Coffee (Coffea arabica L.) is an important crop for Burundian economy, and banana (Musa acuminata) residues are used for coffee mulching. To evaluate the option of producing banana residues in coffee plots and to assess interactions between crops, multi-location field trials were set up at Gitega and Kayanza sites from January 2009 to July 2012. Two density levels for coffee (1333 and 2667 trees ha(-1)) and banana (800 and 1600 plants ha(-1)) were combined in full factorial design complemented with monocropped plots for each density in Randomized Complete Block Design with three replications per site. Banana and coffee yields, land equivalent ratio and competitive ratio, growth characteristics, effect of shading on nutrient content in leaves, and economic benefits were determined. Banana had a significant (p <= 0.05) negative effect on coffee yield and growth. With high density of coffee, banana reduced coffee yield by 35%-40% at low density and 67%-84% at high density. Land equivalent ratio values were always >1 in both sites, showing that intercropping is beneficial. In high density of coffee, net benefit increase was 58% at Gitega and 201% at Kayanza when intercropped with high density of banana compared to monoculture. Growing bananas with young coffee was financially profitable. However, banana density and suckers need to be managed to reduce their negative impact on coffee performance.

Abstract. Urban gullies (UGs) are a rapidly expanding but under-recognized human-induced hazard in cities across the Global South, causing widespread damage to housing and infrastructure. Despite their growing importance, their economic impacts remain largely unquantified. Here, we assess the costs associated with UG expansion in Kinshasa (D.R. Congo), the world’s most affected city and a critical case to evaluate the potential magnitude of this hazard. Using an integrated approach combining field surveys and semi-structured interviews with 802 households, real estate data, and spatial analysis, we quantify direct damages, household-level costs, and system-wide economic impacts. Households experiencing damage (n=666) reported average material losses of 4,320 USD, while most respondents (n=606) contributed to bottom-up stabilization efforts, investing on average 335 USD. These costs are clearly substantial given that most households report monthly incomes below 500 USD. In addition, UGs significantly reduce property values, with total losses in Kinshasa estimated at 979 million USD. These findings reveal the massive and multi-dimensional economic burden of UGs and suggest that their impacts are likely severely underestimated in rapidly urbanizing regions. Urban gullies should therefore be recognized as a major and growing component of urban risk, requiring urgent integration into disaster risk reduction and urban planning strategies.

Surface runoff is a major driver of soil erosion and nutrient losses in agricultural landscapes, highlighting the need for effective nature-based solutions to improve soil and water conservation. Among these solutions, vegetative barriers can reduce runoff by increasing hydraulic resistance and promoting water retention and infiltration. This study aimed to quantify the hydraulic performance of Silphium perfoliatum vegetative strips through the assessment of water depth and Manning’s roughness coefficient during runoff simulations. The experiment was conducted in Belgium on three Silphium perfoliatum strips (3 m × 1 m) established on a 6% slope, with slight differences in plant density. Runoff simulations were performed under different flow rates, and hydraulic resistance was evaluated using Manning’s roughness coefficient. The results showed that the vegetative strips generated substantial hydraulic resistance, with a mean Manning’s roughness coefficient of 0.41 ± 0.05 s m⁻¹ᐟ³. Manning’s roughness coefficient decreased with increasing discharge, reflecting a transition from microtopography-dominated resistance under shallow flow conditions to a vegetation-controlled regime at greater flow depths. Water depth increased consistently with discharge in all repetitions, indicating effective flow attenuation and increased water residence time within the strips. No significant differences in Manning’s coefficient were observed between the highest tested discharges, suggesting that hydraulic resistance reaches a stable regime beyond a threshold flow rate. Slightly higher roughness values were associated with greater plant density, highlighting the influence of vegetation structure on runoff dynamics. These findings demonstrate the potential of Silphium perfoliatum strips to reduce runoff velocity and enhance hydraulic resistance, supporting their integration into sustainable soil and water conservation strategies. Further research should investigate the influence of vegetation density, seasonal variability, and comparisons with control treatments to better assess their effectiveness under field conditions.

