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Deep‐ploughing far beyond the common depth of 30 cm was used more than 50 years ago in Northern Germany with the aim to break root‐restricting layers and thereby improve access to subsoil water and nutrient resources. We hypothesized that effects of this earlier intervention on soil properties and yields prevailed after 50 years. Hence, we sampled two sandy soils and one silty soil (Cambisols and a Luvisol) of which half of the field had been deep‐ploughed 50 years ago (soils then re‐classified as Treposols). The adjacent other half was not deep‐ploughed and thus served as the control. At all the three sites, both deep‐ploughed and control parts were then conventionally managed over the last 50 years. We assessed yields during the dry year 2019 and additionally in 2020, and rooting intensity at the year of sampling (2019), as well as changes in soil structure, carbon and nutrient stocks in that year. We found that deep‐ploughing improved yields in the dry spell of 2019 at the sandy sites, which was supported by a more general pattern of higher NDVI indices in deep‐ploughed parts for the period from 2016 to 2021 across varying weather conditions. Subsoil stocks of soil organic carbon and total plant‐available phosphorus were enhanced by 21%–199% in the different sites. Root biomass in the subsoil was reduced due to deep‐ploughing at the silty site and was increased or unaffected at the sandy sites. Overall, the effects of deep‐ploughing were site‐specific, with reduced bulk density in the buried topsoil stripes in the subsoil of the sandy sites, but with elevated subsoil density in the silty site. Hence, even 50 years after deep‐ploughing, changes in soil properties are still detectable, although effect size differed among sites. [ABSTRACT FROM AUTHOR]

Background and Aims: Root restricting layers often hinder crops from accessing the large reservoir of bioavailable mineral nutrients situated in subsoil. This study aims to explore changes in the mean nutrient uptake depth of cereal crops when removing root restricting layers through subsoil management. Methods: Subsoil management was performed by deep loosening, cultivation of lucerne as deep-rooting pre-crop, and their combination with compost incorporation. Management effects were evaluated by means of shoot biomass and element concentrations in shoots and soil compartments. The mean nutrient uptake depth was fingerprinted by graphically matching the 87Sr/86Sr ratios in shoots with the 87Sr/86Sr ratios in the exchangeable fraction in soil. Nutrient uplift from depth to topsoil was inferred from element concentrations in the exchangeable fraction in soil. Results: Shoot biomass remained constant in management and control plots. The mean nutrient uptake depth changed with subsoil management in the order: deep loosening < control < deep loosening with compost incorporation. The latter coincided with a reallocation of compost-derived Na and hence resulted in increased levels of bioavailable Na below the depth of compost incorporation, which may have led to an improved water use efficiency of the crops. Thus, Na relocation triggered the deepening of the mean uptake depth of water and nutrients. Moreover, nutrient uplift from depth to topsoil was evident 21 months after subsoiling. Conclusion: Subsoil management by deep loosening with compost incorporation provides a sustainable use of soil resources because otherwise unused deep geogenic-derived nutrient reservoirs were additionally involved in crop nutrition. [ABSTRACT FROM AUTHOR]

Background: Even with extensive root growth, plants may fail to access subsoil water and nutrients when root-restricting soil layers are present. Biopores, created from decaying roots or soil fauna, reduce penetration resistance and channel root growth into the deeper soil. Further positive effects on plants result from biopore traits, as the pore walls are enriched in nutrients, microbial abundance, and activity relative to bulk soil. However, negative effects on plant growth have also been observed due to root clumping in biopores, less root-soil contact than in the surrounding bulk soil and leaching of nutrients. Scope: We discuss methods for biopore research, properties of biopores and their impact plant performance based on a literature review and own data. We elucidate potential implications of altered root-soil contact for plant growth and the consequences of root growth in pores for the rhizosphere microbiome. Conclusions: Biopores play an important but ambiguous role in soils. The effects of biopores on plant growth depend on soil properties such as compaction and moisture in an as-yet-unresolved manner. However, pore properties and root-soil contact are key parameters affecting plant yield. Knowledge gaps exist on signaling pathways controlling root growth in pores and on mechanisms modifying rhizosphere properties inside biopores. The degree to which negative effects of biopores on plant growth are compensated in the bulk soil is also unclear. Answering these questions requires interdisciplinary research efforts and novel imaging methods to improve our dynamic understanding of root growth and rhizosphere processes within biopores and at the rhizosphere-biopore interface. [ABSTRACT FROM AUTHOR]

