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Roots and the associated soil directly affected by root activity, termed the rhizosphere, have both been extensively studied and recognized for their crucial role in soil functioning. The formation of the rhizosphere is primarily driven by the effect of roots on shaping the physical structure of the soil, which in turn has direct feedbacks on the interactions between physical, biological and chemical processes. As a result, the rhizosphere is a hot spot for microbial activity, cycling of nutrients and turnover of organic matter. Despite the pivotal role of soil structure in controlling rhizosphere processes, we still lack a quantitative description and understanding of the interrelationships of root-systems and soil in the creation and stabilization of soil structure. We provide a comprehensive review of current knowledge and novel insights into processes that drive the formation and stabilization of soil structure in the rhizosphere. These processes are regulated by multiple indirect and direct pathways, involving root growth, the production of rhizodeposits and root hairs, as well as the activity of soil microorganisms and fauna. Further, we highlight that rhizosphere processes may persist and evolve after root death to an extent currently largely unknown. Finally, we identify five pertinent challenges that should be addressed to fully apprehend rhizosphere processes and thus harness the potential resilience of plant-soil interactions. These challenges include refining structural assessment and sampling of rhizosheaths, examining the rhizosphere in-situ and bridging the gap between solid phase and pore scale research. In our view, overcoming these obstacles can be accomplished by combining the power of imaging and isotopic approaches, especially at the field scale, encompassing diverse soils and plant species. The ultimate objective of future research should be to upscale rhizosphere processes by conducting more field experiments in concert with modeling efforts

What form should agriculture in Germany take in the future? Scientists, policymakers and the general public are currently discussing this question intensively. Sustainable nitrogen use is an important part of this discussion, though it has received little public attention so far. Agriculture adds approximately 1.5 million metric tonnes of reactive nitrogen to the environment in Germany every year. Nitrogen in the form of various compounds is a significant contributor to climate change, biodiversity loss and soil, air and water pollution. As a result, nitrogen inputs from agriculture into the environment are estimated to incur societal costs between €30 billion and €70 billion a year. These problems have been known for decades, and extensive research has been performed in this area. However, measures implemented to date have not been effective, as indicated by the slow decline of nitrogen inputs from agriculture. This acatech POSTION PAPER considers the entire value chain, from agricultural production right up to the end consumer. This provides the basis for a series of recommendations geared towards more efficient and sustainable resource utilisation and a reduction of nitrogen inputs into the environment.

Soil organic matter (SOM) is indispensable for soil health and, in the context of climate change, is considered a significant CO2 sink. Improving agricultural management to increase long-term soil organic carbon (SOC) stocks for mitigating climate change requires tools that estimate short and long-cycling SOM pools. In this study, we analyzed changes in fast-cycling particulate organic matter (POM) and slow-cycling mineral-associated organic matter (MAOM) induced by common management practices, i.e., fertilization and crop rotation in topsoils from 25 Central European long-term field experiments. When relating MAOM-C contents to recent MAOM-C saturation levels, estimated sequestration potentials were only met in coarse-textured soils under appropriate agricultural management or fine-textured soils under extreme organic fertilization. Soil texture, organic fertilization, and below-ground OC inputs through root exudates and root biomass were decisive for estimating MAOM-C, allowing for calibration of a mixed-effects model (Nakagawa’s: marginal R2m = 0.6, conditional R2c = 0.89). While the models containing soil texture and organic fertilization parameters can be validated and generalized (R2 = 0.43), the below-ground OC input predictor substantially decreases the generalizability of the validated models (R2 = 0.14). According to quantile regression models, we estimate the average difference in MAOM-C concentration between well-managed and control site (without organic fertilization) topsoils to 4.1 mg g−1 soil. In dependence on the soil bulk density, this amounts to 1.38 – 1.84 t ha−1 MAOM-C stocks or 5.06 – 10.1 t ha−1 CO2-equivalents. POM-C was difficult to predict (R2 = 0.28), presumably due to strong POM dynamics. The POM-C / MAOM-C ratio can inform on the effects of agricultural practices in before/after management change

