The increasing availability of soil moisture data presents an opportunity for its use in wildfire danger assessments, but research regarding the influence of soil moisture on wildfires is scarce. Our ...objective was to identify relationships between soil moisture and wildfire size for Oklahoma wildfires during the growing (May‐October) and dormant seasons (November‐April). We hypothesized that soil moisture influences wildfire size when vegetation is growing but is less important when most vegetation is dead or dormant. Soil moisture, as fraction of available water capacity (FAW), and commonly measured weather variables were determined for 38,419 wildfires from 2000–2012. Wildfires were grouped by size class (<4.05, ≥4.05 and <40.5, ≥40.5 and <121, ≥121 and <405, and ≥405 ha), and the Kruskal–Wallis test with multiple comparisons was used to identify differences in each variable between wildfire size classes and seasons. Large fires occurred at lower FAW than small fires during both seasons (P < 0.001), but growing‐season wildfires ≥405 ha occurred over a narrow range of FAW (0.05–0.46) whereas dormant‐season fires of this size occurred across the entire range of FAW (0.05–1.05). For growing‐season fires ≥ 121 ha, 91% occurred at FAW < 0.5 and 77% occurred at FAW < 0.2. Our finding that large growing‐season wildfires occurred exclusively under conditions of low soil moisture highlights the need to develop methods to use soil moisture data in wildfire danger assessments.
Because the pattern of climate and thus water demand varies rapidly, an accurate assessment of available water (AW) must be determined in order to manage water resources sustainable. This study ...investigated the components of basin AW using a comprehensive water balance framework based on the SWAT model. It consists of a system of relationships describing different components of water balance to estimate diverse forms of AW. The resulting modelling system is capable of displaying current status and past trends in the components of AW, highlight links between blue and green water components, assess AW at farm and basin scales, and forecast spatial and temporal variations of AW components under different water policies and climate scenarios as well as evaluating potential water shortage. To explore this methodology, the system was applied to the Tashk-Bakhtegan basin (Iran). The results for the historical period showed wide changes in the blue water components, which was very lower for the green water ones. For instance, it was between 63% and − 56% for renewable BW and 11% and − 24% for renewable GW with respect to their long term means. Similarly, blue water was more sensitive than green water to future annual precipitation variations. Evaluation of the construction of the basin’s major dam showed that it has drastic impact on the spatial blue AW components; such that they are increased in the adjacent subbasin up to 97% and reduced to half the status quo in the downstream subbasins. The basin has also experienced 30% increase in cropped areas, resulting in 1500 million meter cubic (MCM) water shortage in the current condition. Considering the framework as a relatively easy-to-use tools with readily available data, is strongly recommended for other regions.
Flowchart of the model structure to retrieve components of available water Display omitted
•The framework integrates green and blue components to evaluate status and trends of available water (AW).•The linkage of framework and SWAT made its possible to simulate and assess climate and management scenarios.•Application of the framework for the case study showed spatial variations of the basin’s AW due to climate variability and major dams.
Soil available water capacity is an important soil property for land use planning, drought risk assessment, and modelling crop production or carbon cycling. Measurements of soil moisture at several ...soil water potentials are expensive and time-consuming, hence it is common to estimate available water capacity with pedotransfer functions (PTFs). Available PTFs for France rarely provide uncertainty estimates for the model coefficients and predictions, which are often required for error propagation analysis and modelling ecological processes. The objectives of this study were: 1) to develop class-PTFs and 2) continuous-PTFs with associated uncertainties, and 3) to assess the domain of applicability of the PTFs across metropolitan France. We used the SOLHYDRO database for calibrating continuous and class PTFs. For continuous PTFs we used linear regression models using sand, clay, organic carbon (SOC), and bulk density (BD) as predictor variables, whereas class-PTFs were defined by texture class, bulk density, and horizon type (all horizons, topsoils, subsoils). The models were validated with an independent validation dataset. The domain of applicability of the PTFs was evaluated calculating the Mahalanobis distance between the calibration dataset and horizon data from the French soil monitoring network (RMQS). At independent validation, texture class-PTFs had a RMSE between 0.047 cm3 cm–3 and 0.058 cm3 cm–3 and continuous-PTFs had a RMSE between 0.040 cm3 cm–3 and 0.053 cm3 cm–3. Texture class-PTFs had similar or better predictive performance than texture-structural class-PTFs. The prediction performance of continuous-PTFs improved slightly when including SOC and BD in the models. The variance of the predictions of continuous-PTFs associated to error in the model coefficients was rather small, and increased as the values of the predictor variables were more distant to the centroid of the calibration data. We provide the PTF users with tools for classifying new samples as within or outside the applicability domain of the PTFs. When applied to the RMQS dataset, >50% of the horizons outside the domain of applicability were located in forests and natural areas or managed pastures. The spatial distribution of RMQS horizons outside the domain of applicability of the PTF can inform future sampling locations for increasing the diversity of the soil properties and site conditions represented by the SOLHYDRO dataset.
