首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 937 毫秒
1.
Carbon dioxide measurements from soil surface may indicate the potential for soil respiration and carbon consumption according to microbial biomass and root activity. These processes may be influenced by land use and cover change, and abandonment especially in the upper soil organic layer. Seven environments from cultivation to late abandonment, with the same soil type classified as Lithic Xerorthent, were tested to ascertain the respiration capacity according to the current use and cover, and to establish the ability to preserve and eventually increase the organic matter pools after abandonment. Given the importance of carbon dioxide measurements at soil surface, a comparison between the classic soda lime method (SL) and a rapid method based on infrared sensor analyzer (IR) was performed from autumn 2008 to autumn 2009 in the field. The field measurements of CO2 proved significant correlations between the values from the two techniques under the same natural conditions and along the period of observation. However, the values of CO2 measured by the soda lime method were always higher than those obtained by the infrared analyzer. This pattern was attributed to the difference in time of measurement, larger in the former method, and type of measurement technique. Despite that the trend of measured CO2 values was rather similar along the year. On average, the highest values of CO2 emission in the field were recorded in the warmest periods of the year and with soil surface moisture not lower than 3% independently on the method used. High soil surface temperature with soil moisture below 3% decreased drastically the CO2 production from the dry soil. The cultivated environments and soil under forests have resulted higher CO2 producers than abandoned soils depending on the age of abandonment, climatic conditions, and within abandonment perturbations. Those abandoned soils preserved by perturbations like wildfire showed a higher potential for accumulating organic carbon, as indicated by the lowest emission of CO2 with respect to SOC content, during the period of observation. Results demonstrated the reliability of the methods used to evaluate the soil carbon dioxide production capacity and allowed to classify through environments with increasing potential for carbon sequestration. The classification was rather similar by using both methods indicating a higher susceptibility to carbon loss in the following order: soil under Vines (V) > under Olives (O) > under Pine trees (PI) > under Cork Trees (S) > under Pasture (PR) > under Cistus scrub (MC) > under Erica scrub (MB) by using the SL method and V > O > PI > S > MC > MB > PR by using the IR method. Indications about the need of management of abandoned areas were also considered in order to recover the landscape heterogeneity.  相似文献   

2.
《Soil & Tillage Research》2005,80(1-2):171-183
As the soil moisture content (w) is a deterministic factor for site-specific irrigation, seeding, transplanting and compaction detection, an on-line measurement system will bring these applications into practice. A fibre-type visible (VIS) and near-infrared (NIR) spectrophotometer, with a light reflectance measurement range of 306.5–1710.9 nm was used to measure w during field operation. The spectrophotometer optical unit was attached to the subsoiler chisel backside to perform the light reflectance measurement from the soil surface on the bottom of the trench opened by the proceeded chisel. The spectrophotometer–optical unit system was calibrated for w under stationary laboratory conditions on samples collected from an Arenic Cambisol field with different soil textures. A partial least square analysis was carried out in order to establish a statistical model relating soil light spectra with the gravimetric w of the 0.005–0.26 kg kg−1 range. This model was validated with the full cross validation method resulting in a small root mean square error of cross validation (RMSECV) of 0.0175 kg kg−1 and a high validation correlation of 0.978. Further validation of the model developed in the laboratory under stationary state showed also a small root mean square error of prediction (RMSEP) of 0.0165 kg kg−1 and a prediction correlation of 0.982. When the NIR sensor-model system was used to determine w, based on on-line field measurement, a relatively larger RMSEP of 0.025 kg kg−1 and lower prediction correlation of 0.75 were found. However, a reasonably similar spatial distribution of w was found between the on-line NIR measurement and oven drying methods. Therefore, the on-line NIR w sensor developed is recommended to provide valuable information towards the site-specific applications in soils.  相似文献   

