•A global meta-analysis on soil physical properties under conservation tillage.•Conservation tillage has higher aggregate size, stability and available water capacity.•Increased bulk density under ...conservation tillage remains non-harmful for crop growth.•Soil pH decreased under conservation tillage.•The response of soil physical properties vary with experiment duration.
Conservation tillage practices, here defined as no-tillage (NT) or reduced tillage (RT) with/without residue retention, have been widely used to alleviate the negative effects caused by intensive tillage practices. Implementing effective and sustainable agriculture requires a deeper understanding of the impacts of conservation tillage practices on soil physical properties. This study examined the effects of conservation tillage practices on soil physical properties, including soil bulk density, aggregate size and stability, hydraulic properties, and soil pH; based on data collected from 264 studies published worldwide since 1980. The results indicated that no-tillage (NT), NT with residue retention (NTS), and reduced tillage (RT) increased bulk density by 1.4, 2.6, and 2.1%, respectively, compared with conventional tillage (CT). Soil bulk density decreased by 2.9% in NTS compared with NT, and 3.9% in RT with residue retention (RTS) compared with RT. The effect size of bulk density significantly decreased with the increasing experimental duration under NT and NTS practices. Compared to CT, conservation tillage practices increased aggregate mean weight diameter (MWD), geometric mean weight diameter and water stable aggregate (WSA) regardless of the residue retention or minimum tillage systems. The largest effect size of MWD (51.9%) and WSA (54.9%) appeared under NTS as compared to the CT. The effect size of MWD and WSA increased under NT with the increasing experimental duration. NT increased saturated hydraulic conductivity by 24.6% compared to CT. All conservation tillage practices increased soil available water capacity (AWC) compared with CT and NTS with a 10.2% increase in AWC compared with NT. The effect size of AWC increased under RT and NT practices with the increasing experimental duration. Soil pH decreased by 1.7 and 1.0% under RTS compared with RT and CT, respectively; and NT led to a 2.8% reduction in soil pH compared with CT. The effect size of soil pH decreased under RT and NT treatments with the increasing experiment duration. Overall, conservation tillage practices positively affected many soil physical properties; and the extent of the effects varied with the duration of the experiment.
Sampling and analysis or visual examination of soil to assess its status and use potential is widely practiced from plot to national scales. However, the choice of relevant soil attributes and ...interpretation of measurements are not straightforward, because of the complexity and site-specificity of soils, legacy effects of previous land use, and trade-offs between ecosystem services. Here we review soil quality and related concepts, in terms of definition, assessment approaches, and indicator selection and interpretation. We identify the most frequently used soil quality indicators under agricultural land use. We find that explicit evaluation of soil quality with respect to specific soil threats, soil functions and ecosystem services has rarely been implemented, and few approaches provide clear interpretation schemes of measured indicator values. This limits their adoption by land managers as well as policy. We also consider novel indicators that address currently neglected though important soil properties and processes, and we list the crucial steps in the development of a soil quality assessment procedure that is scientifically sound and supports management and policy decisions that account for the multi-functionality of soil. This requires the involvement of the pertinent actors, stakeholders and end-users to a much larger degree than practiced to date.
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•We review soil quality and related concepts in terms of definitions and assessment.•The most common indicators are organic matter, pH, available P and water storage.•Biological/biochemical indicators are under-represented but show great potential.•Soil quality assessment should specify targeted soil threats, functions and ecosystem services.•Increasingly interactive assessment tools must be developed with target users.
Approval for glyphosate-based herbicides in the European Union (EU) is under intense debate due to concern about their effects on the environment and human health. The occurrence of glyphosate ...residues in European water bodies is rather well documented whereas only few, fragmented and outdated information is available for European soils. We provide the first large-scale assessment of distribution (occurrence and concentrations) of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in EU agricultural topsoils, and estimate their potential spreading by wind and water erosion. Glyphosate and/or AMPA were present in 45% of the topsoils collected, originating from eleven countries and six crop systems, with a maximum concentration of 2mgkg−1. Several glyphosate and AMPA hotspots were identified across the EU. Soil loss rates (obtained from recently derived European maps) were used to estimate the potential export of glyphosate and AMPA by wind and water erosion. The estimated exports, result of a conceptually simple model, clearly indicate that particulate transport can contribute to human and environmental exposure to herbicide residues. Residue threshold values in soils are urgently needed to define potential risks for soil health and off site effects related to export by wind and water erosion.
