首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
There are few reliable data sets to inspire confidence in policymakers that soil organic carbon (SOC) can be measured on farms. We worked with farmers in the Tamar Valley region of southwest England to select sampling sites under similar conditions (soil type, aspect and slope) and management types. Topsoils (2–15 cm) were sampled in autumn 2015, and percentage soil organic matter (%SOM) was determined by loss on ignition and used to calculate %SOC. We also used the stability of macroaggregates in cold water (WSA) (‘soil slaking’) as a measure of ‘soil health’ and investigated its relationship with SOC in the clay‐rich soils. %SOM was significantly different between management types in the order woodland (11.1%) = permanent pasture (9.5%) > ley‐arable rotation (7.7%) = arable (7.3%). This related directly to SOC stocks that were larger in fields under permanent pasture and woodland compared with those under arable or ley‐arable rotation whether corrected for clay content (F = 8.500, p < .0001) or not (F = 8.516, p < .0001). WSA scores were strongly correlated with SOC content whether corrected for clay content (SOCadj R2 = .571, p < .0001) or not (SOCunadj R2 = 0.490, p = .002). Time since tillage controlled SOC stocks and WSA scores, accounting for 75.5% and 51.3% of the total variation, respectively. We conclude that (1) SOC can be reliably measured in farmed soils using accepted protocols and related to land management and (2) WSA scores can be rapidly measured in clay soils and related to SOC stocks and soil management.  相似文献   

2.
耕作与轮作方式对黑土有机碳和全氮储量的影响   总被引：10，自引：1，他引：9  
土壤有机碳(SOC)及全氮(TN)对土壤肥力、作物产量、农业可持续发展以及全球碳、氮循环等都具有重要影响。为探索不同耕作和轮作方式对耕层黑土SOC和TN储量的影响,本文以吉林省德惠市进行了8 a的田间定位试验中层黑土为研究对象,对免耕、垄作和秋翻三种耕作方式及玉米-大豆轮作和玉米连作两种轮作方式下SOC和TN在各土层的含量变化进行了分析,并采用等质量土壤有机质储量计算方法,对比分析了不同处理对0～30 cm SOC和TN储量的影响。结果表明,与试验开始前相比,玉米-大豆轮作系统中,秋翻下SOC和TN储量均有所降低;免耕显著增加了0～5 cm SOC及TN含量,但SOC在亚表层亏损,导致其储量并未增加;而垄作处理下SOC及TN含量在0～5、5～10 cm的均显著增加,0～30 cm储量亦分别增加了4.9%和10.7%。玉米连作系统的两种耕作处理(免耕和秋翻)下SOC和TN储量均有所增加,且TN储量增幅均高于玉米-大豆轮作系统,其中免耕下TN储量增幅是玉米-大豆轮作的3.2倍。所有处理下C/N均呈降低趋势,其中垄作0～5 cm C/N由12.05降至11.04,降低幅度分别是免耕和秋翻的3.2和2.8倍。综上可知,对质地黏重排水不良的中层黑土,玉米-大豆轮作系统下免耕并不是促进SOC固定的有效形式,而垄作则促进了黑土SOC和TN的积累,这不仅有利于土壤肥力的改善,而且是使农田黑土由CO2"源"变为"汇"的有效形式之一。与玉米-大豆轮作相比,玉米连作下三种耕作方式都有利于SOC和TN积累。  相似文献   

