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1.
In semiarid Mediterranean agroecosystems, low and erratic annual rainfall together with the widespread use of mouldboard ploughing (conventional tillage, CT), as the main traditional tillage practice, has led to a depletion of soil organic matter (SOM) and with increases in CO2 emissions from soil to the atmosphere. In this study, we evaluated the viability of conservation tillage: RT, reduced tillage (chisel and cultivator ploughing) and, especially, NT (no-tillage) to reduce short-term (from 0 to 48 h after a tillage operation) and mid-term (from 0 h to several days since tillage operation) tillage-induced CO2 emissions. The study was conducted in three long-term tillage experiments located at different sites of the Ebro river valley (NE Spain) across a precipitation gradient. Soils were classified as: Fluventic Xerocrept, Typic Xerofluvent and Xerollic Calciorthid. Soil temperature and water content were also measured in order to determine their influence on tillage-induced CO2 fluxes. The majority of the CO2 flux measured immediately after tillage ranged from 0.17 to 6 g CO2 m−2 h−1 and was from 3 to 15 times greater than the flux before tillage operations, except in NT where soil CO2 flux was low and steady during the whole study period. Mid-term CO2 emission showed a different trend depending on the time of the year in which tillage was implemented. Microclimatic soil conditions (soil temperature and water content) had little impact on soil CO2 emission following tillage. In the semiarid Mediterranean agroecosystems studied, NT had low short-term soil CO2 efflux compared with other soil tillage systems (e.g., conventional and reduced tillage) and therefore can be recommended to better manage C in soil.  相似文献   

2.
Topsoil (0–25 cm) and subsoil (30–55 cm) samples were taken from clay soil which had been cropped with reed canarygrass (Phalaris arundinacea). After crumbling the soil into fragments <10 mm and removing visible organic debris, CO2 evolution was measured in the laboratory at four moisture contents (17, 26, 36 and 50% H2O for the topsoil and 16, 23, 31 and 41% for the subsoil) and at constant temperatures of −4, 0.3, 5, 15, 25, and temperatures fluctuating (weekly) between −4 and +5°C. Evolution of CO2 after the addition of roots or stubble of P. arundinacea to the topsoil (25°C, 36% H2O) was also studied. The CO2 evolution increased significantly with temperature and moisture. The CO2 evolution rate per unit of soil carbon was about two times higher for topsoil than for subsoil. Temperature fluctuation between −4 and +5°C did not enhance CO2 evolution significantly compared with incubation at a constant 5°C and was even lower than or not significantly different from samples at 0.3°C.  相似文献   

3.
Surface accumulation of soil organic carbon (SOC) under conservation tillage has significant effects on stratification of other nutrients, on crop productivity and in ameliorating the greenhouse effect via atmospheric CO2 sequestration. A measure of SOC stratification relative to deeper soil layers has been proposed as a soil quality index. Our objective was to determine the effects of the duration of tillage practices upon the SOC and extractable P distribution with depth in Maury silt loams (Typic Paleudalfs) at similar levels of corn (Zea mays L.) productivity without P fertilization. Soil samples (0–20.0 cm in 2.5 cm increments) were collected under moldboard tillage (MT), chisel tillage (CT) and no-tillage (NT) and in surrounding tall fescue (Festuca arundinacea L.) sods selected from three tillage experiments (1–2-, 8- and 29-year durations) in Kentucky. SOC stratification was greater under conservation tillage (CT and NT) and sods than under MT. SOC and soil-test-extractable P stratification were positively related. Increasing the duration under NT caused the thickness of C stratification to increase. In NT soils, C stratification ratio (CSR) approached CSR in the nearby long-term sods with time. Conservation tillage rapidly promoted the occurrence of CSR greater than 2 while MT always resulted in values lower than 2. The rapid initial change in CSR suggests characterization of thin soil layers (i.e. 2.5 cm depth increments) is desirable under conservation tillage.  相似文献   

