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C-TOOL is a simple flexible SOM turnover model competitive with other alternatives that often demands more input information. As most SOC turnover models, C-TOOL rely on plant C inputs derived from measured agricultural yields using simple allometric equations that establish the relation between C inputs and crop yields. The main sources of uncertainty in C turnover models rely on C input calculations and parametrization of initial pool distribution. Since the main output is the temporal dynamic SOC stock, we should refer to long-term data that can be challenging to obtain to appreciate meaningful changes. Nevertheless, in Denmark an experiment from 1981 to 2019 examined the effect of annual additions of different levels of C inputs on SOC storage. This experiment produced a robust validation platform for soil C modelling, permitting to account not only the temporal variability but also the variability beneath each treatment. In this work we implemented the C-TOOL model at a plot level, based on this precise data from spring barley straw disposal at plot level in order to explore SOC turnover modeling uncertainties and validate it performance. We performed a variance-based sensitivity analysis to evaluate how sensitive are C inputs calculations to allometric parametrization using the distributional information on spring barley allometrics (grain yield, harvest index and root biomass and root exudates). After exploring alternatives on the model parametrization related to allometric, initial soil C conditions and initialization period, we arranged a simulation design to test all the possible combinations to assess how accurate is the model in predicting the temporal plot variability of SOC. To be able to perform the numerous scenarios we worked on a feasible computational implementation trough R. Finally, we studied how dependent is the lack of fit to the alternative parametrization and the spatiotemporal variability of field conditions trough a variance component analysis. From the C input variance-based sensitivity analysis we conclude that root exudates and root biomass are the most sensitive parameters. Validation results show that C-TOOL was able to accurately describe the temporal dynamic of SOC in the topsoil due to non-significant differences between simulated and observed data. All the alternative parametrizations register a prediction error below 15 % related to the mean showing differences between observed and predicted between 3.60 and 6.46 Mg C/ha in the top 20 cm depth. This lack of fit was mainly explained by the spatiotemporal (year and block) variability rather than the parametrization alternatives tested. Nevertheless, we conclude that is relevant to focus on the initial soil C condition parametrization but not the in-situ measurements of harvest index. Besides, using a fixed amount of root biomass for spring barley presented better than using the standard allometrics. Further studies dive into a global sensitivity analysis on the multivariate variability distribution of all the inputs involved to get to a robust uncertainty estimation.

Random forest regression (RF) is an extremely popular tool for the analysis of high-dimensional data. Nonetheless, its benefits may be lessened in sparse settings due to weak predictors, and a pre-estimation dimension reduction (targeting) step is required. We show that proper targeting controls the probability of placing splits along strong predictors, thus providing an important complement to RF's feature sampling. This is supported by simulations using representative finite samples. Moreover, we quantify the immediate gain from targeting in terms of increased strength of individual trees. Macroeconomic and financial applications show that the bias-variance trade-off implied by targeting, due to increased correlation among trees in the forest, is balanced at a medium degree of targeting, selecting the best 10--30\% of commonly applied predictors. Improvements in predictive accuracy of targeted RF relative to ordinary RF are considerable, up to 12-13\%, occurring both in recessions and expansions, particularly at long horizons.

A risk-averse insurance company controls its reserve, modeled as a perturbed Cramer-Lundberg process, by choice of both the premium p and the deductible K offered to potential customers. The surplus is allocated to financial investment in a riskless and a basket of risky assets potentially correlating with the insurance risks and thus serving as a partial hedge against these. Assuming customers differ in riskiness, increasing p or K reduces the number of customers n ( p , K ) and increases the arrival rate of claims per customer λ ( p , K ) through adverse selection, with a combined negative effect on the aggregate arrival rate n ( p , K ) λ ( p , K ) . We derive the optimal premium rate, deductible, investment strategy, and dividend payout rate (consumption by the owner-manager) maximizing expected discounted lifetime utility of intermediate consumption under the assumption of constant absolute risk aversion. Closed-form solutions are provided under specific assumptions on the distributions of size and frequency of claims.

