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The soil water retention curve (SWRC) is a key soil property required for predicting basic hydrological processes. SWRC is often obtained in laboratory with non-harmonized methods. Moreover, procedures associated to each method are not standardized. This can induce a lack of reproducibility between laboratories using different methods and procedures or using the same methods with different procedures. The goal of this study was to estimate the inter/intralaboratory variability of the measurement of the wet part (from 10 to 300 hPa) of the SWRC. An interlaboratory comparison was conducted between 14 laboratories, using artificially constructed, porous and structured samples as references. The bulk densities of samples were different at the very beginning of the experiment. This resulted in a variability of retention properties between the samples, which was estimated by a linear mixed model with a "sample" random effect. Our estimate of inter/intralaboratory variability was therefore not affected by intrinsic differences between samples. The greatest portion of the differences in the measurement of SWRCs was due to interlaboratory variability. The intralaboratory variability was highly variable depending on the laboratory. Some laboratories successfully reproduced the same SWRC on the same sample, while others did not. The mean intralaboratory variability over all laboratories was smaller than the mean interlaboratory variability. A possible explanation for these results is that all laboratories used slightly different methods and procedures. We believe that this result may be of great importance regarding the quality of SWRC databases built by pooling SWRCs obtained in different laboratories. The quality of pedotransfer functions or maps that might be derived is probably hampered by this inter-/intralaboratory variability. The way forward is that measurement procedures of the SWRC need to be harmonized and standardized.

Biochar application to a structurally poor tropical soil could potentially alter the soil’s aggregate strength and hydraulic properties. However, very few field studies have investigated the impact of biochar on the aggregate strength and hydraulic properties of tropical soils. A field experiment was therefore conducted to investigate the short-term effects of rice straw biochar on soil hydraulic properties and aggregate stability of an Acrisol in Ghana. The biochar was broadcast at rates of 10 t ha−1 and 20 t ha−1 as single applications that were incorporated into the top 20 cm of the soil using a spade and then the soil was levelled using a rake. Field saturated hydraulic conductivity and laboratory-measured soil water retention, aggregate stability and water-repellency were determined 10 months after the biochar application. Biochar increased aggregate stability against fast wetting by up to 33% compared to the control. This implies that biochar might improve the stability of aggregate of an Acrisol against slaking and erosivity of heavy rainfall. However, aggregate stability against slow wetting and mechanical breakdown after pre-wetting were unaffected by the biochar. Biochar did not affect field saturated hydraulic conductivity, water retention characteristics and water-repellency. Further field studies on weathered tropical soils with low native soil organic matter is recommended to elucidate the effect of repeated biochar addition on soil hydraulic and aggregate characteristics.

The effects of wind-driven rain (WDR) on sand detachment were studied under various raindrop obliquities. Results suggested a significant reduction in compressive stress on sand surfaces for a two-dimensional experimental set-up in a wind tunnel. During experiments, sand particles in splash cups were exposed to both wind-free rain (WFR) and WDR driven by horizontal winds of 6.4, 8.9 and 12.8 m s(-1) and rainfall intensities of 50, 60, 75 and 90-mm h(-1) to assess the sand detachment rate (D, in g m(-2) s(-1)). The effects of sand moisture state (dry and wet) on the detachment of different-sized particles (0.20-0.50 and 0.50-2.00 mm, respectively) were also tested. Factorial analysis of variance showed that shear and compressive stress components evaluated by horizontal and vertical kinetic energy flux terms (KEx and KEy, respectively, in J m(-2) s(-1)) along with their vector sum (KEr, in J m(-2) s(-1)) explained the variation in D. Neither sand size nor sand moisture was statistically significant alone although binary interactions of KEr, KEx and KEy with the sand size and three-way interaction of KEx, sand size and moisture were statistically significant. These results can be explained by size-dependent variation in sand compressibility and surface friction related to the total stress field developed by a given partition of shear and compressive stresses of wind-driven oblique raindrops (KEx/KEy). Further analysis of the variation of the unit sand detachment rate (D-u = D/KEr = g J(-1)) with rain inclination (alpha, in degrees) better revealed the effect of WDR obliquity on D-u that further changed with sand size class and moisture state. Finally, the difference in the resulting stress field differentiable by the oblique raindrop trajectories of the experiment over sand surface significantly affected the non-cohesive particle detachment rates, to some extent interacted with size-dependent compressibility and interface shear strength of sand grains.

Conservation agriculture (CA) systems represent a set of three soil management principles: minimarbance, permanent soil cover and crop rotations - whereas the CA-based systems in this study add the bed and furrow tillage techniques as integral elements of CA. Studies on the effects of long-term CA-based systems on soil health and crop productivity are rare globally, particularly in Ethiopia. This study aimed at investigating the long-term (2005-2013) influence of CA-based systems on soil health and crop productivity in northern Ethiopia. The treatments we used include two types of CA-based systems (permanent raised bed PRB and contour furrowing CF) and conventional tillage (CT) arranged in a randomized complete block design. Soil samples were collected at 0-10 cm soil depth to assess soil health. Piecewise structural equation modeling (PSEM) was used to analyze linkages between management practices, soil health and crop productivity. Arbuscular mycorrhizal fungi spore abundance and root colonization was higher in PRB followed by CF compared to CT (p < 0.05). Significantly different soil N of 1.4 and 0.9 g kg(-1) and available P of 6.7 and 4.1 ppm were recorded for PRB and CT, respectively. Higher straw and grain yield of 12 and 4.3, 10 and 3.5, 8 and 2.8 t ha(-1) were recorded for PRB, CF and CT, respectively. Outputs of the PSEM highlighted two pathways in which CA-based systems contributed to improved productivity: (a) via higher density of bacteria and improved hydraulic conductivity, and (b) via higher density of fungi and increase soil organic carbon content in the topsoil. The study concludes that CA-based systems have the potential to improve crop productivity through improved soil health.

Dust emission from wind erosion is a widespread phenomenon in arid and semi-arid areas having considerable implications for ecosystems and human well-being. However, few studies have examined the efficiency of biochar amended to soil on wind erosion control. Aimed at studying the effect of biochar on resistance of soils against wind erosion, a wind tunnel experiment was conducted. We tested (a) soils amended with hard waste walnut wood biochar and soft maize cob biochar, and (b) soils amended with powdery waste wood and powdery maize cob, and compared them with (c) non-treated soil, in their susceptibility to wind erosion and also the additional effect of various patterns of vegetation cover. Amending soil with biochar and powdery material did significantly increase their resilience to wind erosion because of increased soil aggregation. In comparison with the non-treated control, the mass flux of un-vegetated soil reduced from 4.42 to 1.86 g m(-2)s(-1)for the waste walnut wood biochar, from 4.28 to 1.50 g m(-2)s(-1)for maize cob biochar, from 4.11 to 1.44 g m(-2)s(-1)for powdery maize cob and from 3.97 to 1.14 g m(-2)s(-1)for powdery waste walnut wood. When combining amendments with vegetation, there was still a substantial improvement, though the soil treatments responded differently in terms of soil loss to different vegetation patterns. A single row vegetation pattern had the highest mass flux, while a zigzag vegetation pattern had the lowest. In conclusion, waste wood or maize cobs, whether applied as biochar or as powdery material, are able to fix soil and reduce wind erosion.

Understand the mechanism governing degradation of riparian forests in response to damming streams is needed for a comprehensive impact assessment of dams in relation to protection of river ecosystems. However, the ascription of riparian forest degradation to the hydrological changes induced by dams lacks of direct proof and the hypothesis that dam construction alters the water use strategy of riparian trees is yet to be tested. In this study, the water sources of riparian trees grown upstream and downstream of dams at SW China, were investigated by dual isotopes and a Bayesian model. We observed that xylem water in downstream Populus adenopoda had significantly lower line-conditioned excess values than upstream trees. The water source of upstream trees was barely subjected to evaporation. Upstream mature and young P. adenopoda trees both acquired more streamwater (47.2 +/- 9.8% and 44.8 +/- 7.9%) than groundwater (28.2 +/- 4.4% and 29.2 +/- 3.5%) or soil water (24.5 +/- 5.6% and 26.0 +/- 4.9%). Downstream mature and young P. adenopoda trees both largely used soil water (49.0 +/- 11.6% and 53.0 +/- 6.2%) as main water source. In contrast, Pterocarya stenoptera highly depended on streamwater, regardless of size and location, implying that damming had little effect on this species. Damming streams may increase water competition among downstream riparian trees, which could explain declines in growth rate, canopy dieback, tree death, and eventually downstream land degradation. We believe that this study is of significant value for research into riparian forest degradation resulting from hydrological changes, and in particular to apprehend the impact of small dams, which has barely been studied.