4.
Quality of agricultural soils is largely a function of soil organic matter. Tillage and crop management impact soil organic matter dynamics by modification of the soil environment and quantity and quality of C input. We investigated changes in pools and fluxes of soil organic C (SOC) during the ninth and tenth year of cropping with various intensities under conventional disk-and-bed tillage (CT) and no tillage (NT). Soil organic C to a depth of 0.2 m increased with cropping intensity as a result of greater C input and was 10% to 30% greater under NT than under CT. Sequestration of crop-derived C input into SOC was 22±2% under NT and 9±4% under CT (mean of cropping intensities ± standard deviation of cropping systems). Greater sequestration of SOC under NT was due to a lower rate of in situ soil CO2 evolution than under CT (0.22±0.03 vs. 0.27±0.06 g CO2–C g−1 SOC yr−1). Despite a similar labile pool of SOC under NT than under CT (1.1±0.1 vs. 1.0±0.1 g mineralizable C kg−1 SOC d−1), the ratio of in situ to potential CO2 evolution was less under NT (0.56±0.03) than under CT (0.73±0.08), suggesting strong environmental controls on SOC turnover, such as temperature, moisture, and residue placement. Both increased C sequestration and a greater labile SOC pool were achieved in this low-SOC soil using NT and high-intensity cropping.  相似文献   

5.
Soil organic matter has recently been implicated as an important sink for atmospheric carbon dioxide (CO2). However, the relative impacts of various agricultural management practices on soil organic matter dynamics and, therefore, C sequestration at spatial scales larger than a single plot or times longer than the typical three year experiment have rarely been reported. Results of maintaining agricultural management practices in the forest-derived soils of the eastern Corn (Zea mays L.) Belt states of Kentucky, Michigan, Ohio and Pennsylvania (USA) were studied. We found annual organic C input and tillage intensity were the most important factors in affecting C sequestration. The impact of rotation on C sequestration was primarily related to the way it altered annual total C inputs. The removal of above-ground plant biomass and use of cover crops were of lesser importance. The most rapid changes in soil organic matter content occurred during the first five years after a management practice was imposed with slower changes occurring thereafter. Certain management practices, e.g. no-tillage (NT), increased the soil's ability to sequester atmospheric CO2. The impact of this sequestration will be significant only when these practices are used extensively on a large percentage of cropland and when the C-building practices are maintained. Any soil C sequestered will be rapidly mineralized to CO2 if the soil organic matter building practices are not maintained.  相似文献   

6.
An energy analysis of three cropping systems with different intensities of soil tillage (conventional tillage, CT; ridge tillage, RT; no tillage, NT) was done in a loamy-silt soil (fulvi-calcaric Cambisol) at Legnaro, NE Italy (45°21′N, 11°58′E, 8 m above sea-level (a.s.l.), average rainfall 822 mm, average temperature 11.7°C). This and measurements of the evolution of the organic matter content in the soil also allowed the consequences to be evaluated in terms of CO2 emissions.

The weighted average energy input per hectare was directly proportional to tillage intensity (CT > RT > NT). Compared with CT, total energy savings per hectare were 10% with RT and 32% with NT. Average energy costs per unit production were fairly similar (between 4.5 and 5 MJ kg−1), with differences of 11%. The energy outputs per unit area were highest in CT for all crops, and lowest in NT. The RT outputs were on average more similar to CT (−12%). The output/input ratio tended to increase when soil tillage operations were reduced, and was 4.09, 4.18 and 4.57 for CT, RT and NT, respectively. As a consequence of fewer mechanical operations and a greater working capacity of the machines, there was lower fuel consumption and a consistently higher organic matter content in the soil with the conservation tillage methods.

These two effects result in less CO2 emission into the atmosphere (at 0°C and pressure of 101.3–103 kPa) with respect to CT, of 1190 m3 ha−1 year−1 in RT and 1553 m3 ha−1 year−1 in NT. However, the effect owing to carbon sequestration as organic matter will decline to zero over a period of years.  相似文献   


