Measured Water Retention Research Articles

Towards sustainable agricultural water management in Poland – How to meet water demand for supplemental irrigation?

The global challenge of water scarcity, particularly in agriculture, demands urgent attention due to the overexploitation of water resources and the escalating impacts of climate change. This study focuses on the unique challenges faced by Poland, experiencing increasing concerns related to droughts. It explores the utilization of supplemental irrigation, specifically in the context of Central Europe, where a distinctive approach known as supplemental irrigation is employed. The study emphasizes the need for sustainable water management practices and investigates the potential of small water retention measures (SWRMs), such as ponds and drainage water management, as solutions to enhance water availability in agriculture. A macro-scale water balance study is conducted using the Soil and Water Assessment Tool (SWAT) to estimate spatio-temporal variability of water demand for supplemental irrigation in Poland. The highest demand, approximately 2.5 billion m3 (for arable lands) and 1.3 billion m3 (for grasslands), occurred during the exceptionally dry year of 2015, characterized by severe agricultural drought effects. The study also assesses the efficiency of SWRMs in meeting irrigation demands at national level. The results highlight a paradox in their effectiveness during critical periods, specifically in dry years when water demands are the highest. The outcomes of the model experiment underscored concerns about the insufficiency of meeting the water needs of irrigated agriculture solely through the construction of small retention facilities during very dry years. The outcomes of this research contribute to a better understanding of irrigation water demands in temperate climate region, support evidence-based practices for sustainable water management, and inform policymakers and stakeholders involved in water governance.

Preparation and performance characterization of insoluble dietary fiber-alginate-pea protein ternary composite gels

Increased consumption of plant-based foods and better utilization of by-products could reduce the environmental impact of food consumption. In this study, IDF-SA-PPI ternary composite gels were prepared by a pH-controlled method by adding IDF (insoluble dietary fiber from bamboo shoot by-products) to pea protein isolate (PPI)-sodium alginate (SA) binary gels. The effects of pH and IDF content on the properties of PPI-SA binary gels were systematically investigated. Textural analysis, water retention measurements, and rheological studies showed that the IDF-SA-PPI hydrogels exhibited high gel strength, water retention capacity, and energy storage modulus. Fourier transform infrared (FTIR) spectroscopy indicated the appearance of new absorption peaks in the ternary composite gels, suggesting that hydrogen bonding and electrostatic interactions were the dominant molecular forces. Thermogravimetric analysis (TGA) demonstrated that the addition of IDF enhanced the thermal stability of the gels. Additionally, low-field nuclear magnetic resonance (LF-NMR) analysis revealed that IDF facilitated the conversion of free water to immobilized water within the gel matrix. The advanced ternary composite hydrogel was natural, sustainable, and robust, exhibiting significant potential as a multifunctional material across various applications. Additionally, it could enhance the utilization of bamboo shoot by-products in the food processing industry.

Local and catchment-scale effects of water retention measures at Lake Velence

AbstractClimate change manifested its adverse impacts last year, with an extreme drought leading to a drastically low water level in Lake Velence, Hungary. Nature-based solutions have the potential to alleviate these impacts locally. While a few initiatives have been implemented in Hungary, widespread adoption of these solutions is expected to be a goal for the more distant future.This research focuses on one catchment at Lake Velence to evaluate decision-maker's readiness and urban water management infrastructure for broadly implementing nature-based solutions. Methods include delineating the stormwater system and creating a numerical model to evaluate rainfall-runoff processes and the possible impacts of nature-based retentions. Surveys among local mayors were conducted to assess their perception of existing water infrastructures and implementations of nature-based solutions. Its widespread use may become significant, but its effect on the lake's water level remains negligible.

