Available Water Capacity Research Articles

Can a superabsorbent polymer synthesised a CaCO3 based biofiller improve soil and plant available water and crop growth under salt stress?

ABSTRACT The use of superabsorbent polymers (SAPs) in dryland agricultural areas utilizing brackish irrigation water is a strategy to increase plant available water (AW). However, water retention by SAPs may be adversely affected under salinity. SAP containing calcium carbonate (Ca-SAP) is considered to be more resistant and provide more plant AW under saline conditions compared to conventional SAP (C-SAP) and to control. This research investigated two replicated lettuce trials to evaluate three treatments (Ca-SAP, C-SAP and control) subjected to irrigation water with electrical conductivities of 0.0, 0.5, 1.0, 2.0 and 4.0 dS m−1. Both SAP treatments increased AW by an average of 0.16 m3 m−3 as compared to the control. Decrease in AW with salinity was lower in Ca-SAP (0.07 m3 m−3) as compared with C-SAP (0.13 m3 m−3). Lettuce fresh weight (g plant−1) was higher for Ca-SAP (22.9) as compared to C-SAP (16.4), however, did not differ from control (20.6). As water salinity increased, lettuce fresh biomass was higher in Ca-SAP as compared to C-SAP up to 2 dS m−1 with no significant differences from control. The Ca-SAP is less affected by salts than the C-SAP, although its use did not benefit lettuce growth under saline conditions as expected.

Influence of gully erosion on hydraulic properties of black soil-based farmland

Gully erosion is a severe form of water erosion worldwide. However, the influence of gully vicinity on the soil hydraulic properties has been poorly studied, hindering the understanding of their effect on crop yields. Therefore, this study hypothesizes that gully vicinity influences farmlands and aims to determine the mechanism of their influence on soil hydraulic properties and crop characteristics. The soil properties from nine gullies in cultivated lands inclined at1%, 2%, and 3% in three latitudinal regions were determined at the gully edge (EG0) and 50 m further the edge into the farmlands (EG50) at the following gully units: head, mid-upper, mid, mid-lower, and tail. Soil hydraulic properties (bulk density, saturated hydraulic conductivity, and water retention), soil penetration resistance, and soil organic matter were analyzed. The study findings indicate that the gully existence affected the soil properties at diverse range of intensities. The total-available water content (θ30 - θ1500), the ratio of more-available water to total-available water content (θ30-θ330)/(θ30-θ1500), saturated hydraulic conductivity, and soil organic matter were lower, but the bulk density and soil penetration resistance were higher at EG0 compared with those at EG50. The (θ30-θ330)/(θ30-θ1500) ratio in the gully vicinity was considerably lower in our study than in previous studies, indicating gully erosion substantially deteriorated the hydraulic properties. The differences in soil hydraulic properties between EG0 and EG50 were more evident in higher latitudinal region and in steeper farmlands. In addition, the lower soil organic matter and higher bulk density probably led to a 3–11% decrease in crop yield at EG0 than at EG50. In summary, this study indicates that gully erosion affects farmland not only at its boundaries but also further into its surroundings. Accordingly, managements suited to the hydraulic properties of the gully-surrounded areas may be implemented to maximize the crop yield of farmlands.

Future hydropower production under the framework of NextGenerationEU: The case of Santa Giustina reservoir in Italian Alps

Here we study the effects of climate change upon the dynamics of Santa Giustina Lake, a main reservoir of Trentino, North-eastern Italy, exploited by Taio power plant providing about 282 GWh per year. We used Poli-Hydro model to investigate hydrological regime of the basin during last 30 years, this including snow accumulation and ablation processes. Calibration of Poli-Hydro was carried out using a 10-yrs series of daily natural inflows to the reservoir during 1990–1999. Climate scenarios from Assessment Report 6 of IPCC were used as input to sketch future inflow scenarios. While no univocal trajectory is depicted for total water availability among scenarios, the decrease of snowfall would most reliably reduce spring-summer inflow and increase winter baseflow. Associated scenarios of energy production are analysed on the background of Italian energy goals for 2030–40 under the framework of NextGenerationEU, and possible adaptation policies of reservoir management are suggested. To face volatility in energy production given by deep exploitation of renewable sources, it is compelling to consider chances of installing energy storage systems. A pumped-storage facility could be implemented in the Mollaro Lake, a minor reservoir collecting water from Taio plant, to store surplus energy from renewable sources in Santa Giustina Lake.

