Effects of beech and ash on small‐scale variation of soil acidity and nutrient stocks in a mixed deciduous forest

Trees interact in a complex manner with soils: they recycle and redistribute nutrients via many ecological pathways. Nutrient distribution via leaf litter is assumed to be of major importance. Beech is commonly known to have lower nutrient concentrations in its litter than other hardwood tree species occurring in Central Europe. We examined the influences of distribution of beech (Fagus sylvatica L.), ash (Fraxinus excelsior L.), lime (Tilia cordata Mill. and T. platyphyllos Scop.), maple (Acer spp. L.), and clay content on small‐scale variability of pH and exchangeable Ca and Mg stocks in the mineral soil and of organic‐C stocks in the forest floor in a near‐natural, mature mixed deciduous forest in Central Germany. The soil is a Luvisol developed in loess over limestone. We found a positive effect of the proportion of beech on the organic‐C stocks in the forest floor and a negative effect on soil pH and exchangeable Ca and Mg in the upper mineral soil (0 to 10 cm). The proportion of ash had a similar effect in the opposite direction, the other species did not show any such effect. The ecological impact of beech and ash on soil properties at a sample point was explained best by their respective proportion within a radius of 9 to 11 m. The proportion of the species based on tree volume within this radius was the best proxy to explain species effects. The clay content had a significant positive influence on soil pH and exchangeable Ca and Mg with similar effect sizes. Our results indicate that beech, in comparison to other co‐occurring deciduous tree species, mainly ash, increased acidification at our site. This effect occurred on a small spatial scale and was probably driven by species‐related differences in nutrient cycling via leaf litter. The distribution of beech and ash resulted not only in aboveground diversity of stand structures but also induced a distinct belowground diversity of the soil habitat.     

Soil organic‐C accumulation and N availability under improved pastures established in Mediterranean oak woodlands

Long‐term effects of improved pasture establishment (with high proportion of legumes) on soil organic‐C status and N availability in Mediterranean cork oak (Quercus suber L.) woodlands were assessed. Soils were sampled beneath scattered crowns and in open areas, considering two systems: unmanaged and managed woodlands where improved pastures were installed 26 and 32 years ago. Total and labile C and N pools were measured and C and N mineralization were determined over 24 weeks laboratory incubation. Soils under improved pastures showed higher organic‐C, total‐N and net N mineralization than those under unmanaged pasture, mainly when established beneath trees. Potentially mineralizable C, C mineralization rate and microbial C were not statistically different between the unmanaged and improved pasture sites, but were higher closer to the tree than in the open area (1.8, 1.2 and 1.2 times, respectively). The qCO₂ was higher in improved pastures (1.7 times). Labile pool of C and N extracted with hot water increased under improved pasture (3.4 and 1.7 times, respectively). Results indicate that soil quality amelioration by improved pastures is stronger in the presence of oak trees. Management systems that favour oak tree maintenance and regeneration should be taken into account to reverse soil degradation.     

Conversion of cropland into grassland: Implications for soil organic‐carbon stocks in two soils with different texture

Soil organic‐carbon (SOC) stocks are expected to increase after conversion of cropland into grassland. Two adjacent cropland and grassland sites—one with a Vertisol with 23 y after conversion and one with an Arenosol 29 y after conversion—were sampled down to 60 cm depth. Concentrations of SOC and total nitrogen (N_tot) were measured before and after density fractionation in two light fractions and a mineral‐associated fraction with C adsorbed on mineral surfaces. For the soil profiles, SOC stocks and radiocarbon (¹⁴C) concentrations of mineral associated C were determined. Carbon stocks and mineral‐associated SOC concentrations were increased in the upper 10 cm of the grassland soil compared to the cropland. This corresponded to the root‐biomass distribution, with 59% and 86% of the total root biomass at 0–5 cm soil depth of the grasslands. However, at the Arenosol site, at 10–20 cm depth, C in the mineral‐associated fraction was lost 29 y after the conversion into grassland. Over all, SOC stocks were not significantly different between grassland and cropland at both sites when the whole profile was taken into account. At the Arenosol site, the impact of land‐use conversion on SOC accumulation was limited by low total clay surface area available for C stabilization. Subsoil C (30–50 cm) at cropland of the Vertisol site comprised 32% of the total SOC stocks with high ¹⁴C concentrations below the plowing horizon. We concluded that fresh C was effectively translocated into the subsoil. Thus, subsoil C has to be taken into account when land‐use change effects on SOC are assessed.     

