Understanding rainfall runoff dynamics across various land uses and landscape positions in North Western Ethiopia

The hydrological cycle and soil dynamics in watersheds are significantly influenced by land use and topographical variations. This study explores the rainfall-runoff dynamics across various land uses and landscape positions in the Abagerima watershed, North-Western Ethiopia. In the watershed land degradation, soil erosion, and runoff are critical environmental challenges. The primary objectives were to develop rainfall-runoff relationships for different land use types, establish connections between runoff and soil loss under varying land uses and soil moisture conditions, and evaluate soil water content variations at different depths and land use types. Rainfall data were collected using both automatic and manual rain gauges installed within the watershed. Runoff and sediment loss data were gathered from three distinct plots with different land uses and slope positions, recorded daily at 6:30 a.m. following rainstorm events. The analysis revealed significant rainfall-runoff relationships for all land use types (P < 0.001). The watershed's dominant runoff generation mechanism was identified as saturation excess, based on infiltration rate and rainfall intensity data. Soil moisture measurements were conducted using ECH2O Ec-5 soil moisture sensor probes which indicated that volumetric soil moisture content increased with depth on grazing land, while it decreased on cultivated land, with statistically significant differences among the five soil depths (P < 0.001). The findings suggest that steep slope areas should be protected and afforestation programs initiated. Free grazing grasslands should transition to controlled grazing systems to mitigate soil erosion. This research highlights the importance of land use and soil moisture considerations in understanding rainfall-runoff interactions and soil water content variations, providing critical insights for effective watershed management and soil conservation, particularly in regions vulnerable to runoff and erosion.

Modeling soil acidity (pH) dynamics under extreme agroclimatic conditions in Horro Guduru Wallaga Zone, northwestern Ethiopia

Soil plays a critical role in nutrient availability, microbial activity, and fertility in agriculture. However, the effects of agroclimatic conditions on soil pH are not well understood, particularly in the Horro Guduru Zone of Ethiopia. This study aimed to investigate the soil pH under extremely wet and dry conditions across 3 shared socioeconomic pathway (SSP) scenarios: SSP1-2.6, SSP2-4.5, and SSP5-8.5. Baseline agroclimatic data (1981-2010) and future projections (2041-2070) were obtained from the European Commission Climate Change Services. Soil pH data at a 250 m resolution were extracted from the FAO-UNESCO global soil map. Missing values, multicollinearity, and outliers were addressed before modeling. Predictive models, including neural networks, generalized regression, and bootstrap forests, were validated, with the generalized regression model showing the best performance. The results indicate that soil pH decreases under consecutive dry‒wet conditions and increases with increasing maximum day temperatures across all scenarios. Soil pH is significantly influenced by the number of consecutive dry days, consecutive wet days, and maximum day temperature. The SSP1-2.6 and SSP2-4.5 scenarios resulted in improved pH levels, whereas SSP5-8.5 led to a decrease in soil pH, averaging 5.79 and decreasing to 5.54. These findings suggest that under SSP5-8.5, soil health and farming productivity may be compromised. This study emphasizes the need to adjust soil management practices based on prevailing climatic conditions to ensure soil health and agricultural sustainability.

Patterns of rainfall and temperature and their relationships with potential evapotranspiration rates over the period 1981-2022 in parts of central, western, southern, and southwestern Uganda

Uganda in East Africa is experiencing highly variable rainfall which is exacerbated by temperatures warming at faster rates. This study analyzed rainfall and temperature patterns in comparison with the potential evaporation transpiration rates (PETs) for parts of Central, Western, Southern, and Southwestern Uganda for varying periods from 1981 to 2022. For rainfall onset date (OD), threshold of 0.85 mm for a rainy day, rainfall of 20 mm accumulated over 5 days with at least 3 rain days, and dry spell not exceeding 9 days in the next 30 days were used. The rainfall cessation dates (RCDs) are determined when water balance (WB) falls below 5 mm in 7 days in the last month of the expected season (May and December) for the first and second season, respectively. Standardized rainfall anomaly was utilized to show seasonal and annual rainfall variability. Pearson's correlation (r) coefficient was used to show the relationship between weather variables (rainfall, temperature) and PET at five rainfall stations. Results showed highly varied onset and cessation dates for March-May (MAM) seasonal rainfall compared to those of September-December (SOND). Results showed highly variable onset and cessation of rainfall over the region and statistically significantly increasing trends in both maximum and minimum temperatures across the region, with the highest rate of increase of maximum and minimum temperature of 0.70 and 0.65 °C per decade respectively. Moreover, the maximum temperature and PET showed strong positive correlation coefficient (r) that ranged from 0.76 to 0.90 across the regions, which likely contribute to excess evaporation from the surfaces, soil moisture deficits that negatively affect plant biomass production, low crop yields and food insecurity. PET and rainfall revealed insignificant statistical negative correlation as indicated by the correlation coefficient ranging from - 0.04 to - 0.22. We recommend water management and conservation practices such as mulching, zero tillage, agroforestry, planting drought-resistant crops, and using affordable irrigation systems during period of water deficit.