Changes in selected properties of Calcic Chernozem due to cultivation of Robinia pseudoacacia and Quercus robur

Abstract The results of a comprehensive study on the particle size distribution, soil organic matter (SOM) content, and plant-available water in Calcic Chernozem are presented, along with the impact of Robinia pseudoacacia L. and Quercus robur L. plantations on these indicators. The study revealed that Calcic Chernozem under steppe vegetation and Q. robur plantation exhibited a silty clay loam texture. However, under the influence of R. pseudoacacia plantation, the chernozem’s texture transformed into loam. The planting of R. pseudoacacia resulted in a noticeable decrease in SOM content, while the growth of Q. robur plantations led to an increase in SOM content. Furthermore, both R. pseudoacacia and Q. robur plantations contributed to an increased content of plant-available water in the 0–20 cm layer of chernozem. These findings highlight the more pronounced effect of R. pseudoacacia plantation on the particle size distribution, SOM content, and plant-available water in Calcic Chernozem compared to Q. robur plantation.

Biocrusts intensify water redistribution and improve water availability to dryland vegetation: insights from a spatially-explicit ecohydrological model.

Biocrusts are ecosystem engineers in drylands and structure the landscape through their ecohydrological effects. They regulate soil infiltration and evaporation but also surface water redistribution, providing important resources for vascular vegetation. Spatially-explicit ecohydrological models are useful tools to explore such ecohydrological mechanisms, but biocrusts have rarely been included in them. We contribute to closing this gap and assess how biocrusts shape spatio-temporal water fluxes and availability in a dryland landscape and how landscape hydrology is affected by climate-change induced shifts in the biocrust community. We extended the spatially-explicit, process-based ecohydrological dryland model EcoHyD by a biocrust layer which modifies water in- and outputs from the soil and affects surface runoff. The model was parameterized for a dryland hillslope in South-East Spain using field and literature data. We assessed the effect of biocrusts on landscape-scale soil moisture distribution, plant-available water and the hydrological processes behind it. To quantify the biocrust effects, we ran the model with and without biocrusts for a wet and dry year. Finally, we compared the effect of incipient and well-developed cyanobacteria- and lichen biocrusts on surface hydrology to evaluate possible paths forward if biocrust communities change due to climate change. Our model reproduced the runoff source-sink patterns typical of the landscape. The spatial differentiation of soil moisture in deeper layers matched the observed distribution of vascular vegetation. Biocrusts in the model led to higher water availability overall and in vegetated areas of the landscape and that this positive effect in part also held for a dry year. Compared to bare soil and incipient biocrusts, well-developed biocrusts protected the soil from evaporation thus preserving soil moisture despite lower infiltration while at the same time redistributing water toward downhill vegetation. Biocrust cover is vital for water redistribution and plant-available water but potential changes of biocrust composition and cover can reduce their ability of being a water source and sustaining dryland vegetation. The process-based model used in this study is a promising tool to further quantify and assess long-term scenarios of climate change and how it affects ecohydrological feedbacks that shape and stabilize dryland landscapes.