Hydraulic Property Estimation of Green Roof Substrates from Soil Moisture Time Series

The adoption of green roofs is an effective practice for mitigating environmental issues in urban areas caused by extreme weather conditions. However, certain design aspects of green roofs, such as the characterization of the physical properties of their substrates, need a better understanding. This study proposes a simple method for estimating two hydraulic properties of green roof substrates based on the evolution of moisture during drying periods, or drydowns, where evaporative processes dominate: the weighted-mean diffusivity and the saturated hydraulic conductivity. Soil moisture was monitored using 12 in situ sensors from 2015 to 2020 in a study involving six different green roof plots composed of various mixtures of demolition-recycled aggregates and organic substrates. A universal parameterization for determining water diffusivity in soils was applied to estimate the weighted-mean hydraulic diffusivity. As a by-product, the saturated hydraulic conductivity was estimated from the evaluated diffusivity and the measured water retention data. The median values obtained for and range from 14.5 to 29.9 cm2d−1 and from 22 to 361 cmd−1, respectively. These values fall within the ranges reported by other research groups using direct measurement methods and supports the validity of Brutsaert’s model for green roof substrates. Furthermore, an increase in and a decrease in were observed as the percentage of recycled aggregates in the substrates increased, which could be considered for design purposes.

Identifying the optimal type and locations of natural water retention measures using spatial modeling and cost-benefit analysis

Water management has shifted from solely technical and engineering approaches towards nature-based solutions (NBS), like natural water retention measures (NWRM), offering benefits beyond hydrology, such as improved well-being and biodiversity conservation. Determining the best type and location of these measures is challenging due to diverse options with varying benefits and effects depending on measure type and location characteristics. While most studies regarding the optimal allocation and implementation of NBS focus on the urban environment, this study presents a methodology for decision-makers focusing on inter-urban regions with limited data on NWRM implementation. Through hydrological modeling and cost-benefit analysis (CBA), we identify Pareto optimal NWRM sites and types, considering water quantity and quality alongside economic, environmental, and social objectives. We defined optimal locations that seek the most significant reduction of runoff, sediment, and pollutants, whilst optimal NWRM types are defined to seek the most cost-effective measures based on hydrological, ecological, and social criteria. Using the Open Non-point Source Pollution and Erosion Comparison Tool (OpenNSPECT), we simulated increased infiltration in different inter-urban areas and identified the optimal placement. The criteria for selecting suitable NWRM types for the identified areas are derived from the EU Directorate General for the Environment (DG-ENV) NWRM database. The results show different effective areas for reducing runoff, sediment, and pollutants. While one NWRM (natural bank stabilization) was identified as most beneficial for reducing sediment, several measures were selected for runoff reduction. Interestingly, measures with high potential for pollutant reduction seem to offer limited social and biodiversity benefits, suggesting conflicting objectives and highlighting the importance of accounting for multiple criteria. By employing simplified models and qualitative benefit assessments, this paper presents a practical decision-making approach to facilitate NWRM implementation in data-scarce areas.

Links between soil pore structure, water flow and solute transport in the topsoil of an arable field: Does soil organic carbon matter?

An improved understanding of preferential solute transport in soil macropores would enable more reliable predictions of the fate of agrochemicals and the protection of water quality in agricultural landscapes. The objective of this study was to investigate how soil organic carbon (SOC) and soil texture shape soil pore structure and thereby determine the susceptibility to preferential transport under steady-state near-saturated flow conditions. To do so, we took intact topsoil samples from an arable field that has large variations in SOC content (1.1–2.7%) and clay content (8–42%). Soil pore structure was quantified by X-ray tomography and soil water retention measurements. Non-reactive solute transport experiments under steady-state near-saturated conditions were carried out at irrigation rates of 2 and 5 mm h−1 to quantify the degree of preferential transport. Near-saturated hydraulic conductivities at pressure heads of −1.3 and −6 cm were also measured using a tension disc infiltrometer. The results showed that larger abundances of small macropores (240–720 µm diameter) and mesopores (5–100 µm diameter) resulted in weaker preferential transport, due to larger hydraulic conductivities in the soil matrix that prevented the activation of water flow and solute transport in large macropores. In particular, the degree of preferential transport was most strongly and negatively correlated with the mesoporosity in the 30–100 µm diameter class. In contrast, the degree of preferential transport was not correlated with connectivity measures (e.g. the percolating fraction and critical pore diameter for the macropore network), probably because i.) the pore space of almost all samples was highly connected, being dominated by one percolating cluster, and ii.) only a part of this percolating macroporosity was active under the near-saturated conditions of the experiment. We also found that the degree of preferential transport was strongly and negatively correlated with clay content, whilst the effects of SOC were not significant. Nevertheless, macroporosity in the 240–720 µm diameter class and mesoporosity were positively correlated with SOC content in our soils and in some previous studies. Therefore, SOC sequestration in arable soils may potentially reduce the risk of preferential transport under near-saturated flow conditions through better developed networks of small macropores and mesopores.

