SOC Pool Research Articles

Soil organic carbon pool under different land uses in Tehri Garhwal district of Uttarakhand

The concept of carbon sequestration emerged in eighties due to the consequences of steadily increasing level of carbon dioxide in the atmosphere. No systematic study has been undertaken to estimate the soil organic carbon pool in forests of Uttarakhand, by following uniform methodology for field and laboratory work. This study was conducted in three land uses viz. Forests, Plantations and Horticulture in Tehri Garhwal district. Under forests land use, SOC pool was estimated in Sal, Deodar, Quercus, Chir, Silver fir, Miscellaneous and Kail forests up to 30 cm depth. Under Horticulture land use SOC was estimated in Apple and Letchi and under plantation land use SOC was estimated in Block plantations of Eucalyptus, Chir, Teak and Thuja. Over all 413 soil samples were collected from different locations. Soil organic carbon, bulk density and coarse fragments were estimated in collected samples and SOC pool was calculated by using the equation as suggested by IPCC Good Practice Guidance for LULUCF. Maximum SOC pool (140.95 t/ha) was estimated under Deodar followed by silver fir (134.90 t/ha), Quercus 99.18 t/ha, Sal (81.62 t/ha), Chir (73.52 t/ha), Kail (67.11 t/ha), while Miscellaneous forests has the minimum SOC pool (53.88 t/ha) in Tehri Garhwal district. SOC pool was higher (81.81 t/ha) in the soils under Apple orchards as compared to Letchi orchards (49.95 t/ha). Maximum SOC pool was estimated in the soils under Thuja (54.01 t/ha) followed by Teak (39.43 t/ha), Chir (36.68 t/ha) and the least was under Eucalyptus (31.35 t/ha). On an average Tehri Garhwal’s forests have 93.02 t/ha SOC pool while orchards have 65.88 t/ha and plantations have 40.37 t/ha.

Does expansion of western snowberry enhance ecosystem carbon sequestration and storage in Canadian Prairies?

Aerial expansion of woody species in grasslands is common in arid and semiarid areas. The ecological consequences of shrub expansion, including ecosystem function and carbon sequestration, are complex and dependent on local environmental conditions. This research was conducted in the Northern Mixed Prairie of Canada to determine the effects of western snowberry ( Symphoricarpos occidentalis) expansion on phytomass production and ecosystem carbon storage in grass-dominated plant communities. Total aboveground phytomass in western snowberry communities was more than triple that of the ecotone and 6-times greater than that of the grassland. Similarly, the mass of large roots was greatest in the western snowberry community (1.2 ± 0.19 kg m −2, mean ± SE), intermediate in the ecotone (0.5 ± 0.08 kg m −2), and least in the grassland (0.1 ± 0.04 kg m −2). Conversely, the mass of fine and medium roots was not different ( P > 0.05) among the three communities, averaging 0.7 kg m −2 in all communities. Greater aboveground phytomass did not correspond with greater organic carbon in the soil (SOC) in the western snowberry community possibly due to the poor quality and slow decomposition rate of shrub litter. Soil organic carbon in the upper 50 cm averaged 8.3 ± 0.7, 7.9 ± 1.0, and 7.9 ± 0.7 kg m −2 in western snowberry, ecotone, and grassland communities, respectively. The SOC in fine- and coarse-textured soils averaged 10.4 ± 0.6 and 6.2 ± 0.4 kg m −2, respectively. Expansion of western snowberry into grass-dominated plant communities does not appear to conflict with goals related to maintenance of SOC in the Northern Mixed Prairie. Soil texture had a greater effect on SOC than that of western snowberry. Therefore, the management of western snowberry in the Northern Mixed Prairie should be site specific and focus on aspects other than SOC pools.