7.
Long-term tillage and nitrogen (N) management practices can have a profound impact on soil properties and nutrient availability. A great deal of research evaluating tillage and N applications on soil chemical properties has been conducted with continuous corn (Zea Mays L.) throughout the Midwest, but not on continuous grain sorghum (Sorghum bicolor (L.) Moench). The objective of this experiment was to examine the long-term effects of tillage and nitrogen applications on soil physical and chemical properties at different depths after 23 years of continuous sorghum under no-till (NT) and conventional till (CT) (fall chisel-field cultivation prior to planting) systems. Ammonium nitrate (AN), urea, and a slow release form of urea were surface broadcast at rates of 34, 67, and 135 kg N ha−1. Soil samples were taken to a depth of 15 cm and separated into 2.5 cm increments. As a result of lime applied to the soil surface, soil pH in the NT and CT plots decreased with depth, ranging from 6.9 to 5.7 in the NT plots and from 6.5 to 5.9 in the CT plots. Bray-1 extractable P and NH4OAc extractable K was 20 and 49 mg kg−1 higher, respectively, in the surface 2.5 cm of NT compared to CT. Extractable Ca was not greatly influenced by tillage but extractable Mg was higher for CT compared to NT below 2.5 cm. Organic carbon (OC) under NT was significantly higher in the surface 7.5 cm of soil compared to CT. Averaged across N rates, NT had 2.7 Mg ha−1 more C than CT in the surface 7.5 cm of soil. Bulk density (Δb) of the CT was lower at 1.07 g cm−3 while Δb of NT plots was 1.13 g cm−3. This study demonstrated the effect tillage has on the distribution and concentration of certain chemical soil properties.  相似文献   

8.
The impact of conventional tillage (CT) or no-till (NT) management on soil microbial respiration as well as microbial abundance was studied in soils from the El Salado basin river (Buenos Aires, Argentina) recently subjected to agriculture under a corn-pasture rotation since 1996. Both management systems were monitored for several soil (micro)biological, physical and chemical properties during the second (1997) to fourth (1999) years from the beginning of the experiment. O2 and CO2 composition of the soil atmosphere and the rate at which soil consumes O2 (qO2) or produces CO2 (qCO2), under conditions that approximate the soil environment in the field, were quantitated following an experimental method and a mathematical model developed by ourselves [Soil Sci. 166 (2001) 68] to interpret the data. qO2 and qCO2 expressed in terms of kg O2 or CO2-C per ha per day or per kg C of microbial biomass (microbial respiration), increased from the lowest values measured at 10–30% water-filled pore space (WFPS) up to 60% WFPS, decreasing thereafter. Low respiratory quotients, RQ (qCO2/qO2<1.0), were detected, with gas exchanges being slightly higher in NT than in CT. Correspondingly, higher bacterial and fungal biomass were measured in NT than in CT. Apparently, bacteria were more sensitive to high WFPS than fungi. When aerobic bacteria or fungi counts were compared at low or high WFPS, they differed significantly only in the upper soil profile whereas microaerophilic bacteria and fungi were significatively different in both depths tested (D1=5–10 cm; D2=15–20 cm). The results are discussed in terms of microbial metabolism behavior and abundance as a function of management and soil air/water balance in soils recently subjected to agriculture.  相似文献   

9.
Under semi-arid conditions, the properties of many soils are influenced by the presence of organic matter and calcium carbonate (CaCO3). However, the influence of different tillage systems on the development of these properties has scarcely been studied under semi-arid Mediterranean conditions. We studied the effect of long-term conservation tillage (CT) and traditional tillage (TT) on the stratification ratio of soil organic carbon and on CaCO3 content. The study was conducted in a wheat (Triticum aestivum L.)–sunflower (Helianthus annuus L.) crop rotation established in 1991 under rainfed conditions in Southwestern Spain. As is traditional in this area, wheat was fertilised, but sunflower was not. Conservation tillage was characterised by reduced number of tillage operations and leaving crop residues on the soil surface, while TT was with mouldboard ploughing. Stratification ratio of soil organic C was calculated from C contents in the 0–5 and 5–10 cm soil layers divided by that in the 25–40 cm. Stratification ratio of soil organic C under the CT (>2) was significantly greater than under TT (<2); values >2 indicating better soil quality. Our results show a loss of CaCO3 under both tillage systems. However, the loss of CaCO3 was significantly higher under TT than under CT. Also, P and K accumulated in the soil surface and stratification ratio for both nutrients was greater in CT than in TT.  相似文献   

