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1.
Understanding carbon dynamics in soil is the key to managing soil organic matter. Our objective was to quantify the carbon dynamics in microcosm experiments with soils from long-term rye and maize monocultures using natural 13C abundance. Microcosms with undisturbed soil columns from the surface soil (0-25 cm) and subsoil (25-50 cm) of plots cultivated with rye (C3-plant) since 1878 and maize (C4-plant) since 1961 with and without NPK fertilization from the long-term experiment ‘Ewiger Roggen’ in Halle, Germany, were incubated for 230 days at 8 °C and irrigated with 2 mm 10−2 M CaCl2 per day. Younger, C4-derived and older, C3-derived percentages of soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass (Cmic) and CO2 from heterothropic respiration were determined by natural 13C abundance. The percentage of maize-derived carbon was highest in CO2 (42-79%), followed by Cmic (23-46%), DOC (5-30%) and SOC (5-14%) in the surface soils and subsoils of the maize plots. The percentage of maize-derived C was higher for the NPK plot than for the unfertilized plot and higher for the surface soils than for the subsoils. Specific production rates of DOC, CO2-C and Cmic from the maize-derived SOC were 0.06-0.08% for DOC, 1.6-2.6% for CO2-C and 1.9-2.7% for Cmic, respectively, and specific production rates from rye-derived SOC of the continuous maize plot were 0.03-0.05% for DOC, 0.1-0.2% for CO2-C and 0.3-0.5% for Cmic. NPK fertilization did not affect the specific production rates. Strong correlations were found between C4-derived Cmic and C4-derived SOC, DOC and CO2-C (r≥0.90), whereas the relationship between C3-derived Cmic and C3-derived SOC, DOC and CO2-C was not as pronounced (r≤0.67). The results stress the different importance of former (older than 40 years) and recent (younger than 40 years) litter C inputs for the formation of different C pools in the soil.  相似文献   

2.
For a quantitative analysis of SOC dynamics it is necessary to trace the origins of the soil organic compounds and the pathways of their transformations. We used the 13C isotope to determine the incorporation of maize residues into the soil organic carbon (SOC), to trace the origin of the dissolved organic carbon (DOC), and to quantify the fraction of the maize C in the soil respiration. The maize‐derived SOC was quantified in soil samples collected to a depth of 65 cm from two plots, one ’︁continuous maize’ and the other ’︁continuous rye’ (reference site) from the long‐term field experiment ’︁Ewiger Roggen’ in Halle. This field trial was established in 1878 and was partly changed to a continuous maize cropping system in 1961. Production rates and δ13C of DOC and CO2 were determined for the Ap horizon in incubation experiments with undisturbed soil columns. After 37 years of continuous maize cropping, 15% of the total SOC in the topsoil originated from maize C. The fraction of the maize‐derived C below the ploughed horizon was only 5 to 3%. The total amount of maize C stored in the profile was 9080 kg ha−1 which was equal to about 31% of the estimated total C input via maize residues (roots and stubble). Total leaching of DOC during the incubation period of 16 weeks was 1.1 g m−2 and one third of the DOC derived from maize C. The specific DOC production rate from the maize‐derived SOC was 2.5 times higher than that from the older humus formed by C3 plants. The total CO2‐C emission for 16 weeks was 18 g m−2. Fifty‐eight percent of the soil respiration originated from maize C. The specific CO2 formation from maize‐derived SOC was 8 times higher than that from the older SOC formed by C3 plants. The ratio of DOC production to CO2‐C production was three times smaller for the young, maize‐derived SOC than for the older humus formed by C3 plants.  相似文献   

