Long-term Agricultural Field Experiments Research Articles

A new Rothamsted long-term field experiment for the twenty-first century: principles and practice

Agriculture faces potentially competing societal demands to produce food, fiber and fuel while reducing negative environmental impacts and delivering regulating, supporting and cultural ecosystem services. This necessitates a new generation of long-term agricultural field experiments designed to study the behavior of contrasting cropping systems in terms of multiple outcomes. We document the principles and practices of a new long-term experiment of this type at Rothamsted, established at two contrasting sites in 2017 and 2018, and report initial yield data at the crop and system level. The objective of the Large-Scale Rotation Experiment was to establish gradients of system properties and outcomes to improve our fundamental understanding of UK cropping systems. It is composed of four management factors—phased rotations, cultivation (conventional vs reduced tillage), nutrition (additional organic amendment vs standard mineral fertilization) and crop protection (conventional vs smart crop protection). These factors were combined in a balanced design resulting in 24 emergent cropping systems at each site and can be analyzed at the level of the system or component management factors. We observed interactions between management factors and with the environment on crop yields, justifying the systems level, multi-site approach. Reduced tillage resulted in lower wheat yields but the effect varied with rotation, previous-crop and site. Organic amendments significantly increased spring barley yield by 8% on average though the effect again varied with site. The plowed cropping systems tended to produce higher caloric yield overall than systems under reduced tillage. Additional response variables are being monitored to study synergies and trade-offs with outcomes other than yield at the cropping system level. The experiment has been established as a long-term resource for inter-disciplinary research. By documenting the design process, we aim to facilitate the adoption of similar approaches to system-scale agricultural experimentation to inform the transition to more sustainable cropping systems.

Disentangling the impact of contrasting agricultural management practices on soil microbial communities – Importance of rare bacterial community members

Agriculture has a strong effect on soil microbial communities, but it is still unclear how different management practices drive their diversity and composition. To disentangle the effects of temporally contrasting crop management practices on soil microbial abundance and prokaryotic diversity, we analysed samples from a long-term agricultural field experiment, in which plant residues were exported (RE) or returned to soil, i.e., restituted (RR), over a period of 60 years. For 2.5 years, we followed a cropping sequence of maize, winter wheat and barley, in which, as an additional treatment, wheat cultivation was diversified once with pea intercropping. Based on soil-extracted DNA, abundances of bacteria, archaea and fungi were analysed by domain-specific qPCR and the diversity and composition of the prokaryotic community by 16S rRNA gene amplicon sequencing. The abundance of bacteria and fungi, but not for archaea, increased with the long-term restitution, but this effect was only detectable in spring due to their stabilized abundance during winter. The long-term effect of crop restitution on bacterial diversity became tangible when rare and dominant community members were differentiated, with higher sensitivity shown for the rare. In contrast, the cropping sequence equally affected members of both groups. The short-term effect of crop diversification by intercropping was much stronger in the C-depleted RE soils, than in RR soils where the C-loss was compensated, indicating that crop residue restitution increased the environmental resilience of soil microbial communities. Finally, we could confirm that rare bacterial community members, suspected to represent more oligotrophs and synergistic bacteria, formed stronger network structures to each other than the dominant, suspected to be more copiotrophic and competitive. Therefore, our results emphasize the importance to consider the response of rare microbial community members when evaluating long-term effects of agricultural management on the soil microbiome.

Cropping systems impact changes in soil fungal, but not prokaryote, alpha-diversity and community composition stability over a growing season in a long-term field trial.