3.
Soil organic carbon (SOC) fashions soil structure, which is a key factor of soil fertility. Existing SOC content recommendations are based on SOC:clay ratio thresholds of >1:10. However, the corresponding SOC content might be considered hard to reach in clayey soils, whose structure degradation risk is assumed to be high. Here, we analysed the SOC content and soil structure quality of soils under similar cropping practices with clay contents ranging from 16% to 52%. Five undisturbed soil cores (5–10 cm layer) were collected from 96 fields at 58 farms in the Swiss Jura region. We assessed the soil structure quality visually using the CoreVESS method. Gravimetric air content and water content, and bulk density at −100 hPa were also measured, and the soil structure degradation index was calculated. We found that the relationship between SOC and clay content held over the clay content range, suggesting that reaching an acceptable SOC:clay ratio is not limited by large clay contents. This suggests that the 1:10 SOC:clay ratio may remain useful for clayey soils. In contrast to what was expected, it is not more challenging to reach this ratio in clayey soils even if it implies reaching very large SOC contents. SOC content explained the considered physical properties better than clay content. From a soil management point of view, these findings suggest that the soil texture determines a potential SOC content, while the SOC:clay ratio is determined by farming practices regardless of the clay content.  相似文献   

4.
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 (Ntot) 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.  相似文献   

5.
The agricultural soil carbon pool plays an important role in mitigating greenhouse gas emission ana unaerstanamg the son orgamc carbon-climate-soil texture relationship is of great significance for estimating cropland soil carbon pool responses to climate change. Using data from 900 soil profiles, obtained from the Second National Soil Survey of China, we investigated the soil organic carbon （SOC） depth distribution in relation to climate and soil texture under various climate regimes of the cold northeast region （NER） and the warmer Huang-Huai-Hai region （HHHR） of China. The results demonstrated that the SOC content was higher in NER than in HHHR. For both regions, the SOC content at all soil depths had significant negative relationships with mean annual temperature （MAT）, but was related to mean annual precipitation （MAP） just at the surface 0-20 cm. The climate effect on SOC content was more pronounced in NER than in HHHR. Regional differences in the effect of soil texture on SOC content were not found. However, the dominant texture factors were different. The effect of sand content on SOC was more pronounced than that of clay content in NER. Conversely, the effect of clay on SOC was more pronounced than sand in HHHR. Climate and soil texture jointly explained the greatest SOC variability of 49.0% （0-20 cm） and 33.5% （20-30 cm） in NER and HHHR, respectively. Moreover, regional differences occurred in the importance of climate vs. soil texture in explaining SOC variability. In NER, the SOC content of the shallow layers （0-30 cm） was mainly determined by climate factor, specifically MAT, but the SOC content of the deeper soil layers （30-100 cm） was more affected by texture factor, specifically sand content. In HHHR, all the SOC variability in all soil layers was predominantly best explained by clay content. Therefore, when temperature was colder, the climate effect became stronger and this trend was restricted by soil depth. The regional differences and soil depth influence underscored the importance of explicitly considering them in modeling long-term soil responses to climate change and predicting potential soil carbon sequestration.  相似文献   

6.
The research was carried out to determine the effect of basin‐based conservation agriculture (CA) on selected soil quality parameters. Paired plots (0.01 ha) of CA and conventional tillage based on the animal‐drawn mouldboard plough (CONV) were established between 2004 and 2007 on farm fields on soils with either low (12–18% – sandy loams and sandy clay loams) or high clay levels (>18–46% – sandy clays and clays) as part of an ongoing project promoting CA in six districts in the smallholder farming areas of Zimbabwe. We hypothesized that CA would improve soil organic carbon (SOC), bulk density, aggregate stability, soil moisture retention and infiltration rate. Soil samples for SOC and aggregate stability were taken from 0 to 15 cm depth and for bulk density and soil moisture retention from 0 to 5, 5 to 10 and 10 to 15 cm depths in 2011 from maize plots. Larger SOC contents, SOC stocks and improved aggregate stability, decreased bulk density, increased pore volume and moisture retention were observed in CA treatments. Results were consistent with the hypothesis, and we conclude that CA improves soil quality under smallholder farming. Benefits were, however, greater in high clay soils, which is relevant to the targeting of practices on smallholder farming areas of sub‐Saharan Africa.  相似文献   

