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1.
The ability to evolve increased drought tolerance in response to climate change was investigated in the enchytraeid, Cognettia sphagnetorum. Populations exposed to reduced precipitation or increased night time temperature for more than six years were collected in mixed Calluna/grass heathland at the Mols Laboratory, Denmark. The level of prolonged drought and increased temperature corresponded to a predicted climate change scenario and has been applied since 1999. In autumn 2005, enchytraeids were sampled in 3 cm intervals down to 9 cm depth and total number, biomass, diversity and soil organic matter were determined. The drought treatment resulted in a significant reduction of the density and biomass of enchytraeids, as well as changes in the species composition. In total, five different genera were found at the site in all three treatments (control, temperature and drought). C. sphagnetorum was the dominant species, especially in the upper 0–3 cm, and was clearly affected by the drought treatment. C. sphagnetorum from all plots were cultured in the laboratory to rear second or third generation adults. Results showed that populations of drought treated plots had not developed an increased drought resistance compared to populations of control or warming plots even after several years of a putative severe selection. Lack of adaptive potential in C. sphagnetorum suggests that more frequent periods with drought in the future will have a very strong negative influence on enchytraeid density, biomass and diversity.  相似文献   

2.
Summary The effects of enchytraeid activity on soil structure were recorded in a field study on population dynamics in agro-ecosystems and in a field experiment, using artificially compounded soil cores. It was established that 21–35% of the enchytraeid population contained mineral grains. The estimated transport of mineral material in the upper 0.4 m amounted to 0.001–0.01% of the bulk soil per year. In experimental cores with enchytraeids present, the air permeability, volume of pores in the size class corresponding to the enchytraeid body width, and the proportion of aggregates corresponding to the size of their fecal pellets were higher than in cores without enchytraeids.Dedicated to the late Prof. Dr. W. Kühnelt Communication no. 15 of the Dutch programme on soil ecology of arable farming systems  相似文献   

3.
Organic matter and abiotic conditions seem to influence distribution patterns of Enchytraeidae. In this study effects of changes in management practices on population dynamics of enchytraeids were determined. At two sites (in Athens and Griffin, GA) parts of a fescue (FE) field were converted into conventional tillage (CT) and no-tillage (NT) plots and changes in densities and depth distribution of enchytraeids were followed for 3 years. A site at Watkinsville, containing various soil textures and characterised by very low organic carbon content, which was converted into no-tillage 4 years earlier, was also sampled. Significant reductions in enchytraeid densities, after conversion of fescue into CT, were only found at Griffin. The management practices affected the vertical distribution of enchytraeids. In fescue and NT more enchytraeids were found in the 0–5cm than in the 5–15cm layer. In conventional tillage fields enchytraeids were more evenly distributed over the profile or more abundant in the 5–15cm layer. Management also affected the timing of population dynamics in the different plots. At two sample dates high abundances were found in CT plots only, not in any of the other plots. Enchytraeids were larger at Athens than at Griffin and Watkinsville and contained more soil particles in their gut. At Athens enchytraeids will presumably contribute more to the development of soil structure than at the other sites. We conclude that management affects vertical enchytraeid distributions in soil and changes the timing of population dynamics. Received: 7 January 1996  相似文献   

4.
The present study was conducted to determine the spatial heterogeneity of bulk density, soil moisture, inorganic N, microbial biomass C, and microbial biomass N in the ridge tillage system of Turiel compared to conventional mouldboard ploughing on three sampling dates in May, July, and August. The soil sampling was carried out under vegetation representing the ridge in a high spatial resolution down the soil profile. Bulk density increased with depth and ranged from 1.3 g cm−3 at 10 cm depth to 1.6 g cm−3 at 35 cm in ploughed plots and from 1.0 g m−3 at 5 cm to 1.4 g m−3 at 35 cm in the ridges. In the ploughed plots, the contents of microbial biomass C and microbial biomass N remained roughly constant at 215 and 33 μg g−1 soil, respectively, throughout the experimental period. The microbial biomass C/N ratio varied in a small range around 6.4. In the ridged plots, the contents of microbial biomass C and microbial biomass N were 5% and 6% higher compared to the ploughed plots. Highest microbial biomass C contents of roughly 300 μg g−1 soil were always measured in the crowns in July. The lowest contents of microbial biomass C of 85–137 μg g−1 soil were measured in the furrows. The ridges showed strong spatial heterogeneity in bulk density, soil water content, inorganic nitrogen and microbial biomass.  相似文献   