Crop harvest followed by a fallow period can act as a disturbance on soil microbial communities. Cropping systems intended to improve alpha-diversity of communities may also confer increased compositional stability during succeeding growing seasons. Over a single growing season in a long-term (18 year) agricultural field experiment incorporating conventional (CON), conservation (CA), organic (ORG) and integrated (INT) cropping systems, temporal changes in prokaryote, fungal and arbuscular mycorrhizal fungi (AMF) communities were investigated overwinter, during crop growth and at harvest. While certain prokaryote phyla were influenced by cropping system (e.g. Acidobacteria), the community as a whole was primarily driven by temporal changes over the growing season as distinct overwinter and crop-associated communities, with the same trend observed regardless of cropping system. Species-rich prokaryote communities were most stable over the growing season. Cropping system exerted a greater effect on fungal communities, with alpha-diversity highest and temporal changes most stable under CA. CON was particularly detrimental for alpha-diversity in AMF communities, with AMF alpha-diversity and stability improved under all other cropping systems. Practices that promoted alpha-diversity tended to also increase the similarity and temporal stability of soil fungal (and AMF) communities during a growing season, while prokaryote communities were largely insensitive to management.

Detectability of degradable organic matter in agricultural soils by thermogravimetry

AbstractSustainable agricultural land use requires an assessment of degradable soil organic matter (SOM) because of its key function for soil fertility and plant nutrition. Such an assessment for practical land use should consider transformation processes of SOM and its sources of different origin. In this study, we combined a 120‐day incubation experiment with thermal decay dynamics of agricultural soils altered by added organic amendments. The aim was to determine the abilities and limits of thermal analysis as a rapid approach revealing differences in the degradability of SOM. The carried out experiments based on two independent sampling sets. The first sample set consisted of soil samples taken from non‐fertilized plots of three German long‐term agricultural field experiments (LTAEs), then artificially mixed with straw, farmyard manure, sheep faeces, and charcoal equal to 60 Mg ha−1 under laboratory conditions. The second sample set based on soil samples of different treatments (e.g., crop type, fertilization, cultivation) in LTAEs at Bad Lauchstädt and Müncheberg, Germany. Before and after the incubation experiment, thermal mass losses (TML) at selected temperatures were determined by thermogravimetry indicating the degradability of organic amendments mixed in soils. The results confirmed different microbial degradability of organic amendments and SOM under laboratory conditions. Thermal decay dynamics revealed incubation‐induced changes in the artificial soil mixtures primarily at TML around 300°C in the case of applied straw and sheep faeces, whereas farmyard manure showed mainly changes in TML around 450°C. Charcoal did not show significant degradation during incubation, which was confirmed by TML. Detailed analyses of the artificial soil mixtures revealed close correlations between CO2‐C evolution during incubation and changes in TML at 300°C with R2 > 0.96. Results of the soils from LTAEs showed similar incubation‐induced changes in thermal decay dynamics for fresh plant residues and farmyard manure. We conclude that the practical assessment of SOM could be facilitated by thermal decay dynamics if modified sample preparation and evaluation algorithms are used beyond traditional peak analysis.

Pools and solubility of soil phosphorus as affected by liming in long-term agricultural field experiments

Published laboratory studies suggest minimum solubility of soil phosphorus (P) in the pH range traditionally considered as the target for lime applications on agricultural land. However, the potential significance of these results for the timescale relevant in practical agriculture remains to demonstrate. We revisited four long-term (50–76years) agricultural lime experiments located on Quaternary deposits with topsoil texture ranging from silt loam to silty clay and initial pH between 5.0 and 6.0. Crop uptake data and desorption experiments in the laboratory indicated that liming enhanced the solubility of P added with fertiliser in the decades following the application of lime. An empirical mass-balance model demonstrated that changes in acetate-lactate extractable P (‘P-AL’), previously shown to be related to reactive phosphate adsorbed on soil mineral surfaces, was proportional to field P balances (fertiliser P – harvested P) and inversely proportional to the net proton load to the soil. Extraction data suggest that liming enhanced the incorporation of silica in non-crystalline sesquioxides, which in turn inhibited the conversion of fertiliser P into less extractable forms by migration of P to inside the oxides. Liming induced a lowering of the C/N ratio in one of the experiments, suggesting stimulated decomposition of soil organic matter. However, lime applications did not lead to a decline in the pool of soil organic P, as measured by the combustion method. Mass-balance considerations showed that changes in organic-matter input due to liming were unlikely to result in observable changes in the pool of soil organic P.