3.
A variety of soil properties can directly or indirectly affect nematode community structure. The effects of subsurface clay content (at 20–40 cm depth) on nematodes in the surface layer (0–20 cm depth) of a sandy soil were examined in field experiments in Florida, USA. Plots were established in a site with a relatively uniform sandy upper soil layer (88–91% sand and 5–7% clay at 0–20 cm depth) but with varying levels of clay in the subsurface layer (3–35% clay at 20–40 cm depth). Nematode numbers in the surface soil layer were affected by the amount of clay in the subsurface layer. Population densities of a number of different nematode genera were greater in the surface layer of plots with 35% subsurface clay than in plots with 3% subsurface clay. Indices of nematode community structure were largely unaffected, since effects of subsurface clay were observed across all nematode groups. Most nematodes (70–80% of total numbers) occurred at 0–20 cm depth, although Teratocephalus was more common at 20–40 than at 0–20 cm. Subsurface clay content indirectly affected soil moisture and other environmental factors in the upper soil layer in which most nematodes reside.  相似文献   

4.
A laboratory experiment was performed to assess the impact of ecologically different earthworm species on soil water characteristics, such as soil tension, water content, and water infiltration rate. Three earthworm species (Lumbricus rubellus, Aporrectodea caliginosa, Lumbricus terrestris) were exposed in soil columns (diameter 30 cm, height 50 cm) for 100 days with a total fresh earthworm biomass of 22.7 ± 0.4 g per column, each in duplicate. Each column was equipped with tensiometers at 10 and 40 cm and FD-probes at 10 cm depth, to continuously measure the temporal development of soil tension and soil moisture. Additionally, 30 g of sieved and rewetted horse manure was placed on the soil surface as a food source. Precipitation events (10 mm) were simulated at day 28 and day 64. At the end of the experiment the water infiltration rate and the runoff at 55 cm depth were determined.The results showed considerable evidence, that ecologically different earthworms modify soil water characteristics in different ways. The anecic L. terrestris and the endogeic A. caliginosa showed the tendency to enhance the drying of the topsoil and subsoil. Their intensive and deep burrowing activity might enhance the exchange of water vapor due to a better aeration in soil. In contrast, the epigeic L. rubellus tended to enhance the storage of soil moisture in the topsoil, which might be linked to lower rates of litter loss from soil surface and thus a thicker litter layer remaining. A. caliginosa led to considerable higher water infiltration rates and faster water discharges in the subsoil, relative to the other species, probably due to a high soil dwelling activity.  相似文献   

5.
《Applied soil ecology》2006,33(3):284-292
We examined the response of the temperature coefficient (Q10) for soil respiration to changes in soil temperature and soil moisture through a laboratory incubation experiment. Two types of soils differing in vegetation and moisture status were collected and incubated under two temperatures (10 and 30 °C) and two soil moisture regimes (35 and 75% of water holding capacity, WHC) for 5 weeks. Before and after the incubation experiment, the temperature coefficient of soil respiration was measured using soda-lime method by changing temperature in a water bath. For both soils, the mean Q10 values of the respiration rate were 2.0 in the 30 °C and 2.3 in the 10 °C soil treatments. Higher temperature with lower soil moisture treatment significantly decreased the Q10 value, whereas lower temperature with higher soil moisture treatment significantly enhanced the Q10 value (ANOVA, p < 0.05). These results indicate that soils became less sensitive to temperature when incubated under higher temperature with higher moisture conditions, and more sensitive in lower temperature with higher moisture conditions.There was a significant correlation (r2 = 0.67, p < 0.05) between water-soluble carbon (WSC) and soil respiration rate. However, the correlation between soil respiration rate and microbial biomass carbon (MBC) was weak (r2 = 0.27, p > 0.05). Although incubation temperature and moisture accounted for 40 and 29% (as r2 × 100%), respectively, of variations in Q10, soil water-soluble carbon content alone could have explained 79% of the variation, indicating that the availability of respiratory substrate, rather than the pool of soil microorganisms, played a crucial role in the response of the temperature coefficient to environmental factors. These results suggest that biotic factors should also be taken into consideration when using the Q10 function to predict the response of soil respiration to global warming.  相似文献   