Background: Cover crops (CC) introduced to reduce leaching of nitrate may also improve soil microbial properties and phosphorus (P) uptake in crops that follow. These effects may depend on soil P status and the quality of the CC residues. Aim: Our aim was to quantify the more persistent effects of incorporation of residues of three different CC species on barley growth and P uptake and whether any response in growth and P uptake was related to soil P status and changes in soil microbial properties. Methods: We examined the impact of soil P status, CC species, and residue fraction (shoots and/or roots) on the growth of winter barley (Hordeum vulgare) and soil microbial properties. Shoot and root residues from three contrasting CC (oats, Avena sativa; corncockle, Agrostemma githago; lupine, Lupinus angustifolius) were incubated for 2 months in soil with low and medium P status. Dry matter yield and P offtake characterized effects of CC residues on barley while phospholipid fatty acids (PLFAs), neutral lipid fatty acids (NLFAs), and enzyme activity characterized soil microbial properties after barley harvest. Results: Effects of shoot residues on barley yield and P offtake appeared neutral or positive and not affected by soil P status, while the effect of root residues appeared negative for medium P soil and neutral for low P soil. With lupine shoot biomass, however, barley yield and P offtake increased in both soils. Neither CC treatments nor soil P status affected the microbial community composition (bacterial and fungal specific PLFAs). Lupine roots increased phosphomonoesterase, and lupine residues generally stimulated microbial abundance (total microbial PLFAs) compared to other CC treatments. Conclusion: We conclude that the effect of CC residues on the following crop and soil microorganisms depends on soil P status and that lupine had the largest positive impact on barley growth.

Purpose: The crop uptake and leaching of labelled fertilizer N applied 25-30 years ago was measured in different agricultural cropping systems to improve the understanding and quantification of the long-term fate of fertilizer N. Methods: 15N-labelled mineral fertilizers were added to a field plot with different crops over 5 years. After 12 years arable cropping the top-soil was relocated to lysimeters with set-aside grassland for the next 13 years. The lability of the residual 15N in soil was then tested over a period of two years by either converting to fertilized and cut grass, or by replacing the set-aside grassland with spring barley (+/- autumn cover crop) or vegetation-free fallow, all receiving unlabelled mineral N fertilizers. The crop uptake and leaching of 15N was determined over the 2-year period.Results: The 15N residing in soil before set-aside decreased by 24% during the 13 years under set-aside grassland. Crop uptake and leaching of 15N were generally highest in the first test year after termination of the set-aside. The leaching of residual 15N in soil declined in the order: vegetation-free soil (4.7%), spring barley (1.9%), spring barley + cover crop (0.7%), and production grassland (0.2%). Corresponding losses for the second leaching period were 2.7%, 0.9%, 0.4%, and 0.06%. There was a constant relationship between the leaching loss of 15N and total N. Conclusions: After residing in soil for 25-30 years, the lability of labelled mineral N fertilizer residues were slightly higher than the lability of bulk soil N. Autumn vegetation was crucial for reducing leaching losses.

Partitioning soil organic carbon (SOC) into two kinetically different fractions that are stable or active on a century scale is key for an improved monitoring of soil health and for more accurate models of the carbon cycle. However, all existing SOC fractionation methods isolate SOC fractions that are mixtures of centennially stable and active SOC. If the stable SOC fraction cannot be isolated, it has specific chemical and thermal characteristics that are quickly (ca. 1 h per sample) measurable using Rock-Eval® thermal analysis. An alternative would thus be to (1) train a machine-learning model on the Rock-Eval® thermal analysis data for soil samples from long-term experiments for which the size of the centennially stable and active SOC fractions can be estimated and (2) apply this model to the Rock-Eval® data for unknown soils to partition SOC into its centennially stable and active fractions. Here, we significantly extend the validity range of a previously published machine-learning model (Cécillon et al., 2018) that is built upon this strategy. The second version of this model, which we propose to name PARTYSOC, uses six European long-term agricultural sites including a bare fallow treatment and one South American vegetation change (C4 to C3 plants) site as reference sites. The European version of the model (PARTYSOCv2.0EU) predicts the proportion of the centennially stable SOC fraction with a root mean square error of 0.15 (relative root mean square error of 0.27) at six independent validation sites. More specifically, our results show that PARTYSOCv2.0EU reliably partitions SOC kinetic fractions at its northwestern European validation sites on Cambisols and Luvisols, which are the two dominant soil groups in this region. We plan future developments of the PARTYSOC global model using additional reference soils developed under diverse pedoclimates and ecosystems to further expand its domain of application while reducing its prediction error.