10.
Management practices that simultaneously improve soil properties and yield are crucial to sustain high crop production and minimize detrimental impact on the environment. The objective of this study was to determine the influence of tillage and crop residue management on crop yield, N uptake and C removal in crop, soil organic C and N, inorganic N and aggregation, and nitrous oxide (N2O) emissions on a Gray Luvisol (Boralf) soil near Star City, Saskatchewan, Canada. The 4-year (1998–2001) field experiment was conducted with two tillage systems: no tillage (NT), and conventional tillage (CT); two levels of straw: straw retained (S), and straw removed (NS); and four rates of fertilizer N: 0, 40, 80, and 120 kg N ha−1, except no N to pea phase of the rotation. The plots were seeded to barley (Hordeum vulgare L.) in 1998, pea (Pisum sativum L.) in 1999, wheat (Triticum aestivum L.) in 2000 and canola (Brassica napus L.) in 2001. Tillage and straw treatments generally had no effect on crop yield during the first three years. But in 2001, NT produced 55, 32, and 20% greater canola seed, straw and chaff than CT, respectively, whereas straw retention increased seed and straw yield by 33 and 19% compared to straw removal. Seed, straw and chaff yield of canola increased with N rate up to 40 kg N ha−1, and root mass (0–15 cm depth) with N rate to 80 kg N ha−1. Amount of N uptake and C removed in wheat and canola generally increased with N rate, but tillage and straw management had no consistent effect. After four crop seasons, total organic C (TOC) and N (TN), light fraction organic matter (LFOM), C (LFC), and N (LFN) were generally greater with S than NS treatments. Tillage did not affect TOC and TN in soil, but LFOM, LFC, and LFN were greater or tended to be greater under NT than CT. There was no effect of tillage, straw and N fertilization on NH4-N in soil, but CT and S tended to have higher NO3-N concentration in 0–15 cm soil than NT and NS, respectively. Concentration of NO3-N increased substantially with N rate ≥80 kg ha−1. The NT + S treatment had the lowest proportion (34%) of wind-erodible (<0.83 mm diameter) aggregates and greatest proportion (37%) of larger (>12.7 mm) dry aggregates, compared to highest (50%) and lowest (18%) proportion of corresponding aggregates in CT + NS, indicating less potential for soil erosion when tillage was omitted and crop residues were retained. Amount of N lost as N2O was higher from N-fertilized than from zero-N plots, and it was substantially higher from N-applied CT plots than from N-applied NT plots. Retaining crop residues along with no-tillage improved soil properties and may also be better for the environment.  相似文献   

11.
Anthropogenic conversion of primary forest to pasture for cattle production is still frequent in the Amazon Basin. Practices adopted by ranchers to restore productivity to degraded pasture have the potential to alter soil N availability and N gas losses from soils. We examined short-term (35 days) effects of tillage prior to pasture re-establishment on soil N availability, CO2, NO and N2O fluxes and microbial biomass C and N under degraded pasture at Nova Vida ranch, Rondônia, Brazilian Amazon. We collected soil samples and measured gas fluxes in tilled and control (non tilled pasture) 12 times at equally spaced intervals during October 2001 to quantify the effect of tillage. Maximum soil NH4+ and NO3− pools were 13.2 and 6.3 kg N ha−1 respectively after tillage compared to 0.24 and 6.3 kg N ha−1 in the control. Carbon dioxide flux ranged from 118 to 181 mg C–CO2 m2 h−1 in the control (non-tilled) and from 110 to 235 mg C–CO2 m2 h−1 when tilled. Microbial biomass C varied from 365 to 461 μg g−1 in the control and from 248 to 535 μg g−1 when tilled. The values for N2O fluxes ranged from 1.22 to 96.9 μg N m−2 h−1 in the tilled plots with a maximum 3 days after the second tilling. Variability in NO flux in the control and when tilled was consistent with previous measures of NO emissions from pasture at Nova Vida. When tilled, the NO/N2O ratio remained <1 after the first tilling suggesting that denitrification dominated N cycling. The effects of tilling on microbial parameters were less clear, except for a decrease in qCO2 and an increase in microbial biomass C/N immediately after tilling. Our results suggest that restoration of degraded pastures with tillage will lead to less C matter, at least initially. Further long-term research is needed.  相似文献   

