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1.
Limited nutrient acquisition from soil is a key process limiting productivity in boreal forest. We investigated short-root morphological adaptations and rhizosphere effect in relation to site conditions in interaction with tree mineral nutrition. We studied seven young (8- to 14-year-old) silver birch (Betula pendula Roth.) stands on abandoned agricultural land in Estonia. Soil pH varied from 3.8 to 7.0, and soil N % from 0.07 to 0.26%. Tree nutrient (NPK) status was expressed by leaf nutrient concentrations. Leaf N correlated negatively with short-root specific length and area. Summed activity (SA) and metabolic diversity of bacteria (by BIOLOG Ecoplate™), bacterial community diversity (by DGGE) and pHKCl were determined for rhizosphere (R) and bulk soil (S) to reveal the extent of the rhizosphere effect. Bacterial activity in rhizosphere was 1.4–4.7 times higher than in bulk soil. Ratio SAR/SAS indicating root support to the rhizosphere bacterial communities decreased with increasing bulk soil pH; however, when bulk soil pH was ≥5, the decrease in SAR/SAS was insignificant, i.e. the rhizosphere effect stayed at a stable level. Diversity of bacterial community was 6% higher in bulk soil than in rhizosphere. Rhizosphere acidification occurred in studied stands when bulk soil pHKCl ≥ 5. Short-root N % correlated positively with SAR/SAS. We concluded that tree N-nutritional status was related to short-root morphological parameters but not to studied microbiological characteristics in the soil of young silver birch stands.  相似文献   

2.
Ecological studies commonly demand elaborate knowledge of the distribution pattern of humous horizons, especially in forest ecosystems with high humus variability. Conventional investigative methods are time-consuming and surface-destructive. Ground penetrating radar (GPR), in contrast, offers a fast and non-destructive method of portraying the shallow subsurface. Against this background, the reliability of GPR-derived metric data on terrestrial humous horizons was tested at a study site in the altimontane zone of the Bavarian Alps (1,260 m a.s.l.). The GPR survey, using a shielded bistatic antenna device at 800 MHz, is based on eight parallel lines within a 30 × 30 m plot. The metric interpretation of the GPR results is validated by a trench, which records the thickness of humous horizons at a 10-cm interval, and is compared to conventional sampling methods, represented by 18 soil monolith profiles of both random and grid-based distribution. The results show that it is not possible to resolve the borders of single humous horizons. The delineation of humous against non-humous horizons, however, shows correlation (R = 0.553) with the reference data and delivers reliable data on the average thickness and variation of humous horizons. The observed thickness deviations between GPR and the trench line range between −9.5 and 7.5 cm, with remarkably narrow deviations of −2 to 2 cm or less in 50% of the cases. In summary, supported by the high number of data records (n = 1,727), GPR creates a much better and none destructive image of the actual humus distribution pattern compared to conventional methods.  相似文献   

3.
The vertical distribution of the ectomycorrhizal (ECM) community was studied in four old high-mountain Norway spruce (Picea abies [L.] Karst.) stands in northern Italy. The aim was to verify if the variability in the community structure could be explained by characteristics of the organic and mineral soil horizons. The community structure was evaluated in terms of both fungal species and their ability to explore soil (exploration types). From the 128 humus profiles sampled over the two study periods, 31 ECM species were recorded. The study demonstrated that the number of both non-vital tips and vital non-mycorrhized tips decreases with soil depth, from organic to mineral horizons, while the number of ectomycorrhizal tips mainly increases with soil depth. A preference was found of some ECM species and exploration types for specific organic or mineral soil layers and their features, especially moisture and available nitrogen. These results can help in understanding how the functional role of the single consortia and the ecological features determining this “adaptive diversity” in ectomycorrhizal communities could be of major importance to assess the resilience in forest soil ecosystems.  相似文献   

