1,720,987 research outputs found
Decrease of soil organic matter stabilization with increasing inputs: Mechanisms and controls
No full textImplications of input estimation, residue quality and carbon saturation on the predictive power of the Rothamsted Carbon Model
No full textEffects of fertilisation and cropland management on soil organic carbon (SOC) dynamics can be assessed best in long-term experiments. Using data from the long-term fertilisation experiment in Puch, Germany (part of the series "Internationale Organische Stickstoff Dauerversuche", IOSDV), we tested the performance of the Rothamsted Carbon Model 26.3 (RothC). The objectives of this work were: (i) quantify the C-input and the efficiency of SOC stabilisation, (ii) test the performance of different input estimates on predictive power of the RothC and (iii) test implementations of residue quality and C-saturation on model predictions. The experiment is a full-factorial strip design, the factors being "organic amendment" and "level of N-fertiliser". Each treatment was replicated three times. The crop rotation is silage maize-winter wheat-winter barley. Five levels of the factor "organic amendment" were considered: (i) CON: no organic amendment; (ii) SLU: slurry application (on average 0.8 Mg C ha(-1) year(-1)); (iii) FYM: application of farmyard manure (30 to 40 Mg ha(-1) fresh mass every third year to maize, on average 1.0 Mg C ha(-1) year(-1)). (iv) STR: straw incorporation after harvest of wheat and barley (depending on straw yield on average 0.7 to 2.2 Mg C ha(-1) year(-1)): (v) STSL: slurry application plus straw incorporation (on average 1.1 to 2.4 Mg C ha(-1) year(-1)). All treatments (including CON) were combined with five different levels of N-fertilisation (N0 to N4), whereas N0 was nil N application and N4 averaged 177 kg N ha(-1) year(-1). N-rates increased gradually and differed depending on the crop. Starting values for SOC stocks (Mg hat) were measured in 1983 as a mean among N-rates for organic amendment treatments (CON: 42; SLU: 39.8; FYM: 40.5; STR 39.8; STSL: 40.5). SOC stocks (0-25 cm) in 2004 (35.5 to 46.6 Mg C ha(-1)) were in the order STSL> FYM = SLU > STR = CON (p <= 0.001). However, slightly different starting values indicated a higher loss of SOC after 21 years in the CON (11-14%) compared to the SIR treatments (1-10%). Effect of N-rate was not significant. The observed relation between change of SOC and C-input was quadratic (Y-O = -13.4 + 7.5x - 0.9x(2); R-2 = 0.74, p <= 0.001), which contrasted the linear relationship predicted by RothC (Y-P = -12.9 + 5.5x; R-2 = 0.97, p <= 0.0001). Serious deviation between observed and predicted relationship occurred above C-inputs of 2.5 Mg C ha(-1) year(-1). Mechanistic explanation (e.g. C-saturation or increased mineralisation by N-fertilisation) for the observation needs further exploration, but implication on regional estimates for C-accumulation for different cropland management scenarios is obvious: potential gain in SOC storage by increasing C-inputs may be overestimated, at least under conditions of the Puch site. Independent model predictions (i.e. no parameter adjustment and independent estimation and measurement of C-input) were successful for treatments without straw incorporation (CON, SLU, FYM). Using a regression between crop yields and crop residue input yielded better results than using a constant belowground-to-aboveground biomass ratio. SOC stocks of treatments STR and STSL were seriously overestimated by the model. Using a higher decomposability of crop residue improved result only marginally and required the change of a standard parameter. Using a simple implementation of C-saturtion improved predictions for STR and STSL but failed to simulate dynamics in all other treatments. Overall, our results showed that it is important to recognise that relation between SOC change and C-input is not necessarily linear. However, the RothC model predicted SOC dynamics well at lower input levels. Observation that a regression equation for input estimation is superior to a constant biomass ratio for modelling purposes has to be tested further. An implementation of residue quality or saturation capacity in the RothC model may be promising for a better mechanistic understanding of SOC dynamics. However, this requires careful calibration and will increase the number of parameters to be fitted. (C) 2011 Elsevier B.V. All rights reserved.Bayrische Landesanstalt fur Landwirtschaft, state of Bavaria, German
Soil microbiochemical properties as indicators for success of heathland restoration after military disturbance