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•Data on occurrence and levels of glyphosate residues in EU soils is very limited.•Glyphosate and its metabolite AMPA were tested in 317 EU agricultural topsoils.•21% of the tested EU topsoils contained glyphosate, and 42% contained AMPA.•Both glyphosate and AMPA had a maximum concentration in soil of 2mgkg−1.•Some contaminated soils are in areas highly susceptible to water and wind erosion.
Abstract
Soil, the living terrestrial skin of the Earth, plays a central role in supporting life and is home to an unimaginable diversity of microorganisms. This review explores key drivers for ...microbial life in soils under different climates and land-use practices at scales ranging from soil pores to landscapes. We delineate special features of soil as a microbial habitat (focusing on bacteria) and the consequences for microbial communities. This review covers recent modeling advances that link soil physical processes with microbial life (termed biophysical processes). Readers are introduced to concepts governing water organization in soil pores and associated transport properties and microbial dispersion ranges often determined by the spatial organization of a highly dynamic soil aqueous phase. The narrow hydrological windows of wetting and aqueous phase connectedness are crucial for resource distribution and longer range transport of microorganisms. Feedbacks between microbial activity and their immediate environment are responsible for emergence and stabilization of soil structure—the scaffolding for soil ecological functioning. We synthesize insights from historical and contemporary studies to provide an outlook for the challenges and opportunities for developing a quantitative ecological framework to delineate and predict the microbial component of soil functioning.
Soil microorganisms live in complex pore spaces where nutrient heterogeneity and water dynamics play a fundamental role in shaping their ecology, diversity and functions at all scales.
Although plastic pollution happens globally, the micro- (<5 mm) and macroplastic (5-150 mm) transfer of plastic to terrestrial species relevant to human consumption has not been examined. We provide ...first-time evidence for micro- and macroplastic transfer from soil to chickens in traditional Mayan home gardens in Southeast Mexico where waste mismanagement is common. We assessed micro- and macroplastic in soil, earthworm casts, chicken feces, crops and gizzards (used for human consumption). Microplastic concentrations increased from soil (0.87 ± 1.9 particles g
), to earthworm casts (14.8 ± 28.8 particles g
), to chicken feces (129.8 ± 82.3 particles g
). Chicken gizzards contained 10.2 ± 13.8 microplastic particles, while no microplastic was found in crops. An average of 45.82 ± 42.6 macroplastic particles were found per gizzard and 11 ± 15.3 macroplastic particles per crop, with 1-10 mm particles being significantly more abundant per gizzard (31.8 ± 27.27 particles) compared to the crop (1 ± 2.2 particles). The data show that micro- and macroplastic are capable of entering terrestrial food webs.
Pollution caused by plastic debris is an urgent environmental problem. Here, we assessed the effects of microplastics in the soil surface litter on the formation and characterization of burrows built ...by the anecic earthworm Lumbricus terrestris in soil and quantified the amount of microplastics that was transported and deposited in L. terrestris burrows.
Worms were exposed to soil surface litter treatments containing microplastics (Low Density Polyethylene) for 2 weeks at concentrations of 0%, 7%, 28%, 45% and 60%. The latter representing environmentally realistic concentrations found in hot spot soil locations. There were significantly more burrows found when soil was exposed to the surface treatment composed of 7% microplastics than in all other treatments. The highest amount of organic matter in the walls of the burrows was observed after using the treatments containing 28 and 45% microplastics. The highest microplastic bioturbation efficiency ratio (total microplastics (mg) in burrow walls/initial total surface litter microplastics (mg)) was found using the concentration of 7% microplastics, where L. terrestris introduced 73.5% of the surface microplastics into the burrow walls. The highest burrow wall microplastic content per unit weight of soil (11.8 ± 4.8 g kg-1) was found using a concentration of 60% microplastics. L. terrestris was responsible for size-selective downward transport when exposed to concentrations of 7, 28 and 45% microplastics in the surface litter, as the fraction ≤50 μm microplastics in burrow walls increased by 65% compared to this fraction in the original surface litter plastic. We conclude that the high biogenic incorporation rate of the small-fraction microplastics from surface litter into burrow walls causes a risk of leaching through preferential flow into groundwater bodies. Furthermore, this leaching may have implications for the subsequent availability of microplastics to terrestrial organisms or for the transport of plastic-associated organic contaminants in soil.