7.
Abstract. Knowledge of the stocks and the potential range of soil organic carbon (SOC) in various land–soil combinations is an important precursor to policies aimed at linking, for example, management of SOC to greenhouse gas emission controls. To investigate the factors controlling the percentage of SOC (%SOC) of soils in England and Wales, we made a multiple regression analysis of data for the 2448 arable and ley-arable sites in the 1980 England and Wales National Soil Inventory (NSI). Clay content, average annual precipitation and depth of topsoil explained 25.5% of the variation in %SOC, when calcareous and peaty soils and those susceptible to flooding were excluded. Using 'robust' statistics, 'indicative SOC management ranges' were estimated for different physiotopes, that is, landscape units for which the environmental factors governing %SOC are similar, namely soil clay content and precipitation. These ranges describe the expected %SOC range for an arable soil in a given physiotope. They have potential to support approximate targets for the %SOC of arable soils and for estimating upper and lower limits for sequestered soil carbon in arable systems.  相似文献   

8.
Land Use and Soil Organic Carbon in China’s Village Landscapes   总被引：2，自引：0，他引：2  
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.  相似文献   

9.
Long-term changes in soil organic carbon (SOC) resulting from management change are documented for many experimental situations, and corresponding trends in the field have been observed by national survey. Since these changes are relevant to atmospheric carbon balance a practical measure to confirm the impact of recent management decisions at any location, without resorting to repeated sampling, is highly attractive but none has previously been tested. This study assessed intra-aggregate C to fulfil the role, based on a temporary deviation from its predictable contribution to total SOC under stable management. A total of 166 surface soil samples (0–15 cm) were analyzed for intra-aggregate C using an established physical fractionation protocol or compatible scaled-up procedure. Soils were arable (or ley-arable) managed by conventional or minimum-tillage, or permanent grassland, and assigned ‘stable’ or ‘changing’ status on the basis of a verbal account of management history. Log-normal populations of intra-aggregate C were compared for soils of stable and changing status using F-tests. Intra-aggregate C shows promise as an indicator of changing SOC in arable soils up to 30% clay content, particularly soils <20% clay. A larger dataset is required to establish its utility in grassland soils. It is not certain that intra-aggregate C is capable of confirming direction of change or trajectory (endpoint), and functions to indicate change, rather than confirm stable status. Supplementary information on the history of soil use and management is therefore essential in the interpretation of such measurements.  相似文献   

10.
In rainfed semi‐arid agroecosystems, soil organic carbon (SOC) may increase with the adoption of alternative tillage systems (e.g. no‐tillage, NT). This study evaluated the effect of two tillage systems (conventional tillage, CT vs. NT) on total SOC content, SOC concentration, water stable aggregate‐size distribution and aggregate carbon concentration from 0 to 40 cm soil depth. Three tillage experiments were chosen, all located in northeast Spain and using contrasting tillage types but with different lengths of time since their establishment (20, 17, and 1‐yr). In the two fields with mouldboard ploughing as CT, NT sequestered more SOC in the 0–5 cm layer compared with CT. However, despite there being no significant differences, SOC tended to accumulate under CT compared with NT in the 20–30 and 30–40 cm depths in the AG‐17 field with 25–50% higher SOC content in CT compared with NT. Greater amounts of large and small macroaggregates under NT compared with CT were measured at 0–5 cm depth in AG‐17 and at 5–10 cm in both AG‐1 and AG‐17. Differences in macroaggregate C concentration between tillage treatments were only found in the AG‐17 field at the soil surface with 19.5 and 11.6 g C/kg macroaggregates in NT and CT, respectively. After 17 yr of experiment, CT with mouldboard ploughing resulted in a greater total SOC concentration and macroaggregate C concentration below 20 cm depth, but similar macroaggregate content compared with NT. This study emphasizes the need for adopting whole‐soil profile approaches when studying the suitability of NT versus CT for SOC sequestration and CO2 offsetting.  相似文献   

