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.     

Tropical forests: Their past,present, and potential future role in the terrestrial carbon budget

In this paper we review results of research to summarize the state-of-knowledge of the past, present, and potential future roles of tropical forests in the global C cycle. In the pre-industrial period (ca. 1850), the flux from changes in tropical land use amounted to a small C source of about 0.06 Pg yr^?1. By 1990, the C source had increased to 1.7 ± 0.5 Pg yr^?1. The C pools in forest vegetation and soils in 1990 was estimated to be 159 Pg and 216 Pg, respectively. No concrete evidence is available for predicting how tropical forest ecosystems are likely to respond to CO₂ enrichment and/or climate change. However, C sources from continuing deforestation are likely to overwhelm any change in C fluxes unless land management efforts become more aggressive. Future changes in land use under a “business as usual” scenario could release 41–77 Pg C over the next 60 yr. Carbon fluxes from losses in tropical forests may be lessened by aggressively pursued agricultural and forestry measures. These measures could reduce the magnitude of the tropical C source by 50 Pg by the year 2050. Policies to mitigate C losses must be multiple and concurrent, including reform of forestry, land tenure, and agricultural policies, forest protection, promotion of on-farm forestry, and establishment of plantations on non-forested lands. Policies should support improved agricultural productivity, especially replacing non-traditional slash-and-burn agriculture with more sustainable and appropriate approaches.     

N<Subscript>2</Subscript>O production pathways relate to land use type in acidic soils in subtropical China

Purpose

Agricultural practises impact soil properties and N transformation rate, and have a greater effect on N₂O production pathways in agricultural soils compared with natural woodland soils. However, whether agricultural land use affects N₂O production pathways in acidic soils in subtropical regions remains unknown.

Materials and methods

In this study, we collected natural woodland soil (WD) and three types of agricultural soils, namely upland agricultural (UA), tea plantation (TP) and bamboo plantation (BP) soils. We performed paired ¹⁵N-tracing experiment to investigate the effects of land use types on N₂O production pathways in acidic soils in subtropical regions in China.

Results and discussion

The results revealed that heterotrophic nitrification is the dominant pathway of N₂O production in WD, accounting for 44.6 % of N₂O emissions, whereas heterotrophic nitrification contributed less than 2.7 % in all three agricultural soils, due to a lower organic C content and soil C/N ratio. In contrast, denitrification dominated N₂O production in agricultural soils, accounting for 54.5, 72.8 and 77.1 % in UA, TP and BP, respectively. Nitrate (NO₃ ^?) predominantly affected the contribution from denitrification in soils under different land use types. Autotrophic nitrification increased after the conversion of woodland to agricultural lands, peaking at 42.8 % in UA compared with only 21.5 % in WD, and was positively correlated with soil pH. Our data suggest that pH plays a great role in controlling N₂O emissions through autotrophic nitrification following conversion of woodland to agricultural lands.

Conclusions

Our results demonstrate the variability in N₂O production pathways in soils of different land use types. Soil pH, the quantity and quality of organic C and NO₃ ^? content primarily determined N₂O emissions. These results will likely assist modelling and mitigation of N₂O emissions from different land use types in subtropical acidic soils in China and elsewhere.

     

Net fluxes of CO2, but not N2O or CH4, are affected following agronomic-scale additions of urea to prairie and arable soils

While experimental addition of nitrogen (N) tends to enhance soil fluxes of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), it is not known if lower and agronomic-scale additions of urea-N applied also enhance trace gas fluxes, particularly for semi-arid agricultural lands in the northern plains. We aimed to test if this were true at agronomic rates [low (11 kg N ha⁻¹), moderate (56 kg N ha⁻¹), and high (112 kg N ha⁻¹)] for central North Dakota arable and prairie soils using intact soil cores to minimize disturbance and simulate field conditions. Additions of urea to cores incubated at 21 °C and 57% water-filled pore space enhanced fluxes of CO₂ but not CH₄ and N₂O. At low, moderate, and high urea-N, CO₂ fluxes were significantly greater than control but not fluxes of CH₄ and N₂O. The increases in CO₂ emission with rate of urea-N application indicate that agronomic-scale N inputs may stimulate microbial carbon cycling in these soils, and that the contribution of CO₂ to net greenhouse gas source strength following fertilization of semi-arid agroecosystems may at times be greater than contributions by N₂O and CH₄.     