Nature conservation and restoration in terrestrial ecosystems is often focused on increasing the numbers of megafauna, expecting them to have positive impacts on ecological self‐regulation processes and biodiversity. In sub‐Saharan Africa, conservation efforts also aspire to protect and enhance biodiversity with particular focus on elephants. However, elephant browsing carries the risk of woody biomass losses. In this context, little is known about how increasing elephant numbers affects carbon stocks in soils, including the subsoils. We hypothesized that (1) increasing numbers of elephants reduce tree biomass, and thus the amount of C stored therein, resulting (2) in a loss of soil organic carbon (SOC). If true, a negative carbon footprint could limit the sustainability of elephant conservation from a global carbon perspective. To test these hypotheses, we selected plots of low, medium, and high elephant densities in two national parks and adjacent conservancies in the Namibian component of the Kavango Zambezi Transfrontier Area (KAZA), and quantified carbon storage in both woody vegetation and soils (1 m). Analyses were supplemented by the assessment of soil carbon isotopic composition. We found that increasing elephant densities resulted in a loss of tree carbon storage by 6.4 t ha−1. However, and in contrast to our second hypothesis, SOC stocks increased by 4.7 t ha−1 with increasing elephant densities. These higher SOC stocks were mainly found in the topsoil (0–30 cm) and were largely due to the formation of SOC from woody biomass. A second carbon input source into the soils was megaherbivore dung, which contributed with 0.02–0.323 t C ha−1 year−1 to ecosystem carbon storage in the low and high elephant density plots, respectively. Consequently, increasing elephant density does not necessarily lead to a negative C footprint, as soil carbon sequestration and transient C storage in dung almost compensate for losses in tree biomass. [ABSTRACT FROM AUTHOR]

Bioturbation involves the incorporation of residues from the surface soil into the subsoil; however, common small soil 'bioengineers', such as earthworms or termites, are unlikely to transport human artifacts to deeper soil horizons. However, such artifacts occur in the deeper soil horizons within Amazonian Anthrosols (Terra Preta). Here we test the assumption that such tasks could be carried out by fly larvae, which could thus play a crucial role in waste decomposition and associated soil mixing under tropical conditions. We performed two greenhouse experiments with sandy substrate covered with layers of organic waste, ceramic fragments, and black soldier fly larvae (BSFL) (Hermetia illucens (L.) (Dipt.: Stratiomyidae)). We used in-situ images to assess the rate of bioturbation by BSFL, and then designed our main study to observe waste dissipation (reduction of organic carbon and phosphorus contents from waste model trials with and without charcoal) as related to larval-induced changes in soil properties. We found that the bioturbation of macroinvertebrates like BSFL was able to bury even large (> 5 cm) ceramic fragments within hours, which coincided with high soil growth rates (0.5 cm h-1). The sandy soil was subsequently heavily enriched with organic matter and phosphorus originating from organic waste. We conclude that BSFL, and possibly other fly species, are important, previously overlooked soil 'bioengineers', which may even contribute to the burial of artifacts in Anthrosols and other terrestrial waste dumps. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus (P) is an essential element for crop growth. However, while links of P turnover in soils to carbon (C) and nitrogen (N) availability have been described, it remains to be clarified how combinations of fertilizer C and N additions affect stocks and cycling of distinct P fractions at different soil depths. The objectives of our study were (1) to assess how soil total P stocks are affected by organic amendments and N fertilization, (2) to evaluate how different soil P fractions respond to N fertilization, and (3) to verify whether N fertilization increases soil biological P cycling. Methods: We collected soil samples from a long‐term field experiment established in 1984 in Rauischholzhausen, Germany. The soil is a Haplic Luvisol and received either no organic fertilizer (NOF), farmyard manure (FYM) or a combination of organic and mineral N fertilizer (OMF). Each treatment additionally received three levels of mineral N: 0 kg ha−1 y−1 (N0), 100 kg ha−1 y−1 (N100), and 200 kg ha−1 y−1 (N200). The organic fertilizers were applied by a manure spreader and the N fertilizer (calcium ammonium nitrate) was applied in spring as top dressing by a plot fertilizer machine. We estimated stocks of P in fractions isolated by sequential P fractionation, and assessed the oxygen isotopic composition of 1 M HCl‐extractable phosphate (δ18OP). Results: We found that increased organic matter (OM) addition and mineral N inputs caused significant decreases in the stocks of resin‐ and NaHCO3‐extractable P in the topsoil (0–30 cm). Mineral N fertilization alone resulted in significant increases in stocks of resin‐, NaHCO3‐, and NaOH‐extractable P in the upper subsoil (30–50 cm). These changes occurred for both inorganic and organic P. The subsoil δ18OP values were closer to expected equilibrium values in soil fertilized with mineral N, indicative of more intensive biological P cycling than in the treatments without mineral N inputs. Conclusions: These findings suggest that long‐term OM and mineral N fertilization promotes topsoil P losses from labile fractions by crop uptake with an enrichment of these P forms in the subsoil, and an overall increase in biological P cycling in both top‐ and subsoil horizons upon N fertilization. [ABSTRACT FROM AUTHOR]

Aims: Agricultural soils in Germany store 2.54 Pg of organic carbon (C). However, information about how and when this C entered the soils is limited. This study illustrates how depth profiles of organic matter can shed light on different entry paths of organic C. Methods: Machine learning was used to explain total organic C (TOC), C:N, particulate organic C (POC), δ13C and δ15N values down to 100 cm depth based on pedology, geology, climate and management-related variables from the German Agricultural Soil Inventory. We estimated TOC turnover rates based on the relationship between the proportion of maize (only C4 plant) in crop rotations and soil δ13C values. Results: In the upper 30 cm of cropland, fresh photosynthates added on average 0.2 to 0.8 Mg C ha− 1 year− 1. Organic fertiliser was another source of topsoil C, especially in grassland. Sandy sites in north-west Germany contained historic C from past heathland and peatland. One third of German agricultural land was found to be on colluvial and alluvial deposits, in which allochthonous C from upstream and upslope areas evidently increased the TOC content of subsoils. In and below hardpans, TOC content and C:N and POC:TOC ratios were low, indicating restricted root-derived C input. Conclusions: Our data indicate that ongoing management in German agricultural soils mainly affects topsoil C, while C storage in subsoils reveals significant legacies from allochthonous, buried or translocated C inputs. Specific attention should be focused on the sustainable loosening of hardpans that could result in a slow, but significant increase in subsoil C stocks. [ABSTRACT FROM AUTHOR]

