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1.
湿地土壤质量退化的模糊综合评价   总被引：2，自引：0，他引：2  
Due to frequent soil Cd contamination and wide use of butachlor in China,there is a need to assess their combined toxicity to soil microorganisms.The combined effects of cadmium (Cd,10 mg kg-1 soil) and herbicide butachlor (10,50,and 100 mg kg-1 soil) on enzyme activities and microbial community structure in a paddy soil were assessed using the traditional enzyme assays and random amplified polymorphic DNA (RAPD) analysis.The results showed that urease and phosphatase activities were significantly reduced by high butachlor concentration (100 mg kg-1 soil).When the concentrations of Cd and butachlor added were at a ratio of 1:10,urease and phosphatase activities were significantly decreased whereas enzyme activities were greatly improved at the ratio of 1:5,which indicated that the combined effects of Cd and butachlor on soil urease and phosphatase activities depended largely on their addition concentration ratios.Random amplified polymorphic DNA (RAPD) analysis showed loss of original bands and appearance of new bands when compared with the control soil.Random amplified polymorphic DNA fingerprints suggested substantial differences between the control and treated soil samples,with apparent changes in the number and size of amplified DNA fragments.The addition of high concentration butachlor and the combined impacts of Cd and butachlor significantly affected the diversity of the microbial community.RAPD analysis in conjunction with other biomarkers such as soil enzyme parameters would prove a powerful ecotoxicological tool.Further investigations should be carried out to understand the clear link between RAPD patterns and enzyme activity.  相似文献   

2.
Investigating the effects of residue chemical composition on soil labile organic carbon(LOC) will improve our understanding of soil carbon sequestration.The effects of maize residue chemical composition and soil water content on soil LOC fractions and microbial properties were investigated in a laboratory incubation experiment.Maize shoot and root residues were incorporated into soil at 40%and 70% ?eld capacity.The soils were incubated at 20?C for 150 d and destructive sampling was conducted after 15,75,and 150 d.Respiration,dissolved organic carbon(DOC),hot-water extractable organic carbon(HEOC),and microbial biomass carbon(MBC)were recorded,along with cellulase and β-glucosidase activities and community-level physiological pro?les.The results showed that the cumulative respiration was lower in root-amended soils than in shoot-amended soils,indicating that root amendment may be bene?cial to C retention in soil.No signi?cant differences in the contents of DOC,HEOC and MBC,enzyme activities,and microbial functional diversity were observed between shoot- and root-amended soils.The high soil water content treatment signi?cantly increased the cumulative respiration,DOC and HEOC contents,and enzyme activities compared to the low soil water content treatment.However,the soil water content treatments had little in?uence on the MBC content and microbial functional diversity.There were signi?cantly positive correlations between LOC fractions and soil microbial properties.These results indicated that the chemical composition of maize residues had little in?uence on the DOC,HEOC,and MBC contents,enzyme activities,and microbial functional diversity,while soil water content could signi?cantly in?uence DOC and HEOC contents and enzyme activities.  相似文献   

3.
PFOA对土壤酶活性的影响   总被引：2，自引：0，他引：2  
Perfluorooctanoic acid (PFOA) is a popular additive of the chemical industry; its effect on activities of important soil enzymes is not well understood. A laboratory incubation experiment was carried out to analyze the PFOA-induced changes in soil urease, catalase, and phosphatase activities. During the entire incubation period, the activities of the three soil enzymes generally declined with increasing PFOA concentration, following certain dose-response relationships. The values of EC 10 , the contaminant concentration at which the biological activity is inhibited by 10%, of PFOA for the soil enzyme activity calculated from the modeling equation of the respective dose-response curve suggested a sensitivity order of phosphatase > catalase > urease. The effect of PFOA on soil enzyme activities provided a basic understanding of the eco-toxicological effect of PFOA in the environment. Results of this study supported using soil phosphatase as a convenient biomarker for ecological risk assessment of PFOA-polluted soils.  相似文献   