4.
WILLIAMS  B. L. 《Forestry》1983,56(1):17-32
Samples of litter and humus from beneath 10 m tall, closed-canopySitka spruce planted on a brown forest soil were incubated underboth field and laboratory conditions to measure mineral nitrogenproduction and carbon dioxide evolution. Mineral nitrogen productionin enclosed samples over 12 months was equivalent to 50 and17 kg N ha–1 in litter and humus, respectively. Applicationsof fertilizer NPK (200 kg N ha–1 as ammonium nitrate,100 kg P ha–1 as unground rock phosphate and 150 kg Kha–1 as potassium chloride), 18 months previously, decreasedthese values slightly, but stimulated the production of nitratein both litter and humus. Compared with samples kept under laboratoryconditions at 10°C, those incubated in the field at a similarmean temperature released less carbon dioxide and, in the caseof fertilized humus produced smaller amounts of mineral nitrogen.  相似文献   

5.
To investigate the effect of tree species on soil N dynamics in temperate forest ecosystems, total N (Nt), microbial N (Nmic), net N mineralization, net nitrification, and other soil chemical properties were comparatively examined in beech (64–68 years old) and Norway spruce (53–55 years old) on sites 1 and 2, and beech and Scots pine (45 years old) on site 3. The initial soil conditions of the two corresponding stands at each site were similar; soil types were dystric Planosol (site 1), stagnic Gleysols (site 2), and Podzols (site 3). In organic layers (LOf1, Of2, Oh), Nmic and Nmic/Nt, averaged over three sampling times (Aug., Nov., Apr.), were higher under the beech stands than under the corresponding coniferous ones. However, the Nmic in the organic layers under beech had a greater temporal variation. Incubation (10 weeks, 22 °C, samples from November) results showed that the net N mineralization rates in organic layers were relatively high with values of 8.1 to 24.8 mg N kg–1 d–1. Between the two corresponding stands, the differences in net N mineralization rates in most of the organic layers were very small. In contrast, initial net nitrification rates (0.2–17.1 mg N kg–1 day–1) were considerably lower in most of the organic layers under the conifer than under the beech. In the mineral soil (0–10 cm), Nmic values ranged from 4.1–72.7 mg kg–1, following a clear sequence: August>November>April. Nmic values under the beech stands were significantly higher than those under the corresponding coniferous stands for samples from August and April, but not from November. The net N mineralization rates were very low in all the mineral soils studied (0.05–0.33 mg N kg–1 day–1), and no significant difference appeared between the two contrasting tree species.  相似文献   

6.
Carbon concentrations and stocks in forest soils of Europe   总被引：1，自引：0，他引：1  
This study presents the results of a series of evaluations of a continent-wide soil database (EU/UN-ECE Level I) with the aim to estimate baseline soil carbon concentrations and stocks. The methodology included the biogeographic stratification of soil carbon measurements throughout Europe using climatic zones derived from the Soil Regions Map of Europe. The presented stock estimates range from 1.3 to 70.8 t C/ha for the O-layer, and from 11.3 to 126.3 t C/ha for the mineral soil 0–20 cm (Germany: 0–30 cm) (5 and 95 percentiles). Histosols were excluded because of methodological differences and data gaps. When looking at the median values of the strata investigated, relationships were found. For example, carbon stocks in the O-layer of sandy soils are distinctly higher than those of fine-textured soils. However, the variability is so high that some of these relationships disappear. For example in western and central Europe, the level of carbon stocks in the mineral soil between shallow soils (Leptosols) and more deeply developed soils (Podzols and Cambisols) do not differ very much. It was also found that just the investigation of topsoils is not sufficient to understand the regional pattern of organic matter in forest soils – unless the subsoil becomes included as well. It is hypothesized that for Europe, the impact of site factors such as climate, texture and relief are difficult to extract from such a database if the data are only stratified according to macro-climatic areas. It has to be considered that the effect of systematic error in the database is quite large (but cannot be identified on the level of the current data availability). In order to receive a first impression of the landscape-level distribution of carbon, a map of carbon concentrations in the topsoil was generated. The results support the relationships found between carbon stocks and site factors, such as climatic zones and soil type. Compared to the much lower carbon concentrations of agricultural soils, the results demonstrate clearly the importance of forest soils for the terrestrial carbon cycling in Europe.  相似文献   