Background: In search for more sustainable crop production, the subsoil has recently come into focus as considerable reservoir of nutrients and water. Aims: Dimensions of subsoil phosphorus (P) reserves are yet largely unknown but crucial for identifying regions suitable to include subsoil into sustainable management strategies. Methods: We analyzed stocks of total and plant‐available (calcium acetate lactate‐extractable) P in 96 representative soil profiles of German arable land down to 1 m depth. Results: We found that the German arable soils stored, on average, 8 t ha−1 of total P, of which nearly 500 kg ha−1 were readily plant‐available. Notably, one third of plant‐available P was located below the plow layer and one fifth even at depths below 0.5 m. The depth gradients of plant‐available P stocks were affected more by major reference soil group than by texture. Generally, Chernozem but also Anthrosol, Gleysol and Fluvisol exhibited the largest P stocks in German cropland. The contribution of plant‐available P to total P stocks was larger in sandy and extremely acidic (pH < 4.5) soils compared with more fine‐grained and slightly acidic to alkaline soils, possibly because fertilization compensated for overall lower total P stocks at these sites. Generally, the more P was stored in topsoils, the more P was stored also in subsoils. Conclusions: A hypothetical crop utilization of 10% from plant‐available P stocks and 0.1% from total P stocks from shallow subsoil could compensate for P fertilization by ca. 8 kg ha−1, but the rate of plant‐available P replenishment in subsoil likely remains the crucial factor for the role of subsoil P stocks in crop nutrition. Generally, the large P reserves found in subsoil could act as an 'insurance' system for crops. [ABSTRACT FROM AUTHOR]

Liming is widely used to alleviate soil acidity in western and central Europe, but its role in the cycling of magnesium (Mg) in arable soil–plant systems is still ambiguous. Here, we systematically analysed Mg concentrations and the natural Mg stable isotope compositions (δ26Mg) of two Mg pools in soil profiles and a major crop (winter rye) in a long‐term German agricultural experimental field that has been managed with and without liming since 1923. The results showed that the δ26Mg signatures of the bulk soil Mg pool in the studied Albic Luvisol displayed limited variation with depth and between the liming treatments. In contrast, the exchangeable soil Mg pool exhibited an increase in δ26Mg values with depth down to 50 cm, which was more pronounced in the limed plots. We attributed this enrichment of light Mg isotopes in upper layers to the Mg addition from "Dolokorn 90" lime, as well as to the removal of heavy Mg isotopes by plant uptake. The subsequent use of a simple isotope‐mixing model suggested that only 25% of the remaining Mg in the soil exchangeable pool stemmed from the last liming practice. The other parts of the exchangeable soil Mg pool had either interacted with the bulk soil matrix or had been utilized by the plants. Almost 100 years of liming enhanced Mg uptake by the vegetation, probably via elevated Mg contents in the grain, and reflected by the stronger depletion of heavy Mg isotopes in the soil exchangeable Mg pool relative to non‐limed plots. Whole winter rye plants were enriched in heavy Mg isotopes but they displayed similar Mg isotope compositions among plant organs in all plots, indicating identical Mg uptake and translocation strategies in the different trials. Tracing the stable isotope compositions of soil and plant Mg thus opens novel opportunities to evaluate soil management impacts on the cycling and fate of this essential nutrient in agricultural systems. Highlights: Mg concentrations and stocks in an Albic Luvisol were more heterogeneous in subsoils than in topsoilsThe variation of Mg isotope compositions of bulk soil was limited with depth and between liming treatmentsLiming induced a pronounced negative shift of δ26Mg values in soil exchangeable Mg pools down to a 50‐cm soil depthUptake of Mg by plants in limed plots was enhanced relative to that in non‐limed plots [ABSTRACT FROM AUTHOR]

