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Current soil‐ and land degradation seriously challenge our societies; it contributes to climate change, loss of biodiversity and loss of agricultural productions. Yet, soils are also seen as a major part of the solution, if maintained or restored to provide ecosystem services. Climate‐smart sustainable management of soils can provide options for soil health maintenance and restoration. In the European Union, the resource management and sustainability challenge are addressed in the Green Deal that, among other goals, aspires towards a healthy climate‐resilient agricultural sector that will produce sufficient products without damaging ecosystems and contribute to better biodiversity and mitigate climate change. The European Joint Programme (EJP) SOIL was set up to contribute to these goals by developing knowledge, tools and an integrated research community to foster climate‐smart sustainable agricultural soil management that provides a diversity of ecosystem service, such as adapting to and mitigating climate change, allowing sustainable food production, and sustaining soil biodiversity. This paper provides an overview of the potential of climate‐smart sustainable soil management research to the targets of the Green Deal that are related to soils most directly. The EJP SOIL EU‐wide consultation (interviews and questionnaires) and literature analysis (national and international reports and papers) done in the first year (2020–2021) generated a wealth of data. This data showed that there are specific manners to do research that are essential for it to be effective and efficient and that can actively contribute to the Green Deal targets. We concluded that research needs to be: (i) interdisciplinary, (ii) long‐term, (iii) multi‐scaled, from plot to landscape, (iv) evaluating trade‐offs of selected management options for ecosystem services and (v) co‐constructed with key stakeholders. Research on climate‐smart sustainable soil management should be developed (1) on plot scale when mobilizing soil processes and on landscape scale when addressing sediment and water connectivity and biodiversity management; and (2) address the enabling conditions through good governance, social acceptance and viable economic conditions. [ABSTRACT FROM AUTHOR]

The dramatic increase in anthropogenic reactive nitrogen (Nr) from agricultural activities negatively affects the environment. An additional challenge is to ensure food security while at the same time keeping the environmental impact to a minimum to prevent negative feedback effects on climate. To date, however, few studies have addressed the direct connection between soil N transformations, forms of N, species‐specific N preferences and climate, despite the fact that the fate of N and soil N biochemical cycling are known to be intimately linked. In this paper we review the connections between soil N transformation, species‐specific N preferences and climate, and explore how N‐use efficiency may be enhanced while minimizing the environmental effect. Gross rates of N mineralization and immobilization govern the amount of available N in soil, especially in natural ecosystems, while nitrification plays a central role in regulating the NO3− to NH4+ ratio. Plant species prefer either NH4+‐N or NO3−‐N, depending on the NO3−‐N to NH4+‐N ratio in their habitat. Thus, plant N uptake could be optimized (i.e. Nr losses reduced) if species‐specific N preferences are maintained by matching N sources applied with prevailing soil‐specific N transformations. Therefore, whether N management practices can optimize N‐use efficiencies hinges on the coupling of soil N transformation with climate and species‐specific N preferences. Highlights: We review the inherent connections between the soil N cycle, plant N preference and climate. Nitrification plays a central role in regulating the NO3− to NH4+ ratio in soil and soil solution. Soil N transformations regulate the composition of hydrological N export. Plant N uptake can be optimized if soil N cycle is well matched with plant N preference. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop pedotransfer functions ( PTFs) for converting soil particle-size distribution ( PSD) data from the laser diffraction method ( LDM) to the classical sieve-pipette method ( SPM) for use on a wide range of temperate soil types. Four hundred soil samples, representative of European soil types and climate zones, were selected from the LUCAS ( Land Use/ Land Cover Area Frame Survey) topsoil database and their PSDs were determined with LDM and SPM. The LDM measurements were made on samples with (i) their organic matter ( OM) removed and (ii) their OM content present. The ranges of PSD obtained with the two pretreatment methods enabled clay-silt and silt-sand boundaries from LDM (6.6 and 60.3 µm for soil with OM, respectively, and 5.8 and 69.2 µm for soil without OM, respectively) to be optimized. Optimization of the boundaries of the fractions considerably improved the prediction performance of SPM PSD from LDM PSD. Specific PTFs with different input requirements were developed for continental scale applications in Europe to convert data from LDM to SPM. The predictions of SPM clay, silt and sand contents were the most accurate with PTFs that used PSD from LDM and soil chemical properties ( R2 0.83, 0.81, 0.94; RMSE 6.14, 7.91 and 6.58%, respectively). For the most accurate results no pretreatment for OM removal was required, but data on chemical properties were necessary. If no soil chemical data are available, the most accurate PTFs need input data of LDM PSD that originate from samples on which the OM content was removed prior to the PSD analysis. Highlights PTFs are developed to harmonize PSD data between laser diffraction ( LDM) and sieve-pipette ( SPM) methods., PTFs are derived from a representative dataset from Europe for application at the continental scale., Clay-silt and silt-sand boundaries for LDM without removing OM are at 6.6 and 60.3 µm, respectively., Clay-silt and silt-sand boundaries for LDM with OM removed are at 5.8 and 69.2 µm, respectively. [ABSTRACT FROM AUTHOR]