5.
Studies of biological responses in the terrestrial environment to rapid changes in climate have mostly been concerned with above-ground biota, whereas less is known of belowground organisms. The present study focuses on enchytraeids (Oligochaeta) of heathland ecosystems and how the enchytraeid community has responded to simulated climate change in a long-term field experiment. Either increased temperature or repeated drought was applied for 13 years to field plots located in Wales, The Netherlands and Denmark representing a gradient in precipitation and annual temperature fluctuations thereby providing an opportunity to study biological responses on a local (within sites) and regional scale. Warming treatments increasing night-time temperature (0.5–1 °C higher than ambient at 5 cm soil depth) had no detectable effects on the enchytraeid communities. Increased intensity and frequency of drought had rather weak persistent effects on total enchytraeid abundance suggesting that ecosystem functions of enchytraeids may only be transiently impacted by repeated spring or summer drought. However, drought treatment had persistent negative effects on species richness and community structure across sites. Drought treated plots harboured only 35–65% of the species present in control plots, and the reduction of species richness was most pronounced at the driest sites. It is discussed that soil invertebrates, due to their weak migratory potential, may be more liable to extinction under changing climatic conditions than above-ground species, and therefore consequences of climate change to soil organisms need particular attention in future research.  相似文献   

6.
European earthworms are invading many ecosystems worldwide and fundamentally transform habitats by acting as dominant ecosystem engineers. However, there is little knowledge of the consequences of earthworm invasion on the composition and diversity of native soil organisms. Particularly functionally similar groups, such as enchytraeids (Annelida: Enchytraeidae), may be affected through changes in the chemical and physical properties of the soil, but also due to competition for resources. In 2010–2011, we studied the impact of earthworm invasion on enchytraeids at two sites in the northern hardwood forests of North America: one site within the Chippewa National Forest in northern Minnesota and one site in the Chequamegon-Nicolet National Forest in northern Wisconsin, USA. At each site, three plots were sampled along a transect, representing (1) a non-invaded or very slightly invaded area, (2) the leading edge of earthworm invasion and (3) a heavily invaded area with an established population of the anecic earthworm Lumbricus terrestris (among other species). In total, 29 enchytraeid (morpho)species were identified (some yet to be formally described, several first or second records for the continent); of those 24 occurred at the Minnesota site and 17 at the Wisconsin site. The structure of enchytraeid assemblages differed significantly among the three invasion stages, although this was not equally pronounced at the two sites. Each stage was characterized by one or several indicator species. Mean enchytraeid densities (10,700–30,400 individuals/m2) did not differ significantly among the invasion stages, but were lowest at the leading edge of earthworm invasion at both sites. In the heavily invaded plot at the Minnesota site, the mean enchytraeid density and biomass in L. terrestris middens were significantly higher than in soil in-between the middens. This was due to a pronounced effect of L. terrestris middens in the uppermost 3 cm of soil. Differences in biomass among earthworm invasion stages were most apparent for mean individual biomass. This was significantly higher in the heavily invaded area than at the leading edge or in the non-invaded area at the Minnesota site. Compositional changes of the enchytraeid assemblage are likely to result in changes in the functioning of soil foods webs. Our results suggest that earthworm invasions can cause a loss of native species in soil, including heretofore unknown ones, that might go unnoticed.  相似文献   