Podnebne projekcije temperature zraka in padavin za porečja Ledave, Pesnice in Vipave do konca 21. stoletja

As part of the project ‚CeVoTak‘, Integrated Management of Small Water Retention and Soil Erosion Prevention Measures in Agricultural Catchments, we studied changing temperature and precipitation conditions up to the year 2100. The study was conducted on agricultural lands in the catchments of the Ledava and Pesnica rivers in the sub-Pannonian region and the Vipava river in the sub-Mediterranean region. A common climate database was used to create the climate projections - RCM (Regional Climate Model) simulations from the project EURO-CORDEX and scenarios RCP (Representative Concentration Pathway), RCP2.6, 4.5 and 8.5. The projections were prepared for three time periods 2011-2040; 2041-2070 and 2071-2100 for 6 different regional climate models for average, minimum and maximum air temperatures and precipitation. Analysis of the ensemble of model simulations for all scenarios shows similar results for the basin of all rivers, an increase in temperature (maximum in winter, minimum in spring), with high confidence for all scenarios and periods. Projections of precipitation are less reliable, but show an increase in annual precipitation due to the winter increase. The use of climate change projections with expert interpretation is essential for determining the vulnerability of individual areas and building resilience through the implementation of climate change adaptation.

Solid-liquid particle flow sealing mucus (PFSM) in enhancing coalbed methane (CBM) recovery: Multiple-perspectives analysis and mechanism insights

The paper presents an in-depth investigation of solid-liquid two-phase particle flow sealing mucus (PFSM) for enhanced coalbed methane (CBM) recovery. PFSM is composed of solid waste particles such as fly ash and rubber particles. The PFSM is assessed using multiple-perspectives analysis, which includes measurements of water retention, pressure expansion, rheological characteristics, adhesion, wettability, microscopy and field case studies. Single-factor and multi-factor studies are used to optimize slurry material ratios. The results show that PFSM has outstanding water retention characteristics, with over 80 % retention for 30 days at 30 °C, and impressive expansion performance, with 9.52 % at 0.6 MPa. The shear thinning curve conforms to the Cross model. After 30 s, the final contact angle is 75.17 °, which is about 6 ° smaller than that of cement based materials. Field experiments show that, after applying PFSM, the drainage gas concentration can be improved at least 60 % comparing to other sealing materials. This research findings could offer novel insights into enhancing CBM extraction, indicating potential for safer and more efficient coal mine production.

Landscape-based water retention measures

Landscape-based water retention measures

Comparing structural soil properties of boreal clay fields under contrasting soil management

AbstractSoil management significantly affects soil structure. Tillage and grassland renovation may have destructive influences, while conversion of arable land to grassland can improve pore structure and related soil functions. In crop rotations including perennial grasses, soil structure is affected by these counteracting processes. This work aimed to quantify the impacts of different soil management practices on the structure of boreal clay soils. We studied intact topsoil samples taken from two locations by X‐ray computed microtomography, image‐based flow simulations and water retention measurements. At both locations, adjacent field areas with two contrasting soil management histories were compared. Both locations had at least a 30‐year‐old grassland site, which was compared to arable soils either under no‐till management with annual crop rotation or conventional tillage with crop rotation including perennial grasses. Both imaging and water retention measurements showed significant differences in the soil macropore structure between the long‐term grassland and arable no‐till soil such that macroporosity and hydraulic conductivity of the long‐term grassland were higher than those of soil under agricultural production. On the contrary, at the second study location, differences between long‐term grassland and cultivated fields were minor and the long‐term grassland exhibited lower macroporosity. Our results confirm that soil management affects the macropore structure of boreal clay soil and that no‐till annual cropping and periodically tilled crop rotation including perennial phases exert different effects on the soil structure as compared with long‐term grassland.