Visual Evaluation of Soil Structure (VESS) methods receive increasing attention and are gaining popularity. Since in modern agriculture, soil structure degradation becomes very common, it is essential to protect and improve soil structure quality. Methods that enable its straightforward monitoring are therefore needed. Numerous visual soil evaluation techniques that serve this purpose exist, and are varying in objective, evaluation depth (topsoil/subsoil), evaluation method, number of criteria assessed and their final scoring. In this study, we mainly focus on three VESS methods, two of which were employed in the field along a profile wall (Visual Evaluation of Subsoil Structure, SubVESS, and Double Spade VESS method, DSVESS), and one in the laboratory on soil cores (CoreVESS). The main aim of this research was to test and compare these VESS-based methods in terms of their feasibility and repeatability in detecting soil structure degradation in the topsoil and subsoil. Sixteen cropped fields were chosen in Belgium covering six of seven major soil texture classes according to the Belgian soil textural triangle (i.e., sand, loamy sand, light sandy loam, silt loam, clay, and heavy clay). SubVESS and DSVESS were performed in the same pits until 80 cm and 40 cm, respectively. Soil cores for CoreVESS and for the determination of soil quality indicators (SQi) with conventional laboratory methods were taken from three layers, that is, the ploughed topsoil (∼10–∼20 cm, “TOP”), the compacted subsoil (∼30–∼40 cm, “CSUB”), and the deeper subsoil (∼60–∼70 cm, “SUB”), totalling 96 horizons. While SubVESS and CoreVESS were originally developed to evaluate subsoil and topsoil, respectively, they were thus used here beyond those zones. Moreover, all sampling and field evaluation was done at two positions per field - the more compacted headland and the less compacted in-field zone. It was shown that the soil quality (Sq) scores assigned to the cores with CoreVESS were not significantly influenced by operators with different backgrounds but all having received basic VESS training. When comparing field and laboratory results, positive relationships were found between Sq scores of SubVESS, DSVESS and CoreVESS. All VESS methods were able to assign significantly better soil quality (lower scores) at in-field positions (IN-FIELD) as compared to headland positions (HEAD), and significantly lower quality (higher scores) to CSUB layers than to the other two layers. Laboratory-derived SQi values presented a similar trend, with CSUB layers always indicating worse situations. There were good significant relationships between the SQi values and the different VESS-based Sq scores as well, with DSVESS showing the best correlations among the three VESS methods. The study thus confirmed that the different VESS methods all have a potential for monitoring soil structure quality in a fast, cheap, intuitive and practical way, although they all have their own advantages and disadvantages. Additionally, those methods that were employed at depths other than those for which they were developed did perform well.

Soil structural degradation has become very common and leads to a serious decline in soil health. Improving or maintaining soil structure is key to build resilience against drought and flooding, and thus contributes to assuring food and water security. Quantification of soil structural quality is usually accomplished by traditional laboratory-based methods, which are time-, labour- and money-consuming. Visual soil evaluation and examination methods comprise rapid and simple tests that offer a numeric semi-quantitative assessment of soil structure. The common criteria are aggregate size and shape, ease of break or rupture resistance, and inter- or intra-aggregate porosity. In this study, the CoreVESS method, a variant of the Visual Evaluation of Soil Structure (VESS) method originally developed for topsoil assessment, was applied on 250 cm3 undisturbed soil core samples. Resulting soil quality scores (Sq, ranging between 1, good, and 5, poor) were compared with soil quality indicators (SQi) derived from traditional quantitative methods of soil structure analysis. Tested SQi's included penetration resistance, bulk density, soil hydraulic properties, soil organic carbon and texture (percentage of clay, silt and sand). The objective of the study was to assess and quantify the state of soil structural degradation induced by agricultural operations using a suite of methods of analysis at a regional scale, with a special focus on CoreVESS. Soil core samples were taken in Belgium from 42 cropped fields, at two positions (headland and in-field zone) and from three layers, notably the ploughed topsoil (TOP, 10–20 cm), the compacted subsoil (CSUB, 30–40 cm) and the deeper subsoil (SUB, 60–70 cm), totalling the sample horizons to 252. Test and sampling sites comprised all major soil texture classes within the Belgian soil textural triangle and varied from sand to heavy clay. In-field positions (IN-FIELD) showed significantly better coreVESS-based Sq scores as compared to headland positions (HEAD), with the CSUB layers always exhibiting significantly lower quality than the other two layers. Laboratory-derived soil quality indicator (SQi) values portrayed the same trend, with CSUB layers always indicating the poorest soil quality. Significant differences in SQi's were also found between soils of acceptable (Sq ≤ 3) and degraded (Sq > 3) structure. Likewise, grouping soils into the same categories resulted in significant differences in the soil water retention and hydraulic conductivity curves in their wet ranges. There were good significant relationships between the SQi values and CoreVESS-based Sq scores, with for example Pearson R correlation coefficients of 0.64 for both penetration resistance and bulk density. Also, Sq scores related well with an SQi-based soil quality index (SQI) value averaged per layer and texture class (Pearson R of 0.60). The study confirmed that agricultural operations and their intensity clearly affect soil structural quality across various soil textures, with CoreVESS being as responsive to variation in soil structure quality as traditional quantitative methods, even when applied in the subsoil. VESS methods thus have a potential for monitoring soil structural quality over a variety of textures in a rapid, intuitive, practical and cheap way, as an alternative for or being complementary to more expensive labour-intensive traditional quantitative methods.

Precompression stress (sigma(p)) is commonly used as an indicator for the load carrying capacity of a soil and its stress history. Several calculation methods have been proposed to determine sigma(p), but they have proven to be not interchangeable. The aim of this study was to perform a functional evaluation of seven existing methods to test which method would be most recommended to assess soil strength in cultivated fields. This was achieved by investigating the relation of the obtained sigma(p) of undisturbed soil samples to other soil properties and stress history. Additionally, the robustness of the methods was evaluated by checking their sensitivity to perturbation of the measured strains. The two most commonly used methods, the Casagrande method and Gompertz model fit method, were found to be the least suitable to calculate sigma(p). These methods lack robustness and do not yield a significant relation with the relevant soil properties or stress history. Better results were obtained with Intersecting linear regressions or at the inflection point of a fourth-degree polynomial.

Soil compaction is a serious threat to agricultural production because of an expanding agricultural mechanization. Conservation tillage and use of pioneer plants can be an environmentally solution to alleviate the adverse effects of soil compaction. Root penetration into compacted soil of two winter cover crops with different rooting patterns, i.e. tap-rooted white mustard (Sinapis alba L.), and fibrous-rooted winter rye (Secale cereal L.), and of maize (Zea mays L.) in the consecutive growing season was assessed. Additionally, the effects of two spring tillage methods were evaluated, i.e. strip tillage and intensive tillage (by mouldboard ploughing). Winter rye showed significantly higher root penetration than white mustard in the top 15 cm, while an opposite trend was observed at 20–45 cm depth. After one season, maize root penetration was significantly greater following white mustard than winter rye at 30–40 cm depth. Strip tillage, like intensive tillage, could sufficiently loosen soil for adequate maize growth even though maize root distribution was restricted to tilled rows in contrast with intensive tillage. In conclusion, white mustard already showed positive short-term effects on maize growth, whereas strip tillage did not negatively affect it. Combining both is a viable option to reduce the negative impact of soil compaction on maize growth.

The saturated hydraulic conductivity ( K s ) is considered to be one of the main soil hydraulic properties to simulate water transport in the vadose zone, yet it is notoriously difficult to assess due to its large field-scale variability and sensitivity to preferential flow paths. With the increasing availability of convenient methods to measure the unsaturated hydraulic conductivity ( K u ), the additional value of measuring K s could be questioned. This study investigates the relevance of measuring K s in two ways. Firstly, a sensitivity analysis was performed to evaluate which part of the hydraulic conductivity curve impacts the simulation of unsaturated water transport most. It was found that hydraulic conductivity curve between −10 cm and −1000 cm matric head was affecting the simulation more than at saturation. Secondly, a functional evaluation was performed by simulating water flow in six test fields according to three scenarios, in which the hydraulic properties were determined with the measured K s and/or K u . The simulation of saturation degree at three depths was the least accurate in the scenario where only K s was measured. Remarkably, the most accurate simulation was found in the scenario with only the measured K u . According to these results, measuring K u would be of greater importance than measuring K s for the simulation of water flow in the vadose zone.