Integrating glacio-hydrological and power grid models to assess the climate-resiliency of high mountain hydropower in Nepal

Climate change significantly impacts hydrological systems resulting in hydropower generation uncertainties. In this study, a high-resolution glacio-hydrological model is coupled with an hourly-resolution power grid model to evaluate the climate change influences on hydropower generation across Nepal. Four climate future scenarios namely Cold-Dry, Warm-Dry, Cold-Wet, and Warm-Wet are developed to compare the changes in water availability and optimal power system with historical climate. The total flow increases for the wet scenarios (+11.4% under Cold-Wet for the Koshi basin), compared to the dry scenarios (−24.6% under Warm-Dry for the Karnali basin) for all the major river basins in Nepal. The results illustrate the distribution and magnitude of changes in total water availability and power generation are not proportional for dry and wet scenarios as a ∼20% reduction of water availability in the dry scenarios only results in a ∼2–3% decrease in electricity generation. The capacity requirements of hydro storage decrease by 7.2 GW for Cold-Wet and 6.8 GW for Warm-Wet scenarios compared to historical climate indicating higher capacity requirements in dry scenarios. Larger impacts observed at higher altitudes suggest more attentive adaptation strategies in developing climate-resilient hydropower systems. Results suggest that Nepal should not be entirely focused on exploiting its hydropower potential but rather diversifying the generation mix including solar PV and hydrogen technology. For the least-cost power system expansion, the Warm-Wet climate appears to be the most desirable and a cost savings of about 3.76 billion USD in hydropower development can be realized if better adaptation strategies are employed.

Multidimensional hydrological modeling of a forested catchment in a German low mountain range using a modular runoff and water balance model

Sufficient plant-available water is one of the most important requirements for vital, stable, and well-growing forest stands. In the face of climate change, there are various approaches to derive recommendations considering tree species selection based on plant-available water provided by measurements or simulations. Owing to the small-parcel management of Central European forests as well as small-spatial variation of soil and stand properties, in situ data collection for individual forest stands of large areas is not feasible, considering time and cost effort. This problem can be addressed using physically based modeling, aiming to numerically simulate the water balance. In this study, we parameterized, calibrated, and verified the hydrological multidimensional WaSiM-ETH model to assess the water balance at a spatial resolution of 30 m in a German forested catchment area (136.4 km2) for the period 2000–2021 using selected in situ data, remote sensing products, and total runoff. Based on the model output, drought-sensitive parameters, such as the difference between potential and effective stand transpiration (Tdiff) and the water balance, were deduced from the model, analyzed, and evaluated. Results show that the modeled evapotranspiration (ET) correlated significantly (R2 = 0.80) with the estimated ET using MODIS data (MOD16A2GFv006). Compared with observed daily, monthly, and annual runoff data, the model shows a good performance (R2: 0.70|0.77|0.73; Kling–Gupta efficiency: 0.59|0.62|0.83; volumetric efficiency: 0.52|0.60|0.83). The comparison with in situ data from a forest monitoring plot, established at the end of 2020, indicated good agreement between observed and simulated interception and soil water content. According to our results, WaSiM-ETH is a potential supplement for forest management, owing to its multidimensionality and the ability to model soil water balance for large areas at comparable high spatial resolution. The outputs offer, compared to non-distributed models (like LWF-Brook90), spatial differentiability, which is important for small-scale parceled forests, regarding stand structure and soil properties. Due to the spatial component offered, additional verification possibilities are feasible allowing a reliable and profound verification of the model and its parameterization.

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.

Ecohydrological insight: Solar farms facilitate carbon sink enhancement in drylands

Solar farms are critical to tackling climate change and achieving carbon neutrality. Besides producing renewable energy, a solar farm modifies microclimates and changes water distribution, consequently affecting local carbon sequestration capacity (CSC). Yet, how the CSC of an ecosystem responds to these changes after solar farm construction remains inadequately understood. Herein, the SOFAR model was adopted to reveal the effects of large-scale solar farms (LSFs) on CSC in arid northern China, with a series of numeric experiments along a climate gradient (with precipitation ranging from 70 to 500 mm yr−1). The results show that relative to pristine vegetation background, CSC was non-linearly increased by averages of 3.49–6.68%, 4.43–10.25%, 5.07–9.71% and 5.6% each year after the installation of LSFs in hyper-arid climates (with aridity index or AI = 0.04–0.05), arid climates (AI = 0.14–0.16), semi-arid climates (AI = 0.21–0.3) and semi-humid climates (AI = 0.55), respectively. The increase in available water for plants growing under the drip lines of photovoltaic panels (PVs) in LSFs is confirmed to be the overwhelming factor responsible for CSC enhancement. Although biases remain in the estimation of increased CSC in hyper- and semi-humid regions due to the high variability of climate (e.g., extreme drought events) and serious radiation reduction beneath PVs, it is certain that solar farms facilitate CSC without increasing external land use. These results will deepen our understanding of the feedback between solar farms and ambient environments and be meaningful for vegetation management in solar farms, especially in the context of climate change and carbon neutrality aims.