Which agricultural management interventions are most influential on soil organic carbon (using time series data)?

Loss of soil organic carbon (SOC) from agricultural land is identified as one of the major threats to soils, as it influences both fertility and the production of ecosystem services from agriculture. Losses of SOC across regions are often determined by monitoring in different land use systems. Results from agricultural field experiments can reveal increasing SOC stocks after implementation of specific management practices compared to a control, though in time series experiments the relative rate of change is often negative and implying an overall loss. Long-term agricultural field experiments are indispensable for quantifying absolute changes in SOC stocks under different management regimes. Since SOC responses are seldom linear over time, time series data from these experiments are particularly valuable. This systematic review is based on studies reporting time series data collated in a recently completed systematic map on the topic restricted to the warm temperate climate zone and the snow climate zone. These 53 studies were identified and selected systematically according to CEE guidelines. An update of the original search for studies will be repeated using Web of Science and Google Scholar to include newly published academic and grey literature in the time since the original search was performed in September 2013. Studies will be subject to critical appraisal of the internal and external validity, followed by full data extraction (meta-data describing study settings and quantitative study results). Where possible, studies will be included in a quantitative synthesis using time series meta-analytical approaches. The implications of the meta-analytical findings will be discussed in terms of policy, practice and research along with a discussion of the nature of the evidence base.

Carbon input and crop-related changes in microbial biomarker levels strongly affect the turnover and composition of soil organic carbon

It is increasingly recognized that a detailed understanding of the impacts of land use on soil carbon pools and microbially mediated carbon dynamics is required in order to accurately describe terrestrial carbon budgets and improve soil carbon retention. Toward this understanding, we analyzed the levels of biomarkers including phospholipid fatty acids, amino acids, monosaccharides, amino sugars, and several indicators of labile and stabilized carbon in soil samples from a long-term agricultural field experiment. Our results imply that the composition of soil organic carbon (SOC) strongly depends on both the applied fertilization regime and the cultivated crop. In addition, our approach allowed us to identify possible mechanisms of microbial growth and contributions to soil carbon storage under different long-term agricultural management regimes.Amino acids and monosaccharides were quantitatively the most dominant biomarkers and their levels correlated strongly positively with microbial biomass. The relative contributions of the studied biomarkers to the total SOC varied only slightly among the treatments except in cases of extreme fertilization and without any fertilizer. In case of extreme fertilization and with alfalfa as crop type, we found evidence for accumulation of microbially derived monosaccharides and amino acids within the labile OC pool, probably resulting from soil C saturation. Interestingly, we also found an accumulation of microbially derived monosaccharides and amino acids in completely unfertilized plots, which we assumed to be caused by the smaller pore space volume and subsequent oxygen limitation for microbial growth. Mineral fertilization also had substantial effects on soil organic N when applied to plots containing alfalfa, a leguminous plant. Our results demonstrate that over-fertilization, fertilizer type, and the cultivated crop type can have major impacts on the turnover and composition of soil organic carbon, and should be considered when assessing management effects on soil C dynamics.

Testing for soil carbon saturation behavior in agricultural soils receiving long-term manure amendments

