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.

Land use modification causes slow, but predictable, change in soil microbial community composition and functional potential

BACKGROUND

Bacterial communities are critical to ecosystem functioning and sensitive to their surrounding physiochemical environment. However, the impact of land use change on microbial communities remains understudied. We used 16S rRNA gene amplicon sequencing and shotgun metagenomics to assess soil microbial communities' taxonomic and functional responses to land use change. We compared data from long-term grassland, exotic forest and horticulture reference sites to data from sites that transitioned from (i) Grassland to exotic forest or horticulture and from (ii) Exotic forest to grassland.

RESULTS

Community taxonomic and functional profiles of the transitional sites significantly differed from those within reference sites representing both their historic and current land uses (P < 0.001). The bacterial communities in sites that transitioned more recently were compositionally more similar to those representing their historic land uses. In contrast, the composition of communities from sites exposed to older conversion events had shifted towards the compositions at reference sites representing their current land use.

CONCLUSIONS

Our study indicates that microbial communities respond in a somewhat predictable way after a land use conversion event by shifting from communities reflecting their former land use towards those reflecting their current land use. Our findings help us to better understand the legacy effects of land use change on soil microbial communities and implications for their role in soil health and ecosystem functioning. Understanding the responsiveness of microbial communities to environmental disturbances will aid us in incorporating biotic variables into soil health monitoring techniques in the future.

Soil health and management matters: A survey of field tree nursery producers

Extensive calls for increased tree planning worldwide are highlighting the need for management changes in the field tree nursery sector. Healthy soil is the foundation for sustainable agricultural systems, and best practices for soil management confer tangible benefits to producers as well as broader system-wide benefits. However, field tree producers lack the foundational resources needed to implement, manage, and evaluate soil health practices within their operations. Furthermore, tree producers are unique in that their primary product is central to the sustainable development of urban spaces and are facing increased demand for high-quality trees. There is subsequently a two-pronged need. First, a greater understanding of the key objectives, opportunities, and challenges driving soil management in tree production is required to support the development of specified practices, within the sector. Second, a greater characterization of the short- and long-term value of trees is required to incentivize the soil health practices that will support resilience in tree production systems. The study characterizes the soil health and management practices implemented in Ontario by field tree nursery producers. A questionnaire was administered in the summer of 2020 to Ontario tree nursery producers within the Landscape Ontario Horticultural Trades Association (N = 29). Responding producers provided insight into soil management practices, opportunities and challenges. Tree nursery producers expressed a need for resources to support cover crop usage and comprehensive soil testing to improve tree performance. Reflection on current soil management challenges and opportunities highlights the benefits of considering soil management as one aspect within the broader social-ecological system.

Evaluation of soil ecological health after exposure to environmentally relevant doses of Di (2-ethylhexyl) phthalate: Insights from toxicological studies of earthworms at different ecological niches

As one of the most critical soil faunas in agroecosystems, earthworms are significant in preserving soil ecological health. Di (2-ethylhexyl) phthalate (DEHP) is a major plasticizer and widely used in plastic products like agricultural films. However, it has become ubiquitous contaminant in agricultural soil and poses a potential threat to soil health. Although the awareness of the impacts of DEHP on soil ecology is increasing, its adverse effects on soil invertebrates, especially earthworms, are still not well developed. In this study, the ecotoxicological effects and underlying mechanisms of environmentally relevant doses DEHP on earthworms of different ecological niches were investigated at the individual, cytological, and biochemical levels, respectively. Results showed that the acute toxicity of DEHP to M. guillelmi was higher than E. foetida. DEHP induced reactive oxygen species (ROS) levels and further caused oxidative damage (including cellular DNA and lipid peroxidation damage) in both species, speculating that they may exhibit similar oxidative stress mechanisms. Furthermore, two earthworms presented the alleviated toxicity when re-cultured in uncontaminated circumstances, yet, the accumulated ROS in bodies could not be completely scavenged. Risk assessment indicated that the detrimental impacts of DEHP were more significant in the M. guillelmi than in E. foetida in whole experiments prides, and the biomarkers additionally showed a species-specific trend. Besides, molecular docking revealed that DEHP could bind to the active center of superoxide dismutase/catalase (SOD/CAT) by hydrogen bonding or hydrophobic interactions. Overall, this study will provide a novel insight for accurate contaminant risk assessment, and also highlight that the comprehensive biological effects of different species should be emphasized in soil ecological health diagnostics and environmental toxicology assays, as otherwise it may lead to underestimation or misestimation of the soil health risk of contaminants.