The role of terrain-mediated hydroclimate in vegetation recovery after wildfire

Throughout communities and ecosystems both within and downstream of mountain forests, there is an increasing risk of wildfire. After a wildfire, stakeholder management will vary depending on the rate and spatial heterogeneity of forest re-establishment. However, forest re-establishment and recovery after a wildfire is closely linked to interactions between the temporal evolution of plant-available water (PAW) and spatial patterns in available energy. Therefore, we propose a conceptual model that describes spatial heterogeneity in long-term watershed recovery rate as a function of topographically-mediated interactions between available energy and the movement of water in the subsurface (i.e. subsurface hydrologic redistribution). As vegetation becomes re-established across a burned landscape in response to topographic and subsurface controls on water and energy, canopies shade the ground surface and reduce wind speed creating positive feedbacks that increase PAW. Furthermore, slope aspect differentially impacts the spatial patterns in regrowth and re-establishment. South aspect slopes receive high solar radiation, and consequently are warmer and drier, with lower standing biomass and greater drought stress and mortality compared to north aspect slopes. To date, most assessments of these impacts have taken a bulk approach, or an implicitly one-dimensional conceptual approach that does not include spatial heterogeneity in hydroclimate influenced by topography and vegetation. The presented conceptual model sets a starting point to further our understanding of the spatio-temporal evolution of PAW storage, energy availability, and vegetation re-establishment and survival in forested catchments after a wildfire. The model also provides a template for collaboration with diverse stakeholders to aid the co-production of next generation management tools to mitigate the negative impacts of future wildfires.

Water Retention Characteristics of Superabsorbent Polymers (SAPs) Used as Soil Amendments

Superabsorbent polymers (SAPs) are used as a soil amendment for retaining water, but suitable methods for the application of SAPs have not yet been developed. Here, we characterized a variety of soil–SAP mixtures prepared using four different types of SAP in terms of their water absorption and release characteristics. The teabag method was applied to characterize the soil–SAP mixtures, except for measurements of the matric potential. The results showed that the variations in water absorbency among the four SAPs in isolation became insignificant when they were mixed with sandy soils. The rates of water released from the soil–SAP mixtures under heated conditions were mitigated with decreasing water content, which prolonged the time until desiccation of the mixtures. The water absorbency of the SAPs significantly decreased in salt solutions (KCl and CaCl2), but their absorbency mostly recovered following immersion in tap water. The soil–dry SAP mixtures retained a larger amount of water than the soil–gel SAP mixtures. Swollen SAPs predominantly retained water in the range of −0.98 to −3.92 kPa, suggesting that SAP induces a transition from gravitational water to readily plant-available water by swelling itself. SAPs barely increased the amount of plant-available water in a potential range of −3.92 to −98.1 kPa, but significantly increased the soil water at <−98.1 kPa. The soil water content increased with an increasing SAP application rate, whereas the proportion of plant-available water declined. Our findings indicated that the performance of SAPs depends on the pore space and a saline environment in the soil and that low SAP application rates are suitable for maximizing the water available to plants in sandy soils.