Carbon sequestration in agricultural soils in the Cerrado region of the Brazilian Amazon

The introduction of crop management practices after conversion of Amazon Cerrado into cropland influences soil C stocks and has direct and indirect consequences on greenhouse gases (GHG) emissions. The aim of this study was to quantify soil C sequestration, through the evaluation of the changes in C stocks, as well as the GHG fluxes (N₂O and CH₄) during the process of conversion of Cerrado into agricultural land in the southwestern Amazon region, comparing no-tillage (NT) and conventional tillage (CT) systems. We collected samples from soils and made gas flux measurements in July 2004 (the dry season) and in January 2005 (the wet season) at six areas: Cerrado, CT cultivated with rice for 1 year (1CT) and 2 years (2CT), and NT cultivated with soybean for 1 year (1NT), 2 years (2NT) and 3 years (3NT), in each case after a 2-year period of rice under CT. Soil samples were analyzed in both seasons for total organic C and bulk density. The soil C stocks, corrected for a mass of soil equivalent to the 0–30-cm layer under Cerrado, indicated that soils under NT had generally higher C storage compared to native Cerrado and CT soils. The annual C accumulation rate in the conversion of rice under CT into soybean under NT was 0.38 Mg ha⁻¹ year⁻¹. Although CO₂ emissions were not used in the C sequestration estimates to avoid double counting, we did include the fluxes of this gas in our discussion. In the wet season, CO₂ emissions were twice as high as in the dry season and the highest N₂O emissions occurred under the NT system. There were no CH₄ emissions to the atmosphere (negative fluxes) and there were no significant seasonal variations. When N₂O and CH₄ emissions in C-equivalent were subtracted (assuming that the measurements made on 4 days were representative of the whole year), the soil C sequestration rate of the conversion of rice under CT into soybean under NT was 0.23 Mg ha⁻¹ year⁻¹. Although there were positive soil C sequestration rates, our results do not present data regarding the full C balance in soil management changes in the Amazon Cerrado.     

Land Use and Soil Organic Carbon in China’s Village Landscapes

Village landscapes, which integrate small-scale agriculture with housing, forestry, and a host of other land use practices, cover more than 2 million square kilometers across China. Village lands tend to be managed at very fine spatial scales (≤ 30 m), with managers both adapting their practices to existing variation in soils and terrain (e.g., fertile plains vs. infertile slopes) and also altering soil fertility and even terrain by terracing, irrigation, fertilizing, and other land use practices. Relationships between fine-scale land management patterns and soil organic carbon (SOC) in the top 30 cm of village soils were studied by sampling soils within fine-scale landscape features using a regionally weighted landscape sampling design across five environmentally distinct sites in China. SOC stocks across China’s village regions (5 Pg C in the top 30 cm of 2 × 10 6 km 2 ) represent roughly 4% of the total SOC stocks in global croplands. Although macroclimate varied from temperate to tropical in this study, SOC density did not vary significantly with climate, though it was negatively correlated with regional mean elevation. The highest SOC densities within landscapes were found in agricultural lands, especially paddy, the lowest SOC densities were found in nonproductive lands, and forest lands tended toward moderate SOC densities. Due to the high SOC densities of agricultural lands and their predominance in village landscapes, most village SOC was found in agricultural land, except in the tropical hilly region, where forestry accounted for about 45% of the SOC stocks. A surprisingly large portion of village SOC was associated with built structures and with the disturbed lands surrounding these structures, ranging from 18% in the North China Plain to about 9% in the tropical hilly region. These results confirmed that local land use practices, combined with local and regional variation in terrain, were associated with most of the SOC variation within and across China’s village landscapes and may be an important cause of regional variation in SOC.     

