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1.
Heterotrophic respiration from agricultural soils can be differentiated as originating from microbial decomposition of recent litter inputs or crop residue carbon (CRC) and resident soil organic carbon (SOC) pools of varying age and stages of decomposition. Our objective was to determine the relative contributions of these pools to respiration in a northern agroecosystem where the non-growing season is long. A tunable diode laser trace gas analyzer was used to determine atmospheric stable C isotope ratio (δ13C) values and 12CO2 and 13CO2 fluxes over an agricultural field in the Red River Valley of southern Manitoba, Canada. Measurement campaigns were conducted in the fall of 2006 and spring of 2007 following harvest of a maize (C4) crop from soil having SOC derived from previous C3 crops. Stable CO2 isotopologue gradients were measured from the center of four 200 × 200 m experimental plots, and fluxes were calculated using the aerodynamic flux gradient method. The soil in two of the experimental plots underwent intensive tillage, while the other two plots were managed using a form of reduced tillage. Approximately 70% and 20-30% of the total respiration flux originated from the maize C4-CRC during the fall of 2006 and spring of 2007, respectively. At least 25% of the maize residue was lost to respiration during this non-growing period. No difference in the partitioning of heterotrophic respiration into that derived from CRC and SOC was detected between the intensive tillage and recently established reduced tillage treatments at the site.  相似文献   

2.
Reduction in soil disturbance can stimulate soil microbial biomass and improve its metabolic efficiency, resulting in better soil quality, which in turn, can increase crop productivity. In this study we evaluated microbial biomass of C (MB-C) by the fumigation-extraction (FE) or fumigation-incubation (FI) method; microbial biomass of N (MB-N); basal respiration (BR) induced or not with sucrose; metabolic quotient (obtained by the ratio BR/MB-C) induced (qCO2(S)), or not with sucrose (qCO2); and crop productivity in a 14-year experiment in the state of Paraná, southern Brazil. The experiment consisted of three soil-tillage systems [no-tillage (NT), conventional tillage (CT) and no-tillage using a field cultivator every 3 years (FC)] and two cropping systems [a soybean–wheat-crop sequence (CS), and a soybean–wheat–white lupin–maize–black oat–radish crop rotation (CR)]. There were six samplings in the 14th year, starting at the end of the winter crop (wheat in the CS and lupin in the CR plots) and finishing at full flowering of the summer crop (soybean in the CS and maize in the CR). Differences in microbiological parameters were greater than those detected in the total C (TCS) and total N (TNS) contents of the soil organic matter (SOM). Major differences were attributed to tillage, and on average NT was higher than the CT in the following parameters: TCS (19%), TNS (21%), MB-C evaluated by FE (74%) and FI (107%), and MB-N (142%). The sensibility of the microbial community and processes to soil disturbance in the tropics was highlighted, as even a moderate soil disturbance every 3 years (FC) affected microbial parameters but not SOM. The BR was the parameter that most promptly responded to soil disturbance, and strong differences were perceived by the ratio of qCO2 evaluated with samples induced and non-induced with sucrose. At plowing, the qCO2(S):qCO2 was five times higher under CT, indicating a C-starving low-effective microbial population in the C-usage. In general, crop rotation had no effect on microbial parameters or SOM. Grain yield was affected by tillage and N was identified as a limiting nutrient. Linear regressions between grain yields and microbial parameters showed that soybean was benefited from improvements in the microbial biomass and metabolic efficiency, but with no significant effects observed for the maize crop. The results also indicate that the turnover of C and N in microbial communities in tropical soils is rapid, reinforcing the need to minimize soil disturbance and to balance inputs of N and C.  相似文献   