Abundance, classification and genetic potential of Thaumarchaeota in metagenomes of European agricultural soils: a meta-analysis

BACKGROUND

For a sustainable production of food, research on agricultural soil microbial communities is inevitable. Due to its immense complexity, soil is still some kind of black box. Soil study designs for identifying microbiome members of relevance have various scopes and focus on particular environmental factors. To identify common features of soil microbiomes, data from multiple studies should be compiled and processed. Taxonomic compositions and functional capabilities of microbial communities associated with soils and plants have been identified and characterized in the past few decades. From a fertile Loess-Chernozem-type soil located in Germany, metagenomically assembled genomes (MAGs) classified as members of the phylum Thaumarchaeota/Thermoproteota were obtained. These possibly represent keystone agricultural soil community members encoding functions of relevance for soil fertility and plant health. Their importance for the analyzed microbiomes is corroborated by the fact that they were predicted to contribute to the cycling of nitrogen, feature the genetic potential to fix carbon dioxide and possess genes with predicted functions in plant-growth-promotion (PGP). To expand the knowledge on soil community members belonging to the phylum Thaumarchaeota, we conducted a meta-analysis integrating primary studies on European agricultural soil microbiomes.

RESULTS

Taxonomic classification of the selected soil metagenomes revealed the shared agricultural soil core microbiome of European soils from 19 locations. Metadata reporting was heterogeneous between the different studies. According to the available metadata, we separated the data into 68 treatments. The phylum Thaumarchaeota is part of the core microbiome and represents a major constituent of the archaeal subcommunities in all European agricultural soils. At a higher taxonomic resolution, 2074 genera constituted the core microbiome. We observed that viral genera strongly contribute to variation in taxonomic profiles. By binning of metagenomically assembled contigs, Thaumarchaeota MAGs could be recovered from several European soil metagenomes. Notably, many of them were classified as members of the family Nitrososphaeraceae, highlighting the importance of this family for agricultural soils. The specific Loess-Chernozem Thaumarchaeota MAGs were most abundant in their original soil, but also seem to be of importance in other agricultural soil microbial communities. Metabolic reconstruction of Switzerland_1_MAG_2 revealed its genetic potential i.a. regarding carbon dioxide (CO[Formula: see text]) fixation, ammonia oxidation, exopolysaccharide production and a beneficial effect on plant growth. Similar genetic features were also present in other reconstructed MAGs. Three Nitrososphaeraceae MAGs are all most likely members of a so far unknown genus.

CONCLUSIONS

On a broad view, European agricultural soil microbiomes are similarly structured. Differences in community structure were observable, although analysis was complicated by heterogeneity in metadata recording. Our study highlights the need for standardized metadata reporting and the benefits of networking open data. Future soil sequencing studies should also consider high sequencing depths in order to enable reconstruction of genome bins. Intriguingly, the family Nitrososphaeraceae commonly seems to be of importance in agricultural microbiomes.

Challenges and technological interventions in rice-wheat system for resilient food-water-energy-environment nexus in North-western Indo-Gangetic Plains: A review

Rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system in north-western Indo-Gangetic Plains performed a crucial role in the national food security. However, the widespread and intensive cultivation of this system has led to serious problems such as declining groundwater table (~1 meter year-1) with sharp increase in number of districts under over-exploitation category, residue burning, higher greenhouse gases emission and herbicide resistance in weeds, causing stagnant crop productivity and lesser profitability. In this review article, an attempt has been made to discuss the major issues pertaining to intensive rice-wheat cultivation amidst climate vagaries and futuristic approach to address these challenges. Different tillage- and crop-specific recommendations such as adoption of direct seeded rice, diversification with lesser resource guzzling crops such as maize (Zea mays L.) at least on the periodic manner especially in light-medium soils, inclusion of summer legumes and alternative tillage systems (permanent beds and zero tillage with residue retention) have been suggested to address these issues. However, crop performance under these techniques has been found to be location, soil and cultivar specific. The absence of aerobic tailored genotypes and weeds have been identified as the major constraints in adoption of direct seeded rice. The integrated strategies of conservation tillage, crop breeding program and resource conserving region- and soil-specific agronomic measures with crop diversification would be helpful in tackling the sustainability issues. It requires future efforts on developing crop genotypes suited to conservation tillage, effective weed control strategies and trainings and demonstrations to farmers to switch from conventional rice-wheat system to alternative cropping systems.

Microplastics stimulated nitrous oxide emissions primarily through denitrification: A meta-analysis

Microplastics can profoundly alter nitrogen cycling. However, it remains poorly understood how microplastics impact soil nitrogen processes and generate N₂O. A meta-analysis was conducted for this investigation based on 60 published studies to elucidate the effects of microplastics on soil nitrogen cycling, from genes to processes. Under microplastic exposure, the emissions of soil N₂O was significantly increased (140.6%), while the nitrate reductase activities increased by 4.8%. The denitrification rate and number of denitrifier genes were increased by 17.8% and 10.6%, respectively. Meanwhile, the nitrification rate and nitrifier genes were not significantly altered, so did the nitrogen immobilization and mineralization rates. The additional emission of soil N₂O might primarily from stimulated denitrification. Soil N₂O emission and denitrification genes were always increased, regardless of the concentrations of microplastic or experiment duration. As a result, the nitrite was increased by 38.8% and nitrate was decreased by 22.4%, respectively. Interestingly, the N₂O emission increments and copy number of denitrifiers genes diminished over time. This study revealed divergent changes in soil nitrogen processes and highlighted N₂O emissions with a greater denitrification rate under microplastic exposure. The negative impacts of microplastics on soil health were revealed from the perspective of soil nitrogen availability and N₂O emissions.