Recovery of Soil C and N in a Tropical Pasture: Passive and Active Restoration

Soil degradation by deforestation and introduction of exotic grasses is a grave consequence of land‐use change in tropical regions during the last decades. Soil restoration following natural succession (i.e., passive restoration) is slow because of low tree establishment. Introduction of tree plantings by human intervention (i.e., active restoration) results in a promising strategy to accelerate forest succession and soil recovery in tropical region. The present research was carried out to explore the restoration of soil properties after cattle exclusion and of grazing combined with native tree planting introduction (legumes and nonlegumes) in a tropical pasture in Veracruz, southeast Mexico. Results indicate that land‐use changes decreased soil C and N pools in both litter and mineral soil. In addition, soil heterogeneity increased by land‐use changes at both temporal and spatial scales. In the short term, passive succession (i.e., cattle exclusion) favors the recovery of C and N content in labile soil pools, indicated by the increase in litter C and N masses as well as C and N concentrations in soil microbial biomass. Soils under active restoration showed trends to recover the N cycling, such as a greater accumulation of N in litter, in soil total N concentrations, soil microbial biomass N concentrations, rates of net N transformations, and extractable water and microbial biomass C:N ratios mainly under legumes species. Active restoration including legume introduction is a key factor for rapid recovery of soil fertility. Copyright © 2013 John Wiley & Sons, Ltd.     

Land‐Use Type Effects on Soil Organic Carbon and Microbial Properties in a Semi‐arid Region of Northeast Brazil

Land‐use change is one of the most important anthropogenic environmental change drivers affecting the biodiversity and functioning of ecosystems. However, there is limited knowledge of the consequences for soil processes in many regions around the globe. The Brazilian semi‐arid ecosystem known as Caatinga has experienced the transformation from native forest into agricultural land, with heretofore unknown effects on soil processes and microbial properties. The aim of this study was to evaluate the impact of five land‐use changes (to maize and cowpea cropland, grape orchard, and cut and grazed pasture) on total organic C (TOC) and total N (TN) stocks and soil microbial properties of Ultisol from Caatinga. Soil samples (0–10 and 10–20 cm depth) were collected during the wet and dry periods. Split–split plot analysis of variance was used to test the effects of land use, soil depth, season and the interaction between land‐use and soil depth on soil microbial properties, TOC and TN stocks. Land‐use effects were more pronounced in the top soil layer than in the lower layer, while the pattern was less consistent in soil microbial properties. Land conversion from native forest to cropland may cause C losses from the soil, but conversion to pastures may even increase the potential of soils to function as C sinks. Grazed pastures showed not only high C and N stocks but also the highest soil microbial biomass and lowest respiratory quotients, all indications for elevated soil C sequestration. Thus, grazed pastures may represent a land‐use form with high ecosystem multifunctionality in Caatinga. Copyright © 2014 John Wiley & Sons, Ltd.     

How do hedgerows influence soil organic carbon stock in livestock‐grazed pasture?

