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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.

Near surface geophysical electromagnetic techniques are proven tools to support ecosystem services such as agriculture, soil remediation, nutrient management, and heritage conservation. Key influencing geophysical properties are electrical conductivity (σ, or resistivity (ρ)), dielectric permittivity (𝜀) or magnetic susceptibility (μ), that are targeted to model soil properties and state variables such as texture, bulk density, cation exchange capacity (CEC) or water content. To translate geophysical properties into quantitative information on the targeted soil properties, relationships between these have to be considered in appropriate models. These so-called pedophysical models can then be integrated into interpretation schemes (e.g., after inversion, or through incorporating this into forward modelling procedures). This modelling step, translating geophysical properties into soil properties (and vice versa), thus constitutes a key aspect of near surface exploration.While hundreds of pedophysical models exist to perform this task, these often depend on many properties and parameters defined within a specific range e.g., electromagnetic frequency, texture, and salinity; impeding applications to cases where information about the studied soil is scarce. Therefore, selecting an appropriate pedophysical model for a given scenario is often a very complex task.To facilitate solutions for pedophysical modelling we present pedophysics, an open source python package for soil geophysical characterization. The package implements up-to-date models from the literature and, based on the user’s needs, automatically provides an optimal solution given a set of input parameters and the targeted output.First, a virtual soil is defined by inputting any of its available properties. This soil can be defined in discrete states to simulate the evolution of its properties over time. Secondly, a module (predict) is called to predict the target property of interest. Following this workflow, for example, a soil with a given texture and changing water content could be defined to obtain its 𝜀 or σ at a predefined frequency, or, inversely, its water content could be predicted based on changing σ.However, as soil properties required as input parameters for pedophysical models are often unknown, it can, in such cases, be impossible to obtain a viable prediction outcome. The pedophysics package accounts for such limitations by implementing pedotransfer functions, that allow obtaining the missing properties from the available ones. For example, if CEC is unknown, it is determined based on soil texture and a location.In summary, the package synthesizes specific pedophysical modeling knowledge. Time-varying properties can be calculated in a straightforward way, and, through the integration of pedotransfer functions, target properties can be predicted with a minimum of information about the studied soil. Thus, by translating known properties to targeted ones, pedophysics is contributing to improve interpretability of near surface modeling schemes; enhancing soil electromagnetic geophysical exploration techniques in ecosystem services applications.

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.

Soil surface crusting is a common phenomenon on agricultural soils susceptible to rainfall drop impact. Crust affects soil hydrological properties, erosion, crop quality and yield, which implicates both agriculture and the environment. Whereas methods for determining hydraulic or basic properties of soil layers (such as thicker than 2 cm) are well established, measuring the soil characteristics of a thin crust (< 5 mm) remains a challenge. Therefore, in this study, we combine traditional lab methods and advanced techniques to test the variation in soil properties during the crust forming process. Composite samples from two soil textures were collected, dry-sieved at 8 mm, packed in soil pans and exposed to a range of rainfall amounts and two rainfall intensities, using a laboratory nozzle-type rainulator. Intact soil ring samples were collected after each rainfall event and scanned using X-ray Computed Tomography (CT) to gain more insight into rainfall-induced crust formation. Soil porosity, bulk density and the thickness of crust were derived from CT scans. Meanwhile, a scanning electron microscope (SEM) was employed to verify the variation of the crust layer thickness and soil properties. In addition, the water retention and infiltration dynamics of the developing seals were investigated with a minidisk infiltrometer placed on the crusts developed in the pans and a falling head permeameter (KSAT®) and evaporation method (HYPROP®) on soil cores taken. Shear strength was evaluated by hand vane. Disturbed soil was collected to explore variation in organic matter content and texture with rainfall. During the simulated rain events, soil loss, splash and runoff were followed as well. Overall, the purpose of this study was to reveal temporal variations of seal micro-morphology and their effect on soil properties with increasing rainfall amount. Our results showed the runoff volume and sediment mass increased, while splash and infiltration volume decreased with the increase in rainfall amount. Shear strength increased until 200 mm of rainfall. Additionally, (crust forming) rainfall amount had a rapid and strong effect on the hydraulic properties, with the unsaturated hydraulic conductivity being reduced as rainfall duration increased and the high rainfall intensity having a greater impact. These results were associated with rainfall-induced aggregate breakdown processes, which was confirmed by SEM images. It also demonstrated that crust development occurred up to at least 200 mm rainfall after cultivation. In summary, it was possible to illustrate the structural seal formation process and the temporal interrelated dominance and significance of the associated sub-processes which contribute to overcoming the challenge of testing the thin crust (< 5 mm).