Modeling the impacts of extreme climate scenarios on soil acidity (pH and exchangeable aluminum) in Abbay River Basin, Ethiopia

The Abbay River Basin faces the looming threat of extreme climate events, including prolonged droughts and erratic rainfall patterns, which can significantly affect soil health and fertility. This study aimed to explore the influence of extreme climate conditions on soil pH and exchangeable aluminum, aiming to promote sustainable agricultural practices in Ethiopia. The Africa Soil Information Service (ASIS) provided datasets on soil pH and exchangeable aluminum. The European Copernicus Climate Change Data Store was used to download historical and future datasets of extreme climatic indices from 1980 to 2010 and 2015-2050, respectively. The Coupled Model Intercomparison Project Phase 6 model ensemble was used to predict future climate impacts under three shared socioeconomic scenarios: SSP1-2.6, SSP2-4.3, and SSP5-8.5. Data extraction, quality control, and clustering were conducted before analysis, and the model was validated for its accuracy and reliability in predicting soil parameter changes. An artificial neural network model was utilized to predict the effects of extreme climate indices on soil pH and exchangeable aluminum concentrations. The model was designed to accurately and reliably predict changes in soil parameters. This study compared the changes in soil pH and aluminum concentrations using paired t tests. The model's diagnostic results indicated a significant impact of extreme climate scenarios on soil pH and exchangeable aluminum. Extreme climate factors such as heavy precipitation and cooler night time temperatures significantly contribute to soil acidification and an increase in aluminum concentration. Under the SSP1-2.6 and SSP2-4.5 emission scenarios, soil pH levels are expected to increase by 8.38 % and 3.79 %, respectively. These changes in soil pH are expected to have significant impacts on the exchangeable aluminum content in the soil, with increases of 37 % and 5.38 %, respectively, under the same emission scenarios. However, the SSP5.8 scenario predicted a 45 % increase in exchangeable aluminum and a 9.36 % decrease in soil pH. Therefore, this study significantly enhances our understanding of the influence of climate change on soil health. The development of strategies to mitigate climate change impacts on agriculture in the region must consider the effects of extreme climate indices.

Enhancement of soil aggregation and physical properties through fungal amendments under varying moisture conditions

Soil structure and aggregation are crucial for soil functionality, particularly under drought conditions. Saprobic soil fungi, known for their resilience in low moisture conditions, are recognized for their influence on soil aggregate dynamics. In this study, we explored the potential of fungal amendments to enhance soil aggregation and hydrological properties across different moisture regimes. We used a selection of 29 fungal isolates, recovered from soils treated under drought conditions and varying in colony density and growth rate, for single-strain inoculation into sterilized soil microcosms under either low or high moisture (≤-0.96 and -0.03 MPa, respectively). After 8 weeks, we assessed soil aggregate formation and stability, along with soil properties such as soil water content, water hydrophobicity, sorptivity, total fungal biomass and water potential. Our findings indicate that fungal inoculation altered soil hydrological properties and improved soil aggregation, with effects varying based on the fungal strains and soil moisture levels. We found a positive correlation between fungal biomass and enhanced soil aggregate formation and stabilization, achieved by connecting soil particles via hyphae and modifying soil aggregate sorptivity. The improvement in soil water potential was observed only when the initial moisture level was not critical for fungal activity. Overall, our results highlight the potential of using fungal inoculation to improve the structure of agricultural soil under drought conditions, thereby introducing new possibilities for soil management in the context of climate change.