Runoff initiation is a major uncertainty in event-scale erosion modelling, particularly in small agricultural catchments where sediment export is controlled by threshold-like hydrological responses. This study developed a regime-based framework to analyse how alternative representations of runoff initiation affect runoff volume, peak discharge, and sediment-yield prediction in a small temperate agricultural loess catchment in Wallonia, Belgium. The analysis included 154 rainfall–runoff events monitored between 2015 and 2023, of which 46 had complete suspended-sediment observations. Runoff initiation was represented by the initial abstraction ratio λ of the Soil Conservation Service Curve Number model. Event-specific optimised λ values were derived from observed rainfall–runoff responses and generalised using K-means regimes and continuous regression based on hydro-meteorological descriptors. These formulations were used to estimate runoff volume and peak discharge, which were then supplied as inputs to the Modified Universal Soil Loss Equation. Fixed and literature-based λ formulations performed poorly, with a best runoff-volume Nash–Sutcliffe efficiency (NSE) of 0.13. Five regimes provided a strong diagnostic summary, preserving runoff volume (NSE = 0.94) and peak discharge (NSE = 0.67). Under out-of-sample prediction, regime performance declined to NSE = 0.21 for runoff volume and − 0.26 for peak discharge, whereas the continuous formulation achieved NSE = 0.40 and 0.34, respectively. Predictive sediment-yield performance remained poor for both approaches (NSE = −0.03 and 0.01). The framework distinguishes diagnostic structure from predictive performance and clarifies how hydrological uncertainty affects event-scale sediment-export modelling.

Abstract. Accurate pluvial flood mapping in ungauged agricultural catchments is often constrained by a lack of calibration data. This study evaluates a parsimonious, high-resolution (1 m) distributed framework assessing peak discharge along concentrated flow paths, validated against 39 events in two nested experimental catchments (84 and 111 ha). The framework decouples the rainfall-runoff process to systematically compare adjusted SCS-CN formulations against two spatially explicit routing algorithms (SCS vs. SWRRB). Within this specific local context, findings demonstrate that the Jain initial abstraction method significantly reduces volumetric bias, with the distributed approach statistically outperforming lumped modelling. However, performance remains strictly regime-dependent, driven by rainfall intensity rather than total depth. This exposes the structural limits of static Curve Number (CN) parameterizations in capturing rapid Hortonian dynamics, causing the model to dampen minor events while amplifying high-intensity storms. Regarding hydraulic transfer, both routing strategies yield statistically equivalent performance (median KGE 0.40 vs. 0.37). Crucially, while the routing phase acts as a mechanical propagator of volumetric uncertainty, it consistently synchronizes the overall runoff window. Applied to 25- and 100-year design storms, this framework successfully identifies hydrodynamic attenuation and kinematic synchronization at confluences. Based on these empirical observations, we propose this approach as a transferable blueprint to pinpoint hydraulic hotspots and strategically allocate proactive mitigation measures in vulnerable, unmonitored regions.

Urban gullies (UGs) are an increasingly urgent concern in many cities of the Global South. Rapid and largely unplanned urban expansion, combined with inadequate drainage infrastructure, erodible soils, and intense rainfall, have led to the formation of thousands of large UGs —often several tens of meters wide and deep and extending over hundreds of meters— in cities across the Democratic Republic of the Congo. These gullies cause loss of life, destroy housing and critical infrastructure, and further exacerbate the vulnerability of already marginalized populations. The situation is particularly severe in Kinshasa, where more than 800 UGs have already been recorded, threatening over one million people.A wide range of initiatives has been implemented to stop UG expansion. These include large-scale engineering interventions led by the state or non-governmental organizations, such as concrete reinforcement of gully heads and canalizing the gully channel. However, many measures are expensive and/or often fail.Nevertheless, emerging evidence highlights promising strategies for urban gully prevention and control. A key principle is to prevent rainwater from leaving individual parcels by installing water retention structures, as the accumulation of runoff along roads is a primary driver of gully initiation and expansion. A critical requirement for success is that a majority of households actively participate in such initiatives. Improving risk awareness and creating synergies between UG control and water accessibility will therefore be crucial to achieving this.Here we aim to demonstrate the effectiveness of such a strategy. For this purpose, we installed water retention structures in a representative catchment in Kinshasa affected by UGs. This is done in close collaboration with local stakeholders. By monitoring and studying participation rates as well as the resulting hydrological effects (e.g., through the involvement of local students), we will develop actionable guidelines to this growing problem in Kinshasa and elsewhere, thereby enhancing both urban resilience and water security in vulnerable neighborhoods.