3.
Soil changes induced by crop rotations and soil management need to be quantified to clarify their impact on yield and soil quality. The objective of this study was to investigate the effect of continuous oat (Avena sativa L.) and a lupin (Lupinus albus L.)‐oat rotation with and without tillage on soil enzymes, crop biomass and other soil properties In year 1, oat and lupin were grown in undisturbed plots or in plots subjected to disc tillage. Crop residues were incorporated before oat was sown in year 2 in the disc‐tilled plots or remained on the soil surface of untilled plots. Soil samples were collected regularly and analysed for pH, organic C, Kjeldahl‐N, mineral N, extractable P, and the enzyme activities of β‐glucosidase, cellulases, acid phosphatase, proteases, urease, and culturable bacteria and fungi. The main crop and tillage effects on soil parameters were: β‐glucosidase activity was greater after lupin than after oat, and the opposite was true for the number of culturable fungi. Organic carbon, phosphatase, cellulase and protease were greater in tilled soil than in the absence of tillage. Associations between variables that were stable over the 2 yr were those for mineral N and urease activity, cellulase activity and pH, and that of phosphatase activity and organic C. Our results contrast with most of the previous information on the effect of tillage on soil enzymes, where the activities were reported to be unchanged or decreased following tillage. This difference may be related to the small organic C content of the soil and to the fact that it was under fallow prior to the start of the experiment. In consequence, incorporation of residues would provide new sources of labile organic C for soil microbes, and result in increased enzymatic activity. The results obtained suggest that in coarse‐textured soils poor in organic matter, tillage with residue conservation after a period of fallow rapidly improves several soil characteristics and should be carried out even if it were to be followed by a no‐till system in the following years. This should be taken into consideration by land managers and technical advisers.  相似文献   

4.
Abstract

Wheel‐traffic induced soil compaction has been shown to limit crop productivity, and its interaction with tillage method could affect soil nutrient transformations. A study was conducted during 1993–1994 to determine interactive effects of tillage method (conventional tillage and no‐tillage) and wheel‐traffic (traffic and no traffic) on soil carbon (C) and nitrogen (N) at a long‐term (initiated 1987) research site at Shorter, Alabama. The cropping system at this study site is a corn (Zea mays L.) ‐ soybean [Glycine max (L.) Merr] rotation with crimson clover (Trifolium incarnatum L.) as a winter cover crop. Soil organic C, total N, and microbial biomass carbon (MBC) were not significantly affected by six years of traffic and tillage treatments. However, conventional tillage compared to no‐tillage almost doubled the amount of CO2‐C respired over the entire observation period and during April 1994 field operations. Soil respiration was stimulated immediately after application of wheel‐ traffic, but nontrafficked soils produced greater amounts of CO2‐C compared to trafficked soils during other periods of observation. Nitrogen mineralization was significantly lower from no‐tillage‐trafficked soils compared to conventional tillage‐trafficked and no‐tillage‐nontrafficked soils for the 1993 growing season. A laboratory incubation indicated the presence of relatively easily mineralizable N substrates from conventional tillage‐trafficked soil compared to conventional tillage‐nontrafficked and no‐till‐trafficked soils. For the coarse textured soil used in this study it appears that conventional tillage in combination with wheel‐traffic may promote the highest levels of soil microbial activity.  相似文献   

5.
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   

6.
Abstract

There is increasing interest in use of isotopic tracers to study nutrient liberation and transformation in plant tissues and soils. We developed a technique for pulse‐labeling plants in the field with 14C. Spatial distribution of radioactivity was measured in plots of maize (Zea mays L.) plants exposed to 14CO2. Two clear polyvinyl chambers measuring 1 m wide × 2 m long × 1 m high were used to 14C‐ label maize plants in conventional tillage and no‐tillage treatments. A closed loop in‐line with a pump allowed injection of 14CO2 and unlabeled CO2, and subsampling through an infrared gas analyzer. Cooling and mixing of the air within the chambers was achieved through the use of a free‐standing automobile radiator with fan placed in the center of each plot. The specific activities of leaf tips differed by an order of magnitude among maize plants within the plot. Tillage and time after labeling within the first 48 h had no significant effect on specific activity of maize plants. Plant activity significantly differed by row. The row closest to the inlet and along the edge of the chamber was significantly lower in several plots. Despite differences among leaf tip specific activities, total aboveground activity was uniform within the plot. Plant allometry and plant sampling immediately after labeling would help in correcting for within chamber variability in future field labeling studies.  相似文献   