Long-term agricultural field experiments are essential for quantifying changes in soil properties and associated crop productivity that occur slowly but continue over long periods. Initiated in 1894 in the South of Denmark, the Askov long-term experiment (LTE) is among the few LTEs in the world that continued for more than 125 years. The experiment compares different rates of nitrogen, phosphorus, and potassium applied in mineral fertilizers or animal manure with abundant treatment replicates. With well-managed treatments, detailed yield records, and a soil archive dating back to 1923, today the Askov-LTE represents a unique platform for research not envisioned at the start of experiments. Here, we provide a short description of site characteristics and experimental layout, examples of historic crop yields and changes in soil carbon (C) content. We provide short overviews of some of the studies that have used the Askov-LTE as a research platform. These include crop yield-related research; models simulating changes in soil C; availability of soil P reserves; indicators of biological, chemical, and physical soil quality; and studies related to prehistoric archaeology. Finally, we offer some reflections on long-term field experimentation.

Silage maize (Zea mays L.) is an important crop for forage on Northwestern European dairy cattle farms. We examined the effect of readily available soil phosphorus (P) on early maize growth and linked in-season height growth to final harvest yield using field plots with contrasting P supply in a one-year study embedded in a long-term experiment. Water-extractable P (Pw) was used as a proxy for readily available P in soil. Plant height, dry matter (DM) accumulation, P and nitrogen (N) uptakes were determined eight times from the two-leaf stage until final whole-crop harvest and fitted to logistic growth models. The models revealed that the final yield was significantly related to the time required to reach the maximum rate of height growth (occurring from 330 to 485 accumulated growing degree units, GDU), but not the time required to reach the maximum rate of DM accumulation (occurring from 561 to 649 GDU). Furthermore, plant height at the four-leaf stage and onwards was significantly related to the final harvest yield. Soil Pw linked closely to height growth parameters; higher levels of Pw gave earlier peaks in height growth. For this light sandy loam with a wide gradient in P content, we conclude that suboptimal P supply postpones height growth and reduces final yields. A sufficient P supply links to an early rapid increase in plant height and forms the potential for optimum nutrient uptake and high forage yields. Thus, early-season plant height may serve as a simple morphometric indicator for final yields.

Broomcorn and foxtail millet are the only major domesticated plants indigenous to prehistoric Eurasia to rely on the C4photosynthetic pathway. Here we study the impact of animal manure (AM) on broomcorn millet (Panicum miliaceum) and foxtail millet (Setaria italica), grown in the Askov Long-Term Experiment, using unmanured soil and soil dressed with phosphorus plus potassium (PK) as reference treatments. Animal manure had a marked effect on yields and on the δ15N values of grains. For broomcorn millets grown on manured soil, the average δ15N value was 5.8‰. When grown on unmanured and PK-treated soils, the δ15N values were 0.4‰ and 0.2‰, respectively. For foxtail millet the δ15N values also differed between grains from unmanured (-1.0‰), PK (0.7‰) and manured (6.3‰) treatments. Thus, when compared to unmanured soil, the offset due to manure was 7.3‰ forSetariaand 5.3‰ for the twoPanicumvarieties. In accordance with previous studies on C3crops, our study suggests that δ15N values in charred millet grains recovered fromarchaeological sitescould provide a robust indicator of prehistoric manuring intensity.