11.
The effects of manure and chemical fertilizer on soil bulk density, soil organic carbon (SOC), and the role of carbon management index (CMI) in soil quality evaluation were studied under a double-cropping rice system in a long-term experiment. The experiment included five fertilizer treatments: without fertilizer input (CK), chemical fertilizer alone (MF), rice straw residue plus chemical fertilizer (RF), 30% organic matter plus 70% chemical fertilizer (LOM), and 60% organic matter plus 40% chemical fertilizer (HOM). RF, LOM, HOM treatments increased SOC content relative to MF treatment in the paddy fields at 0–20 cm. RF, LOM, HOM treatments were more effective for increasing CMI, lability index, lability of C, and SOC stocks, as compared with MF treatment. Based on rice grain yield and carbon storage, integrated fertilization of chemical fertilizer and organic manure proved to be the most effective practices for improving crop productivity and SOC sequestration.  相似文献   

12.
黄土丘陵区不同退耕还林地土壤颗粒结合态碳库分异特征   总被引：3，自引：0，他引：3  
为揭示黄土丘陵区不同退耕还林土壤有机碳库差异及变化机制,比较分析了15 a生刺槐、山杏、杨树、沙棘、柠条5种退耕还林地土壤砂粒(≥53~2000μm)、粉粒(≥2~53μm)、黏粒(2μm)结合碳的质量分数与分布变化状况。结果表明,与坡耕地比较,不同退耕林地从表层0~10cm到40~60 cm土层土壤总有机碳质量分数增加了1.0~1.9 g/kg,砂粒碳、粉粒碳、黏粒碳质量分数分别增加了0.5~0.1、1.0~0.6、0.4~0.3 g/kg。同时,各林地0~20 cm土层土壤总有机碳和粉粒碳密度差异为杨树=柠条沙棘山杏刺槐,两种碳库增幅分别为2.4~5.8和1.2~3.5 Mg/hm2;但不同林地该土层黏粒碳和砂粒碳基本无显著差异,平均增幅分别为0.7和0.9 Mg/hm2。土层深度为0~60 cm时,土壤总有机碳、粉粒碳、黏粒碳密度均表现为沙棘=杨树=柠条山杏=刺槐,3种碳库增幅分别7.1~12.1、3.8~6.8、1.8~3.2 Mg/hm2;该土层砂粒碳密度在不同林地间仍无显著差异,平均提高了1.5 Mg/hm2。不同林地土壤颗粒碳组分占全有机碳比例均以粉粒碳最高(56.8%)、黏粒碳次之(29.3%),砂粒碳最低(13.8%)。综上,不同退耕林地均以粉粒碳为土壤碳库变化和累积的主要形式,但以刺槐和山杏林提升退耕土壤总有机碳及颗粒碳组分库效应最明显,可作为该区域优选的退耕还林生态固碳技术。  相似文献   

13.
Low soil organic carbon (SOC) levels in dry areas can affect soil functions and may thus indicate soil degradation. This study assesses the significance of SOC content in Mediterranean arable soils based on the analysis of a broad data set of 2613 soils sampled from Mediterranean grasslands and agricultural land. The distribution in values of SOC, pH, clay and carbonates was analysed according to different climatic areas (semi‐arid, Mediterranean temperate, Mediterranean continental and Atlantic) and with respect to six different land uses (grassland, cereal crops, olives and nuts, vineyards, fruit trees and vegetable gardens). The general trend was for low SOC in arable land and decreased with aridity. In wet areas (Atlantic and Mediterranean continental), acidic soils had a higher SOC content than did calcareous soils, whereas in the Mediterranean temperate area SOC had little relationship to soil pH. In low SOC arable soils, the SOC content was related to clay content. In calcareous arable soils of the Mediterranean temperate zone, SOC content was more closely related to carbonates than to clay. In contrast to the Atlantic area, Mediterranean grassland soils had much lower amounts of SOC than forest soils. Mediterranean calcareous and temperate acidic soils under grassland had SOC‐to‐clay ratios similar to or only slightly greater than that under a crop regime. In contrast, Mediterranean continental acidic soils under grassland had a much higher SOC‐to‐clay ratio than arable soils. This suggests a low resilience of the Mediterranean temperate and calcareous arable soils in terms of SOC recovery after the secession of ploughing, which may be a result of intensive use of these soils over many centuries. Consequently, we hypothesize that the Mediterranean calcareous soils have undergone significant changes that are not readily reversed after ploughing ceases. Such changes may be related to alterations in soil aggregation and porosity which, in turn, are associated with soil carbonate dynamics. Decarbonation processes (the depletion of active carbonates) may therefore be relevant to the reclamation of highly calcareous arable soils through fostering soil re‐aggregation. The article concludes by discussing the suitability of zero tillage, manuring or the introduction of woody species to increase SOC in calcareous arable soils that are highly depleted of organic matter.  相似文献   

