Differences In Soil Organic Carbon Research Articles

Inorganic Fertilization Effects on the Structure of a Calcareous Silt Loam Soil

Core Ideas Long‐term inorganic fertilization decreased aggregate stability. Long‐term inorganic fertilization decreased soil macroporosity. Long‐term inorganic fertilization did not change soil organic C content. Soil water‐holding capacity was not affected by inorganic fertilization. Swine manure combined with inorganic fertilizers improved soil structure. Inorganic fertilizers have been intensely used in the North China Plain (NCP) to maintain or increase crop yields, but their effects on soil physical properties, especially soil structure, are unclear. The objective of this study was to evaluate the effects of 12 yr of successive application of inorganic fertilization on soil aggregate stability, pore structure, and hydraulic properties of a calcareous silt loam soil. A long‐term field experiment (2001–2013) was established at Luancheng Ecosystem Station, NCP. The experiment included three fertilization treatments: (i) inorganic fertilizer, NPK; (ii) inorganic fertilizer and organic manure, NPKOM; and (iii) a control treatment with no fertilizer, CK. Results showed plots receiving long‐term NPK and NPKOM had significantly greater wheat (Triticum aestivum L.) (275 and 307%, respectively) and maize (Zea mays L.) yields (59 and 107%, respectively) than the control. However, the application of inorganic fertilizer significantly decreased aggregate stability and macroporosity, by 55.3 and 36.1%, respectively, relative to the control. No differences in soil organic carbon (SOC), bulk density (BD), saturated conductivity (Ks), and water‐holding capacity were found between the NPK and the CK treatments. On the other hand, the addition of organic manure with inorganic fertilizers increased SOC, total porosity, and saturated conductivity by 38.5, 5.2, and 75%, respectively, compared with the CK treatment. This study indicated inorganic fertilization alone could not improve soil structure of the calcareous silt loam, although it maintained high yields. Use of organic amendments along with inorganic fertilizers can improve soil structure and crop yields.

Previous land use and climate influence differences in soil organic carbon following reforestation of agricultural land with mixed-species plantings

Reforestation of agricultural land with mixed-species environmental plantings (native trees and shrubs) can contribute to mitigation of climate change through sequestration of carbon. Although soil carbon sequestration following reforestation has been investigated at site- and regional-scales, there are few studies across regions where the impact of a broad range of site conditions and management practices can be assessed. We collated new and existing data on soil organic carbon (SOC, 0–30cm depth, N=117 sites) and litter (N=106 sites) under mixed-species plantings and an agricultural pair or baseline across southern and eastern Australia. Sites covered a range of previous land uses, initial SOC stocks, climatic conditions and management types. Differences in total SOC stocks following reforestation were significant at 52% of sites, with a mean rate of increase of 0.57±0.06MgCha−1y−1. Increases were largely in the particulate fraction, which increased significantly at 46% of sites compared with increases at 27% of sites for the humus fraction. Although relative increase was highest in the particulate fraction, the humus fraction was the largest proportion of total SOC and so absolute differences in both fractions were similar. Accumulation rates of carbon in litter were 0.39±0.02MgCha−1y−1, increasing the total (soil+litter) annual rate of carbon sequestration by 68%. Previously-cropped sites accumulated more SOC than previously-grazed sites. The explained variance differed widely among empirical models of differences in SOC stocks following reforestation according to SOC fraction and depth for previously-grazed (R2=0.18–0.51) and previously-cropped (R2=0.14–0.60) sites. For previously-grazed sites, differences in SOC following reforestation were negatively related to total SOC in the pasture. By comparison, for previously-cropped sites, differences in SOC were positively related to mean annual rainfall. This improved broad-scale understanding of the magnitude and predictors of changes in stocks of soil and litter C following reforestation is valuable for the development of policy on carbon markets and the establishment of future mixed-species environmental plantings.

Differences in soil organic carbon and total nitrogen and their impact factors under different restoration patterns in the Loess Plateau.