4.
Soil enzymes activities and microbial biomass have an important influence on nutrient cycling. The spatial distribution of soil enzymes activities and microbial biomass were examined along a latitudinal gradient in farmlands of Songliao Plain, Northeast China to assess the impact of climatic changes along the latitudinal transect on nutrient cycling in agroecosystems. Top soils （0-20 cm depth） were sampled in fields at 7 locations from north （Hallun） to south （Dashiqiao） in the end of October 2005 after maize harvest. The contents of total C, N, and P, C/N, available N, and available P increased with the latitude. The activities of invertase and acid phosphatase, microbial biomass （MB） C and N, and MBC/MBN were significantly correlated with latitude （P 〈 0.05, r^2 = 0.198, 0.635, 0.558, 0.211 and 0.317, respectively）, that is, increasing with the latitude. Significant positive correlations （P 〈 0.05） were observed between invertase activity and the total N and available P, and between acid phosphatase activity and the total C, C/N, available N, total P and available P. The urease, acid phosphatase, and dehydrogenase activities were significantly correlated with the soil pH and electrical conductivity （EC） （P 〈 0.05）. MBC and MBN were positively correlated with the total C, C/N, and available P （P 〈 0.05）. The MBC/MBN ratio was positively correlated with the total C, total N, C/N, and available N （P 〈 0.05）. The spatial distribution of soil enzyme activities and microbial biomass resulted from the changes in soil properties such as soil organic matter, soil pH, and EC, partially owing to variations in temperature and rainfall along the latitudinal gradient.  相似文献   

5.
Enzyme activities have the potential to indicate biological functioning of soils. In this study, soil urease, dehydrogenase, acid phosphatase and invertase activities and fluorescein diacetate（FDA） hydrolysis were measured in two red soils spiked with Pb^2＋ ranging from 0 to 2 400 mg kg^-1 to relate the enzyme activity values to both plant growth and the levels of available and total Pb^2＋ concentrations in soils, and to examine the potential use of soil enzymes to assess the degrees of Pb contamination. Soil samples were taken for enzyme activities assaying during 3 month’s incubation and then after planting of celery（Apium graveolens L.） and Chinese cabbage（Brassica chinensis L.）. Enzyme activities in the red soil derived from arenaceous rock（RAR） were generally lower than those in the red soil developed on Quaternary red earths（REQ）. At high Pb^2＋ loadings, in both incubation and greenhouse studies, urease activity and FDA hydrolysis were significantly inhibited. But there were no significant relationships between soil dehydrogenase, acid phosphatase or invertase activity and soil Pb^2＋ loadings in both RAR and REQ soils. The growth of celery and Chinese cabbage increased soil urease activity and FDA hydrolysis, but had minimal effect on dehydrogenase and invertase activities. There were positive correlations between celery biomass and soil urease activity and FDA hydrolysis. These results demonstrate that urease activity and FDA hydrolysis are more sensitive to Pb^2＋ than acid phosphatase, dehydrogenase and invertase activities in the RAR and REQ soils.  相似文献   

6.
Indigenous grasses have been effectively used to rehabilitate degraded African drylands. Despite their success, studies examining their effects on soil bioindicators such as microbial biomass carbon(C) and enzyme activities are scarce. This study elucidates the effects of drought stress and phenological stages of a typical indigenous African grass, Enteropogon macrostachyus, on microbial biomass and enzyme activities(β-glucosidase, cellobiohydrolase, and chitinase) in the rhizosphere soil. Enteropogon macrostachyus was grown under controlled conditions. Drought stress(partial watering) was simulated during the last 10 d of plant growth, and data were compared with those from optimum moisture conditions. The rhizosphere soil was sampled after 40 d(seedling stage), 70 d(elongation stage), and 80 d(simulated drought stress). A high root:shoot ratio at seedling stage compared with elongation and reproduction stages demonstrated that E. macrostachyus invested more on root biomass in early development, to maximise the uptake of nutrients and water. Microbial biomass and enzyme activities increased with root biomass during plant growth. Ten-day drought at reproduction stage increased the microbial biomass and enzyme activities, accompanying a decrease in binding affinity and catalytic efficiency. In conclusion, drought stress controls soil organic matter decomposition and nutrient mobilization, as well as the competition between plant and microorganisms for nutrient uptake.  相似文献   