6.
《Soil biology & biochemistry》2001,33(7-8):1077-1093
We studied soil moisture dynamics and nitrous oxide (N2O) fluxes from agricultural soils in the humid tropics of Costa Rica. Using a split-plot design on two soils (clay, loam) we compared two crop types (annual, perennial) each unfertilized and fertilized. Both soils are of andic origin. Their properties include relatively low bulk density and high organic matter content, water retention capacity, and hydraulic conductivity. The top 2–3 cm of the soils consists of distinct small aggregates (dia. <0.5 cm). We measured a strong gradient of bulk density and moisture within the top 7 cm of the clay soil. Using automated sampling and analysis systems we measured N2O emissions at 4.6 h intervals, meteorological variables, soil moisture, and temperature at 0.5 h intervals. Mean daily soil moisture content at 5 cm depth ranged from 46% water filled pore space (WFPS) on clay in April 1995 to near saturation on loam during a wet period in February 1996. On both soils the aggregated surface layer always remained unsaturated. Soils emitted N2O throughout the year. Mean N2O fluxes were 1.04±0.72 ng N2O-N cm−2 h−1 (mean±standard deviation) from unfertilized loam under annual crops compared to 3.54±4.31 ng N2O-N cm−2 h−1 from the fertilized plot (351 days measurement). Fertilization dominated the temporal variation of N2O emissions. Generally fluxes peaked shortly after fertilization and were increased for up to 6 weeks (‘post fertilization flux’). Emissions continued at a lower rate (‘background flux’) after fertilization effects faded. Mean post-fertilization fluxes were 6.3±6.5 ng N2O-N cm−2 h−1 while the background flux rate was 2.2±1.8 ng N2O-N cm−2 h−1. Soil moisture dynamics affected N2O emissions. Post fertilization fluxes were highest from wet soils; fluxes from relatively dry soils increased only after rain events. N2O emissions were weakly affected by soil moisture during phases of low N availability. Statistical modeling confirmed N availability and soil moisture as the major controls on N2O flux. Our data suggest that small-scale differences in soil structure and moisture content cause very different biogeochemical environments within the top 7 cm of soils, which is important for net N2O fluxes from soils.  相似文献   

7.
An investigation of the detection of water stress in non-homogeneous crop canopies such as orchards using high-spatial resolution remote sensing thermal imagery is presented. An airborne campaign was conducted with the Airborne Hyperspectral Scanner (AHS) acquiring imagery in 38 spectral bands in the 0.43–12.5 μm spectral range at 2.5 m spatial resolution. The AHS sensor was flown at 7:30, 9:30 and 12:30 GMT in 25 July 2004 over an olive orchard with three different water-deficit irrigation treatments to study the spatial and diurnal variability of temperature as a function of water stress. A total of 10 AHS bands located within the thermal-infrared region were assessed for the retrieval of the land surface temperature using the split-window algorithm, separating pure crowns from shadows and sunlit soil pixels using the reflectance bands. Ground truth validation was conducted with infrared thermal sensors placed on top of the trees for continuous thermal data acquisition. Crown temperature (Tc), crown minus air temperature (Tc − Ta), and relative temperature difference to well-irrigated trees (Tc − TR, where TR is the mean temperature of the well-irrigated trees) were calculated from the ground sensors and from the AHS imagery at the crown spatial resolution. Correlation coefficients for Tc − TR between ground IRT sensors and airborne image-based AHS estimations were R2 = 0.50 (7:30 GMT), R2 = 0.45 (9:30 GMT) and R2 = 0.57 (12:30 GMT). Relationships between leaf water potential and crown Tc − Ta measured with the airborne sensor obtained determination coefficients of R2 = 0.62 (7:30 GMT), R2 = 0.35 (9:30 GMT) and R2 = 0.25 (12:30 GMT). Images of Tc − Ta and Tc − TR for the entire field were obtained at the three times during the day of the overflight, showing the spatial and temporal distribution of the thermal variability as a function of the water deficit irrigation schemes.  相似文献   