Knowledge of the effect of different vegetation restoration measures on soil organic carbon (SOC) and total soil nitrogen (TN) is of importance to better understand carbon and nitrogen cycling in terrestrial ecosystems and deal with the global greenhouse effect. The differences in SOC and TN content in 0-100 cm soil profile between different restoration measures and their impact factors were investigated in the Loess Plateau. The results showed that artificial vegetation restoration led to a significant increase in both SOC and TN content in the 0-100 cm soil profile compared with that of cropland. The highest increase in average SOC content was observed in the artificial woodland(1.43 times that of the cropland), followed by the artificial shrubland (1.36 times) and artificial grassland (1.21 times); whereas the highest increase in average TN content was observed in the artificial woodland (1.30 times that of the cropland), followed by the artificial grassland (1.21 times) and artificial shrubland (1.13 times). Compared with the cropland, there was a significant difference in SOC and TN content and fine root density up to a maximum depth of >100 cm in the artificial woodland and shrubland, but about 60 cm in the artificial grassland. The fine root density, soil C:N ratio and aboveground litter production of artificial woodland, shrubland and grassland were significantly higher than that of cropland, and fine root density was significantly linearly correlated with SOC and TN (P<0.01). The quantity and quality of fine root and litter biomass might be the dominant factors contributing to the observed difference in SOC and TN contents between the different artificial vegetation types in the Loess Plateau.

Multi-scale variability of soil carbon and nitrogen in the middle reaches of the Heihe River basin, northwestern China

Insight into the variability of soil carbon and nitrogen at multiple scales is essential for accurately recognizing their distribution and stocks in arid inland river basins where landscape patterns are complex. For this objective, soil sampling and vegetation survey were conducted in 2012 to estimate the regional distribution and analyze the differences of soil organic carbon (SOC), total carbon (TC, the summation of organic and inorganic carbon) and total nitrogen (TN) among landscapes (cropland, desert, woodland and grassland) and sub-regions in the middle reaches of the Heihe River basin, northwestern China. The effects of soil properties, vegetation conditions and management practices on soil C and TN were determined. The results showed that the average regional densities of SOC, TC and TN were 68.2, 216.9 and 6.90Mgha−1 in the 0–80cm soil profile, respectively, and approximately 16% and 31% were stored in the 0–10 and 0–20cm layers, respectively. Cropland stored the highest SOC and TN, whereas grassland stored the highest TC and woodland had the lowest SOC and TC. Variability in soil texture, frequency and amount of irrigation, fertilizer type and fertilization rate contributed to the differences in SOC and TN densities among croplands in the three sub-regions. Cropland and woodland far from the river bank (approximately 16–18km away) accumulated more SOC, TC and TN than those near the river bank (approximately 4km away). Soil texture was the predominant factor influencing SOC and TN in the surface soil of woodland. Aboveground biomass of shrubs and herbs, especially fresh weight, was regarded as a dominant factor affecting TC in desert soil and SOC, TC and TN in grassland soil. The results of this study are essential for accurately recognizing the status and variability of soil C and TN in complex landscape patterns in arid regions.

Comparative Evaluation of Inductively Coupled Plasma–Optical Emission Spectroscopy and Atomic Absorption Spectrophotometry for Determining DTPA-Extractable Micronutrients in Soils

A study was conducted for comparative evaluation of atomic absorption spectrophotometry (AAS) and inductively coupled plasma–optical emission spectroscopy (ICP-OES) for determining extractable zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) in sixty diverse soil samples having a wide range in pH and organic carbon (C). The results were significantly affected by the method of analysis and soil type but generally did not follow a definite trend. Results for extractable Fe in Alfisol samples were significantly greater when using ICP-OES than AAS; and the results for Zn, Cu, and Mn were not significantly different for the two methods. For Vertisol samples, the results for extractable Cu were significantly greater by ICP-OES than by AAS, whereas extractable Fe and Zn were significantly greater by AAS than by ICP-OES, and the results for Mn were not significantly different for the two methods. The results are discussed relative to soil type and differences in soil organic carbon and pH of the samples used in the study.