Not only do soils provide 98.7% of the calories consumed by humans, they also provide numerous other functions upon which planetary survivability closely depends. However, our continuously increasing focus on soils for biomass provision (food, fiber, and energy) through intensive agriculture is rapidly degrading soils and diminishing their capacity to deliver other vital functions. These tradeoffs in soil functionality – the increased provision of one function at the expense of other critical planetary functions – are the focus of this review. We examine how land-use change for biomass provision has decreased the ability of soils to regulate the carbon pool and thereby contribute profoundly to climate change, to cycle the nutrients that sustain plant growth and ecosystem health, to protect the soil biodiversity upon which many other functions depend, and to cycle the Earth’s freshwater supplies. We also examine how this decreasing ability of soil to provide these other functions can be halted and reversed. Despite the complexity and the interconnectedness of soil functions, we show that soil organic carbon plays a central role and is a master indicator for soil functioning and that we require a better understanding of the factors controlling the behavior and persistence of C in soils. Given the threats facing humanity and their economies, it is imperative that we recognize that Soil Security is itself an existential challenge and that we need to increase our focus on the multiple functions of soils for long-term human welfare and survivability of the planet.

Soil salinization is an emerging problem worldwide as a result of unsustainable land management practices and climate change. However, salt-affected soils under agricultural use could act as a C sink if these negative effects can be offset by combination of sustainable land management practices (SLM). In this study, we assessed the effect of (i) intensive tillage along with flood irrigation (IT); (ii) combination of no-tillage with pruning residues (branches and leaves) as mulch, and drip-irrigation (NT + PM); and (iii) combination of reduced tillage with the incorporation of pruning residues and drip-irrigation (RT + PI), on physico-chemical soil parameters, aggregate stability, amount and quality of organic matter fractions and soil organic carbon (SOC) sequestration in a lemon tree orchards (Citrus limon var. Verna) under semi-arid climate conditions. The RT + PI management system showed a decrease in salinity and bulk density, and increased soil porosity, soil OC and N stocks, and percentage of OC-rich macroaggregates as compared to the IT system. The aggregate-occluded particulate organic matter fraction (oPOM) played a key role in macroaggregate stability. The NT + PM treatment also showed positive effects on the investigated soil properties, but this was limited to the upmost topsoil (0−5 cm). The IT management system revealed highest values of salinity and bulk density, and considerably lower SOC stocks. Moreover, a degradation of soil structure with a low percentage of macroaggregates depleted in SOC was observed. We conclude that the incorporation of pruning residues in combination with reduced tillage and drip-irrigation is an effective management system to improve soil structure and facilitate SOC sequestration. Therefore, conventional management systems based on intensive tillage and flood irrigation should be abandoned in salt-affected soils under semi-arid climate conditions in favour of systems with higher organic matter inputs incorporated into the

Introduction Intensive land use and especially overgrazing in semi‐arid grasslands results in degradation of steppe vegetation associated with changes in the amount ,composition ,and turnover of soil organic matter (SOM) . The concurrent degradation of soil structure and destruction of aggregation leads to enhanced soil erosion .The effectof intensive grazing on the amount and composition of SOM was assessed by comparison of grazed and ungrazed plots in Leymus chinensis and Stipa grandis dominated steppe types in Inner Mongolia ,China

Resilience of soils, i.e., their ability to maintain functions or recover after disturbance, is closely linked to the root-soil interface, the soil's power house. However, the limited observability of key processes at the root-soil interface has so far limited our understanding of how such resilience emerges. Here, we hypothesize that resilience emerges from self-organized spatiotemporal patterns which are the result of complex and dynamic feedbacks between physical, chemical, and biological processes occurring in the rhizosphere. We propose that the combination of modern experimental and modeling techniques, with a focus on imaging approaches, allows for understanding the complex feedbacks between plant resource acquisition, microbiome-related plant health, soil carbon sequestration, and soil structure development. A prerequisite for the identification of patterns, underlying processes, and feedback loops is that joint experimental platforms are defined and investigated in their true 2D and 3D geometry along time. This applies across different scientific disciplines from soil physics/chemistry/microbiology to plant genomics/physiology and across different scales from the nano/microscopic scale of the root soil interface, over the radial profiles around single roots, up to the root architecture and plant scale. Thus, we can move beyond isolated reductionist approaches which have dominated in rhizosphere research so far.

