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Poeplau C.,Swedish University of Agricultural Sciences | Poeplau C.,Thuenen Institute of Climate Smart Agriculture | Katterer T.,Swedish University of Agricultural Sciences | Bolinder M.A.,Swedish University of Agricultural Sciences | And 3 more authors.
Geoderma | Year: 2015

Soil organic carbon (SOC) storage can be increased by incorporating crop residues such as straw. However, the use of straw as a bioenergy source is an alternative option. There is currently great uncertainty concerning the effects of residue incorporation/removal, but estimates can be improved by using well-documented, frequently sampled long-term experiments (LTEs). This study examined the effect of straw incorporation on SOC stocks in six Swedish LTEs (duration of 27-56years), using data from 5 to 28 sampling occasions. A total of 16 pairs of straw incorporation (SI) and straw removal (SR) treatments were compared and modelled with the ICBM/2 model (two young pools with distinct humification coefficients, h), which enabled us to clearly isolate the effect of straw carbon input. The model results were compared to the Ultuna frame trial, as the first and only parameterization site of ICBM. At five out of six sites, the humification coefficient for straw (hlitter) was much smaller (0-0.09) than the ICBM default h value for plant material (0.125). The derived hlitter values and thus the stabilization of straw derived carbon increased significantly with clay content. An Italian site with five pairs of SI and SR treatments was used to test the performance of ICBM/2 under contrasting pedoclimatic conditions. Similar to the Swedish sites, the best model fits were found with hlitter values ranging from 0 to 0.05 increasing with nitrogen fertilization (range of 0-240kgNha-1yr-1), which was attributed to changes in substrate use efficiency of microbes. However, this trend was not consistent for all sites. For future applications of ICBM/2, we suggest using the validated clay function to derive hlitter for common levels of nitrogen fertilization. The efficiency of incorporating straw to increase SOC stocks depends on soil texture and using it for bioenergy production could be a more sustainable and climate-smart option. © 2014 Elsevier B.V.


Leiber-Sauheitl K.,Thuenen Institute of Climate Smart Agriculture | Fuss R.,Thuenen Institute of Climate Smart Agriculture | Burkart S.,Thuenen Institute of Climate Smart Agriculture | Buegger F.,Helmholtz Center Munich | And 4 more authors.
Soil Biology and Biochemistry | Year: 2015

Large areas of peatlands in Germany and the Netherlands are affected by drainage and high nitrogen deposition. Sheep grazing is a common extensive management activity on drained peatlands, in particular on nature protection areas. However, input of easily mineralisable material such as sheep excrements could enhance degradation of soil organic carbon (Corg), thereby increasing the effect of these ecosystems on national GHG budgets. Thus, a microcosm experiment on the influence of sheep excreta on GHG emissions from a histic Gleysol with strongly degraded peat was set up. The 15N and 13C stable isotope tracer technique was used to partition sources of CO2 and N2O. Labeled sheep faeces and urine were obtained by feeding enriched material. Undisturbed soil columns were treated with surface application of urine, faeces or mixtures of both in different label combinations to distinguish between direct effects and possible priming effects. Incubation was done under stable temperature and precipitation conditions. Fluxes as well as 15N and 13C enrichment of N2O and CO2, respectively, were measured for three weeks. Addition of sheep excreta increased emission of total CO2 in proportion to the added carbon amounts. There was no CO2 priming in the peat. No effect on CH4 and N2O was observed under the aerobic experimental conditions. The N2O-N source shifted from peat to excreta, which indicates negative priming, but priming was not significant. The results indicate that sheep excreta do not significantly increase GHG emissions from degraded peat soils. Considering the degraded peatland preserving benefits, sheep grazing on peatlands affected by drainage and high nitrogen deposition should be further promoted. © 2015 The Authors.