14.
Soil restoration is a means of combating desertification in semi‐arid and arid parts of the world. There, vast areas of the cropped soil degrade, particularly because of the loss of organic matter. One approach to reverse this loss is the conversion of cropland into permanent grassland for use as pasture. This study was designed to evaluate how fast and to what degree degraded cropland may re‐sequester soil organic carbon (SOC) when converted into permanent secondary pasture. Topsoil samples (0–5, 5–10 and 10–20 cm) were taken from chronosequences of secondary pastures (1 to 31 years old) at three agro‐ecosystems in the semi‐arid Highveld of South Africa. Long‐term croplands and primary grassland used as pastures served as the controls. In bulk soil samples (<2 mm) and their clay (<2 µm), silt (2–20 µm), fine sand (20–250 µm) and coarse sand (250–2000 µm) fractions, the contents of carbon (C) and nitrogen were determined. In all three agro‐ecosystems, using a mono‐exponential model, the SOC stocks increased exponentially until a maximum was reached 10–95 years after land conversion. This gain in SOC was clearly pronounced for the top 0–5 cm of soil, but hardly detectable at 10–20‐cm depth. The sand fractions recovered organic C more rapidly but less completely than did the finer size separates. Overall, between 9.0 and 15.3 t of SOC were sequestered in the 0–20 cm of surface soil by this land conversion. Thus, the SOC recovery in the secondary pastures resulted in SOC stocks that were 29.6–93.9% greater than those in the arable land. Yet, in no agro‐ecosystem, at any soil depth, nor in any soil fraction, did the measured SOC content reach that of the primary grassland. In part this can be attributed to a slightly finer texture of the primary grassland that had not lost silt through wind erosion or had never been used as arable land because of slightly elevated clay contents. Overall it appears, however, that previous losses of SOM cannot easily be rectified, suggesting that the native primary grassland soils are only partially resilient to land‐use change.  相似文献   

15.
Reclamation of disturbed soils is done with the primary objective of restoring the land for agronomic or forestry land use. Reclamation followed by sustainable management can restore the depleted soil organic carbon (SOC) stock over time. This study was designed to assess SOC stocks of reclaimed and undisturbed minesoils under different cropping systems in Dover Township, Tuscarawas County, Ohio (40°32·33′ N and 81°33·86′ W). Prior to reclamation, the soil was classified as Bethesda Soil Series (loamy‐skeletal, mixed, acid, mesic Typic Udorthent). The reclaimed and unmined sites were located side by side and were under forage (fescue—Festuca arundinacea Schreb. and alfa grass—Stipa tenacissima L.), and corn (Zea mays L.)—soybean (Glycine max (L.) Merr.) rotation. All fields were chisel plowed annually except unmined forage, and fertilized only when planted to corn. The manure was mostly applied on unmined fields planted to corn, and reclaimed fields planted to forage and corn. The variability in soil properties (i.e., soil bulk density, pH and soil organic carbon stock) ranged from moderate to low across all land uses in both reclaimed and unmined fields for 0–10 and 10–20 cm depths. The soil nitrogen stock ranged from low to moderate for unmined fields and moderate to high in some reclaimed fields. Soil pH was always less than 6·7 in both reclaimed and unmined fields. The mean soil bulk density was consistently lower in unmined (1·27 mg m−3 and 1·22 mg m−3) than reclaimed fields (1·39 mg m−3 and 1·34 mg m−3) planted to forage and corn, respectively. The SOC and total nitrogen (TN) concentrations were higher for reclaimed forage (33·30 g kg−1; 3·23 g kg−1) and cornfields (21·22 g kg−1; 3·66 g kg−1) than unmined forage (17·47 g kg−1; 1·98 g kg−1) and cornfield (17·70 g kg−1; 2·76 g kg−1). The SOC stocks in unmined soils did not differ among forage, corn or soybean fields but did so in reclaimed soils for 0–10 cm depth. The SOC stock for reclaimed forage (39·6 mg ha−1 for 0–10 cm and 28·6 mg ha−1 for 10–20 cm depths) and cornfields (28·3 mg ha−1; 32·2 mg ha−1) were higher than that for the unmined forage (22·7 mg ha−1; 17·6 mg ha−1) and corn (21·5 mg ha−1; 26·8 mg ha−1) fields for both depths. These results showed that the manure application increased SOC stocks in soil. Overall this study showed that if the reclamation is done properly, there is a large potential for SOC sequestration in reclaimed soils. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