Conservation Agriculture (CA) and Integrated Soil Fertility Management (ISFM) have been promoted in Sub Saharan Africa as a means to improve soil quality. A four season research (March, 2017 to March, 2019) was conducted to evaluate CA-based treatment, no tillage with residue retention (NTR), ISFM-based treatment, conventional tillage with use of manure (CTM), a combination of CA + ISFM, no tillage with residue retention and use of manure (NTRM) and a control, (C) on soil quality attributes. In the two locations (sub-humid and semi-arid) the effect of soil fertility gradients (high and low) were considered. Trials were set out using a one farm one replicate randomized design. In either high or low fertility fields, soil chemical and physical properties were significantly different between the control and NTR, CTM and NTRM with no significant differences between NTR, CTM and NTRM. SOC was higher under NTR and NTRM practices, which consequently had higher hydraulic conductivity, air permeability, mean weight diameter and available phosphorus. For all the treatments and in both locations, the low fertility fields had significantly lower agronomic use efficiency (AUE) compared to the high fertility fields. In both soil types, plant available water capacity and relative water capacity values were below the recommended thresholds indicating low soil water uptake, suboptimal microbial activity and consequently low nutrient uptake which explains the observed low AUE.

Although it has been proven to be of considerable importance, it remains unclear how to model the effect of traction on soil compaction. This study used multiple approaches to simulate the stress under an active wheel with the pseudo-continuous Söhne model, and compared it to a discrete element method (DEM) model of the same scenario. It was found that the differences in normal horizontal stress (σy) due to these different boundary conditions in the Söhne model were limited. According to these simulations, the effect on normal vertical stress (σz) was negligible. This was in contrast with the DEM simulations, where the impact of traction on σy was also stronger and less shallow. Advanced numerical models can be used to gain insight in the importance of traction, and could be used to improve the boundary condition of the Söhne model. However, further experimental validation is needed.

Crop production in Sub-Saharan Africa (SSA) is constrained by rainfall variability and declining soil fertility. This has over time led to a decrease in crop yield, among them also maize. This decrease is also experienced in the sub-humid and semi-arid locations of Kenya. Among the commonly used soil and water management practices in SSA are Conservation Agriculture (CA) and integrated soil fertility management (ISFM). Crop response to these management practices is influenced by the existence of soil fertility gradients which are common among smallholder farmers. This paper presents results from a study done in the sub-humid and semi-arid location of Kenya, focusing on the effects of CA- and/or ISFM-based practices on maize yield. Trials were set out on farms within the two locations using a one farm one replicate randomized design. In each farm, CA-based treatment, no tillage with residue retention (NTR), ISFM-based treatment, conventional tillage with use of manure (CTM), a combination of CA + ISFM, no tillage with residue retention and use of manure (NTRM) and a control, (C) were laid down on fields representing high and low fertility soils. The trials started in the long rains of 2017 (LR2017) running for four seasons i.e., LR2017, short rains 2017 (SR2017), long rains 2018 (LR2018) and short rains 2018 (SR2018). Soil water content (SWC) and nitrogen use efficiency (NUE) were also monitored and evaluated. In either high or low fertility fields, maize grain yield was significantly different between the control and both NTR, CTM and NTRM with no significant differences between NTR, CTM and NTRM. Maize grain yield increase compared to the control was highest under ISFM in the low fertility fields in both locations and all seasons. For example, during the last season, SR2018, NTR, CTM and NTRM significantly increased maize grain yield by 136 %, 297 %, and 208 %, respectively, compared to the control, in the low fertility fields of sub-humid Kibugu. In the semi-arid Machang’a, the increase by NTR, CTM and NTRM, respectively, in the low fertility fields was 146 %, 379 % and 183 % for SR2018. This was linked to the tendency of ISFM to improve crop yield in the short run. For both locations, SWC and NUE were highest under NTR. In the sub-humid Kibugu, during SR2018, at the grain filling stage, 78 days after sowing, SWC under NTR, CTM and NTRM was higher by 16 %, 9 % and 20 %, respectively, compared to the control. Also at 78 days after sowing, in the semi-arid Machang’a, SWC was 18 %, 7 % and 15 % significantly higher under NTR, CTM and NTRM, respectively, compared to the control. The higher SWC observed under NTR and NTRM was related to no tillage with residue retention while under CTM it was related to improved soil organic matter through manure addition. NUE, on the other hand, was 26 % and 23 % in Kibugu and Machang’a, respectively, and lowest under the combined practice (NTRM), i.e., 19 % and 15 % in Kibugu and Machang’a, respectively. The high NUE under CA was attributed to the placement of urea in the planting holes while maintaining residue on the soil surface. The low NUE under NTRM was linked to fertilizer N immobilization. Lastly, from the biomass yield, our study showed that monocrop maize under NTR requires a kick-starting by an ISFM-based practice in the low fertility fields of the semi-arid region.

To assess recharge through floodwater spreading, three wells, approx. 30 m deep, were dug in a 35-year-old basin in southern Iran. Hydraulic parameters of the layers were measured. One well was equipped with pre-calibrated time domain reflectometry (TDR) sensors. The soil moisture was measured continuously before and after events. Rainfall, ponding depth and the duration of the flooding events were also measured. Recharge was assessed by the soil water balance method, and by calibrated (inverse solution) HYDRUS-1D. The results show that the 15 wetting front was interrupted at a layer with fine soil accumulation over a coarse layer at the depth of approx. 4 m. This seemed to occur due to fingering flow. Estimation of recharge by the soil water balance and modelling approaches showed a downward water flux of 55 and 57% of impounded floodwater, respectively.

The objective of this study was to evaluate the use of chemical and physical fractions of soil organicmatter (SOM), rather than SOM per se, as indicators of soil physical quality (SPQ) based on theireffect on aggregate stability (AS). Chemically extracted humic and fulvic acids (HA and FA) wereused as chemical fractions, and heavy and light fractions (HF and LF) obtained by density separationas physical fractions. The analyses were conducted on medium-textured soils from tropical andtemperate regions under cropland and pasture. Results show that soil organic carbon (SOC), SOMfractions and AS appear to be affected by land use regardless of the origin of the soils. A generalseparation of structurally stable and unstable soils between samples of large and small SOC content,respectively, was observed. SOM fractions did not show a better relationship with AS than SOC perse. In both geographical regions, soils under cropland showed the smallest content of SOC, HA andcarbon concentration in LF and HF, and the largest HF/LF ratio (proportion of the HF and LF inpercent by mass of bulk soil). With significant associations between AS and SOC content (0.79**),FA/SOC (r = 0.83**), HA/FA (r = 0.58**), carbon concentration of LF (r = 0.69**) and HF(r = 0.70**) and HF/LF ratio (r = 0.80**), cropland showed lowest AS. These associations indicatethat SOM fractions provide information about differences in SOM quality in relation to AS and SPQof soils from tropical and temperate regions under cropland and pasture.

The deep percolation and actual evapotranspiration from flood irrigation in tropical floodplains were predicted using a numerical model, Hydrus-1D, and a bucket type water balance model. Field experiments were conducted on onion and maize crops grown from December 2015 to May 2016 in small irrigation schemes found in the Lake Tana floodplains of Ethiopia. Experimental fields were selected along a topographic transect to account for soil and groundwater variability. Irrigation volumes were measured using V-notches and irrigation depths (400–550 mm) were calculated, and daily groundwater levels were monitored manually from piezometers installed in the fields. The soil profiles were described at each field and physical properties (texture, FC, PWP, BD, and OM) were measured at each horizon which were used to derive model input parameters. Soil hydraulic properties (residual and saturated moisture content, saturated hydraulic conductivity, parameters related to: pore size distribution n, air entry α and pore connectivity l) were derived using KNN pedotransfer functions for tropical soils and fitted using Retention Curve Program for Unsaturated Soils, RETC. The seasonal actual evapotranspiration estimated by Hydrus and water balance models ranged from 320 to 360 mm for onion and from 400 to 470 mm for maize. The seasonal deep percolation estimated from both models was 12–41% of applied irrigation and with this flood irrigation management; the deep percolation is very high. Implementing precise irrigation and water saving practices that minimize deep percolation and unproductive excessive consumptive use are required to achieve the growing food demand with the available water. When less detailed information is available, the water balance model can be an alternative to predict deep percolation and actual evapotranspiration.