3.
Soil tillage is an agricultural practice that directly affects the global carbon cycle. Our study sought to assess the implications of adopting sunn hemp cover crops with different tillage practices on CO2 emissions for two soil types (clayey and sandy soil) cultivated with sugarcane in Brazil. The experimental design was a split‐plot with randomized blocks, with the main plots being with cover crop or fallow and sub‐plots being under conventional or minimum tillage. Our results indicate that during the first 50 days after soil tillage, the variation in soil CO2 emissions was stimulated by cover crop and soil tillage, while after that, it became dominated by the root respiration of sugarcane plants. We also found that over the first 97 days after the tillage, the clayey soil showed differences between minimum tillage with cover crop and fallow. Conversely, for sandy soil over the first 50 days following, there were differences between the tillage systems under cover cropping. Emissions from sugarcane rows were found to be greater than those from inter‐row positions. We concluded that soils under different textural classes had distinct patterns in terms of soil CO2 emissions. The correct quantification of CO2 emissions during the sugarcane renovation period should prioritize having a short assessment period (~50 days after soil tillage) as well as including measurements at row and inter‐row positions.  相似文献   

4.
利用~(13)C标记和自然丰度三源区分玉米根际CO_2释放   总被引：1，自引：1，他引：0  
石灰性土壤中,根际土壤释放的CO_2有三个来源,即根源呼吸、土壤有机碳(SOC)分解和土壤无机碳(SIC)溶解,三源区分土壤释放的CO_2是量化土壤碳平衡的前提。分别在玉米拔节期、抽穗期和灌浆期进行7 h的~(13)O_2脉冲标记,经过27 d示踪期后破坏性取样,测定~(13)标记与自然丰度处理中,玉米地上部、根系、土壤和土壤CO_2的碳含量和δ~(13)值,利用~(13)示踪并结合自然丰度法区分玉米土壤CO_2的来源。研究结果显示,随着玉米生长,根源呼吸对土壤CO_2的贡献呈降低趋势,从拔节期的66.7%降低至灌浆期的25.8%。整个玉米旺盛生育期内(从拔节期到生育期末),根源呼吸和土壤总碳释放对土壤CO_2具有同等贡献,SOC和SIC释放对土壤总碳释放的贡献率分别为30%和20%。玉米生长对土壤的碳输入(根系+根际沉积物)超过土壤总碳(SIC+SOC)的释放,总体表现为土壤碳汇。研究表明,SIC溶解对全球碳库稳定性和调节CO_2浓度的影响非常重要,若忽视石灰性土壤中SIC溶解,则会高估SOC的分解,进而影响SOC激发效应以及土壤碳平衡的评估。  相似文献   

5.
Experimentation with dynamics of soil carbon pools as affected by elevated CO2 can better define the ability of terrestrial ecosystems to sequester global carbon. In the present study, 6 N HCl hydrolysis and stable-carbon isotopic analysis (δ13C) were used to investigate labile and recalcitrant soil carbon pools and the translocation among these pools of sorghum residues isotopically labeled in the 1998-1999 Arizona Maricopa free air CO2 enrichment (FACE) experiment, in which elevated CO2 (FACE: 560 μmol mol−1) and ambient CO2 (Control: 360 μmol mol−1) interact with water-adequate (wet) and water-deficient (dry) treatments. We found that on average 53% of the final soil organic carbon (SOC) in the FACE plot was in the recalcitrant carbon pool and 47% in the labile pool, whereas in the Control plot 46% and 54% of carbon were in recalcitrant and labile pools, respectively, indicating that elevated CO2 transferred more SOC into the slow-decay carbon pool. Also, isotopic mixing models revealed that increased new sorghum residue input to the recalcitrant pool mainly accounts for this change, especially for the upper soil horizon (0-30 cm) where new carbon in recalcitrant soil pools of FACE wet and dry treatments was 1.7 and 2.8 times as large as that in respective Control recalcitrant pools. Similarly, old C in the recalcitrant pool under elevated CO2 was higher than that under ambient CO2, indicating that elevated CO2 reduces the decay of the old C in recalcitrant pool. Mean residence time (MRT) of bulk soil carbon at the depth of 0-30 cm was significantly longer in FACE plot than Control plot by the averages of 12 and 13 yr under the dry and wet conditions, respectively. The MRT was positively correlated to the ratio of carbon content in the recalcitrant pool to total SOC and negatively correlated to the ratio of carbon content in the labile pool to total SOC. Influence of water alone on the bulk SOC or the labile and recalcitrant pools was not significant. However, water stress interacting with CO2 enhanced the shift of the carbon from labile pool to recalcitrant pool. Our results imply that terrestrial agroecosystems may play a critical role in sequestrating atmospheric CO2 and mitigating harmful CO2 under future atmospheric conditions.  相似文献   

6.