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•Denser and heavier burrow walls are found under litter microplastics.•7%w/w surface microplastics enhances the highest bioturbation.•65% of microplastics found in the burrows walls are ≤50 μm while on the surface was 40%.
This study shows that small-fraction microplastics are biogenically incorporated into the soil by anecic earthworms in reduced sizes and are deposited in burrow walls.
•A linear source infiltrability measurement system was applied to capture the complete infiltration processes.•Grasses promote soil physical properties and infiltrability better than shrubs in ...heavy-textured soil.•The effects of plant roots on soil infiltrability are mediated via soil aggregate stability and soil porosity.•Species mixtures require inclusion of high fine root length density grasses to mitigate overland flow and erosion.
Soil degradation impairs ecosystem functions, and vegetation restoration is a major eco-engineering method that is used to restore soils globally. Despite the fundamental role that plants play in enhancing soil functions and ecosystem services, little is known about the relationships among root traits, soil physical properties, and water infiltration. The objectives of this study were to therefore evaluate changes in soil infiltrability due to different vegetation types and identify soil properties and root trait predictors of variation in soil infiltrability. The influences of four plant species (two gramineous grasses and two leguminous shrubs) on physical properties of soil and water infiltration in heavy-textured soils with 43 % clay content following five years of restoration after surface soil removal were investigated. These data were subsequently incorporated into a conceptual path model to quantify the direct and indirect effects of root traits and root-induced soil properties on infiltration. Soil organic matter, aggregate stability, soil total porosity, and non-capillary porosity were significantly higher in planted soil than in bare soil (p < 0.05), following the order of grass-planted > shrub-planted > bare soils. The infiltration rates during the initial and steady states were 63 % and 38 % higher in grass-planted soils than in shrub-planted soils, respectively. Among all evaluated root traits, fine root length density was the best predictor of these changes. Furthermore, the conceptual path model explained 82 % of the variance in water infiltration and confirmed the important role of roots in soil infiltration. Modeling indicated that this might not be a direct effect, but is rather mediated via soil physical properties like soil aggregate stability and soil porosity. These observations have important implications for designing efficient strategies in restoration of human-induced disturbed soils to mitigate overland flows and erosion.
China’s Loess Plateau is the largest loess deposit in the world in terms of both depth and area. Water storage in soils of the Plateau has direct impacts on food security, human health and ecosystem ...function. Despite extensive research on the behavior and function of soil water in the Plateau, there is no state-of-the-art review that presents research achievements, gaps and future perspectives. This paper reviews the advances in soil water research and highlights future research needs and challenges in the Loess Plateau, and thereby provides informed decision on sustainable water management. We report that considerable efforts have been made to investigate: i) soil water movement and hydraulic property estimation in the typical loess regions; ii) spatial and temporal variations in soil water content and storage at multiple scales; iii) dried soil layers induced by excessive water use from unreasonable artificial revegetation; and iv) soil water availability and water carrying capacity of typical vegetation types on the Loess Plateau. These studies have greatly enhanced our understanding about the fundamental characteristics, spatio-temporal patterns and natural and anthropogenic controls of soil water distribution and water cycles in the Loess Plateau, which in turn have important implications for the regulation and management of water resources toward sustainable ecological construction. Based on the identified key issues and future research priorities, recommendations were drawn to address unsolved problems, including: i) processes and mechanisms controlling water transport and interactions within the groundwater–soil–plant–atmosphere continuum; ii) how soil hydrological processes couple nutrient cycles in response to climate change and human activities; and iii) development of quantitative models across spatial scales for modeling changes in thresholds of soil water carrying capacity for vegetation. The incorporation of research findings into policy and practice can improve soil water management that will in turn significantly benefit the promotion of ecosystem services and functions in the Loess Plateau.
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