7.
Tillage-induced changes in soil quality are important to understanding soil strength and water retention and transmission properties. Thus, this study was conducted to assess the effects of two tillage systems under un-drained and drained conditions on tensile strength (TS) of 5–8 mm aggregates, soil water characteristics (SWC), plant available water (PAW), and the water infiltration rate (i). Soil properties were determined mainly in the surface (0–10 cm) layer on a Crosby (fine, mixed, mesic, Aeric Ochraqualf) silt loam soil at the Waterman Farm of the Ohio State University, Columbus, OH on a 14-year-old field study. Effect of two tillage treatments comprising no-tillage (NT) and conventional tillage (CT) were studied for two levels of drainage: un-drained (UD) and tile drained (D). The TS for 0–10 cm depth was significantly (P ≤ 0.01) affected by tillage and drainage treatments, and was higher in CT than NT by 61% in UD and by 48% in D soil. In comparison, TS increased by 13% in NT and 4% in CT in D compared with the UD treatments. Soil organic carbon (SOC) in 0–10 cm depth of NT–UD treatment was 23% higher than CT–UD treatment and 38% more than NT–D treatments. Tillage and drainage impact on SWC was non-significant at 0 kPa suction, but significant (P ≤ 0.1) at −3, −6, −10, −30, −100 and −300 kPa suctions indicating that water was retained more in NT–UD than CT–UD soil. The PAW was significantly influenced by drainage (P ≤ 0.01) but not by tillage treatments. Yet, there existed a general trend of about 8% more PAW in NT–UD than CT–UD treatments. In contrast, PAW was 48% more in soil from NT–UD than NT–D treatments. PAW increased with increase in the SOC concentration (R2 = 0.89; P ≤ 0.01). There were also differences in soil water sorptivity (S), and equilibrium infiltration rate (ic) in NT–UD compared with CT–UD treatments. A positive and significant correlation (r = 0.57, P ≤ 0.05) occurred between ic and SOC concentration. The value of S was more in NT–UD by 70% than CT–UD, and 46% in NT–D than CT–D. Similarly, the ic was more in NT than CT by 119% in UD compared with 82% in D soil. The value of A in NT was higher than that in CT by 39% and 12% in UD and D treatments, respectively. The mean cumulative infiltration (I) in 3 h was 71.4 cm in NT versus 44.0 cm in CT in UD compared with 62.1 cm in NT and 48.4 cm in CT for the D treatment. The I was positively and significantly correlated with SOC concentration (r = 0.32, n = 12, P ≤ 0.1) indicating improvement of I with increase in SOC concentration. Results of this study suggest that conversion from CT to NT management system may reduce the risk of surface runoff, increase soil aggregation, and improve soil hydrological properties.  相似文献   

8.
A soil mechanical resistance sensor with a large-diameter disc coulter was developed to delineate areas of differing soil strength across agricultural fields. The instrumented disc coulter consisted of a 76.2 cm disc with two depth-measuring sensors (rotary potentiometer and ultrasonic proximity sensor) along with a global positioning system (GPS) receiver to georeference operating depth measurements. The consistency and repeatability of the system response were evaluated by making six passes across long-term tillage comparison plots with different degrees of soil disturbance, including: 20 cm plowing, 15 cm disking, 30 cm chiseling, and no-till in several combinations. At the time of testing, standard soil cone penetrometer measurements were taken. The relationship between the average cone index in the 0–30 cm soil profile (CI0–30 cm) and the disc operating depth was evaluated. In addition, the cumulative energy density of the given depth of penetration defined as specific cone penetration energy (J m−2 or N cm−1) for each tillage plot was calculated using the cone index profiles. The average measured depth in each tillage plot was compared to the average predicted depth (dci) of a fixed specific cone penetration energy (Pci). Static calibration tests on the depth sensors showed excellent linearity with coefficients of determination (R2) greater than 0.99. The results showed that, on the average, the changes in the depth measured with the rotary potentiometer were 44 and 68% of the changes in the depth measured with the ultrasonic proximity sensor while the disc coulter was passing across, or along, the tillage plots. This difference was primarily due to the sinkage of the tractor wheels. The depth measured with the ultrasonic sensor had significant correlation with both CI0–30 cm and dci. This was partially due to the fact that a significantly high correlation (R2 = 0.97) between the CI0–30 cm and dci was observed, which was not expected and originated from the type of soil profiles present. The instrumented disc coulter is a low soil disturbance system and could be used as an inexpensive and simple sensor to obtain information about the mechanical condition of the soil for spot tillage or other management decisions.  相似文献   