Purpose

The aim of this study was to understand the effect of nitrogen fertilization on soil respiration and native soil organic carbon (SOC) decomposition and to identify the key factor affecting soil respiration in a cultivated black soil.

Materials and methods

A field experiment was conducted at the Harbin State Key Agroecological Experimental Station, China. The study consisted of four treatments: unplanted and N-unfertilized soil (U0), unplanted soil treated with 225?kg?N?ha?1 (UN), maize planted and N-unfertilized soil (P0), and planted soil fertilized with 225?kg?N?ha?1 (PN). Soil CO2 and N2O fluxes were measured using the static closed chamber method.

Results and discussion

Cumulative CO2 emissions during the maize growing season with the U0, UN, P0, and PN treatments were 1.29, 1.04, 2.30 and 2.27?Mg?C?ha?1, respectively, indicating that N fertilization significantly reduced the decomposition of native SOC. However, no marked effect on soil respiration in planted soil was observed because the increase of rhizosphere respiration caused by N addition was counteracted by the reduction of native SOC decomposition. Soil CO2 fluxes were significantly affected by soil temperature but not by soil moisture. The temperature sensitivity (Q 10) of soil respiration was 2.16?C2.47 for unplanted soil but increased to 3.16?C3.44 in planted soil. N addition reduced the Q 10 of native SOC decomposition possibly due to low labile organic C but increased the Q 10 of soil respiration due to the stimulation of maize growth. The estimated annual CO2 emission in N-fertilized soil was 1.28?Mg?C?ha?1 and was replenished by the residual stubble, roots, and exudates. In contrast, the lost C (1.53?Mg?C?ha?1) in N-unfertilized soil was not completely supplemented by maize residues, resulting in a reduction of SOC. Although N fertilization significantly increased N2O emissions, the global warming potential of N2O and CO2 emissions in N-fertilized soil was significantly lower than in N-unfertilized soil.

Conclusions

The stimulatory or inhibitory effect of N fertilization on soil respiration and basal respiration may depend on labile organic C concentration in soil. The inhibitory effect of N fertilization on native SOC decomposition was mainly associated with low labile organic C in tested black soil. N application could reduce the global warming potential of CO2 and N2O emissions in black soil.  相似文献   

7.
Conservation agriculture might have the potential to increase soil organic C content compared to conventional tillage based systems. The present study quantified soil organic carbon (SOC) and soil C derived from C3 (wheat) and C4 (maize) plant species using δ13C stable isotope. Soil with 16 y of continuous application of zero tillage (ZT) or conventional tillage (CT), monoculture (M) or rotation (R) of wheat and maize, and with (+r) and without retention (−r) in the field of crop residues were studied in the central highlands of Mexico. The highest SOC content was found in the 0-5 cm layer under ZTM and ZTR with residues retention. The soil cultivated with maize showed a higher SOC content in the 0-10 cm layer with residue retention than without residue. In the 10-20 cm layer, the highest SOC content was found in the CT treatment with residue retention. The SOC stock expressed as equivalent soil mass was greatest in the 0-20 cm layer of the ZTM (wheat and maize) and ZTR cultivated treatments with residue retention. After 16 y, the highest content of soil δ13C was found in ZTM + r and CTM + r treated soil cultivated with maize; −16.56‰ and −18.08‰ in the 0-5 cm layer, −18.41‰ and −18.02‰ in the 5-10 cm layer and −18.59‰ and −18.72‰ in the 10-20 cm layer respectively. All treatments had a higher percentages of C-C3 (derived from wheat residues or the earlier forest) than C-C4 (derived from maize residues). The highest percentages of C-C4, was found in ZTM + r and CTM + r treated soil cultivated with maize, i.e. 33.0% and 13.0% in 0-5 cm layer, 9.1% and 14.3% in the 5-10 cm layer and 5.0% and 6.8% in 10-20 cm layer, respectively. The gross SOC turnover was lower in soil with residue retention than without residues. It was found that the ZT system with residue retention and rotation with wheat is a practice with a potential to retain organic carbon in soil.  相似文献   

