steady-state and transient data analysis methods were applied. K(h) values were determined for van Genuchten hydraulic parameters taken from different sources (two versions of User’s manual, Rosetta). The results show suitability of MDI to determine K(h) of tested soil; clear differences have been observed between the K(h) values measured on plots with different tillage treatment. However, these values were significantly lower (ANOVA, α = 0.05) than those measured by HI. MDI based data were reflecting seasonal changes in structure and pore-size distribution with quantification of macropore contribution to the total saturated flux. Application of K(h) MDI data for fine-textured and structural soils evaluated before 2010 should be reconsidered.

Temporal variations of the hydraulic conductivity characteristic under conventional and conservation tillage

Conservation agriculture promotes as one of its three key principles the reduction of tillage intensity to minimize soil physical disturbances. The choice of tillage system alters hydraulic conductivity at (Ks) and near saturation. Drier regions of the hydraulic conductivity characteristic (HCC) may be affected as well. Temporal variations of the HCC along with water retention characteristics of tilled soils have come into the focus of researchers in recent years. It was shown that it may be preferable to account for such variations in soil water modelling.Here, the effects of a conventional tillage (CT), reduced tillage (RT) and no tillage (NT) system on the HCC were investigated on an experimental field with a Haplic Luvisol in Eastern Germany throughout part of a winter wheat growing season. This included changes following agricultural management such as stubble breaking and seedbed preparation. Hood infiltrometer measurements were conducted in the field and transient evaporation experiments in the laboratory were performed on undisturbed soil cores to describe the HCC over a wide range of pressure heads (h) from saturation to −1000 cm (pF 3).On tilled plots, Ks and hydraulic conductivity at h = −2 cm (K−2 cm) were more variable with time than observed spatial variability. Overall, Ks was significantly (p < 0.05) higher under RT compared to NT while for CT they ranged in between. Correlation and multiple linear regression indicated a distinctly different soil structure between tilled and untilled treatments. While bulk density and macro-and mesoporosity could explain some variability in Ks and K−2 cm on CT and RT, it was meaningless for the untilled soil. A denser soil matrix on NT with few conducting macro-and biopores was attributed to those findings. Under tillage, the loosened soil matrix and decaying organic matter mixed into the topsoil likely govern water transport at and near saturation. Over the entire HCC, variability decreased with drier conditions on NT while this was less pronounced on tilled soil, especially RT, indicating that tillage may affect not only soil macroaggregates but also the soil matrix. In this specific case, variability of the HCC with time was shown to be large for tilled plots, and modeling of soil water may benefit from an explicit consideration of these changes. Contrasts in soil structure under tilled and untilled soil should also be reflected in the future development of pedotransfer functions for the prediction of (near-) saturated K. Different soil physical property predictors may be needed for a valid estimation.

Long-term effects of conventional tillage and no-tillage on saturated and near-saturated hydraulic conductivity – Can their prediction be improved by pore metrics obtained with X-ray CT?