Accelerated erosion can have detrimental effects on the chemical, physical, and biological quality of soils and surface water bodies. It impacts agricultural productivity and soil ecosystem services. Vegetative barriers can help address this challenge by regulating flows within agricultural watersheds, reducing runoff velocity, and trapping eroded sediments. However, only a limited number of documented studies have quantified the effectiveness of Miscanthus giganteus and short rotation coppice (SRC) against surface runoff. Therefore, this study specifically aims to investigate the effectiveness of these two vegetative barriers in reducing surface runoff and facilitating infiltration. A series of runoff simulation experiments were conducted on silt loam soils in Wallonia (Belgium) between 2021 and 2024, focusing on Miscanthus giganteus and SRC willow strips with varying planting densities and ages (2 to 12 years) on slopes ranging from 4 to 12%. This allowed to determine the hydraulic roughness based on the water depth in the vegetation strip. The runoff simulation results reveal a Manning coefficient (n) ranging between 0.37 and 0.8 s.m-1/3 for Miscanthus giganteus and between 0.32 and 0.59 s.m-1/3 for SRC depending on different factors (slope, plant density, flow rate and age of plantation). These findings suggest that vegetation strips, particularly Miscanthus giganteus, may be more effective than conventionally used grass strips in slowing down surface flows. Moreover, measurements using the water balances of the runoff tests indicate an infiltration rate of 130 +/- 30 mm/h for SRC and 83 +/- 20 mm/h for Miscanthus giganteus, showcasing the ability of both barriers to absorb upland runoff. Overall, these results underscore the potential of Miscanthus giganteus and SRC willow strips to improve hydrological functioning of agricultural catchments.

As a result of intensive agricultural practices, cultivated soils of the European loess belt can experience high levels of degradation by erosive runoff. Given the sometimes severe and costly on- and off-site impacts, the agricultural community is urged to adopt alternative cropping techniques to mitigate runoff and erosion. Several cropping practices related to conservation agriculture are known for their ability to mitigate surface flows, but the magnitude of their effectiveness is associated with a wide variability due to environmental or management factors. The influence of these factors on the practices’ effectiveness is still poorly understood in quantitative terms. We therefore quantitatively reviewed the effectiveness of three common conservation farming practices at controlling runoff and soil loss. A systematic search was performed, focused on the plot scale and the Western European context, and meta-analyses were carried out on the 35 collated relevant studies involving 239 individual trials (plot-years). Two different approaches suitable for hierarchically structured datasets were used for the meta-analyses: hierarchical nonparametric bootstrapping and linear random effects models. Both methods yielded very similar outcomes, but the lack of primary data sometimes restricted the ability to account for all hierarchical levels of the dataset in the random effects models. We found that, on average, winter cover crops decrease cumulative seasonal (autumn-winter) runoff by 68% and soil erosion by 72% compared to a bare soil. The level of stubble tillage on the control plot, the number of successive years of cover cropping, and the maximum vegetation cover reached are three key variables explaining the mitigation effect of winter cover crops. In potato crops, tied-ridging (=(micro)basin tillage) cut cumulative seasonal (spring-summer) overland flow by a mean of 70% and soil loss by 92% compared to conventional furrows, but no moderators could be identified to explain the variability across studies or trials. Conservation (non-inversion) tillage techniques alleviate cumulative seasonal runoff by 27% and associated sediments losses by 66% on average, but a publication bias is strongly suspected for this meta-dataset. These mitigation effects are much greater for spring crops than for winter crops, and increase over time since ploughing stopped. The type of conservation tillage schemes also affects the capacity to attenuate surface flows. Intensive non-inversion tillage schemes based on multiple (powered) tillage operations turns out to be the least effective at reducing both water and soil losses. The best performing scheme against runoff appears to be a deep non-inversion tillage (-61%), while against erosion it would be a direct drilling system (-82%). Coarser-textured soils (sandy loam) also respond slightly better to conservation tillage than (clay-)loams. Although several factors could partly explain the effectiveness of two of the three conservation practices considered in this study, there remains a high (unexplained) variability between trial effect sizes, thus not attributable to sampling variability. Meanwhile, this review provides farm advisors or policy makers with guidance on the conditions in which such conservation practices are expected to achieve the greatest benefits.