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

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

Micro-Catchments, Macro Effects: Natural Water Retention Measures in the Kylldal Catchment, Germany

Floods are among the most devastating and financially burdensome natural disasters in Europe. The combined impact of climate change and land use change is expected to exacerbate and intensify the destructive consequences of river floods. In this study, we analysed the effects of wetland restoration on peak and base flows and on water quality in the Kylldal catchment of the Kyll River in the German Middle Mountains using the Soil and Water Assessment Tool+ (SWAT+). Monthly median daily discharge increases varied between 3% and 33% in the studied (micro)catchments. The higher median flow rates show that discharge peaks were attenuated and distributed over a longer period, making both extreme peak flows and low flows less common. Peak flows tended to decrease, with the largest effects between late fall and early spring when peak flow values decreased by up to 18%. The annual maximum peak flows in each of the three micro-catchments decreased by 12–24% on average. The occurrence of daily average flow rates larger than 1 m3 s−1 was up to 45% lower after wetland restoration. Low flows increased by up to 21% and 13% in the summer and fall, respectively, which suggests that drought risk also decreases after wetland restoration. Average nitrogen exports decreased by 38–50% in the project areas and by 20% at the catchment level. Average phosphorus exports decreased by 52–67% in the project areas and by 25% at the catchment level. The study highlights the potential of wetland restoration for improving hydrological services, mitigating flood risks, and enhancing water quality. Restoring and maintaining freshwater ecosystems and their natural sponge functions is crucial for effectively managing water resources and addressing the challenges posed by climate change and land use changes.

Natural/Small Water Retention Measures: Their Contribution to Ecosystem-Based Concepts

The increasing incidence of droughts and heavy rainfall events is exacerbating conflicts between human and environmental demands for water. However, through providing multiple water-related ecosystem services and benefits simultaneously, Natural/Small Water Retention Measures (NSWRM) can mitigate such competing claims. Thus, they also contribute to the achievement of various Sustainable Development Goals and environmental targets set out in water- and agriculture-related policies of the European Union. In particular, NSWRM provide for the sound management of watersheds, which can significantly contribute to improved water quality and availability—as well as improving the resilience of agriculture and society. This paper demonstrates how NSWRM fit into the framework of ecosystem-based concepts, including Natural Water Retention Measures (NWRM), Green Infrastructure (GI), Sustainable Land Management (SLM), Ecosystem-based Adaptation (EbA), and Nature-based Solutions (NbS). NSWRM, as a distinct concept, bring added value to the other concepts by focussing on easy-to-implement, modestly sized, localised technical solutions to problems associated with water management, sediment, and nutrient loss. Through experience under the EU Horizon 2020 project OPTAIN (“OPtimal strategies to retAIN and re-use water and nutrients in small agricultural catchments across different soil-climatic regions in Europe”), we show what NSWRM are, how they are linked to each of the ecosystem-based concepts, and how they can help add value to these concepts. Fourteen case studies are drawn upon from diverse countries across Europe. As a result of this analysis, we present the potential for the application of NSWRM in the context of these concepts, while helping to identify planning tools, the expertise required, and potential funding mechanisms.