9.
Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. The 21-yr effects of the combinations of tillage and cropping sequences was evaluated on dryland crop grain and biomass (stems + leaves) N, soil surface residue N, soil N fractions, and N balance at the 0–20 cm depth in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat–barley (Hordeum vulgare L.) (1984–1999) followed by spring wheat–pea (Pisum sativum L.) (2000–2004) (FSTW-B/P), and spring-tilled spring wheat–fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4-N, and NO3-N. Annualized crop grain and biomass N varied with treatments and years and mean grain and biomass N from 1984 to 2004 were 14.3–21.2 kg N ha−1 greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue N was 9.1–15.2 kg N ha−1 greater in other treatments than in STW-F in 2004. The STN at 0–20 cm was 0.39–0.96 Mg N ha−1, PON 0.10–0.30 Mg N ha−1, and PNM 4.6–9.4 kg N ha−1 greater in other treatments than in STW-F. At 0–5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5–20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO3-N was greater in FSTW-B/P than in NTCW and FSTCW. Estimated N loss through leaching, volatilization, or denitrification at 0–20 cm depth increased with increasing tillage frequency or greater with fallow than with continuous cropping and ranged from 9 kg N ha−1 yr−1 in NTCW to 46 kg N ha−1 yr−1 in STW-F. Long-term no-till or spring till with continuous cropping increased dryland crop grain and biomass N, soil surface residue N, N storage, and potential N mineralization, and reduced N loss compared with the conventional system, such as STW-F, at the surface 20 cm layer. Greater tillage frequency, followed by pea inclusion in the last 5 out of 21 yr in FSTW-B/P, however, increased N availability at the subsurface layer in 2004.  相似文献   

10.
Effects of two tillage treatments, tillage (T) with chisel plough and no-till (NT), were studied under un-drained and drained soil conditions. Soil physical properties measured were bulk density (ρb), total porosity (ƒt), water stable aggregates (WSA), geometric mean diameter (GMD), mean weight diameter (MWD), organic carbon (OC) and total N concentrations in different aggregate size fractions, and total OC and N pools. The experiment was established in 1994 on a poorly drained Crosby silt loam soil (fine mixed, mesic, Aeric Ochraqualf) near Columbus, Ohio. In 2007, soil samples were collected (0–10, 10–20, and 20–30 cm) from all treatments and separated into six aggregate size classes for assessing proportions of macro (5–8, 2–5, 1–2, 0.5–1, 0.25–0.5) and micro (<0.25 mm) aggregates by wet sieving. Tillage treatments significantly (P ≤ 0.05) influenced WSA, MWD, and GMD. Higher total WSA (78.53 vs. 58.27%), GMD (0.99 vs. 0.68 mm), and MWD (2.23 vs. 0.99 mm) were observed for 0–10 cm depth for NT than T treatments. Relative proportion of macro-aggregates (>0.25-mm) was also more in NT than T treatment for un-drained plots. Conversely, micro-aggregates (<0.25-mm) were more in T plots for both drained and un-drained treatments. The WSA, MWD and GMD decreased with increase in soil depth. The OC concentration was significantly higher (P ≤ 0.05) in NT for un-drained (P ≤ 0.01) treatment for all soil depths. Within macro-aggregates, the maximum OC concentrations of 1.91 and 1.75 g kg−1 in 1–2 mm size fraction were observed in NT for un-drained and drained treatments, respectively. Tillage treatments significantly (P < 0.01) affected bulk density (ρb), and total porosity (ft) for all soil depths, whereas tillage × drainage interaction was significant (P < 0.01) for 10–20 and 20–30 cm depths. Soil ρb was negatively correlated (r = −0.47; n = 12) with OC concentration. Tillage treatments significantly affected (P ≤ 0.05) OC pools at 10–20 cm depth; whereas drainage, and tillage × drainage significantly (P ≤ 0.05) influenced OC pools for 0–10 cm soil layer. The OC pool in 0–10 cm layer was 31.8 Mg ha−1 for NT compared with 25.9 Mg kg−1 for T for un-drained treatment. In comparison, the OC pool was 23.1 Mg ha−1 for NT compared with 25.2 Mg ha−1 for T for the drained plots. In general, the OC pool was higher in NT system, coupled with un-drained treatment than in drained T plots. The data indicate the importance of NT in improving the OC pool.  相似文献   