Feng, W., Xu, M., Fan, M., Malhi, S. S., Schoenau, J. J., Six, J. and Plante, A. F. 2014. Testing for soil carbon saturation behavior in agricultural soils receiving long-term manure amendments. Can. J. Soil Sci. 94: 281–294. Agricultural soils are typically depleted in soil organic matter compared with their undisturbed counterparts, thus reducing their fertility. Organic amendments, particularly manures, provide the opportunity to restore soil organic matter stocks, improve soil fertility and potentially sequester atmospheric carbon (C). The application of the soil C saturation theory can help identify soils with large C storage potentials. The goal of this study was to test whether soil C saturation can be observed in various soil types in agricultural ecosystems receiving long-term manure amendments. Seven long-term agricultural field experiments from China and Canada were selected for this study. Manure amendments increased C concentrations in bulk soil, particulate organic matter+sand, and silt+clay fractions in all the experiments. The increase in C concentrations of silt+clay did not fit the asymptotic regression as a function of C inputs better than the linear regression, indicating that silt+clay did not exhibit C saturation behavior. However, 44% of calculated C loading values for silt+clay were greater than the presumed maximal C loading, suggesting that this maximum may be greater than 1 mg C m−2for many soils. The influences of soil mineral surface properties on C concentrations of silt+clay fractions were site specific. Fine soil particles did not exhibit C saturation behavior likely because current C inputs were insufficient to fill the large C saturation deficits of intensely cultivated soils, suggesting these soils may continue to act as sinks for atmospheric C.

Microplate-scale fluorometric soil enzyme assays as tools to assess soil quality in a long-term agricultural field experiment

We investigated the potential of microplate-scale fluorometric soil enzyme assays to differentiate plots under contrasting long-term organic and mineral N fertilization regimens to determine the relevance of this analytical approach to soil quality related studies.Enzymes involved in the breakdown of cellulose and hemicellulose showed maximum activities in plots amended with manure. Conversely, the enzymes involved in the hydrolysis of starch and phosphate esters peaked under mineral N fertilization. Linear regression analysis indicated close associations between enzyme activities and other fundamental soil properties related to soil quality, and principal component analysis separated the soil samples according to their responses to organic and mineral N fertilization. We conclude that microplate-scale fluorimetry is a fast throughput tool for the measurement of multiple soil enzyme activities as soil quality indicators.

Fungal community structure in soils of conventional and organic farming systems

Abstract Analysis of soil microbiota may help to describe and understand effects of agricultural management on soil quality. In the present study, effects on soil fungal communities were analysed in the DOK long-term agricultural field experiment in Switzerland. The temporally shifted 7-yr crop rotation allowed evaluation of the temporal stability of effects of organic and conventional farming systems. The influence of farming systems, crops and time on soil fungal community structures was compared between 2000 and 2007 using ribosomal internal spacer analysis. Richness of the fungal communities remained largely stable at the two different sampling dates, whereas the abundance of individual components changed. Despite this temporal stability, the most pronounced difference in the fungal communities was between the two sampling time points, whereas the influence of crops and farming systems were smaller. The time effect may be mainly induced by system-independent factors including changes in climatic conditions but also by system-dependent factors such as changes in preceding crops and farmyard manure characteristics between 2000 and 2007.

Ranking the magnitude of crop and farming system effects on soil microbial biomass and genetic structure of bacterial communities

Biological soil characteristics such as microbial biomass, community structures, activities, and functions may provide important information on environmental and anthropogenic influences on agricultural soils. Diagnostic tools and detailed statistical approaches need to be developed for a reliable evaluation of these parameters, in order to allow classification and quantification of the magnitude of such effects. The DOK long-term agricultural field experiment was initiated in 1978 in Switzerland for the evaluation of organic and conventional farming practices. It includes three representative Swiss farming systems with biodynamic, bio-organic and conventional fertilization and plant protection schemes along with minerally fertilized and unfertilized controls. Effects on microbial soil characteristics induced by the long-term management at two different stages in the crop rotation, i.e. winter wheat after potato or corn, were investigated by analyzing soil bacterial community structures using analysis of PCR-amplified rRNA genes by terminal restriction fragment length polymorphism and ribosomal intergenic spacer analysis. Application of farmyard manure consistently revealed the strongest influence on bacterial community structures and biomass contents. Effects of management and plant protection regimes occurred on an intermediate level, while the two stages in the crop rotation had a marginal influence that was not significant.