Evaluating carbon storage in restoration plantings in the Tasmanian Midlands, a highly modified agricultural landscape

In recent years there have been incentives to reforest cleared farmland in southern Australia to establish carbon sinks, but the rates of carbon sequestration by such plantings are uncertain at local scales. We used a chronosequence of 21 restoration plantings aged from 6 to 34 years old to measure how above- and belowground carbon relates to the age of the planting. We also compared the amount of carbon in these plantings with that in nearby remnant forest and in adjacent cleared pasture. In terms of total carbon storage in biomass, coarse woody debris and soil, young restoration plantings contained on average much less biomass carbon than the remnant forest (72 versus 203 Mg C ha–1), suggesting that restoration plantings had not yet attained maximum biomass carbon. Mean biomass carbon accumulation during the first 34 years after planting was estimated as 4.2 ± 0.6 Mg C ha–1 year–1, with the 10th and 90th quantile regression estimates being 2.1 and 8.8 Mg C ha–1 year–1. There were no significant differences in soil organic carbon (0–30-cm depth) between the plantings, remnant forest and pasture, with all values in the range of 59–67 Mg ha–1. This is in line with other studies showing that soil carbon is slow to respond to changes in land use. Based on our measured rates of biomass carbon accumulation, it would require ~50 years to accumulate the average carbon content of remnant forests. However, it is more realistic to assume the rates will slow with time, and it could take over 100 years to attain a new equilibrium of biomass carbon stocks.

Can vegetation types work as an indicator of soil organic carbon? An insight from native vegetations in Nepal

Soil is the largest pool of carbon after the ocean. The assessment of soil organic carbon (SOC) stocks under different types of vegetations is critical for evidence-based implementation of soil carbon trading under different market mechanisms. Using data from 490 permanent soil sample plots with elevations ranging from 271m to 3238m above sea level, from three different watersheds in Nepal, this study aims to compare SOC under five different forest types and determine whether forest types could be indicator of SOC: Shorea robusta; mixed broadleaf; Schima-Castanopsis; pine; and Rhododendron-Quercus forests. In each vegetation type forests with dense canopies (≥70% canopy cover) have higher amounts of SOC than that of open canopy forests (<70% canopy cover). On average, with up to 30cm soil depth, dense canopy Rhododendron-Quercus forest has the highest amount of SOC (14,136gC/m2), followed by dense canopy mixed broadleaf forest (12,576gC/m2). One-way analysis of variance (ANOVA) indicates significant differences in soil organic carbon (SOC) amounts across the five forest types (df=485, F=17.299, p=0.000) and therefore forest types could be indicator of SOC. Moreover, within the similar altitudinal zone and topographic, edaphic and climatic environments: soils under the mixed species forests have higher amounts of SOC than that of single species dominated forests; and soils under forests with nitrogen fixing trees have a higher amount of SOC than those from other forests. Therefore, in addition to forest types these two conditions within the given vegetation types could work as sub-indicators of SOC. In comparison with global studies, all Nepalese forest types had much higher levels of SOC. Only two of the seven factors/indicators investigated (altitude and average age of dominant trees) were found to have significant impacts (r=0.33 to 0.64) on SOC and only in the dense and sparse canopy pine forests. The reasons of not having any impacts of all other factors on SOC in different vegetation types have been discussed.

Soil CO2 Emissions as Affected by 20-Year Continuous Cropping in Mollisols

Long-term continuous cropping of soybean (Glycine max), spring wheat (Triticum aesativum) and maize (Zea mays) is widely practiced by local farmers in northeast China. A field experiment (started in 1991) was used to investigate the differences in soil carbon dioxide (CO2) emissions under continuous cropping of the three major crops and to evaluate the relationships between CO2 fluxes and soil temperature and moisture for Mollisols in northeast China. Soil CO2 emissions were measured using a closed-chamber method during the growing season in 2011. No remarkable differences in soil organic carbon were found among the cropping systems (P>0.05). However, significant differences in CO2 emissions from soils were observed among the three cropping systems (P<0.05). Over the course of the entire growing season, cumulative soil CO2 emissions under different cropping systems were in the following order: continuous maize ((829±10) g CO2 m−2)>continuous wheat ((629±22) g CO2 m−2)>continuous soybean ((474±30) g CO2 m−2). Soil temperature explained 42–65% of the seasonal variations in soil CO2 flux, with a Q10 between 1.63 and 2.31; water-filled pore space explained 25–47% of the seasonal variations in soil CO2 flux. A multiple regression model including both soil temperature (T, °C) and water-filled pore space (W, %), log(f)=a+bT log(W), was established, accounting for 51–66% of the seasonal variations in soil CO2 flux. The results suggest that soil CO2 emissions and their Q10 values under a continuous cropping system largely depend on crop types in Mollisols of Northeast China.