Soil compaction forms a major threat to the well-functioning of agricultural soils. By reducing the pore volume and continuity both crop growth and ecological services, like water infiltration and storage, can be negatively impacted. It is often most severe at the interface between topsoil and subsoil, just out of reach of regular tillage operations. At this depth a plough pan can be formed, restricting interaction between top- and subsoil for roots, and gas and water transport. In this study we looked at a combination of mechanical and biological remediation to alleviate this problem. The experiment was performed on a sandy loam field near Ghent, Belgium with a highly compacted plough pan, which almost completely restricted roots to reach the subsoil and was practically impermeable for gases. Subsoiling was performed once in three different maize-based cropping systems: forage maize in monoculture, a ley-arable crop rotation with two years of alfalfa and a maize-winter cereal rotation.The mechanical remediation (subsoiling) clearly helped to break open the restricting plough pan. Rootablility and air permeability clearly increased, leading to a significant increase in maize yield. On a longer time scale, however, we observed that this loosened soil was very prone to recompaction. In the second year after the subsoiling the highly compacted plough pan returned. This same year also showed no difference between the subsoiled and untreated control in maize yield.To see if deep rooting crops can help stabilize the loosened soil after subsoiling, this study included treatments with fodder radish and alfalfa as (cover) crops. These crops showed a high rooting density in the subsoil, especially where the tines of the subsoiler had passed. Although this did not seem to improve the overall physical soil quality, it did protect the soil from complete recompaction. The penetration resistance did not markedly increase after standard agricultural practice.

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.

African agriculture is adversely impacted by arable soil compaction, the degree of which is affected by the speed at which the tractor is maneuvered on the fields, which affects the degree of soil compaction. However, there is no reliable, existing mathematical correlation between the extent of compaction on the one hand, and the tractor speed/s and soil moisture levels on the other. This paper bridges this gap in knowledge by resorting to the artificial neural networks (ANNs) method to predict the effects of tractor speed and soil moisture on the state of soil compaction. The models were ‘trained’ with penetration resistance (CPR) and bulk density test data obtained from field measurements. The resulting correlation coefficient (R = 0.9) showed good compliance of the prediction made with the ANN models with on-field data. It follows, thereby, that the model developed by the authors in this study can be effectively used for predicting the effects of speed, soil density, and moisture content on compaction of alluvial, poorly developed soil with much greater precision, thereby providing guidance to farmers around the world.

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.

Improving irrigation water management and enhancing water productivity (WP) is required to address future water scarcity in the sub-Saharan region. Maximizing WP by exposing the crop to a certain level of water stress using deficit irrigation (DI) is considered a promising strategy. To adopt DI strategies, a shred of comprehensive evidence concerning DI for different crops is required. This review aims to provide adequate information about the effect of DI on WP. The result showed that DI considerably increased WP compared to full irrigation. Despite higher WP, the reduced yield was obtained in some of the studied DI practices compared to full irrigation. It was also found that yield reduction may be low compared to the benefits gained by diverting the saved water to irrigate extra arable land. Maize revealed the highest (2.7 kg m(-3)) and lowest (0.5 kg m(-3)) WP when irrigated at only the initial stage compared with being fully irrigated in all growth stages. Also, onion showed a decreasing WP with increased irrigation water from 60% crop water requirement (ETc) (1.8 kg m(-3)) to 100% ETc (1.3 kg m(-3)). Increasing water deficit from 100 to 30% ETc led to an increase of wheat WP by 72%. For tomato, the highest WP (7.0 kg m(-3)) was found at 70% ETc followed by 50% ETc (7.0 kg m(-3)) and 85% ETc (6.9 kg m(-3)), while 100% ETc showed the least WP (6.8 kg m(-3)). Teff showed the lowest WP (1.7 kg m(-3)) under optimal irrigation, while it was highest (3.0 kg m(-3)) under 75% ETc throughout the growing season. The regression analysis for WP increment and yield reduction versus saved water showed higher values, indicating that DI could be an option for WP increment and increasing overall yield by expanding irrigated area and applying the saved water in water-scarce regions.