Offsetting global CO2 emissions by restoration of degraded soils and intensification of world agriculture and forestry

Increase in atmospheric concentration of CO₂ from 285 parts per million by volume (ppmv) in 1850 to 370 ppm in 2000 is attributed to emissions of 270 ± 30 Pg carbon (C) from fossil fuel combustion and 136 ± 55 Pg C by land‐use change. Present levels of anthropogenic emissions involve 6·3 Pg C by fossil fuel emissions and 1·8 Pg C by land‐use change. Out of the historic loss of terrestrial C pool of 136 ± 55 Pg, 78 ± 12 Pg is due to depletion of soil organic carbon (SOC) pool comprising 26 ± 9 Pg due to accelerated soil erosion. A large proportion of the historic SOC lost can be resequestered by enhancing the SOC pool through converting to an appropriate land use and adopting recommended management practices (RMPs). The strategy is to return biomass to the soil in excess of the mineralization capacity through restoration of degraded/desertified soils and intensification of agricultural and forestry lands. Technological options for agricultural intensification include conservation tillage and residue mulching, integrated nutrient management, crop rotations involving cover crops, practices which enhance the efficiency of water, plant nutrients and energy use, improved pasture and tree species, controlled grazing, and judicious use of inptus. The potential of SOC sequestration is estimated at 1–2 Pg C yr⁻¹ for the world, 0·3–0·6 Pg C yr⁻¹ for Asia, 0·2–0·5 Pg C yr⁻¹ for Africa and 0·1–0·3 Pg C yr⁻¹ for North and Central America and South America, 0·1–0·3 Pg C yr⁻¹ for Europe and 0·1–0·2 Pg C yr⁻¹ for Oceania. Soil C sequestration is a win–win strategy; it enhances productivity, improves environment moderation capacity, and mitigates global warming. Copyright © 2003 John Wiley & Sons, Ltd.     

农田改为农林(草)复合系统对红壤CO2和N2O排放的影响

以鄂南玉米地、紫穗槐/玉米地、香根草/玉米地、紫穗槐林地、香根草草地与撂荒地6种土地利用类型为研究对象,利用静态箱法,对夏玉米生长期间土壤CO2和N2O通量及影响因子进行了测定,研究我国北亚热带丘陵红壤区农田改变为林(草)地和农林(草)复合系统后土壤CO2和N2O排放特征。研究结果表明:(1)土地利用方式改变后,撂荒地土壤CO2排放量明显低于其他5种土地利用类型,但紫穗槐/玉米地、单作玉米地、香根草/玉米地、紫穗槐林地、香根草草地5种土地利用类型之间土壤CO2排放量差异不显著。(2)玉米生长期间,6种不同土地利用方式下,土壤N2O排放总量从高到低依次为紫穗槐/玉米地(508 g·hm-2·a-1)、紫穗槐林地(470 g·hm-2·a-1)、撂荒地(390 g·hm-2·a-1)、香根草/玉米地(373 g·hm-2·a-1)、香根草草地(372 g·hm-2·a-1)、单作玉米地(285 g·hm-2·a-1)。(3)土壤CO2通量与土壤有机碳、土壤微生物生物量碳和土壤含水量无显著相关关系;土壤N2O通量与土壤氮素净矿化率呈显著线性相关,但与土壤无机氮和土壤含水量无显著相关关系。农田改变为农林(草)复合系统可能潜在地增加土壤CO2和N2O排放;农田改变为林(草)地可能潜在地减少土壤CO2排放,增加土壤N2O排放。     

RothCUK – a dynamic modelling system for estimating changes in soil C from mineral soils at 1-km resolution in the UK