Sustainable soil carbon sequestration practices need to be rapidly scaled up and implemented to contribute to climate change mitigation. We highlight that the major potential for carbon sequestration is in cropland soils, especially those with large yield gaps and/or large historic soil organic carbon losses. The implementation of soil carbon sequestration measures requires a diverse set of options, each adapted to local soil conditions and management opportunities, and accounting for site-specific trade-offs. We propose the establishment of a soil information system containing localised information on soil group, degradation status, crop yield gap, and the associated carbon-sequestration potentials, as well as the provision of incentives and policies to translate management options into region- and soil-specific practices.

After reclamation of open-cast mining pits, soil formation starts from the deposited calcareous loess characterised by its basic physical and chemical properties whereas soil biology and structure need to develop to achieve a fully functional soil. In this study we used a chronosequence approach to elucidate soil formation on agriculturally reclaimed loess soils in an open-cast lignite mining area in Garzweiler (Germany). We selected six fields aged 0, 1, 3, 6, 12, and 24 years after the first seeding in order to observe the initial stage of development of soil properties and assess the role of management with conventional crop rotation in soil structure formation and soil organic carbon (SOC) accumulation. Loess parent material had a strong impact on aggregation, as CaCO3 acted as a strong cementing agent. Alfalfa cultivation in the pioneering phase was of high importance in the development of microbial biomass, as it protects microbes from N limitation. Soil macroporosity and pore connectivity increased only after compost application and ploughing during agricultural crop rotation. Soil organic matter (SOM) build-up was strongly dependent on the addition of compost, as crop residues from conventional crop rotation are not sufficient to maintain high SOC contents.

The capacity of soils to store organic carbon represents a key function of soils that is not only decisive for climate regulation but also affects other soil functions. Recent efforts to assess the impact of land management on soil functionality proposed that an indicator- or proxy-based approach is a promising alternative to quantify soil functions compared to time- and cost-intensive measurements, particularly when larger regions are targeted. The objective of this review is to identify measurable biotic or abiotic properties that control soil organic carbon (SOC) storage at different spatial scales and could serve as indicators for an efficient quantification of SOC. These indicators should enable both an estimation of actual SOC storage as well as a prediction of the SOC storage potential, which is an important aspect in land use and management planning. There are many environmental conditions that affect SOC storage at different spatial scales. We provide a thorough overview of factors from micro-scales (particles to pedons) to the global scale and discuss their suitability as indicators for SOC storage: clay mineralogy, specific surface area, metal oxides, Ca and Mg cations, microorganisms, soil fauna, aggregation, texture, soil type, natural vegetation, land use and management, topography, parent material and climate. As a result, we propose a set of indicators that allow for time- and cost-efficient estimates of actual and potential SOC storage from the local to the regional and subcontinental scale. As a key element, the fine mineral fraction was identified to determine SOC stabilization in most soils. The quantification of SOC can be further refined by including climatic proxies, particularly elevation, as well as information on land use, soil management and vegetation characteristics. To enhance its indicative power towards land management effects, further “functional soil characteristics”, particularly soil structural properties and changes in the soil m

The central importance of soil for the functioning of terrestrial systems is increasingly recognized. Critically relevant for water quality, climate control, nutrient cycling and biodiversity, soil provides more functions than just the basis for agricultural production. Nowadays, soil is increasingly under pressure as a limited resource for the production of food, energy and raw materials. This has led to an increasing demand for concepts assessing soil functions so that they can be adequately considered in decision-making aimed at sustainable soil management. The various soil science disciplines have progressively developed highly sophisticated methods to explore the multitude of physical, chemical and biological processes in soil. It is not obvious, however, how the steadily improving insight into soil processes may contribute to the evaluation of soil functions. Here, we present to a new systemic modeling framework that allows for a consistent coupling between reductionist yet observable indicators for soil functions with detailed process understanding. It is based on the mechanistic relationships between soil functional attributes, each explained by a network of interacting processes as derived from scientific evidence. The non-linear character of these interactions produces stability and resilience of soil with respect to functional characteristics. We anticipate that this new conceptional framework will integrate the various soil science disciplines and help identify important future research questions at the interface between disciplines. It allows the overwhelming complexity of soil systems to be adequately coped with and paves the way for steadily improving our capability to assess soil functions based on scientific understanding.