Soil quality is indicated by the interaction of physical, chemical and biological soil properties. The importance of physical properties, for example soil structure, lies in the fact that they enhance chemical and biological soil functions. Consequently, periodic assessment of structural quality is an important aspect of soil quality management. Quantitative soil properties can be used as indirect indicator parameters for soil structural changes. However, measuring these properties is not applicable, especially for smallholder farmers who cannot afford to pay for laboratory tests. This study contributes to the validation of visual field assessments by comparing the performance of such methods on ‘tropical’ soils. The study was conducted across two regions with contrasting soil types and land use, in the sub-humid with clay Nitiosl and semi-arid with sandy loam Cambisol locations of Kenya. At both locations, visual methods were tested on soils under cropland and under natural forests (NF). Under the cropland, evaluation sites were selected from researcher and farmer managed sites. Visual scores from visual soil assessment (VSA), visual evaluation of soil structure (VESS) and visual evaluation of soil structure using the core (coreVESS) were correlated with soil physical and chemical properties measured in the laboratory. Under the clay Nitisol, absolute values of Pearson r between VSA scores and laboratory measured soil properties ranged from 0.84 to 0.54, for VESS, they varied between 0.75 and 0.37 while for coreVESS, they ranged from 0.84 to 0.60. For the sandy loam Cambisol, absolute Pearson r values between laboratory measured soil properties and VSA scores ranged from 0.83 to 0.29, the r values were between 0.88 and 0.45 for VESS and between 0.81 and 0.40 for coreVESS. From the obtained correlations, we concluded that the visual methods tested are capable of distinguishing structural quality due to different land use and are therefore suitable for assessing soil structural quality of tropical soils in Africa. Management thresholds were determined using bulk density (BD). The target value for good soil quality (Sq

Proper sets of soil hydraulic parameters are important for modeling water flow and solute transport. Using field saline water and laboratory tap water, this study systematically analyzed and compared laboratory saturated hydraulic conductivity, Kls and soil water retention curve, SWRC of saline soil within three soil multi-layered profiles to find out the adequate initial hydraulic parameter set of a hydrological model. Falling and constant head methods were applied on three undisturbed samples per pedogenic horizon. SWRC were established on the same samples, using both saline and tap water. Results showed the spatial variability of hydraulic properties in vertical and horizontal dimensions when comparing soil profiles' properties. The constant head method with saline water resulted in the highest Kls values followed by the falling head method with saline water, the constant head method with fresh water, and the falling head method with fresh water. The differences in Kls were up to two orders of magnitude when comparing all datasets. Fresh water reduced soil water retention significantly. A significant correlation between the hydraulic properties and some physical and chemical properties suggests that the effects of soil texture, structure, calcium carbonate and gypsum content, and CEC (clay mineralogy) were larger than those of salt content. The change in hydraulic properties and the dependency on the procedure use may be attributed to aggregate breakdown and plugging of macropores, clay heterogeneity and dispersion, calcium carbonate and gypsum dissolution, all damaging soil structure. Simulation runs illustrated that hydraulic properties obtained with saline water resulted in better model performance than when using the conventional procedures with fresh/tap water. A proper set of initial hydraulic parameter values is an important step in model calibration and thus must be characterized correctly. Therefore, to hydraulically characterize saline soil, procedures should be standardized. Moreover, the approach and results of this study may provide a reference for characterization of soil hydraulic properties of saline and sodic soils effectively.

This study aims to assess how responsive visual examination methods are to the effect of land use on soil structural quality (SSQ), and whether they are sensitive enough to detect significant changes on SSQ over a given sampling interval. The visual soil assessment (VSA), the visual evaluation of soil structure (VESS), the visual assessment of aggregate stability (VAAS) and the visual type of aggregates index (Tyagg) were used to evaluate the SSQ of a sandy loam and a silt loam soil. The land uses comprised cropland (CP) and grassland (PP). The survey was conducted twice in an agricultural cycle (in August and November). Results showed that VESS and Tyagg were in agreement with soil physical parameters when evaluating structural quality of a sandy loam, in contrast to VSA and VAAS. In the silt loam, all methods were responsive to land use effects on soil quality and sensitive in detecting changes in SSQ between evaluation times. We further showed that soils under PP resulted in the best SSQ compared to CP after harvesting, whereas SSQ of CP was better during cereal flowering than after harvesting. Despite the majority of the visual examination methods used in this survey were responsive in evaluating the effect of land use on SSQ and capable of representing structural dynamics (related to soil management) in an agricultural cycle, the lack of agreement between visual examinations and their interrelationships with the soil physical properties evaluated, however, highlight the need to conduct further work for exploring: a) method limitations, b) key factors such as soil moisture content and minimum number of samples for visual examination according to soil texture and spatial variability, and c) a judicious selection of a minimum data set of SSQ indicators omitting redundant material.

Spatial variability of hydro-physical properties has long been observed, whereas temporal variation is much less documented and considered in studies and applications, particularly of paddy clay soils under different cropping systems. The objective of this study was therefore to assess the seasonal- and inter-seasonal variation of selected hydro-physical properties of a paddy clay soil under different rice-based cropping systems with contrasting tillage. In a long-term experiment, plots were arranged in a randomized complete block design with four treatments and four replications: (i) rice–rice–rice, (ii) rice–maize–rice, (iii) rice–mung bean–rice, and (iv) rice–mung bean–maize. Soil samples were collected at three depths (0-10, 10-20 and 20-30 cm) at three times during two cropping seasons, i.e., 15 days after soil preparation (DASP), 45 DASP and 90 DASP during the winter-spring and spring-summer seasons. Results show that temporal variability of soil bulk density (BD), macro-porosity (MacP) and matrix-porosity (MatP) within both seasons and between seasons was limited for cropping systems with upland crop rotations, whereas within season variation was significant for rice monoculture system. Observed variation in BD, MatP and MacP was mainly associated with cropping system and soil depth. Field saturated hydraulic conductivity (Kfs) of topsoil showed great temporal variability, both seasonal and inter-seasonal, in correspondence with MacP (r = 0.58). These results highlight the need of depth differentiated soil sampling and time consideration when evaluating management practices on soil physical properties and modeling the hydrological behavior of paddy soil.

International audience; Assisted phytoremediation procedures have been widely employed as soil removal instrument of heavy metals from contaminated soils. Rhizosphere processes have a major impact on pb and Zn availability and its fractions in soils. The present study evaluates the effects of EDTA, citric acid (CA) and poultry manure extract (PME) on bioavailability and fractionation of pb, Zn in both the rhizosphere of sunflower (Helianthus annuus L.) and bulk soil. EDTA and CA were added to soils at the rates of 0, 0.5 and 1 mmol kg(-1) soil and PME at 0, 0.5 and 1 g kg(-1) soil as factorial in a completely randomized pattern with three replicates in greenhouse condition. Results showed that chelator application had a significant impact (p < 0.05) on pb, Zn extraction by different extractants and its fractions in soils. The order of concentrations of pb, Zn present in different fractions in soil treated by chelators was: oxides-bounded fraction > residual fraction > OM-bounded fraction > carbonate-bounded fraction > exchangeable fraction. Biochemical soil characteristics in the sunflower rhizosphere change resulting from its roots contributing to pb, Zn decline in mobile soil fractions, and change in soil pb, Zn fractions that are generally regarded as more stable.

Soil is an integral component of the global environmental system which supports the quality and diversity of terrestrial life on Earth. Therefore, it is vital to consider the processes and impacts of soil degradation on society, especially on the provision of environmental goods and services, including food security and climate change mitigation and adaptation. Scientific societies devoted to soil science play significant roles in reducing soil degradation and promoting soil conservation by advancing scientific knowledge, education and environmental sustainability. The ESSC was founded on 4 November 1988, with the aims to: 1. Support research on soil degradation, soil protection and soil and water conservation. 2. Provide a network for the exchange of knowledge about soil degradation processes and soil conservation research and practises. 3. Produce publications on major issues relating to soil degradation and soil and water conservation. 4. Advise regulators and policy-makers on soil issues, especially soil degradation, protection and conservation. The societal challenges that can be addressed through better soil protection, advancing knowledge and scientific approaches to soil protection and sustainable management, mean the ESSC embraces the on-going development, application, review and constructive criticism of highly innovative scientific soil conservation methods. In this context, the ESSC analyses and publicizes the roles and functions of soil in natural and human-modified systems and the functional optimization of soils to ensure sustainable environmental protection. "The thin layer of soil that forms a patchy covering over the continents controls our own existence and that of every other animal of the land" (Rachel Carson (1962) in 'Silent Spring'). (C) 2018 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. Production and Hosting by Elsevier B.V.