Microbial impact on initial soil formation in arid and semiarid environments under simulated climate change

The microbiota is attributed to be important for initial soil formation under extreme climate conditions, but experimental evidence for its relevance is scarce. To fill this gap, we investigated the impact of in situ microbial communities and their interrelationship with biocrust and plants compared to abiotic controls on soil formation in initial arid and semiarid soils. Additionally, we assessed the response of bacterial communities to climate change. Topsoil and subsoil samples from arid and semiarid sites in the Chilean Coastal Cordillera were incubated for 16 weeks under diurnal temperature and moisture variations to simulate humid climate conditions as part of a climate change scenario. Our findings indicate that microorganism-plant interaction intensified aggregate formation and stabilized soil structure, facilitating initial soil formation. Interestingly, microorganisms alone or in conjunction with biocrust showed no discernible patterns compared to abiotic controls, potentially due to water-masking effects. Arid soils displayed reduced bacterial diversity and developed a new community structure dominated by Proteobacteria, Actinobacteriota, and Planctomycetota, while semiarid soils maintained a consistently dominant community of Acidobacteriota and Proteobacteria. This highlighted a sensitive and specialized bacterial community in arid soils, while semiarid soils exhibited a more complex and stable community. We conclude that microorganism-plant interaction has measurable impacts on initial soil formation in arid and semiarid regions on short time scales under climate change. Additionally, we propose that soil and climate legacies are decisive for the present soil microbial community structure and interactions, future soil development, and microbial responses.

Fostering plant growth performance under drought stress using rhizospheric microbes, their gene editing, and biochar

Stress due to drought lowers crop yield and frequently leads to a rise in food scarcity. Plants' intricate metabolic systems enable them to tolerate drought stress, but they are unable to handle it well. Adding some external, environmentally friendly supplements can boost plant growth and productivity when it comes to drought-stressed plants. In order to prevent the detrimental effects of drought in agricultural regions, environmentally friendly practices must be upheld. Plant growth-promoting rhizobacteria (PGPR) can exhibit beneficial phytostimulation, mineralization, and biocontrol activities under drought stress. The significant impact of the PGPR previously reported has not been accepted as an effective treatment to lessen drought stress. Recent studies have successfully shown that manipulating microbes can be a better option to reduce the severity of drought in plants. In this review, we demonstrate how modifying agents such as biochar, PGPR consortia, PGPR, and mycorrhizal fungi can help overcome drought stress responses in crop plants. This article also discusses CRISPR/Cas9-modifiable genes, increase plant's effectiveness in drought conditions, and increase plant resistance to drought stress. With an eco-friendly approach in mind, there is a need for practical management techniques having potential prospects based on an integrated strategy mediated by CRISPR-Cas9 editing, PGPR, which may alleviate the effects of drought stress in crops and aid in achieving the United Nation Sustainable Development Goals (UN-SDGs-2030).

Integrated Land Suitability Assessment for Depots Siting in a Sustainable Biomass Supply Chain

A sustainable biomass supply chain would require not only an effective and fluid transportation system with a reduced carbon footprint and costs, but also good soil characteristics ensuring durable biomass feedstock presence. Unlike existing approaches that fail to account for ecological factors, this work integrates ecological as well as economic factors for developing sustainable supply chain development. For feedstock to be sustainably supplied, it necessitates adequate environmental conditions, which need to be captured in supply chain analysis. Using geospatial data and heuristics, we present an integrated framework that models biomass production suitability, capturing the economic aspect via transportation network analysis and the environmental aspect via ecological indicators. Production suitability is estimated using scores, considering both ecological factors and road transportation networks. These factors include land cover/crop rotation, slope, soil properties (productivity, soil texture, and erodibility factor) and water availability. This scoring determines the spatial distribution of depots with priority to fields scoring the highest. Two methods for depot selection are presented using graph theory and a clustering algorithm to benefit from contextualized insights from both and potentially gain a more comprehensive understanding of biomass supply chain designs. Graph theory, via the clustering coefficient, helps determine dense areas in the network and indicate the most appropriate location for a depot. Clustering algorithm, via K-means, helps form clusters and determine the depot location at the center of these clusters. An application of this innovative concept is performed on a case study in the US South Atlantic, in the Piedmont region, determining distance traveled and depot locations, with implications on supply chain design. The findings from this study show that a more decentralized depot-based supply chain design with 3depots, obtained using the graph theory method, can be more economical and environmentally friendly compared to a design obtained from the clustering algorithm method with 2 depots. In the former, the distance from fields to depots totals 801,031,476 miles, while in the latter, it adds up to 1,037,606,072 miles, which represents about 30% more distance covered for feedstock transportation.