8.
Nitrogen mineralization and nitrification in the soil of sub-alpine ruderal community of Mount Uludağ, Bursa, Turkey was measured for 1 year, under field conditions with Verbascum olympicum and Rumex olympicus being the dominant pioneer species under dry and wet sites, respectively. Seasonal fluctuations were observed in N mineralization and nitrification. The net N mineralization and nitrification were high in early summer and winter, due to high moisture. The annual net N mineralization rate (for the 0–15 cm soil layer) was higher under R. olympicus (188 kg N ha−1 yr−1) than under V. olympicum (96 kg N ha−1 yr−1). A significant positive correlation between net N mineralization and soil organic C (r2 = 0.166), total N (r2 = 0.141) and water content (r2 = 0.211) was found. Our results indicate that N mineralization rate is high in soils of ruderal communities on disturbed sites and varies with dominant species and, a difference in net N mineralization rate can be attributed to organic C, total N and moisture content of soils.  相似文献   

9.
《Applied soil ecology》2007,35(1):128-139
We tested the effect of soil moisture on the performance of four entomopathogenic nematodes species that have recently shown promise for the control of white grubs, i.e., Heterorhabditis bacteriophora, H. zealandica, Steinernema scarabaei, and S. glaseri. Experiments for all four nematodes were conducted in sandy loam, for S. scarabaei also in loamy sand and silt loam. Infectivity was tested by exposing third-instar Japanese beetle, Popillia japonica, to nematodes in laboratory experiments and determining nematode establishment in the larvae and larval mortality. Nematode infectivity was the highest at moderate soil moistures (−10 to −100 kPa), and tended to be lower in wet (−1 kPa) and moderately dry (−1000 kPa) soil. In dry soil (−3000 kPa), only S. scarabaei showed some activity. S. scarabaei was active from −1 to −3000 kPa in all soil types but the range of highest activity was wider in loamy sand (−1 to −1000 kPa) than in loamy sand and silt loam (−10 to −100 kPa). Persistence was determined in laboratory experiments by baiting nematode-inoculated soil with larvae of the greater wax moth, Galleria mellonella. For both Heterorhabditis spp. persistence was short at −10 kPa, improved slightly at −100 kPa, significantly at −1000 kPa, and was the highest at −3000 kPa. Both Steinernema spp. persisted very well at −10 kPa. However, S. glaseri persistence was the shortest at −10 kPa but did not differ significantly at −100 to −3000 kPa, whereas S. scarabaei persistence was not affected by soil moisture. Our observations concur with previous observations on the effect of soil moisture on entomopathogenic nematodes but also show that moisture ranges for infectivity and persistence vary among species. Differences among species may be based on differences in size and behavioral and physiological adaptations.  相似文献   

10.
《Soil & Tillage Research》2007,92(1-2):22-29
Sustainable agricultural use of cultivated desert soils has become a concern in Hexi Corridor in Gansu Province of China, because loss of topsoil in dust storms has been recently intensified. We chose four desert sites to investigate the effects of cultivation (cropping) on (i) soil organic C and its size fractions and (ii) soil aggregate stability (as a measure of soil erodibility). These parameters are of vital importance for evaluating the sustainability of agricultural practices.Total organic C as well as organic C fractions in soil (coarse organic C, 0.1–2 mm; young organic C, 0.05–0.1 mm; stable organic C, <0.05 mm) generally increased with the duration of the cultivation period from 0 (virgin soil, non-cultivated) to more than 30 years (p < 0.05). Compared to total organic C in virgin soils (2.3–3.5 g kg−1 soil), significantly greater values were found after 10 to >20 years of cultivation (6.2–7.1 g kg−1 soil). The increase in organic C in desert soils following prolonged cultivation was mainly the consequence of an increase in the coarse organic C. The increase in total organic C in soil was also dependent on clay content [total organic C = 0.96 + 0.249 clay content (%) + 0.05 cultivation year, R2 = 0.48, n = 27, p < 0.001]. This indicates that clay protected soil organic C from mineralization, and also contributed to the increase in soil organic C as time of cultivation increased.There was a significant positive correlation between aggregate stability and total organic C across all field sites. The water stability of aggregates was low (with water-stable aggregate percentage ∼4% of dry-sieved aggregates of size 1–5 mm). There was no consistent pattern of increase in the soil aggregate stability with time of cultivation at different locations, suggesting that desert soils might remain prone to wind erosion even after 50 years of cultivation. Alternative management options, such as retaining harvested crop residues on soil surface and excluding or minimizing tillage, may permit sustainable agricultural use of desert soils.  相似文献   