Hedgerows have the potential to influence ecosystem function in livestock‐grazed pasture. Despite this, they are often ignored when quantifying farmland ecosystem service delivery. In this study, we assess the contribution of hedgerows to the ecosystem function of carbon (C) storage, with a particular emphasis on soil organic carbon (SOC). We measured SOC stock (kg C m^?2), on an equivalent soil mass basis, at 0–0.15 m depth in pasture adjacent to 38 hedgerows (biotic) and 16 stone walls or fences (abiotic controls) across ten farms in the county of Conwy, Wales, UK. Pasture SOC stock (~7 kg C m^?2) was similar adjacent to biotic and abiotic field boundaries, positively associated with soil moisture and negatively with soil bulk density (BD). For biotic boundaries, two further variables were significantly associated with SOC stock, distance from hedgerow (decrease in SOC stock) and slope orientation (upslope SOC stock greater than downslope). For pasture adjacent to hedgerows, a model combining the aforementioned variables (BD, soil moisture, distance from hedgerow, slope orientation) explained 78% of variation in SOC stock. This study demonstrates that whilst hedgerows do have subtle positive effects on SOC stock in adjacent pasture, SOC storage adjacent to field boundaries is influenced more by soil moisture content and BD than field boundary type.     

Soil nutrient supply and biomass production in a mixed forest on a skeleton‐rich soil and an adjacent beech forest

In the natural forest communities of Central Europe, beech (Fagus sylvatica L.) predominates in the tree layer over a wide range of soil conditions. An exception with respect to the dominance of beech are skeleton‐rich soils such as screes where up to 10 broad‐leaved trees co‐exist. In such a Tilia‐Fagus‐Fraxinus‐Acer‐Ulmus forest and an adjacent mono‐specific beech forest we compared (1) soil nutrient pools and net nitrogen mineralization rates, (2) leaf nutrient levels, and (3) leaf litter production and stem increment rates in order to evaluate the relationship between soil conditions and tree species composition. In the mixed forest only a small quantity of fine earth was present (35 g l^—1) which was distributed in patches between basalt stones; whereas a significantly higher (P < 0.05) soil quantity (182 g l^—1) was found in the beech forest. In the soil patches of the mixed forest C and N concentrations and also concentrations of exchangeable nutrients (K, Ca, Mg) were significantly higher than in the beech forest. Net N mineralization rates on soil dry weight basis in the mixed forest exceeded those in the beech forest by a factor of 2.6. Due to differences in fine earth and stone contents, the volume related soil K pool and the N mineralization rate were lower in the mixed forest (52 kg N ha^—1 yr^—1, 0—10 cm depth) than in the beech forest (105 kg N ha^—1 yr^—1). The leaf N and K concentrations of the beech trees did not differ significantly between the stands, which suggests that plant nutrition was not impaired. In the mixed forest leaf litter fall (11 %) and the increment rate of stem basal area (52 %) were lower than in the beech forest. Thus, compared with the adjacent beech forest, the mixed forest stand was characterized by a low volume of patchy distributed nutrient‐rich soil, a lower volume related K pool and N mineralization rate, and low rates of stem increment. Together with other factors such as water availability these patterns may contribute to an explanation of the diverse tree species composition on Central European screes.     

Acidity,nutrient stocks,and organic‐matter content in soils of a temperate deciduous forest with different abundance of European beech (Fagus sylvatica L.)