No full textDecline of heathlands in Central Europe raises the question of successful restoration of degraded heathlands. We examined the impact of different restoration techniques oil soil microbial biomass carbon (C(mic)) and nitrogen (N(mic)) and enzyme activity on an abandoned military training site in the Luneburger Heaths. The aim was to determine which technique resulted in typical heathland soil conditions. The training site was ill use for about 50 years. Vegetation and soils were degraded in large areas. Restoration actions were: (1) spreading of heath plaggen (sods, containing the organic layer and a few centimetres mineral soil), (2) spreading of heath plaggen and grass seeds (Festuca filiformis Pourr.). (3) spreading of F. filiformis-seeds and (4) succession (episodical tree removal). Ten years after restoration. we measured pH, bulk density, abundance of roots, soil organic carbon (SOC), nitrogen (N(1)), phosphorus (P(1)) C(mic), N(mic) and acid phosphatase activity (AcP) in the first 10cm of the mineral soil. Four restoration treatments were compared with one reference site. The reference site is heathland located near the training site, where no military actions took place. At all disturbed sites, bulk density and pH proved to be higher than oil the reference site. Relative to the reference site, SOC storage reached from 37 to 91 per cent, regeneration of N(1) was slightly lower. In contrast to the advanced development of SOC and Nt, the regeneration of C(mic) and N(mic) was much lower (15-44 per cent). The succession site showed a low pool of SOC, Nt, C(mic) and N(mic), but microbial ratios indicated a less disturbed C- and N-cycle. AcP pronounced differences in nutrient demand between disturbed sites and reference. On this base, recommendations for restoration management were given. Copyright (C) 2008 John Wiley & Soils, Ltd
Measurement of organic and inorganic carbon in dolomite‐containing samples
No full textIt is still open to question which method is the best for quantifying organic carbon (OC) and inorganic carbon (IC) in soils containing dolomite. The aims of this study were (1) to compare the accuracy of a novel thermal gradient (ThG), the classical calcimeter (CALC) and the loss-on-ignition (LOI) methods on a reference sample set with known proportions of OC present as soil organic matter (SOM) and IC present as dolomite and (2) to compare the results of the different methods on a set of soil samples with different dolomite and SOM contents. The CALC and LOI methods rely on separate quantification or removal of IC by acid or heat, whereas IC and OC can be quantified in a single run by the ThG analysis. The ThG method was the most accurate method for the reference sample set, especially when dolomite contents were high. On the soil sample set, the ThG and CALC methods performed equally well, but only when two outliers were eliminated. The LOI method was not satisfactory for either sample set. Overall, ThG was the most reliable method for measuring IC and OC in dolomite-containing samples over a wide range of concentrations, but the more widely used CALC method was also acceptable
Higher subsoil carbon storage in species-rich than species-poor temperate forests
No full textForest soils contribute ca. 70% to the global soil organic carbon (SOC) pool and thus are an important element of the global carbon cycle. Forests also harbour a large part of the global terrestrial biodiversity. It is not clear, however, whether tree species diversity affects SOC. By measuring the carbon concentration of different soil particle size fractions separately, we were able to distinguish between effects of fine particle content and tree species composition on the SOC pool in old-growth broad-leaved forest plots along a tree diversity gradient (1-, 3- and 5-species). Variation in clay content explained part of the observed SOC increase from monospecific to mixed forests, but we show that the carbon concentration per unit clay or fine silt in the subsoil was by 30–35% higher in mixed than monospecific stands indicating a significant species identity or species diversity effect on C stabilization. Underlying causes may be differences in fine root biomass and turnover, in leaf litter decomposition rate among the tree species, and/or species-specific rhizosphere effects on soil. Our findings may have important implications for forestry offering management options through preference of mixed stands that could increase forest SOC pools and mitigate climate warming.Open-Access-Publikationsfonds 201
Decadal Nitrogen Fertilization Decreases Mineral‐Associated and Subsoil Carbon: A 32‐Year Study