7.
[目的]研究民勤荒漠绿洲区免耕(Tn)、少耕(Tm)、深松(Ts)和秋翻(Tf)4种耕作方式下土壤呼吸速率的动态变化及其与土壤酶活性的关系,为制定科学有效的土壤碳调控管理措施提供依据。[方法]在2a的田间定位试验基础上,利用LI-8100土壤碳通量测量系统测定不同生育时期(苗期、抽穗期和成熟期)玉米田土壤呼吸速率动态变化,同时取0—20cm土样测定土壤酶活性和理化性质。[结果](1)民勤荒漠绿洲区土壤呼吸具有典型的日动态变化,4种耕作措施土壤呼吸速率日变化在玉米整个生育期呈单峰曲线变化,土壤呼吸速率依次为:TfTmTsTn,有机碳含量与土壤呼吸速率呈显著正相关(p0.05),说明在民勤荒漠绿洲区,传统耕作明显加快了玉米农田土壤碳的释放。(2)土壤脲酶、蔗糖酶、蛋白酶、过氧化氢酶和β-葡萄糖苷酶活性与土壤呼吸有较好相关性(p0.05),其中与过氧化氢酶、脲酶、蔗糖酶活性达到极显著水平(p0.01);pH值、速效钾、有机碳与脲酶、蔗糖酶、β-葡糖糖苷酶活性达到极显著水平(p0.01)。[结论]耕作方式可以通过改变荒漠绿洲区土壤理化性质、激发酶活性从而使土壤呼吸速率发生不同程度的改变,影响玉米田CO2的释放。  相似文献   

8.
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   

9.
Abstract

Tree clearing is a topical issue the world over. In Queensland, the high rates of clearing in the past were mainly to increase pasture production. The present research evaluates the impact of clearing on some soil biological properties, i.e. total soil respiration, root respiration, microbial respiration, and microbial biomass (C and N), and the response of soil respiration to change in temperature.

In-field and laboratory (polyhouse) experiments were undertaken. For in-field studies, paired cleared and uncleared pasture plots were selected to represent three major tree communities of the region, i.e. Eucalyptus populnea, E. melanophloia, and Acacia harpophylla. The cleared sites were chosen to represent three different time-since-clearing durations (5, 11–13, and 33 years; n=18 for cleared and uncleared plots) to determine the temporal impact of clearing on soil biological properties. Experiments were conducted in the polyhouse to study in detail the response of soil respiration to changes in soil temperature and soil moisture, and to complement in-field studies for estimating root respiration.

The average rate of CO2 emission was 964 g CO2/m2/yr, with no significant difference (P<0.05) among cleared and uncleared sites. Microbial respiration and microbial biomass were greater at uncleared compared with those at cleared sites. The Q 10-value of 1.42 (measured for different seasons in a year) for in-field measurements suggested a small response of soil respiration to soil temperature, possibly due to the limited availability of soil moisture and/or organic matter. However, results from the polyhouse experiment suggested greater sensitivity of root respiration to temperature change than for total soil respiration. Since root biomass (herbaceous roots) was greater at the cleared than at uncleared sites, and root respiration increased with an increase in temperature, we speculate that with rising ambient temperature and consequently soil temperature, total soil respiration in cleared pastures will increase at a faster rate than that in uncleared pastures.  相似文献   

10.
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   

11.
The effects of agricultural land use on organic matter content and related soil microbial and physical properties were compared with those under undisturbed native grassland in KwaZulu-Natal, South Africa. Two separate farms situated on Oxisols were used and both contained fields with continuous long-term (>20 y) cropping histories. At site 1, soil organic C content in the surface 30 cm followed the order permanent kikuyu pasture > annual ryegrass pasture > native grassland > sugarcane > maize under conventional tillage (CT). At site 2, organic C in the surface 30 cm decreased in the order kikuyu pasture > native grassland > annual ryegrass pasture > maize under zero tillage (ZT) > maize CT. Organic C, microbial biomass C, percentage organic C present as organic C, basal respiration and aggregate stability were substantially greater in the surface 5 cm under maize ZT than maize CT but this trend tended to be reversed in the 10- to 30-cm layer. In the undisturbed sites (e.g. native grassland and kikuyu pasture) the metabolic quotient increased with depth. By contrast, under maize CT and sugarcane there was no significant stratification of organic C, yet there was a sharp decrease in the metabolic quotient with depth. Aggregate stability was high under both native grassland and kikuyu pasture and it remained high to 40 cm depth under the deep-rooted kikuyu pasture. Although soil organic C content was similar under maize CT and sugarcane, values for microbial biomass C, percentage of organic present as microbial biomass, basal respiration and aggregate stability were lower, and those for metabolic quotient and bulk density were higher, under sugarcane. This was attributed to the fallow nature of the soil in the interrows of sugarcane fields. It was concluded that the loss of organic matter, microbial activity and aggregate stability is potentially problematic under maize CT, sugarcane and annual pasture and measures that improve organic matter status should be considered.  相似文献   