바이오매스량과 식생구조가 토양 탄소함유량에 미치는 영향 분석 - 서서울호수공원과 양재 시민의 숲을 대상으로 -

탄소축적량 증진을 위한 도시공원 설계 및 계획에 적합한 식재구조와 토양 관리방법에 대한 분석이 필요하다. 본 연구에서는 탄소저감에 기여하는 도시공원 설계와 관리를 위하여, 서서울호수공원과 양재시민의 숲을 대상으로 바이오매스량과 공원조성 시기 및 식재구조가 다른 조사구에서의 토양 탄소함유량을 지상부 지하부 탄소저장량의 측정을 통해 분석하였다. 대상 도시공원으로 조성시기가 다른 서서울호수공원(2009년)과 양재 시민의 숲(1986년)을 선정하였다. 식생과 토양 특성에 따른 토양 탄소함유량의 차이를 분석하기 위하여, 바이오매스량과 토양의 물리적 화학적 특성 측정을 통해 지상부 지하부 탄소저장량을 분석하였다. 바이오매스량 측정에는 상대생장식을 적용하였으며, 토양에 관해서는 토양 탄소함유량(TOC)과 pH, 양이온치환용량(CEC), 전질소량(TN), 토양 총 균수와 같은 화학적 특성을 측정하였다. 이 결과, 바이오매스량은 양재 시민의 숲이 서서울호수공원보다 높아, 조성된 지 오래된 공원의 바이오매스량이 높은 것으로 나타났다. 한편, 토양 탄소함유량은 양재시민의 숲이 서서울호수공원 보다 낮았으며, 이는 양재시민의 숲에서의 대기오염과 산성비 노출에 의한 토양의 산성화 진행에 따른 영향 때문인 것으로 분석되었다. 또한, 토양 탄소함유량은 단층식재지가 다층식재지 보다 높은 것으로 나타났다. 장기적 시점에서 볼 때, 토양 개선은 식생 생장을 도모한다. 따라서 도시공원의 토양 특성 개선을 위하여, 석회성 비료 시비에 의한 pH 조절과 답압 제어 및 낙엽층 방치에 의한 토양 양분 증진을 통한 공원관리가 필요하다. Identification of methods to optimize the growth of a plant community, including the capacity of the soil to further sequester carbon, is important in urban design and planning. In this study, to construct and manage an urban park to mitigate carbon emissions, soil organic carbon of varying biomass, different park construction times, and a range of vegetation types were analyzed by measuring aboveground and belowground carbon in Seoseoul Lake Park and Yangjae Citizen's Forest. The urban parks were constructed during different periods; Seoseoul Lake Park was constructed in 2009, whereas Yangjae Citizen's Forest was constructed in 1986. To identify the differences in soil organic carbon in various plant communities and soil types, above and belowground carbon were measured based on biomass, as well as the physical and chemical features of the soil. Allometric equations were used to measure biomass. Soil total organic carbon (TOC) and chemical properties such as pH, cation exchange capacity (CEC), total nitrogen (TN), and soil microbes were analyzed. The analysis results show that the biomass of the Yangjae Citizen's Forest was higher than that of the Seoseoul Lake Park, indicating that older park has higher biomass. On the other hand, TOC was lower in the Yangjae Citizen's Forest than in the Seoseoul Lake Park; air pollution and acid rain probably changed the acidity of the soil in the Yangjae Citizen's Forest. Furthermore, TOC was higher in mono-layered plantation area compared to that in multi-layered plantation area. Improving the soil texture would, in the long term, result in better vegetation growth. To improve the soil texture of an urban park, park management, including pH control by using lime fertilization, soil compaction control, and leaving litter for soil nutrition is necessary.