Poeplau C.,Thuenen Institute of Climate Smart Agriculture | Don A.,Thuenen Institute of Climate Smart Agriculture
GCB Bioenergy | Year: 2014

Bioenergy has to meet increasing sustainability criteria in the EU putting conventional bioenergy crops under pressure. Alternatively, perennial bioenergy crops, such as Miscanthus, show higher greenhouse gas savings with similarly high energy yields. In addition, Miscanthus plantations may sequester additional soil organic carbon (SOC) to mitigate climate change. As the land-use change in cropland to Miscanthus involves a C3-C4 vegetation change (VC), it is possible to determine the dynamic of Miscanthus-derived SOC (C4 carbon) and of the old SOC (C3 carbon) by the isotopic ratio of 13C to 12C. We sampled six croplands and adjacent Miscanthus plantations exceeding the age of 10 years across Europe. We found a mean C4 carbon sequestration rate of 0.78 ± 0.19 Mg ha-1 yr-1, which increased with mean annual temperature. At three of six sites, we found a significant increase in C3 carbon due to the application of organic fertilizers or difference in baseline SOC, which we define as non-VC-induced SOC changes. The Rothamsted Carbon Model was used to disentangle the decomposition of old C3 carbon and the non-VC-induced C3 carbon changes. Subsequently, this method was applied to eight more sites from the literature, resulting in a climate-dependent VC-induced SOC sequestration rate (0.40 ± 0.20 Mg ha-1 yr-1), as a step toward a default SOC change function for Miscanthus plantations on former croplands in Europe. Furthermore, we conducted a SOC fractionation to assess qualitative SOC changes and the incorporation of C4 carbon into the soil. Sixteen years after Miscanthus establishment, 68% of the particulate organic matter (POM) was Miscanthus-derived in 0-10 cm depth. POM was thus the fastest cycling SOC fraction with a C4 carbon accumulation rate of 0.33 ± 0.05 Mg ha-1 yr-1. Miscanthus-derived SOC also entered the NaOCl-resistant fraction, comprising 12% in 0-10 cm, which indicates that this fraction was not an inert SOC pool. © 2013 Blackwell Publishing Ltd.


Poeplau C.,Swedish University of Agricultural Sciences | Poeplau C.,Thuenen Institute of Climate Smart Agriculture | Bolinder M.A.,Swedish University of Agricultural Sciences | Kirchmann H.,Swedish University of Agricultural Sciences | Katterer T.,Swedish University of Agricultural Sciences
Biogeosciences | Year: 2016

Increasing soil organic carbon (SOC) in agricultural soils can mitigate atmospheric CO2 concentration and also contribute to increased soil fertility and ecosystem resilience. The role of major nutrients in SOC dynamics is complex, due to simultaneous effects on net primary productivity (NPP) that influence crop residue carbon inputs and in the rate of heterotrophic respiration (carbon outputs). This study investigated the effect on SOC stocks of three different levels of phosphorus and potassium (PK) fertilisation rates in the absence of nitrogen fertilisation and of three different levels of nitrogen fertiliser in the absence of PK fertiliser. This was done by analysing data from 10 meta-replicated Swedish long-term field experiments (> 45 years). With N fertilisation, SOC stocks followed yield increases. However, for all PK levels, we found average SOC losses ranging from -0.04 ± 0.09 Mg ha-1 yr-1 (ns) for the lowest to -0.09 ± 0.07 Mg ha-1 yr-1 (p = 0.008) for the highest application rate, while crop yields as a proxy for carbon input increased significantly with PK fertilisation by 1, 10 and 15 %. We conclude that SOC dynamics are mainly output-driven in the PK-fertilised regime but mostly input-driven in the N-fertilised regime, due to the much more pronounced response of NPP to N than to PK fertilisation. It has been established that P rather than K is the element affecting ecosystem carbon fluxes, where P fertilisation has been shown to (i) stimulate heterotrophic respiration, (ii) reduce the abundance of arbuscular mycorrhizal fungi and (iii) decrease the crop root: shoot ratio, leading to higher root-derived carbon input. The higher export of N in the PK-fertilised plots in this study could (iv) have led to increased N mining and thus mineralisation of organic matter. More integrated experiments are needed to gain a better understanding of the relative importance of each of the above-mentioned mechanisms leading to SOC losses after P addition. © 2016 Author(s).