11.
Carbon sequestration in agroecosystems represents a significant opportunity to offset a portion of anthropogenic CO2 emissions. Climatic conditions in the Virginia coastal plain and modern production practices make it possible for high annual photosynthetic CO2 fixation. There is potential to sequester a substantial amount of C, and concomitantly improve soil quality, with the elimination of tillage for crop production in this region. The objectives of our research were to: (1) measure C sequestration rate with continuous no-till management of grain cropping systems of the Virginia middle coastal plain; (2) determine the influence of biosolids application history on C content and its interaction with tillage management; and (3) evaluate the impact of continuous no-till C stratification as an indicator of soil quality. Samples were collected from 63 sites in production fields using a rotation of corn (Zea mays L.)–wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.)/soybean double-crop (Glysine max L.) across three soil series [Bojac (coarse-loamy, mixed, semiactive, thermic Typic Hapludults), Altavista (fine-loamy, mixed semiactive, thermic Aquic Hapludults), and Kempsville (fine-loamy, siliceous, subactive, thermic Typic Hapludults)] with a history of continuous no-till management ranging from 0 to 14 years. Thirty-two of the sites had a history of biosolids application. Five soil cores were collected at each site from 0–2.5, 2.5–7.5 and 7.5–15 cm and analyzed for bulk density and soil C. Bulk density in the 0–2.5 cm layer decreased and C stratification ratio (0–2.5 cm:7.5–15 cm) increased with increasing duration of continuous no-till due to the accumulation of organic matter at the soil surface. A history of biosolids application resulted in an increase of 4.19 ± 1.93 Mg C ha−1 (0–15 cm). Continuous no-till resulted in the sequestration of 0.308 ± 0.280 Mg C ha−1 yr−1 (0–15 cm). Our results provide quantitative validation of the C sequestration rate and improved soil quality with continuous no-till management in the region using on-farm observations.  相似文献   

12.
This study aimed at investigating the effects of agricultural exploitation on desert soil organic C, N and P, and soil aggregation. Four land uses were assessed: (1) 5-year wheat (Triticum aestivum L.)/barley (Hordeum vulgare L.) + 5-year maize (Zea mays L.); (2) 5-year wheat/barley + 5-year alfalfa (Medicago sativa L.); (3) 6-year wheat/barley + 4-year acacia (Robinia pseudoacacia L.) and (4) uncultivated desert soil. The desert soil contained total organic C (TOC) of 3.1, 3.7 and 4.2 g kg−1 and particulate organic C (POC) of 0.6, 0.7 and 0.8 g kg−1 at 0–10, 10–20 and 20–30 cm depths, respectively. The soil TOC concentration was increased by 32–68% under wheat–maize rotation and by 27–136% under wheat–acacia at 0–20 cm depth, and by 48% under wheat–alfalfa only at 0–10 cm depth. This contrasted with an increase in the soil POC concentration by 143–167% at depth 0–20 cm under wheat–maize and by 217%, 550% at depth 0–10 cm under wheat–alfalfa and wheat–acacia, respectively. The desert soil had 13 Mg ha−1 TOC stock and 2 Mg ha−1 POC stock at depth 0–30 cm, whereas crop rotations increased the soil TOC stock by 30–65% and POC stock by 200–350%. Over the 10-year period, the rates of TOC accumulation were 0.6, 0.3, 0.8 Mg ha−1 year−1 and the rates of POC accumulation were 0.4, 0.4 and 0.7 Mg ha−1 year−1 under wheat–maize, wheat–alfalfa and wheat–acacia rotations, respectively. At 0–30 cm depth, total soil N was increased by 61–64% under wheat–maize and wheat–acacia, but total soil P was reduced by 38% under wheat–alfalfa. A significant improvement in clay stability but not in aggregate water-stability was observed in cultivated soils. The results showed a significant increase in soil organic C pool but unimproved macro-aggregation of the desert soil after 10 years of cultivation.  相似文献   

13.
Earthworm burrows contribute to soil macroporosity and support diverse microbial communities. It is not well known how fluctuations in soil temperature and moisture affect the burrowing activities of earthworms. The objective of this experiment was to evaluate the maximum depth and length of burrows created by the endogeic earthworm Aporrectodea caliginosa (Savigny) and the anecic earthworm Lumbricus terrestris L. for a range of temperatures (5–20 °C) and soil water potentials (−5 and −11 kPa). The laboratory microcosm was a plexiglass chamber (45 cm high, 45 cm wide) containing 0.14 m2 of pre-moistened soil and litter, designed to house a single earthworm for 7 days. Earthworm mass, surface casting and burrowing activities were affected significantly by soil temperature, moisture and the temperature×moisture interaction. Burrow length and maximum burrow depth increased with increasing temperature, but there was less burrowing in wetter soil (−5 kPa) than drier soil (−11 kPa). Weight gain and surface casting, however, were greater in soil at −5 kPa than −11 kPa. Our results suggest more intensive feeding and limited burrowing in wetter soil than drier soil. Earthworms inhabiting the non-compacted, drier soil may have pushed aside particles without ingesting them to create burrows. The result was that earthworms explored a larger volume of soil, deeper in the chamber, when the soil was drier. How these burrowing activities may affect the community structure and activity of soil microorganisms and microfauna in the drilosphere remains to be determined.  相似文献   