Short- and long-term responses of total soil organic carbon to harvesting in a northern hardwood forest

The long-term response of total soil organic carbon pools (‘total SOC’, i.e. soil and dead wood) to different harvesting scenarios in even-aged northern hardwood forest stands was evaluated using two soil carbon models, CENTURY and YASSO, that were calibrated with forest plot empirical data in the Green Mountains of Vermont. Overall, 13 different harvesting scenarios that included four levels of aboveground biomass removal (20%, 40%, 60% and 90%) and four different rotation lengths (60 year, 90 year, 120 year, and No Rotation (NR)) were simulated for a 360 year period. Simulations indicate that following an initial post-harvest increase, total SOC decreases for several decades until carbon inputs into the soil pool from the re-growth are greater than losses due to decomposition. At this point total SOC begins to gradually increase until the next harvest. One consequence of this recovery pattern is that between harvests, the size of the SOC pool in a stand may change from −7 to 18% of the pre-harvest pool, depending on the soil pool considered. Over 360 years, the average annual decrease in total SOC depends on the amount of biomass removed, the rotation length, and the soil pool considered. After 360 years a stand undergoing the 90yr-40% scenario will have 15% less total SOC than a non-harvested stand. Long-term declines in total SOC greater than 10% were observed in the 60yr-60%, 60yr-90%, and 90yr-90% scenarios. Long-term declines less than 5% were observed in scenarios with 120 year rotations that remove 60% or less of the aboveground biomass. The long-term decreases simulated here for common management scenarios in this region would require intensive sampling procedures to be detectable.

Tillage Effects on Carbon Sequestration and Microbial Biomass in Reclaimed Farmland Soils of Southwestern Indiana

Carbon sequestration in reclaimed mine soils (RMSs) could partly mitigate C emissions associated with coal mining, but our knowledge of C storage in RMSs is derived almost exclusively from studies conducted in restored grasslands and forests. Limited information exists regarding intensively managed RMSs under agricultural land use. A study was conducted to assess the impact of tillage on recent soil organic C (SOC, total organic C minus geogenic C), total microbial biomass C (t‐MBC) and active microbial biomass C (a‐MBC) in RMSs under no‐till (NT, 13 yr) and moldboard plowing (MP, 9 and 13 yr). An undisturbed second‐growth forest and a newly reclaimed (NR, 1 yr) grassland were also included. Significant effects (P < 0.01) of tillage on SOC, t‐MBC, a‐MBC, and metabolic quotient (qCO2) were detected in the 0‐ to 5‐cm soil layer. These soil properties were strongly (r2 > 0.66) correlated with recent SOC, but moderately (r2 = 0.21–0.60) with geogenic C. Rates of C sequestration were estimated from the temporal trend in the recent SOC pool (0–40 cm in NR (23.2 Mg C ha−1), 9‐yr MP (32.9 Mg C ha−1) and 13‐yr MP (33 Mg C ha−1), and ranged between 0.8 and 0.25 Mg C ha−1 yr−1 during the first and second decades of restoration. Despite a similar amount of crop residue returned (2.8 Mg C ha−1 yr−1), recent SOC under 13‐yr NT (36.8 Mg C ha−1) exceeded that under 13‐yr MP by 3.8 Mg C ha−1 This finding, in conjunction with the lower qCO2 in the surface soil layer of NT, suggests a more efficient C utilization by soil microbes under NT than under MP. These results illustrate the benefits of NT to the restoration of SOC stocks and biological properties of severely disturbed soil systems.

Soil organic carbon pool under different plantations in some districts of Uttarakhand and Haryana

A study was conducted to estimate the soil organic carbon pool under Eucalyptus, Poplar, Shisham and Teak plantations in Haridwar and Dehra Dun, districts of Uttarakhand and Yamunanagar District of Haryana State. Over all, SOC pool under Eucalyptus, Shisham and Teak plantations was higher in the study area in Uttarakhand except Poplar plantation where SOC pool, in the study area in Haryana was higher. It indicated that soils under Eucalyptus, Shisham and Teak plantations were better enriched by soil organic carbon in Uttarakhand as compared to Haryana. The SOC pool in all the plantations in Uttarakhand was statistically different while in Haryana SOC pool among Poplar, Eucalyptus and Shisham were non-significant. SOC pool in Shisham, Teak and Eucalyptus grown in Uttarakhand was significantly different from similar plantation grown in Haryana. Variations in SOC pool in plantation and barren land was also statistically significant in study area of both the states.