Background: Intensive agriculture systems have paved the way for a growing human population. However, the abundant use of mineral fertilisers and pesticides may negatively impact nutrient cycles and biodiversity. One potential alternative is to harness beneficial relationships between plants and plant-associated rhizobacteria to increase nutrient-use efficiency and provide pathogen resistance. Plant-associated microbiota profiling can be achieved using high-throughput 16S rRNA gene amplicon sequencing. Interrogation of this data is limited by confident taxonomic classifications at high taxonomic resolution (genus- or species-level), which is often not possible with the commonly applied universal reference databases. The development of high-throughput full-length 16S rRNA gene sequencing combined with automated taxonomy assignment (AutoTax) can be used to create amplicon sequence variant resolved ecosystems-specific reference databases that are superior to the traditional universal reference databases. Results: Synthetic long-read sequencing of 987,353 full-length 16S rRNA genes was used to create a reference database (AsCoM) with AutoTax for bacteria and archaea based on Askov and Cologne soils. We evaluated the performance of AsCoM using short-read amplicon data and found that it resulted in increased genus- and species-level classification compared to commonly used universal reference databases. AsCoM was utilised to evaluate the ecosystem-specific primer bias and taxonomic resolution of amplicon primers targeting the V5-V7 region of the 16S rRNA gene as these are commonly used within the plant microbiome field. Finally, we demonstrate the benefits of AsCoM through the analysis of V5-V7 amplicon data to identify new plant-associated microbes for two legume (Lotus japonicus and Medicago truncatula) and two cereal (Hordeum vulgare and Zea mays) species. Conclusion: We presented AsCoM, the first comprehensive ecosystem-specific 16S rRNA reference database for Askov and Cologne soil. AsCoM provides unprecedented taxonomic resolution in 16S rRNA amplicon profiling of soil-grown plant microbiota. It also represents a valuable tool for ecosystem-specific evaluation of amplicon primers and development of species-level hybridization probes for in situ studies.

Background: The fertilizer value of phosphorus (P) in waste products relies heavily on its availability to the subsequent crop. Aim: We studied the link between extractable P in waste products and apparent P recovery (APR, i.e., difference in plant P uptake between P amended and un-amended soils divided by the amount of P added) using spring barley grown on three sandy soils. Methods: The products included sewage sludge, biomass ash, struvite, compost, meat and bone meal, biochar from sewage sludge, and industrial sludge. Soft rock phosphate and triple-superphosphate (TSP) were included for comparison. Availability of P was characterized by extraction with water and solutions of sodium bicarbonate, citric acid, oxalic acid, hydrochloric acid, ammonium acetate, ammonium fluoride and anion exchange resin membranes. TSP was used to establish mineral-fertilizer-equivalents (MFE). Water and bicarbonate extractions were also applied to products incubated with soil before extraction. Results: The APR ranged 26 to 31% for TSP and 0 to 30% for waste products. APR correlated most strongly with bicarbonate extractable P. The correlation increased when products were incubated with soil before extraction. Conclusions: We conclude that bicarbonate extraction is a good indicator of potential P availability. However, interactions between waste products and soil properties modify P availability.

We develop a new empirical approach to term structure analysis that allows testing for time-varying risk premiums and arbitrage opportunities in models with both unobservable factors and factors identified as the innovations to observed macroeconomic variables. Factors can play double roles as both covariance-generating common shocks driving yields and determinants of market prices of risk in cross-sectional pricing. The evidence favors time-varying risk prices significantly related to the second Stock–Watson principal component of macroeconomic variables and to changes in the industrial production index. Our preferred specification includes these two observable and two unobservable factors, with the no-arbitrage condition imposed.

Reduced use of fossil energy by removing cereal straw for bioenergy potentially threatens soil organic carbon (SOC) storage. Straw incorporation plays a key role for SOC storage in cereal-based cropping systems, but the use of cover crops (CCs) may compensate for straw removal. However, assessing the SOC sequestration potential of management changes requires field experiments with long continued treatments and frequent soil sampling. Based on a field experiment initiated in 1981 on a sandy loam soil at Askov Experimental Station (Denmark), we examined the effect of annual additions of spring barley straw (0, 4, 8 and 12 Mg ha−1) and undersown ryegrass CC on SOC storage in the 0- to 20-cm layer. The effect of straw incorporation and CC on SOC was additive. At steady-state conditions, the SOC stock based on equivalent soil mass (SOC stockFM) increased 3.9, 6.7 and 9.3 Mg C ha−1 after annual incorporation of 4, 8 and 12 Mg straw ha−1, respectively. The ryegrass CC increased SOC stockFM by 3.3 Mg C ha−1 and thus almost compensated for removal of 4 Mg straw ha−1. An asymptotic regression model best described the temporal changes in SOC and showed that the effect of straw incorporation and ryegrass CC on SOC sequestration peaks after 10–15 years when a new equilibrium between input and output of C is reached. Clearly, reliable assessments of SOC sequestration potentials following changes in management require field experiments with frequent soil sampling until reaching steady-state conditions.