14.
The effect of soil incorporations of lantana (Lantana spp.) biomass, an obnoxious weed, on physical environment of a silty clay loam soil (Typic Hapludalf) under rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping was studied in a long-term field experiment conducted in a wet temperate region of north India. Fresh lantana biomass was incorporated into the plough layer at 10, 20 and 30 Mg ha−1 annually, 7–10 days before puddling. Plant-available water capacity (PAWC), non-limiting water range (NLWR) and NLWR:PAWC ratio were determined to characterize soil physical environment during wheat crop in the tenth cropping cycle.

Ten annual applications of lantana at 10, 20 and 30 Mg ha−1, increased organic carbon (OC) content over control by 12.6, 17.6 and 27.9% in 0–15 cm soil layer, and 17.1, 26.3 and 39.5% in 15–30 cm soil layer, respectively. The OC content in 0–15 and 15–30 cm soil layer of control plots was 11.1 and 7.6 g kg−1 soil. Bulk density decreased by 3–14% in 7.5–10.5 cm layer and 1–6% in 15–18 cm layer. Volumetric moisture contents at 10% air-filled porosity were 38.4, 40.0, 54.5 and 55.7% at 7.5–10.5 cm depth, and 31.4, 32.2, 33.9 and 34.6% at 15–18 cm depth corresponding to 0, 10, 20 and 30 Mg ha−1 lantana treatment, respectively. At 15–18 cm soil depth, volumetric moisture contents at 2 MPa soil penetration resistance were 26.9, 24.8, 23.0 and 19.6% in zero, 10, 20 and 30 Mg ha−1 lantana-treated plots, respectively. Lower soil water contents associated with 10% air-filled porosity and greater soil water contents associated with a limiting penetration resistance of 2 MPa resulted in a lower NLWR (4.3%) for control as compared to lantana-treated soil (7.4–15.1%). The PAWC showed slight increase from 12.9 to 13.4–14.9% due to lantana additions. The NLWR:PAWC ratio was also lower in control (0.33) as compared to lantana-treated soil (0.55–1.01). The NLWR was significantly and positively correlated with wheat grain yield (r=0.858**).  相似文献   


15.
A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes – Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides – were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997–1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57–151 mm) and 1999 (206–397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39–51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha−1 observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha−1) and Mucuna-mulched (1.4 Mg ha−1) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3–5.3 Mg ha−1). There were no significant differences in soil loss in 1998 (1–3.2 Mg ha−1) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha−1) than mulched cowpea (6.9 Mg ha−1) and Pueraria (5.4 Mg ha−1). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3–2.3 cm of soil from mounds in 1997, 3.5–6.9 cm in 1998 and 2.3–4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from −1 to −1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at −1 cm water head (14.3 cm h−1/2) was higher than furrow sorptivity (8.5 cm h−1/2), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h−1/2, whereas the least value of 6.96 cm h−1/2 was observed in furrow of Mucuna-burned residue. Pueraria phas eoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.  相似文献   