12.
Crop rotation and tillage impact microbial C dynamics, which are important for sequestering C to offset global climate change and to promote sustainable crop production. Little information is available for these processes in tropical/subtropical agroecosystems, which cover vast areas of terrestrial ecosystems. Consequently, a study of crop rotation in combination with no tillage (NT) and conventional tillage (CT) systems was conducted on an Oxisol (Typic Haplorthox) in an experiment established in 1976 at Londrina, Brazil. Soil samples were taken at 0–50, 50–100 and 100–200 mm depths in August 1997 and 1998 and evaluated for microbial biomass carbon (MBC) and mineralizable C and N. There were few differences due to crop rotation, however there were significant differences due to tillage. No tillage systems increased total C by 45%, microbial biomass by 83% and MBC:total C ratio by 23% at 0–50 mm depth over CT. C and N mineralization increased 74% with NT compared to CT systems for the 0–200 mm depth. Under NT, the metabolic quotient (CO2 evolved per unit of MBC) decreased by 32% averaged across soil depths, which suggests CT produced a microbial pool that was more metabolically active than under NT systems. These soil microbial properties were shown to be sensitive indicators of long-term tillage management under tropical conditions.  相似文献   

13.
Recent research indicates tillage operations result in a rapid physical release of CO2 and water vapor from soil. However, effects of soil disturbance on gas fluxes during planting operations have not been adequately explored. Our objective was to measure short-term gas loss resulting from the use of different planting preparation implements on long-term residue-covered soil (no-till) on a Norfolk loamy sand (Typic Kandiudults; FAO classification Luxic Ferralsols) in east-central Alabama, USA. A crimson clover (Trifolium incarnatum L.) cover crop was killed with herbicide two weeks prior to the study. Due to dry soil conditions, 15 mm of water was applied 24 h prior to study. Gas fluxes were measured with a large canopy chamber (centered over two rows) for an integrated assessment of equipment-induced soil disturbance. Increased losses of CO2 and water vapor were directly related to increases in soil disturbance. Although these short-term C losses are minor in terms of predicting long-term C turnover in agro-ecosystems, results suggest that selecting planting equipment that maintains surface residue and minimizes soil disturbance could help to conserve soil water needed for successful seedling establishment in these coarse textured soils.  相似文献   

14.
Soil carbon (C) losses and soil translocation from tillage operations have been identified as causes of soil degradation and soil erosion. The objective of this work was to quantify the variability in tillage-induced carbon dioxide (CO2) loss by moldboard (MP) and chisel (CP) plowing across an eroded landscape and relate the C loss to soil properties. The study site was a 4 ha wheat (Triticum aestivum L. cv. Marshall) field with rolling topography and five soil types in the Svea-Barnes complex in west central Minnesota (N. Latitude = 45°41′W, Longitude = 95°43′). Soil properties were measured at several depths at a 10 m spacing along north–south (N–S) and west–east (W–E) transects through severely eroded, moderately eroded and non-eroded sites. Conventional MP (25 cm deep) and CP (15 cm deep) equipment were used along the pre-marked transects. Gas exchange measurements were obtained with a large, portable chamber within 2 m of each sample site following tillage. The measured CO2 fluxes were largest with the MP > CP > not tilled (before tillage). The variation in 24 h cumulative CO2 flux from MP was nearly 3-fold on the N–S transect and 4-fold on the W–E transect. The surface soil organic C on the transects was lowest on the eroded knolls at 5.1 g C kg−1 and increased to 19.6 g C kg−1 in the depositional areas. The lowest CO2 fluxes were measured from severely eroded sites which indicated that the variation in CO2 loss was partially reflected by the degradation of soil properties caused by historic tillage-induced soil translocation with some wind and water erosion.

The spatial variation across the rolling landscape complicates the determination of non-point sources of soil C loss and suggests the need for improved conservation tillage methods to maintain soil and air quality in agricultural production systems.  相似文献   


15.
CO2和H2O气体浓度是农田小气候的2个重要指标,一般采用CO2/H2O分析仪进行测定,为减少人为干扰,需使用气管将待测区域气体传输至分析器,而气管的材质及其长度会影响CO2/H2O测定时读数稳定所需的时间。本研究采用8种常用材质的气管及5种气管长度进行双因素随机区组试验,以筛选CO2/H2O测定所需的最佳气管材质及长度。结果表明：不同材质气管测定CO2浓度的稳定时间为9.20～11.47s,测定H2O气体浓度的稳定时间为9.67～18.93s。利用主效可加互作可乘（Additive main effects and multi-plicative interaction,AMMI）模型对CO2/H2O气体浓度达到稳定的时间进行方差分析和稳定性分析发现,在CO2浓度观测过程中,气管长度的固定效应导致的变异最大,材质次之,材质与长度互作效应较小;各材质中,CO2读数稳定时间最短的为蠕动泵管;在H2O气体浓度观测过程中,存在显著的材质和长度间的互作效应,其中材质的固定效应导致的变异最大,长度次之,PVC管的读数稳定时间最短。不同材质与不同长度的交互作用不同,每种材质对不同长度都有其特殊的适应性。因此,应根据测定指标,选择稳定时间短的材质和长度,以提高农田CO2和H2O气体浓度的测定效率。  相似文献   