We describe the development and application of an integrated data and modelling system for estimating soil carbon (C) fluxes from mineral soils caused by changes in climate, land use and land management at 1‐km resolution in the UK (RothCUK). The system was developed with the aim of improving methods for United Nations Framework Convention on Climate Change (UNFCCC) and Kyoto Protocol accounting and integrates national scale data sets of soil properties, land use and climate with the Rothamsted carbon model (RothC). A preliminary estimate of soil C fluxes because of land use change (LUC) over the period 1990–2000 is presented as an example application of the system. RothCUK shows LUC to be a net source of CO₂ from 1990 to 2000 although the RothC estimate was smaller (6488 kt C) than the estimate from the single exponential model (SEM) method currently used to calculate C fluxes due to LUC for the UK National Greenhouse Gas Inventory (mean: 9412 kt C). Based on previous studies, an uncertainty range in our estimates of ±50–100% seems plausible. In agreement with the SEM, RothCUK suggests that the largest single contributor to soil C fluxes from LUC was conversion of grassland to arable land. Differences between the results may be attributed to differences in the two models and the assumptions and underlying data used in making the calculations. The RothCUK system provides a powerful method for estimating changes in soil C stocks, enabling areas and management systems with particularly large changes in soil C stocks to be located at fine resolution.     

1992-2015年中亚五国LUCC特征及耕地驱动力研究

中亚五国地处亚欧大陆的中心地带,是"一带一路"重要的沿线节点之一。借助GIS空间统计分析方法,以欧洲太空局气候变化项目全球土地覆盖数据为基础,利用土地利用程度、动态度和转移矩阵对中亚五国1992—2015年土地利用/覆盖变化(LUCC)特征进行分析,并运用地理探测器对耕地驱动力进行深入研究。结果表明:1)1992—2015年,中亚五国的土地利用格局总体上表现为耕地和城镇用地持续增加,林地、草地和水域呈减少的趋势。耕地的增加主要来自林地(7.88万km~2)和草地(5.27万km~2)的转入,城镇用地的增加主要来自耕地(0.50万km~2)的转入,耕地是仅次于城镇用地增速较快、变化最为显著的土地利用类型;城镇用地在各国均呈现增加的趋势,耕地除乌兹别克斯坦之外,在其他4国均呈现增加的趋势。2)1992—2015年中亚五国土地利用程度总体呈缓慢上升趋势(土地利用程度综合指数从1992年的193.34增加到2015年的197.41),即土地利用处于发展阶段;土地利用程度为耕地林地草地未利用地水域城镇用地。3)地理探测器对耕地变化驱动因素的分析结果表明,自然因素中年平均降水量对耕地变化的作用较为显著,但在短时间内社会和农业因素发挥决定性的作用;因子探测表明人口总数(0.882)和农村人口(0.881)对耕地扩张的影响力最大,其次为粮食单产(0.746);交互探测表明各因子交互作用均为互相增强,其中,农村人口与粮食单产的叠加作用对耕地扩张的解释力度最大(0.972),影响耕地扩张的主要因素可归纳为人口增长和粮食单产提高。本研究可为中亚五国土地利用格局演变、区域土地利用规划和土地资源可持续利用提供决策支持。     

Carbon fluxes and the carbon budget in agroecosystems on agro-gray soils of the forest-steppe in the Baikal region

Field studies devoted to the transformation of the carbon cycle in agroecosystems on agro-gray soils (including soils contaminated with fluorides from aluminum smelters) in dependence on the changes in the hydrothermic conditions were performed for the first time within the framework of the long-term (1996–2010) soil monitoring in the forest-steppe zone of the Baikal region. The major attention was paid to the impact of the environmental factors on the synthesis and microbial destruction of organic carbon compounds. Certain differences in the fluxes and budget of carbon were found for the plots with cereal and row crops and for the permanent and annual fallow plots. The adverse effect of fluorides manifested itself in the enhanced C-CO₂ emission under unfavorable water and temperature conditions. The long-term average C-CO₂ emission from the soils contaminated with fluorides in agroecosystems with wheat after fallow was higher than that from the uncontaminated soil (179 and 198 g of C/m², respectively) and higher than that in the agroecosystems with a potato monoculture (129 and 141 g of C/m², respectively). At the same time, no significant variations in the content of the carbon of the microbial biomass (C_micr) in dependence on the environmental factors were found. The utilization of carbon for respiration and for growth of the soil microorganisms on the contaminated soil were unbalanced in particular years and for the entire period of the observations. The ratio between the fluxes of the net mineralized and re-immobilized carbon was used for the integral assessment of the functioning regime of the agroecosystems and the loads on them. Independently from the soil contamination with fluorides, the loads on the agroecosystems with wheat were close to the maximum permissible value, and the loads on the agroecosystems with potatoes were permissible. It was shown that the carbon deficit in the uncontaminated soils was similar under the wheat and potatoes (?30 and ?28 g of C/m², respectively). In the contaminated soils, it was higher under the potato monoculture and reached ?41 g of C/m².     