Water Productivity Indices of Onion (Allium cepa) under Drip Irrigation and Mulching in a Semi-Arid Tropical Region of Colombia

Efficient water management is crucial for sustainable agriculture and water resource conservation, particularly in water-scarce regions. This study investigated the effect of different irrigation depths on onion (Allium cepa L.) yield and water use patterns in a semi-arid tropical region of Colombia, using a completely randomized design with five treatments. The treatments ranged from 0–100% of total available water (TAW), T1 (100% of TAW), T2 (80% of TAW), T3 (60% of TAW), T4 (40% of TAW), and T5 (20% of TAW). The experiment was conducted in a greenhouse during one growing season (2022–2023). The normalized water productivity (WP *), irrigation water productivity (IWP), consumptive water productivity, blue water footprint (WFblue), marginal water use efficiency (MWUE), and elasticity of water productivity (EWP), as well as some parameters of quality onion, were determined. The soil in the experimental field was classified as sandy loam; the results show that the WP * of onion is 17.42 g m−2, the water production function shows the maximum production will be achieved at a water application depth of approximately 943 mm, and beyond that, the biomass yield will decrease with additional water application, IWP values for onion ranged from 2.18 to 3.42 kg m−3, the highest Wfblue was in T5 (34.10 m3 t−1), and low Wfblue was T1 (20.95 m3 t−1). In terms of quality, treatment T1 had the most favorable effects on bulb weight, polar diameter, and equatorial diameter, while treatment T5 had the least favorable effects. The study highlights the importance of efficient irrigation on sandy loam soils to maximize yield and water use efficiency. It provides valuable data for evaluating the potential yield benefits of precision irrigation in the study area. Optimizing irrigation depth can significantly improve onion yield and water use efficiency in semi-arid regions.

Structural characteristics of the moss (bryophyte) layer and its underlying soil structure and water retention characteristics

The influence of the moss layer on soil structure and soil water retention is not well understood. Therefore, this study aims to investigate the changes in soil structure and soil water retention under moss layer and to reveal the influencing factors of these changes. 3D networks of moss layer and soil macropores were quantified using CT scanning and image analysis techniques, and soil water retention characteristics were explored through soil water retention curves (SWRCs) and VG model. The length densities of the soil macropores under the thin moss and thick moss layers were approximately 2.7 and 1.6 times higher than that under no moss cover. The soil water retention under the thin and thick moss layers were greater than those under no moss cover, with the highest plant-available water capacity under the thin moss layer. The maximum water-holding capacity of the moss layer was significantly positively correlated with the field water-holding capacity of the soil and negatively correlated with the equivalent diameter of the macropores, while the storage capacity of the moss layer was significantly and negatively correlated with the maximum effective water content of the soil. The field capacity (FC) and permanent wilting point (PWP) were significantly and positively correlated with the soil organic matter. The effect of the moss layer on water retention may be mainly realized by influencing the pore distribution and organic matter accumulation. The moss layer had a positive ecohydrological effect on soil water retention and even water conservation in forest soils.

Development of high-resolution gridded data for water availability identification through GRACE data downscaling: Development of machine learning models

Estimation of total water availability has paramount importance in planning sustainable development of a region, particularly in arid water-scarce areas. Coarse-resolution of existing total water availability or terrestrial water storage anomaly (TWSA) data is the major limitation of their applications in different sectors. An attempt has been made to downscale Gravity Recovery and Climate Experiment (GRACE) TWSA data to develop a high-resolution gridded data product of the total water availability of Iraq. European reanalysis (ERA5) precipitation, evapotranspiration, surface runoff, subsurface runoff and soil water contents data were used to downscale GRACE 1.0° spatial resolution monthly TWSA to 0.1° spatial resolution for the period 2002–2020. A machine learning (ML)-based recursive feature elimination algorithm was used to identify the optimum input combination according to the nonlinear relationship of ERA5 variables with GRACE water equivalence data. The selected subset of inputs was used to develop the downscaling models using three classical ML algorithms for the available GRACE measurement points over Iraq. The models were calibrated at 70% of GRACE grid point locations and validated in the rest of the points. Finally, the model was used to predict TWSA at each ERA5 grid point to generate Iraq's high-resolution water availability dataset. The results showed higher performance of random forest in downscaling TWSA compared to other algorithms. The model estimated the TWSA at validation points with Kling-Gupta Efficiency (KGE) in the range of 0.5–0.91 and Nash-Sutcliff Efficiency (NSE) between 0.54 and 0.88. The modelled high-resolution TWSA data shows higher availability of water resources in the north, particularly northeast of Iraq, and the least in the southeast. The technique developed in this study can be implemented in developing a high-resolution gridded water availability dataset from satellite GRACE data in the region where in-situ estimation is very limited.