Response of Carbon Dioxide Emissions to Warming under No-Till and Conventional Till Systems

Differences in soil organic carbon (SOC) distribution, water holding capacity, and soil temperature between no-tillage (NT) and conventional tillage (CT) systems can result in different soil CO2 emissions which could affect global warming but few studies have addressed this concern. An open warming experiment was conducted in situ by infrared heating of long-term conservation tillage management plots in North China Plain (NCP) to determine the effects of warming on soil CO2 emissions and the correlation to changes in soil temperature and moisture. This experiment was conducted from February 2010 to June 2012 and included CT and NT plots with and without warming. Warming treatment increased soil temperature by 2.1 and 1.5 degrees C, and decreased volumetric soil-water content by 14 and 10% for CT and NT systems, respectively. Soil CO2 emissions tended to decrease with time in CT while it consistently increased in NT system over the three wheat seasons and two maize seasons under warming. Our results suggest that differences in soil temperature and soil moisture between the two tillage systems could be enlarged with time by warming, and the potential exist for warming to promote more soil CO2 emission under NT relative to CT. There is a need to consider the differences in response to global warming between these two tillage systems to properly assess the benefits of NT to C sequestration.

Comparative Carbon Storage of Lanzones (Lansium domesticum) – fruit tree and Falcata (Paraserianthes falcataria) – forest tree based Agroforestry Systems

Two agroforestry systems, a fruit tree-based with lanzones (Lansium domesticum) as dominant fruit tree and a forest tree-based with falcata (Paraserianthes falcataria) as dominant wood tree, were studied to compare their total carbon stocks in the above ground biomass (upperstorey and understorey), floor litters and soil and to determine any differences of soil organic carbon(SOC) in three soil depths: 0-30, 31-60 and 61-100 cm. Each site representing one agroforestry systems was grouped according to vegetation stand. For each vegetation stand, representative samples were taken from upper storey and under storey above ground biomass, floor litters and soil. Samples were analyzed for carbon content at International Rice Research Institute’s (IRRI) Analytical Service Laboratories(ASL), Los Baños, Laguna using Dumas Combustion Method. The SOC in the soil depths (0-30, 31-60 and 61-100 cm) did not vary significantly in the two agroforestry systems. The above ground upperstorey biomass had the most carbon followed by the carbon stored in the soil, then, above ground understorey biomass and lastly, floor litters. The above ground upperstorey biomass of the fruit tree-based agroforestry system had slightly higher carbon stock at 38.92 tC ha-1 compared with the forest tree-based agroforestry system at 34.66 tC ha-1 due to the lanzones fruit tress. The 4 – year old falcata-based agroforestry systems had higher annual C sequestration of 14 tC ha-1 yr-1 while the lanzones-based agroforestry system had 1.8 tC ha-1 yr-1. Nevertheless, whatever is the main tree component, agroforestry performs ecological services as in carbon sequestration and at the same time provides financial benefits.

Water-Retention Characteristics and Available Water Capacity in Three Cropping Systems of Lower Indo-Gangetic Alluvial Plain

This study was conducted in Chinchura-Mogra and Polba-Dapur Blocks of Hugli District, West Bengal to determine the changes in cropping systems on water-retention characteristics (WRC) and available water capacity (AWC) and their relations with other soil properties. In the present study, three sites contained adjacent cropping systems of banana and mango orchard, paddy–paddy, and paddy–potato–vegetables were selected. Soil samples were collected from depths of 0–30 and 30–60 cm in three representative sites of each cropping system with three replications guided by land use and soil map of study area. Analysis of variance was performed to compare the impact of cropping systems on available water content and water-retention characteristics. The mean clay content was greater both on the surface (61.70%) and in the subsurface (55.06%) in the soils under the paddy–paddy cropping system than banana and mango orchard and paddy–potato–vegetable cropping systems. Paddy–potato–vegetables cropping system (0.55%) has lower soil organic carbon compared to the banana and mango orchard (0.63 %) and paddy–paddy cropping system (0.65%) at 0–30 cm deep, whereas no significant difference in soil organic carbon was recorded in 30–60 cm deep. The results of available water capacity indicated that paddy–paddy cropping system recorded lower available water capacity at both ranges of depth. Available water capacity is significantly positively correlated with silt and organic carbon. The results of water-retention studies indicated that 75 and 85% of available water was removed from the soil of paddy–potato–vegetable cropping system by 0.5 M Pa at 0–30 and 30–60 cm deep, respectively, whereas only 56–62% of available water was removed by 0.5 M Pa in the other two systems. The results show that the paddy–potato–vegetable cropping system is more vulnerable to moisture stress during drought periods.