Use of Cs to estimate tillage- and water-induced soil redistribution rates on agricultural land under different use and management in central-south Chile

The purpose of this research was to evaluate the applicability of conventional ¹³⁷Cs sampling and a simplified approach, for estimating medium-term tillage- and water-induced soil erosion and sedimentation rates on agricultural land in Chile. For this purpose, four study sites under contrasting land use and management were selected in central-south Chile. First, a conventional ¹³⁷Cs approach, based on grid sampling was applied, adapting a mass balance conversion model incorporating soil movement by tillage to the site specific conditions of the study region. Secondly, using the same conversion model, the feasibility of estimating soil redistribution rates from measurements of ¹³⁷Cs inventories based on composite soil samples taken along contour lines was also tested at all four sites. The redistribution rates associated with tillage and water and the total rates estimated using both methods correlated strongly at all four sites. The conventional method provides more detailed information concerning the redistribution processes operating over the landscape. The simplified method is suitable for assessing soil loss and sediment accumulation in areas exhibiting simple topography and almost similar slopes along the contour lines. Under these conditions, this method permits faster estimation of soil redistribution rates, providing the possibility of estimating soil redistribution rates over larger areas in a shorter time. In order to optimise the costs and benefits of the methods, the sampling and inventory quantification strategy must be selected according to the resolution of the required information, and the scale and complexity of the landscape relief. Higher tillage- and water-induced erosion rates were observed in the annually ploughed cropland sites than in the semi-permanent grassland sites. Subsistence managed crop and grassland sites also show greater erosion effects than the commercially managed sites. The ¹³⁷Cs methods used permit discrimination between redistribution rates observed on agricultural land under different land use and management. The ¹³⁷Cs technique must be seen as an efficient method for estimating medium-term soil redistribution rates, and for planning soil conservation and sustainable agricultural production under the climatic conditions and the soil type of the region of Chile investigated.     

Modeling Regional Carbon Dynamics and Soil Erosion in Disturbed and Rehabilitated Ecosystems as Affected by Land Use and Climate

The quantification of carbon (C) and nitrogen (N) cycling inecosystems is important for (a) understanding changes inecosystem structure and function with changes in land use, (b)determining the sustainability of ecosystems, and (c) balancingthe global C budget as it relates to global climate change.A meso-scale study was conducted to determine regional effectsof climate change on C and N cycling within disturbedecosystems. Objectives of the research were to quantify (a)sediment yield, (b) current C storage in vegetation and soils,and (c) soil C efflux from both abandoned and rehabilitatedcoal surface-mined lands in Ohio. A dynamic model was developedto simulate sediment yield, grassland production, and C and Ncycling on surface-mined lands. Evaluation of plant productionand soil erosion submodels with data sets from surface-minedlands in the mid-western U.S. resulted in r² values of 0.99 and0.97, respectively. Depending on the initial values of soil organic carbon (SOC),model simulations estimated that unvegetated surface-mined landsin Ohio yield approximately 441,325 Mg yr^-1 of sediment andemit between 2,000–20,000 Mg yr^-1 of C to the atmosphere fromdecomposition of SOC. While rehabilitated lands had a higher Cefflux rate than barren lands, a positive C sequestration rateof 18.4 Mg km^-2 yr ^-1 was estimated as a result oforganic matter additions. This sequestion rate increasedconsiderably under projected climate change scenarios, while itdecreased when simulated rehabilitated grasslands were harvestedfor hay. Changes in land use and cover can cause surface-minedlands to be either a net sink or source for C. Successful rehabilitation of mined lands can decrease erosion and promotesoil C sequestration, while at the same time providingadditional lands for the management of natural resources.     