Knowledge of soil hydraulic properties is of major importance for land management in dry-land areas. The most important properties are the soil–water retention curve (SWRC) and hydraulic conductivity characteristics. Direct measurement of the SWRC is time and cost prohibitive. Pedotransfer functions (PTFs) use data mining tools to predict SWRC. Modern data mining techniques enable accurate predictions and good generalization of SWRC data. In this research we explore whether the use of support vector machines (SVMs) could improve the accuracy of prediction of SWRC. The novelty of our work is in the application of SVM data mining techniques, which are seldom used in soil research, to a limited dataset from Syria. The soil studied is calcareous and the climate is arid, for which no PTFs have been developed. Seventy-two undisturbed soil samples were taken from four different agro-climatic zones of Syria. The soil water contents at eight matric potentials were determined and selected as output variables. The data were split into two subsets: a training set with 54 samples for model calibration or PTF development and a test set with 18 samples for PTF validation. An overview of the theoretical foundation of this new approach and the use of specific kernel functions is given. Then, the model parameters were optimized with ninefold cross-validation and a grid search method. The predictions of the SVM-based PTFs were analysed with the coefficient of determination (R2) and root mean square error (RMSE). Our results showed that the accuracy of SVM was better in terms of RMSE and R2 than multiple linear regression (MLR) and the artificial neural network (ANN). The results support previous findings that the SVM approach performs better than MLR and the ANN. Furthermore, improvements in predictions of SWRC with the three data mining techniques were obtained by replacing the more conventional organic matter in the PTF with the plastic limit (PL). Therefore, SVM and PL markedly improved the accuracy of prediction of SWRC for calcareous soil. Highlights Pedotransfer functions (PTFs) to predict the soil–water retention curve of calcareous soil. Improved prediction of water retention with support vector machines (SVMs) The plastic limit (PL) appeared to be a significant predictor variable. The results suggest the use of SVMs and PL to improve and develop PTFs further.

Field water flow processes can be precisely delineated with proper sets of soil hydraulic properties derived from in situ and/or laboratory experiments. In this study we analyzed and compared soil hydraulic properties obtained by traditional laboratory experiments and inverse optimization tension infiltrometer data along the vertical direction within two typical Podzol profiles with sand texture in a potato field. The main goal was to identify proper sets of hydraulic parameters and to evaluate their relevance on hydrological model performance for irrigation management purposes. Tension disc infiltration experiments were carried out at four and five different depths for both profiles at consecutive negative pressure heads of 12, 6, 3 and 0.1 cm. At the same locations and depths undisturbed samples were taken to determine Mualem-van Genuchten (MVG) hydraulic parameters (theta(r), residual water content, theta(s), saturated water content, alpha and n, shape parameters and K-ls, saturated hydraulic conductivity) in the laboratory. Results demonstrated horizontal differences and vertical variability of hydraulic properties. The tension disc infiltration data fitted well in inverse modeling using Hydrus 2D/3D in combination with final water content at the end of the experiment, theta(f). Four MVG parameters (theta(s), alpha, n and field saturated hydraulic conductivity K-fs) were estimated (theta(r) set to zero), with estimated K-ls and alpha values being relatively similar to values from Wooding's solution which used as initial value and estimated theta(s) corresponded to (effective) field saturated water content, theta(f). The laboratory measurement of K-ls yielded 2-30 times higher values than the field method K-fs from top to subsoil layers, while there was a significant correlation between both K-s values (r = 0.75). We found significant differences of MVG parameters theta(s), n and alpha values between laboratory and field measurements, but again a significant correlation was observed between laboratory and field MVG parameters namely K-s, n, theta(s) (r >= 0.59). Assessment of the parameter relevance in 1-D model simulations, illustrated that the model over predicted and under predicted top soil-water content using laboratory and field experiments data sets respectively. The field MVG parameter data set resulted in better agreement to observed soil-water content as compared to the laboratory data set at nodes 10 and 20 cm. However, better simulation results were achieved using the laboratory data set at 30-60 cm depths. Results of our study do not confirm whether laboratory or field experiments data sets are most appropriate to predict soil water fluctuations in a complete soil profile, while field experiments are preferred in many studies. (C) 2016 Elsevier B.V. All rights reserved.

Continuous intensive monocultures of rice can lead to subsoil compaction, reduced topsoil quality and decline in rice yield. The objectives of this study were to evaluate the effect of rotating rice with upland crops on properties of an alluvial paddy clay soil, rice yield components, and economic profitability. A field experiment was established in the Vietnamese Mekong Delta for 10 years with a randomized complete block design including four rice based crop rotations and four replications: (i) rice–rice–rice (control, i.e., farmers’ practice), (ii) rice–maize–rice, (iii) rice–mung bean–rice, and (iv) rice–mung bean–maize. Rice alternated with upland crops significantly improved physical quality of soil in terms of bulk density, soil porosity, soil aggregate stability, and soil penetration resistance compared to the traditional rice monoculture practice, especially in the 10–20 and 20–30 cm depth layers. As a consequence, also rice rooting depth and root mass density was strongly increased in all three rice upland crop rotations. This resulted in a higher plant height, total number of tillers and panicles, filled grain percentage and a rice yield that was 32–36% higher compared to the control, and farmer’s profitability even increased 2.5–2.9 times. The reason for improved rice growth upon deeper root development should be investigated further, with specific attention to micronutrient availability.

In a concurrent paper, we compared a continuum model and a discrete element method (DEM) model in simulating stress transmission in soil under a wheel. Here, those models are evaluated with measurements of vertical normal stress (σz) under the wheels of a tractor-slurry spreader setup. It was found that the variation in the measured σz could be explained by the heterogeneous stress distribution in our structured soil, similar to what is observed in the DEM simulation. Furthermore, comparison of the continuum and DEM model showed that the lack of horizontal forces and dynamic load transfer at the boundary condition in the continuum model lead to a systematic underestimation of the measured σz. Traction and drawbar forces have a significant impact on the stress state under a wheel. The continuum model and its boundary conditions should be modified to include these forces accurately.

Subsoil compaction is a major threat to soil quality. The use of bio-subsoilers has been proposed as a mitigation practice. There is, however, a paucity of knowledge on the effects of potential bio-subsoiling crops in alleviating severely compacted subsoil. X-ray Computed Tomography (CT) was used to assess the changes caused by different crops in the pore network of a severely compacted subsoil. The potential bio-subsoilers, chicory, lucerne, radish and tall fescue, with spring barley as reference, were grown for one year in undisturbed soil columns (Ø = 0.20 m, h = 0.50 m) with soil originating from a heavily compacted soil after mechanical impact. Soil columns were X-ray CT-scanned before and after the experiment. CT-pore soil characteristics were quantified by image analysis. Crop treatments affected the soil porosity differently on the studied soil. Radish and tall fescue did not show a significant impact on CT-derived pore characteristics at any depth. In the compacted layer, the macropore density, the branches number, and the number of pores (for volume sizes of < 100 mm3 and diameter ≤ 1.5 mm) were larger for chicory and lucerne compared to barley (P < 0.05). Chicory and Lucerne appear to contribute to the development of a large number of complex-shaped pores. Differences in the CT-derived pore network indicate that chicory and lucerne are likely to perform better than the other crops when used as bio-subsoilers by creating a larger, more connected and complex pore network. Longer-term growth is needed to obtain a marked loosening effect in the compacted layer.