Tillage practices have a profound impact on soil structure and soil hydrology, which may affect ecosystem functions like plant productivity. There is an ongoing debate whether a conversion from conventional tillage (CT) to no-till (NT) leads to an increase in (near-)saturated hydraulic conductivity. This is because true effects are often disguised by large spatial and temporal variability, but also by the deficiencies in the measurement technique.In this paper, we measured (near-) saturated hydraulic conductivity (Ks and K-2) in a long-term tillage trial (26 years) in Germany with three different methods: hood infiltrometer (HI) in the field, tension disc infiltrometer (TI) on undisturbed soil cores and direct simulation (DS) of water flow on X-ray CT images of macropore structure in these soil cores with a Stokes-Brinkmann solver. On average the absolute values varied by two orders of magnitude in the order TI < HI < DS with very low correlation (R2 < 0.05) between log10(Ks) measurements. The conversion from CT to NT caused an increase in bulk density, a decrease in air capacity and a small but consistent decrease in grain yields. Ks was increased with NT when measured with HI but decreased in TI and indifferent when measured with DS. This inconsistency is caused by the proportion at which large biopores that are more frequent in NT soil due to higher earthworm abundance contribute to total flow in each measurement technique. Regression analyses between pore space attributes measured with X-ray CT and Ks (and K-2) showed very strong agreement with DS values, but poorer agreement with HI and TI, suggesting that those values are afflicted with measurement artifacts like poor contact, entrapped air, different average volumes and so on.The pore metric with highest predictive power (>90%) on simulated Ks in NT soil cores was the critical pore diameter because it represents the bottleneck that restricts a large contribution to flow by elongated biopores. However, in plowed soil (CT) pore metrics that best describe flow through the loose soil matrix, like macroporosity and pore connectivity, have a higher predictive power and the critical pore diameter is rendered meaningless. The relative importance of various pore metrics as good predictors of hydraulic conductivity does not only change in a very small pressure range (Ks vs. K-2) but also between measurement techniques (HI vs. TI vs. DS). These inconsistencies raise the question if and how existing pedo-transfer functions for estimating (near-) saturated hydraulic conductivities can be extended by image-derived pore metrics in a meaningful way.

Soil hydraulic response to conservation agriculture under irrigated intensive cereal-based cropping systems in a semiarid climate

Assessment of soil hydraulic response to conservation agriculture (CA) practices may assist in better management decisions in agriculturally sensitive and environmentally fragile agroecosystems. Although, the potential of management induced temporal changes of soil hydraulic properties (SHPs) has been studied particularly in relation to tillage, few studies have evaluated combined effects of tillage, crop residue retention and cropping sequence, which are essential components of CA, on near-saturated SHPs under field conditions. The objective of this study was thus to evaluate the long-term effect after eight years of CA practices and short-term effect of crops on near-saturated soil hydraulic conductivity, k(h), and water transmission properties under irrigated intensive cereal-based cropping systems in a semiarid climate (NW Indo-Gangetic Plains, India). There were four treatments: (1) conventionally tilled rice-wheat cropping system, (2) reduced till CA-based rice-wheat-mungbean system, (3) no-till CA-based rice-wheat-mungbean system and (4) no-till CA-based maize-wheat-mungbean system. Steady state infiltration rates were obtained at four pressure heads by hood infiltrometer consecutively over two cropping seasons, i.e., during harvest season of rice/maize (October 2017) and maximum crop growth stage of wheat (February 2018). Data were analysed in terms of k(h), flow weighted mean pore radius (r0), hydraulically active porosity (ε) and threshold pore radius (rbp), a new pore measure indicative of macropore stability derived by substituting soil’s bubble pressure in the capillary equation. Our results showed that no till-based CA enhanced k(h) as compared with conventional cultivation practice. Although the interaction effect of treatments with crop seasons were statistically non-significant (p < 0.05), considerable changes of soil hydraulic properties were observed over crop seasons under CA treatments. Transition from maize to wheat in the crop sequence reduced k(h) values by about 55, 44, 34 and 40% at pressure heads of 0, −1, −2 and −4 cm, respectively. In contrast, transition from rice to wheat in rice-based no till CA increased k(h) values by 129, 164, 124 and 24% in the same pressure head ranges. Irrespective of crop seasons, higher k(h) was observed under CA due to formation of macropores with better continuity, greater size and numbers as compared with conventional intensive tillage treatment. Reduced till-based CA showed an intermediate effect with respect to the different soil hydraulic characteristics in both crop seasons. Moreover, higher r0 values were observed for a given k(h) for CA treatments suggesting that interaggregate pores are the dominant pathways of infiltration flux in CA. A relatively smaller temporal variation of rbp was indicative of a more stable macropore system established by rice-based CA as compared with maize-based CA. CA also enhanced hydraulically active macropores as compared with intensive tillage based conventional agriculture. Overall, the results revealed that the potential impacts of CA on near-saturated SHPs are largely governed by characteristic changes in macro- and interaggregate pores.