11.
Documented approaches for measuring soil microbial activities and their controlling factors under field conditions are needed to advance understanding of soil microbial processes for numerous applications. We manipulated field plots with carbon (C) and nitrogen (N) additions to test the capability of a respiratory assay to: (1) measure respiration of endogenous soil C in comparison to field-measured CO2 fluxes; (2) determine substrate-induced respiratory (SIR) activities that are consistent with substrate availability in the field; and, (3) report N availability in the field based on assay responses with and without added N. The respiratory assay utilizes a microplate containing an oxygen-sensitive fluorescent ruthenium dye. Respiratory activities measured with this approach have previously been shown to occur within short (6–8 h) incubation periods using low substrate concentrations that minimize enrichment during the assay. Field treatments were conducted in a randomized full-factorial design with C substrate (casamino acids, glucose, or none) and inorganic N (±) as the treatment factors. With one exception, we found that respiration of endogenous soil C in the assay responded to the field treatments in a similar manner to CO2 fluxes measured in the field. Patterns of SIR with low concentrations of added amino acid or carbohydrate substrate (200 μg C g−1 soil) were consistent with field treatments. The ratio (Nratio) of carbohydrate respiration with added N (25 μg N g−1 soil) to the same without N in the assay was significantly (P < 0.05) decreased by field N amendment. The carbohydrate Nratio exhibited a logarithmic relationship (r = 0.64, P < 0.05) with extractable inorganic soil nitrate and ammonium concentrations. These data significantly extend and support the capability of this oxygen-based respiratory assay to evaluate in situ soil activities and examine factors that limit these activities.  相似文献   

12.
The forest–savanna transition zone is widely distributed on nutrient-poor oxisols in Central Africa. To reveal and compare the nutrient cycle in relation to soil microbes for forest and savanna vegetation in this area, we evaluated seasonal fluctuations in microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP) for 13 months as well as soil moisture, temperature, soil pH levels, and nutrients for both vegetation types in eastern Cameroon. Soil pH was significantly lower in forest (4.3) than in savanna (5.6), and soil N availability was greater in forest (87.1 mg N kg−1 soil) than in savanna (32.9 mg N kg−1 soil). We found a significant positive correlation between soil moisture and MBP in forest, indicating the importance of organic P mineralization for MBP, whereas in savanna, we found a significant positive correlation between soil N availability and MBP, indicating N limitation for MBP. These results suggest that for soil microbes, forest is an N-saturated and P-limited ecosystem, whereas savanna is an N-limited ecosystem. Additionally, we observed a significantly lower MBN and larger MB C:N ratio in forest (50.7 mg N kg−1 soil and 8.6, respectively) than in savanna (60.0 mg N kg−1 soil and 6.5, respectively) during the experimental period, despite the rich soil N condition in forest. This may be due to the significantly lower soil pH in forest, which influences the different soil microbial communities (fungi-to-bacteria ratio) in forest versus savanna, and therefore, our results indicate that, in terms of microbial N dynamics, soil pH rather than soil substrate conditions controls the soil microbial communities in this area. Further studies should be focused on soil microbial community, such as PLFA, which was not evaluated in the present study.  相似文献   

13.
We used natural gradients in soil and vegetation δ13C signatures in a savannah ecosystem in Texas to partition soil respiration into the autotrophic (Ra) and heterotrophic (Rh) components. We measured soil respiration along short transects from under clusters of C3 trees into the C4 dominated grassland. The site chosen for the study was experiencing a prolonged drought, so an irrigation treatment was applied at two positions of each transect. Soil surface CO2 efflux was measured along transects and CO2 collected for analysis of the δ13C signature in order to: (i) determine how soil respiration rates varied along transects and were affected by localised change in soil moisture and (ii) partition the soil surface CO2 efflux into Ra and Rh, which required measurement of the δ13C signature of root- and soil-derived CO2 for use in a mass balance model.The soil at the site was unusually dry, with mean volumetric soil water content of 8.2%. Soil respiration rates were fastest in the centre of the tree cluster (1.5 ± 0.18 μmol m?2 s?1; mean ± SE) and slowest at the cluster–grassland transition (0.6 ± 0.12 μmol m?2 s?1). Irrigation produced a 7–11 fold increase in the soil respiration rate. There were no significant differences (p > 0.5) between the δ13C signature of root biomass and respired CO2, but differences (p < 0.01) were observed between the respired CO2 and soil when sampled at the edge of the clusters and in the grassland. Therefore, end member values were measured by root and soil incubations, with times kept constant at 30 min for roots and 2 h for soils. The δ13C signature of the soil surface CO2 efflux and the two end member values were used to calculate that, in the irrigated soils, Rh comprised 51 ± 13.5% of the soil surface CO2 efflux at the mid canopy position and 57 ± 7.4% at the drip line. In non-irrigated soil it was not possible to partition soil respiration, because the δ13C signature of the soil surface CO2 efflux was enriched compared to both the end member values. This was probably due to a combination of the very dry porous soils at our study site (which may have been particularly susceptible to ingress of atmospheric CO2) and the very slow respiration rates of the non-irrigated soils.  相似文献   