8.
Studies of rice-based systems in the Indo-Gangetic Plain (IGP) have demonstrated the beneficial effects of Conservation Agriculture on soil organic carbon (SOC) status, along with increased soil health and crop productivity. However, it remains unclear as to the time for such treatments to have a positive effect. In this study of lentil-mung bean-rice and wheat-mung-rice rotations in Bangladesh positive effects of strip planting or bed planting, along with residue return, on SOC pools were apparent after 1.5 years, compared with intensive conventional tillage and limited residue return. Conventional tillage resulted in higher CO2 emission compared with strip planting or bed planting as did high residue return. In the cereal-dominated rotation, the strip planting system sequestered carbon at a rate of 0.24–0.53 Mg C ha−1 year−1 (at 0–0.15 m depth) while conventional tillage was associated with a carbon loss of 0.52–0.82 Mg C ha−1 year−1. In the legume-dominated rotation, neither practice sequestered SOC. Under strip planting, a minimum annual crop residue input of 1.7 Mg C ha−1 for the cereal-dominated system and 5.2 Mg C ha−1 for the legume-dominated system was required to maintain SOC at equilibrium. We conclude that strip planting with high levels of crop residue return can be an effective and quick strategy in either slowing the loss of SOC or improving C sequestration in the intensive rice-based systems of the Eastern IGP.  相似文献   

9.
Abstract

Sampling on different plots of a field located in Pehuajó, Buenos Aires Province, Argentina, on an Entic Hapludoll, was conducted to determine the: effect of different soil management procedures on carbon cycle components. The plots studied were: A) eight years of mixed pasture followed by oat (Avena saliva L.) crop, B) five years of mixed pasture followed by maize (Zea mays L.) with direct drilling, and C) five years of mixed pasture followed by maize crop with conventional tillage. The sampling was done during the month of June 1994. By that time, plot A was in oat production and plots B and C were in fallow. Microbial biomass carbon (MBC) values differed significantly between the three plots, whereas no differences were found in the organic carbon (OC) content. Plots B and C differed both in respiration and qCO2 (the ratio between C‐CO2 released by respioration and the microbial biomass C). For the latter, no differences had been found as a function of the tillage system in a previous work that was carried out on another region of Argentina. Theoretical calculations on the CO2 release from the soil to the atmosphere were inferred from the respiration values previously found.  相似文献   

10.
Soil organic carbon (SOC), microbial biomass carbon (MBC), their ratio (MBC/SOC) which is also known as microbial quotient, soil respiration, dehydrogenase and phosphatase activities were evaluated in a long-term (31 years) field experiment involving fertility treatments (manure and inorganic fertilizers) and a maize (Zea mays L.)-wheat (Triticum aestivum L.)-cowpea (Vigna unguiculata L.) rotation at the Indian Agricultural Research Institute near New Delhi, India. Applying farmyard manure (FYM) plus NPK fertilizer significantly increased SOC (4.5-7.5 g kg−1), microbial biomass (124-291 mg kg−1) and microbial quotient from 2.88 to 3.87. Soil respiration, dehydrogenase and phosphatase activities were also increased by FYM applications. The MBC response to FYM+100% NPK compared to 100% NPK (193 vs. 291 mg kg−1) was much greater than that for soil respiration (6.24 vs. 6.93 μl O2 g−1 h−1) indicating a considerable portion of MBC in FYM plots was inactive. Dehydrogenase activity increased slightly as NPK rates were increased from 50% to 100%, but excessive fertilization (150% NPK) decreased it. Acid phosphatase activity (31.1 vs. 51.8 μg PNP g−1 h−1) was much lower than alkali phosphatase activity (289 vs. 366 μg PNP g−1 h−1) in all treatments. Phosphatase activity was influenced more by season or crop (e.g. tilling wheat residue) than fertilizer treatment, although both MBC and phosphatase activity were increased with optimum or balanced fertilization. SOC, MBC, soil respiration and acid phosphatase activity in control (no NPK, no manure) treatment was lower than uncultivated reference soil, and soil respiration was limiting at N alone or NP alone treatments.  相似文献   