Agricultural Expansion-Induced Infiltration Rate Change in a West African Tropical Catchment

Land use and land cover in the Dano catchment is characterized by a rapid conversion from seminatural vegetation (fallow) to agriculture (cropland). The study compares both the saturated (Ks) and the unsaturated (Kh) hydraulic conductivities under cropland and fallow in the catchment to gain insights into the effect of the current land use on soil water dynamics. Hydraulic conductivity was measured under forty-two (42) pairs of adjacent cropland-fallow plots using a Hood infiltrometer. Ks, Kh, bulk density, and soil texture were further compared using a paired two-tailed Student’s t-test (p=0.05). The results showed that both Ks and Kh are highly variable irrespective of the land use type (coefficient of variation &gt; 100%). The results also showed that Ks was significantly higher (1.16-fold on average) under fallow compared to cropland. As for Kh, the results showed that, from −2 cm to zero tension heads (h), Kh under cropland and fallow is not significantly different; however, as the supplied tension decreases up to the saturation state, Kh under fallow becomes statistically higher compared to cropland. No significant difference was found between soil textures and bulk density under cropland and fallow meaning that the observed differences of Ks and Kh under cropland and fallow were caused by land use and not preexisting difference in texture. These results suggest an increasing risk of erosion, soil fertility reduction, and flood in the catchment because of agricultural land expansion.

Combination of Measurement Methods for a Wide-Range Description of Hydraulic Soil Properties

Established measurement methods for hydraulic soil properties cover a limited soil moisture range. Simulations of soil water dynamics based on such observations are therefore rarely representative for all conditions from saturation to drought. Recent technical developments facilitate efficient and cheap collecting of soil water characteristics data, but the quantitative benefit of extended measurement campaigns has not been adequately tested yet. In this study, a combination of four methods to measure water retention and hydraulic conductivity at different moisture ranges was applied. Evaporation method, dewpoint psychrometry, hood infiltrometer experiments, and falling head method for saturated conductivity were conducted at two experimental sites in eastern Austria. Effects of including the particular methods in the measurement strategy were examined by visual evaluation and a 1D-modelling sensitivity study including drainage, infiltration and drought conditions. The evaporation method was considered essential due to its broad measurement range both for water retention and hydraulic conductivity. In addition to that, the highest effect on simulated water balance components was induced by the inclusion of separate conductivity measurements near saturation. Water content after three days of drainage was 15 percent higher and the transpiration rate in a drought period was 22 percent higher without near-saturated conductivity measurements. Based on relative comparisons between different combinations, we suggested combining evaporation method and hood infiltrometer experiments as the basis for representative predictions of soil water dynamics.

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.

Plant species diversity affects infiltration capacity in an experimental grassland through changes in soil properties

Soil hydraulic properties drive water distribution and availability in soil. There exists limited knowledge of how plant species diversity might influence soil hydraulic properties. We quantified the change in infiltration capacity affected by soil structural variables (soil bulk density, porosity and organic carbon content) along a gradient of soil texture, plant species richness (1, 2, 4, 8, 16 and 60) and functional group composition (grasses, legumes, small herbs, tall herbs). We conducted two infiltration measurement campaigns (May and October 2012) using a hood infiltrometer. Plant species richness significantly increased infiltration capacity in the studied grasslands. Both soil porosity (or inversely bulk density) and organic carbon played an important role in mediating the plant species richness effect. Soil texture did not correlate with infiltration capacity. In spring 2012, earthworm biomass increased infiltration capacity, but this effect could not be attributed to changes in soil structural variables. We experimentally identified important ecological drivers of infiltration capacity, suggesting complex interactions between plant species richness, earthworms, and soil structural variables, while showing little impact of soil texture. Changes in plant species richness may thus have significant effects on soil hydraulic properties with potential consequences for surface run-off and soil erosion.