16.
Conservation tillage (no-till and reduced tillage) brings many benefits with respect to soil fertility and energy use, but it also has drawbacks regarding the need for synthetic fertilizers and herbicides. Our objective was to adapt reduced tillage to organic farming by quantifying effects of tillage (plough versus chisel), fertilization (slurry versus manure compost) and biodynamic preparations (with versus without) on soil fertility indicators and crop yield. The experiment was initiated in 2002 on a Stagnic Eutric Cambisol (45% clay content) near Frick (Switzerland) where the average annual precipitation is 1000 mm. This report focuses on the conversion period and examines changes as tillage intensity was reduced. Soil samples were taken from the 0–10 and 10–20 cm depths and analysed for soil organic carbon (Corg), microbial biomass (Cmic), dehydrogenase activity (DHA) and earthworm density and biomass. Among the components tested, only tillage had any influence on these soil fertility indicators. Corg in the 0–10 cm soil layer increased by 7.4% (1.5 g Corg kg−1 soil, p < 0.001) with reduced tillage between 2002 and 2005, but remained constant with conventional tillage. Similarly, Cmic was 28% higher and DHA 27% (p < 0.001) higher with reduced than with conventional tillage in the soil layer 0–10 cm. In the 10–20 cm layer, there were no significant differences for these soil parameters between the tillage treatments. Tillage had no significant effect on total earthworm density and biomass. The abundance of endogeic, horizontally burrowing adult earthworms was 70% higher under reduced than conventional tillage but their biomass was 53% lower with reduced tillage. Wheat (Triticum aestivum L.) and spelt (Triticum spelta L.) yield decreased by 14% (p < 0.001) and 8% (p < 0.05), respectively, with reduced tillage, but sunflower (Helianthus annuus L.) yield was slightly higher with reduced tillage. Slurry fertilization enhanced wheat yield by 5% (p < 0.001) compared to compost fertilization. Overall, Corg, Cmic, and DHA improved and yields showed only a small reduction with reduced tillage under organic management, but long-term effects such as weed competition remain unknown.  相似文献   

17.
We measured microbial biomass C and soil organic C in soils from one grassland and two arable sites at depths of between 0 and 90 cm. The microbial biomass C content decreased from a maximum of 1147 (0–10 cm layer) to 24 g g-1 soil (70–90 cm layer) at the grassland site, from 178 (acidic site) and 264 g g-1 soil (neutral site) at 10–20 cm to values of between 13 and 12 g g-1 soil (70–90 cm layer) at the two arable sites. No significant depth gradient was observed within the plough layer (0–30 cm depth) for biomass C and soil organic C contents. In general, the microbial biomass C to soil organic C ratio decreased with depth from a maximum of between 1.4 and 2.6% to a minimum of between 0.5 and 0.7% at 70–90 cm in the three soils. Over a 24-week incubation period at 25°C, we examined the survival of microbial biomass in our three soils at depths of between 0 and 90 cm without external substrate. At the end of the incubation experiment, the contents of microbial biomass C at 0–30 cm were significantly lower than the initial values. At depths of between 30 and 90 cm, the microbial biomass C content showed no significant decline in any of the four soils and remained constant up to the end of the experiment. On average, 5.8% of soil organic C was mineralized at 0–30 cm in the three soils and 4.8% at 30–90 cm. Generally, the metabolic quotient qCO2 values increased with depth and were especially large at 70–90 cm in depth.  相似文献   

18.
The objective of this study was to investigate the effects of biogas slurry derived from straw-rich farmyard manure on the soil microbial biomass, on the mineralization in the field and on the related crop yield. The experiment was carried out in the following four treatments: (1) fallow, (2) fallow + biogas slurry, (3) spring barley, and (4) spring barley + biogas slurry. The CO2 evolution rate ranged between 15 and 120 mg C m−2 h−1 in both fallow treatments and showed a significant exponential relationship with the soil temperature at 5 cm depth. According to the extrapolation of the CO2 evolution rates into amounts per hectare, approximately 200 kg C ha−1 or 27% of the biogas slurry derived C were mineralized to CO2 during a 50 days’ period to 18 June in the fallow treatment with biogas slurry. An additional amount of up to 29.5 kg inorganic N ha−1 could be calculated as the sum of NH4-N already present in biogas slurry at the time of amendment and from the amount of biogas slurry mineralized in the soil to NO3-N. A good agreement between measured and modelled stocks of inorganic N at 0–60 cm depth was obtained after having five-fold increased soil organic C turnover compared to the default values of the model DNDC. The mineralization data are in line with an amount of up to 21 kg ha−1 more N transferred by the barley plants to their aboveground biomass in biogas slurry treatment. The N not accounted for by the aboveground plant biomass could be explained by the belowground plant-derived N. CO2 evolution from the soil surface, inorganic N content at 0–60 cm depth and N transfer into barley aboveground biomass lead apparently to similar results after the application of biogas slurry. The soil ATP content after harvest of the barley was significantly larger in the two treatments with biogas slurry, especially in the fallow treatment indicating a positive effect on the soil microbial community.  相似文献   