Poeplau C.,Swedish University of Agricultural Sciences | Poeplau C.,Thuenen Institute of Climate Smart Agriculture | Eriksson J.,Swedish University of Agricultural Sciences | Katterer T.,Swedish University of Agricultural Sciences
Soil and Tillage Research | Year: 2015

Measurement of soil organic carbon (SOC) or other elements in air-dried soil samples leads to underestimation of mass fraction per unit dry soil (concentration) unless the residual water (RW) content is accounted for. However, RW measurements are time-consuming and costly and thus often neglected. The resulting bias can lead to dramatic erroneous results, especially when two differently treated datasets are compared. We therefore, derived pedotransfer functions to estimate residual water content in air-dried soil samples from: (i) SOC content, (ii) clay content and (iii) both variables together. The uncertainty of prediction decreased in the order (i)-(iii), with root mean squared deviation (RMSD) values of 0.64, 0.46 and 0.34% of RW content, respectively. These functions represent a potential step towards more harmonized and transparent SOC determination. © 2014 Elsevier B.V.


Poeplau C.,Thuenen Institute of Climate Smart Agriculture | Don A.,Thuenen Institute of Climate Smart Agriculture
Journal of Plant Nutrition and Soil Science | Year: 2014

Ultrasonic dispersion is a prevalent tool for soil fractionation. It is widely ignored that variation in ultrasonic power might lead to significantly different dispersion. We evaluated the effect of power variation with constant energy on the fine fraction mass, its organic C content and quality. All parameters increased significantly with power. The term "stable aggregates" as used in fractionation schemes cannot be defined by ultrasonic energy alone but power needs to be standardized, too. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Poeplau C.,Thuenen Institute of Climate Smart Agriculture
Plant and Soil | Year: 2016

Background and aims: Carbon inputs to soil are mostly site- and management-nonspecific estimates based on measured yield. However, in grasslands most carbon input is root-derived and plant carbon allocation patterns are known to vary strongly across sites and management regimes. The aim here was to estimate carbon inputs by fitting the RothC model to time series of soil organic carbon (SOC) data from field sites and to explain the observed variability in root: shoot ratio (R:S). Methods: Time series of SOC stocks in 15 different temperate grasslands were simulated using eight different literature-derived R:S values, which were compared to the optimised, site-specific R:S. The model-derived root inputs were validated with literature-derived root biomass data. Results: A single, static R:S for yield-based carbon input estimation for all grasslands was not appropriate. Nitrogen fertilisation (R2 = 0.57) significantly reduced the optimised R:S, which can be explained by the higher investment of plants in roots for nitrogen acquisition under nitrogen deficiency. The average R:S derived was 5.9 ± 1.9 for unfertilised soils and 2.4 ± 1.5 for fertilised soils. Conclusions: The results enable distinction of unfertilised and fertilised temperate grasslands regarding carbon input parameterisation for the RothC model and highlight the importance of nutrient regime for the carbon cycle. © 2016, Springer International Publishing Switzerland.


Poeplau C.,Thuenen Institute of Climate Smart Agriculture | Poeplau C.,Swedish University of Agricultural Sciences | Don A.,Thuenen Institute of Climate Smart Agriculture
Agriculture, Ecosystems and Environment | Year: 2015

A promising option to sequester carbon in agricultural soils is the inclusion of cover crops in cropping systems. The advantage of cover crops as compared to other management practices that increase soil organic carbon (SOC) is that they neither cause a decline in yields, like extensification, nor carbon losses in other systems, like organic manure applications may do. However, the effect of cover crop green manuring on SOC stocks is widely overlooked. We therefore conducted a meta-analysis to derive a carbon response function describing SOC stock changes as a function of time. Data from 139 plots at 37 different sites were compiled. In total, the cover crop treatments had a significantly higher SOC stock than the reference croplands. The time since introduction of cover crops in crop rotations was linearly correlated with SOC stock change (R2=0.19) with an annual change rate of 0.32±0.08Mgha-1yr-1 in a mean soil depth of 22cm and during the observed period of up to 54 years. Elevation above sea level of the plot and sampling depth could be used as explanatory variables to improve the model fit. Assuming that the observed linear SOC accumulation would not proceed indefinitely, we modeled the average SOC stock change with the carbon turnover model RothC. The predicted new steady state was reached after 155 years of cover crop cultivation with a total mean SOC stock accumulation of 16.7±1.5Mgha-1 for a soil depth of 22cm. Thus, the C input driven SOC sequestration with the introduction of cover crops proved to be highly efficient. We estimated a potential global SOC sequestration of 0.12±0.03PgCyr-1, which would compensate for 8% of the direct annual greenhouse gas emissions from agriculture. However, altered N2O emissions and albedo due to cover crop cultivation have not been taken into account here. Data on those processes, which are most likely species-specific, would be needed for reliable greenhouse gas budgets. © 2014 Elsevier B.V.