11.
华北平原农田生态系统碳过程与环境效应研究   总被引：1，自引：0，他引：1  
本文总结了25年来针对华北平原小麦-玉米两熟系统,农田的碳循环对气候变化(温度升高)和管理措施(氮肥施入、秸秆还田和耕作方式等)响应机制的研究成果。自2001年起我们在中国科学院栾城农业生态系统试验站建立了3个长期定位碳循环试验:耕作试验、有机循环试验和增温试验,并完善了4种农田碳过程监测方法体系:隔离罐-碱液吸收CO_2法、静态箱-气相色谱法、涡度相关技术和浓度梯度法。量化了华北平原小麦-玉米两熟系统碳输入-输出的平衡,并对华北平原施氮农田土壤碳截留进行了再评价,指出秸秆还田下高水高肥的精细管理农田正在以77 g(C)·m~(-2)·a~(-1)的速度丢失碳;此外长期氮施入虽然显著增加0~100 cm土体的土壤有机碳含量,但同时会造成0~60 cm土体土壤无机碳含量显著降低。我们在对碳过程环境效应的研究中进一步指出:增温和施氮均会降低CH4汇强度,但对土壤呼吸无显著影响,这可能主要是由于试验增温诱发的土壤干旱抵消了土壤温度的部分影响和土壤呼吸对土壤温度升高的适应性造成的。我们对剖面土壤气体的研究表明施氮对剖面CH4和CO_2均无显著影响。进一步将静态箱法和浓度梯度法相结合的研究结果表明0~40cm土层是北方旱地无氮农田土壤CO_2产生和CH4吸收的主要发生层。  相似文献   

12.
Residue retention and reduced tillage are both conservation agricultural practices that may enhance soil organic carbon (SOC) stabilization in soil. We evaluated the long‐term effects of no‐till (NT) and stover retention from maize on SOC dynamics in a Rayne silt loam Typic Hapludults in Ohio. The six treatments consisted of retaining 0, 25, 50, 75, 100 and 200% of maize residues on each 3 × 3 m plot from the crop of previous year. Soil samples were obtained after 9 yrs of establishing the experiment. The whole soil (0–10 and 10–20 cm of soil depths) samples under different treatments were analysed for total C, total N, recalcitrant C (NaOCl treated sample) and 13C isotopic abundance (0–10 cm soil depth). Complete removal of stover for a period of 9 yrs significantly (P < 0.01) decreased soil C content (15.5 g/kg), whereas 200% of stover retention had the maximum soil C concentration (23.1 g/kg). Relative distribution of C for all the treatments in different fractions comprised of 55–58% as labile and 42–45% as recalcitrant. Retention of residue did not significantly affect total C and N concentration in 10–20 cm depth. 13C isotopic signature data indicated that C4‐C (maize‐derived C) was the dominant fraction of C in the top 0–10 cm of soil layer under NT with maize‐derived C accounting for as high as 80% of the total SOC concentration. Contribution of C4‐C or maize‐derived C was 71–84% in recalcitrant fraction in different residue retained plots. Residue management is imperative to increase SOC concentrations and long‐term agro‐ecosystem necessitates residue retention for stabilizing C in light‐textured soils.  相似文献   