12.
Solar vegetable greenhouse soils show low soil organic carbon content and thus also low rates of soil respiration. Processing vegetable residues to biochar and mixing biochar with maize straw might improve soil respiration and increase soil organic carbon stocks, while preventing the spread of soil-borne diseases carried by vegetable residues. In an incubation experiment, we tested how additions of maize straw (S) and biochar (B) added in varying ratios (100S, 75S25B, 50S50B, 25S75B, 100B and 0S0B (control)) affect soil respiration and fraction of added C remaining in soil. Daily CO2 emissions were measured over 60 days incubation, the natural abundance of 13C in soil and in the added biochar and maize straw were analysed. Our result shows that (a) soil CO2 emissions were significantly increased compared to soil without the straw additions, while addition of biochar only decreased soil respiration; (b) cumulative CO2 emissions decreased with increasing ratio of added biochar to maize straw; (c) the abundance of soil 13C was significant positively correlated with cumulative CO2 emissions, and thus with the ratio of straw addition. Our results indicate that incorporation of maize straw in greenhouse soils is a meaningful measure to increase soil respiration and to facilitate greenhouse atmosphere CO2 limitation while producing vegetables. On the other hand, additions of biochar from vegetable residues will increase soil organic carbon concentration. Therefore, the simultaneous application of maize straw and biochar obtained from vegetable residues is an effective option to maintain essential soil functions for vegetable production in sunken solar greenhouses.  相似文献   

13.
The effect of tillage systems and crop rotation on microbial biomass phosphorus (MBP) and acid phosphatase (P‐ase) activity, and the amount of different phosphorus (P) forms measured by 31P‐NMR spectroscopy were studied on a field experiment carried out in a temperate Ultisol from southern Chile. Two tillage systems, no tillage (NT) and conventional tillage (CT) and two crop rotations, oat–wheat (OW) and lupine–wheat (LW) were evaluated 4 yr after the start of the experiment to determine the effects of such management on some soil biological parameters and P forms at three depths (0–5, 0–10 and 10–20 cm). Microbial biomass P ranged from 6.5 to 22.6 mg/kg, whereas the mean total P (PT) was 1995 mg/kg for all treatments (OW and LW). Microbial biomass carbon (MBC) and surface P accumulation (at 0–5 cm depth), including Olsen P, MBP, orthophosphate monoesters (monoester‐P), were larger under NT than CT. Tillage effects were greater than crop rotation effects in enhancing P availability. The LW rotation showed enhanced P‐ase activity and increased monoester‐P forms (57 vs. 30% of the total integral area of the spectra, in average) compared with OW. Nevertheless, OW rotation increased orthophosphate (ortho‐P), especially at 10–20 cm. Microbial biomass carbon ranged from 532 to 2351 mg/kg, which represented 1.2–4.5% of total organic C (Co). Furthermore, MBP correlated positively with MBC (r = 0.80), Olsen P (r = 0.77), Co (r = 0.77), pH (r = 0.65), PT (r = 0.65) and P‐ase activity (r = 0.57), suggesting the importance of the microbial biomass on soil P availability.  相似文献   