•We calibrated class and continuous-PTFs for estimating soil moisture at pF = 2.0 and pF = 4.2•RMSE ranged between 0.040 cm3 cm−3 and 0.058 cm3 cm−3 at independent validation•The PTFs are suitable for estimating available water capacity in most agricultural French soils•Users can assess whether their samples are within the applicability domain of the PTFs
Biochar can significantly alter water relations in soil and therefore, can play an important part in increasing the resilience of agricultural systems to drought conditions. To enable matching of ...biochar to soil constraints and application needs, a thorough understanding of the impact of biochar properties on relevant soil parameters is necessary. This meta-analysis of the available literature for the first time quantitatively assess the effect of not just biochar application, but different biochar properties on the full sets of key soil hydraulic parameters, i.e., the available water content (AWC), saturated hydraulic conductivity (Ksat), field capacity (FC), permanent wilting point (PWP) and total porosity (TP). The review shows that biochar increased soil water retention and decreased Ksat in sandy soils and increased Ksat and hence decreased runoff in clayey soils. On average, regardless of soil type, biochar application increased AWC (28.5%), FC (20.4%), PWP (16.7%) and TP (9.1%), while it reduced Ksat (38.7%) and BD (0.8%). Biochar was most effective in improving soil water properties in coarse-textured soils with application rates between 30 and 70 t/ha. The key factors influencing biochar performance were particle size, specific surface area and porosity indicating that both soil-biochar inter-particle and biochar intra-particle pores are important factors. To achieve optimum water relations in sandy soils (>60% sand and <20% clay), biochar with a small particle size (<2 mm) and high specific surface area and porosity should be applied. In clayey soil (>50% clay), <30 t/ha of a high surface area biochar is ideal.
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•Biochar effect on soil water was analysed using a Meta-analysis of 37 articles.•Biochar generally increased the AWC (28.5%), FC (20.4%) and PWP (16.7%) of soils.•Soil texture influenced how water characteristics responded to biochar addition.•Biochar decreased Ksat of sandy soils and increased the Ksat of clayey soils.•The effect of biochar was also dependent on its particle size, SSA, and porosity.
Biochar application to agricultural soils has been proposed as a way to increase crop production by improving soil chemical and physical properties. Liming potential and improved nutrient exchange on ...biochar surfaces are the most reported mechanisms. Wherever crops experience drought stress, improvements in soil water holding capacity (WHC) might also be an important mechanism. However, reported effects on soil structure and WHC are mixed. Therefore, we studied the effects of biochar on soil bulk density (BD) and WHC in a laboratory column study using two agricultural soils from Portugal: a sandy and a sandy loam soil. Mixed woody feedstock was pyrolysed at 620 °C, creating a wettable biochar that was used unsorted as well as sieved into large (2–4 mm) and small (0.05–1.00 mm) particles, mixed into the soils at 1, 5, 10 and 20% (by volume), and incubated for 10 days at field capacity to allow aggregation. Soil samples were analysed for BD and WHC using soil columns.
We found biochar to decrease soil BD and increase maximum WHC, expressed as gravity-drained equilibrium water content, for both soils. The sandy soil was more responsive with significant effects at the lowest application rate (1%), while the sandy loam soil started to show significant effects at 5% biochar. Small biochar particles reduced the BD of sandy soil more, while large biochar particles caused a greater reduction in the BD of the sandy loam soil. The effect of biochar particle size on WHC was less clear, except for small particles at 20% volumetric concentration, which showed a 60% increase in gravimetric WHC. When expressed as total soil water storage (SWS), 20% biochar incorporation to 15 cm depth would increase the total SWS of sandy soil from 0.56 mm (control) to 0.83–0.91 (mm), and of the sandy loam soil from 0.56 to 0.79–0.96 (mm), depending on biochar particle size. Our results suggest that biochar particle sizes can be used to achieve specific effects in soils, while mechanisms and trade-offs (agro-economic and environmental) need further exploration.
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•Small biochar particles reduced bulk density more for sandy than sandy loam soil.•Large biochar particles reduced bulk density more for sandy loam than sandy soil.•Small particles at 20% increased gravimetric water holding capacity by 60%.•The total soil water storage of sandy soil increased from 56 to 83–91 (mm).•The total soil water storage of sandy loam soil increased from 56 (mm) to 79–96 (mm).
A growing body of research into the effects of biochar on soil physical characteristics suggests that it is most effective in coarse-textured soils. In this study, we set out to test this theory by ...comparing the effects of a woodchip biochar on a Chernozem, Cambisol and a coarse-textured Planosol in a pot experiment. We also compared the effect of different biochars on the Planosol, including woodchip biochar, straw biochar, and two vineyard-pruning biochars produced at different pyrolysis temperatures. Three characteristics were measured as indicators of good soil structure: bulk density, soil aggregate stability and plant available water.
The woodchip biochar induced greater decreases in bulk density in the coarse textured Planosol than in the other soils. It also had a greater effect on soil aggregate stability in the Planosol than in the Cambisol, but had no effect on the Chernozem. Woodchip biochar had no effect on plant available water in any of the three soils. Straw biochar was the most effective at improving soil aggregate stability in the coarse-textured Planosol, with a 98% increase. Straw biochar also improved plant available water in the Planosol by 38% relative to the control, compared with 24% and 21% increases in the vineyard-pruning biochars, produced at 525°C and 400°C, respectively.