7.
Brazilian industry produces huge amounts of tannery sludge as residues, which is often disposed by landfilling or land application. However, consecutive amendment of such composted industrial wastes may cause shifts in soil microbial biomass （SMB） and enzyme activity. This study aimed to evaluate SMB and enzyme activity after 3-year consecutive composted tannery sludge （CTS） amendment in tropical sandy soils. Different amounts of CTS （0.0, 2.5, 5.0, 10.0, and 20.0 t ha-1） were applied to a sandy soil. The C and N contents of SMB, basal and substrate-induced respiration, respiratory quotient （qCO2）, and enzyme activities were determined in the soil samples collected after CTS amendment for 60 d at the third year. After 3 years, significant changes were found in soil microbial properties in response to different CTS amounts applied. The organic matter and Cr contents significantly increased with increasing CTS amounts. SMB and soil respiration peaked following amendment with 10.0 and 20.0 t ha-1 of CTS, respectively, while qCO2 was not significantly affected by CTS amendment. However, soil enzyme activity decreased significantly with increasing CTS amounts. Consecutive CTS amendment for 3 years showed inconsistent and contrasting effects on SMB and enzyme activities. The decrease in soil enzyme activities was proportional to a substantial increase in soil Cr concentration, with the latter exceeding the permitted concentrations by more than twofold. Thus, our results suggest that a maximum CTS quantity of 5.0 t ha-1 can be applied annually to tropical sandy soil, without causing potential risks to SMB and enzyme activity.  相似文献   

8.
一种新的提高树苗盐容量的移植方法   总被引：2，自引：0，他引：2  
The influence of quinclorac (3,7-dichloroquinoline-8-carboxylic acid) on enzyme activities in flooded paddy soils was assessed under laboratory conditions. The enzymes differed markedly in their response to quinclorac. Quinclorac inhibited proteinase, hydrogen peroxidase, phosphorylase, and urease activities. The higher the concentration of quinclorac applied, the more significant the inhibition to these observed activities with a longer time required to recover to the level of the control. However, soils supplemented with quinclorac were nonpersistent for proteinase~ phosphorylase and urease as opposed to soils without quinclorac. Dehydrogenase activity was also sensitive to quinclorac. Three soil samples with concentrations of quinclorac higher than 1 μg g^-1 soil declined to less than 20% of that in the control. However, the highest dehydrogenase activity (up to 3.28-fold) was detected in soils with 2 μg g^-1 soil quinclorac on the 25th day after treatment. Quinclorac had a relatively mild effect on saccharase activity at the concentrations used in this experiment and a stimulatory one on soil respiration when added to soil at normal field concentrations. Nonetheless it was inhibited at higher concentrations in paddy soils. Quinclorac is still relatively safe to the soil ecosystem when applied at a normal concentration (0.67 μg g^-1 dried soil) but may have some effects on soil enzymes at higher concentrations.  相似文献   

9.
Activities of selected soil enzymes (invertase, acid phosphatase, proteinase, catalase, peroxidase and polyphenoloxidase) were determined under different spruce forests with restoration histories of 5, 13, 18, 23, 27 years and an old growth forest over 400 years old in the eastern Qinghai-Tibetan Plateau, China, and their possible use as indicators of ecosystems health were analyzed. Plots 10 × 10 m with 4 replications were established to investigate three hypotheses: soil enzyme activities a) would increase with the restoration process; b) would be greater in surface soils than at lower depths; and c) would be correlated to selected physicochemical properties. Results showed that as the forests developed after restoration, invertase and peroxidase activities usually increased up to the 23 year point. Also soil enzyme activities were associated with surface soils and decreased with depths, suggesting that in earlier restoration stages surface addition of organic fertilizer to soils might be more effective than additions at depth. In the 0-20 cm soil, there were significant correlations (P < 0.01 or < 0.05) between some soil enzyme activities and some selected chemical properties. Therefore, temporal changes in enzyme activities should be included as an indicator when evaluating sustainable forest management practices.  相似文献   