Impacts of land use and cropland management on soil organic matter and greenhouse gas emissions in the Brazilian Cerrado

The Brazilian Cerrado is a large and expanding agricultural frontier, representing a hotspot of land-use change (LUC) from natural vegetation to farmland. It is known that this type of LUC impacts soil organic matter (SOM) dynamics, particularly labile carbon (C) pools (living and non-living), decreasing soil health and agricultural sustainability, as well as increasing soil greenhouse gas (GHG) emissions, and accelerating global climate change. In this study, we quantified the changes in the quantity and quality of SOM and GHG fluxes due to changes in land use and cropland management in the Brazilian Cerrado. The land uses studied were native vegetation (NV), pasture (PA) and four croplands, including the following management types: conventional tillage with a single soybean crop (CT), and three no-tillage systems with two crops cultivated in the same year (i.e., soybean/sorghum (NT_SSo), soybean/millet (NT_SMi) and maize/sorghum (NT_MSo)). Soil and gases were sampled in the rainy season (November, December and January) and dry season (May, July and September). The highest soil C and nitrogen (N) stocks (6.7 kg C m⁻² and 0.5 kg N m⁻², 0–0.3-m layer) were found under NV. LUC reduced C stocks by 25% in the CT and by 10% in the PA and NT. Soil N stocks were 30% lower in the PA and NT_MSo and 15% lower in the croplands with soybean compared to NV. δ¹³C values clearly distinguished between the C-origin from NV (−25‰) and that from other land uses (−16‰). Soil (0–0.1 m) under NV also presented higher labile-C (625 g C m⁻²), microbial-C (70 g C m⁻²) and microbial-N (5.5 g N m⁻²), whereas other land uses presented values three times lower. GHG emissions (expressed as C-equivalent) were highest in the NV (1.2 kg m⁻² year⁻¹), PA (1.3 kg m⁻² year⁻¹) and NT_MSo (0.9 kg m⁻² year⁻¹) and were positively related to the higher SOM turnover in these systems. Our results suggest that in order to maintain SOM, it is necessary to adopt “best” management practices, that provide large plant residue inputs (above- and belowground). This can be seen as a pathway to achieving high food production with low GHG emissions.     

Water quality in relation to land use and land cover in the upper Han River Basin,China

A total of 42 sampling sites were selected in the riverine network of the upper Han River basin (approximately 95, 200 km²) of China. Over the time period of 2005–2006, 252 water samples were collected and analyzed for physico-chemical variables in order to investigate their spatio-temporal variability in particular the relationship with land use and land cover. Analysis of variance (ANOVA) indicated significant spatial variability in pH, EC, TDS, turbidity, SPM, ORP and nitrogen across the basin. Meanwhile, nitrogen, ORP, I_Mn and turbidity generally displayed higher values in the rainy season. Correlation analysis and regression analysis indicated that water temperature, I_Mn, and nitrogen were significantly related to vegetated coverage, and subwatersheds with higher vegetation cover had relative lower turbidity, SPM, I_Mn, nutrients and TDS. Bare lands had significant influence on nitrogen concentration in the riverine network, implying its large geologic sources in the basin. Percentage of urban area was the predictor for pH and DP, while agricultural land for SPM and I_Mn. The research could provide critical information in sustainable land use practice for water resource conservation for the basin.     