Reply to Leifeld et al.: Enhanced top soil carbon stocks under organic farming is not equated with climate change mitigation

In their letter, Leifeld et al. (1) argue that our metaanalysis to identify differences in soil organic carbon (SOC) between organic (OF) and nonorganic farming [conventional farming (CF)] (2) selected CF systems that were nonrepresentative. This was not the case. We included data from all available pairwise field comparisons between OF and CF identified in the literature. The observed difference in external carbon (C) inputs between OF and CF did not result from a bias in the selection of studies/treatments but was attributable to the fact that the field comparisons we analyzed (2) were not from fertilization experiments but from pairwise farming system comparisons where the design and the underlying treatments reflected the current farming practices in the region in which the studies were conducted at the time the experiments were initiated.

Sub-tropic degraded red soil restoration: Is soil organic carbon build-up limited by nutrients supply

The long-term Forest Restoration Experimental Project (FREP) was established in 1991 on a subtropical, barren, degraded, red soil sparsely vegetated grassland in Taihe County, Jianxi province, China. The objective of the FREP was to evaluate the effects of restoration on ecological functions through afforestation by using various local species. This information will provide guidance for future restorations at severely deteriorated landscapes, which are very common in southern China. In this study, we selected five restoration forests: Chinese sweetgum (Liquidamber formosana), schima (Schima superb), masson’s pine (Pinus massoniana), slash pine (Pinus elliottii), Chinese sweetgum×slash pine mixtures, and one experimental control (grassland with low coverage of annual and perennial plants). These were selected to evaluate the differences in soil organic carbon (TC), soil nitrogen including total soil nitrogen (TN) and available nitrogen (Av-N), soil phosphorus including total phosphorus (TP) and available phosphorus (Av-P), and their molar ratios (C:N, C:P, and N:P). A similar assessment was also conducted on the species functional groups (coniferous forest, broad-leaved forest, and mixed-species forest) based on groupings of studied species. Furthermore, we evaluated the relationships between TC and soil N and P, and their stoichiometry to explore the biochemical mechanisms of soil organic matter buildup. Finally, we explored the recovery trajectory of TC and TN in the FREP’s evergreen broad-leaved forest by comparing it with local evergreen climax ecosystems.Over the 19-year study period, restoration significantly improved the TC and soil N and P compared to the control sites, but there were no significant differences in the TC and soil N and P among the restoration functional groups and among forest stand types. The TN and C:P ratios were closely related to soil organic carbon contents suggesting that they were good predicator of soil organic carbon. The overall data clearly demonstrated that the restoration through local species and nutrient cycling concentrating C, N, and P in topsoil. The recover trajectory suggests that the evergreen forest (schima) in FREP is still in the early developmental stages, and its projected rate of TC and TN growth is much slower than the average growth rate in the region. This case study clearly demonstrated that although the recovery is at its early stage with a very slow process, the active restoration can enhance soil carbon sequestration, nutrients availability, and the capability of soil organic carbon sequestration is regulated by the soil nutrients supply.

The influence of changes in forest management over the past 200 years on present soil organic carbon stocks

Forest ecosystems in Europe have been affected by human activities for many centuries. Here we investigate, if current forest soil organic carbon stocks are influenced not only by present ecological conditions and land use, but also by land management in the past. Based on the forest management history of the Hainich-Dün region a total of 130 inventory plots were selected in age-class forest and selectively cut forests under present management practice. The age-class forest originated from (1) former coppice-with-standards, (2) former selectively cut forests and (3) afforestation. The selectively cut forest contains “early regulated” forest where selective cutting has been practised for centuries, and forest, which was managed as coppice-with-standards through the 18th and the 19th centuries. We hypothesise that past management influences present soil organic carbon stocks. Density fractionation of soils in three physical fractions (HF: heavy fraction, o-LF: occluded light fraction, f-LF: free light fraction) was carried out to increase the probability of detecting long-lasting effects of management history. No detectable differences in soil organic carbon (SOC) stocks, as measured in kgm−2 ground area, of the mineral soil and the heavy fractions, were found between present and historical forest management types (average total organic carbon (OC) stocks of mineral soil: 9.7±2.3kgm−2; average OC stocks of the organic layer: 0.5±0.3kgm−2; average total inorganic carbon (IC) stocks of mineral soil: 5.0±3.7kgm−2). The variation of samples was overlapping. There was no consistent trend with management history. The upper mineral soil (0–30cm) contained about 74% of total SOC, with f-LF contributing 24% in 0–10cm and 20% in 10–30cm, and o-LF 9% in 0–10cm and 6% in 10–30cm. The HF contained 85% (0–10cm) and 86% (10–30cm) of SOC stocks in the bulk soil. There was a significant decrease of total SOC stocks in the 0–10 and 10–30cm depth increment with increasing abundance of beech. Mean 14C concentrations in the HF were 102.0 pMC in 0–10cm, and 93.4 pMC in 10–30cm, corresponding to a mean 14C age of around 100years and 550years, respectively. Modelling C-dynamics based on the present measurements reveals that disturbances depleting 50% of soil C-stocks would equilibrate after 80years. Thus, there is no memory effect of 19th century forest management. We conclude that past and present management has no detectable effect on present SOC.