Large urban gullies cause damage in many tropical cities across the Global South1,2. They can result from inappropriate urban planning and insufficient infrastructure to safely store and evacuate rainfall in environments that are already highly sensitive to soil erosion1,3,4. Although they can cause large destruction and societal impacts such as population displacement1,2,5, the magnitude of this geo-hydrological hazard remains poorly documented and understood6,7. Here we provide an assessment of the extent and impact of urban gullies at the scale of the Democratic Republic of the Congo (DRC). Through mapping, we identify 2,922 urban gullies across 26 cities. By combining their formation and growth rates with population density data8, we estimate that around 118,600 people (uncertainty range: ± 44,400 people) have been displaced by urban gullies over the period 2004-2023. We find that average displacement rates increased from about 4,650 persons yr-1 (pre-2020) to about 12,200 persons yr-1 (post-2020). Between 2010 and 2023, the number of people living in the potential expansion zone of urban gullies doubled from 1.6 (±0.6) to 3.2 (±1.3) million, with more likely to be exposed due to urban sprawl9,10 and climate change11. We suggest that there is a need for tools and strategies to prevent and mitigate this hazard.

In Western Europe, the silt loam belt is highly vulnerable to erosion, especially in spring on fields cultivated with spring crops such as maize. Identifying conservation farming practices that reconcile agricultural production with soil and water protection is therefore critical. To this end, we evaluated the suitability of red fescue or white clover undersowing as well as strip-tillage to control runoff, soil loss, and herbicide surface loss in maize under natural rainfall conditions. Results were compared to a sole-maize control. The treatments were implemented in triplicate across six trial sites, distributed over three cropping seasons from 2021 to 2023. Weed control in the undersowing treatment proved particularly challenging due to herbicide constraints. Furthermore, no mitigation effect was observed on water, sediment, and herbicide surface flows, while maize yields were reduced by 11% on average compared to the control treatment. Although strip-tillage also resulted in an 11% loss in maize yields on average, it significantly decreased runoff (-31%) and soil loss (-60%) compared to the control. Based on the measured runoff and soil losses for the control and strip-tillage treatments, the process-based CREHDYS model was calibrated using a parsimonious approach. It was then used to conduct scenario analyses across a range of soil, rainfall and slope conditions found across the Belgian loess belt. On average across all scenarios, pluvial flood hazard was reduced by about half. Modelling of soil losses in strip-tillage proved insufficiently reliable, highlighting the need for improved characterisation of sediment fluxes in such systems. In spite of the disappointing results of undersowing in terms of yields and reduction in surface flows, future research could focus on other environmental benefits of this technique. For strip-tillage, strategies should be investigated to promote its adoption by farmers as a stepping stone towards no-till systems.

In Northwestern Europe, sediment transport from agricultural fields to rivers has significant off-site impacts, influenced by connectivity between landscape elements. Sediment connectivity, assessed using the index of connectivity (IC) developed by Borselli et al. (2008), is shaped by landscape configuration, including features like field boundaries that divide land parcels. Effective management requires understanding these interactions to mitigate soil erosion. IC depends on factors enhancing (upstream area and slope) or impeding (downstream distance and impedance) connectivity, with impedance estimation being particularly challenging to quantify due to vegetation effects. This study proposes to refine the IC weighting factor by incorporating parcel connectivity, better reflecting agricultural landscape fragmentation's impact. Focusing on the Dyle sub-catchment in Belgium, we applied the Revised IC using high-resolution data (1 m x 1 m). Fragmented landscapes yield lower connectivity values, indicating greater sediment disconnection. This is especially pronounced along concentrated flow paths, where up to 49 % of the least connected flow paths are disconnected compared to non-fragmented setups. Isoline-based parcel fragmentation emerged as highly effective, promoting larger parcel sizes and better disconnection on concentrated flow paths. These results emphasize the opportunities for improved management of agricultural landscapes in order to reduce sediment connectivity through appropriate land use practices and parcel configurations. Furthermore, by identifying potential vegetation barriers at the intersection of concentrated flow paths and field boundaries, our analysis shows that around 40 % of these barriers consist of adjacent fields with the same crop. It highlights opportunities for more effective crop rotations strategies.