Identification and Specific Detection of a Novel Pseudomonadaceae Cluster Associated with Soils from Winter Wheat Plots of a Long-Term Agricultural Field Experiment

The genus Pseudomonas (sensu stricto) represents a group of microorganisms directly involved in functions conferring plant health. We performed a study in the DOK long-term agricultural field experiment on the basis of previously published Pseudomonas-selective PCR primers in order to investigate the community structure of the microbial groups defined by the target range of these primers. Three different agricultural management systems, i.e., conventional, biodynamic, and bio-organic, along with mineral and unfertilized controls were investigated, with each system planted with either winter wheat or a grass-clover ley. Amplified small-subunit rRNA gene fragments were analyzed using the genetic profiling techniques restriction fragment length polymorphism (RFLP) and denaturing gradient gel electrophoresis (DGGE), revealing distinct differences between soils planted with winter wheat and grass clover but only minor differences between the management systems. Phylogenetic analyses of 59 clone sequences retrieved from bio-organic and unfertilized systems identified sequences related to Pseudomonas fluorescens and a novel cluster termed Cellvibrio-related Pseudomonadaceae (CRP). The CRP clones were exclusively isolated from winter wheat soil samples and were responsible for the crop-specific differences observed in RFLP and DGGE profiles. New primers were designed for the amplification of CRP targets directly from soil DNA, yielding strong signals exclusively for winter wheat soils. We concluded that crop-associated CRP exist in agricultural soils and that genetic profiling followed by specific probe design represents a valuable approach for identification as well as sensitive and rapid monitoring of novel microbial groups in the environment.

Management effects on topsoil carbon and nitrogen in Swedish long-term field experiments—budget calculations with and without humus pool dynamics

The annual input and output of nitrogen (N) to and from agricultural land is relatively small compared with the total stock of organic N in soil. However, the long-term humus N pool dynamics is seldom considered in fertilisation planning, and thus N surpluses in budgets are considered as losses. In this paper, we analyse the consequences of this assumption and investigate how observed data precision affect the precision of model projections. We used available data sets from long-term agricultural field experiments in Sweden (topsoil C and N concentrations, crop yields as well as soil type and climate data) for calculating topsoil C and N mass dynamics. ICBM/2N, a simple C and N soil model (available at: www.mv.slu.se/vaxtnaring/olle/ICBM.html), was used for calculating soil organic matter balances. We parameterised this model for two field trials, and for specific crops, using available data and educated guesses and compared the results with those obtained from the conventional approach, not including humus pool C and N dynamics. In spite of the corrections for bulk densities, etc., the soil carbon measurements were too variable for a critical model validation or a sensitive test of the effects of including pool dynamics. In other words, we had to rely on the model assumptions for the projections and soil data could only be used to obtain general means, e.g., for the whole duration of the experiment. We think this is a general problem, not limited to this data set and model. We also show, at least in principle, how estimates of organic N pool dynamics can be used to produce improved N balance sheets for individual crops. For example, the apparent N use efficiency by sugar beet increased from 58 to 99% when organic N pool dynamics were included.

Nitrogen distribution and 15N natural abundances in particle size fractions of a long-term agricultural field experiment