14.
《Geoderma》2007,137(3-4):318-326
Increasing areas of altered wetland are being restored by re-flooding the soil. Evidence in the literature indicates that this practice can induce the redox-mediated release of soil nutrients, thereby increasing the risk of diffuse water pollution. However, for the sake of improving wetland management decisions, there is a need for more detailed studies of the underlying relationship between the hydrological and redox dynamics that explain this risk; this is particularly the case in agricultural peatlands that are commonly targeted for the creation of lowland wet grassland. A 12-month field study was conducted to evaluate the relationship between hydrological fluctuations and soil redox potential (Eh) in a nutrient-rich peat field (32 g N kg− 1 and 1100 mg P kg− 1 in the surface 0–30 cm soil) that had been restored as lowland wet grassland from intensive arable production. Field tensiometers were installed at the 30-, 60- and 90-cm soil depths, and Pt electrodes at the 10-, 30-, 60- and 90-cm depths, for daily logging of soil water tension and Eh, respectively. The values for soil water tension displayed a strong negative relationship (P < 0.001) with monthly dip well observations of water table height. Calculations of soil water potential from the logged tension values were used, therefore, to provide a detailed profile of field water level and, together with precipitation data, explained some of the variation in Eh. For example, during the summer, alternating periods of aerobism (Eh > 330 mV) in the surface, 0–10 cm layer of peat coincided with intense precipitation events. Redox potential throughout the 30–100 cm profile also fluctuated seasonally; indeed, at all depths Eh displayed a strong, negative relationship (P < 0.001) with water table height over the 12-month study period. However, Eh throughout the 30–100 cm profile remained relatively low (< 230 mV), indicating permanently reduced conditions that are associated with denitrification and reductive dissolution of Fe-bound P. The implications of these processes in the N- and P-rich peat for wetland plant diversity and water quality are discussed.  相似文献   

15.
The potential of near infrared (NIR) reflectance spectroscopy to predict various physical, chemical and biochemical properties in Mediterranean soils from SE Spain was evaluated. Soil samples (n = 393) were obtained by sampling 13 locations during three years (2003–2005 period). These samples had a wide range of soil characteristics due to variations in land use, vegetation cover and specific climatic conditions. Biochemical properties also included microbial biomarkers based on phospholipid fatty acids (PLFA). Partial least squares (PLS) regression with cross validation was used to establish relationships between the NIR spectra and the reference data from physical, chemical and biochemical analyses. Based on the values of coefficient of determination (r2) and the ratio of standard deviation of validation set to root mean square error of cross validation (RPD), predicted results were evaluated as excellent (r2 > 0.90 and RPD > 3) for soil organic carbon, Kjeldahl nitrogen, soil moisture, cation exchange capacity, microbial biomass carbon, basal soil respiration, acid phosphatase activity, β-glucosidase activity and PLFA biomarkers for total bacteria, Gram-positive bacteria, actinomycetes, vesicular-arbuscular mycorrhizal fungi and total PLFA biomass. Good predictions (0.81 < r2 < 0.90 and 2.5 < RPD < 3) were obtained for exchangeable calcium and magnesium, water soluble carbon, water holding capacity and urease activity. Resultant models for protozoa and fungi were not accurate enough to satisfactorily estimate these variables, only permitting approximate predictions (0.66 < r2 < 0.80 and 2.0 < RPD < 2.5). Electrical conductivity, pH, exchangeable phosphorus and sodium, metabolic quotient and Gram-negative bacteria were poorly predicted (r2 < 0.66 and RPD < 2). Thus, the results obtained in this study reflect that NIR reflectance spectroscopy could be used as a rapid, inexpensive and non-destructive technique to predict some physical, chemical and biochemical soil properties for Mediterranean soils, including variables related to the composition of the soil microbial community composition.  相似文献   