Rapid and chaotic urbanization leads to the formation of urban gullies in many tropical cities of the Global South. To prevent and limit the destructive impacts of these gullies, runoff retention structures are often constructed. Yet, earlier research indicates that these measures are largely ineffective in reducing urban gully expansion. This study aims to understand why. We conducted detailed field surveys in two representative catchments affected by urban gullies in Kinshasa (Democratic Republic of the Congo) and characterized all existing runoff retention structures. We then used the Soil Water Management Model (SWMM) to evaluate the likely influence of these structures on runoff volumes and peak discharges. Although most parcels (77%-88%) in the catchments have at least one runoff retention structure, their overall effect catchment runoff is limited (e.g., only 25-30% reduction of the total runoff volume for an event with a return period of 2 years). One key reason is that many structures are too small and poorly maintained, reducing their already limited storage capacities. Additionally, they are typically unequally distributed within the catchments (with fewer measures upstream) and not proportional to the parcel size, leading to some oversized and many undersized structures. Overall, we demonstrate that, while current efforts are largely ineffective, coordinated implementations of runoff retention structures proportional to parcel size offer promising perspectives for better controlling urban gully erosion. (c) 2024 International Research and Training Center on Erosion and Sedimentation, China Water and Power Press, and China Institute of Water Resources and Hydropower Research. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Abstract Besides its carbon sequestration potential, biochar application generally improves soil physical properties, but the magnitude of its impact and the underlying mechanisms remain debated and depend on soil type, biochar application rate, and age. The objective was therefore to determine the effect of biochar application rate and age on physical properties of agricultural soils in a temperate climate. On a silt loam and a sandy loam soils, we compared the physical properties of fresh biochar (1% and 2% w/w) or century‐old biochar (0.5%–1% w/w; 19th‐century kiln sites)‐enriched soil samples with biochar‐free soil samples. Biochar pore network characteristics were determined using helium pycnometry, mercury intrusion porosimetry, scanning electron microscopy observation, and electron dispersive X‐ray spectrometry, whereas location of biochar particles within soil structure was analyzed using optical microscopy observations. Fresh biochar application decreased bulk density by 16.8% and increased saturated water content by 16.0% and macroporosity by 78.8%. These effects were attributed to soil structure improvement rather than to biochar porosity. Soil type and biochar application rate had a limited impact. In the long‐term, biochar effects were mostly nonsignificant, which might result from its fairly low content in kiln sites and from the clogging of its internal porosity by clay particles. Biochar was thus able to improve some soil physical properties in the short‐term, but these effects could no longer be detected in the very long‐term. Further investigating the time rate of change in soil physical properties over several decades following biochar additions to soil would therefore seem particularly relevant.

Landslides are processes that naturally occur on numerous hillslopes across the world. In inhabited regions, landslides are commonly seen as a threat and a land degradation process. Yet, in densely-populated rural mountainous regions in the tropics, local communities have often no choice but to live on steep terrains naturally impacted by landslides. Besides, landslides may also be a source of opportunities for these communities. However, little is known on the rationale underlying land use in landslides. The aim of this study was to assess the extent, modes of valorization and degree of satisfaction of famers exploiting landslides in a populated rural mountainous environment of DR Congo (territory of Kalehe). We interviewed 82 farmers living on 57 representative landslides, these mass movements having been selected according to their characteristics (size, type) and position along the hillslopes and taking into account accessibility or safety constraints. We show that almost all landslides are being exploited by farmers and that they adapt their land use to the type of landslide. Indeed, significant contrasts are observed between landslides and the surrounding hillslopes for subsistence crops, forests, eucalyptus plantations and pasture. Farmers also adapt land use according to local variations in slope or wetness within a given landslide. Nearly half of the farmers reported that their land was more valuable inside than outside landslides. Better soil fertility, higher soil moisture, lower sand or stone content, lower slopes are some of the main factors that increase the land value, offering more favorable conditions for cropping than on land outside landslides. Despite the perceived risk of landsliding, famers settlement on unstable slopes appears justified by the immediacy of the benefits that outweigh the potential dangers. Better understanding the reasons for the settlement of populations on unstable slopes may help devise better risk reduction strategies.