The present study combined a physical fractionation procedure with the determination of the natural abundance of 15N to investigate the impact of organic manure and mineral fertilizer application, and fallow on changes of N associated with different soil particle size fractions. The long-term field experiment was conducted since 1956 in Ultuna, Sweden, on an Eutric Cambisol. Nitrogen in bulk soil and in particle size fractions changed significantly since 1956. The Nt concentrations in bulk soil decreased in all treatments not receiving organic materials. Comparing the N contribution of particle-size fractions to the total N amount revealed the following ranking: silt > clay > fine clay > fine sand > coarse sand. The relative contribution of N in silt sized particles significantly increased from low to high bulk soil N contents, whereas N in clay and fine clay fractions decreased. The C : N ratios of particle size fractions differed considerably more between treatments than C : N ratios in bulk soils. Generally, the C : N ratios decreased from coarse to fine fractions emphasizing the tendency of smaller fractions being more significant as N sink than as Corg sink. 15N abundances varied more between particle size fractions of single treatments than between bulk soil from differently treated plots. Within treatments we observed differences of up to 7.1 ‰ between particle size fractions. In most cases δ 15N values increased with decreasing particle sizes. This pattern on average was similar to changes in δ 13 C. Our results suggest that silt sized particles acted as medium-term sink of introduced N and that 15N abundances in particle size fractions sensitively reflect changes in N status in response to soil management. N-Verteilung und natürliche 15N-Häufigkeiten in Korngrößenfraktionen in einem landwirtschaftlichen Langzeitfeldversuch Die gegenwärtige Studie basiert auf einer physikalischen Fraktionierung in Kombination mit der Bestimmung der natürlichen Häufigkeiten von 15N in Korngrößenfraktionen von Böden eines Kleinparzellenversuches in Ultuna, Schweden, der 1956 auf einer eutrophen Braunerde angelegt wurde. Ziel dabei war es, den Einfluss unterschiedlicher organischer Materialien und eines mineralischen Düngers und der Dauerschwarzbrache auf den N-Status der Böden zu untersuchen. Die Nt-Gehalte sanken im Oberboden in all jenen Behandlungen ab, die keine organischen Materialien erhielten. Die höchsten N-Mengen fanden sich in der Schlufffraktion gefolgt von Ton, Feinton, Feinsand und Grobsand. Der relative Beitrag von N in der Schlufffraktion stieg mit zunehmenden Nt-Gehalten des Gesamtbodens an, gleichzeitig nahmen die Beiträge der Tonfraktionen ab. Die C : N-Verhältnisse variierten wesentlich stärker zwischen Korngrößenfraktionen als zwischen den Böden verschiedener Behandlungen. Generell stieg das C : N-Verhältnis mit abnehmender Teilchengröße an, was die tendenziell größere Bedeutung der Feinfraktionen als N-Senke denn als Corg-Senke unterstreicht. Die δ 15N-Werte wurden stärker von der Partikelgröße als von den Behandlungen beeinflusst. Innerhalb der Behandlungen fanden wir Unterschiede von bis zu 7,1 ‰ zwischen Korngrößenfraktionen. In den meisten Fällen nahmen die δ 15N-Werte mit abnehmender Teilchengröße zu. Unsere Ergebnisse zeigten, dass Schluffpartikel als mittelfristige N-Senke bedeutsam sind und 15N-Häufigkeiten in Korngrößenfraktionen sehr sensitiv auf längerfristige Bewirtschaftungsänderungen reagieren.

A new approach to determine the total airborne N input into the soil/plant system using 15N isotope dilution (ITNI): results for agricultural areas in Central Germany.

The atmospheric deposition of nitrogen (N) in the environment is of great concern due to its impact on natural ecosystems including affecting vegetation, reducing biodiversity, increasing tree growth in forests, and the eutrophication of aquatic systems. Taking into account the average annual N emission into the atmosphere in Germany of about 2 million t N (ammonia/ammonium, NOx), and assuming homogeneous distribution throughout Germany, an average N deposition of 45 kg/ha x year can be calculated. Such high atmospheric N deposition could be confirmed by N balances from long-term field experiments in Central Germany (e.g., the Static Fertilization Experiment in Bad Lauchstädt). By contrast, estimates by standard methods indicate a deposition of only about 30 kg N/ha x year. This is because the standard methods are using wet-only or bulk collectors, which fail to take into account gaseous deposition and the direct uptake of atmospheric N by aerial plant parts. Therefore, a new system was developed using N isotope dilution methodology to measure the actual total atmospheric N input into a soil/plant system (Integrated Total Nitrogen Input, ITNI). A soil/plant system is labeled with [N]ammonium-[N]nitrate and the total input of airborne N is calculated from the dilution of this tracer by N from the atmosphere. An average annual deposition of 64 ± 11 kg/ha x year from 1994–2000 was measured with the ITNI system at the Bad Lauchst?dt research farm in the dry belt of Central Germany. Measurements in 1999/2000 at three other sites in Central Germany produced deposition rates of about 60 kg/ha x year. These data clearly show that the total atmospheric N deposition into the soil/plant system determined by the newly developed ITNI system significantly exceeds that obtained from standard wet-only and bulk collectors. The higher atmospheric N depositions found closely match those postulated from the N balances of long-term agricultural field experiments.