Enhancing rhizosphere soil water retention in wheat through colonization with endophytic fungus Serendipita indica

Effect of S. indica colonization of wheat (Triticum aestivum) on water retention and physical quality of the rhizosphere soil was investigated in a greenhouse study. Colonized and uncolonized seedlings of four wheat cultivars (i.e., Roshan, Ghods, Pishtaz, and Kavir) were grown in rhizoboxes. Plants were harvested and intact samples were taken from the rhizosphere to measure soil organic carbon (SOC), hot-water soluble carbohydrates (HWSC), and soil water retention curve (SWRC). Water contents at field capacity (θFC) and permanent wilting point (θPWP), and plant available water (PAW) were obtained from the measured SWRC data. The integral energy (EI(PAW)) and integral water storage (WI(PAW)), two alternative indices of soil water availability and physical quality, were computed by integration of SWRCs over the PAW range with respect to water content and matric potential, respectively. Low EI(PAW) and high WI(PAW) indicate improved soil physical quality and better soil water availability to plant. The results showed that the SOC storage and HWSC of the wheat rhizosphere were approximately 146 and 83% greater than those of unplanted soils, respectively. Moreover, compared with the uncolonized counterparts, S. indica colonization significantly increased the SOC and HWSC by 76 and 134%, respectively. The presence of plant roots and S. indica colonization improved soil water retention by increasing SOC and HWSC and subsequently enhancing portion of structural porosity (i.e., pore space between the soil aggregates in the size range of 0.5–500 μm, mainly includingmacropores and mesopores). Despite having the same PAW, colonized soil samples had lower EI(PAW) (≈ 133 J kg−1) compared to uncolonized counterparts (≈ 153 J kg−1). This finding implies that plant roots take up water from the colonized wheat-planted soils easier than from the uncolonized counterparts. Compared to uncolonized samples, an increase of 50% in S1 (Dexter's index of soil physical quality) of the colonized Kavir cultivar [with the lowest root extension, SOC (i.e., 0.97 g kg−1), and HWSC (i.e., 0.059 g kg−1)] showed that S. indica can improve soil physical quality due to greater structural pores. Among the four wheat cultivars, the rhizosphere of Roshan (≈ 1.60 g kg−1) and Ghods (1.61 g kg−1) had the highest SOC values. Higher HWSC (i.e., 0.138 g kg−1) and more extensive root distribution for Roshan, especially upon co-cultivation with S. indica, led to greater contribution of structural pores in water retention in the rhizosphere soil when compared with three other cultivars. To conclude, S. indica colonization not only in the presence of plant roots and by increasing SOC and HWSC improves the physical quality of the rhizosphere soil but also the fungus by itself enhances soil physical quality due to enhancing portion of structural porosity involving in water transition and storage.