Carbon stocks in Ethiopian soils in relation to land use and soil management

AbstractThe effect of soil management and land use change are of interest to the sustainable land management for improving the environment and advancing food security in developing countries. Both anthropogenic changes and natural processes affect agriculture primarily by altering soil quality. This paper reviews and synthesizes the available literatures related to the influence of soil management and land use changes on soil carbon (C) stock in Ethiopia. The review shows that topsoil C stock declines approximately 0–63%, 0–23%, and 17–83% upon land use conversion from forest to crop land, to open grazing, and to plantation, respectively. An increase of 1–3% in soil C stock was observed within 10 years of converting open grazed land to protected enclosures. However, there was a little change in soil C stock below 20 cm depth.There is a large potential of increasing SOC pool with adoption of land restorative measures. Total potential of soil C sequestration with the adoption of restoration measures ranges 0·066–2·2 Tg C y−1 on rain‐fed cropland and 4·2–10·5 Tg C y−1 on rangeland. Given large area and diverse ecological conditions in Ethiopia, research data available in published literature are rather scanty. Therefore, researchable priorities identified in this review are important. Copyright © 2008 John Wiley & Sons, Ltd.

US investment in bioethanol raises prospects for Danisco and Novozymes

Traditional solid fuels account for more than 90% of the energy supply for 3 billion people in developing countries. However, liquid biofuels (e.g., ethanol) are perceived as an important alternative to fossil fuel. Global crop residue production is estimated at about 4 billion Mg for all crops and 3 billion Mg per annum for lignocellulosic residues of cereals. One Mg of corn stover can produce 280 L of ethanol, compared with 400 L from 1 Mg of corn grains; 1 Mg of biomass is also equivalent to 18.5 GJ of energy. Thus, 3 billion Mg of residues are equivalent to 840 billion L of ethanol or 56 × 109 GJ of energy. However, removal of crop residues exacerbates soil degradation, increases net emission of CO2, and aggravates food insecurity. Increasing the SOC pool by 1 Mg C ha−1 yr−1 through residue retention on soil can increase world food grain production by 24–40 million Mg yr−1, and root/tuber production by 6–11 million Mg yr−1. Thus, identifying alternate sources of biofuel feedstock (e.g., biofuel plantations, animal waste, municipal sold waste) is a high priority. Establishing biofuel plantations on agriculturally marginal or degraded lands can off-set 3.5–4 Pg C yr−1.

Crop residues as soil amendments and feedstock for bioethanol production

Traditional solid fuels account for more than 90% of the energy supply for 3 billion people in developing countries. However, liquid biofuels (e.g., ethanol) are perceived as an important alternative to fossil fuel. Global crop residue production is estimated at about 4 billion Mg for all crops and 3 billion Mg per annum for lignocellulosic residues of cereals. One Mg of corn stover can produce 280L of ethanol, compared with 400L from 1Mg of corn grains; 1Mg of biomass is also equivalent to 18.5GJ of energy. Thus, 3 billion Mg of residues are equivalent to 840 billion L of ethanol or 56x10(9)GJ of energy. However, removal of crop residues exacerbates soil degradation, increases net emission of CO2, and aggravates food insecurity. Increasing the SOC pool by 1 Mg C ha(-1)yr(-1) through residue retention on soil can increase world food grain production by 24-40 million Mg yr(-1), and root/tuber production by 6-11 million Mg yr(-1). Thus, identifying alternate sources of biofuel feedstock (e.g., biofuel plantations, animal waste, municipal sold waste) is a high priority. Establishing biofuel plantations on agriculturally marginal or degraded lands can off-set 3.5-4 Pg Cyr(-1).