Application of phosphorus amendments reduces metal uptake and increases yield of Oryza saliva L. (rice) in Cd/Cu-contaminated paddy field

To alleviate worldwide food safety issues caused by metal contamination, an easily available material is urgently needed for extensive application. In this study, calcium magnesium phosphate fertiliser (Pcm) was applied to a Cd/Cu co-contaminated paddy field in comparison with limestone and organic fertiliser. The results showed that only Pcm is effective in simultaneously reducing Cd uptake by 56.7% and Cu uptake by 36.2% in Oryza saliva L. (rice). The rice yield, reduced mainly by Cu, also increased by 30.1% with respect to the enhancement of soil pH, cation exchange capacity and availability of phosphorus, as well as the reduction in availabilities of Cd and Cu. Additionally, Pcm dramatically shaped the bacterial community structure, with Proteobacteria and Firmicutes predominant in the soils. The beneficial genera Exiguobacterium, Citrobacter, and Acinetobacter, which are vital for phosphate dissolution and Cd/Cu immobilisation, were also enriched. The results demonstrated that the application of Pcm at 0.4% (w:w) was able to enhance both crop quantity and quality in Cd/Cu co-contaminated paddy fields by reducing Cu/Cd availability, promoting rice yield, and reshaping bacterial community structures.

Biochar and metal-tolerant bacteria in alleviating ZnO nanoparticles toxicity in barley

The constant use of zinc oxide nanoparticles (ZnO NPs) in agriculture could increase their concentration in soil, and cause a threat to sustainable crop production. The present study was designed to determine the role of spore-forming and metal-tolerant bacteria, and biochar in alleviating the toxic effects of a high dose of ZnO NPs (2000 mg kg^-1) spiked to the soil (Haplic Chernozem) on barley (Hordeum sativum L). The mobile compounds of Zn in soil and their accumulation in H. sativum tissues were increased significantly. The addition of biochar (2.5% of total soil) and bacteria (10¹⁰ CFU kg^-1) separately and in combination showed a favorable impact on H. sativum growth in ZnO NPs polluted soil. The application of bacteria (separately) to the contaminated soil reduced the mobility of Zn compounds by 7%, due to loosely bound Zn compounds, whereas only biochar inputs lowered Zn mobile compounds mobility by 33%, even the combined application of biochar and bacteria also suppressed the soil Zn mobile compounds. Individual application of biochar and bacteria reduced the Zn plant uptake, i.e., underground parts (roots) by 44% and 20%, and in the above-ground parts of H. sativum plants by 39% and 13%, respectively, compared to ZnO NPs polluted soil treatments. Biochar, both separately and in combination with bacteria improved the root length by 48 and 85%, and plant height by 53 and 40%, respectively, compared to the polluted control. The root length and plant height decreased by 52 and 40% in ZnO NPs spiked soil compared clean soil treatments. Anatomical results showed an improvement in the structural organization of cellular-sub-cellular tissues of root and leaf. The changes in ultrastructural organization of assimilation tissue cells were noted all treatments due to the toxic effects of ZnO NPs compared with control treatment. The results indicate that metal-tolerant bacteria and biochar could be effective as a soil amendment to reduce metal toxicity, enhance crop growth, and improve soil health.

Are there universal soil responses to cover cropping? A systematic review

Cover cropping is commonly acknowledged to promote soil health in agriculture. However, contradictory findings on the benefits of cover crops for soil health, crop productivity, economic and ecological factors, as well as the influence of inherent soil parameters on such benefits exist in the scientific literature. Here, we critically assessed evidence of cover crop benefits through a systematic review of the published literature. To access relevant papers, we searched the literature for cover crops and soil health indicators using Scopus (1996-2020), ScienceDirect (1996-2020) and Google scholar (1970-1996) with specific keywords and combinations. Only English research papers including experimental plots and control groups were considered. We analyzed 102 unique peer-reviewed papers and 1494 corresponding unique plots encompassing various cover crops, soil textures, climates, management systems and experimental duration (1-3 years, 4-6 years, 7-10 years and over 10 years). Strong evidence suggests that cover crops can enhance soil structure and promote soil health by improving soil physical and chemical properties, including saturated hydraulic conductivity (mean net change of 105.6 %), total organic carbon (10.1 %), and total nitrogen (20.2 %). On the other hand, cover crops exhibit weak effects on properties like bulk density and microporosity with fairly low values of net change. In most cases, cover crops increase the soil carbon content, including microbial biomass carbon (19.5 %) and particulate organic carbon (49.5 %). In this systematic review, we found limited studies on the effect of cover crops on soil health as influenced by soil texture, regional climate, rainfall and duration of the cover crop practices. The paucity of long-term regional systematic research of soil physics, chemistry and biology makes it difficult to forecast future implications of cover crops on soil health indicators.