Tree roots penetrate the soil to several meters depth, but the role of subsoils for the supply of nutrient elements such as phosphorus (P) to the trees is poorly understood. Here, we tested the hypothesis that increased P deficiency in the topsoil results in an increased microbial recycling of P from the forest subsoil. We sampled soils from four German temperate forest sites representing a gradient in total P stocks. We analyzed the oxygen isotopic composition of HCl-extractable phosphate (δ18OP) and identified differences in P speciation with increasing soil depth using X-ray absorption near-edge structure (XANES) spectroscopy. We further determined microbial oxygen demand with and without nutrient supply at different soil depths to analyse nutrient limitation of microbial growth and used nanoscale secondary ion mass spectrometry (NanoSIMS) to visualize spatial P gradients in the rhizosphere. We found that δ18OP values in the topsoil of all sites were close to the isotopic signal imparted by biological cycling when oxygen isotopes in phosphate are exchanged by enzymatic activity. However, with increasing soil depth and increasing HCl-P concentrations, δ18Ο values continuously decreased towards values expected for primary minerals in parent material at depths below 60 cm at sites with high subsoil P stocks and below more than 2 m at sites with low subsoil P stocks, respectively. For these depths, XANES spectra also indicated the presence of apatite. NanoSIMS images showed an enrichment of P in the rhizosphere in the topsoil of a site with high P stocks, while this P enrichment was absent at a site with low P stocks and in both subsoils. Addition of C, N and P alone or in combination revealed that microbial activity in subsoils of sites with low P stocks was mostly P limited, whereas sites with high P stocks indicated N limitation or N and P co-limitation. We conclude that subsoil P resources are recycled by trees and soil microorganisms. With continued weathering of the bedrock and mobilisation of P from the weathered rocks, P cycling will proceed to greater depths, especially at sites characterised by P limitation. [ABSTRACT FROM AUTHOR]

Electromagnetic induction (EMI) data are often used to investigate spatial and temporal patterns of soil texture, soil water content and soil salinity. We hypothesized that the EMI methodology might thus also offer potential to detect agricultural legacy effects originating from fertilizer application and irrigation of different fields. Therefore, we performed EMI measurements on two long‐term field experiments (LTFE) at Thyrow near Berlin (Germany) that differed in agricultural management with regard to long‐term irrigation in combination with mineral (NPK and lime) and organic amendments (straw and farmyard manure). Two different rigid‐boom multi‐coil EMI instruments were used to measure simultaneously the apparent electrical conductivity (ECa) over nine different depth ranges to study the entire soil profile from topsoil to deep subsoil. Additionally, soil samples were taken from the different treatments to ground‐truth the measurements and disentangle the nutrient application or irrigation effects from natural soil heterogeneity. The soil samples indicated a rather homogenous soil and the correlation between soil parameters or states were not significant. However, the treatments showed significant differences in measured ECa values. In general, ECa values were largest on regularly irrigated as well as on mineral and organic fertilized plots, with regular irrigation exhibiting the largest impact on EMI records even though the last application was months before the EMI measurement. Overall, this study reveals that EMI data can support the classical in situ assessment of agricultural management effects within LTFE, while offering new potentials in detecting and understanding legacy effects of agricultural management on spatial soil properties at farm level. [ABSTRACT FROM AUTHOR]

More than 50% of the world's population feeds on rice. Soils used for rice production are mostly managed under submerged conditions (paddy soils). This management, which favors carbon sequestration, potentially decouples surface from subsurface carbon cycling. The objective of this study was to elucidate the long-term rates of carbon accrual in surface and subsurface soil horizons relative to those of soils under nonpaddy management. We assessed changes in total soil organic as well as of inorganic carbon stocks along a 2000-year chronosequence of soils under paddy and adjacent nonpaddy management in the Yangtze delta, China. The initial organic carbon accumulation phase lasts much longer and is more intensive than previously assumed, e.g., by the Intergovernmental Panel on Climate Change ( IPCC). Paddy topsoils accumulated 170-178 kg organic carbon ha−1 a−1 in the first 300 years; subsoils lost 29-84 kg organic carbon ha−1 a−1 during this period of time. Subsoil carbon losses were largest during the first 50 years after land embankment and again large beyond 700 years of cultivation, due to inorganic carbonate weathering and the lack of organic carbon replenishment. Carbon losses in subsoils may therefore offset soil carbon gains or losses in the surface soils. We strongly recommend including subsoils into global carbon accounting schemes, particularly for paddy fields. [ABSTRACT FROM AUTHOR]

Abstract: In arable farming systems, the term ‘subsoil’ refers to the soil beneath the tilled or formerly tilled soil horizon whereas the latter one is denoted as ‘topsoil’. To date, most agronomic and plant nutrition studies have widely neglected subsoil processes involved in nutrient acquisition by crop roots. Based on our current knowledge it can be assumed that subsoil properties such as comparatively high bulk density, low air permeability, and poverty of organic matter, nutrients and microbial biomass are obviously adverse for nutrient acquisition, and sometimes subsoils provide as little as less than 10% of annual nutrient uptake in fertilised arable fields. Nevertheless, there is also strong evidence indicating that subsoil can contribute to more than two-thirds of the plant nutrition of N, P and K, especially when the topsoil is dry or nutrient-depleted. Based on the existing literature, nutrient acquisition from arable subsoils may be conceptualised into three major process components: (I) mobilisation from the subsoil, (II) translocation to the shoot and long-term accumulation in the Ap horizon and (III) re-allocation to the subsoil. The quantitative estimation of nutrient acquisition from the subsoil requires the linking of field experiments with mathematical modelling approaches on different spatial scales including Process Based Models for the field scale and Functional–Structural Plant Models for the plant scale. Possibilities to modify subsoil properties by means of agronomic management are limited, but ‘subsoiling’ – i.e. deep mechanical loosening – as well as the promotion of biopore formation are two potential strategies for increasing access to subsoil resources for crop roots in arable soils. The quantitative role of biopores in the nutrient acquisition from the subsoil is still unclear, and more research is needed to determine the bioaccessibility of nutrients in subsoil horizons. [Copyright &y& Elsevier]