Bolinder M.A.,Swedish University of Agricultural Sciences | Katterer T.,Swedish University of Agricultural Sciences | Poeplau C.,Swedish University of Agricultural Sciences | Poeplau C.,Thuenen Institute of Climate Smart Agriculture | And 2 more authors.
Canadian Journal of Soil Science | Year: 2015

Root crops are significant in agro-ecosystems of temperate climates. However, the amounts of crop residues for these crop types are not well documented and they need to be accounted for in the modeling of soil organic carbon dynamics. Our objective was to review field measurements of root biomass left in the soil as crop residues at harvest for potato and sugar beet. We considered estimates for crop residue inputs as root biomass presented in the literature and some unpublished results. Our analysis showed that compared to, for example, cereals, the contribution of below-ground net primary productivity (NPP) to crop residues is at least two to three times lower for root crops. Indeed, the field measurements indicated that root biomass for topsoils only represents on average 25 to 30 g dry matter (DM) m-2 yr-1. Other estimates, albeit variable and region-specific, tended to be higher. We suggest relative plant DM allocation coefficients for agronomic yield (RP), above-ground biomass (RS) and root biomass (RR) components, expressed as a proportion of total NPP. These coefficients, representative for temperate climates (0.739:0.236:0.025 for potato and 0.626:0.357:0.017 for sugar beet), should be useful in the modeling of agro-ecosystems that include root crops. © 2015, Routledge. All rights reserved.


Poeplau C.,Swedish University of Agricultural Sciences | Poeplau C.,Thuenen Institute of Climate Smart Agriculture | Herrmann A.M.,Swedish University of Agricultural Sciences | Katterer T.,Swedish University of Agricultural Sciences
Soil Biology and Biochemistry | Year: 2016

Nitrogen (N) and phosphorus (P) availability plays a crucial role for carbon cycling in terrestrial ecosystems. However, the effect of nutrient supply on soil organic matter decomposition and microbial metabolism is generally not well understood. In this study, we incubated soils with three contrasting nutrient regimes from each of three Swedish long-term agricultural experiments (>45 years, 7-30% clay), namely an unfertilised control (0NPK), high P but no N fertilisation (PK0N) and high N but no P fertilisation (N0PK). In the laboratory, we amended all soils with no fertiliser or with N, P and N + P, with and without glucose, and monitored CO2 and heat production over five hours. Significant effects of the treatments were observed when nutrients were added in combination with glucose. Averaged over all field treatments, Glucose + N addition reduced CO2 and heat production by 14% and 14%, respectively, compared with glucose addition alone, while glucose + P addition increased CO2 and heat production by 17% and 9%, respectively. Similar results were found comparing the contrasting long-term field-treatments: PK0N showed higher glucose-induced CO2 and heat production per unit SOC than 0NPK, while both variables were suppressed in N0PK-fertilised soils. Basal respiration per unit soil organic carbon (SOC) proved to be linked to long-term losses in SOC stocks, which were highest in the PK0N-fertilised plots at all three sites. Combined analyses of field and laboratory treatments revealed that the suppressing effect of laboratory N-addition on respiration only occurred in N-deficient soils, which clearly indicates that long-term N-addition alleviated N-mining. In conclusion, N and P showed opposing effects on the microbial metabolic processes, including respiration. The observed effects were similar in the short- and long-term and across different sites, which suggests that direct physiological controls of nutrients on microbial metabolism strongly regulate SOC turnover. Short-term nutrient effects were only observed in combination with a labile C source and the N-effect was restricted to N-deficient soils. Therefore, we conclude that those findings might be more important for nutrient-poor but carbon-rich ecosystems exposed to sudden nutrient inputs in comparison with nutrient rich and relatively carbon poor agricultural systems. © 2016 Elsevier Ltd.

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