Topsoil organic carbon mineralization and CO 2 evolution of three paddy soils from South China and the temperature dependence

Carbon mineralization and its response to climatic warming have been receiving global attention for the last decade. Although the virtual influence of temperature effect is still in great debate, little is known on the mineralization of organic carbon (SOC) of paddy soils of China under warming. SOC mineralization of three major types of China's paddy soils is studied through laboratory incubation for 114 d under soil moisture regime of 70% water holding capacity at 20°C and 25°C respectively. The carbon that mineralized as CO 2 evolved was measured every day in the first 32 d and every two days in the following days. Carbon mineralized during the 114 d incubation ranged from 3.51 to 9.22 mg CO 2-C/gC at 20°C and from 4.24 to 11.35 mg CO 2-C/gC at 25°C respectively; and a mineralizable C pool in the range of 0.24 to 0.59 gC/kg, varying with different soils. The whole course of C mineralization in the 114 d incubation could be divided into three stages of varying rates, representing the three subpools of the total mineralizable C: very actively mineralized C at 1–23 d, actively mineralized C at 24–74 d and a slowly mineralized pool with low and more or less stabilized C mineralization rate at 75–114 d. The calculated Q 10 values ranged from 1.0 to 2.4, varying with the soil types and N status. Neither the total SOC pool nor the labile C pool could account for the total mineralization potential of the soils studied, despite a well correlation of labile C with the shortly and actively mineralized C, which were shown in sensitive response to soil warming. However, the portion of microbial C pool and the soil C/N ratio controlled the C mineralization and the temperature dependence. Therefore, C sequestration may not result in an increase of C mineralization proportionally. The relative control of C bioavailability and microbial metabolic activity on C mineralization with respect to stabilization of sequestered C in the paddy soils of China is to be further studied.

Chemical Composition of Crop Biomass Impacts Its Decomposition

Understanding the interaction between plant components and their subsequent decomposition provides insights on how plant quality differences may influence C sequestration within a given management system. Our hypothesis was that decomposition is a function of biochemical composition when all other variables are constant (e.g., particle size, temperature and moisture). Recognizing the challenges of reconciling laboratory and field studies, this study examined the decomposition dynamics of five selected crops with varying composition under controlled temperature and moisture regimes. Residue materials were partitioned into leaf, stem, and root organs to give a clearer indication of compositional control on decomposition. Plant quality varied among species (alfalfa [Medicago sativa L.], corn [Zea mays L.], cuphea [Cuphea viscosissima Jacq. · Cuphea lanceolata W.T. Aiton], soybean [Glycine max (L.) Merr.] and switchgrass [Panicum virgatum L.]). A two‐component litter decomposition model was used to describe decomposition observed during 498 d. Stepwise multivariate regression indicated initial N concentration, starch, total lignin, and acid‐insoluble ash (AI ash) were the four best predictors (r2 = 0.83) of the rate of active component decomposition (ka); however, initial composition poorly predicted the rate of passive decomposition (kp). The best four‐component model (r2 = 0.43) identified by stepwise multiple regression for kp included AI ash, hemicellulose, N concentration, and C/N ratio. Rate constants are a function of the incubation period, thus making direct comparison among separate experiments difficult. Chemical recalcitrance appears to slow root decomposition; such chemical recalcitrance to decay may partially explain why roots have been found to contribute more C to the SOC pool than surface residues.

Carbon sequestration potential estimates with changes in land use and tillage practice in Ohio, USA

Soil C sequestration through changes in land use and management is one of the important strategies to mitigate the global greenhouse effect. This study was conducted to estimate C sequestration potential of the top 20 cm depth of soil for two scenarios in Ohio, USA: (1) with reforestation of both current cropland and grassland where SOC pools are less than the baseline SOC pool under current forest; (2) with the adoption of NT on all current cropland. Based on Ohio Soil Survey Characterization Database and long-term experimental data of paired conservation tillage (CT) versus no-till (NT), we specified spatial variations of current SOC pools and C sequestration potentials associated with soil taxa within each major land resource area (MLRA). For scenario I, there would be 4.56 Mha of cropland having an average SOC sequestration capacity of 1.55 kg C m −2 and 0.80 Mha of grassland with that of 1.35 kg C m −2 . Of all potential area, 73% are associated with Alfisols and 15% with Mollisols, but the achievable potential could vary significantly with individual MLRAs. Alternately, an average SOC sequestration rate of 62 g C m −2 year −1 was estimated with conversion from CT to NT for cultivated Alfisols, by which a cumulative increase of 71 Tg C resulted from reforestation of cropland could be realized in 25 years. Soils with lower antecedent C contents have higher C sequestration rates. In comparison with the results obtained at the state scale, the estimates of SOC sequestration potentials taxonomically associated with each specific MLRA may be more useful to the formulation of C credit trading programs.