National and international initiatives have been undertaken in Uganda to improve soil quality and increase crop production. However, means to evaluate and examine soil quality, particularly soil physical quality, is lacking in the country. In this study, visual soil evaluation and examination (VSEE) spade and core tests, which comprise rapid and simple methods to semi-quantitatively assess soil structure, have been tested. The derived soil quality scores Sq were compared with soil quality indicators SQi derived from traditional lab-based methods of soil structure analysis. Tests were conducted and samples taken in Uganda on highly-weathered soils with sandy clay loam texture. Both the 0–15 cm topsoil and the 15–30 cm moderately compacted subsoil were considered. Test and sampling sites comprised 18 farmers’ fields (maize, Zea mays L.) that were under conventional tillage, permanent planting basins and rip lines for three years, as well as four locations in a natural forest. All VSEE approaches tested showed a significantly better Sq score in the natural forest (good quality) as compared to maize fields (fair/moderate quality), with the subsoil always showing lower quality than the topsoil. Methods based on Visual Evaluation of Soil Structure (VESS) were more responsive to differences in soil quality than the Visual Soil Assessment (VSA) approach. Statistical analysis showed that there was a good to moderate correlation between the VSEE-based Sq scores and lab-derived SQi values, with Pearson r correlation coefficients of 0.52–0.69 for bulk density, 0.66-0.78 for air capacity, 0.53–0.73 for air permeability, 0.52–0.72 for hydraulic conductivity, 0.18-0.48 for mean weight diameter under fast wetting. The correlation with an overall integrated index of soil quality SQI ranged between 0.56 and 0.77. Minimizing the potential effect of local variability by averaging Sq scores and SQi or SQI values per treatment and depth, improved the correlation, with e.g., Pearson r ranging from 0.84 to 0.95 when relating Sq to SQI. We also found a significant correlation between VESS Sq scores and the shape of the water retention curve, particularly in the wet range (r > 0.50). Our results show that in general, VSEE methods are promising alternatives to evaluate differences in physical soil quality of highly-weathered soils in a rapid, intuitive, practical and cheap way.

The discrete element method (DEM) is an appealing technique to study the effect of wheel loads and traction on the soil. Unlike in continuum-based soil mechanics, the soil is modelled as an assembly of particles, which move and interact with each other and transmit stress through force chains. In this study, the simulation of stress transmission under wheeling with the continuum method and with DEM was compared. Both methods showed a good agreement in the simulation of the vertical normal stress. The horizontal stresses were strongly different due to traction and draw-bar forces. Stresses in the DEM simulation were transmitted via a heterogeneous network of force chains: there was a coexistence of a distinct load-bearing and a dissipative force network in the shallow layers. Furthermore, the effect of the DEM material parameters (normal and shear stiffness and cohesion, and friction angle), wheel radius and traffic speed on the transmission of stress was evaluated. The normal and shear stiffness mainly influenced the depth of the stress transmission, and the friction angle influenced the horizontal stress transmission. The wheel radius influenced the stress distribution in the topsoil, but did not have a significant effect in deeper layers. Contrary to findings in literature on soil compaction, the increased traffic velocity caused higher stresses. DEM allows to simulate the geomechanical process of soil compaction and can give more insight in the role of heterogeneous stress transmission.

Poor soil fertility remains a threat to crop production and livelihoods in the Sahel. Understanding the impacts of proposed soil fertility management technologies on soil fertility status and millet yield is essential. We conducted a 2-year experiment to assess changes in selected physical properties of an Arenosol and their impacts on millet yields at Karabedji, Niger. Treatments consisted of four fertilizer rates applied on top and bottom farm types selected from a long-term experiment. Mixed-model analyses indicated considerable effects (P = 0.055) of fertilizer rates and farm types on soil structural stability being higher in the top farm than in the bottom farm type. Dexter’s soil physical quality index (S) varied significantly with soil depth. A significant correlation (R2 = 0.24) was found between the aggregate stability index and S. Plant available water recorded in fertilizer-treated soil was higher than the control and higher on the top farm than in the bottom farm. Fertilizer rates and ...

The hazard for recurring food insecurity in the Sahel is largely affected by insufficient biomass productivity of degraded, marginal lands. In general, water and soil conservation (WSC) techniques are believed to tackle the deterioration of soil quality by enhancing soil hydraulic properties, soil life, and soil organic carbon (SOC) content, but this beneficial effect on soil quality is hardly ever quantified in WSC research. This study therefore evaluates the effect of WSC on soil chemical, physical, and biological quality indicators by means of an in situ experiment, which was installed in 2011 nearby Sadore, Niger. The treatments include the following: zai + manure (Z), demi-lunes + manure, scarification + manure, control + manure, and control. WSC increases grain yields up to 0·7 ± 0·2 Mg ha−1 on degraded, marginal lands, which is similar to yields produced on fertile lands in the area. Nevertheless, a trade-off between biomass production and SOC accumulation was observed. After three growing seasons, SOC was found to rise significantly for the treatments provided with manure, from ±2·5 to ±5 g kg−1, but the increase was lowest for Z, which produced the highest yields. WSC also showed significantly elevated nematode counts but did not considerably affect other soil chemical and soil physical properties. Hence, on the short term, WSC does not improve soil quality, as was widely proclaimed. Therefore, future research should include the assessment of long-term WSC effects and the evaluation of integrated management combining WSC with alternative, yield-enhancing strategies. Copyright © 2015 John Wiley & Sons, Ltd.

Using basic soil properties could save time and costs in determining field capacity (FC) and permanent wilting point (PWP). The objectives of this study were to investigate the relationship between FC and PWP and basic soil properties, develop two new equations for estimating FC and PWP, and evaluating their performance as compared to some existing pedotransfer functions (PTFs) in predicting FC and PWP. For this purpose, 210 soil samples of UNSODA dataset and 45 soil samples of HYPRES dataset were used for development and validation of the PTF, respectively. Graphical exploration of relations between soil texture component, geometric mean particle-size diameter (dg), bulk density (BD), and organic matter (OM) with FC and/or PWP showed that relations of FC was nonlinearly related to percentage of clay (positive) and dg (negative) and relations of PWP was linearly and nonlinearly related to percentage of clay (positive) and dg (negative), respectively. Based on standardized independent variable weight (W), ...

Appropriate management of irrigation and drainage, which require the information of soil water retention characteristics (SWRC), is of crucial importance for sustainable paddy rice production in tropical deltas. SWRC, however, is usually missing due to the lack of facilities, cost, and personnel training involved in direct measurement methods. Pedotransfer functions (PTFs) that provide the estimation of SWRC from other basic soil properties are the alternative source of SWRC for practical soil water managements or modeling purposes. Since developing new PTFs is a very arduous task which requires a large soil database of good quality, utilizing existing PTFs where possible is highly recommended. The objective of this study was therefore to evaluate the applicability and reliability of published SWRC-PTFs for soils in tropical Vietnamese Mekong Delta (VMD) where paddy rice is the main agricultural practice. A number of well-known statistical regression and pattern-recognition PTFs were selected for the evaluation. By assessing the correspondence between measured and PTF predicted values of SWRC, the results show that the PTFs derived from large databases of soils in the regions having similar climatological and pedological conditions to VMD soils are more reliable for predicting SWRC (RMSE varies in the range of 0.06–0.07 m3 m−3, and of 0.05–0.06 m3 m−3 for the prediction of soil water content at −33 kPa and −1500 kPa, respectively). The applicability index together with geographical information, therefore, could be used as integral indicators to select appropriate PTFs in cases no SWRC data are available for timely uses. Detailed evaluation of PTFs’ performance however revealed the limited potential of investigated PTFs to VMD soils. Further researches to develop specific PTFs for tropical delta soils are recommended for accurate SWRC estimation in such regions.

Knowing the soil water retention curve (WRC) is essential for analyzing soil hydraulic behavior within the vadose zone. The van Genuchten (VG) soil hydraulic equation is one of the most frequently adopted models to parameterize the WRC. Some measured water retention points are needed to fit the VG model, but direct measurement of water content versus matric potential is expensive and time consuming. A pedotransfer function (PTF) enables indirect determination of a WRC from basic soil information. The typical method employed to derive a PTF using the VG model (VG-PTF) is to establish a mathematical relationship between the parameters of the VG model and basic soil data. However, both establishing and reusing a VG-PTF for new soils are challenging due to several reasons, such as over-parameterization, low correlation between basic soil data and VG parameters, and interdependency among parameters. In this study, a nonparametric approach based on the k nearest neighbor technique was designed and tested to establish a VG-PTF. A subset of soils from the UNSODA database (n = 554)) and a data set from Belgium (n = 69) were used as the model development and validation data sets, respectively. The proposed PTF showed reasonable accuracy and reliability and was comparable to well-known parametric VG-PTFs available in the literature.