The EU Water Framework Directive (WFD) aims to protect the ecological status of coastal waters. To establish acceptable boundaries between good and moderate ecological status, the WFD calls for reference conditions practically undisturbed by human impact. For Denmark, the nitrogen (N) concentrations present around year 1900 have been suggested to represent reference conditions. As the N load of coastal waters relates closely to runoff from land, any reduction in load links to agricultural activity. We challenge the current use of historical N balances to establish WFD reference conditions and initiate an alternative approach based on parish-level land-use statistics collected 1896/1900 and N concentrations in root zone percolates from experiments with year 1900-relevant management. This approach may be more widely applicable for landscapes with detailed historic information on agricultural activity. Using this approach, we find an average N concentration in root zone percolates that is close to that of current agriculture. Thus, considering Danish coastal waters to be practically unaffected by human activity around year 1900 remains futile as 75% of the land area was subject to agricultural activity with a substantial potential for N loss to the environment. It appears unlikely that the ecological state of coastal waters around year 1900 may serve as WFD reference condition.

Straw incorporation and cover cropping are important measures for reducing loss of nitrate by leaching and supporting soil quality in cereal cropping systems. However, cereal straw also represents an important source of bioenergy, while concerns still exist regarding a negative effect of annual straw incorporation on crop yields. Based on a field experiment initiated in 1981 on a sandy loam soil at Askov Experimental Station (Denmark), we examined the effect of annual addition of straw (0, 4, 8 and 12 Mg ha−1), undersown cover crops (ryegrass and ryegrass-clover), and ploughing time (autumn and spring) on spring barley yields and N uptake in grain and grain-free aboveground biomass. During 1981–2019, grain yields showed an annual increase of 0.05 Mg DM ha−1 while grain N concentration decreased 0.019 %-point yr−1. Straw incorporation rate had a significant effect on grain yield in only six out of 31 years. The effect of increasing straw rates was slightly negative in two of the initial years but positive in the extreme drought year 2018. During 2004–2018, an undersown grass-clover cover crop increased grain yield with 0.41 Mg DM ha−1 and grain N concentration with 0.13 %-point, corresponding to relative increases of 9% when compared to no cover crop. In contrast, an undersown ryegrass cover crop reduced grain yield with 0.21 Mg DM ha−1 corresponding to a relative reduction of 5%, and increased grain N concentration with 0.03 %-point corresponding to a relative increase of 2%, as compared to no cover crop. The time of incorporating straw and cover crop residues had a minor effect on barley yield and quality. Our results suggest that removal of straw for bioenergy does not compromise yields of spring barley grown at this site, while an inclusion of undersown leguminous cover crops had a pronounced positive impact on crop yield and quality. However, implementation of these management measures needs to be site-specific and consider trade-offs between effects on crop yield and quality, environmental benefits, and soil quality.