16.
Field experiments were conducted for 6 years on a silty clay loam to study the effect of soil management on soil physical properties, root growth, nutrient uptake and yield of rainfed maize (Zea mays L.) and wheat (Triticum aestivum L.) grown in a sequence. Treatments were: no-tillage (NT), NT+pine needle mulch at a rate of 10 t ha−1 (NT+M), conventional tillage (CT), CT+pine needle mulch at a rate of 10 t ha−1 (CT+M) and deep tillage (DT). The soil is classified as a Typic Hapludalf and has compact sub-surface layers. The NT treatment increased the bulk density of the surface layer but this problem was not observed in the no-tilled treatment having mulch at the surface (NT+M). The CT+M and NT+M treatments favourably moderated the hydro-theregime resulting in greater root growth, nutrient uptake and grain yields of maize and wheat. The DT treatment, imposed only once, at the beginning of the study, also enhanced root growth and grain yields. The yields were similar to the mulched treatments for maize and somewhat less than the mulched treatments for wheat. Mulched treatments generally showed significantly greater total uptake of N, P and K than corresponding unmulched ones. Since NT+M was comparable to CT for maize and superior for wheat, the latter is preferable since it does not require ellaborate tillage.  相似文献   

17.
Conservation farming practices are often considered effective measures to increase soil organic C (SOC) sequestration and/or to reduce CO2 emissions resulting from farm machinery operation. The long-term CO2 mitigation potentials of no-till (NT) versus conventional till (CT), stubble retention (SR) versus stubble burning (SB) and N fertilisation (NF) versus no N application (N0) as well as their interactions were examined on a Vertosol (Vertisol) in semi-arid subtropical Queensland, Australia by taking into account their impacts on SOC content, crop residue C storage, on-farm fossil fuel consumption and CO2 emissions associated with N fertiliser application. The experimental site had been cropped with wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) with a summer fallow for 33 years.

Where NT, SR or NF was applied alone, no significant effect on SOC was found in the 0–10, 10–20 and 0–20 cm depths. Nonetheless, the treatment effects in the 0–10 cm depth were interactive and maximum SOC sequestration was achieved under the NT + SR + NF treatment. Carbon storage in crop residues decreased substantially during the fallow period, to a range between 0.4 Mg CO2-e ha−1 under the CT + SB + NF treatment and 2.4 Mg CO2-e ha−1 under the NT + SR + N0 treatment (CO2-e stands for CO2 equivalent). The cumulative fossil fuel CO2 emission over 33 years was estimated to be 2.2 Mg CO2-e ha−1 less under NT than under CT systems. Cumulative CO2 emissions from N fertiliser application amounted to 3.0 Mg CO2 ha−1. The farm-level C accounting indicated that a net C sequestration of 4.5 Mg CO2-e was achieved under the NT + SR + NF treatment, whilst net CO2 emissions ranging from 0.5 to 6.0 Mg CO2-e ha−1 over 33 years occurred under other treatments.  相似文献   