This study aims at identifying the influence of soil surface roughness from small to large aggregates (random roughness) on runoff and soil loss and to investigate the interaction with soil surface seal formation. Bulk samples of a silty clay loam soil were sieved to four aggregate-size classes of 3 to 12, 12 to 20, 20 to 45, 45 to 100 mm, and packed in soil trays set at a 5% slope. Rainfall simulations using an oscillating nozzle simulator were conducted for 90 min at an average rainfall intensity of 50.2 mm h(-1). Soil surface roughness was measured using an instantaneous profile laser scanner and surface sealing was studied by macroscopic analysis of epoxy impregnated soil samples. The rainfall simulations revealed longer times to initiate runoff with increasing soil surface roughness. For random roughness levels up to 6 mm, a decrease in final runoff rate with increasing roughness was observed. This can be attributed to a decreased breakdown of the larger roughness elements on rougher surfaces, thus keeping infiltration rate high. For a random roughness larger than 6 mm, a greater final runoff rate was observed. This was caused by the creation of a thick depositional seal in the concentrated flow areas, thus lowering the infiltration rates. Analysis of impregnated soil sample blocks confirmed the formation of a structural surface seal on smooth surfaces, whereas thick depositional seals were visible in the depressional areas of rougher surfaces. Therefore, from our observations it can be learned that soil surface roughness as formed by the presence of different aggregate sizes reduces runoff but that its effect diminishes due to aggregate breakdown and the formation of thick depositional seals in the case of rough soil surfaces. Sediment concentration increased with increasing soil surface roughness, due to runoff concentration in flow paths. Nevertheless, final soil loss rates were comparable for all soil roughness categories, indicating that random roughness is only important in influencing runoff rates and the time to initiate runoff, but not in influencing sediment export through soil loss rates.

Bulk density (BD) is a key soil property for sustainable land management and C stock assessment. However, data on BD are often missing in various soil survey reports in Central Africa because its measurement is laborious, time consuming at large scales, and may pose expense and facilities challenges, particularly in resource-poor countries. Therefore, there was a need for developing pedotransfer functions (PTFs) to predict BD for soils of Central Africa as an alternative solution. To do so, two approaches, namely multiple linear regression (MLR) and a pattern-recognition approach (k-nearest neighbor [k-NN]) were tested to predict BD for 196 soils of the Lower Congo. Based on their needs and familiarity with one or both of the two approaches, potential users interested in predicting the BD of strongly weathered soils of Lower Congo in particular or of Central Africa in general can immediately use the proposed equations or later apply the k-NN algorithm. Using an independent data set of low-activity clay soils from different tropical countries, nine individual PTFs and three ensemble PTFs were tested for their predictive capability. The results showed that despite the use of various modeling approaches—MLR, k-NN, or ensembles—BD remains a soil property that is difficult to predict with a satisfactory level of reliability because it can have substantial short-term variability in response to natural as well as human-induced causes. We achieved a minimum root mean square difference value of 0.179 Mg m⁻³.

In the Mekong Delta, alluvial clay soils have been used intensively over many generations for rice monoculture. Currently, farmers are confronted by problems of declining land productivity. Rotations comprising rice and upland crops can increase soil quality, but appropriate cropping systems for paddy soils have received relatively little attention. We therefore established a multiyear field experiment to evaluate the long-term effects of cropping systems with different rotations on soil chemical quality. Systems laid out in a randomized complete block design with four replications were as follows: (i) traditional rice monoculture with three rice crops per year (R-R-R), (ii) rotation with two rice crops and maize (R-M-R), (iii) rotation with two rice crops and mung bean (R-Mb-R) and (iv) rotation with one rice crop and two upland crops – mung bean and maize (R-Mb-M). We hypothesized that systems with rotations of upland crops and their temporary beds improve chemical quality of paddy rice soil. Soil chemical parameters were determined to better understand and evaluate the sustainability of the cropping systems. Results showed an improvement in soil chemical quality for cropping systems with rotations of rice and mung bean or maize grown on temporary beds (R-M-R, R-Mb-R and R-Mb-M), particularly the content of soil organic carbon and a presumed hydrolysable labile carbon fraction compared with rice monoculture. Less pronounced improvements in EC, CEC and total acidity were also found with inclusion of upland crops. Cropping systems of rice with upland crops improved rice grain and straw yield in subsequent season in contrast with rice monoculture.

Biochar is often proposed to increase soil quality and crop yield, while sequestering carbon. Despite the growing number of studies in temperate regions, the claimed positive effects are still unsure for northwestern European soils. Moreover, there is a need to upscale results from lab and pot studies in these soil types to field experiments. The objectives of this study were therefore to investigate the effect of biochar application to a temperate agricultural soil on soil chemical, physical and biological properties, and on crop growth and nutrient uptake under field circumstances. A field trial, located in Merelbeke (Belgium), was established in October 2011 and monitored until August 2013. The biochar applied was produced from a mixture of hard- and softwood at 480 °C. The biochar dose was 0 (control) or 20 t ha−1 (on dry weight basis). Over two years, biochar addition to soil did not affect soil chemical properties, except for organic carbon content and C:N ratios. Effects on bulk density, porosity and soil water retention curves were non-consistent over time, possibly due to interaction with tillage operations. Biochar increased soil water content in 2012, although mostly not significantly. However, in 2013, when soil water content was overall lower compared to 2012, it was not affected by biochar addition. Soil temperature, as measured at a soil depth interval of 8–20 cm, was not changed by biochar addition. Furthermore, biochar addition to soil did only slightly influence soil microbiological community structure during the first year after biochar application, as only certain bacterial biomarker PLFAs were significantly affected by biochar addition, but no fungal biomarker PLFAs. Hence, it was not surprising that biochar addition did not affect crop yield, N or P uptake during the first two years after biochar application.

In situ water and soil conservation (WSC) practices are a promising intervention to improve rainwater management particularly in the semi-arid to dry sub-humid tropics. This study applies a fully coupled surface–subsurface process-based model (HydroGeoSphere) to simulate in detail rainwater partitioning as affected by two in situ WSC practices [terwah+ (TER+) and derdero+ (DER+)] currently under study on Vertisols in Tigray, Ethiopia and to evaluate the treatments in terms of rainwater partitioning. In the TER+ practice, contour furrows of 0·2 m wide and 0·1 m deep are created at 1·5 m intervals between permanent broad beds, whereas in DER+, permanent raised beds 0·6 m wide with furrows 0·2 m wide and 0·1 m deep are created, to minimize runoff and water logging. The model accurately reproduced measured surface runoff (e.g. in DER+: Nash–Sutcliffe model efficiency E = 0·6 for calibration and 0·7 for verification) and soil moisture content (DER+: E = 0·6 for calibration and 0·8 for verification). Runoff depth was lowest under DER+ (50 mm) followed by TER+ (67 mm) and significantly higher in conventional tillage (CT) (160 mm). Simulated transpiration, evaporation and drainage out of the root zone were all higher under DER+ and TER+ compared with CT. The effects of DER+ and TER+ practices on rainwater partitioning were more pronounced in wet years than in dry years. The model proved to be a promising and versatile tool to assess the impact of WSC practices on rainwater partitioning at the field scale. Copyright © 2014 John Wiley & Sons, Ltd.

The soil physical quality (SPQ) index S can provide inconsistent designations of SPQ and has a lack of consistency with other physical indicators for some soils. The aim of this study was to compare the suitability of S in identifying SPQ against 12 SPQ indicators, including water-release-related indicators, physical properties, and visual examinations. This study was conducted on medium-textured soil samples taken from tropical and temperate soils. Comparisons of SPQ class and relationships between indicators were used to judge the S SPQ designation. For the studied soils, S classified SPQ in the same way as other indicators when the condition of the soil was optimal or degraded but not when it was intermediate. This demonstrates that the proposed critical limits for S are not generally valid and do not apply for all soil conditions. Porosity parameters from the water release curve were more consistent indicators of SPQ than S. Our work also demonstrates that scores from visual examinations have at least similar resolution (P > 0.05) to the other indicators of SPQ evaluated. The use of S as an indicator to be considered as part of a minimum data set of indicators of SPQ assessment is less viable when other indicators such as bulk density, porosity, and visual examination are much more easily determined and more consistent than S. Therefore, it is too ambitious to consider that a unique indicator such as the S index could be used to evaluate SPQ as such.