Various large-scale risk maps show that the eastern part of Austria, in particular the Pannonian Basin, is one of the regions in Europe most vulnerable to wind erosion. However, comprehensive assessments of the severity and the extent of wind erosion risk are still lacking for this region. This study aimed to prove the results of large-scale maps by developing high-resolution maps of wind erosion risk for the target area. For this, we applied a qualitative soil erosion assessment (DIN 19706) with lower data requirements and a more data-demanding revised wind erosion equation (RWEQ) within a GIS application to evaluate the process of assessing wind erosion risk. Both models defined similar risk areas, although the assignment of severity classes differed. Most agricultural fields in the study area were classified as not at risk to wind erosion (DIN 19706), whereas the mean annual soil loss rate modeled by RWEQ was 3.7 t ha−1 yr−1. August was the month with the highest modeled soil loss (average of 0.49 t ha−1 month−1), due to a low percentage of vegetation cover and a relatively high weather factor combining wind speed and soil moisture effects. Based on the results, DIN 19706 is suitable for a general classification of wind erosion-prone areas, while RWEQ can derive additional information such as seasonal distribution and soil loss rates besides the spatial extents of wind erosion.

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.

Soil structure is a complex and dynamic soil property that constitutes a key aspect of soil health. Soil structure assessment can be evaluated in the field by visual soil evaluation techniques. Development and improvement of these techniques/methods have been the focus of numerous soil scientists worldwide since the mid-20th century. Divided into topsoil and soil profile methods, they differ in principle and level of detail of the assessment. The development and protocols of selected methods are presented in this chapter in chronological order of development, to show differences in methodological approaches. The description given for each of the methods includes guidance for the appropriate selection of the method to be used by stakeholders. Two case studies are given as examples of i) how visual techniques can contribute to achieving the challenges for developing sustainable agricultural management focused on nurturing soil fertility, and ii) the use of visual techniques as tools to assess and monitor soil health in developing countries.

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.

Water scarcity is a major limiting factor for crop production by irrigation in sub-Saharan countries. Improved irrigation scheduling that can ensure the optimal use of the allocated water and enhance water productivity (WP) is required to address future water scarcity in the region. Maximizing WP by exposing the crop to a certain level of water stress using deficit irrigation (DI) is considered a promising strategy. To adopt DI strategies, a shred of comprehensive evidence concerning DI for different crops is required. This review aims to provide adequate information about the effect of DI on WP. We reviewed 90 research papers from Ethiopia and summarize the effect of DI on WP and yield. It is shown that DI considerably increased WP compared to full irrigation. Despite higher WP, reduced biomass yield was obtained in some of the studied DI practices compared to full irrigation. It was also found that yield reduction may be low compared to the benefits gained by diverting the saved water to irrigate extra arable land. From this review, we understood that growers must recognize specific soil management and crops before applying DI strategies. Maize revealed the highest (2.65 kg m-3) and lowest (0.50 kg m-3) WP when irrigated at only the initial stage compared with being fully irrigated in all growth stages, respectively. Also, onion showed a decreasing WP with increased irrigation water from 60% crop water requirement (ETc) (1.84 kg m-3) to 100% ETc (1.34 kg m-3). Increasing water deficit from 100 to 30% ETc led to an increase of wheat WP by 72.2%. For tomato, the highest WP (7.02 kg m-3) was found at 70% ETc followed by 50% ETc (6.98 kg m-3) and 85% ETc (6.92 kg m-3), while the water application of 100% ETc (or full irrigation) showed the least WP (6.79 kg m-3). Teff showed the lowest WP (1.72 kg m-3) under optimal irrigation, while it was highest (2.96 kg m-3) under 75% ETc throughout the growing season. The regression analysis (R2) for WP increment and yield reduction versus saved water showed higher values, indicating that DI could be an option for WP increment and increasing overall yield by expanding irrigated area and applying the saved water in water-scarce regions. In conclusion, in areas where drought stress is the limiting factor for crop production, the application of DI is feasible. Keywords: Overall yield increase, water productivity, water saved, yield reduction