18.
Tillage stimulates soil carbon (C) losses by increasing aeration, changing temperature and moisture conditions, and thus favoring microbial decomposition. In addition, soil aggregate disruption by tillage exposes once protected organic matter to decomposition. We propose a model to explain carbon dioxide (CO2) emission after tillage as a function of the no-till emission plus a correction due to the tillage disturbance. The model assumes that C in the readily decomposable organic matter follows a first-order reaction kinetics equation as: dCsail(t)/dt = −kCsoil(t) and that soil C-CO2 emission is proportional to the C decay rate in soil, where Csoil(t) is the available labile soil C (g m−2) at any time (t). Emissions are modeled in terms soil C available to decomposition in the tilled and non-tilled plots, and a relationship is derived between no-till (FNT) and tilled (FT) fluxes, which is: FT=a1FNT e−a2t, where t is time after tillage. Predicted and observed fluxes showed good agreement based on determination coefficient (R2), index of agreement and model efficiency, with R2 as high as 0.97. The two parameters included in the model are related to the difference between the decay constant (k factor) of tilled and no-till plots (a2) and also to the amount of labile carbon added to the readily decomposable soil organic matter due to tillage (a1). These two parameters were estimated in the model ranging from 1.27 and 2.60 (a1) and −1.52 × 10−2 and 2.2 × 10−2 day−1 (a2). The advantage is that temporal variability of tillage-induced emissions can be described by only one analytical function that includes the no-till emission plus an exponential term modulated by tillage and environmentally dependent parameters.  相似文献   

19.
A novel approach, at least for laboratory conditions, for analysis of the dependence of soil C evolution on temperature is presented. A two-component (labile and refractory organic C) parallel first-order model was fitted to CO2 evolution rates from top- and subsoil, incubated at different combinations of temperature (constant −4, 0.3, 5, 15, 25, weekly fluctuating between −4 and +5°C) and moisture (17, 26, 36 and 50% H2O for the topsoil and 16, 23, 31 and 41% for the subsoil) and to the evolution of CO2 after the addition of roots or stubble of Phalaris arundinacea in the topsoil, measured at 25°C and 36% H2O (Lomander et al., 1998). The size of the pools and their respective first-order rate constants were optimized simultaneously by a least-squares method. The optimization was carried out separately for top- and subsoil. Quadratic functions were fitted to the temperature and moisture responses. For topsoil samples in which roots or stubble were added, a three-component model (labile, refractory and stubble or roots) was used. The initial partitioning of the soil C, the decomposition rate constants for each partition and the temperature and moisture responses were all assumed to be identical to those of pure topsoil, while the initial pool sizes of added roots and straw were measured. The calculated temperature at which CO2 evolution ceased (Tmin) was −0.83°C, and a recalculation to Q10-values resulted in increasing temperature response with decreasing temperature (Q10=2.2 at 25°C and 12.7 at 0.3°C). Simulated CO2 evolution rates agreed well with the measurements (Radj2=0.96 and 0.81) for top- and subsoil, respectively. The multi-compartment approach was superior to the single-compartment approach, which gave Radj2=0.88 and 0.76 for top- and subsoil, respectively. In general, CO2 evolution rates obtained from the laboratory experiment were higher than those measured in the field, even after differences in temperature and moisture were taken into account. After 300 d in the laboratory at 25°C and 36% H2O, 99% and 86% of the added straw and roots, respectively, had disappeared according to the described model. The CO2-evolution rate per unit of soil carbon was about two times higher for topsoil than for subsoil.  相似文献   

20.
The effects of disturbance and glucose addition on N2O and CO2 emissions from a paddy soil at 45% WFPS (water-filled pore space) and at 25 °C were determined. During a 45-day incubation, disturbances with and without glucose addition were imposed 0, 1, 3, and 5 times. The total amount of glucose added to soil with 1, 3, and 5 disturbances was equal (0.6% of oven-dry soil basis). Strong nitrification occurred in the paddy soil during the incubation. Disturbance alone did not influence N2O and CO2 emissions significantly, but disturbance with glucose addition did (P < 0.01). A flush of N2O as well as CO2 was always observed following disturbance with glucose addition. The discrepancy in N2O emission between disturbance alone and disturbance with glucose addition was ascribed to the different magnitude of denitrification and/or heterotrophic nitrification. Greater cumulative emission of N2O was observed in the treatment of three disturbance times with glucose addition (4.3 mg N kg−1 soil), compared with five disturbances with glucose addition (2.5 mg N kg−1 soil) and one disturbance with glucose addition (2.5 mg N kg−1 soil). Cumulative CO2 emission was significant larger in one and three disturbances with glucose addition than that five disturbance with glucose addition. Supplies of available organic C appear to be a critical factor controlling denitrification and/or heterotrophic nitrification processes and N2O emission under relatively low moisture conditions, i.e. 45% WFPS.  相似文献   

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