Enhanced top soil carbon stocks under organic farming

It has been suggested that conversion to organic farming contributes to soil carbon sequestration, but until now a comprehensive quantitative assessment has been lacking. Therefore, datasets from 74 studies from pairwise comparisons of organic vs. nonorganic farming systems were subjected to metaanalysis to identify differences in soil organic carbon (SOC). We found significant differences and higher values for organically farmed soils of 0.18 ± 0.06% points (mean ± 95% confidence interval) for SOC concentrations, 3.50 ± 1.08 Mg C ha(-1) for stocks, and 0.45 ± 0.21 Mg C ha(-1) y(-1) for sequestration rates compared with nonorganic management. Metaregression did not deliver clear results on drivers, but differences in external C inputs and crop rotations seemed important. Restricting the analysis to zero net input organic systems and retaining only the datasets with highest data quality (measured soil bulk densities and external C and N inputs), the mean difference in SOC stocks between the farming systems was still significant (1.98 ± 1.50 Mg C ha(-1)), whereas the difference in sequestration rates became insignificant (0.07 ± 0.08 Mg C ha(-1) y(-1)). Analyzing zero net input systems for all data without this quality requirement revealed significant, positive differences in SOC concentrations and stocks (0.13 ± 0.09% points and 2.16 ± 1.65 Mg C ha(-1), respectively) and insignificant differences for sequestration rates (0.27 ± 0.37 Mg C ha(-1) y(-1)). The data mainly cover top soil and temperate zones, whereas only few data from tropical regions and subsoil horizons exist. Summarizing, this study shows that organic farming has the potential to accumulate soil carbon.

Growing woody biomass for bioenergy in a tree-based intercropping system in southern Ontario, Canada

During the spring of 2006, three willow varieties (SV1, SX67 and 9882-41) were established on marginal land in an agroforestry tree-intercropping arrangement where plots of short rotation willows were planted between rows (spaced 15 m apart) of 21-year-old mixed tree species. As a control, the same varieties were established on an adjacent piece of land without established trees (conventional willow system). This study investigated the magnitude of carbon pools, fine root and leaf biomass inputs and clone yields in both the tree-based intercropping (agroforestry) and conventional monocropping systems. Willow biomass yield was significantly higher in the agroforestry field (4.86 odt ha−1 y−1) compared to the conventional field (3.02 odt ha−1 y−1). In both fields, varieties SV1 and SX67 produced higher yields than the variety 9882-41. Willow fine root biomass in the top 20 cm of soil was significantly higher in the intercropping system (3,062 kg ha−1) than in the conventional system (2,536 kg ha−1). Differences in fine root biomass between clones were similar to that observed for differences in biomass yield: SV1 > SX67 > 9882-41. Leaf input was higher in the intercropping system (1,961 kg ha−1) than in the conventional system (1,673 kg ha−1). Clonal differences in leaf inputs followed the same trends as those for root biomass and yield: SV1 > SX67 > 9882-41. Soil organic carbon was significantly higher in the agroforestry field (1.94 %) than in the conventional field (1.82 %). A significant difference in soil organic carbon was found between the three clones: soils under clone 9882-41 had the lowest soil organic carbon at 1.80 %.