16.
In order to assess the potential of soils as C reservoir at regional scale, accurate estimates of soil organic carbon (SOC) are required, and different approaches can be used. This study presents a method to assess and map topsoil organic carbon stock (Mg ha−1) at regional scale for the whole Emilia Romagna plain in Northern Italy (about 12 000 km2). A Scorpan Kriging approach is proposed, which combines the trend component of soil properties as derived from the 1:50 000 soil map with geostatistical modeling of the stochastic, locally varying but spatially correlated component. The trend component is described in terms of varying local means, calculated taking into account soil type and dominant land use. The resulting values of SOC, sand, silt, and clay contents are retained for calculating topsoil SOC stocks, using a set of locally calibrated pedotransfer functions (PTFs) to estimate bulk density. The maps of each soil attribute are validated over a subset of 2000 independent and randomly selected observations. As compared to the standard approach based on the mean values for delineation, results show lower standard errors for all the variables used for SOC stock assessment, with a relative improvement (RI) ranging from 4 per cent for SOC per cent to 24 per cent for silt. The total C stock (0–30 cm) in the study area is assessed as 73·24 ± 6·67 M t, with an average stock of 62·30 ± 5·55 Mg ha−1. The SOC stock estimates are used to infer possible SOC stock changes in terms of carbon sequestration potential and potential carbon loss (PCL). Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

17.
Soils play a key role in the global carbon cycle, and can be a source or a sink of atmospheric carbon (C). Thus, the effect of land use and management on soil C dynamics needs to be quantified. This study was conducted to assess: (1) the role of aggregation in enhancing soil organic carbon (SOC) and total soil nitrogen (TSN) concentrations for different mulch rates, (2) the association of SOC and TSN with different particle size fractions, and (3) the temporal changes in the SOC concentration within aggregate and particle size fractions with duration of mulching. Two experiments were initiated, one each in 1989 and 1996, on a Crosby silt loam (Aeric Ochraqualf or Stagnic Luvisol) in central Ohio. Mulch treatments were 0, 8, and 16 Mg ha−1 yr−1 without crop cultivation. Soil samples from 0–5 cm and 5–10 cm depths were obtained in November 2000; 4 and 11 years after initiating the experiments. Mulch rate significantly increased SOC and TSN concentrations in the 0–5 cm soil layer only. The variation in the SOC concentration attributed to the mulch rate was 41 per cent after 4 years of mulching and 52 per cent after 11 years of mulching. There were also differences in SOC and TSN concentrations among large aggregate size fractions, up to 2 mm size after 4 years and up to 0ċ5 mm after 11 years of mulching. There were also differences in SOC and TSN concentrations among particle size fractions. Variation in the SOC concentration in relation to particle size was attributed to clay by 45–51 per cent, silt by 34–36 per cent, and to sand fraction by 15–19 per cent. Bulk of the TSN (62–67 per cent) was associated with clay fraction and the rest was equally distributed between silt and sand fractions. The enrichment of SOC and TSN concentrations in the clay fraction increased with depth. The C:N ratio was not affected by the mulch rate, but differed significantly among particle size fractions; being in the order of sand >silt >clay. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