13.
The effect of three land use types on decomposition of 14C-labelled maize (Zea mays L.) residues and soil organic matter were investigated under laboratory conditions. Samples of three Dystric Cambisols under plow tillage (PT), reduced tillage (RT) and grassland (GL) collected from the upper 5 cm of the soil profile were incubated for 159 days at 20 °C with or without 14C-labelled maize residue. After 7 days cumulative CO2 production was highest in GL and lowest in PT, reflecting differences in soil organic C (SOC) concentration among the three land use types and indicating that mineralized C is a sensitive indicator of the effects of land use regime on SOC. 14CO2 efflux from maize residue decomposition was higher in GL than in PT, possibly due to higher SOC and microbial biomass C (MBC) in GL than in PT. 14CO2 efflux dynamics from RT soil were different from those of PT and GL. RT had the lowest 14CO2 efflux from days 2 to 14 and the highest from days 28 to 159. The lowest MBC in RT explained the delayed decomposition of residues at the beginning. A double exponential model gave a good fit to the mineralization of SOC and residue-14C (R2 > 0.99) and allowed estimation of decomposition rates as dependent on land use. Land use affected the decomposition of labile fractions of SOC and of maize residue, but had no effect on the decomposition of recalcitrant fractions. We conclude that land use affected the decomposition dynamics within the first 1.5 months mainly because of differences in soil microbial biomass but had low effect on cumulative decomposition of maize residues within 5 months.  相似文献   

14.
Soil tillage has been shown to affect long‐term changes in soil organic carbon (SOC) content in a number of field experiments. This paper presents a simplified approach for including effects of tillage in models of soil C turnover in the tilled‐soil layer. We used an existing soil organic matter (SOM) model (CN‐SIM) with standard SOC data for a homogeneous tilled layer from four long‐term field experiments with conventionally tilled (CT) and no‐till (NT) treatments. The SOM model was tested on data from long‐term (>10 years) field trials differing in climatic conditions, soil properties, residue management and crop rotations in Australia, Brazil, the USA and Switzerland. The C input for the treatments was estimated using data on crop rotation and residue management. The SOM model was applied for both CT and NT trials without recalibration, but incorporated a ‘tillage factor’ (TF) to scale all decomposition and maintenance parameters in the model. An initial value of TF = 0.57 (parameter uncertainty, PU = 0.15) for NT (with TF set to 1.0 for CT) was used on the basis of a previous study with observations of soil CO2 respiration. The simulated and observed changes in SOC were then compared using slopes of linear regressions of SOC changes over time. Results showed that the SOM model captured observed changes in SOC content from differences in rotations, N application and crop residue management for conventional tillage. On the basis of SOC change data a mean TF of 0.48 (standard deviation, SD = 0.12) was estimated for NT. The results indicate that (i) the estimated uncertainty of tillage effects on SOC turnover may be smaller than previously thought and (ii) simple scaling of SOM model parameters may be sufficient to capture the effects of soil tillage on SOM turnover in the tilled layer. Scenario analyses showed that the average extra C input needed to compensate for soil tillage was 762 (SD = 351) kg C ha−1 year−1. Climatic conditions (temperature and precipitation) also affected how much extra C was needed, with substantially larger inputs being required for wetter and warmer climates.  相似文献   

15.
Quantifying carbon dioxide (CO2) fluxes in terrestrial ecosystems is critical for better understanding of global carbon cycling and observed changes in climate. This study examined year-round temporal variations of CO2 fluxes in two biennial crop rotations during 4 year of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production. We monitored CO2 fluxes using eddy-covariance (EC) and soil chambers in adjacent production fields near Ames, Iowa. Under the non-limiting soil water availability conditions predominant in these fields, diel and seasonal variations of CO2 fluxes were mostly controlled by ambient temperature and available light. Air temperature explained up to 81% of the variability of soil respiratory losses during fallow periods. In contrast, with full-developed canopies, available light was the main driver of daytime CO2 uptake for both crops. Furthermore, a combined additive effect of both available light and temperature on enhanced CO2 uptake was identified only for corn. Moreover, diurnal hysteresis of net CO2 uptake with available light was also found for both crops with consistently greater CO2 uptake in the mornings than afternoons perhaps primarily owing to delay in peak of soil respiration relative to the time of maximum plant photosynthesis. Annual cumulative CO2 exchange was mainly determined by crop species with consistently greater net uptake for corn and near neutral exchange for soybean (−466 ± 38 and −13 ± 39 g C m−2 year−1). Concomitantly, within growing seasons, CO2 sink periods were approximately 106 days for corn and 90 days for soybean, and peak rates of CO2 uptake were roughly 1.7-fold higher for corn than soybean. Apparent changes in soil organic carbon estimated after accounting for grain carbon removal suggested soil carbon depletion following soybean years and neutral carbon balance for corn. Overall, results suggest changes in land use and cropping systems have a substantial impact on dynamics of CO2 exchange.  相似文献   