Termites can play a localized prominent role in soil nutrient availability and cycling because mound materials are often enriched in nutrients relative to surrounding soil. Mound materials may thus prove to be useful amendments, though evidently mound spatial arrangement needs to be considered as well. Furthermore, it is not known if gradients of soil properties exist from termite mound to interspace sites. Studying both aspects would be required to decide whether spreading of mounds or spatially differentiated management of surrounding crop to accommodate soil fertility gradients would be valid nutrient-management strategies. Mound abundance and mass were estimated at 9 and 4 mounds ha−1, representing 38.9 and 6.3 t ha−1 on Nitisols and Vertisols, respectively. Soil physical and chemical properties were measured on samples collected from internal and external parts of mounds and adjacent soils at 0.5, 1 and 10 m away from mounds. In general, termite mounds were enriched in plant nutrients and SOC on Vertisols but not on Nitisols. Termite mounds constituted only 0.3 to 1.3% of the 0–15 cm SOM stock on a per ha basis but nevertheless the immediate vicinity of termite mounds was a relative fertile hotspot. Hence, under the studied condition, we suggest spatial arrangement of crop around termite mounds according to soil fertility gradient and spatially differentiated nutrient management strategies. Our result suggests recommendation of termite mound spreading for soil nutrient amendment has to consider plant nutrient stock in termite mounds on per ha basis besides their nutrient enrichment. Interesting topics for future investigation would be growth experiment for different crops with mound materials treatment. It would also be interesting to study the effect mound building termite on soil properties under different soil conditions, slope class and land use.

Soil compaction in cropping systems, caused by the external pressure of machinery, creates impermeable layers that restrict water and nutrient cycles reducing agricultural production. To evaluate the matric suction effects on distribution with depth of stresses in a soil, caused by the use of agricultural machinery, Jet Fill tensiometers were installed at two different depths (i.e. 0.15 m, 0.30 m) in a soil profile constituted by silty sand with gravel (SM); to register the increments on subsoil vertical stresses, two miniaturized load cells (i.e. 16. 5 mm in diameter) were installed in a horizontal position under the centre line of the vehicle wheels’ path, at approximately 0.15 m and 0.30 m depth. Care was taken to calibrate the load cells in field conditions. A vehicle was made to pass over the soil surface, at a speed less than 5 km/h; the tyre inflation pressure applied on wheel was 380 kPa. Response of load cells to vehicle loading was evaluated at different average matric suction measured on soil profile. Finally, measured stresses have been compared with values obtained by applying well-known elastic theoretical methods used to assess stresses applied by tyres on bare soils. The corresponding results show that the increment of vertical stresses decreases as matric suction increases, and a good correlation between measurements and simulations of the increment on subsoil vertical stress.

This study assessed farmers’ soil and irrigation water management practices, perceptions, and major constraints at Koga, a large-scale irrigation scheme in Ethiopia. Key informant interviews, structured and semi-structured questionnaires, focus group discussions, and field visits were used for data collection. Soil samples were collected for the assessment of soil properties and a comparison with the respondents’ perception of soil-related constraints. A total of 385 respondents were involved in the questionnaire. All of the respondents had a good perception of soil acidity and its management strategies. Respondents’ perception was in line with the mean soil pH, soil texture, infiltration rate, exchangeable acidity, and soil organic carbon obtained from lab analysis and field tests. Soil acidity, unwise use of water, water scarcity, and lack of market linkages hampered the performance of the Koga irrigation scheme. Yet, respondents had a low awareness of irrigation water management. Farmers never used irrigation scheduling, but apply the same amount of water regardless of the crop type. As a result, low yield and water use efficiency were reported. To reduce soil acidity, an adequate lime supply for farmers with hands-on training on how to apply it would be desirable. Farmers should be aware of how to design effective irrigation scheduling and adopt water-saving management strategies.