Effects of long-term fertilization with contemporary Danish human urine, composted household waste and sewage sludge on soil nematode abundance and community structure

It is desirable to recycle the urban waste products human urine, composted household waste and sewage sludge as fertilizers to agricultural fields. This could minimize the use of NPK fertilizer, improve soil structure and store carbon. However, waste products may contain heavy metals, persistent organic pollutants (POP) and plastics, and there are concerns that long-term build-up of these substances will cause unwanted effects on soil health. Nematodes are ubiquitous and numerous in soil ecosystems. Abundance and community structure of soil nematodes can be used as indicators of soil health, as some species are vulnerable to pollution. There are well-developed methods for detecting environmental changes based on nematode community structure. At the long-term CRUCIAL field experiment, where alternative fertilizer products have been applied since 2003, we measured effects of long-term fertilization with human urine, composted household waste and sewage sludge on soil properties (pH, soil organic matter and nitrogen availability), abundance of soil microorganisms (bacteria, fungi, small protozoa and ciliates) and nematode trophic groups compared to plots with unfertilized, NPK and cattle manure treatment. Sampling and assessments were done three times during a growth season. Further, we assessed the composition of nematode communities using metabarcoding. Treatments with a high input of organic matter (cattle manure, composted household waste and sewage sludge) had high abundances of bacteria and thus bacterial grazers (small protozoa, ciliates, and bacterial feeding nematodes). We found a significant correlation between nematode community structure and pH and organic matter. We calculated the nematode Maturity Index 2-5 (pollution indicator) based on metabarcoding data, which did not differ significantly between the treatments. We conclude that long-term fertilization with different types of contemporary Danish urban waste products affects both soil properties and abundance of soil organisms, the latter largely reflecting the organic matter input of the fertilizer treatments. We found no adverse effect on nematode communities that could indicate pollution-induced stress on nematofauna or decreased soil fertility.

Soil organic carbon, aggregation and fungi community after 44 years of no-till and cropping systems in the Central Great Plains, USA

Implementing sustainable agricultural land management practices such as no-till (NT) and diversified crops are important for maintaining soil health properties. This study focuses on the soil health of three long-term (44 years) tillage systems, NT, reduced tillage (RT), and conventional tillage (CT), in monoculture winter wheat-fallow (W-F) (Triticum aestivum L.) and wheat-soybean (W-S) (Glycine max (L.) Merrill) rotation. Soil organic carbon (C) was higher in NT than CT in the surface 0-5 cm, but not different in the 5-15 cm, demonstrating SOC stratification on the soil profile. The soil water content was higher in NT followed by RT and CT in the top 0-5 cm. We found an association between increased carbon, aggregation, and AMF biomass. Greater soil aggregation, carbon and AMF were observed in NT at 0-5 cm soil depth. The W-S cropping system had greater soil microbial community composition based on fungi biomass, AMF and fungal to bacteria ratio from phospholipid fatty acid analysis (PLFA). Large macroaggregates were positively correlated with total C and N, microbial biomass, Gram + , and AMF. Soil water content was positively correlated with macroaggregates, total C and N, and AC. No-till increased soil carbon content even after 44 years of cultivation. By implementing conservation tillage systems and diversified crop rotation, soil quality can be improved through greater soil organic C, water content, greater soil structure, and higher AMF biomass than CT practice in the Central Great Plains.

Green remediation of cadmium-contaminated soil by cellulose nanocrystals

Cellulose nanocrystals (CNC) were used as a novel, green eluent to remediate Cd-contaminated soil in this study. The influence of washing conditions on the removal of Cd, including CNC concentration, pH value, liquid/solid (L/S) ratio, contact time and temperature were investigated. The effect of CNC remediation of Cd-contaminated soil on soil health and the possible remediation mechanism were also explored. The results showed that CNC concentration, pH value and contact time had a significant effect on the removal efficiency of Cd. CNC rapidly removed heavy metals in soil within 30 min. When the pH value of the eluent was 9.0, the removal efficiency of Cd could reach 86.3 %. The eluent mainly removed exchangeable and reducible fractions of Cd, which could effectively reduce the bioavailability of heavy metals. CNC washing had no negative effects on seed growth, species abundance and Shannon index. C-O, -COO^- groups on CNC played an important role in the reaction between CNC and soil Cd, and other oxygen-containing functional groups on CNC could also assist in adsorption, ion exchange and chemical complexation processes. Therefore, cellulose nanocrystals had the potential to remediate heavy metal-contaminated soils in a green and efficient manner.

Can Application of Pressmud Mediated Plant Nutrient Dynamics Under Lead Contaminated Soils of Indian Vertisol?