The production and composition of leaf litter, soil acidity, exchangeable nutrients, and the amount and distribution of soil organic matter were analyzed in a broad‐leaved mixed forest on loess over limestone in Central Germany. The study aimed at determining the current variability of surface‐soil acidification and nutrient status, and at identifying and evaluating the main factors that contributed to the variability of these soil properties along a gradient of decreasing predominance of European beech (Fagus sylvatica L.) and increasing tree‐species diversity. Analyses were carried out in (1) mature monospecific stands with a predominance of beech (DL 1), (2) mature stands dominated by three deciduous‐tree species (DL 2: beech, ash [Fraxinus excelsior L.], lime [Tilia cordata Mill. and/or T. platyphyllos Scop.]), and (3) mature stands dominated by five deciduous‐tree species (DL 3: beech, ash, lime, hornbeam [Carpinus betulus L.], maple [Acer pseudoplatanus L. and/or A. platanoides L.]). The production of leaf litter was similar in all stands (3.2 to 3.9 Mg dry matter ha^–1 y^–1) but the total quantity of Ca and Mg deposited on the soil surface by leaf litter increased with increasing tree‐species diversity and decreasing abundance of beech (47 to 88 kg Ca ha^–1 y^–1; 3.8 to 7.9 kg Mg ha^–1 y^–1). The soil pH_(H2O) and base saturation (BS) measured at three soil depths down to 30 cm (0–10 cm, 10–20 cm, 20–30 cm) were lower in stands dominated by beech (pH = 4.2 to 4.4, BS = 15% to 20%) than in mixed stands (pH = 5.1 to 6.5, BS = 80% to 100%). The quantities of exchangeable Al and Mn increased with decreasing pH and were highest beneath beech. Total stocks of exchangeable Ca (0–30 cm) were 12 to 15 times larger in mixed stands (6660 to 9650 kg ha^–1) than in beech stands (620 kg ha^–1). Similar results were found for stocks of exchangeable Mg that were 4 to 13 times larger in mixed stands (270 to 864 kg ha^–1) than in beech stands (66 kg ha^–1). Subsoil clay content and differences in litter composition were identified as important factors that contributed to the observed variability of soil acidification and stocks of exchangeable Ca and Mg. Organic‐C accumulation in the humus layer was highest in beech stands (0.81 kg m^–2) and lowest in stands with the highest level of tree‐species diversity and the lowest abundance of beech (0.27 kg m^–2). The results suggest that redistribution of nutrients via leaf litter has a high potential to increase BS in these loess‐derived surface soils that are underlain by limestone. Species‐related differences of the intensity of soil–tree cation cycling can thus influence the rate of soil acidification and the stocks and distribution of nutrients.     

Modelling the Effect of Land Management Changes on Soil Organic Carbon Stocks in a Mediterranean Cultivated Field

Land management in agricultural lands has important effects on soil organic carbon (SOC) dynamics. These effects are particularly relevant in the Mediterranean region, where soils are fragile and prone to erosion. Increasing interest of modelling to simulate SOC dynamics and the significance of soil erosion on SOC redistribution have been linked to the development of some recent models. In this study, the SPEROS‐C model was implemented in a 1.6‐ha cereal field for a 150‐year period covering 100 years of minimum tillage by animal traction, 35 years of conventional tillage followed by 15 years of reduced tillage by chisel to evaluate the effects of changes in land management on SOC stocks and lateral carbon fluxes in a Mediterranean agroecosystem. The spatial patterns of measured and simulated SOC stocks were in good agreement, and their spatial variability appeared to be closely linked to soil redistribution. Changes in the magnitude of lateral SOC fluxes differed between land management showing that during the conventional tillage period the carbon losses is slightly higher (0.06 g C m⁻² yr⁻¹) compared to the period of reduced till using chisel (0.04 g C m⁻² yr⁻¹). Although the results showed that the SPEROS‐C model is a potential tool to evaluate erosion induced carbon fluxes and assess the relative contribution of different land management on SOC stocks in Mediterranean agroecosystems, the model was not able to fully represent the observed SOC stocks. Further research (e.g. input parameters) and model development will be needed to achieve more accurate results. Copyright © 2016 John Wiley & Sons, Ltd.     