Cropping practices have a great potential to improve soil quality through changes in soil biota. Yet the effects of these soil improving cropping systems on soil fungal communities are not well known. Here, we analysed soil fungal communities using standardized measurements in 12 long‐term experiments and 20 agricultural treatments across Europe. We were interested in whether the same practices (i.e. tillage, fertilization, organic amendments and cover crops) applied across different sites have predictable and repeatable effects on soil fungal communities and guilds. The fungal communities were very variable across sites located in different soil types and climatic regions. The arbuscular mycorrhizal fungi (AMF) were the fungal guild with most unique species in individual sites while plant pathogenic fungi were most shared between the sites. The fungal communities responded to the cropping practices differently in different sites and only fertilization showed a consistent effect on AMF and plant pathogenic fungi while the response to tillage, cover crops and organic amendments were site, soil and crop species specific. We further show that the crop yield is negatively affected by cropping practices aimed at improving soil health. Yet, we show that these practices have the potential to change the fungal communities and that change in plant pathogenic fungi and in AMF is linked to the yield. We further link the soil fungal community and guilds to soil abiotic characteristics and reveal that especially Mn, K, Mg and pH affect the composition of fungi across sites. In summary, we show that fungal communities vary considerably between sites and that there are no clear directional responses in fungi or fungal guilds across sites to soil improving cropping systems but that the responses vary based on soil abiotic conditions, crop type, and climatic conditions. Details on experiments related to the data is provided in supplementary materials of the related article,Fungi: DNA was extracted using the modified Power Soil protocol (Harkes et al., ), with 0.25 g soil per sample and Lysing matrix E beads tubes (MP Biomedicals). Fungal DNA was amplified using primers ITS4ngs and ITS3mix1‐5 (Tedersoo et al., , ) and purified using AMPure magnetic beads (Beckman Coulter). Polymerase chain reactions (PCRs) were performed with 12.5‐μL Hotstart ready mix (Fisher scientific) and approximately 50 ng of DNA per reaction. Dual tags were added to samples (Illumina dual indexing kits v1‐3) using seven cycles of PCR. PCR products were further purified using magnetic beads. The DNA was quantified using a Qubit fluorometer and equimolar pooled into libraries of 285 and 250 samples each. Mock community samples with eight fungal strains were sequenced along with the experimental samples. Sequencing was performed using Illumina MiSeq pair‐end 2x300bp. Here we give the OTU table and taxa files as well as report all OTUs unique to one site. Soil Chemistry: Chemical soil properties were determined by AgroCares BV (Wageningen, the Netherlands). Soils for chemical analysis were dried at 50°C using fruit dryers, crushed and sieved (2 mm sieve). One part of the soil sample was homogenized and pulverized (

Designing cropping systems with low yield variability (or high yield stability) is becoming increasingly important because of the ongoing climatic and agronomic challenges. The trends in yield variability under various agronomic managements can be evaluated by conducting long-term experiments. By using a novel statistical analysis method, we estimated the long-term yield variability trends for winter wheat and spring barley grown in the Askov Long-term Experiment (Denmark) with different rates of mineral fertilizers (½, 1, and 1½ NPK) and animal manure (½, 1, and 1½ AM). Yield data from 1932 to 2019 were analyzed using a mixed model approach with restricted maximum likelihood (REML)-based parameter estimates. Across all nutrient treatments, winter wheat showed lower temporal yield variability than spring barley in the first decade. However, particularly, since 2006, the wheat yield variability trend increased mainly under treatments with higher NPK rates (1 and 1½). Spring barley also showed an increasing trend in yield variability; however, compared to wheat, this trend was less pronounced. Therefore, wheat yields were less stable than barley yields during the last decade. Wheat and barley yields fluctuated more under higher NPK rates (1 and 1½) than under a reduced rate (½ NPK). In general, animal manure provided more stable yields than NPK for wheat as well as for barley. The long-term trends in yield variability of cropping systems with winter wheat and spring barley were affected by the choice of crop, nutrient source and application rate, and increasing climatic variability.

Two insurance companies I 1 , I 2 with reserves R 1 ( t ) , R 2 ( t ) compete for customers, such that in a suitable stochastic differential game the smaller company I 2 with R 2 ( 0 ) R 1 ( 0 ) aims at minimizing R 1 ( t ) − R 2 ( t ) by using the premium p 2 as control and the larger I 1 at maximizing by using p 1 . The dependence of reserves on premia is derived by modelling the customer’s problem explicitly, accounting for market frictions V , reflecting differences in cost of search and switching, information acquisition and processing, or preferences. Assuming V to be random across customers, the optimal simultaneous choice p 1 ∗ , p 2 ∗ of premiums is derived and shown to provide a Nash equilibrium for beta distributed V . The analysis is based on the diffusion approximation to a standard Cramer–Lundberg risk process extended to allow investment in a risk-free asset.