Carbon fluxes in soil

Terrestrial ecosystems represent the second largest carbon reservoir, and the C balance in terrestrial ecosystems can be directly impacted by human activities such as agricultural management practices and land-use changes. This paper focuses on the C-sequestration in soil. Although many studies showed that the concentration of SOC is much higher in the shallow soils (0–30 cm), the deeper horizons represent a much greater mass of soil and represent a huge C-storage pool. The process of preferential retention of more strongly adsorbing components, along with competitive displacement of weakly binding components are the key processes that enhance the movement of organic carbon to deeper soil horizons. DOC represents the most dynamic part of organic carbon in soils, and thus can be used as a timely indicator of the short-term change of C-sequestration. Long-term experiments have demonstrated that higher SOC levels in shallow soils would lead to increased fluxes of DOC to deeper horizons, but more data on a wider range of soils and treatment strategies are needed to fully evaluate the linkages between changes in SOC in shallow soil, vertical fluxes of DOC to deeper soil horizons, and enhanced C-inventories in deeper, slow-turnover SOC pools.

World crop residues production and implications of its use as a biofuel

Reducing and off-setting anthropogenic emissions of CO 2 and other greenhouse gases (GHGs) are important strategies of mitigating the greenhouse effect. Thus, the need for developing carbon (C) neutral and renewable sources of energy is more than ever before. Use of crop residue as a possible source of feedstock for bioenergy production must be critically and objectively assessed because of its positive impact on soil C sequestration, soil quality maintenance and ecosystem functions. The amount of crop residue produced in the US is estimated at 367×10 6 Mg/year for 9 cereal crops, 450×10 6 Mg/year for 14 cereals and legumes, and 488×10 6 Mg/year for 21 crops. The amount of crop residue produced in the world is estimated at 2802×10 6 Mg/year for cereal crops, 3107×10 6 Mg/year for 17 cereals and legumes, and 3758×10 6 Mg/year for 27 food crops. The fuel value of the total annual residue produced is estimated at 1.5×10 15 kcal, about 1 billion barrels (bbl) of diesel equivalent, or about 8 quads for the US; and 11.3×10 15 kcal, about 7.5 billion bbl of diesel or 60 quads for the world. However, even a partial removal (30–40%) of crop residue from land can exacerbate soil erosion hazard, deplete the SOC pool, accentuate emission of CO 2 and other GHGs from soil to the atmosphere, and exacerbate the risks of global climate change. Therefore, establishing bioenergy plantations of site-specific species with potential of producing 10–15 Mg biomass/year is an option that needs to be considered. This option will require 40–60 million hectares of land in the US and about 250 million hectares worldwide to establish bioenergy plantations.

Comparison of Labile Soil Organic Matter Fractionation Techniques

Labile soil organic carbon (SOCL), soil organic carbon with a relatively short turnover time, is an important source of energy for the belowground portion of ecosystems and is sensitive to land management changes. Many techniques exist to differentiate and quantify labile SOC, but rarely have these been directly compared. Here we compare the results of four common chemical, physical, and biological methods of empirically measuring labile SOC with soils taken from 33 restored grasslands that differ in length of time since cessation of agriculture. Among sites, microbial biomass C, acid‐hydrolyzable C, the amount of C respired after 12 d of a laboratory incubation, and light fraction carbon (LFC) were all positively correlated with one another, although there were large differences in the sizes of the pools estimated with each method. Acid‐hydrolyzable C consistently provided the largest estimate and 12‐d incubations the smallest estimate of labile SOC. The quantity of labile SOC obtained by fitting respiration data from a laboratory incubation with a two‐pool model with separate decay constants for each pool was also positively correlated with the three measures of labile soil C not derived from respiration data, although this technique was sensitive to whether the decay constant of the recalcitrant pool was constrained or not. All methods showed increases in labile SOC pools with increases in total soil organic carbon (SOCT) pools, although the rate of change varied between techniques. The size of stable aggregates correlated positively with hydrolyzable C and SOCT, supporting the idea that aggregates may physically protect soil C from decomposition, although the degree to which this C is labile is unclear.