10.
Cover crops can have beneficial effects on soil microbiology by increasing carbon (C) supply, but these beneficial effects can be modulated by precipitation conditions. The objective of this study was to compare a fallow-winter wheat (Triticum aestivum L.) rotation to several cover crop-winter wheat rotations under rainfed and irrigated conditions in the semiarid US High Plains. Experiments were carried out at two sites, Sidney in Nebraska and Akron in Colorado, USA, with three times of soil sampling in 2012--2013 at cover crop termination, wheat planting, and wheat maturity. The experiments included four single-species cover crops, a 10-species mixture, and a fallow treatment. The variables measured were soil C and nitrogen (N), soil community structure by fatty acid methyl ester (FAME) profiles, and soil β-glucosidase, β-glucosaminidase, and phosphodiesterase activities. The fallow treatment, devoid of living plants, reduced the concentrations of most FAMEs at cover crop termination. The total FAME concentration was correlated with cover crop biomass (R = 0.62 at Sidney and 0.44 at Akron). By the time of wheat planting, there was a beneficial effect of irrigation, which caused an increase in mycorrhizal and protozoan markers. At wheat maturity, the cover crop and irrigation effects on soil FAMEs had subsided, but irrigation had a positive effect on the β-glucosidase and phosphodiesterase activities at Akron, which was the drier of the two sites. Cover crops and irrigation were slow to impact soil C concentration. Our results show that cover crops had a short-lived effect on soil microbial communities in semiarid wheat-based rotations and irrigation could enhance soil enzyme activity. In the semiarid environment, longer time spans may have been needed to see beneficial effects of cover crops on soil microbial community structure, soil enzyme activities, and soil C sequestration.  相似文献   

11.
Microorganisms are the regulators of decomposition processes occurring in soil, they also constitute a labile fraction of potentially available N. Microbial mineralization and nutrient cycling could be affected through altered plant inputs at elevated CO2. An understanding of microbial biomass and microbial activity in response to belowground processes induced by elevated CO2 is thus crucial in order to predict the long-term response of ecosystems to climatic changes. Microbial biomass, microbial respiration, inorganic N, extractable P and six enzymatic activities related to C, N, P and S cycling (β-glucosidase, cellulase, chitinase, protease, acid phosphatase and arylsulphatase) were investigated in soils of a poplar plantation exposed to elevated CO2. Clones of Populus alba, Populus nigra and Populus x euramericana were grown in six 314 m2 plots treated either with atmospheric (control) or enriched (550 μmol mol−1 CO2) CO2 concentration with FACE technology (free-air CO2 enrichment). Chemical and biochemical parameters were monitored throughout a year in soil samples collected at five sampling dates starting from Autumn 2000 to Autumn 2001.

The aim of the present work was: (1) to determine if CO2 enrichment induces modifications to soil microbial pool size and metabolism, (2) to test how the seasonal fluctuations of soil biochemical properties and CO2 level interact, (3) to evaluate if microbial nutrient acquisition activity is changed under elevated CO2.

CO2 enrichment significantly affected soil nutrient content and three enzyme activities: acid phosphatase, chitinase and arylsulphatase, indicators of nutrient acquisition activity. Microbial biomass increased by a 16% under elevated CO2. All soil biochemical properties were significantly affected by the temporal variability and the interaction between time and CO2 level significantly influenced β-glucosidase activity and microbial respiration. Data on arylsulphatase and chitinase activity suggest a possible shift of microbial population in favour of fungi induced by the FACE treatment.  相似文献   


12.
An experiment was conducted in the laboratory on a cultivated soil incubated in serum bottles with a range of C-to-nitrate concentrations. C was added in form of glucose and nitrate in form of Ca(NO3)2. It was shown that an C-N concentration of respectively 500 μg C (glucose-equivalent, Glc-Eq.) and 36 μg N g− dry soil was optimal for denitrification. Results obtained either in the laboratory, in soil columns or in the field were in good agreement with one another. In particular, the root zone was shown to be favorable for denitrifying activity because the water-soluble C (Glc-Eq.) and N concentrations were more favorable than in bare soil. Furthermore, the water-soluble extractable Glc-Eq. appeared to be closely related to the denitrification rate and is thus likely to represent the energetic C pool supporting denitrification.