Potential carbon stock in Japanese forest soils – simulated impact of forest management and climate change using the CENTURY model

Forest management and climate change may have a substantial impact on future soil organic carbon (SOC) stocks at the country scale. Potential SOC in Japanese forest soils was regionally estimated under nine forest managements and a climate change scenario using the CENTURY ecosystem model. Three rotations (30, 50, 100 yr) and three thinning regimes were tested: no‐thinning; 30% of the trees cut in the middle of the rotation (e.g. 15 year in a 30‐yr rotation) and thinned trees all left as litter or slash (ThinLef) and the trees from thinning removed from the forest (ThinRem). A climate change scenario was tested (ca. 3 °C increase in air temperature and 9% increase in precipitation). The model was run at 1 km resolution using climate, vegetation and soil databases. The estimated SOC stock ranged from 1600 to 1830 TgC (from 6800 to 7800 gC/m²), and the SOC stock was largest with the longest rotation and was largest under ThinLef with all three rotations. Despite an increase in net primary production, the SOC stock decreased by 5% under the climate change scenario.     

Potential of multi‐objective models for risk‐based mapping of the resilience characteristics of soils: demonstration at a national level

Policy makers rely on risk‐based maps to make informed decisions on soil protection. Producing the maps, however, can often be confounded by a lack of data or appropriate methods to extrapolate using pedotransfer functions. In this paper, we applied multi‐objective regression tree analysis to map the resistance and resilience characteristics of soils onto stress. The analysis used a machine learning technique of multiple regression tree induction that was applied to a data set on the resistance and resilience characteristics of a range of soils across Scotland. Data included both biological and physical perturbations. The response to biological stress was measured as changes in substrate mineralization over time following a transient (heat) or persistent (copper) stress. The response to physical stress was measured from the resistance and recovery of pore structure following either compaction or waterlogging. We first determined underlying relationships between soil properties and its resistance and resilience capacity. This showed that the explanatory power of such models with multiple dependent variables (multi‐objective models) for the simultaneous prediction of interdependent resilience and resistance variables was much better than a piecewise approach using multiple regression analysis. We then used GIS techniques coupled with an existing, extensive soil data set to up‐scale the results of the models with multiple dependent variables to a national level (Scotland). The resulting maps indicate areas with low, moderate and high resistance and resilience to a range of biological and physical perturbations applied to soil. More data would be required to validate the maps, but the modelling approach is shown to be extremely valuable for up‐scaling soil processes for national‐level mapping.     

Sampling procedure simulating on‐the‐go sensing for soil nutrients

The emergence of a new sensor technology based on the use of ion‐selective membranes provides an increasing number of opportunities for on‐the‐go field measurements of soil nutrients and soil pH. In the future, on‐the‐go sensing should provide a cost‐effective monitoring of heterogeneous soils with high sampling resolution. It is suitable for site‐specific management because it can be focused on the spatial representativity of observation. This study evaluates the on‐the‐go‐sensing sampling design by comparing it with a standard approach to soil sampling for soil pH and the base nutrients P, K, and Mg under local field conditions in Germany. Soil samples were taken in two test sites at a resolution and in a manner as if they were sampled with an on‐the‐go sensing system and were compared with soil samples taken at a coarser resolution and with standard methods. In general, a higher variability was observed among the on‐the‐go samples due to their smaller sample support. The finer sampling resolution of the on‐the‐go design improved field‐scale semivariogram‐analysis results, identifying the spatial structures for soil pH, P, and Mg clearly. In addition, kriged maps of these soil parameters had predominantly higher estimation accuracies. However, the on‐the‐go samples were strongly influenced by the small‐scale variability of K in one of the test sites. This variability increased the kriging standard deviation for K by 50% compared with standard sampling design. Despite of this problem, the on‐the‐go‐sensing sampling design revealed field‐scale spatial variability for base nutrient status more accurately. Except for K, the mean absolute error of fertilizer‐application maps was reduced when using the on‐the‐go sample design in comparison with the standard sample design (Ca: 210/268 kg ha^–1, P: 2.85/6.75 kg ha^–1, K: 13.7/6.0 kg ha^–1, Mg 5.7/6.8 kg ha^–1). This will reduce over‐ and underfertilization using variable‐rate fertilizer‐application systems. In the future, it will be of interest if real on‐the‐go soil‐sensor measurements exhibit the same variability behavior addressed here or if results will differ substantially.     