Urban gullies (UGs) are a growing concern in many tropical cities of the Global South. Addressing this new geohydrological hazard requires good insights into the rates and controlling factors of this process. Therefore, we investigate the expansion rates of a representative sample of UGs in Kinshasa (n = 17) and Bukavu (n = 29), two contrasting cities in D.R. Congo. We reconstruct long-term (10-17 years) expansion rates, making a distinction between headcut retreat and sidewall widening, and analyse the environmental factors potentially explaining these rates. Total expansion rates varying between 12.6 and 863 m(2)y(-1). Most of this expansion happens through sidewall widening. In Kinshasa, which is mainly characterized by sandy soils, contrasts in expansion rates are mainly correlated to the characteristics of the upslope drainage area of the gullies. Especially the road density and a hypothetical runoff index (combining drainage area, land use and soil characteristics) explain a significant part of the observed variation. In Bukavu, such trends are less apparent. This is likely because the clayey nature of the soils provides more resistance against gullying, resulting in overall smaller and less actives UGs. Furthermore, the already low infiltration rates of these soils probably make the relative impact of urbanization on runoff production smaller. Our results also indicate that UGs located in recent landslides have higher gully expansion rates. The mechanisms behind remain poorly understood. Overall, our work opens promising perspectives to model and predict gully expansion rates in urban settings but may also guide efforts aiming to stabilize UGs.

Context: Soil water and fertility management have been the main challenges of crop production in West Africa, and their impacts are exacerbated by climate variability. While research has been conducted to optimize fertility and water applications for rainfed crops production in this region, little is known about the management of these resources for off-season cereal crops production. Objective: This study assessed the optimal combination of irrigation and fertilizer levels for off-season maize production in Benin, using the DSSAT CERES-Maize crop model. Methods: Two years' experiments (2018 and 2019) of 4 levels of deficit nutrient (DN) and two years' experiments (2019 and 2020) of 4 levels of deficit irrigation (DI) were conducted and data were collected on maize growth and yield. DSSAT model was calibrated using crop data from DN experiment in 2018 (DN2018) and DI experiment in 2019 (DI2019), and validated using the DN2019 and the DI2020 experimental data. Then, a long-term scenarios analysis (40-years, 1980-2019) was performed to optimize (i) DI levels, (ii) DN rates; and (iii) combined DI levels and DN rates. Results: The model predicted the grain yield (GY) and total aboveground biomass (TB), with a relative root mean square error and a coefficient of efficiency of 18.3 % and 0.38 for the GY and 11.7 % and 0.50 for the TB during the validation, respectively. However, the model did not account for the effects of DI or DN on the phenological dates, which led to similar predicted values for the anthesis and maturity dates among DI and DN treatments during calibration and validation. Moreover, the model was sensitive to periods with high values of temperature (>45(degrees)C) recorded during the DI period, inducing a reduction of the grain filling rate in DI treatments. DI treatments were more sensitive to a change in DUL, SLL, SAT, RGFIL and RUE than the DN treatments; while the DN treatments were more sensitive to the CTCNP2. Reducing maize water requirements by 40% at the vegetative stage resulted in similar predicted grain yield as in the full irrigation treatment; while reducing the water requirements by 60% resulted in similar predicted water use efficiency (WUE) as in the full irrigation treatment. Furthermore, the inter-annual variability of grain yield was lower under the optimal DI combined with no fertilizer but higher under high DI combined with higher fertilizer rates. Finally, a combination of 40-60 % of deficit irrigation at the vegetative stage and one-third to half of the recommended fertilizer rates depending on resources availability was the optimum combination of DI and DN rates for off-season maize production. Conclusions: The projected grain yield and WUE under optimal DI and DN levels were likely underestimated due to shortcomings in the model structure to deal with effects of water and nutrient stresses on phenological dates. For reliable assessments of the effects of water and nutrient stresses on grain yield and WUE, there is need to update parameterization and code of the CERES crop models in DSSAT to have a sufficiently strong effect of water and nutrient stress on phenological dates, and the contribution of phenology to LAI and yields predictions.