Agricultural production in Central Europe increasingly suffers from extreme drought events. Improving root access to nutrient and water resources in the subsoil below the plow layer is a potential option to maintain productivity during dry summers. Here, we tested a strip-wise subsoil amelioration method that combines subsoil loosening with organic matter incorporation into the subsoil (biowaste or green waste compost) and compared it with a treatment of only subsoil loosening and a non-ameliorated control. A field experiment with randomized block design was conducted on a Luvisol with an argic horizon (Bt), with a rotation of spring barley and winter wheat. In the first two years after amelioration, we monitored soil physico-chemical parameters, microbial biomass, and shoot and root growth at anthesis as well as harvested grain yield and quality. Subsoil loosening with organic matter incorporation significantly decreased soil bulk density at the depth of compost incorporation when biowaste compost was used, but not when green waste compost had been incorporated. Nutrient stocks, nutrient availability and microbial biomass were not consistently affected by the subsoil amelioration. Nevertheless, the incorporation of organic material, especially biowaste compost, significantly increased root growth into the subsoil and subsequently significantly enhanced crop nutrient uptake, biomass and grain yield production. Green waste compost incorporation had less pronounced effects, with an increase in grain yield only in the second year after amelioration. Differences in crop development could not be explained by any single soil parameter, suggesting that it was rather a combined effect of loosened subsoil and better supply of subsoil resources that resulted in an increase in subsoil root length density and subsequently led to better crop performance. • Only loosening of subsoil did not affect soil bulk density and nutrient availability. • Root growth into subsoil was enhanced after loosening with compost addition. • Also yields after subsoil loosening were increased with compost addition. [ABSTRACT FROM AUTHOR]

Agricultural management can influence soil organic carbon (SOC) stocks and thus may contribute to carbon sequestration and climate change mitigation. The soil depth to which agricultural management practices affect SOC is uncertain. Soil depth may have an important bearing on soil carbon dynamics, so it is important to consider depth effects to capture fully changes in SOC stocks. This applies in particular to the evaluation of carbon farming measures, which are becoming increasingly important due to climate change. We sampled and analysed the upper metre of mineral cropland soils from ten long-term experiments (LTEs) in Germany to quantify depth-specific effects on SOC stocks of common agricultural management practices: mineral nitrogen (N) fertilisation, a combination of N, phosphorus (P) and potassium (K) fertilisation, irrigation, a crop rotation with preceding crops (pre-crops), straw incorporation, application of farmyard manure (FYM), liming, and reduced tillage. In addition, the effects of soil compaction on SOC stocks were examined as a negative side effect of agricultural management. Results showed that 19 ± 3 % of total management effects on SOC stocks were found in the upper subsoil (30–50 cm) and 3 ± 4 % in the lower subsoil (50–100 cm), including all agricultural management practices with significant topsoil SOC effects, while 79 ± 7 % of management effects were in the topsoil (0–30 cm). Nitrogen and NPK fertilisation were the treatments that had the greatest effect on subsoil organic carbon (OC) stocks, followed by irrigation, FYM application and straw incorporation. Sampling down to a depth of 50 cm resulted in significantly higher SOC effects than when considering topsoil only. A crop rotation with pre-crops, liming, reduced tillage and soil compaction did not significantly affect SOC stocks at any depth increment. Since approximately 20 % of the impact of agricultural management on SOC stocks occurs in the subsoil, we recommend soil monitoring programs and carbon farming schemes extend their standard soil sampling down to 50 cm depth to capture fully agricultural management effects on SOC. • Ten 32- to 112-year-old long-term experiments were sampled down to 100 cm depth. • Sampling only topsoil ignores 20 % of agricultural management effects on SOC stocks. • Mineral fertilisation had the greatest effect on subsoil organic carbon stocks. • None of the agricultural measures had significant effects deeper than 50 cm. • Standard soil sampling should therefore be extended to 50 cm depth. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition to soils is globally rising, but its effect on soil organic carbon (SOC) turnover is still uncertain. Moreover, common theories of stoichiometric decomposition and microbial N mining predict opposing effects of N supply on SOC turnover. We hypothesized that the effect of N deposition on SOC turnover depends on initial soil nutrient conditions. Thus, we sampled tropical forests and rubber gardens with pronounced gradients of nutrient availability from the topsoil to the deep subsoil (up to 400 cm) and measured substrate-induced respiration (SIR) for 30 days in four treatments (C, CN, CP, CNP additions). A natural 13 C abundance approach was conducted to quantify priming effects (PE) of the added C on SOC mineralization. For this purpose we assessed the 13 CO 2 isotope composition after adding a C4 sugar to the C3 soil; to correct for isotopic fractionation a treatment with C3 sugar additions served as control. We found that nutrient additions to topsoil did neither alter cumulative CO 2 release within 30 days (SIR acc ) nor PE (PE = 1.6, i.e., sugar additions raised the release of SOC-derived CO 2 by a factor of 1.6). In the upper subsoil (30–100 cm), however, both CN and CP additions increased SIR acc (by 239% and 92%, respectively) and the PE (PE = 5.2 and 3.3, respectively) relative to the treatments that received C only (PE = 1.7), while CNP additions revealed the largest increase of SIR acc (267%) and PE (PE = 6.0). In the deep subsoil (>130 cm depth), only the CNP addition consistently increased SIR acc (by 871%) and PE (PE = 5.2) relative to only C additions (PE = 2.0). We conclude that microbial activity was not limited by nutrients in the topsoil but was co-limited by both N and P in the subsoil. The results imply that microbes mine nutrients from previously unavailable pools under the conditions that 1) deficiency actually exists, 2) co-limitation is alleviated, and 3) nutrient reserves are present. Yet, as opposed to microbial nutrient mining theories, we showed that the subsoil PE is highest when nutrient supply matches microbial demand. As a result also N deposition might exert variable effects on SOC turnover in tropical soils: it might have no effect in nutrient-rich topsoils and in co-limited subsoils without P reserves but might increase SOC turnover in co-limited subsoils with potentially acquirable P reserves. [ABSTRACT FROM AUTHOR]