Changing Global Climate: Historical Carbon and Nitrogen Budgets and Projected Responses of Ohio?s Cropland Ecosystems

As the evidence of global climate change continues to mount, its consequences for cropland productivity assume particular significance. Against the backdrop of past agricultural practices, simulation models offer a glimpse into the future, showing the effect of temperature changes on crop production. In this study, we first quantified the carbon (C) and nitrogen (N) budgets of Ohio’s cropland ecosystems using inventory yield data of corn for grain, oat, and all wheat for the period 1866–1996 and soybean for the period 1924–96. Then we explored the responses of Ohio’s continuous soybean croplands to changes in temperature, carbon dioxide (CO2) concentration, initial soil organic C and N (SOC-N) pools, soil texture, and management practices by developing a simple cropland ecosystem model (CEM) and performing a long-term sensitivity analysis. Finally, CEM simulations were evaluated against independent observations of SOC values (0–19 cm) averaged over 470 northwest Ohio sites between 1954 and 1987 under conventional tillage and rotations of corn–soybean–winter wheat by using the historical yield data (r 2 = 0.8). The C contents per hectare of crop harvests increased by 178% for oats, 300% for corn for grain, and 652% for all wheat between 1866 and 1996 and by 305% for soybean between 1924 and 1996. Ohio croplands acted as C–N sources, releasing average net ecosystem emissions (NEE), including the removal of harvested C–N, of 4,598 kg CO2 ha−1 and 141 kg N ha−1 in 1886 and 205 kg CO2 ha−1 (except for the corn-for-grain cropland) and 39 kg N ha−1 in 1996. The continuous corn croplands continued to become a C sink, sequestering 255 kg C ha−1 in 1996. Results of the sensitivity analysis for Ohio’s continuous soybean croplands revealed that the SOC pool increased by 6.9% and decreased by 7.5% in response to a doubled CO2 concentration and a temperature increase of 2.8°C over 100 years, respectively. The sequestration potential of the SOC pool increased by 6.5% at a rate of 24.6 kg C ha−1 y−1 for the same period with finer soil texture (loam to silty clay loam). The shift from conventional to conservation residue practice led to an 11% increase in the steady-state SOC storage at a rate of 42 kg C ha−1 y−1 for 100 years.

Simulating SOC changes in long‐term experiments with RothC and CENTURY: model evaluation for a regional scale application

Abstract. Predictive, regional use of soil organic matter (SOM) models requires evaluation of the performance of models with datasets from long‐term experiments relevant to the scenarios of interest to the regional scale study, and relevant to the climate of the study region. Datasets from six long‐term experiments were used to evaluate the performance of RothC and CENTURY, two of the most widely used and tested SOM models. Three types of model run were completed for each site: (1) CENTURY model alone; (2) RothC model run to fit measured SOC values, by iteratively adjusting C inputs to soil; and (3) RothC model run using C inputs derived from CENTURY runs. In general, the performance of both models was good across all datasets. The runs using RothC (iteratively changing C inputs to fit measured SOC values) tended to have the best fit to model data, since this method involved direct fitting to observed data. Carbon inputs estimated by RothC were, in general, lower than those estimated by CENTURY, since SOC in CENTURY tends to turn over faster than SOC in RothC. The runs using RothC with CENTURY C inputs tended to have the poorest fit of all, since CENTURY predicted greater C inputs than were required by RothC to maintain the same SOC content. A plausible model fit to measured SOC data may be obtained with widely differing C input values, due to differences in predicted decomposition rates between models. It remains unclear which, if either, modelling approach most closely represents reality since both C inputs to soil and decomposition rates for bulk SOM are difficult to determine experimentally. Further progress in SOM modelling can only be the result of research leading to better process understanding, both of net C inputs to soil and of SOM decomposition rates. The use of default methods for estimating initial SOC pools in RothC and CENTURY may not always be appropriate and may require adjustment for specific sites. The simulations presented here also suggest details of SOC dynamics not shown by available measured data, especially trends between sampling intervals, and this emphasizes the importance of archived soil samples in long‐term experiments.