Long- term application of marginal quality water accumulated significant amount of pollutant into the soil. It reduces soil health parameters, and crop yield and their quality. In this regards, graded application of pressmud (PM), i.e. 0, 2.5, 5 and 10 g/kg was applied on lead (Pb) contamination level (0, 100, 150, 300 mg/kg) and evaluated interaction effect on plant nutrients uptake by spinach. Analytical data showed that increasing the PM levels enhanced the macro (phosphorus, potassium, sulphur) and micro-nutrient (zinc, copper, manganese, iron) concentration into the soil. Whereas, increasing the level of Pb significantly (p ≤ 0.05) reduced the P, K and S nutrient concentration and uptake pattern by spinach crop. Increasing PM levels (control to 10 g/kg soil) improved P, K and S by 46.99, 98.96 and 76.79%, respectively in soil. This study is useful to formulate management strategies for minimizing Pb contamination in the food chain by the application of PM mostly in peri-urban areas.

An overview of underutilized benefits derived from Azolla as a promising biofertilizer in lowland rice production

Currently, there is no doubt that Azolla can compensate for the nitrogen requirements of rice in different agroecological zones. Compared to synthetic N-fertilizers, Azolla has various positive impacts on lowland rice production, including improving soil fertility, minimizing weeds, increasing soil organic carbon, improving microbial biomass, and thus nutrient cycling and enhancing rice growth and yield. However, Azolla has not been accepted globally by rice farmers for field use and so far, farmers are relying on increasing rates of synthetic N fertilizers instead of taking advantage of Azolla which will improve long-term soil fertility and health. This systematic literature review and scientific evidence could help policymakers, scientists and researchers to understand the benefits, limitations, and innovative ways of utilizing Azolla as a cost-effective and eco-friendly amendment in rice production. The paper uses Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) method to review the hidden potential of Azolla as a biofertilizer in paddy and summarizes its benefits and problems by collecting information from different sources and presenting under different subheadings such as critical factors affecting Azolla growth and nitrogen fixation, nitrogen fixation of Anabaena Azollae and their contribution in soil health, release and availability of Azolla-N to rice, amounts and time of Azolla inoculation, influence of Azolla on ammonia volatilization, contribution of Azolla to yield and yield components of rice, and impact of Azolla on weed emergence in rice cropping system. Literature indicated that the use of Azolla as green manure incorporated before rice transplanting or grown together with rice and left until a few days of harvest alone or in combinations with other synthetic fertilizers in the lowland rice production saved the nitrogen requirement of rice up to 60 kg N ha^-1, it enhances the availability of nutrients, improves physiochemical properties of soils, minimizes soil salinity, reduces the soil pH, and minimize weed germination. However, it was observed that incorporating Azolla as green manure is labor-intensive, and maintaining the Azolla inocula and phosphorous requirement are major restrictions for farmers. Therefore, understanding mechanism of spore production, educating farmers on cheaper alternative ways of Azolla application, and testing different species of Azolla over different agroecological zones will help in maintaining Azolla biomass and applying it at low cost for further environmental conservation.

Biodiesel Co-Product enhances microbial stability and beneficial microbial communities along a gradient of soil water content

Biodiesel Co-Product (BCP) is a complex carbonaceous liquid formed during the commercial production of biodiesel. Previously, BCP was shown to decrease nitrogen (N) leaching from the soil, but the effects of BCP on the diversity, composition, and structure of soil microbial communities are not well understood. Here, we applied 1.5 mg BCP-C to acidic soil (pH 3.5) at a range of different water contents (from 40 % to 100 % water holding capacity) to investigate the interactions between BCP and increasing water holding capacity on the diversity, composition, and interactions of soil microbial communities. Distance-based multivariate linear model (DistLM) and non-metric multidimensional scaling (NMDS) analyses showed that BCP caused larger changes in fungal than bacterial communities, while soil water content had a greater effect on bacterial communities relative to fungal communities. Co-occurrence network analyses indicated that BCP amendment produced more robust and complex bacterial networks and more stable fungal ones. BCP significantly increased the OTU numbers of beneficial microbes (e.g., Trichoderma spp.) in all water contents, with fewer OTU numbers of putative pathogenetic species (Fusarium spp. and Aspergillus spp.). These findings indicate that BCP addition may be conducive to the health and stability of soil ecosystems.

Soil quality cannot be improved after thirty years of land use change from forest to rangeland

Soil quality can be assessed by measuring its physical, chemical and biological properties. In terrestrial ecosystems, the knowledge of the status of soil quality under different land use/cover can increase our understanding of processes related to soil functioning and help to properly managing ecosystems and increase their services. Conversion of the forest to rangelands is one of the most common forms of land use change having a significant effect on soil quality indicators. Here, we addressed the following objectives: (ii) to study the current status of soil physical, chemical and biological characteristics after more than thirty years of land use change from forest (dominated by Carpinus betulus and Parrotia persica) to rangeland, and (ii) to provide an overview of the spatial distributions of soil properties in forest and rangeland covers using a geostatistical method. For this, two sites (i.e., forest and rangeland) were selected in northern Iran. Within each site, 50 soil samples were collected at 0-10 cm depth along two sampling lines (250 m length) with a total of 100 soil samples for each site. Results showed that following the change of land use from forest to rangeland soil porosity, aggregate stability, pH, electrical conductivity and nutrient (i.e., total N and available P, K, Ca and Mg) contents increased, whereas soil bulk density and C/N ratio decreased. In addition, the population of soil biota (i.e., earthworms, acarina, collembola, nematode, protozoa, bacteria and fungi), microbial and enzyme activities decreased after more than thirty years of land use change from forest to rangeland. Principal component analysis confirmed that forest site had a more fertile soil and a higher biological activity than rangeland cover. Based on heat plots of soil properties, forest ecosystems created hot spots of soil quality indicators in the study area. Based on the geostatistical approach, most of the soil variables in the rangeland site followed a linear model, while in the forest site, most models were exponential and spherical. The fractal dimension values of the soil properties in the forest (1.62-1.99) had larger variations than in the rangeland (1.75-1.99) site. As a general conclusion, soil quality was not improved after more than thirty years of land use change from forest to rangeland, suggesting that degraded forest habitats should be restored by native tree species rather than converted to other land uses.