Belowground carbon allocation patterns in a dry Mediterranean ecosystem: A comparison of two models

Total belowground C allocation (TBCA) accounts for a large fraction of gross primary production, it may overtake aboveground net primary production, and contributes to the primary source of detrital C in the mineral soil. Here, we measure soil respiration, water erosion, litterfall and estimate annual changes in C stored in mineral soil, litter and roots, in three representative land uses in a Mediterranean ecosystem (late-successional forest, abandoned agricultural field, rain-fed olive grove), and use two C balance approaches (steady-state and non-steady-state) to estimate TBCA. Both TBCA approaches are compared to assess how different C fluxes (outputs and inputs) affect our estimates of TBCA within each land use. In addition, annual net primary productivity is determined and C allocation patterns are examined for each land use. We hypothesized that changes in C stored in mineral soil, litter and roots will be slight compared to soil respiration, but will still have a significant effect on the estimates of TBCA. Annual net primary productivity was 648 ± 31.5, 541 ± 42.3 and 324 ± 22.3 g C m⁻² yr⁻¹ for forest, abandoned agricultural field and olive grove, respectively. Across land uses, more than 60% of the C was allocated belowground. Soil respiration (F_S) was the largest component in the TBCA approaches across all land uses. Annual C losses through water erosion were negligible compared to F_S (less than 1%) and had little effect on the estimates of TBCA. Annual changes in C stored in the soil, litter layer and roots were low compared to F_S (16, 24 and 10% for forest, abandoned agricultural field and olive grove, respectively), but had a significant effect on the estimates of TBCA. In our sites, an assumption that Δ[C_S + C_R + C_L]/Δt = 0 will underestimate TBCA, particularly in the abandoned agricultural field, where soil C storage may be increasing more rapidly. Therefore, the steady-state model is unsuited to these Mediterranean ecosystems and the full model is recommended.     

Historical influences on the vegetation and soils of the Martha’s Vineyard, Massachusetts coastal sandplain: Implications for conservation and restoration

Both disturbance history and previous land use influence present-day vegetation and soils. These influences can have important implications for conservation of plant communities if former disturbance and land use change species abundances, increase colonization of nonnative plant species or if they alter soil characteristics in ways that make them less suitable for species of conservation interest. We compared the plant species composition, the proportion of native and nonnative plant species, and soil biogeochemical characteristics across seven dominant land use and vegetation cover types on the outwash sandplain of Martha’s Vineyard that differed in previous soil tillage, dominant overstory vegetation and history of recent prescribed fire. The outwash sandplain supports many native plant species adapted to dry, low nutrient conditions and maintenance of native species is a management concern. There was broad overlap in the plant species composition among pine (Pinus resinosa, P. strobus) plantations on untilled soils, pine plantations on formerly tilled soils, scrub oak (Quercus ilicifolia) shrublands, tree oak (Q. velutina, Q. alba) woodlands, burned tree oak woodlands, and sandplain grasslands. All of these land cover categories contained few nonnative species. In contrast, agricultural grasslands had high richness and cover of nonnative plants. Soil characteristics were also similar among all of the woodland, shrubland and grassland land cover categories, but soils in agricultural grasslands had higher pH, extractable Ca²⁺ and Mg²⁺ in mineral soils and higher rates of net nitrification. The similarity of soils and significant overlap in vegetation across pine plantations, scrub oak shrublands, oak woodlands and sandplain grasslands suggests that the history of land use, current vegetation and soil characteristics do not pose a major barrier to management strategies that would involve conversion among any of these vegetation types. The current presence of high cover of nonnative species and nutrient-enriched soils in agricultural grasslands, however, may pose a barrier to expansion of sandplain grasslands or shrublands on these former agricultural lands if native species are not able to outcompete nonnative species in these anthropogenically-enriched sites.     