Shifting cultivation on the tidal floodplains of Amazônia: impacts on soil nutrient status

Studies of the impact of traditional agroforestry practices on soil nutrient status in the Amazon Basin have largely been limited to upland sites, many of which are oligotrophic. However, rural population density in Amazonia is highest on the floodplains of the major rivers and shifting cultivation has been practiced on the floodplains for millennia. We established a slash-and-burn cultivation plot and an untreated forest plot in tidal floodplain successional forest in the Islands of Abaetetuba, Para, Brazil, and sampled soils (0–10 cm) during four phases of the agroforest cycle (n = 9 in each plot for each sampling period): (1) prior to clearing, (2) following burning, (3) harvest one (rice at four months), and (4) harvest two (sugar cane at 15 months). During the course of this pilot experiment, background temporal variability in SOC, total N and available mineral nutrient pools (P, K, Ca, Mg) exceeded treatment effects, suggesting that soil nutrient pools in this environment are well-buffered against the effects of shifting cultivation. These results contrast markedly with those reported for Amazonian upland sites where nutrient pulses and declines associated with the agroforest cycle have been demonstrated and may restrict the potential for low-input, continuous cultivation. Physical limitations imposed by flooding and fluvial erosion, rather than nutrient constraints, restrict the potential of agricultural intensification in the tidal floodplains.

Aspects of carbon and nitrogen cycling in soils of the Bornhöved Lake district. II. Modelling the influence of temperature increase on soil respiration and organic carbon content in arable soils under different managements

Based on field measurements in two agriculturalecosystems, soil respiration and long-term response ofsoil organic carbon content (SOC) was modelled. Themodel predicts the influence of temperature increaseas well as the effects of land-use over a period ofthirty years in a northern German glacial morainelandscape. One of the fields carried a maizemonoculture treated with cattle slurry in addition tomineral fertilizer (“maize monoculture”), the otherwas managed by crop rotation and recieved organicmanure (“crop rotation”). The soils of both fieldswere classified as cambic Arenosols. The soilrespiration was measured in the fields by means of theopen dynamic inverted-box method and an infrared gasanalyser. The mean annual soil respiration rates were 268 (maizemonoculture) and 287 mg CO2 m-2 h-1(crop rotation). Factors controlling soil respirationwere soil temperature, soil moisture, root respirationand carbon input into the soil. Q10-valuesof soil respiration were generally higher in winterthan in summer. This trend is interpreted as anadaptive response of the soil microbial communities.In the model a novel mathematical approach withvariable Q10-values as a result oftemperature and moisture adjustment is proposed. Withthe calibrated model soil respiration and SOC werecalculated for both fields and simulations over aperiod of thirty years were established. Simulationswere based on (1) local climatic data, 1961 until1990, and (2) a regional climate scenario for northernGermany with an average temperature increase of 2.1 K.Over the thirty years period with present climateconditions, the SOC pool under “crop rotation” wasnearly stable due to the higher carbon inputs, whereasabout 16 t C ha-1 were lost under “maizemonoculture”. Under global warming the mean annualsoil respiration for both fields increased and SOCdecreased by ca. 10 t C ha-1 under “croprotation” and by more than 20 t C ha-1 under“maize monoculture”. It was shown that overestimationof carbon losses in long-term prognoses can be avoidedby including a Q10-adjustment in soilrespiration models.