Crude oil associated heavy metals (HMs) contamination in agricultural land: Understanding risk factors and changes in soil biological properties

Ecological and human risks of crude oil associated heavy metals (HMs) in the contaminated agricultural lands were evaluated employing different indices. The indices that were employed includes enrichment factor (EF), contamination factor (C_f),pollution load index (PLI), geo-accumulation index (I_geo), ecological risk index (ERI), contamination degree (C_d), Nemerow's pollution index (P_N), exposure factor (ExF), hazard quotient (HQ) and hazard index (HI). Besides, the adverse effects of crude oil associated HMs on the soil biological properties were also analyzed. The results of C_f and EF were found consistent with each other showing the HMs in the decreasing order of contamination as Mn > Zn > Cr > Ni > Cu. The I_geo and ERI fall in the grade (I_geo>5) and (ERI ≥40) respectively. The results of PLI, C_d, P_N and ExF values clearly indicate a high environmental risk of crude oil-associated HMs. The results of the human health risks assessment revealed the maximum level of HMs enters the body via ingestion. There were significant(p < 0.05) decreases (5.7-15.5 folds) in the activities of cellulase (0.194 ± 0.02-0.998 ± 0.1), phosphatase (0.173 ± 0.3-0.612 ± 1.5), catalase (0.328 ± 0.3-2.036 ± 1.5), urease (0.44 ± 0.3-1.80 ± 1.2), dehydrogenase (0.321 ± 0.2-0.776 ± 0.7),polyphenol oxidase (0.21 ± 0.5-0.89 ± 2.5)and peroxidase (0.13 ± 0.4-0.53 ± 1.03)in crude oil-contaminated soil. The Pearson's correlation confirmed the significant negative impact of HMs on the soil's biological properties.

Imidacloprid degrading efficiency of Pseudomonas plecoglossicida MBSB-12 isolated from pesticide contaminated tea garden soil of Assam

Long-term use of toxic pesticides in agricultural grounds has led to adverse effects on the environment and human health. Microbe-mediated biodegradation of pollutants is considered an effective strategy for the removal of contaminants in agricultural and environmental sustainability. Imidacloprid, a neonicotinoid class of pesticides, was widely applied insecticide in the control of pests in agricultural fields including the tea gardens of Assam. Here, native bacteria from imidacloprid contaminating tea garden soils were isolated and screened for imidacloprid degradation efficiency under laboratory conditions. Out of the 30 bacterial isolates, 4 were found to tolerate high concentrations of imidacloprid (25,000 ppm), one of which isolate MBSB-12 showed the highest efficiency for imidacloprid tolerance and utilization as the sole carbon source. Morphological, biochemical, and 16 S ribosomal RNA gene sequencing-based characterization revealed the isolate as Pseudomonas plecoglossicida MBSB-12. The isolate reduced 87% of extractable imidacloprid from the treated soil in 90 days compared to the control soil (without bacterial treatment). High-Resolution Mass Spectrometry (HRMS) analysis indicated imidacloprid breakdown to comparatively less harmful products viz., imidacloprid guanidine olefin [m/z = 209.0510 (M + H)⁺], imidacloprid urea [m/z = 212.0502 (M + H)⁺] and a dechlorinated degraded product of imidacloprid with m/z value 175.0900 (M + H)⁺. Further investigation on the molecular machinery of P. plecoglossicida MBSB-12 involved in the degradation of imidacloprid is expected to provide a better understanding of the degradation pathway.

Soil macroaggregation drives sequestration of organic carbon and nitrogen with three-year grass-clover leys in arable rotations