No full textCrop residues and manure are important sources of carbon (C) for soil organic matter (SOM) formation. Crop residue return increases by nitrogen (N) fertilization because of higher plant productivity, but this often results only in minor increases of SOM. In our study, we show how N fertilization and organic C additions affected SOM and its fractions within a 32-year-long field-experiment at Puch, Germany. Five organic additions, no-addition (control), manure, slurry, straw and straw+slurry, were combined with three mineral N fertilization rates (no, medium and high fertilization), which resulted in 117-486Mg C-input ha(-1) y(-1). Topsoil (0-25cm) SOM content increased with N fertilization, mainly because of the C in free light fraction (f-LF). In contrast, subsoil (25-60cm) SOM decreased with N fertilization, probably because of roots' relocation in Ap horizon with N fertilization at the surface. Despite high inputs, straw contributed little to f-LF but prevented C losses from the mineral-associated SOM fraction (>16gcm(-3)) with N fertilization, which was observed without straw addition. Above (straw) and belowground (roots) residues had opposite effects on SOM fractions. Root C retained longer in the light-fractions and was responsible for SOM increase with N fertilization. Straw decomposed rapidly (from f-LF) and fueled the mineral-associated SOM fraction. We conclude that SOM content and composition depended not only on residue quantity, which can be managed by the additions and N fertilization, but also on the quality of organics. This should be considered for maintaining the SOM level, C sequestration, and soil fertility. Copyright (c) 2016 John Wiley & Sons, Ltd
Simultaneous measurement of soil organic and inorganic carbon: evaluation of a thermal gradient analysis
No full textThe best method for determining soil organic carbon (SOC) in carbonate-containing samples is still open to debate. The objective of this work was to evaluate a thermal gradient method (ThG), which can determine simultaneously inorganic carbon (SIC) and SOC in a wide range of soil samples. The determination of SOC by ThG (SOCThG) was compared to the following widespread standard methods: (1) acidification (ACI) as pretreatment and subsequent dry combustion (SOCACI) and (2) volumetric quantification of SIC by a calcimeter (CALC) and subtraction of the total carbon content as determined by dry combustion (SOCCALC). Precision (F test) and bias (t test) were tested on a subset of seven samples (n = 3). Comparison of the ThG and CALC methods was performed by regression analysis (n = 76) on samples representing a wide range of SOC (5.5 to 212.0 g kg(-1)) and SIC (0 to 59.2 g kg(-1)) contents. Tests on the replicated subset showed that the precision of ThG was not significantly different from ACI or CALC (F values < 39, n = 3) for SOC and SIC measurements. However, SOCACI and SOCCALC contents were systematically and significantly lower compared to SOCThG contents. The positive bias for SOCThG relative to SOCCALC contents appeared also in the regression analysis (given numbers +/- standard errors) of the whole data set (y = (4.67 +/- 0.70) + (0.99 +/- 0.01)x, R (2) = 0.99, n = 76). When performing a regression with carbonate-free samples, the bias between the methods was negative (-2.90 +/- 0.63, n = 29) but was positive in the set with carbonate-containing samples (3.95 +/- 1.41, n = 47). This observation corroborated the suspicion that the use of acid for carbonate decomposition can lead to an underestimation of SOC. All methods were suitable for differentiation between SIC and SOC, but the use of acid resulted in lower estimates of SOC contents. When comparing soil samples with different carbonate concentrations, the use of the ThG method is more reliable
Microbial decomposition of soil organic matter is mediated by quality and quantity of crop residues: mechanisms and thresholds
No full textCrop residue quality and quantity have contrasting effects on soil organic matter (SOM) decomposition, but the mechanisms explaining such priming effect (PE) are still elusive. To reveal the role of residue quality and quantity in SOM priming, we applied two rates (5.4-10.8 g kg(-1)) of C-13-labeled wheat residues (separately: leaves, stems, roots) to soil and incubated for 120 days. To distinguish PE mechanisms, labeled C was traced in CO2 efflux and in microbial biomass and enzyme activities (involved in C, N, and P cycles) were measured during the incubation period. Regardless of residue type, PE intensity declined with increasing C additions. Roots were least mineralized but caused up to 60% higher PE compared to leaves or stems. During intensive residue mineralization (first 2-3 weeks), the low