Field study on macropore flow in typical Black soils of northeast China

Jiang, X., Wang, E., Chen, X., Xia, X. and Shi, C. 2012. Field study on macropore flow in typical Black soils of northeast China. Can. J. Soil Sci. 92: 559-566. Macropores are important preferential pathways for the transport of water and contaminants in soil. A series of hood infiltration experiments were conducted using dye tracers (Brilliant Blue FCF) at pressure heads of -5.0 cm, -3.0 cm, and -1.0 cm at a conventional tilled site on Keshan Farm, northeast China. The study objective was to combine the test method of dye tracing with a hood infiltrometer to analyze soil subjected to conventional tillage methods. Dye staining patterns and macroporous networks were analyzed by excavation, mapping, photography, and image analysis. Results showed that macropore flow began very near the soil surface under three pressures heads of -5.0 cm, -3.0 cm and -1.0 cm, and that a pressure head of -1.0 cm resulted in more lateral flow. Soil deeper than 40.0 cm was less disturbed, which resulted in good continuity. At p...

Field study on macropore flow in typical Black soils of northeast China

Jiang, X., Wang, E., Chen, X., Xia, X. and Shi, C. 2012. Field study on macropore flow in typical Black soils of northeast China. Can. J. Soil Sci. 92: 559–566. Macropores are important preferential pathways for the transport of water and contaminants in soil. A series of hood infiltration experiments were conducted using dye tracers (Brilliant Blue FCF) at pressure heads of −5.0 cm, −3.0 cm, and −1.0 cm at a conventional tilled site on Keshan Farm, northeast China. The study objective was to combine the test method of dye tracing with a hood infiltrometer to analyze soil subjected to conventional tillage methods. Dye staining patterns and macroporous networks were analyzed by excavation, mapping, photography, and image analysis. Results showed that macropore flow began very near the soil surface under three pressures heads of −5.0 cm, −3.0 cm and −1.0 cm, and that a pressure head of −1.0 cm resulted in more lateral flow. Soil deeper than 40.0 cm was less disturbed, which resulted in good continuity. At pressure heads of −5.0, −3.0 and −1.0 cm, the dye staining technique resulted in maximum stained depths of 74.3, 60.7 and 64.7 cm, respectively, with maximum stained widths of 41.6, 41.5 and 47.9 cm, respectively (at depths from 14.0 to 28.0 cm). Soil under a pressure head of −1.0 cm had the highest initial and steady infiltration rates of 13.0 and 4.1 mm min−1, respectively. Soil under a pressure head of −5.0 cm showed the most connectivity. To distinguish the macropores from the interaction area of macropore flow and the soil matrix surrounding the macropores, the stained area was separated into different classes based on dye color.

Land-use effects on flood generation – considering soil hydraulic measurements in modelling

Abstract. The investigation in the catchment of the Mulde (51°0'55" N, 13°15'54" E Saxony, Germany) researches the effect of afforestation measures on the soil hydraulic properties. The concept of a "false chronosequence" was used to quantify the time-dependent dynamical character of the forest impact. Four adjacent plots were identified at a test location with comparable pedological start conditions and a set of tree stands of different age: (1) arable field (initial state); (2) 6-year-old afforestation; (3) 50-year-old afforestation; (4) ancient natural forest ("target" stocking). Water retention curves and unsaturated conductivities were analysed in the lab. In the field, the undisturbed infiltration capacities were measured quantitatively (hood infiltrometer) and qualitatively (brilliant blue tracer). Pronounced differences between all 4 plots were detected. The afforestation causes an increased infiltration and soil water retention potential. Especially the topsoil layers showed a distinct increase in conductivity and portion of coarse/middle pores. The influence of these changes on rainfall-runoff calculations at the test location was analysed in this study.