In arable fields, biopores are primarily formed by taproots, but may also be bored by earthworms. Irrespective of the pore origin, repeated use by anecic earthworms yields a wall coating that is rich in carbon, nutrients and microorganisms. However, this effect is halted by routine tillage, and it remains unclear how quickly earthworms are able to alter biopore properties in subsoil. We conducted an earthworm incubation field experiment in arable soil to test the capacity of Lumbricus terrestri s to i. increase total nutrient contents including plant available P, ii. alter the microbial community and iii. increase enzyme activities in biopore walls over one vegetation period. Firstly, biopores that contained chicory roots were identified on a plot scale (4.2 × 1.5 m). After two years under fallow, roots were decomposed. We then inserted individual earthworms at 45 cm depth into a subset of these pores, afterwards refilling with topsoil. After six months, earthworms were removed and soil was opened at 45–75 cm and 75–105 cm soil depth layers. The inner pore wall (1 mm) of individual root biopores (‘RBP’) or root biopores modified by earthworms (‘EBP’) as well as the bulk soil were sampled in 6 depth intervals of 10 cm each and analyzed for total C, N, S content, plant available P, microbial biomass, phospholipid fatty acids (PLFA) and enzyme activity. Biochemical properties of bulk soil, RBP and EBP clearly differed after one vegetation period as indicated by principal component analysis. PLFA markers of fungi and protozoa were detected only in biopores. Compared with the bulk soil, total C, N, S were enriched in RBP by a factor of 2.0–3.1, plant available P by a factor of 8–10, and microbial biomass by a factor of 12–36. In EBP, all of these parameters were as in RBP or elevated even further (C, N, S: factor 1.0–1.4, plant available P: factor 1.3–1.5, microbial biomass: factor 1.5–2.0, PLFA markers of fungi: factor 2.6–4.4, PLFA markers of protozoa: factor 9.2–14.2). PLFA markers indicative of the ratio of Gram-positive to Gram-negative bacteria (G+: G−) were 5–10 fold lower in RBP than in bulk soil, the microbial metabolic quotient ( q CO 2 ) was 0.4–0.6 times as high. In EBP, these parameters were further reduced (ratio G+: G−: factor 0.7, q CO 2 : factor 0.7–0.8). RBP were particularly characterized by high contents of 10-methyl branched fatty acid indicators of actinobacteria. Activities of enzymes involved in the C-cycle (xylanase, cellobiohydrolase, ß-glucosidase) and N-cycle (chitinase, chitotriosidase, leucine aminopeptidase) were also elevated in RBP as compared to the bulk soil (factor 1.1–3.6) and further increased in EBP (factor 1.2–3.7). All these effects were more pronounced in the 45–75 cm soil layer. We conclude that, in only six months, L. terrestris in arable fields modified ordinarily nutrient-rich biopores into ‘super-hotspots’ of microbial biomass, enzyme activity and nutrient availabilities. Hence, even short-term promotion of earthworm populations by agricultural management practices can increase microbial biomass and enzyme activity in biopores and its coupling to nutrient mobilization in the subsoil. [ABSTRACT FROM AUTHOR]