Predicting root zone soil moisture using observations at 2121 sites across China

Root zone soil moisture (RZSM) is particularly useful for understanding hydrological processes, plant-land-atmosphere exchanges, and agriculture- and climate-related research. This study aims to estimate RZSM across China by using a one-parameter (T) exponential filter method (EF method) together with a random forest (RF) regionalization approach and by using a large dataset containing in situ observations collected at 2121 sites across China. First, at each site, T is optimized at each of four soil layers (10-20 cm, 20-30 cm, 30-40 cm and 40-50 cm) by using 0-10-cm soil layer observations and the corresponding calibration layers. Second, an RF classifier is built for each layer according to the calibrated T values and 14 soil, climate and vegetation parameters across 2121 sites. Third, the calibrated T at each soil layer is regionalized with an established RF classifier. Spatial T maps are given for each soil layer across China. Our results show that the EF method performs reasonably well in predicting RZSM at the 10-20-cm, 20-30-cm, 30-40-cm and 40-50-cm layers, with Nash-Sutcliffe efficiency (NSE) medians of 0.73, 0.52, 0.38 and 0.27, respectively, between the observations and estimations. The T parameter shows a spatial pattern in each soil layer and is largely controlled by climate regimes. This study offers an improved RZSM estimation method using a large dataset containing in situ observations; the proposed method also has the potential to be used in other parts of the world.

A Method to Assess Agroecosystem Resilience to Climate Variability

Agroecosystems are influenced by climate variability, which puts their productivity at risk. However, they tend to maintain a functional state through their resilience. The literature presents several methods for assessing general resilience, but for specific resilience to climate variability, there are very few methods. An index is proposed that assesses the resilience of agroecosystems to climate variability, based on approaches and indicators that consider the interrelationships of agricultural systems with the environment. The index is made up of a set of multidimensional indicators, which give weight to the role that these play in the resilience of an agroecosystem. As a result, decision-making is assisted in the attempt to adapt or modify components of a farm, technology, and the culture of farmers. This index conceptually introduces structural and linkage indicators that assess ecological connections within farms and between farms and their environment. To demonstrate the effectiveness of the method, an application was implemented to evaluate the resilience to climate variability of fifty-one farms, located in Colombia, dedicated to citrus production, and it was verified that the most resilient farms were those that have the best qualified indicators, as well as being the ones with the highest level of production and profitability.

The Ubiquitin Proteasome System and Nutrient Stress Response

Plants utilize different molecular mechanisms, including the Ubiquitin Proteasome System (UPS) that facilitates changes to the proteome, to mitigate the impact of abiotic stresses on growth and development. The UPS encompasses the ubiquitination of selected substrates followed by the proteasomal degradation of the modified proteins. Ubiquitin ligases, or E3s, are central to the UPS as they govern specificity and facilitate the attachment of one or more ubiquitin molecules to the substrate protein. From recent studies, the UPS has emerged as an important regulator of the uptake and translocation of essential macronutrients and micronutrients. In this review, we discuss select E3s that are involved in regulating nutrient uptake and responses to stress conditions, including limited or excess levels of nitrogen, phosphorus, iron, and copper.

Recent Trends in Microbial Approaches for Soil Desalination

Soil salinization has become a major problem for agriculture worldwide, especially because this phenomenon is continuously expanding in different regions of the world. Salinity is a complex mechanism, and in the soil ecosystem, it affects both microorganisms and plants, some of which have developed efficient strategies to alleviate salt stress conditions. Currently, various methods can be used to reduce the negative effects of this problem. However, the use of biological methods, such as plant-growth-promoting bacteria (PGPB), phytoremediation, and amendment, seems to be very advantageous and promising as a remedy for sustainable and ecological agriculture. Other approaches aim to combine different techniques, as well as the utilization of genetic engineering methods. These techniques alone or combined can effectively contribute to the development of sustainable and eco-friendly agriculture.

Carbon storage assessment in soil and plant organs: the role of Prosopis spp. on mitigate soil degradation

Carbon sequestration is a process for stable storage of carbon dioxide. In this process, excess atmospheric carbon dioxide is stored by the aerial and underground organs of rangeland plants to reduce global warming. The aim of this study was to identify the relationship between some chemical properties of soil and ability of carbon storage in two plants, namely Prosopis cineraria and Prosopis juliflora in soil depth ranging between 0-15 and 15-30 cm. This research was carried out in Anbarabad region which is located at 258 km in the southeast of Kerman during 2016-2018. The present research was performed as a factorial experiment so that the first factor was the plant species and the control treatment and the second component was soil depth. Sampling was done from the shady soil of plants and the control area. Soil properties including organic carbon, bulk density, acidity, electrical conductivity and organic matter were analysed. The results indicated that the carbon stored at depths of 0-15 cm and 15-30 cm in the shade soil of P. cineraria was 21.39 and 24.36 t/ha, and in P. juliflora was 23.70 and 24.85 t/ha, and in control area is 19.83 and 21.31 t/ha. Also, the results of stepwise regression study showed that organic carbon percentage and bulk density are the most important factors affecting soil carbon sequestration.