7.
Monitoring of soil nitrogen (N) cycling is useful to assess soil quality and to gauge the sustainability of management practices. We studied net N mineralization, nitrification, and soil N availability in the 0 10 cm and 11 30 cm soil horizons in east China during 2006 2007 using an in situ incubation method in four subtropical evergreen broad-leaved forest stands aged 18-, 36-, 48-, and 65-years. The proper- ties of surface soil and forest floor varied between stand age classes. C:N ratios of surface soil and forest floor decreased, whereas soil total N and total organic C, available P, and soil microbial biomass N increased with stand age. The mineral N pool was small for the young stand and large for the older stands. NO 3 - -N was less than 30% in all stands. Net rates of N mineralization and nitrification were higher in old stands than in younger stands, and higher in the 0 10 cm than in the 11 30 cm horizon. The differences were significant between old and young stands (p < 0.031) and between soil horizons (p < 0.005). Relative nitrification was somewhat low in all forest stands and declined with stand age. N trans- formation seemed to be controlled by soil moisture, soil microbial bio- mass N, and forest floor C:N ratio. Our results demonstrate that analyses of N cycling can provide insight into the effects of management distur- bances on forest ecosystems.  相似文献   

8.
Nitrogen (N) deposition exceeds the critical loads for this element in most parts of Switzerland apart from the Alps. At 17 sites (8 broadleaved stands, 8 coniferous stands, and 1 mixed stand) of the Swiss Long-term Forest Ecosystem Research network, we are investigating whether N deposition is associated with the N status of the forest ecosystems. N deposition, assessed from throughfall measurements, was related to the following indicators: (1) nitrate leaching below the rooting zone (measured on a subset of 9 sites); (2) the N nutrition of the forest stand based on foliar analyses (16 sites); and (3) crown defoliation, a non specific indicator of tree vitality (all 17 sites). Nitrate leaching ranging from about 2 to 16 kg N ha−1 a−1 was observed at sites subjected to moderate to high total N deposition (>10 kg ha−1 a−1). The C/N ratio of the soil organic layer, or, when it was not present, of the upper 5 cm of the mineral soil, together with the pool of organic carbon in the soil, played a critical role, as previous studies have also found. In addition, the humus type may need to be considered as well. For instance, little nitrate leaching (<2 kg N ha−1 a−1) was recorded at the Novaggio site, which is subjected to high total N deposition (>30 kg ha−1 a−1) but characterized by a C/N ratio of 24, large organic C stocks, and a moder humus type. Foliar N concentrations correlated with N deposition in both broadleaved and coniferous stands. In half of the coniferous stands, foliar N concentrations were in the deficiency range. Crown defoliation tended to be negatively correlated with N concentrations in the needles. In the majority of the broadleaved stands, foliar N concentrations were in the optimum nutritional range or, on one beech plot with high total N deposition (>25 kg ha−1 a−1), above the optimum values. There was no correlation between the crown defoliation of broadleaved trees and foliar concentrations.  相似文献   

9.
Aspen (Populus tremula) is capable of reproducing both sexually and asexually from root suckers, the latter being more common. Seedlings are rare even though potential seed production is enormous. The aim of this study was to find out how different moisture conditions affect emergence and survival of aspen seedlings on burned soil. We set up a sowing experiment on mineral soil and on humus. The sowing was done at 240 microsites (θ7 cm) in 15 blocks (1×1 m). Treatments were sowing time, watering and sowing shelter. A total of 1463 seedlings emerged on mineral soil and 26 on humus. Watering, covering, their interaction, block and sowing time had significant effects on the number of seedlings. The largest numbers of seedlings were recorded at microsites that were watered and covered. The survival of seedlings was 20% during the growing season and 45% over winter. We conclude that seedbed conditions and moisture are the most essential factors for sexual reproduction of aspen. Short-term weather conditions have an important effect on seedling emergence and are likely to greatly affect field studies.  相似文献   