14.
The input of labeled C into the pool of soil organic matter, the CO2 fluxes from the soil, and the contribution of root and microbial respiration to the CO2 emission were studied in a greenhouse experiment with continuous labeling of oat plants with 13CO2 using the method of the natural 13C abundance in the air. The carbon of the microbial biomass composed 56 and 39% of the total amounts of 13C photoassimilates in the rhizosphere and in the bulk soil, respectively. The contribution of root respiration to the CO2 emission from the soil reached 61–92%, including 4–23% of the rhizomicrobial respiration. The contribution of the microbial respiration to the total CO2 emission from the soil varied from 8 to 39%. The soil organic matter served as the major carbon-containing substrate for microorganisms in the bulk soil and in the rhizosphere: 81–91% of the total amount of carbon involved in the microbial metabolism was derived from the soil organic matter.  相似文献   

15.
In this study, leguminous crops like Atylosia scarabaeoides, Centrosema pubescens, Calopogonium mucunoides, and Pueraria phaseoloides. grown as soil cover individually in the interspaces of a 19‐yr‐old coconut plantation in S. Andaman (India) were assessed for their influence on various microbial indices (microbial biomass C, biomass N, basal respiration, ergosterol, levels of ATP, AMP, ADP) in soils (0–50 cm) collected from these plots after 10 years. The effects of these cover crops on . CO2 (metabolic quotient), adenylate energy charge (AEC), and the ratios of various soil microbial properties viz., biomass C : soil organic C, biomass C : N, biomass N : total N, ergosterol : biomass C, and ATP : biomass C were also examined. Cover cropping markedly enhanced the levels of organic matter and microbial activity in soils after the 10‐yr‐period. Microbial biomass C and N, basal respiration, . CO2, ergosterol and levels of ATP, AMP, ADP in the cover‐cropped plots significantly exceeded the corresponding values in the control plot. While the biomass C : N ratio tended to decrease, the ratios of biomass N : total N, ergosterol : biomass C, and ATP : biomass C increased significantly due to cover cropping. Greater ergosterol : biomass C ratio in the cover‐cropped plots indicated a decomposition pathway dominated by fungi, and high . CO2 levels in these plots indicated a decrease in substrate use efficiency probably due to the dominance of fungi. The AEC levels ranged from 0.80 to 0.83 in the cover‐cropped plots, thereby reflecting greater microbial proliferation and activity. The ratios of various microbial and chemical properties could be assigned to three different factors by principal components analysis. The first factor (PC1) with strong loadings of ATP : biomass C ratio, AEC, and . CO2 reflected the specific metabolic activity of soil microbes. The ratios of ergosterol : biomass C, soil organic C : total N, and biomass N : total N formed the second factor (PC2) indicating a decomposition pathway dominated by fungi. The biomass C : N and biomass C : soil organic C ratios formed the third principal component (PC3), reflecting soil organic matter availability in relation to nutrient availability. Overall, the study suggested that Pueraria phaseoloides. or Atylosia scarabaeoides were better suited as cover crops for the humid tropics due to their positive contribution to soil organic C, N, and microbial activity.  相似文献   

16.
The Sanjiang Plain, one of the largest freshwater marshes in China, has experienced intensive cultivation over the past 50 years. However, there were few reports of short-term dynamics of soil carbon and nitrogen and CO2 emission after tillage. In this paper, we studied the short-term dynamics of carbon and nitrogen after tillage in a freshwater marsh of northeast China. The results showed that response of carbon and nitrogen dynamic to tillage was different for intact wetland and soil cultivated for 10 years. Tillage was followed by immediate and significant increases in CO2 efflux, which peaked at 0.25 h after tillage, four times higher than control in the wetland soils; while, only 2.5 times higher than control in the cultivated soils. Although, dissolved organic C (DOC) increased, the relative stability of microbial biomass C (MBC) pools together with the decreased respiration in the wetland soil suggested that the tillage did not lead to a burst in microbial activity and growth. Other factors such as moisture content before and after tillage may play an important role in determining microbial activity in the intact wetland. On the contrary, although dissolved organic C did not change, MBC pools, and soil respiration increase after tillage, suggesting tillage led to an increase in microbial activity and growth in the cultivated soil. Tillage initiated changes in soil aeration that was an important factor affecting soil microbiology in the long history of cultivation. Net N mineralization and nitrification occurred in both wetland and cultivated soils, but at different rates after tillage that in the intact wetland soil was higher than cultivated soil. Macroaggregates in the wetland soil would be expected to contain larger amounts of organic matter, and thus release a larger source of newly available substrate for microbes after tillage. In the intact wetland soil, ammonium, nitrate, and dissolved organic N (DON) concentrations were significantly negatively correlated to soil moisture (p < 0.01), suggesting high soil moisture in the natural wetland was not in favor of N mineralization.  相似文献   