Changes in soil C,N, and P with long‐term (58 years) cattle grazing on rough fescue grassland

We investigated soil response to long‐term cattle grazing at stocking rates 0 (CK), 2.4 (MG), and 4.8 (HG) animal unit months ha^–1 on a Rough Fescue (Festuca campestris Rydb.) grassland. Soil organic C and N stocks and available nutrients were not affected by grazing while soil bulk densities (0–30 cm) were higher and P stocks (15–30 cm) were lower under grazing than CK. The slow rate change of soil C and N suggest the rich black grassland soils appear to tolerate intensive grazing.     

Soil Properties and Macro Cations Status impacted by Long‐Term Applied Poultry Litter

Abstract

Most ethnic populations worldwide consume poultry products. Whereas poultry litter (PL) is a traditionally inexpensive and effective fertilizer to improve soil quality and agricultural productivity, overapplication to soils has raised concerns because excess nutrients in runoff could accelerate the eutrophication of fresh bodies of water. A long‐term field experiment of land application of PL to soils used for pasture growth has been maintained for nearly two decades in the Sand Mountain region of north Alabama, USA. In this work, several soil parameters impacted by the long‐term applied litter were characterized. The findings clearly support previous general observations that long‐term applied litter on pasture soils altered soil properties and macrocation levels. Unlike other studies, however, the effects of applied litter at multiple rates and years were examined, thus revealing the dynamic impacts on soil properties. Hay yields increased with the increase of years of PL application, regardless of the applied rate. This observation was consistent with previous observations that the labile phosphorus (P) portion in these soils increases with application years whereas total P increases with the cumulative applied PL amounts. Poultry litter application did not markedly affect soil electric conductivity, bulk density, or sodium (Na) or potassium (K) levels, especially at the soil surface (0–20 cm). Soil pH, carbon (C), C/nitrogen (N) ratio, calcium (Ca), and magnesium (Mg) were profoundly affected at all three soil depths (0–20, 20–40, and 40–60 cm). Most soil parameters analyzed in this study reached peak values with 10–15 years of applied litter. This observation suggests that there was a turning point of impact for applied litter around 10 years: prior to that the soil macrocations were altered positively as a result of accumulative functions. Continuous litter application may negatively alter a soil's capacity to retain macrocations, leading to less impact observed in this study. In other words, pasture soils with more than 10 years of applied litter would have higher potential for leaching and runoff. Our observation suggested that best management practices for land application of PL should take into consideration the different effects of PL application history.     

Indirect host effect on ectomycorrhizal fungi: Leaf fall and litter quality explain changes in fungal communities on the roots of co-occurring Mediterranean oaks

Host trees can modify their soil abiotic conditions through their leaf fall quality which in turn may influence the ectomycorrhizal (ECM) fungal community composition. We investigated this indirect interaction using a causal modelling approach. We identified ECM fungi on the roots of two coexisting oak species growing in two forests in southern Spain - Quercus suber (evergreen) and Quercus canariensis (winter deciduous)-using a PCR-based molecular method. We also analysed the leaf fall, litter and soil sampled beneath the tree canopies to determine the concentrations of key nutrients. The total mycorrhizal pool was comprised of 69 operational taxonomic units (OTUs). Tomentella and Russula were the most species-rich, frequent and abundant genera. ECM fungi with epigeous and resupinate fruiting bodies were found in 60% and 34% of the identified mycorrhizas, respectively. The calcium content of litter, which was significantly higher beneath the winter-deciduous oak species due to differences in leaf fall quality, was the most important variable for explaining ECM species distribution. The evaluation of alternative causal models by the d-sep method revealed that only those considering indirect leaf fall-mediated host effects statistically matched the observed covariation patterns between host, environment (litter, topsoil, subsoil) and fungal community variables.     