Effect of stocking density on soil, water quality and nitrogen budget inPenaeus monodon(Fabricius, 1798) culture under zero water exchange system

Soil and water interactions and their influence on growth and production in different densities (SD8 & SD16) under zero water exchange were studied in two successive crops of Penaeus monodon in Tamil Nadu, India during 2007 and 2008. Scraping and tilling during pond preparation increased the mineralization rate than scraping only. During crop, there was no significant difference in soil organic carbon and total nitrogen between the SDs. However, as the crop progressed, organic carbon and total nitrogen content of the soil showed significant difference under both the SDs. Between the SDs, nitrate and phosphate content in water significantly differed, whereas the progress of the crop significantly increased both available and total nutrients. Mass balance of nitrogen indicated that applied feed contributed to 97.4–98.5% of input nitrogen, of which nitrogen in sediment accounted for 16.5–27.3%, nitrogen recovery in shrimp was 34.2–43.6% and the nitrogen lost through denitrification and volatilization varied from 4.7% to 34.7%. Zero water exchange system is highly efficient as nitrogen recovery is higher in shrimp and lower in discharge water. Lack of significant difference in metabolites between the SDs indicates the role of aeration and probiotics in sustaining SD16 cultures.

Sorption and dissipation of aged metolachlor residues in eroded and rehabilitated soils

Sorption and dissipation of aged metolachlor were characterized in rehabilitated and eroded prairie soils using sequential batch slurry (conventional) and accelerated solvent extraction (ASE). In spite of an almost twofold difference in soil organic carbon (OC) content, S-metolachlor sorption coefficients (K(d)) and dissipation rates (DT(50)) were the same in soils from different landscape positions within an eroded landform. Soil was moved within the landform to increase productivity. In areas receiving topsoil addition, S-metolachlor K(d) was higher and DT(50) was longer than in eroded areas. The efficiency of extraction was higher for ASE than for conventional extractions. No consistent aging effect on K(d) was observed. Mineralization in 8 weeks accounted for < 10% of the applied metolachlor. The results of this laboratory study support a field dissipation study. Both showed that S-metolachlor has the same retention and dissipation rate throughout an eroded landform, which was not expected owing to the large variability in soil properties, including OC concentrations. Altering soil properties by adding topsoil increased metolachlor sorption and persistence. The method of extraction (conventional versus ASE) affected calculated sorption coefficients and dissipation rates. In all cases, groundwater ubiquity scores (GUSs) categorized metolachlor as having intermediate mobility.

SOIL ORGANIC CARBON STOCK AND FRACTIONS IN RELATION TO LAND USE AND SOIL DEPTH IN THE DEGRADED SHIWALIKS HILLS OF LOWER HIMALAYAS

ABSTRACTThe proportional differences in soil organic carbon (SOC) and its fractions under different land uses are of significance for understanding the process of aggregation and soil carbon sequestration mechanisms. A study was conducted in a mixed vegetation cover watershed with forest, grass, cultivated and eroded lands in the degraded Shiwaliks of the lower Himalayas to assess land‐use effects on profile SOC distribution and storage and to quantify the SOC fractions in water‐stable aggregates (WSA) and bulk soils. The soil samples were collected from eroded, cultivated, forest and grassland soils for the analysis of SOC fractions and aggregate stability. The SOC in eroded surface soils was lower than in less disturbed grassland, cultivated and forest soils. The surface and subsurface soils of grassland and forest lands differentially contributed to the total profile carbon stock. The SOC stock in the 1.05‐m soil profile was highest (83.5 Mg ha−1) under forest and lowest (55.6 Mg ha−1) in eroded lands. The SOC stock in the surface (0–15 cm) soil constituted 6.95, 27.6, 27 and 42.4 per cent of the total stock in the 1.05‐m profile of eroded, cultivated, forest and grassland soils, respectively. The forest soils were found to sequester 22.4 Mg ha−1 more SOC than the cultivated soils as measured in the 1.05‐m soil profiles. The differences in aggregate SOC content among the land uses were more conspicuous in bigger water‐stable macro‐aggregates (WSA &gt; 2 mm) than in water‐stable micro‐aggregates (WSA &lt; 0.25 mm). The SOC in micro‐aggregates (WSA &lt; 0.25 mm) was found to be less vulnerable to changes in land use. The hot water soluble and labile carbon fractions were higher in the bulk soils of grasslands than in the individual aggregates, whereas particulate organic carbon was higher in the aggregates than in bulk soils. Copyright © 2012 John Wiley &amp; Sons, Ltd.