16.
A natural‐13C‐labeling approach—formerly observed under controlled conditions—was tested in the field to partition total soil CO2 efflux into root respiration, rhizomicrobial respiration, and soil organic matter (SOM) decomposition. Different results were expected in the field due to different climate, site, and microbial properties in contrast to the laboratory. Within this isotopic method, maize was planted on soil with C3‐vegetation history and the total CO2 efflux from soil was subdivided by isotopic mass balance. The C4‐derived C in soil microbial biomass was also determined. Additionally, in a root‐exclusion approach, root‐ and SOM‐derived CO2 were determined by the total CO2 effluxes from maize (Zea mays L.) and bare‐fallow plots. In both approaches, maize‐derived CO2 contributed 22% to 35% to the total CO2 efflux during the growth period, which was comparable to other field studies. In our laboratory study, this CO2 fraction was tripled due to different climate, soil, and sampling conditions. In the natural‐13C‐labeling approach, rhizomicrobial respiration was low compared to other studies, which was related to a low amount of C4‐derived microbial biomass. At the end of the growth period, however, 64% root respiration and 36% rhizomicrobial respiration in relation to total root‐derived CO2 were calculated when considering high isotopic fractionations between SOM, microbial biomass, and CO2. This relationship was closer to the 50% : 50% partitioning described in the literature than without fractionation (23% root respiration, 77% rhizomicrobial respiration). Fractionation processes of 13C must be taken into account when calculating CO2 partitioning in soil. Both methods—natural 13C labeling and root exclusion—showed the same partitioning results when 13C isotopic fractionation during microbial respiration was considered and may therefore be used to separate plant‐ and SOM‐derived CO2 sources.  相似文献   

17.
Intensity of tillage practices can enhance organic matter decomposition, increasing CO2 emissions from soil to the atmosphere. Conservation tillage （CT） has been proposed as a means of counteracting potential damages to the environment. In this study the effects of two CT systems, reduced tillage in a long-term experiment （RTL） and no-tillage in a short-term experiment （NTs）, were compared to traditional tillage （TT） in the long （TTL） and short-term experiments （TTs）. CO2 fluxes, total soil organic carbon （SOC） and dehydrogenase activity （DHA） were evaluated at 0-5, 5-10 and 10-15 cm depths throughout the three years studied （Oct. 2006 Jul. 2009）. Traditional tillage increased C02 emissions compared to CT. The CT treatments （RTL and NTs） accumulated more SOC in the surface layer （0 5 cm） than the TT treatments （TTL and TTs）. SOC accumulation was moderate but DHA consistently increased in CT in the surface soil, especially with a legume crop included in the crop rotation. Values of stratification ratio of all parameters studied were higher in the CT treatments （RTL and NTs）. The agricultural and environmental benefits derived from CT make this system recommendable for semi-arid Mediterranean rain-fed agriculture.  相似文献   