This was related to an inhibiting effect of increasing NO3− and NO2− concentrations on NO3− loss and N2O production. Such inhibition can affect short-term measurements of denitrification in the field.  相似文献   


13.
Field observations have shown that root residues maintain root-adhering soil for several months after harvest. The aim of this work was to compare post-harvest effect of Amaranthus hypochondriacus (amaranth), Phaseolus vulgaris (common bean) and Zea mays (maize) roots on root-adhering soil, aggregation and organic carbon content. The experimental site was located on a volcanic sandy soil (Typic Ustifluvent) in the Valley of Mexico. In 1999 and 2000, maize had the highest root mass (92 and 94 g m−2) and the highest root-adhering soil (9051 and 5876 g m−2) when a root–soil monolith of 0.20 m × 0.20 m × 0.30 m was excavated after harvest. In contrast, bean roots (2 and 5 g m−2) had only 347 and 23 g m−2 of adhering soil per monolith in each year. Amaranth had intermediate values between maize and bean. Dry soil aggregate classes (<0.25, 0.5, 1, 2, 5 and >5 mm) were similarly distributed among the three species. The sum of the three soil macro-aggregates classes >1 mm was 0.1 g g−1 in both years. Neither water stability of the 2–5 mm aggregates (0.05–0.09 g g−1) nor soil organic C (SOC) in three aggregate classes (<0.25, 1–2 and >5 mm; mean 14.6 mg g−1) was affected by species (P < 0.05) in either year. Observations of thin sections (10× and 40×) revealed absence of macro-aggregates under maize. Soil compaction was attributed to high mass of maize roots in the sampled soil volume. Root systems sampled after harvest had the capacity to maintain a well structured soil mass, which was proportional to root mass. Root-adhering soil measured in the field could be used to select species promoting soil adhesion by roots.  相似文献   

14.
Cultivation machinery applies large amounts of mechanical energy to the soil and often brings about a decrease in soil organic carbon (SOC). New experiments on the effects of mechanical energy inputs on soil respiration are reported and the results discussed. In the laboratory, a specific energy, K, of 150 J kg−1, similar to that experienced during typical cultivation operations, was applied to soil aggregates using a falling weight. Respiration (carbon dioxide, CO2 emission) of the samples was then measured by an electrical conductimetric method. Basal respiration (when K=0) measured on Chromic Luvisol aggregates, was found to increase with increasing SOC, from 1.88 μg CO2 g−1 h−1 for a permanent fallow soil (SOC=11 g kg−1) to 8.25 μg CO2 g−1 h−1 for a permanent grassland soil (SOC=32 g kg−1). Basal respiration of a Calcic Cambisol, more than doubled (2.0–5.2 μg CO2 g−1 h−1) with increasing gravimetric soil water contents. Mechanical energy inputs caused an initial burst of increased respiration, which lasted up to 4 h. Over the following 4–24 h period, arable soils with lower SOC contents, (11–21 g kg−1), respiration rates dropped back to a level, approximately 1.14 times higher than the basal value. However, grassland soils with higher SOC contents (28–32 g kg−1), increases in this longer-term respiration rate following 150 J kg−1 of energy, were negligible. A field experiment, in which CO2 was measured by infra-red absorption, also showed that tillage stimulated increased levels of soil respiration for periods ranging from 12 h to more than one week. The highest respiration rates, 80 mg CO2 m−2 h−1 were associated with high energy, powered tillage on clay soils. On the same soil, low energy draught tillage resulted in a respiration rate of approximately half this value. The results of these experiments are discussed in relation to equilibrium levels of soil organic matter. The application of known quantities of mechanical energy to soil aggregates under laboratory conditions, in order to simulate the effect of different cultivation practices, when combined with the subsequent measurement of soil respiration, can provide useful indication of the likely consequences of soil management on SOC.  相似文献   