18.
Increasing soil carbon (C) in arable soils is an important strategy to achieve sustainable yields and mitigate climate change. We investigated changes in soil organic and inorganic carbon (SOC and SIC) under conservation agriculture (CA) in a calcareous soil of the eastern Indo-Gangetic Plains of India. The treatments were as follows: conventional-till rice and wheat (CT-CT), CT rice and zero-till wheat (CT-ZT), ZT direct seeded rice (DSR) and CT wheat (ZT-CT), ZTDSR and ZT wheat without crop residue retention (ZT-ZT), ZT-ZT with residue (ZT-ZT+R), and DSR and wheat both on permanent beds with residue (PB-PB+R). The ZT-ZT+R had the highest total SOC in both 0–15 and 15–30 cm soil layers (20% and 40% higher (p < .05) than CT-CT, respectively), whereas total SIC decreased by 11% and 15% in the respective layers under ZT-ZT+R compared with CT-CT. Non-labile SOC was the largest pool, followed by very labile, labile and less labile SOC. The benefits of ZT and residue retention were greatest for very labile SOC, which showed a significant (p < .05) increase (~50%) under ZT-ZT+R compared with CT-CT. The ZT-ZT+R sequestered ~2 Mg ha−1 total SOC in the 0–15 cm soil layer in 6 years, where CT registered significant losses. Thus, the adoption of CA should be recommended in calcareous soils, for C sequestration, and also as a reclamation technique.  相似文献   

19.
Carbon fractions in soils apparently vary not only in space, but also over time. A lack of knowledge on the seasonal variability of labile carbon fractions under arable land hampers the reliability and comparability of soil organic carbon(SOC) surveys from different studies. Therefore, we studied the seasonal variability of two SOC fractions, particulate organic matter(POM) and dissolved organic carbon(DOC), under maize cropping: POM was determined as the SOC content in particle-size fractions, and DOC was measured as the water-extractable SOC(WESOC) of air-dried soil. Ammonium, nitrate, and water-extractable nitrogen were measured as potential regulating factors of WESOC formation because carbon and nitrogen cycles in soils are strongly connected. There was a significant annual variation of WESOC(coefficient of variation(CV) = 30%). Temporal variations of SOC in particle-size fractions were smaller than those of WESOC. The stocks of SOC in particle-size fractions decreased with decreasing particle sizes, exhibiting a CV of 20%for the coarse sand-size fraction(250–2 000 μm), of 9% for the fine sand-size fraction(50–250 μm), and of 5% for the silt-size fraction(20–50 μm). The WESOC and SOC in particle-size fractions both peaked in March and reached the minimum in May/June and August, respectively. These results indicate the importance of the time of soil sampling during the course of a year, especially when investigating WESOC.  相似文献   

20.
The dynamics of soil organic carbon (SOC) pools determine potential carbon sequestration and soil nutrient improvement. This study investigated the characteristics of SOC pools in five types of cultivated topsoils (0–15 cm) in subtropical China using laboratory incubation experiments under aerobic conditions. The sizes and turnover rates of the active, slow and resistant C pools were simulated using a first‐order kinetic model. The relative influence of soil environmental properties on the dynamics of different SOC pools was evaluated by applying principal component analysis (PCA) and aggregated boosted trees (ABTs) analysis. The results show that there were significantly greater sizes of different SOC pools and lower turnover rates of slow C pool in two types of paddy soils than in upland soils. Land use exerted the most significant influence on the sizes of all SOC pools, followed by clay content and soil pH. The soil C/N ratio and pH were the major determinants for turnover rates of the active and slow C pools, followed by clay content which had more impact on the turnover rates of the active C pool than the slow C pool. It is concluded that soil type exerts a significant impact on the dynamics of SOC.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号