Study region Upper Blue Nile Basin, Ethiopia. Study focus This study was conducted at the Koga Irrigation Scheme in the upper Blue Nile basin (Ethiopia) to investigate the influence of irrigation activity on the groundwater system. Representative samples of six shallow wells in the irrigated fields and four shallow wells in the adjacent non-irrigated (rain-fed agricultural lands) were selected. Dipmeter and hand GPS (GARMIN 60) were used for the monitoring of water table depth and fixing the location of the wells respectively. Arc GIS 10.5 has been applied for interpolation of water table depth (WTD). Water samples were collected and analyzed in the laboratory following international standards. New hydrological insights for the region The result shows that irrigation contributed to the water table rises of wells located in the irrigated fields which range from 0.77 m to 0.52 m and water table drops were observed in wells located in the non-irrigated fields. Investigations on the groundwater quality (GWQ) indicated that no significant effect was observed in the irrigated and non-irrigated fields. The study shows that good irrigation water management, continuous follow-up of the groundwater table and its physico-chemical properties are essential for the sustainability of the Koga Irrigation Scheme.

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.

Stable carbon isotope values of fatty acids (>20 C-atoms) (δ13C-FAs) have been increasingly used to apportion sediment sources using isotope mixing models. Understanding the variation of δ13C-FAs within catchment land uses is crucial for correct classification of sediment sources but it has rarely been evaluated. Here, we assessed the variability of δ13C values of FAs (C22–32) in soils under land uses within a catchment (23 km2) in the mid-hills of Nepal. High δ13C-FA variability in agricultural terraces (−32.8‰ to −20.2‰) and mixed forest (−37.3‰ to −22.3‰) was observed. This is due to differences in inputs of FAs of different chain-lengths with variable δ13C-FAs values by C3 and C4 crops as well as from farmyard manure in agricultural terraces. The pine plants succession in the forest and differences in FA preservation explained the observed variation in δ13C-FA values in a mixed forest. A pine forest transect that had undergone land cover change about 40 years ago showed high variability of δ13C-FA values strongly linked to legacy effects of previous C4 crops. Importantly, soils from the border of a land use and fresh surface deposits mostly increased the within-land use variability of δ13C-FAs values. Overall, δ13C-FA values have low potential to function as a robust tracer for high resolution discrimination of land uses and the validity of a priori sediment source classification is most questionable in catchments that have undergone land cover change. Cluster analysis was promising for identifying and combining functionally similar land uses to define more meaningful sediment sources at the catchment scale., Organic Geochemistry, 146, ISSN:0146-6380

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.

Soil erosion by water is critical for soil, lake and reservoir degradation in the mid-hills of Nepal. Identification of the nature and relative contribution of sediment sources in rivers is important to mitigate water erosion within catchments and siltation problems in lakes and reservoirs. We estimated the relative contribution of land uses (i.e. sources) to suspended and streambed sediments in the Chitlang catchment using stable carbon isotope signature (δ13C) of long-chain fatty acids as a tracer input for MixSIAR, a Bayesian mixing model used to apportion sediment sources. Our findings reveal that the relative contribution of land uses varied between suspended and streambed sediment, but did not change over the monsoon period. Significant over- or under-prediction of source contributions could occur due to overlapping source tracer values, if source groups are classified on a catchment-wide basis. Therefore, we applied a novel deconvolutional framework of MixSIAR (D-MixSIAR) to improve source apportionment of suspended sediment collected at tributary confluences (i.e. sub-catchment level) and at the outlet of the entire catchment. The results indicated that the mixed forest was the dominant (41 ± 13%) contributor of sediment followed by broadleaf forest (15 ± 8%) at the catchment outlet during the pre-wet season, suggesting that forest disturbance as well as high rainfall and steep slopes interact for high sediment generation within the study catchment. Unpaved rural road tracks located on flat and steep slopes (11 ± 8 and 9 ± 7% respectively) almost equally contributed to the sediment. Importantly, agricultural terraces (upland and lowland) had minimal contribution (each

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.