16.
Pit digging and manually revising soil blocks is a frequently used method used for field studies of earthworm communities. The aim of this study was to compare the efficiency of hand-sorting (HS) to extract small earthworms, ca. 0.2 g, and the usefulness in studies of population dynamics and cohort analysis. Many earthworms are not recovered when revising manually the soil. Factors include soil characteristics, i.e. moisture, texture, etc. and also a human factor, which is more relevant if the study is conducted in the long-term. We used data collected in a field study of earthworm communities during 2 years in the savannas of Colombia. Small soil blocks (20 × 20 × 20 cm) were dug out in order to collect the smallest earthworms by washing-sieving (WS) and compare the results with the standard HS of large monoliths (100 × 100 × 50 cm). In fact, this methodology has rarely been addressed in earthworm population field studies. Our results showed that HS efficiency varied owing to the species and ranged from 31.4% up to 100% in the savanna and from 44% to 80% in the pasture, for two small species, i.e Aymara n. sp. (epigeic) and Ocnerodrilidae sp. (endogeic). In the case of the Glossodrilus n. sp. (endogeic) these values were similar, i.e. 51.7% and 58.1%, in the savanna and pasture, respectively. We also used frequency tables to calculate the average efficiency of HS 1 m2 soil cores for each weight class in each species in order to obtain a population density correction factor. This allowed us to make corrections in earthworm density in the histograms for population dynamics analysis. We conclude that this method should be the modus operandi in long-term earthworm demography studies.  相似文献   

17.
《Applied soil ecology》2006,32(3):199-210
Common root rot (causal agent Aphanomyes euteiches) is a major disease of commercially grown snap bean (Phaseolus vulgaris L.). Organic amendments hold potential to suppress plant diseases, which may be due to changes in soil biology and other soil properties. The objective of this study was to determine the potential of paper-mill residual by-products to suppress common root rot of snap bean in relation to soil properties. The study was done on soil (Plainfield sandy loam, Hancock, WI) from a field trial comparing annual applications of fresh paper-mill residuals (0, 22 or 33 dry Mg ha−1) or composted paper-mill residuals (0, 38 or 78 dry Mg ha−1). Soil was removed from each treatment that had been in place 3 years in April 2001 (1 year after last amendment) and on September 2001 (4 months after last amendment) and brought to the laboratory. Soils were incubated at field moisture content (25 °C) and periodically bioassayed with bean seedlings (9, 44, 84, 106, 137, 225 or 270 days after removal from the field) for snap bean root rot. Soils were sampled on the same day as the root rot bioassay and assayed for β-glucosidase, arylsulfatase and fluorescein diacetate hydrolysis activities (FDA), microbial biomass-C (MBC) (by chloroform fumigation), water stable aggregation, and total C. There were large differences in snap bean root rot incidence between the field amendment treatments. The unamended field soil had high levels of disease incidence throughout the experiment but disease incidence tended to decrease over time in amended soils. The disease was suppressed by both fresh and composted paper-mill residuals, but the composted residuals at high rates had the lowest disease incidence (<40%) and produced healthiest plants. Root rot severity was strongly negatively correlated with total C (0.001 ≤ p) and arylsulfatase activity (0.001 ≤ p). β-Glucosidase activity was negatively correlated (0.05 ≤ p) with disease severity while soil MBC showed inconsistent negative correlations with disease severity over the incubation sampling periods. Arylsulfatase activity was the best indicator for reflecting disease suppression. The amendments improved soil quality, which was exemplified by improved aggregation.  相似文献   