Potential Impacts of Climate Change on the Toxicity of Pesticides towards Earthworms

This review examined one of the effects of climate change that has only recently received attention, i.e., climate change impacts on the distribution and toxicity of chemical contaminants in the environment. As ecosystem engineers, earthworms are potentially threatened by the increasing use of pesticides. Increases in temperature, precipitation regime changes, and related extreme climate events can potentially affect pesticide toxicity. This review of original research articles, reviews, and governmental and intergovernmental reports focused on the interactions between toxicants and environmental parameters. The latter included temperature, moisture, acidification, hypoxia, soil carbon cycle, and soil dynamics, as altered by climate change. Dynamic interactions between climate change and contaminants can be particularly problematic for organisms since organisms have an upper and lower physiological range, resulting in impacts on their acclimatization capacity. Climate change variables such as temperature and soil moisture also have an impact on acidification. An increase in temperature will impact precipitation which might impact soil pH. Also, an increase in precipitation can result in flooding which can reduce the population of earthworms by not giving juvenile earthworms enough time to develop into reproductive adults. As an independent stressor, hypoxia can affect soil organisms, alter bioavailability, and increase the toxicity of chemicals in some cases. Climate change variables, especially temperature and soil moisture, significantly affect the bioavailability of pesticides in the soil and the growth and reproduction of earthworm species.

Climate Change and Salinity Effects on Crops and Chemical Communication Between Plants and Plant Growth-Promoting Microorganisms Under Stress

During the last two decades the world has experienced an abrupt change in climate. Both natural and artificial factors are climate change drivers, although the effect of natural factors are lesser than the anthropogenic drivers. These factors have changed the pattern of precipitation resulting in a rise in sea levels, changes in evapotranspiration, occurrence of flood overwintering of pathogens, increased resistance of pests and parasites, and reduced productivity of plants. Although excess CO2 promotes growth of C3 plants, high temperatures reduce the yield of important agricultural crops due to high evapotranspiration. These two factors have an impact on soil salinization and agriculture production, leading to the issue of water and food security. Farmers have adopted different strategies to cope with agriculture production in saline and saline sodic soil. Recently the inoculation of halotolerant plant growth promoting rhizobacteria (PGPR) in saline fields is an environmentally friendly and sustainable approach to overcome salinity and promote crop growth and yield in saline and saline sodic soil. These halotolerant bacteria synthesize certain metabolites which help crops in adopting a saline condition and promote their growth without any negative effects. There is a complex interkingdom signaling between host and microbes for mutual interaction, which is also influenced by environmental factors. For mutual survival, nature induces a strong positive relationship between host and microbes in the rhizosphere. Commercialization of such PGPR in the form of biofertilizers, biostimulants, and biopower are needed to build climate resilience in agriculture. The production of phytohormones, particularly auxins, have been demonstrated by PGPR, even the pathogenic bacteria and fungi which also modulate the endogenous level of auxins in plants, subsequently enhancing plant resistance to various stresses. The present review focuses on plant-microbe communication and elaborates on their role in plant tolerance under changing climatic conditions.

The role of hopanoids in fortifying rhizobia against a changing climate

Bacteria are a globally sustainable source of fixed nitrogen, which is essential for life and crucial for modern agriculture. Many nitrogen-fixing bacteria are agriculturally important, including bacteria known as rhizobia that participate in growth-promoting symbioses with legume plants throughout the world. To be effective symbionts, rhizobia must overcome multiple environmental challenges: from surviving in the soil, to transitioning to the plant environment, to maintaining high metabolic activity within root nodules. Climate change threatens to exacerbate these challenges, especially through fluctuations in soil water potential. Understanding how rhizobia cope with environmental stress is crucial for maintaining agricultural yields in the coming century. The bacterial outer membrane is the first line of defence against physical and chemical environmental stresses, and lipids play a crucial role in determining the robustness of the outer membrane. In particular, structural remodelling of lipid A and sterol-analogues known as hopanoids are instrumental in stress acclimation. Here, we discuss how the unique outer membrane lipid composition of rhizobia may underpin their resilience in the face of increasing osmotic stress expected due to climate change, illustrating the importance of studying microbial membranes and highlighting potential avenues towards more sustainable soil additives.