We determined the 13C/ 12C ratio (expressed as δ 13C ‰) of microbial biomass and nematode trophic groups in a small-plot field experiment with soil converted from C3- to C4-crop (silage maize) 20 years ago. During this period, the plots were subjected to three different organic input treatments: 1) maize stubbles and roots left after harvest (MS), 2) MS plus annual addition of aboveground maize biomass (MS + B), and 3) MS plus annual addition of faeces from sheep fed exclusively with maize (MS + F). The different δ 13C value of C3- and C4-crops allowed us to distinguish between old (>20 years old) C3-derived C and recent (13C value of phytophagous nematodes closely matched that of the maize. Bacterivorous nematodes had higher δ 13C values than fungivorous nematodes and microbial biomass indicating that the C sources of bacterivorous nematodes are more recent than those of fungivorous nematodes and microbial biomass. At low abundance of fungivorous nematodes (MS and MS + F), the microbial biomass had higher δ 13C values than the fungivorous nematodes, whereas their δ 13C values were comparable at higher densities of fungivorous nematodes (MS + B). The higher C4-derived input in MS + F and MS + B treatments increased the δ 13C values of bacterivorous nematodes and microbial biomass. In MS and MS + B treatments, recent C4-derived C accounted for 50 and 70% of microbial biomass-C, respectively. Corresponding values for fungivorous and bacterivorous nematodes were 30 and 75%, and 65 and 85%, respectively. We conclude that fungal-based decomposition pathways contribute more to the turnover of old soil C than bacterial-based decomposition. A substantial fraction of the microbial biomass and fungivorous nematode C in the MS treatment (50 and 70%, respectively) was C deposited in the soil more than 20 years ago, confirming that decade-old SOC remains biologically active.

Summary: Converting arable land to permanent grassland remains an efficient option for increased carbon (C) storage in agricultural land. We quantified changes in C and nitrogen (N) in topsoil from the Sandmarken experiment (initiated in 1894 in Denmark) before and after its conversion to semi-natural grassland in 1998. Because of different fertilizer application in the arable phase, the grass was established on soils with different initial fertility. Archived soils sampled during 1942–2012 from plots subjected to different treatments in the arable phase were analysed for C, N, 13 C and 15 N. With crop yields, topsoil C contents and the C-TOOL model, we estimated mean C inputs in the arable phase of 0.4, 1.4 and 1.7 Mg C ha −1 year −1 for unmanured, mineral-fertilized and animal-manured plots, respectively, and C inputs in the grassland phase of 3.2–3.8 Mg C ha −1 year −1 . In the arable phase, topsoil showed mean losses of 0.10 Mg C and 0.012 Mg N ha −1 year −1 , whereas δ 13 C increased by 0.002‰ and δ 15 N by 0.013‰. Grassland establishment reverted losses of C and N to gains of 0.29 Mg C and 0.017 Mg N ha −1 year −1 ; δ 13 C now decreased by 0.065‰ and δ 15 N by 0.074‰. Fertilizer history did not affect these changes markedly. Converting this low-yielding sandy soil from arable to grassland use provided an overall annual gain of 0.39 Mg C and 0.029 Mg N ha −1 in the topsoil. Changes in δ 13 C and δ 15 N indicated a reduced rate of C turnover and a less leaky N cycle under grassland. Highlights: Assessed change in C and N storage with change in land use from arable to semi-natural grassland Overall soil C sequestration was 0.39 Mg C ha −1 year −1 because C loss was avoided from continued arable use Soil δ 13 C and δ 15 N decreased when arable land was converted into grassland In the grassland phase, the modelled C input was not affected by fertilizer history.