An Automated Hanging Water Column for Water Retention Measurements

An Automated Hanging Water Column for Water Retention Measurements

Opportunities and limitations for Nature-Based Solutions in EU policies – Assessed with a focus on ponds and pondscapes

Nature-Based Solutions (NBS) are growing in popularity to mitigate and adapt to climate change, enhance biodiversity, and secure human well-being. However, the emergence of NBS has not generated equal attention for all ecosystems. One such neglected ecosystem are ponds and pondscapes (i.e. groups of ponds in a landscape), which are deteriorating in quality and diminishing in quantity. As the European Union (EU) is regarded as influential in the conceptualisation and operationalisation of NBS, we conducted a qualitative content analysis of 38 EU policies to identify opportunities and limitations for the implementation of ponds and pondscapes as NBS. We focus our analysis on ponds and pondscapes, but their prevalence in different landscapes and their multitude of benefits allows us to also make some inferences about the implications of the EU policy context for NBS at large. We find that EU policies strengthen NBS linked to existing and potential Natura 2000 sites, as well as to ecosystems protected through the EU’s Birds and Habitats Directives and Water Framework Directive. However, if ecosystems fall outside of these already established policies – as is the case with the vast majority of ponds and pondscapes – their implementation as NBS may be hampered. We also find that the EU emphasises natural water retention measures and carbon-rich ecosystems for climate change adaptation and mitigation, but mostly does not explicitly include ponds and pondscapes despite their potential contributions. Other findings are that the EU’s Horizon Europe research policy will likely influence which ecosystems will be used and financed as NBS, while the exact ambition and selection of NBS rests with lower-level authorities or individuals. Therefore, further studies tracing the impact of the supra-national EU policy framework at lower governance levels are vital.

Small biochar particles added to coarse sandy subsoil greatly increase water retention and affect hydraulic conductivity

AbstractSandy soils can benefit greatly from the addition of biochar, but the benefits depend on the properties of both the soil and the biochar. This study investigated the role of biochar particle size in controlling pore size distribution, hydraulic conductivity and water retention after careful mixing with coarse sandy subsoil. Intact commercial pellets of straw biochar (SB; approx. 8 × 5 mm) and ground pellets separated into 6 size fractions (median diameter 15, 33, 44, 81, 135 and 205 μm) were investigated at two concentrations (1.50 and 3.00 wt%). The results were compared with effects obtained with another feedstock (wood; WB) and another soil. Light microscopy and water retention measurements showed that smaller biochar particles settled into large existing soil pores, creating smaller interstitial pores to a much greater extent than larger particles. Accordingly, small particles (≤44 μm) had large enhancing effects on water retention and hydraulic conductivity in the medium suction range (pF1.7‐pF3.0), which were not found to a similar extent after the addition of larger particles (>81 μm). It was not possible to systematically distinguish the effects obtained with the three smallest particle fractions (SB15, WB18 and SB33). All effects measured were greatest at the highest biochar concentration level. In one soil, amendment with 3.00 wt% of SB15 decreased the fractional volume of drainable pores with an equivalent diameter of ≥60 μm from 31.3 vol% in the control to 19.1 vol%, while increasing the volume of pores in the 0.2–60 μm range that could potentially retain plant‐available water from 8.7 vol% to 20.1 vol%. Hydraulic conductivity at pF1.7 was increased by a factor of 10 (from 2.3 to 22.5 cm/day) and at pF3.0 by a factor of 14 (from 0.1*10−3 to 1.4*10−3 cm/day). Similar effects were observed in the other soil but at slightly different levels. The PDI version of the bimodal van Genuchten model was successfully fitted to measured water retention and log‐transformed hydraulic conductivity data (RMSE values in the interval 0.0011–0.0029 and 0.024–0.215, respectively). Dynamic simulation under variable field conditions including the hydraulic properties of biochar‐amended soil layers could be a useful method to investigate the effects on crop water supply, water and fertilizer utilization and yields.

Automated hanging water column for characterizing water retention and hysteresis of coarse‐textured porous media