A sustainable use of soil resources is urgently required to cope with the increasing demand for agricultural products during climate change. To inspire farmers on new soil cultivation methods like subsoil management requires not only yield measurements but also nutrient use efficiency measurements for which analytical tools are still missing. Stable isotopes of the macronutrient magnesium (Mg) are a potential novel subsoil management evaluation tool in agronomy and soil/plant sciences because its isotope ratios shift considerably during Mg uptake by crops. The feasibility of Mg stable isotopes was first demonstrated conceptually by simulating subsoil management on soils with low, middle, and high inventories of bioavailable Mg and crop plants typically cultivated in Germany. This simulation showed that the magnitude of Mg isotope shifts among crops and the exchangeable fraction of Mg in soil is resolvable from the long-term external precision of Mg isotope analyses only if three conditions are met. First, the crop uptake-related Mg isotope fractionation factor should be at the upper end of hitherto published fractionation factors. Second, a high Mg uptake flux of crop plants (e.g., sugar beets) is matched by a low Mg supply from the exchangeable fraction in soil (e.g., sandy soils). Third, subsoil management causes a considerable deepening of the rooting system (e.g., flipping the topsoil root cluster below 30 cm depth). If these conditions are met, Mg stable isotopes can be used in a qualitative manner to identify the main Mg uptake depth, and in a quantitative manner by calculating the Mg use efficiency, defined here as the ratio of Mg uptake versus Mg supply, solely from Mg isotope ratios. This concept was tested for Alfisols on field trials by conducting deep loosening with and without the incorporation of compost. Magnesium isotope shifts in crops and the exchangeable fraction of Mg in soil were mostly unresolvable from the long-term external precision of Mg isotope analyses, which positively tested the Mg isotope concept for well nurtured soils. However, systematic Mg isotope shifts among bulk crops cultivated on and beside a melioration strip were found and attributed to the uplift of isotopically distinct compost-derived Mg on the melioration strip and root restricting layers beside the melioration strip. Given that the Mg isotope composition of the exchangeable fraction barely varies with depth, field-based crop uptake-related 'apparent' Mg isotope fractionation factors of winter wheat and spring barley could be determined, which differed from one another (Δ26Mg wheat-rem. exch. = 0.63 ± 0.05‰, Δ26Mg barley-rem. exch. = 0.37 ± 0.12‰). Nonetheless, the quantitative approach of Mg isotopes was violated when calcareous fertilizer was applied to the field as differences in the isotope-derived Mg use efficiency could be attributed to the uneven distribution of lime-derived Mg with depth. Using Mg stable isotopes as a new geochemical routine for agronomy and soil/plant sciences requires future work focussing on isotope fractionation factors related to crop uptake and intra-plant translocation of Mg – which may depend on species, environmental conditions, and nutrient status – to allow minimally invasive sampling of the soil-plant system and to reduce sample sets. • A conceptual Mg isotope model was established and positively tested in the field. • Mg stable isotopes are a powerful novel tool for subsoil management evaluation. • Mg use efficiency of crops can solely be quantified from Mg stable isotopes. • Lime application limits Mg use efficiency determination solely from Mg isotopes. • A criteria catalogue ensures a successful application of Mg isotopes in agronomy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Black carbon (BC) was preserved in up to 130,000yr old loess–palaeosol. [•] No vertical translocation of BC to loess and palaeo-subsoils found. [•] Palaeosol BC provided comprehensive regional information on past fire regimes. [•] Maximum BC amount occurred at times of intensive pedogenesis. [Copyright &y& Elsevier]

Peatlands comprise major global stocks of soil organic carbon (SOC). Many degraded peatlands are currently being restored, but little is known to which degree former disturbances leave a 'legacy' in such restored peatlands, and subsequently how this impacts their response to global change. Our aims were to investigate if after 20 years of restoration (i) carbon stability may still be affected by the former land use and if (ii) restored bogs are less susceptible to nutrient input but (iii) more sensitive to temperature rise. We sampled the top- and subsoil of a formerly drained, a previously drained and afforested part and an unmanaged control site of a Scottish bog. We incubated peat from each part for determination of potential basal respiration, nutrient limitation and temperature sensitivity (Q 10) of aerobic peat degradation. Lowest respiration rates were identified at the afforested site while nutrient addition had no significant effect on topsoil organic matter decomposition at all sites. Q 10 values were significantly higher in the topsoil (2.6 ± 0.3 to 2.8 ± 0.2) than in the subsoil. For the subsoil, the drained site (2.0 ± 0.0) showed significantly lower Q 10 values than the afforested one (2.6 ± 0.6), while the control site had a Q 10 of 2.1 ± 0.0, indicating contrasting temperature sensitivities of potential SOC losses following specific forms of disturbance. Overall, our data indicate that afforestation left a legacy on potential subsoil SOC losses with global warming. Such effects must be considered when integrating restored bogs into global data bases on peatlands' responses to global change. Image 1 • The rate of aerobic peat decomposition depends on former land use. • Formerly afforested peat shows reduced respiration and high temperature sensitivity. • Former drainage of peat does not affect its temperature sensitivity. • 20 years of restoration have levelled effects of former drainage on respiration rates. [ABSTRACT FROM AUTHOR]

At the land surface, the availability of water controls the evolution of life as well as the morphological development. It is currently hardly known how far both evolutionary processes interact in water-limited environments. While it is well considered that biotic processes contribute to weathering and therewith also prepare the landscape for erosion, little is known to what degree different landforms form barriers and corridors of life across geological time scales. Here, we present an example of how to tackle this complex interplay of biology and landscape evolution by introducing the Collaborative Research Centre CRC 1211 'Earth – Evolution at the dry limit'. A CRC is a German Research Foundation funding program, bringing together scientists from different disciplines to tackle jointly complex emergent research questions for up to twelve years. The CRC 1211 focuses on the arid cores of the Atacama Desert and the Namib Desert. Main objective is to disentangle how the shaping of land-surfaces by past episodes of wetter climate coevolved with the evolution of life. It is hypothesized that aridity was interrupted by punctuated wetter periods, which left fingerprints in surface processes and the radiation of the biota, with climatic thresholds beyond which biota could adapt to and influence landscape development. Specific desert landscape elements such as soil surface crusts, desiccation cracks and subsoil water potentially form underexplored refugia of life at particular sites, while old channels and alluvial fan systems potentially structure its dispersal at small to intermediate scales (< 100 m2), In addition, there are large-scale (>10,000 km2) gradients in surface processes and biodiversity, likely controlled by the intensity and duration of fog or rainfall. To substantiate these hypotheses we combine expertise from the fields of population and (phylo-) genetics, molecular biology, biogeography, ecology, soil sciences, Earth-surface sciences, geomorphology, meteorology, (paleo-) climatology, (isotope-) geochemistry and physical dating to discover and evaluate the trajectories and thresholds of the evolution and isolation of life. While presenting here our current research strategy, we invite scientists from all over the world to link their research on related questions for the joint development of a global picture on how evolution of life was triggered and regulated by land-surface processes. • Interdisciplinary research in extremely water-limited environments • Investigating coevolution of life and landscape in response to climatic change • Long-term climate records of the oldest deserts on Earth-Methodological development to date climate archives and determine dates and rates of surface processes [ABSTRACT FROM AUTHOR]