Agricultural site productivity: principles derived from long-term experiments and their implications for intensively managed forests

Long-term agricultural field experiments provide relevant information for questions being asked about the sustainability of managed forests, particularly as management regimes become more intensive. In this paper, concepts and criteria related to sustainable site productivity are reviewed and findings from a range of long-term agricultural field experiments are evaluated. Based on this evaluation, the following site productivity principles are identified: (1) soil organic matter is the link between most management systems and sustainable site productivity; (2) nutrient deficiencies can be corrected; (3) soil texture is a key variable affecting soil organic matter and site productivity; (4) return of crop residues enhances soil organic matter and site productivity; and (5) productive cropping systems have environmental benefits. While technological advances have proven to be highly successful for enhancing long-term crop yields, they also have the potential to mask underlying declines in site productivity. This hypothesis needs to be rigorously tested. Agricultural field experiments show that crop productivity can be sustained for long time periods when appropriate management approaches are applied. Management requirements to achieve sustainability differ, however, depending on site-specific edaphic and climatic characteristics and the needs of the crop. Site productivity principles derived from agricultural field studies are also highly relevant to sustaining site productivity of managed forests. Several characteristics of managed forests should be considered when extrapolating conclusions from agricultural experiments. These include harvest removals of biomass and nutrients, residue type and distribution, management and system characteristics, and soil types used. Many characteristics associated with even intensively managed forests are sought as goals of conservation cropping systems and should contribute toward sustaining long-term site productivity.

Long-term agricultural field experiments in Northern Europe: analysis of the influence of management on soil carbon stocks using the ICBM model

Land use in general and particularly agricultural practices can significantly influence soil carbon (C) storage. Changes in topsoil C mass measured in long-term agricultural field trials in Sweden and other Northern European countries were compiled and aggregated into seven treatment classes, including manured, fertilized and straw exported. The impact of crop rotations and management practices on C stocks in the topsoil was analyzed using both a static model and a dynamic soil carbon model (introductory C Balance Model; ICBM). ICBM consists of two state variables and four fluxes (governed by four rate-determining parameters), and one parameter, r e, combining most external factors affecting C mineralization (temperature, precipitation, drainage, etc.). Simple `front-end models' were used to estimate values for two of the parameters, i (annual C input) and h (humification coefficient) initially based on incomplete records from the field trials, official agricultural statistics and other literature. The r e parameter was then optimized for each class of treatments, using an algorithm for non-linear least squares. Initial soil C mass, present C inputs and abiotic conditions, such as soil temperature and moisture, were the deciding factors in whether C stocks declined or increased. Steady-state values calculated using the static and dynamic model were similar for both models, but differed greatly between treatment classes. For cereal-dominated cropping systems where the straw was removed, manure application increased steady-state values about three times (from 3 to 9 g C m −2), compared with corresponding treatments. Incorporation of straw resulted in intermediate steady-state values (5–6 g C m −2). C mineralization rates were highest in bare fallow treatments. For one class of soils, C retention in the soil was found to increase significantly with increasing clay content. The hypothesis that the climatic gradients in Northern Europe affect decomposition and primary production rates similarly, leading to the same soil C stocks, could not be rejected.