Active plant biomass inputs influence pore system functioning in no-till soils

Available knowledge about the exact impact of plant growth on the properties and functioning of no-till soils is somewhat limited, especially in tropical and subtropical regions. The starting hypothesis for this work was that long-term active plant biomass Input-APBI (aboveground plant shoot biomass) would improve pore system functioning in surface and subsurface soil layers by playing different, complementary roles in a previously degraded subtropical Acrisol. The hypothesis was checked by examining the results of a 34-yr field experiment involving five different cropping systems, namely: bare soil (BS), perennial pasture (PAST), oat/maize (O/M), oat + vetch/maize (O + V/M) and oat + vetch/ maize + cowpea (O + V/M + C). The soil was supplied with APBIs varying from 0.13 to 1.48 kg dry matter ha−1 yr−1. The APBIs for each cropping system were very low (BS), low (O/M), medium (O + V/M), high (O + V/M + C), and very high (PAST). The surface (0–5 cm) and subsurface (5–15 cm) soil layer were analyzed for static and dynamic properties of the pore system including bulk density; total, macro, and microporosity; the ability of the system to conduct air and water; continuity in soil pores; and plant-available water capacity. Micromorphological images of the soil revealed a complex pore network whose structure and functioning were both improved by the action of plants. In the surface soil layer, very high APBIs from pasture and high inputs from O + V/M + C increased total porosity by 11 and 14 %, respectively; pore continuity (Ncont) by 11 and 40 %, respectively; and microporosity by 31 and 23 %, respectively —all relative to bare soil. In the subsurface soil layer, pasture, and O + V/M + C decreased Ncont by 44 and 40 %, respectively, but increased water permeability (kw) by a factor of 6.5 and 7, respectively. In addition, very high APBIs increased continuity and permeability to air in macropores relative to BS. Organized large macropores in the subsurface soil layer efficiently conducted water and air from the soil surface and acted as bridges between the surface and subsurface soil layer. Overall, our findings suggest that APBIs helped develop a pore system with differential properties and complementary functions that influenced water infiltration and air fluxes in the surface soil layer, and water availability to crops in the subsurface soil layer, through long-term self-organization in the system. Future research with a view to understanding the influence of species richness and roots on physical quality in no-till soils is recommended.

Use of archived data to derive soil health and water quality indicators for monitoring shifts in natural resources.

Current gaps impeding researchers from developing a soil and watershed health nexus include design of long-term field-scale experiments and statistical methodologies that link soil health indicators (SHI) with water quality indicators (WQI). Land cover is often used to predict WQI but may not reflect the effects of previous management such as legacy fertilizer applications, disturbance, and shifts in plant populations) and soil texture. Our research objectives were to use nonparametric Spearman rank-order correlations to identify SHI and WQI that were related across the Fort Cobb Reservoir experimental watershed (FCREW); use the resulting rho (r) and p values (P) to explore potential drivers of SHI-WQI relationships, specifically land use, management, and inherent properties (soil texture, aspect, elevation, slope); and interpret findings to make recommendations regarding assessment of the sustainability of land use and management. The SHI values used in the correlation matrix were weighted by soil texture and land management. The SHI that were significantly correlated with one or more WQI were available water capacity (AWC), Mehlich III soil P, and the sand to clay ratio (S:C). Mehlich III soil P was highly correlated with three WQI: total dissolved solids (TDS) (0.80; P<0.01), electrical conductivity of water (EC-H2 O) (0.79; P<0.01), and water nitrates (NO3 -H2 O) (0.76; P<0.01). The correlations verified that soil texture and management jointly influence water quality (WQ), but the size of the soils dataset prohibited determination of the specific processes. Adoption of conservation tillage and grasslands within the FCREW improved WQ such that water samples met the U.S. Environmental Protection Agency (EPA) drinking water standards. Future research should integrate current WQI sampling sites into an edge-of-field design representing all management by soil series combinations within the FCREW.