19.
Soil texture can be an important control on soil organic carbon (SOC) retention and dynamics. The (clay + silt)-sized SOC pool (SOC < 20 μm) in non-cultivated or grassland soils has been proposed to reach an equilibrium or maximum level named protective capacity. Proper knowledge of SOC in this size fraction in non-cultivated and cultivated Black soils is important to evaluate management-induced changes in SOC in NE China. Twenty-seven paired soil samples (non-cultivated vs. cultivated) were collected in the Black soil zone in Heilongjiang and Jilin provinces. Bulk soil was dispersed in water with an ultrasonic probe and then soil size fractions were collected using the pipette technique for SOC analyses. Soil organic carbon in bulk soil and size fractions was measured by dry combustion. Average content of SOC < 20 μm was 23.2 g C kg−1 at the 0–30 cm depth for the non-cultivated soils, accounting for 75.1% of the total SOC at the same depth. There was significant positive relationship between soil clay plus silt content and SOC < 20 μm in non-cultivated soils. Accordingly, a model of the maximum SOC < 20 μm in 0–30 cm depth of non-cultivated Black soils was developed: y = 0.36x where y is the maximum SOC < 20 μm pool (g C kg−1) and x is the percentage of clay + silt (<20 μm) content. The average content of SOC < 20 μm was 18.7 g C kg−1 at 0–30 cm depth for cultivated soils, accounting for 81.5% of total SOC. This average value of SOC was 4.4 g C kg−1 less than the maximum value (23.1 g C kg−1) and accounted for 55.0% of the difference of SOC between non-cultivated and cultivated Black soils. Cultivation resulted in 45.0% loss of sand-sized (>20 μm) SOC concentration relative to SOC < 20 μm. This result indicates that SOC < 20 μm and sand-sized SOC both play important roles in SOC dynamics resulting from management practices. This model can be applied to calculate the actual potential to restore SOC for cultivated Black soils under conservation tillage in NE China.  相似文献   

20.
To determine the sum of ‘direct’ and ‘indirect’ effects of climatic change on enchytraeid activity and C fluxes from an organic soil we assessed the influence of temperature (4, 10 and 15 °C incubations) on enchytraeid populations and soil CO2 and CH4 fluxes over 116 days. Moisture was maintained at 60% of soil dry weight during the experimental period and measurements of enchytraeid biomass and numbers, and CO2 and CH4 fluxes were made after 3, 16, 33, 44, 65, 86 and 116 days. Enchytraeid population numbers and biomass increased in all temperature treatments with the greatest increase produced at 15 °C (to over threefold initial values by day 86). Results also showed that enchytraeid activity increased CO2 fluxes by 10.7±4.5, 3.4±4.0 and 26.8±2.6% in 4, 10 and 15 °C treatments, respectively, with the greatest CO2 production observed at 15 °C for the entire 116 day incubation period (P<0.05). The soil respiratory quotient analyses at lower temperatures (i.e. 4-10 °C) gave a Q10 of 1.7 and 1.9 with and without enchytraeids, respectively. At temperatures above 10 °C (i.e. 10-15 °C) Q10 significantly increased (P<0.01) and was 25% greater in the presence of enchytraeids (Q10=3.4) than without (Q10=2.6). In contrast to CO2 production, no significant relationships were observed between net CH4 fluxes and temperature and only time showed a significant effect on CH4 production (P<0.01).Total soil CO2 production was positively linked with enchytraeid biomass and mean soil CO2-C production was 77.01±6.05 CO2-C μg mg enchytraeid tissue−1 day−1 irrespective of temperature treatment. This positive relationship was used to build a two step regression model to estimate the effects of temperature on enchytraeid biomass and soil CO2 respiration in the field. Predictions of potential CO2 production were made using enchytraeid biomass data obtained in the field from two upland grassland sites (Sourhope and Great Dun Fell at the Moor House Nature Reserve, both in the UK). The findings of this work suggest that a 5 °C increase in atmospheric temperature above mean ambient temperature could have the potential to produce a significant increase in enchytraeid biomass resulting in a near twofold increase in soil CO2 release from both soil types. The interaction between temperature and soil biology will clearly be an important determinant of soil respiration responses to global warming.  相似文献   

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