Although carbon (C) stored deep in soils of tree-dominated land use systems in the tropics represents a large reservoir of organic matter its vulnerability to land use change has been hardly assessed. To fill this gap, we sampled Acrisols down to 3 m under three different land use systems; namely, recent cacao agroforestry (<2 years old; not deeper than 1 m), young and old rubber gardens (<10 years and >50 years), and secondary forest (>50 years) all located in Kapuas Hulu regency, West Kalimantan, Indonesia. We then assessed soil organic carbon (SOC) stocks as well as C accumulated in above- and belowground biomass, litter and dead wood debris at the soil surface. The amount of C stored in soils to a depth of 1 m exceeded the amount stored in living biomass (Σ C stored in roots, understorey and overstorey) strongly in the cacao agroforestry systems (69 Mg SOC vs. 12 Mg biomass-C ha−1), slightly in young rubber gardens (85 Mg SOC vs. 69 Mg C ha−1), but not in old rubber gardens (87 Mg SOC vs. 200 Mg C ha−1) and secondary forests (65 Mg SOC vs. 138 Mg C ha−1). Additionally in the older systems, up to 140 Mg C ha−1 (old rubber gardens) and 116 Mg C ha−1 (secondary forest) were found in soils to a depth of 3 m, thus raising soil C stocks by 60 to 80% relative to C stored in upper soil (0 to 1 m). We conclude that (1) the form of land use and land use change can substantially affect C stocks in living biomass, with aboveground biomass in old rubber gardens comparable to that of secondary forests; and (2) that land use change can reduce SOC in topsoil, but that substantial C stocks found in deep (down to 3 m) subsoil remain stable. • Old secondary forests stored up to 140 Mg C ha−1 in soils to a depth of 3 m • Carbon stored up to a depth of 1 m varied between 65 and 87 Mg C ha−1 • Above ground biomass varied strongly between forest types and age. • Living and dead biomass stored between 9 and 200 Mg C ha−1 [ABSTRACT FROM AUTHOR]

The Atacama Desert is the oldest and driest desert on earth, nevertheless traces of life have been observed in several places, accumulating residues of organic matter (OM) on the desert surface, i.e., in its soil. We asked if these OM traces of life preferentially accumulate in topsoil, or whether also enrichment of OM in deeper subsoil layers appears. We also evaluated to which degree spatial and vertical heterogeneity in the distribution of soil organic carbon (SOC) stocks depends on increasing aridity in the desert ecosystem. We sampled an east-west directed aridity transect with several replicates spanning the Atacama Desert from north to south, i.e. Codpa (18.4°S), Rio Tana (19.2°S), Quebrada Aroma (19.4°S), Yungay (24.6°S) and Paposo (25.1°S). With a nested sampling design (3≥n≤18) we addressed topsoil heterogeneity at each sampling site (n=433). For 13 of these sites soil profiles were dug to 0.8 to 3.9 m depth depending on soil thickness. This amounted to a total of 637 samples. Bulk density was taken for each site and depth of 15 cm. SOC concentrations were taken for each sample by thermally resolved dry combustion with a Soli TOC (Elementar Analysensysteme, Hanau, Germany DIN 19539GS). We found that with decreasing precipitation (~7 to <0.1 mm yr-1), SOC stocks decreased from 3.42±4.08 to 0.09±0.01 kg SOC m-2 in the 15 cm of topsoil. Hence, traces of life were ubiquitously preserved both in the arid and hyper-arid desert areas. Intriguingly, relatively large amounts of soil organic matter were also found at depth below 15cm, adding an extra of 52.9 to 95.9 % of subsoil C to the topsoil SOC stock. Furthermore, the subsoil SOC concentrations peaked between 40 and 150 cm depth in the soil, irrespectively of the presence or absence of visible vegetation. Biomarker analyses are currently performed to reveal the origin of SOC found in the various depths. We conclude that C accrual in this arid to hyper-arid system shifts from the preferential C enrichment in topsoil to that in the subsoil, therewith providing the potential for deep(er) biosphere foodwebs and demonstrating the likelyhood to need to dig into soil for discovering traces of (active) life in comparable environments, including other planets such as Mars. [ABSTRACT FROM AUTHOR]