Digital mapping of the soil available water capacity: tool for the resilience of agricultural systems to climate change

Soil available water capacity (AWC) is a key function for human survival and well-being. However, its direct measurement is laborious and spatial interpretation is complex. Digital soil mapping (DSM) techniques emerge as an alternative to spatial modeling of soil properties. DSM techniques commonly apply machine learning (ML) models, with a high level of complexity. In this context, we aimed to perform a digital mapping of soil AWC and interpret the results of the Random Forest (RF) algorithm and, in a case study, to show that digital AWC maps can support agricultural planning in response to the local effects of climate change. To do so, we divided this research into two approaches: In the first approach, we showed a DSM using 1857 sample points in a southeastern region of Brazil with laboratory-determined soil attributes, together with a pedotransfer function (PTF), remote sensing and DSM techniques. In the second approach, the constructed AWC digital soil map and weather station data were used to calculate climatological soil water balances for the periods between 1917–1946 and 1991–2020. The result showed the selection of covariates using Shapley values as a criterion contributed to the parsimony of the model, obtaining goodness-of-fit metrics of R2 0.72, RMSE 16.72 mm m−1, CCC 0.83, and Bias of 0.53 over the validation set. The highest contributing covariates for soil AWC prediction were the Landsat multitemporal images with bare soil pixels, mean diurnal, and annual temperature range. Under the current climate conditions, soil available water content (AW) increased during the dry period (April to August). May had the highest increase in AW (∼17 mm m−1) and decrease in September (∼14 mm m−1). The used methodology provides support for AWC modeling at 30 m resolution, as well as insight into the adaptation of crop growth periods to the effects of climate change.

Impact of wood-derived biochar on the hydrologic performance of bioretention media: Effects on aggregation, root growth, and water retention

Bioretention systems are one example of green stormwater infrastructure that may mitigate the hydrologic impact of stormwater runoff. To improve water retention while maintaining rapid stormwater infiltration, conventional bioretention soil media (BSM) might be augmented with biochar. Biochar may improve the BSM's structure by increasing soil aggregation, which might improve water retention and increase stormwater infiltration while also improving root growth. Pots with BSMs representing high and moderate sand content media were amended with a wood-derived biochar, planted with switchgrass, and subjected to weekly storms for 20 weeks, followed by a 10-week drought. In the high sand content medium (NC mix), biochar amendment increased hydraulic conductivity (Ksat), and this effect increased with time. At 0 weeks, 2% and 4% (w/w) biochar increased Ksat by 4 ± 2% and 10 ± 4%, respectively, while at 30 weeks the increase was 30 ± 10 and 70 ± 20%, respectively, above biochar-free media. Similar improvements were seen in plant available water (PAW) in NC mix. However, minimal improvements in Ksat and PAW from biochar amendment were found in the moderate sand content BSM that contained compost and mulch (DE mix). Where biochar promoted Ksat, this was correlated with increased water-stable aggregate size (r = 0.86), fine root volume (r = 0.88), and below ground biomass (r = 0.83). Important factors affecting Ksat and aggregation in the NC mix were biochar's influence on organo-mineral association, fungal hyphae length, and plant roots. Wood-derived biochar amendment to BSM may obviate the need for compost/mulch since biochar has similar effects on improving BSM hydrology and root growth without the risk of undesired nutrient leaching.

Role of Rice Husk Biochar in Improving Soil Physical Properties of ex Gold-Mined Soil

Mining causes destructive soil properties, especially soil texture, water retention, and transmission. Applying biochar is the best way to improve soil physical properties. A glasshouse experiment was conducted to evaluate the role of biochar on soil physical properties based on a Completely Randomized Design (CRD) with four replicates. The research comprised six treatments (0, 4, 8, 12, 16, 20 t biochar ha-1). The results showed that the ex-gold-mined soil had coarse soil texture (sandy loam), high Bulk Density (BD) (1.43 g cm-3), low Total Soil Pores (TSP) (46.45%), low soil organic matter (SOM) content (1.27 %), very fast hydraulic conductivity (198.8 cm h-1). After biochar incubation, SOM increased (to 3.11%), soil BD decreased (to 1.16 g cm-3), TSP increased (to 54.17 %), water retention increased (at pF 1.0, 2.0, 2.54, and 4.2), plant available water (PAW) increased (into 8.33 %), and hydraulic conductivity decreased (into 24.70 cm h-1). However, applying 20 t biochar ha-1 still needs to bring the soil physical properties of the ex-gold-mined soil back into suitable soil for farming land.