18.
Abstract

The study aimed at quantifying the rates of soil CO2 efflux under the influence of common tillage systems of moldboard plow (PT), chisel plow (CT), rotary tiller (RT), heavy disc harrow (DT), and no-tillage (NT) for 46 days in October and November in a field left fallow after wheat harvest located in southern Turkey. The NT and DT plots produced the lowest soil CO2 effluxes of 0.3 and 0.7 g m?2 h?1, respectively, relative to the other plots (P < 0.001). Following the highest rainfall amount of 87 mm on the tenth day after the tillage, soil CO2 efflux rates of all the plots peaked on the 12th day, with less influence on soil CO2 efflux in the NT plot than in the conventional tillage plots. Soil evaporation in NT (64 mmol m?2 s?1) was significantly lower than in the PT (85 mmol m?2 s?1) and RT (89 mmol m?2 s?1) tillage treatments (P < 0.01). The best multiple-regression model selected explained 46% of variation in soil respiration rates as a function of the tillage treatments, soil temperature, and soil evaporation (P < 0.001). The tillage systems of RT, PT, and CT led, on average, to 0.23, 0.22, and 0.18 g m?2 h?1 more soil CO2 efflux than the baseline of NT, respectively (P≤0.001).  相似文献   

19.
The effects of tillage on the interaction between soil structure and microbial biomass vary spatially and temporally for different soil types and cropping systems. We assessed the relationship between soil structure induced by tillage and soil microbial activity at the level of soil aggregates. To this aim, organic C (OC), microbial biomass C (MBC) and soil respiration were measured in water-stable aggregates (WSA) of different sizes from a subtropical rice soil under two tillage systems: conventional tillage (CT) and a combination of ridge with no-tillage (RNT). Soil (0–20 cm) was fractionated into six different aggregate sizes (> 4.76, 4.76–2.0, 2.0–1.0, 1.0–0.25, 0.25–0.053, and < 0.053 mm in diameter). Soil OC, MBC, respiration rate, and metabolic quotient were heterogeneously distributed among soil aggregates while the patterns of aggregate-size distribution were similar among properties, regardless of tillage system. The content of OC within WSA followed the sequence: medium-aggregates (1.0–0.25 mm and 1.0–2.0 mm) > macro-aggregates (4.76–2.0 mm) > micro-aggregates (0.25–0.053 mm) > large aggregates (> 4.76 mm) > silt + clay fractions (< 0.053 mm). The highest levels of MBC were associated with the 1.0–2.0 mm aggregate size class. Significant differences in respiration rates were also observed among different sizes of WSA, and the highest respiration rate was associated with 1.0–2.0 mm aggregates. The Cmic/Corg was greatest for the large-macroaggregates regardless of tillage regimes. This ratio decreased with aggregate size to 1.0–0.25 mm. Soil metabolic quotient (qCO2) ranged from 3.6 to 17.7 mg CO2 g− 1 MBC h− 1. The distribution pattern of soil microbial biomass and activity was governed by aggregate size, whereas the tillage effect was not significant at the aggregate scale. Tillage regimes that contribute to greater aggregation, such as RNT, also improved soil microbial activity. Soil OC, MBC and respiration rate were at their highest levels for 1.0–2.0 mm aggregates, suggesting a higher biological activity at this aggregate size for the present ecosystem.  相似文献   

20.
The effect of conversion of short‐rotation coppices (SRCs) to agricultural land on soil organic carbon (SOC), soil microbial properties and crop yield is largely unknown. The objective of this study was to assess the effects of subsequent land use and tillage depth after conversion of SRCs on (i) total SOC (ii) soil C fractions with differentiation of total harvest residues and woody harvest residues from SRC and maize by 13C analysis and (iii) dry matter and N yield of grassland and maize. For this purpose, field trials were established after conversion of SRCs at three sites in Germany and cultivated with maize and grassland with shallow (5 cm), medium (15 cm) and deep tillage depth (30 cm). Crops were sampled for 5 yrs, and soil samples were collected at a depth of 0–5, 5–15 and 15–30 cm. Amount of total carbon and soil carbon fractions immediately and 4 yrs after conversion of SRC were compared. Tillage depth had no effect on dry matter yield of maize and grassland. The amount of woody harvest residues decreased over time following conversion at all sites irrespective of land use or tillage depth, but SOC decreased only at one site. Microbial biomass was particularly sensitive to land use, but microorganisms reacted differently to tillage depth depending on the soil conditions. Our results reveal that decomposition of woody harvest residues is rapid and that effects of tillage and land use on different soil C‐pools are site specific.  相似文献   

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