AbstractModeling and characterizing hysteretic water retention is critical for predicting hydrodynamic behavior in porous media. This is especially true in coarse‐textured media used in geotechnical engineering, greenhouse, and landscape industries, where subtle changes in water status may lead to plant stress. However, based on the traditional hanging water column method, water retention measurements are laborious and time consuming because of the stepwise manual water potential adjustments and wait‐time requirements for equilibrium conditions to develop. Therefore, we designed and fabricated an automated system to collect wetting‐ and drying‐water retention data from coarse porous media. The basic system consisted of (1) a compound pressure transducer (± 70‐cm range) providing both the porous medium's volumetric water content (θ) and matric potential (h) determinations, (2) a 70‐cm linear actuator to vertically position a 50‐mL burette, and (3) a diffuse laser distance sensor positioned by a 10‐cm linear actuator to monitor the burette's vertical position relative to the sample position. This automated system determined the initial drying process beginning with a fully saturated sample (h = 0 cm) and determined subsequent wetting‐ and drying‐water retention curves. Our automated water retention measurements in quartz sand (ASTM C778‐21) exhibited maximum‐ and minimum‐standard deviation in θ of 0.013 and 0.00044 cm3 cm−3, respectively. Parameters of the hysteretic water retention model of quartz sand were characterized using repeated measurements. Results of this research included the creation of an automated water retention system and the well‐characterized hydraulic parameters for the original well‐graded and narrowly sieved particle sizes of quartz sand.

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

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

Widening Gap of Land Evaporation to Reference Evapotranspiration Implies Increasing Vulnerability to Droughts in Hungary

Severe droughts of 2022 in Europe raise the question if one has sufficient knowledge and tools to predict and prevent such events. Analysis of 40 years of meteorological data for Hungary between 1981 and 2020 confirms significant upward trends with p = 0.05 in temperature, relative humidity, and net radiation. Shortwave net radiation has increased by 89.6 mm in water equivalent. Estimates of land evaporation and reference evapotranspiration also show a significantly increasing trend. The gap between them is widening with a significant trend in northeast Hungary. The demand (reference evapotranspiration) is increasing by 2.23 ± 0.3 mm yr–1, while supply (land evaporation) by 1.64 ± 0.2 mm yr–1. The opening gap can be interpreted as a decreasing stability of the energy distribution system, where water is the dominant energy transfer medium for climatic energy. This change could lead to an increased risk of droughts, a symptom of system underperformance. The climatic energy distribution process – a key environmental service - is shifting to a new operating point where more water would be needed to transport energy. These trends call for a process capability approach. Desertification cannot be stopped by chasing water use efficiency and using less water, but vice versa: water scarcity can only be eliminated by ensuring that there is sufficient water available for evapotranspiration. This will raise the priority for initiatives to design and implement a wide range of preventing actions, such as nature-based solutions and water retention measures.

Contrasting effects of biochar application rate in an alkaline desert cropland soil

Improving water and nutrient retention in desert croplands using soil organic amendments can be a major challenge because organic matter decomposes quickly under irrigated conditions in a hot climate. Biochar—a long-lasting carbon-rich soil organic amendment—has been proposed to improve soil water and nutrient retention, but only by carefully selecting an appropriate application rate. To better understand effects of biochar application rate on soil water and nutrient retention in desert croplands, we set up a mesocosm-scale experiment with biochar added at rates of 0, 19.8, 39.7, 79.4, 119.0, and 158.7 t ha−1 to an alkaline, sandy loam soil. After initial water retention measurements, we added fertilizer and then measured gaseous nitrogen losses as well as soil nitrate (NO3−) and phosphate (PO₄³⁻) leaching. Then, we measured biochar's effect on the soil's capacity to hold plant-available water (i.e., available water capacity, or AWC) using Tempe cells and a dewpoint potentiometer. We found contrasting effects of low and high biochar application rates. First, we found that applying a minimum of 79.4 t ha−1 biochar was necessary to improve soil water and PO₄³⁻ retention; application rates below 79.4 t ha−1 exacerbated PO₄³⁻ leaching whereas treatments above 79.4 t ha−1 improved AWC by up to 34% compared to the control treatment. While biochar application rate did not affect soil nitric oxide or ammonia emissions, we did find that low biochar application rates increased soil nitrous oxide emission while higher application rates reduced emission compared to soil with no biochar. Overall, we found that lower and higher rates of biochar application can have contrasting effects on soil water and nutrient retention in an alkaline, desert cropland soil. Therefore, farmers and other land managers must consider potential drawbacks of lower application rates and threshold responses of higher application rates prior to large-scale biochar use in arid agroecosystems.