Conservation farming practices are known for their capacity to mitigate runoff and erosion, but the magnitude of their effectiveness is highly variable across studies. In order to better understand the contribution of environmental and management factors to their effectiveness, up to 37 studies reporting 271 individual trials were collated for a quantitative review regarding 3 common conservation agriculture-related practices, at the plot scale and in a Western European context. Two different methods suitable for hierarchically structured data sets were used for the meta-analyses-hierarchical nonparametric bootstrapping and linear random effects models-, yielding nearly identical average outcomes but differing in terms of confidence intervals. We found that, on average, winter cover crops reduce cumulative seasonal (autumn-winter) runoff by 68% and soil losses by 72% compared with a bare soil. The occurrence and intensity of stubble tillage on the control plot is a key explanatory variable for the mitigation effect of winter cover crops. In potato crops, tied ridging reduces cumulative seasonal (spring-summer) runoff by a mean of 70% and soil erosion by 92%. Conservation (non-inversion) tillage techniques alleviate cumulative seasonal overland flow by 27% and associated sediments losses by 66%, but strong evidence of publication bias was detected for this farming practice, probably leading to an overestimation of its effectiveness. These mitigation effects are shown to be much greater for spring crops than for winter crops, and to increase with time since ploughing was stopped. The type of conservation tillage scheme strongly affects the ability to attenuate surface flows. Intensive non-inversion tillage systems relying on repeated use of (powered) tillage operations appear to be the least effective for reducing both water and sediment losses. The best performing scheme against runoff would be a deep (non-inversion) tillage (-61%), while against erosion it would be a no-till system (-82%). Although several explanatory factors were identified, there remains a high (unexplained) variability between trials effect sizes, thus not attributable to pure sampling variability. Meanwhile, this review provides farm advisors or policy makers with guidance on the contexts in which implementation of such conservation practices should be supported so as to maximize expected benefits.

Reliable hydrological monitoring is crucial for effective water resource management, but establishing observatories in remote areas with extreme weather presents significant challenges. This study aimed at identifying cost-effective methods for streamflow estimation in such environments. We evaluated the performance of the Soil and Water Assessment Tool (SWAT) model using various precipitation data sources: ground-based rain gauge networks with different densities (one-gauge (1RG), two-gauge (2RG), and five-gauge (5RG) configurations) and satellite-derived Integrated Multi-satellite Retrievals for GPM (IMERG) data. The study focused on the Sahafihitry catchment, a 200 km² area in northeastern Madagascar. The results demonstrated that denser rain gauge networks (5RG and 2RG) captured the spatial variability of rainfall more effectively than a single gauge or IMERG data. This translated into superior SWAT model performance. Denser networks achieved higher statistical metrics (R², slope of regression a, Nash-Sutcliffe efficiency NSE, root mean square error RMSE, Kling-Gupta efficiency KGE) indicating a better fit between simulated and observed streamflow. Specifically, 5RG: R² = 0.84, a = 0.92, NSE = 0.83, RMSE = 3.33, KGE = 0.82; 2RG: R² = 0.85, a = 0.95, NSE = 0.83, RMSE = 3.36, KGE = 0.88; 1RG: R² = 0.73, a = 0.80, NSE = 0.72, RMSE = 4.28, KGE = 0.88; IMERG: R² = 0.48, a = 0.63, NSE = 0.37, RMSE = 6.46, KGE = 0.66. Furthermore, rain gauge data outperformed IMERG in simulating both flood events and low-flow periods. While IMERG offers low cost, readily available data, its lower performance introduces significant uncertainty into hydrological modeling. In contrast, the two-gauge network (2RG) achieved satisfactory streamflow simulations and represents the most cost-effective option for establishing reliable observatories within the specific characteristics of this study area.

Adding biochar to soils is being advocated to mitigate soil erosion. However, given biochar aging and persistency in soils, the effects of biochar on soil in the long-term are important to investigate yet remain largely unknown. The objective was therefore to determine the long-term effect of biochar on interrill erosion on cropland soils. Experiments were conducted using topsoil from three fields of different textures (silt loam, loam and sandy loam). Each field was characterized by the presence of kiln sites containing century-old charcoal used as proxy to investigate the long-term impact of biochar. Aggregate stability was measured using the method of Le Bissonnais (1996), whereas interrill erosion was studied using two successive (24-h apart) rainfall simulation experiments (84 mm h(-1), 90 min.). The presence of historical charcoal in kiln sites did not affect soil aggregate stability, irrespective of charcoal-C content or soil type. For the first rainfall simulation only, the century-old charcoal reduced both the final runoff and soil loss rates by, respectively, 15.4 mm h(-1) and 12.1 g m(-2) h(-1) for each percent increase in charcoal-C content. As a result, Meyer's interrill erodibility decreased with increasing charcoal-C content. However, because the final runoff and soil loss rates decreased to a similar extent with increasing charcoal-C content, Kinnell's interrill erodibility was unaffected by charcoal-C content. These effects on interrill erosion parameters were independent of soil type and could not be related to changes in soil chemical properties. The measured reduction in runoff and soil loss were attributed to delayed crust development, which could be related to increasing proportions of clods in the soil samples with increasing charcoal-C content. Further research may be needed to confirm the observed trends and underlying mechanisms over a wider range of soil types.