15.
Soil biological parameters, such as soil respiration or N-mineralization, may be more sensitive to soil compaction than physical parameters. Therefore we studied the effects of soil compaction on net N-mineralization and microbial biomass dynamics in the field. The soils were silty clay loams (Typic Endoaquepts) in either a well-structured permanent pasture with high organic-C content (46 mg g−1) or a site which had been continuously cropped with cereals for 28 years with low organic-C content (21 mg g−1) and a very poor structure. Compaction treatments were applied by five passes of a tractor (total weight 4880 kg, speed 2.2 m s−1). An energy flux of either 2712 J m−2 (assuming deflecting tyres) or 6056 J m−2 (assuming rigid tyres) per pass of the rear tyres was estimated. Soil dry bulk densities were initially 1.00 and 1.30 Mg m−3 in the pasture and cropped sites, respectively, and increased significantly only in the less dense pasture site. However, soil surface CO2-fluxes decreased substantially after compaction on both sites (57–69%) because of the highly reduced air permeability of the topsoil. At the cropped site this was also accompanied by a significant decrease in oxygen-diffusion rate (45%). Using the in situ core technique with covered cores the apparent net N-mineralization rate was less in compacted than in non-compacted areas of the pasture ((0.27 and 0.38 μg N g−1 day−1, respectively), but did not differ at the cropped site (average 0.15 μg N g−1 day−1). However, N-mineralization measurements by the in situ core technique were found to be problematic as denitrification possibly occurred and concealed actual net N-mineralization. Microbial biomass did not change significantly as a result of the compaction treatment, but was shown to either decrease or increase over time depending on the methodology used to estimate microbial biomass.  相似文献   

16.
Residue retention and reduced tillage are both conservation agricultural management options that may enhance soil organic carbon (SOC) stabilization in tropical soils. Therefore, we evaluated the effects of long-term tillage and residue management on SOC dynamics in a Chromic Luvisol (red clay soil) and Areni-Gleyic Luvisol (sandy soil) in Zimbabwe. At the time of sampling the soils had been under conventional tillage (CT), mulch ripping (MR), clean ripping (CR) and tied ridging (TR) for 9 years. Soil was fully dispersed and separated into 212–2000 μm (coarse sand), 53–212 μm (fine sand), 20–53 μm (coarse silt), 5–20 μm (fine silt) and 0–5 μm (clay) size fractions. The whole soil and size fractions were analyzed for C content. Conventional tillage treatments had the least amount of SOC, with 14.9 mg C g−1 soil and 4.2 mg C g−1 soil for the red clay and sandy soils, respectively. The highest SOC content was 6.8 mg C g−1 soil in the sandy soil under MR, whereas for the red clay soil, TR had the highest SOC content of 20.4 mg C g−1 soil. Organic C in the size fractions increased with decreasing size of the fractions. In both soils, the smallest response to management was observed in the clay size fractions, confirming that this size fraction is the most stable. The coarse sand-size fraction was most responsive to management in the sandy soil where MR had 42% more organic C than CR, suggesting that SOC contents of this fraction are predominantly controlled by amounts of C input. In contrast, the fine sand fraction was the most responsive fraction in the red clay soil with a 66% greater C content in the TR than CT. This result suggests that tillage disturbance is the dominant factor reducing C stabilization in a clayey soil, probably by reducing C stabilization within microaggregates. In conclusion, developing viable conservation agriculture practices to optimize SOC contents and long-term agroecosystem sustainability should prioritize the maintenance of C inputs (e.g. residue retention) to coarse textured soils, but should focus on the reduction of SOC decomposition (e.g. through reduced tillage) in fine textured soils.  相似文献   

17.
Effects of N-enriched sewage sludge on soil enzyme activities   总被引：5，自引：0，他引：5  
Sewage sludge is increasingly used as an organic amendment to soil, especially to soil containing little organic matter. However, little is known about utility of this organic amendment with N-enriched or adjusted C:N ratios in soil. We studied the effects of adding of different doses (0, 100, 200 and 300 t ha−1) and C:N ratios (3:1, 6:1 and 9:1) of sewage sludge on enzyme activities (β-glucosidase, alkaline phosphatase, arylsulphatase and urease) in a clay loam soil at 25 °C and 60% soil water holding capacity. Nitrogen was added in the form of (NH4)2 SO4 solution to the sludge to reduce the C:N ratio from 9:1 to 6:1 and 3:1. The addition of different doses and C:N ratios of the sludge caused a rapid and significant in the enzymatic activities in soils, this increase was specially noticeable in soil treated with high doses of the sludge. In general, enzymatic activities in sludge-amended soils tended to decrease with the incubation time. All activities reached peak values at 30 days incubation and then gradually decreased up to 90 days of incubation. Sewage sludges also the increased available metal (Cu, Ni, Pb and Zn) contents in the soils. However, the presence of available soil metals due to the addition of the sludge at all doses and C:N ratios did negatively affect all enzymatic activities in the soils. This experiment indicated that all doses and C:N ratios of sewage sludge applied to soil would have harmful effects on enzymatic activity. Some heavy metals found in sewage sludge may negatively influence soil enzyme activities during the decomposition of the sludge.  相似文献   