Our study supports the theory that coarse-textured soils have the most to gain structurally from biochar amendments. We also show that straw biochar was the most effective at improving soil aggregate stability and plant available water in a coarse-textured Planosol.
•Biochar permanently decreased bulk density in three agricultural soils.•Biochar improved soil aggregate stability in Planosol and Cambisol soils.•Biochars effect on soil aggregate stability correlated strongly with electrical conductivity.•Straw biochar improved plant available water in a Planosol soil by 38%.
AIMS: This study aims to (i) determine the effects of incorporating 47 Mg ha⁻¹ acacia green waste biochar on soil physical properties and water relations, and (ii) to explore the different mechanisms ...by which biochar influences soil porosity. METHODS: The pore size distribution of the biochar was determined by scanning electron microscope and mercury porosimetry. Soil physical properties and water relations were determined by in situ tension infiltrometers, desorption and evaporative flux on intact cores, pressure chamber analysis at −1,500 kPa, and wet aggregate sieving. RESULTS: Thirty months after incorporation, biochar application had no significant effect on soil moisture content, drainable porosity between –1.0 and −10 kPa, field capacity, plant available water capacity, the van Genuchten soil water retention parameters, aggregate stability, nor the permanent wilting point. However, the biochar-amended soil had significantly higher near-saturated hydraulic conductivity, soil water content at −0.1 kPa, and significantly lower bulk density than the unamended control. Differences were attributed to the formation of large macropores (>1,200 μm) resulting from greater earthworm burrowing in the biochar-amended soil. CONCLUSION: We found no evidence to suggest application of biochar influenced soil porosity by either direct pore contribution, creation of accommodation pores, or improved aggregate stability.
•Gasification biochar increased plant-available water capacity and soil pH.•Straw gasification biochar improved plant and root development in coarse sandy soil.•Wood gasification biochar had either ...no or slightly negative effect on plant growth.
Gasification biochar (GB) contains recalcitrant carbon that can contribute to soil carbon sequestration and soil quality improvement. However, the impact of GB on plant-available water capacity (AWC) and plant growth in diverse soil types still needs to be explored.
A pot experiment with spring barley (Hordeum vulgare L.) was conducted to investigate the effect of soil amendment by 1% straw and wood gasification biochar (SGB and WGB), respectively, on AWC and plant growth responses under two levels of water supply in a temperate sandy loam and a coarse sandy subsoil. In the sandy loam, the reduced water regime significantly affected plant growth and water consumption, whereas the effect was less pronounced in the coarse sand. Irrespective of the soil type, both GBs increased AWC by 17–42%, with the highest absolute effect in the coarse sand. The addition of SGB to coarse sand led to a substantial increase in plant biomass under both water regimes: shoot growth by 40–165% and root growth by 50–57%. However, no positive effects were achieved by the addition of WGB. In the sandy loam, soil application of GB had no or negative effects on plant growth.
Our results suggest that SGB has considerable potential for enhancing crop productivity in coarse sandy soils by increasing soil water retention and improving root development.
Biochar application has been a promising approach to improve soil quality but their optimal amount in improving physical and hydraulic properties remains contradictory and inconclusive. The objective ...of this study was to examine and propose an optimal biochar application amount in saline alkali soil considering their impact on soil physical and hydraulic properties. A three-year field experiment was conducted in the saline-alkali soils under plastic film-mulched drip irrigation in Xinjiang, China. The studied physical and hydraulic properties included bulk density, soil porosity, saturated soil water content (θs), permanent wilting point (PWP), field capacity (FC), plant available water (PAW), spatial distribution of soil water content, planar soil water storage (PSWS), and soil evaporation. The treatments included biochar application amounts of 0 (CK), 10 (B10), 50 (B50), and 100 t ha−1 (B100) in 2018. Additional two treatments with 25 t ha−1 (B25) and 30 t ha−1 (B30) were added in 2019 and 2020, respectively. A four-parameter Gaussian function was fitted to the single-peak curves of the studied hydraulic properties vs. biochar application amounts to determine the most optimal biochar application amount. The results indicated that: (1) All of the biochar treatments significantly decreased bulk density and increased soil porosity over CK; (2) B10 and B25 treatments significantly increased θs, FC, PAW, PWP, and PSWS of root zones in the film-mulched zones over CK, but reverse results were observed in the B50 and B100 treatments; (3) Daily and cumulative soil evaporation were increased in no mulch zones of all biochar treatments over CK; (4) A dose of 21.9 t ha−1 was recommended as the most optimal biochar application amount for improving physical and hydraulic properties of saline-alkali soil. This research provided useful information on biochar application amounts for improving physical and hydraulic properties in saline-alkali soil.
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•Biochar decreased bulk density and increased soil porosity of saline-alkali soil.•Biochar increased field capacity and plant available water of saline-alkali soil.•Excessive biochar had negative impact on hydraulic properties of the saline soil.•21.9 t ha−1 was recommended as an appropriate biochar application strategy.
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