18.
《Soil & Tillage Research》2007,92(1-2):109-119
Soil compaction may affect N mineralization and the subsequent fate of N in agroecosystems. Laboratory incubation and field experiments were conducted to determine the effects of surface soil compaction on soil N mineralization in a claypan soil amended with poultry litter (i.e., Turkey excrement mixed with pine shavings as bedding). In a laboratory study, soil from the surface horizon of a Mexico silt loam soil was compacted to four bulk density levels (1.2, 1.4, 1.6 and 1.8 Mg m−3) with and without poultry litter and incubated at 25 °C for 42 days. A field trial planted to corn (Zea mays L.) was also conducted in 2002 on a Mexico silt loam claypan soil in North Central Missouri. Soil was amended with litter (0 and 19 Mg ha−1) and left uncompacted or uniformly compacted. Soil compaction decreased soil inorganic N by a maximum of 1.8 times in the laboratory study; this effect was also observed at all depths of the field trial. Compacted soil with a litter amendment accumulated NH4+-N up to 7.2 times higher than the noncompacted, litter-amended soil until Day 28 of the laboratory incubation and in the beginning of the growing season of the field study. Ammonium accumulation may have been due to decreased soil aeration under compacted conditions. Application of litter increased soil N mineralization throughout the growing season. In the laboratory study, soil inorganic N in unamended soil was negatively correlated with soil bulk density and the proportion of soil micropores, but was positively related with soil total porosity and the proportion of soil macropores. These results indicate that soil compaction, litter application and climate are interrelated in their influences on soil N mineralization in agroecosystems.  相似文献   

19.
Trifluralin is a herbicide intensively used in Turkish cotton agriculture. The recommended field dose [(RFD), 480 g active ingredient l?1], 2 × RFD, 4 × RFD and 6 × RFD of this herbicide were added to virgin (previously no trifluralin applied) and cotton field soils (previously trifluralin applied) from a district (Yumurtal?k, Adana) under Mediterranean climate conditions in order to determine their effects on soil microbial activity as measured by carbon mineralization at the different temperature conditions (20 °C, 25 °C and 30 °C). C mineralization of all samples was determined by the CO2 respiration method over 30 days (20 °C, 25 °C and 30 °C at constant moist). The ratio (%) of carbon mineralization at all doses of cotton field soil at 30 °C was significantly higher than all other field dose–temperature combinations (P < 0.001). Based on these results, trifluralin is used as a carbon source by soil microorganisms. The herbicide trifluralin was degraded completely in the cotton field but a small fraction remained in the virgin field. This result can be explained by the cotton field soil having both more active microbial populations and more microorganisms adapted to the trifluralin applications than the virgin field.  相似文献   

20.
To minimize application of nematicides in banana fields, crop systems have been developed in the French West Indies that combine fallow or rotation crops and nematode-free in vitro plants. After two to four years, populations of the burrowing nematode Radopholus similis have developed enough to cause economic losses, leading banana growers to use nematicides. To understand how banana fields are recontaminated, we studied the dissemination of R. similis by water flow. At a 1-m scale, we analyzed the dispersion of R. similis under a rainfall simulator: we isolated a 1-m2 study plot, placed a R. similis suspension on the upstream soil surface, and simulated a 60 mm/h rainfall for 72 min. We collected soil samples every 10 cm downstream after 12 min of rainfall, and subsequently at 20-min intervals, and extracted the nematodes using a Seinhorst elutriator and then a Baermann funnel. Our results showed that the nematode dissemination follows an inverse exponential law, and depends more on soil moisture at the beginning of rainfall than on the length of rainfall: in fresh soil, 69–80% of the R. similis recovered were found less than 10 cm downstream from the nematode inoculation line, whereas in wetted soil, 76–85% of the recovered individuals were collected in the outlet tub located downstream from the apparatus. This passive dissemination model partially explains the distance covered by individual nematodes but not the low percentage of motile nematodes recovered in the outlet tub (10% and 36% in fresh and wet soils) compared to the percentage of motile nematodes found in the soil (80% and 84% in fresh and wet soils). Indeed, water runoff is likely to disseminate R. similis over long distances only when soil moisture is close to field capacity.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

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