The difficult question of which variables to include as a minimum data set of soil quality (SQ) indicators may be simplified by statistical methods, which allow working with databases including categorical and numerical variables commonly used for assessing SQ. The aims of this study were: i) to identify soil structural related parameters that may associate to SQ at different geographic areas and ii) to test the potential power of using decision trees in setting up a framework for SQ assessment, and in determining structural soil properties, visually evaluated, that could be included in the estimation of soil physical properties such as saturated hydraulic conductivity (Ks). SQ was evaluated by visual soil assessment (VSA) in the field and a limited number of physical and chemical soil properties (bulk density (BD), air capacity, plant available water capacity (PAWC), saturated hydraulic conductivity (Ks), water stable aggregates (WSA), particle size distribution, soil organic carbon (SOC) and cation exchange capacity (CEC)) determined in the laboratory. Using categorical and numerical data of those physical, chemical and morphological properties of soils in both tropical and temperate areas, classification trees and model trees were grown. Parameters related to SQ differed between geographic areas. Ks was the strongest variable determining the SQ in ‘tropical’ soils, but WSA, SOC and PAWC were also key variables in determining differences in SQ. For ‘temperate’ soils PAWC was the only variable selected by the tree building algorithm. SOC, clay, and CEC were the discriminating variables of the model constructed from the combined data set. Statistically significant relationships between measured and visual parameters are promising in demonstrating the SQ description required for merging morphological, physical and chemical properties for minimum data set of SQ indicators. Thresholds of different predicting variables could be better established when SQ frameworks involve VSA. We also proved that prediction of KS with a model tree was more accurate when morphological parameters were included as predictor variables, and that in that case the model tree showed a simpler structure compared to the tree built only from chemical and physical soil properties. In conclusion, decision trees are encouraging in the selection of SQ indicators. Moreover, including morphological properties in the prediction of key soil properties such as Ks seems promising. VSA could render morphological response variables for predicting other soil properties and developing SQ frameworks (agricultural interest) more capable of representing structural dynamic.

Compound-specific stable isotope (CSSI) fingerprinting of sediment sources is a recently introduced tool to overcome some limitations of conventional approaches for sediment source apportionment. The technique uses the 13C CSSI signature of plant-derived fatty acids (δ13C-fatty acids) associated with soil minerals as a tracer. This paper provides methodological perspectives to advance the use of CSSI fingerprinting in combination with stable isotope mixing models (SIMMs) to apportion the relative contributions of different sediment sources (i.e. land uses) to sediments. CSSI fingerprinting allows quantitative estimation of the relative contribution of sediment sources within a catchment at a spatio-temporal resolution, taking into account the following approaches. First, application of CSSI fingerprinting techniques to complex catchments presents particular challenges and calls for well-designed sampling strategies and data handling. Hereby, it is essential to balance the effort required for representative sample collection and analyses against the need to accurately quantify the variability within the system. Second, robustness of the CSSI approach depends on the specificity and conservativeness of the δ13C-FA fingerprint. Therefore, saturated long-chain (>20 carbon atoms) FAs, which are biosynthesised exclusively by higher plants and are more stable than the more commonly used short-chain FAs, should be used. Third, given that FA concentrations can vary largely between sources, concentration-dependent SIMMs that are also able to incorporate δ13C-FA variability should be standard operation procedures to correctly assess the contribution of sediment sources via SIMMs. This paper reflects on the use of δ13C-FAs in erosion studies and provides recommendations for its application. We strongly advise the use of saturated long-chain (>20 carbon atoms) FAs as tracers and concentration-dependent Bayesian SIMMs. We anticipate progress in CSSI sediment fingerprinting from two current developments: (i) development of hierarchical Bayesian SIMMs to better address catchment complexity and (ii) incorporation of dual isotope approaches (δ 13C- and δ 2H-FA) to improve estimates of sediment sources.

Traditionally, research on soil degradation focused on water erosion. Recent studies, however, point to the importance of tillage operations as a source of soil translocation in traditional animal-powered farming systems comparable to those applied in the Cuyaguateje watershed, Cuba. Together with the effect of some controlling factors, the extent of tillage erosion on a Ferralsol (Ferralitico Rojo) caused by the traditional ox-drawn mouldboard plough, the ‘arado americano’, and a harrow, the ‘rastrillo’, were studied with a tracer experiment on a Ferralsol with 30 plots on moderate slopes ranging from 4% to 16.5%. Two tillage directions were considered: (i) parallel to the contour and (ii) up and down the slope. Due to the shallow average tillage depth of tillage with the ‘rastrillo’ (3.8 cm), net mean downslope displacement could not be observed. Average tillage depth with the ‘arado americano’ was relatively shallow (11.5 cm) as well and resulted only in the up and downslope direction in a significant downslope soil flux. This downward movement showed no significant relation with the slope gradient, nor with tillage depth, tillage speed and plant cover. While the potential for tillage erosion is considerable with the ‘arado americano’, actual erosion rates in our study were low compared to previous tillage erosion studies. Single soil movements up to 44 cm were detected, but taking crop rotation and tillage frequencies into account, soil transportation rates of accumulated tillage operations only ranged from 8.78 to 26.34 kg m− 1 yr− 1. This is mainly due to the moderate slope range, the low tillage depth and the good farmers' practice of tilling alternately in opposing direction.

Cropping systems are thought to alter soil quality in paddy rice fields. This study was conducted to quantify the long-term effects of continuous crop production under different cropping systems with different crop rotations on physical properties of alluvial clay soil in the Mekong Delta, Vietnam. Soil samples were collected from four treatments: (i) traditional intensive rice monoculture with three rice crops per year (R–R–R); (ii) rotation with two rice crops and maize (R–M–R); (iii) rotation with two rice crops and mung bean (R–Mb–R); and (iv) rotation with one rice and two upland crops, mung bean and maize (R–Mb–M). We hypothesized that cropping systems with rotations of upland crops and their temporary beds improve the physical quality of paddy rice soil; hence, they are better options towards sustainable agriculture. Results show an improvement of soil physical quality for systems with two rice crops and one upland crop (R–M–R and R–Mb–R) and those with one rice crop with two upland crops (R–Mb–M) compared with intensive rice monoculture (R–R–R). This was translated in decreased bulk density and soil strength, increased soil organic carbon and total porosity, and higher aggregate stability index, plant-available water capacity, and Dexter's S index, especially at depths of 10–20 and 20–30 cm. The systems with different upland crops (maize or mung bean) showed similar high physical quality improvement. To maintain soil quality in future seasons, introducing a cropping system with at least one upland crop in rotation with rice is recommended. Copyright © 2014 John Wiley & Sons, Ltd.

Using easily measurable soil properties could save time and cost for field capacity (FC) prediction. The objective of this study was to compare Mamdani fuzzy inference system (MFIS) and regression tree (RT) for FC predicting using such properties. One hundred and sixty-five soil samples from Unsaturated Soil hydraulic database data-set and 45 from Hydraulic Properties of European Soils data-set were used for the development and validation of MFIS and RT, respectively. Fuzzy rules and tree diagram based on the relationships between these predictor variables and the response variable FC were defined and 48 rules were written. Results showed a positive linear relevancy in terms of standardized independent variable weight, W*, between clay content and FC and negative linear relevancy between geometric mean particular size diameter (dg) and FC. Among predictor variables, dg (W* = 0.81) and bulk density (BD) (W* = 0.49) had the highest and lowest influence on FC, respectively. A tree diagram is presented for th...

A comparative study was carried out of annual ridge tillage (RT) and short-term effects of conservation agriculture (CA) on soil properties in fields of small-scale farmers. Soil samples were collected at depths of 0–10 and 10–20 cm from a total of 12 fields which had been under CA for two and four seasons, respectively, and from adjacent RT fields for direct comparisons. CA fields were converted from fields previously under continuous RT. Soil organic carbon, total nitrogen and available phosphorus were greater in CA fields while extractable potassium, pH and salt content were moderated under CA. Conversion of long-term RT to CA did not significantly influence bulk density and aggregate stability (geometric mean diameter) although structural stability was greater under CA practices. Total porosity, macroporosity and matrix porosity, and volumetric water content at saturation, field capacity and permanent wilting point did not substantively respond to tillage effects. Relative water capacity and air–water storage parameter, hfc/PORt, were significantly greater after 4 yr of CA. Soils under CA showed greater values for field-saturated hydraulic conductivity compared with RT fields. With the highest loadings in a principal component analysis, this work suggests that variables related to volumetric water content and aeration of the soil matrix, organic carbon, available phosphorus and soil texture were the most useful indices for future field comparison of RT and CA practices.