Conventional arable cropping with annual crops established by ploughing and harrowing degrades larger soil aggregates that contribute to storing soil organic carbon (SOC). The urgent need to increase SOC content of arable soils to improve their functioning and sequester atmospheric CO₂ has motivated studies into the effects of reintroducing leys into long-term conventional arable fields. However, effects of short-term leys on total SOC accumulation have been equivocal. As soil aggregation may be important for carbon storage, we investigated the effects of arable-to-ley conversion on cambisol soil after three years of ley, on concentrations and stocks of SOC, nitrogen and their distributions in different sized water-stable aggregates. These values were benchmarked against soil from beneath hedgerow margins. SOC stocks (0-7 cm depth) rose from 20.3 to 22.6 Mg ha^-1 in the arable-to-ley conversion, compared to 30 Mg ha^-1 in hedgerows, but this 2.3 Mg ha^-1 difference (or 0.77 Mg C ha^-1 yr^-1) was not significant). However, the proportion of large macroaggregates (> 2000 μm) increased 5.4-fold in the arable-to-ley conversion, recovering to similar abundance as hedgerow soils, driving near parallel increases in SOC and nitrogen within large macroaggregates (5.1 and 5.7-fold respectively). The total SOC (0-7 cm depth) stored in large macroaggregates increased from 2.0 to 9.6 Mg ha^-1 in the arable-to-ley conversion, which no longer differed significantly from the 12.1 Mg ha^-1 under hedgerows. The carbon therefore accumulated three times faster, at 2.53 Mg C ha^-1 yr^-1, in the large macroaggregates compared to the bulk soil. These findings highlight the value of monitoring large macroaggregate-bound SOC as a key early indicator of shifts in soil quality in response to change in field management, and the benefits of leys in soil aggregation, carbon accumulation, and soil functioning, providing justification for fiscal incentives that encourage wider use of leys in arable rotations.

Legacy effects of fumigation on soil bacterial and fungal communities and their response to metam sodium application

BACKGROUND

Soil microorganisms are integral to maintaining soil health and crop productivity, but fumigation used to suppress soilborne diseases may affect soil microbiota. Currently, little is known about the legacy effects of soil fumigation on soil microbial communities and their response to fumigation at the production scale. Here, 16S rRNA gene and internal transcribed spacer amplicon sequencing was used to characterize the bacterial and fungal communities in soils from intensively managed crop fields with and without previous exposure to metam sodium (MS) fumigation. The effect of fumigation history, soil series, and rotation crop diversity on microbial community variation was estimated and the response of the soil microbiome to MS application in an open microcosm system was documented.

RESULTS

We found that previous MS fumigation reduced soil bacterial diversity but did not affect microbial richness and fungal diversity. Fumigation history, soil series, and rotation crop diversity were the main contributors to the variation in microbial β-diversity. Between fumigated and non-fumigated soils, predominant bacterial and fungal taxa were similar; however, their relative abundance varied with fumigation history. In particular, the abundance of Basidiomycete yeasts was decreased in fumigated soils. MS fumigation also altered soil bacterial and fungal co-occurrence network structure and associations. In microcosms, application of MS reduced soil microbial richness and bacterial diversity. Soil microbial β-diversity was also affected but microbial communities of the microcosm soils were always similar to that of the field soils used to establish the microcosms. MS application also induced changes in relative abundance of several predominant bacterial and fungal genera based on a soil's previous fumigation exposure.

CONCLUSIONS

The legacy effects of MS fumigation are more pronounced on soil bacterial diversity, β-diversity and networks. Repeated fumigant applications shift soil microbial compositions and may contribute to differential MS sensitivity among soil microorganisms. Following MS application, microbial richness and bacterial diversity decreases, but microbial β-diversity was similar to that of the field soils used to establish the microcosms in the short-term (< 6 weeks). The responses of soil microbiome to MS fumigation are context dependent and rely on abiotic, biotic, and agricultural management practices.

Sulfur enriched slow-release coated urea produced from inverse vulcanized copolymer

Slow-release fertilizers are developed to enhance the nutrient use efficiency (NUE), by coating urea with less water soluble or hydrophobic material. Diverse range of materials have been utilized to coat urea, however, their inherit non-biodegradability, hydrophilicity, crystallinity, and high synthesis cost limits their scalability. Herein, we reported the preparation of a novel slow-release sulfur enriched urea fertilizers using sustainable hydrophobic, biodegradable, crosslinked copolymer made from sulfur and rubber seed oil (Poly(S-RSO)) through the use of dip coating method. Scanning electron microscopy (SEM) was employed to study the fertilizers morphology and estimate the coating film thickness. A nitrogen release test was carried out in distilled water, which revealed that the coated fertilizers with a coating thickness of 165 μm, 254 μm and 264 μm released only 65 % of its total nutrient content after 2, 19 and 43 days of incubation, respectively: hence, showing an excellent slow-release property. In soil, fertilizer with 264 μm coating thickness released only 17 % nitrogen after 20 days of incubation, in line with the European standard (EN 13266, 2001). The release kinetic data best fits the Ritger-Peppas model with a R² value of 0.99 and the n value of 0.65 indicated the release was mainly due to diffusion. Submerged cultivation (SmC) demonstrated the potential of poly(S-RSO) to enhance sulfur oxidation; it was observed that the copolymer oxidation was 50 % greater than that of elemental sulfur. A comparison between the newly developed fertilizers and existing coated fertilizers was also presented. On the whole, the results demonstrated outstanding slow-release characteristics and improved sulfur oxidation.