17.
The use of annually sown pastures to provide winter forage is common in dairy farming in many regions of the world. Loss of organic matter and soil structural stability due to annual tillage under this management may be contributing to soil degradation. The comparative effects of annual ryegrass pastures (conventionally tilled and resown each year), permanent kikuyu pastures and undisturbed native vegetation on soil organic matter content, microbial size and activity, and aggregate stability were investigated on commercial dairy farms in the Tsitsikamma region of the Eastern Cape, South Africa. In comparison with soils under sparse, native grassy vegetation, those under both annual ryegrass and permanent kikuyu pasture had higher soil organic matter content on the very sandy soils of the eastern end of the region. By contrast, in the higher rainfall, western side, where the native vegetation was coastal forest, there was a loss of organic matter under both types of pasture. Nonetheless, soil organic C, K2SO4-extractable C, microbial biomass C, basal respiration, arginine ammonification and fluorescein diacetate hydrolysis rates and aggregate stability were less under annual than permanent pastures at all the sites. These results reflect the degrading effect of annual tillage on soil organic matter and the positive effect of grazed permanent pasture on soil microbial activity and aggregation. Soil organic C, microbial biomass C, K2SO4-extractable C, basal respiration and aggregate stability were significantly correlated with each other. The metabolic quotient and percentage of organic C present as microbial biomass C were generally poorly correlated with other measured properties but negatively correlated with one another. It was concluded that annual pasture involving conventional tillage results in a substantial loss of soil organic matter, soil microbial activity and soil physical condition under dairy pastures and that a system that avoids tillage needs to be developed.  相似文献   

18.
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   

19.
《Soil biology & biochemistry》2001,33(7-8):1067-1075
Placement of plant residues in conventional tillage (CT) and no-tillage (NT) soils affects organic matter accumulation and the organization of the associated soil food webs. Root-derived C inputs can be considerable and may also influence soil organic matter dynamics and soil food web organization. In order to differentiate and quantify C contributions from either roots or litter in CT and NT soils, a 14C tracer method was used.To follow root-derived C, maize plants growing in the field were 14C pulse-labeled, while the plant litter in those plots remained unlabeled. The 14C was measured in NT and CT soils for the different C pools (shoots, roots, soil, soil respiration, microbial biomass). Litter-derived C was followed by applying 14C labeled maize litter to plots which had previously grown unlabeled maize plants. The 14C pools measured for the litter-derived CT and NT plots included organic matter, microbial biomass, soil respiration, and soil organic C.Of the applied label in the root-derived C plots, 35–55, 6–8, 3, 1.6, and 0.4–2.4% was recovered in the shoots, roots, soil, cumulative soil respiration, and microbial biomass, respectively. The 14C recovered in these pools did not differ between CT and NT treatments, supporting the hypothesis that the rhizosphere microbial biomass in NT and CT may be similar in utilization of root-derived C. Root exudates were estimated to be 8–13% of the applied label. In litter-derived C plots, the percentage of applied label recovered in the particulate organic matter (3.2–82%), microbial biomass (4–6%), or cumulative soil respiration (12.5–14.7%) was the same for CT and NT soils. But the percentage of 14C recovered in CT soil organic C (18–69%) was higher than that in NT (12–43%), suggesting that particulate organic matter (POM) leaching and decomposition occurred at a higher rate in CT than in NT. Results indicate faster turnover of litter-derived C in the CT plots.  相似文献   

20.
耕作对土壤生物碳动态变化的影响   总被引：20，自引：2，他引：20  
本文讨论了耕作方法对作玉米地土壤生物碳动态变化的影响。实验证明，传统耕法、短期免耕和长期免耕处理中的不同点位，土壤生物碳量分布有系统的差异。  相似文献   

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