or negative PE resulted from pool substitution. Thereafter (15-60 days), a large decline in microbial biomass along with increased enzyme activity suggested that microbial necromass served as SOM primer. Finally, incorporation of SOM-derived C into remaining microbial biomass corresponded to increased enzyme activity, which is indicative of SOM cometabolism. Both PE and enzyme activities were primarily correlated with residue-metabolizing soil microorganisms. A unifying model demonstrated that PE was a function of residue mineralization, with thresholds for strong PE increase of up to 20% root, 44% stem, and 51% leaf mineralization. Thus, root mineralization has the lowest threshold for a strong PE increase. Our study emphasizes the role of residue-feeding microorganisms as active players in the PE, which are mediated by quality and quantity of crop residue additions
Nitrogen Uptake in an Alpine Kobresia Pasture on the Tibetan Plateau: Localization by N-15 Labeling and Implications for a Vulnerable Ecosystem
No full textGrasslands are very important regionally and globally because they store large amounts of carbon (C) and nitrogen (N) and provide food for grazing animals. Intensive degradation of alpine grasslands in recent decades has mainly impacted the upper root-mat/soil horizon, with severe consequences for nutrient uptake in these nutrient-limited ecosystems. We used N-15 labeling to identify the role of individual soil layers for N-uptake by Kobresia pygmaea-the dominating plant in the degraded Tibetan pasture ecosystems. We hypothesized a very efficient N-uptake corresponding mainly to the vertical distribution of living roots (topsoil > subsoil). We assume that K. pygmaea develops a very dense root-mat, which has to be maintained by small aboveground biomass, to enable this efficient N-uptake. Consequently, a higher N-investment into roots compared to shoots was hypothesized. The N-15 recovery in whole plants (similar to 70%) indicated very efficient N-uptake from the upper injection depths (0-5 cm). The highest N-15 amounts were recovered in root biomass, whereby N-15 recovery in roots strongly decreased with depth. In contrast, N-15 recovery in shoots was generally low (similar to 18%) and independent of the N-15 injection depth. This clearly shows that the low N demand of Kobresia shoots can be easily covered by N-uptake from any depth. Less living root biomass in lower versus upper soil was compensated by a higher specific activity of roots for N-uptake. The N-15 allocation into roots was on average 1.7 times higher than that into shoots, which agreed well with the very high R/S ratio. Increasing root biomass is an efficient strategy of K. pygmaea to compete for belowground resources at depths and periods with available resources. This implies high C-costs to maintain root biomass (similar to 6.0 kg DM m(-2)), which must be covered by a very low amount of photosynthetically active shoots (0.3 kg DM m(-2)). It also suggests that Kobresia grasslands react extremely sensitively toward changes in climate and management that disrupt this above-/belowground trade-off mechanism
Effect of fertilization on respiration from different sources in a sandy soil of an agricultural long-term experiment
No full textAnnual changes in stocks of soil organic carbon may be detected by measurement of heterotrophic respiration, but field studies of heterotrophic respiration in long-term fertilization experiments on sandy soils are scarce. Our objectives were to: (1) investigate the influence of fertilizer type on mineralization of soil organic carbon and crop residue, and (2) show how fertilization treatments affect the annual C balance (net ecosystem carbon balance, NECB; negative values indicate a CO2-source) in the sandy soil of the Darmstadt experiment. Treatments were long-term mineral fertilization with cereal straw incorporation (MSI) and application of rotted farmyard manure (FYM), both treatments receiving 14 g N m(-2) year(-1). This study used delta C-13 natural abundance after introduction of a C-4 crop to distinguish between different sources of respiration. Mineralization derived from C-3 sources was similar for MSI and FYM treatments (similar to 270 g C m(-2) year(-1)). The rate of residue mineralization in MSI treatments was higher, resulting in a mineralization of 49 and 37% of initial residue C in the soil of MSI and FYM treatments, respectively. The NECB (g C m(-2) year(-1)) indicated the MSI treatment (approximately - 190) as a stronger source compared with the FYM treatment (similar to-30).Deutsche Forschungsgemeinschaft (DFG) [GRK 1397/1
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