Soil carbon and nitrogen changes after clearing mulga (Acacia aneura) vegetation in Queensland,Australia: Observations,simulations and scenario analysis

In the work reported here we examine the changes in soil (organic) carbon and nitrogen that are observed after converting a stand of nitrogen-fixing mulga trees (Acacia aneura) to buffel-grass (Cenchrus ciliaris) pasture that contained no nitrogen-fixing legumes. A range of previously reported field measurements was compared against the output of CenW 3.1, a reformulated version of the CENTURY model.The model successfully reproduced the observed patterns of soil carbon, C:N ratios and nitrogen mineralisation rates under mulga vegetation. This included relatively small changes in carbon concentration down to 1 m, C:N ratios of around 11–13 across all soil depths, substantial nitrogen mineralisation rates to a depth of 90 cm and, after clearing, an on-going decrease in soil organic carbon and nitrogen stocks.Interpretation of experimental observations was made difficult by the addition of a large amount of ‘dead’ organic matter from killed mulga roots after clearance. This material may be excluded through sieving (to 2 mm) in measurements taken shortly after tree removal, but may be included in later-year sampling as the partly decomposed material might be able to pass through sieves. Past work has usually ignored consideration of dead coarse roots. For the site carbon budget, changes in live biomass and surface litter significantly outweighed the small changes in soil organic carbon, and changes in decaying coarse roots were quantitatively more important than changes in other organic carbon pools.Modelled nitrogen mineralisation rates were lower under buffel-grass than those under mulga and showed significant year-to-year variations that were in line with varying rainfall. It showed no consistent trend over the first 20 years after clearing because the effect of decreasing nitrogen stocks was balanced by an increase in organic matter quality with the change from lignin-rich mulga litter to buffel-grass litter with lower lignin concentration. Nitrogen mineralisation rates gradually decreased thereafter as nitrogen stocks continued to decrease but litter quality stabilised.A scenario analysis showed that soil carbon and nitrogen trends could be affected by changing the nitrogen budget through inclusion of legumes or cessation of nutrient removal by grazing animals. Inclusion of legumes was needed to halt the decline in soil nitrogen and to ensure the long-term maintenance, or increase, in nitrogen stocks.     

Soil carbon and related soil properties along a soil type and land‐use intensity gradient,New South Wales,Australia

The aim of this study was to systematically quantify differences in soil carbon and key related soil properties along a replicated land‐use intensity gradient on three soil landscapes in northwest New South Wales, Australia. Our results demonstrate consistent land‐use effects across all soil types where C, N and C:N ratio were in the order woodland > unimproved pasture = improved pasture > cultivation while bulk density broadly showed the reverse pattern. These land‐use effects were largely restricted to the near surface soil layers. Improved pasture was associated with a significant soil acidification, indicating that strategies to increase soil carbon through pasture improvement in these environments might also have associated soil degradation issues. Total soil carbon stocks were significantly larger in woodland soils, across all soil types, compared with the other land‐uses studied. Non‐wooded systems, however, had statistically similar carbon stocks and this pattern persisted whether or not carbon quantity was corrected for equivalent mass. Our results suggest that conversion from cultivation to pasture in this environment would yield between 0.06 and 0.15 t C/ha/yr which is at the lower end of predicted ranges in Australia and well below values measured in other cooler, wetter environments. We estimate that a 10% conversion rate (cultivation to pasture) across NSW would yield around 0.36 Mt CO₂‐e/yr which would contribute little to emission reductions in NSW. We conclude that carbon accumulation in agricultural soils in this environment might be more modest than current predictions suggest and that systematically collected, regionally specific data are required for the vegetation communities and full range of land‐uses before accurate and reliable predictions of soil carbon change can be made across these extensive landscapes.     