Pedogenesis under aerobic conditions is usually associated with an increase in magnetic susceptibility (χ, mass-specific), which results from the formation of nano-sized magnetite and/or maghaemite. In this study, we systematically investigated the χ trend in Xeralfs from a chronosequence of 13 river terraces in an area with a Mediterranean climate in Spain. The soils in the younger terraces are well drained and reddened, but those of the older terraces exhibit redoximorphic features and reduced χ values, because of the presence of a perched water table. In the well-drained members of the chronosequence, the frequency dependent magnetic susceptibility, χFD, which is a proxy for the concentration of nano-sized pedogenic ferrimagnets such as maghaemite, was highly correlated with the concentration of haematite (Hm), but not with that of goethite (Gt). Also, the peak χFD increased with increasing age in the younger freely drained soils, indicating that no steady state had been reached, and decreased with increasing depth. The formation of maghaemite can be explained by either or both of two formation models, namely: (i) ferrihydrite → maghaemite → haematite solid state transformations; and (ii) the reaction of bacterially produced Fe(II) with an Fe hydroxide phase to form magnetite, which is later oxidized to maghaemite. Comparison between these soils and those in other climatic regions indicates that the Hm/χFD ratio increases with increasing soil temperature and with the degree of weathering. In the horizons exhibiting redoximorphic features on the higher terraces, there was significantly less Hm and χFD in clay than in the well-drained younger soils, possibly because of reductive dissolution of haematite and maghaemite. Laboratory experiments showed that susceptibility to reductive dissolution increased in the sequence goethite < maghaemite < haematite, which is consistent with the relative abundance of these minerals in the redoximorphic horizons. [ABSTRACT FROM AUTHOR]

A new model, RothPC-1, is described for the turnover of organic C in the top metre of soil. RothPC-1 is a version of RothC-26.3, an earlier model for the turnover of C in topsoils. In RothPC-1 two extra parameters are used to model turnover in the top metre of soil: one, p, which moves organic C down the profile by an advective process, and the other, s, which slows decomposition with depth. RothPC-1 is parameterized and tested using measurements (described in Part 1, this issue) of total organic C and radiocarbon on soil profiles from the Rothamsted long-term field experiments, collected over a period of more than 100 years. RothPC-1 gives fits to measurements of organic C and radiocarbon in the 0–23, 23–46, 46–69 and 69–92 cm layers of soil that are almost all within (or close to) measurement error in two areas of regenerating woodland (Geescroft and Broadbalk Wildernesses) and an area of cultivated land from the Broadbalk Continuous Wheat Experiment. The fits to old grassland (the Park Grass Experiment) are less close. Two other sites that provide the requisite pre- and post-bomb data are also fitted; a prairie Chernozem from Russia and an annual grassland from California. Roth-PC-1 gives a close fit to measurements of organic C and radiocarbon down the Chernozem profile, provided that allowance is made for soil age; with the annual grassland the fit is acceptable in the upper part of the profile, but not in the clay-rich Bt horizon below. Calculations suggest that treating the top metre of soil as a homogeneous unit will greatly overestimate the effects of global warming in accelerating the decomposition of soil C and hence on the enhanced release of CO2 from soil organic matter; more realistic estimates will be obtained from multi-layer models such as RothPC-1. [ABSTRACT FROM AUTHOR]