18.
Soil compaction can affect the turnover of C and N (e.g. by changing soil aeration or by changing microbial community structure). In order to study this in greater detail, a laboratory experiment simulating total soil porosities representative of field conditions in cropped and pasture soils was set up. Soils were silty clay loams (Typic Endoaquepts) from a site that had been cropped with cereals continuously for 28 years, a permanent pasture and a site that had been cropped with maize continuously for 10 years. Soils from the three sites were compacted into cores to different total porosities (corresponding bulk densities ranging from 0.88 to 1.30 Mg m−3). The soil cores were equilibrated to different matric potentials (ranging from −1 to −100 kPa), yielding values for the fraction of air-filled pores of < 0.01 to 0.53 m3 m−3, and then incubated at 25°C for 21 days. C-mineralization was on average 15, 33 and 21 μg C g−1 day−1 for soils from the cropped, pasture and maize sites, respectively, and was positively correlated with soil water contents. Net N-mineralization showed a similar pattern only for well-aerated, high total porosity cores (corresponding bulk density 0.88 Mg m−3) from the pasture soil. Denitrification at < 0.20 m3 m−3 for the fraction of air-filled pores may have caused the low N-mineralization rates observed in treatments with high water content or low porosity. Microbial biomass estimates decreased significantly with increasing water contents if measured by fumigation-extraction, but were not significantly affected by water content if estimated by the substrate-induced respiration method. The degree of soil compaction did not affect the microbial biomass estimates significantly but did affect microbial activity indirectly by altering aeration status.  相似文献   

19.
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   

20.
Tillage alters corn root distribution in coarse-textured soil   总被引：3，自引：0，他引：3  
Root responses to tillage vary and the driving factors are not well understood. Characterization of root response is requisite to optimize fertilizer placement and to understand limitations to no-till production. Corn (Zea mays L.) root length and weight were measured in the top 0.3 m of coarse-textured soil (Psammentic Hapludalf) in southwestern Ontario, Canada after 5, 6 and 7 yr of conventional and no-till management. Root length density in the top 0.1 m was greater under no-till (17 km m−3) than under conventional till (7 km m−3) 2 yr out of 3. Root length density was 4 km m−3 lower under no-till than under conventional till in the 0.15 to 0.3 m layer 1 yr out of 3, but otherwise root growth below 0.1 m was unaffected by tillage. Each year, root length and weight were distributed more horizontally under no-till than under conventional till. Corn grain yields did not vary with tillage, even though soil water content was often greater under no-till. The increase in soil water (of between 0.01 and 0.03 m3 m−3) was partly due to increased water holding capacity—water held between −8 and −200 kPa matric potential was usually greater under no-till (0.07 m3 m−3) than under conventional till (0.06 m3 m−3) in the top 0.15 m. The shift in root distribution was apparently driven by soil structure because variation in bulk density with tillage and depth followed the same trends as variation in root length. Bulk density was greater under no-till (1.5 Mg m−3) than under conventional till (1.4 Mg m−3) in the top 0.15 m. In the top 0.075 m, the proportion of the total space occupied by capillary pores (<36 μm diameter) was greater under no-till (17%) than under conventional till (15%), there were more dry-stable aggregates under no-till (9% of total soil in the 0.85–5.7 mm size fraction) than under conventional till (7%), and a greater proportion of these aggregates were water-stable under no-till (25%) than under conventional till (16%). Greater bulk density may trigger formation of lateral roots, and greater aggregation contribute to the more superficial development by deflecting roots from their gravitropic pathway. Given the more superficial root distribution under no-till, shallower placement of downwardly mobile nutrients such as nitrogen may be more efficient than knife-injection.  相似文献   

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