基于一种逆建模方法的法国土壤碳输入量估算研究

Development of a quantitative understanding of soil organic carbon (SOC) dynamics is vital for management of soil to sequester carbon (C) and maintain fertility, thereby contributing to food security and climate change mitigation. There are well-established process-based models that can be used to simulate SOC stock evolution; however, there are few plant residue C input values and those that exist represent a limited range of environments. This limitation in a fundamental model component (i.e., C input) constrains the reliability of current SOC stock simulations. This study aimed to estimate crop-specific and environment-specific plant-derived soil C input values for agricultural sites in France based on data from 700 sites selected from a recently established French soil monitoring network (the RMQS database). Measured SOC stock values from this large scale soil database were used to constrain an inverse RothC modelling approach to derive estimated C input values consistent with the stocks. This approach allowed us to estimate significant crop-specific C input values (P < 0.05) for 14 out of 17 crop types in the range from 1.84 ± 0.69 t C ha^-1 year^-1 (silage corn) to 5.15 ± 0.12 t C ha^-1 year^-1 (grassland/pasture). Furthermore, the incorporation of climate variables improved the predictions. C input of 4 crop types could be predicted as a function of temperature and 8 as a function of precipitation. This study offered an approach to meet the urgent need for crop-specific and environment-specific C input values in order to improve the reliability of SOC stock prediction.     

Organic Carbon Dynamics in Different Soil Types After Conversion of Forest to Agriculture

State‐of‐the‐art predictive models of soil organic carbon (SOC) dynamics associated with land use changes are unable to reflect the diversity of tropical soil types as the knowledge of contrasting site‐specific factors in mediating the response of the SOC pool is sparse. This paper examines the influence of soil type and management on SOC dynamics following the conversion of forests to annual cropping in Ghana. Soil from primary forests and from areas with short (2–7 years) and long (20 years) histories of maize cultivation was sampled from a Vertisol dominated by smectite and Ultisol dominated by kaolinite. Wet sieving was used to separate soil fractions below and above 250 µm. SOC concentrations and δ¹³C signatures of SOC in soil fractions and bulk soil were determined. SOC stocks were calculated by the commonly used fixed depth approach and by the equivalent soil mass approach. After 20 years of cultivation of the Vertisol, the total SOC content was 40 per cent lower than under forest, and about 95 per cent of the forest‐derived SOC had been lost. After 20 years of cultivation of the Ultisol, total SOC content was only about 20 per cent lower than under forest and merely 30 per cent of the forest‐derived SOC had been lost. Both soil types were managed as they would typically be in small scale farming systems, thus the higher SOC losses and the substantial loss of forest‐derived SOC from the Vertisol question the conventional concept of smectite having a higher SOC‐stabilizing potential than kaolinite under field conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

S‐World: A Global Soil Map for Environmental Modelling

The research community increasingly analyses global environmental problems like climate change and desertification with models. These global environmental modelling studies require global, high resolution, spatially exhaustive, and quantitative data describing the soil profile. This study aimed to develop a pedological approach that takes stock of available legacy and auxiliary data to create a global, 30 arc second soil property database for modelling. The methodology uses the Harmonized World Soil Database and the ISRIC‐WISE 3.1 soil profile database. Auxiliary information at 30 arc second resolution for various landscape properties is used to describe the variation in landscape properties (temperature and precipitation, topography, elevation, land use, and land cover). Complex mapping units of the HWSD were first disaggregated using a digital elevation model and toposequences to generate delineated areas described by a single soil type. Secondly, ranges of soil properties per soil type were determined using the soil profile data. Then a meta‐analysis on a broad literature survey was used to develop a simple model that, based on landscape properties at a particular location, determines the position within these ranges and thus provides an estimation of the local soil properties. Finally, the model was implemented at the global level to determine the distribution of soil properties. The methodology, denominated S‐World (Soils of the world) resulted in readily available, high resolution, global soil property maps that are now available for environmental modelling. © 2016 The Authors Journal of Behavioral Decision Making Published by John Wiley & Sons Ltd.