Streptomyces consortia-mediated plant growth-promotion and yield performance in chickpea

Fourteen Streptomyces strains reported earlier as plant growth promoters (PGP) in chickpea were characterized for production of ammonia and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and solubilization of silica and zinc. The results showed that nine (CAI-17, CAI-78, KAI-26, CAI-21, CAI-26, MMA-32, CAI-140, CAI-155 and KAI-180) and six (CAI-17, CAI-21, CAI-26, CAI-13, CAI-93 and KAI-180) strains were found to produce ammonia and ACC deaminase, respectively, while one (KAI-180) and eight (CAI-17, CAI-21, CAI-26, MMA-32, CAI-13, CAI-85, CAI-93 and KAI-180) strains solubilized silica and zinc, respectively. The selected 14 Streptomyces strains were categorized into three consortia groups, consortium-1 (CAI-17, CAI-68, CAI-78, KAI-26 and KAI-27), consortium-2 (CAI-21, CAI-26 and MMA-32) and consortium-3 (CAI-13, CAI-85, CAI-93, CAI-140, CAI-155 and KAI-180), based on their compatibility, and evaluated for their PGP traits in chickpea. The experiment was conducted under field conditions with two chickpea varieties over two years. The consortia-treated plots enhanced nodule number up to 23%, nodule weight up to 36%, root weight up to 27% and shoot weight up to 26% at 30 days after sowing and pod weight up to 35%, pod number up to 34% and grain yield up to 24% at harvest over the un-inoculated control plots. The harvested grains of consortia treatments were found to enhance crude protein up to 14%, crude fibre up to 17% and crude fat up to 16% over the grains from un-inoculated control. The rhizosphere soils of the consortia-treated plots enhanced total nitrogen up to 21%, organic carbon up to 8% and available phosphorous up to 16% over the un-inoculated control plots. This investigation demonstrated the potential use of the selected consortium of Streptomyces strains in the farmers' fields to improve the chickpea yields and soil fertility.

Impact of arsenic on microbial community structure and their metabolic potential from rice soils of West Bengal, India

Paddy soil is a heterogenous ecosystem that harbours diverse microbial communities critical for maintaining ecosystem sustainability and crop yield. Considering the importance of soil in crop production and recent reports on its contamination with arsenic (As) across the South East Asia, its microbial community composition and biogeochemical functions remained inadequately studied. We have characterized the microbial communities of rice soil from eleven paddy fields of As-contaminated sites from West Bengal (India), through metagenomics and amplicon sequencing. 16S rRNA gene sequencing showed considerable bacterial diversity [over 0.2 million Operational Taxonomic Units (OTUs)] and abundance (upto 1.6 × 10⁷ gene copies/g soil). Existence of a core-microbiome (261 OTUs conserved out of a total 141,172 OTUs) across the samples was noted. Most of the core-microbiome members were also found to represent the abundant taxa of the soil. Statistical analyses suggested that the microbial communities were highly constrained by As, Fe K, N, PO₄^3-, SO₄^2- and organic carbon (OC). Members of Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Planctomycetes and Thaumarchaeota constituted the core-microbiome. Co-occurrence network analysis displayed significant interaction among diverse anaerobic, SO₄^2- and NO₃^- reducing, cellulose and other organic matter or C1 compound utilizing, fermentative and aerobic/facultative anaerobic bacteria and archaea. Correlation analysis suggested that taxa which were positively linked with soil parameters that maintain soil health and productivity (e.g., N, K, PO₄^3- and Fe) were adversely impacted by increasing As concentration. Shotgun metagenomics highlighted major metabolic pathways controlling the C (3-hydroxypropionate bicycle), N (Denitrification, dissimilatory NO₃^- reduction to ammonium), and S (assimilatory SO₄^2- reduction and sulfide oxidation) cycling, As homeostasis (methylation and reduction) and plant growth promotion (polyphosphate hydrolysis and auxin biosynthesis). All these major biogeochemical processes were found to be catalyzed by the members of most abundant/core-community.

Quantifying the effect of waste on soil health in European Union: what are the roles of technology, natural capital, and institutional quality?

With a surge in both hazardous and non-hazardous waste in recent decades, European Union countries are losing their soil quality which in turn affects the agricultural production of their economies. Taking this into account, this study presents the effect of hazardous and non-hazardous waste, plastic waste, and electronic waste on soil health for 24 European Union (EU) countries during 2004-2018 period. The impacts of several other variables such as technological innovation, ICT, natural capital, fossil fuel energy consumption, and institutional quality on soil health are also examined. To achieve the above objectives, we employ Driscoll-Kraay technique as the main methodology as well as panel spatial correlation consistent (PSCC) standard errors and quantile estimation at median. The results demonstrate that electronic waste has a negative effect on soil health while the effect of total hazardous and non-hazardous waste and plastic waste on soil health remains insignificant. Technological innovation, ICT, and institutional quality, as well as fossil fuel energy consumption, have positive impacts on soil health. Furthermore, natural capital moderates the effect of plastic and electronic waste on soil health. The study finally provides precise policy recommendations for the EU countries such as proper handling of wastes, promoting strong institutional quality as well as use of technology to enrich the soil nutrient balance.