Partitioning soil organic carbon (SOC) into two kinetically different fractions that are centennially stable or active is key information for an improved monitoring of soil health and for a more accurate modelling of the carbon cycle. However, all existing SOC fractionation methods isolate SOC fractions that are mixtures of centennially stable and active SOC. If the stable SOC fraction cannot be isolated, it has specific chemical and thermal characteristics that are quickly (ca. 1 h per sample) measureable using Rock-Eval® thermal analysis. An alternative would thus be to (1) train a machine-learning model on the Rock-Eval® thermal analysis data of soil samples from long-term experiments where the size of the centennially stable and active SOC fractions can be estimated, and (2) apply this model on the Rock-Eval® data of unknown soils, to partition SOC into its centennially stable and active fractions. Here, we significantly extend the validity range of the machine-learning model published by Cécillon et al. [Biogeosciences, 15, 2835–2849, 2018, https://doi.org/10.5194/bg-15-2835-2018], and built upon this strategy. The second version of this statistical model, which we propose to name PARTYSOC, uses six European long-term agricultural sites including a bare fallow treatment and one South American vegetation change (C4 to C3 plants) site as reference sites. The European version of the model (PARTYSOCv2.0EU) predicts the proportion of the centennially stable SOC fraction with a conservative root-mean-square error of 0.15 (relative root-mean-square error of 0.27) in a wide range of agricultural topsoils from Northwestern Europe. We plan future expansions of the PARTYSOC global model using additional reference soils developed under diverse pedoclimates and ecosystems, and we already recommend the application of PARTYSOCv2.0EU in European agricultural topsoils to provide accurate information on SOC kinetic pools partitioning that may improve the simulations of simple models of SOC dynamics.

The plant availability of manure nitrogen (N) is influenced by manure composition in the year of application whereas some studies indicate that the legacy effect in following years is independent of the composition. The plant availability of N in pig and cattle slurries with variable contents of particulate matter was determined in a 3-year field study. We separated cattle and a pig slurry into liquid and solid fractions by centrifugation. Slurry mixtures with varying proportions of solid and liquid fraction were applied to a loamy sand soil at similar NH4+-N rates in the first year. Yields and N offtake of spring barley and undersown perennial ryegrass were compared to plots receiving mineral N fertilizer. The first year N fertilizer replacement value (NFRV) of total N in slurry mixtures decreased with increasing proportion of solid fraction. The second and third season NFRV averaged 6.5% and 3.8% of total N, respectively, for cattle slurries, and 18% and 7.5% for pig slurries and was not related to the proportion of solid fraction. The estimated net N mineralization of residual organic N increased nearly linearly with growing degree days (GDD) with a rate of 0.0058%/GDD for cattle and 0.0116%/GDD for pig slurries at 2000–5000 GDD after application. In conclusion NFRV of slurry decreased with increasing proportion of solid fraction in the first year. In the second year, NFRV of pig slurry N was significantly higher than that of cattle slurry N and unaffected by proportion between solid and liquid fraction.

We present a novel approach to analyzing stock return predictability that accommodates (i) arbitrary predictor persistence, (ii) panels with common factors, (iii) multiple predictors, (iv) short- and long-horizon analysis, and relies on standard inference from least-squares estimation of a suitably adjusted predictive regression. We analyze US and international equity premia and find that dividend- and earnings-related price ratios have negligible predictive power over long horizons, whereas the dividend yield has considerable predictive power over short horizons, with positive coefficients, consistent with present value theory. Long-term government bond yields exhibit predictive power over all horizons from one month through five years.

Using annual data from 1978 through 2016, and monthly data from January 2005 through November 2017 from Denmark, we provide a precise estimate of the upper bound on the potential impact of the adoption of wind energy on the reduction of CO2 emissions from energy production. We separate causal impacts from endogenous effects in regressions using instrumental variables including average wind speed, and from spurious effects in dynamic systems using impulse-response analysis and cointegration techniques. A one percentage point increase in the share of wind in total energy production is found to cause a reduction in CO2 emissions of the order 0.3%, based on endogeneity-corrected regression, and 0.5% over 2 years in a fractional vector error-correction model, after allowing the cumulative effects to take place. This corresponds to an upper bound estimate of 0.69 tonnes of CO2 emissions avoided per additional MWh of wind energy produced. We find that after a structural break at the time of introduction of the EU ETS and the Kyoto Protocol in 2005, the country has been on track towards meeting its long-term goals for emission reduction and green energy production, but not before.