Changes in soil carbon and crop yield over 60 years in the Zurich Organic Fertilization Experiment,following land‐use change from grassland to cropland

Changes in land‐use and agricultural management affect soil organic C (SOC) storage and soil fertility. Grassland to cropland conversion is often accompanied by SOC losses. However, fertilization, crop rotation, and crop residue management can offset some SOC losses or even convert arable soils into C sinks. This paper presents the first assessment of changes in SOC stocks and crop yields in a 60‐year field trial, the Zurich Organic Fertilization Experiment A493 (ZOFE) in Switzerland. The experiment comprises 12 treatments with different organic, inorganic and combined fertilization regimes. Since conversion to arable land use in 1949, all treatments have lost SOC at annual rates of 0.10–0.25 t C ha^?1, with estimated mean annual C inputs from organic fertilizers and aboveground and belowground plant residues of 0.6–2.4 t C ha^?1. In all treatments, SOC losses are still in progress, indicating that a new equilibrium has not yet been reached. Crop yields have responded sensitively to advances in plant breeding and in fertilization. However, in ZOFE high yields can only be ensured when mineral fertilizer is applied at rates typical for modern agriculture, with yields of main crops (winter wheat, maize, potatoes, clover‐grass ley) decreasing by 25–50% when manure without additional mineral fertilizer is applied. ZOFE shows that land‐use change from non‐intensively managed grassland to cropland leads to soil C losses of 15–40%, even in rotations including legumes and intercrops, improved agricultural management and organic fertilizer application.     

Carbon stock assessment and soil carbon management in agricultural land‐uses in Thailand

The organic carbon pool in agricultural land‐uses is capable of enhancing agricultural sustainability and serving as a potential sink of atmospheric carbon dioxide. A study was carried out to estimate and map carbon stock of different agricultural land‐uses in a sub‐watershed of Thailand and to assess the land‐use sustainability with respect to carbon management. A quadrat sampling methodology was adopted to estimate the biomass and its carbon content of 11 different land‐uses in the study area. Existing soil data were used to calculate the soil carbon. GIS was used for integrating biomass carbon, soil carbon and carbon stock mapping. Roth carbon model was used to project the soil carbon of present land‐uses in the coming 10 years and based on which the sustainability of land‐uses was predicted. The total carbon stock of agricultural land‐uses was estimated to be 20·5 Tg, of which 41·49 per cent was biomass carbon and 58·51 per cent was soil carbon. Among the land‐uses, para rubber had the highest average biomass C (136·34 Mg C ha⁻¹) while paddy had the lowest (7·08 Mg C ha⁻¹). About four‐fifths of agricultural land‐uses in the watershed are sustainable in maintaining the desired level of soil carbon in coming 10 years while one‐fifths are unstable. Such information on carbon stock could be valuable to develop viable land‐use options for agricultural sustainability and carbon sequestration. Copyright © 2007 John Wiley & Sons, Ltd.     

Potential for greenhouse gas emissions from soil carbon stock following biofuel cultivation on degraded lands

Consequent to the interest in converting degraded lands for cultivation of biofuel crops, concerns have been expressed about greenhouse gas (GHG) emissions resulting from changes in soil‐carbon (C) stock following land conversions. A literature‐based study was undertaken for estimating the magnitude of emission of GHGs, particularly carbon dioxide (CO₂), following an assessment of the extent and causes of land degradation and the nature of CO₂ emission from soils. The study estimated the potential for CO₂ emission resulting from changes in soil‐carbon stock following land conversions, using oil palm (Elaeis guineensis Jacq.) as a case study. The analysis indicated that, overall, the magnitude of CO₂ emission resulting from changes in soil C stock per se following opening up of degraded land would be low compared with other potential sources of CO₂ emission. However, lack of data on critical aspects such as baseline soil C status was a limitation of the study. Soil respiration is the single best measure of GHG emission from soils. Fixation of C in additional biomass will compensate, over time, for C loss through soil respiration following a change in land use or land management, unless such changes involve conversion of existing large C stocks. Therefore, any net CO₂ emission from soils resulting from changes in soil C stock following opening up of degraded land is likely to be a short‐term phenomenon. The estimations used in the study are based on various assumptions, which need to be validated by experimental field data. Copyright © 2010 John Wiley & Sons, Ltd.