10.
Chemical characteristics of forest soils subjected to long-term deposition of alkaline and acid air pollutants were analysed in spruce (Picea abies (L.) Karst.) stands in eastern Germany. Three forest sites along an emission gradient of 3, 6, and 15 km downwind of a coal-fired power plant were selected, representing high, intermediate, and low fly-ash input rates. Past emissions caused an accumulation of mineral fly-ash constituents in the organic layer, resulting in an atypically high mass of organic horizons of forest soils, especially in the F and H horizons. Total mass of organic layers at the site with heavy deposition loads was as high as 128 t ha–1, compared to 58 t ha–1 at the low input site. Fly-ash deposition significantly increased the pH values in the L, F and H horizons and mineral topsoil (0–10 cm). Significantly higher concentrations of NH4Cl-extractable cations (i.e. effective cation exchange capacities) and base saturations of >66% were found in the humic horizons at sites where the pH was increased due to the direct and indirect (i.e. higher proportions of deciduous trees) effects of fly-ash emissions. Stocks of basic cations were dominated by Ca2+ and decreased significantly along the fly-ash deposition gradient from 33.6 to 5.3 kmolc ha–1. Proportions of water-soluble basic cations out of the total potentially exchangeable (i.e. NH4Cl-extractable) basic cations generally increased in the forest soil with decreasing deposition loads following the cation exchange capacity and base saturation along the fly-ash gradient. Higher proportions of monovalent cations, such as K+ and Na+, were observed in the water extracts from fly-ash-affected forest soils, while the NH4Cl-extracts were dominated by bivalent cations, such as Ca2+ and Mg2+. These results suggest a greater leaching tendency for monovalent cations in these soils. Stocks of organic C and total N in the humus layer decreased from sites with high fly-ash deposition levels to sites with low levels, from 57.4 to 46.4 t C ha–1 and from 2.43 to 1.99 t N ha–1. The C/N ratios of the organic horizons varied from 22 to 25, revealing no distinct pattern along the fly-ash gradient. Measurements of hot-water-extractable and water-soluble organic C suggested a reduced availability or a faster decomposition of soil organic matter in soils with historically high fly-ash loads.  相似文献   

11.
We hypothesized that tree-based intercropping in southwestern Québec, Canada, would stimulate soil microbial activity and increase soil nutrient supply, thereby benefiting the growth of trees. Our experimental design comprised alternating rows of hybrid poplar (Populus nigra L. × P. maximowiczii A. Henry) and high-value hardwood species spaced 8 m apart, between which two alley treatments were applied 5–6 years after planting the trees. The first alley treatment consisted of a fertilized soybean (Glycine max (L.) Merr.) intercrop grown over two consecutive years, while the second consisted of repeatedly harrowing to minimize vegetation in the alley. Tree rows were mulched with a 1.5 m wide polythene mulch. Microbial respiration and biomass, and mineral N concentrations and mineralization rates were measured on five or six dates at 0, 2 and 5 m from hybrid poplar rows. On some of the sampling dates, we found significantly higher soil microbial biomass, mineral N concentrations and nitrification rates, and a significantly lower microbial metabolic quotient (qCO2), in the soybean intercropping than in the harrowing treatment. Over the 2 year period, hybrid poplar biomass increment and N response efficiency (NRE) were significantly higher (51 and 47%, respectively) in the intercropping than in the harrowing treatment. Microbial biomass and mineral N supply were significantly lower beneath the polyethylene mulch than in the alleys, and we posit that this may stimulate the growth of tree roots into the alley. We conclude that soybean intercropping improves nutrient turnover and supply for hybrid poplar trees, thereby increasing the land equivalent ratio (LER).  相似文献   

12.
Agroforestry and grass buffers have been proposed for improving water quality in watersheds. Soil porosity can be significantly influenced by buffer vegetation which affects water transport and water quality. The objective of the study was to compare differences in computed tomography (CT)-measured macroporosity (>1,000-μm diam.) and coarse mesoporosity (200- to 1,000-μm diam.) parameters for agroforestry and grass buffer systems associated with rotationally grazed and continuously grazed pasture systems. Soils at the site were Menfro silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalf). Six replicate intact soil cores, 76.2 mm diam. by 76.2 mm long, were collected using a core sampler from the four treatments at five soil depths (0–50 cm at 10-cm intervals). Images were acquired using a hospital CT scanner and subsequently soil bulk density and saturated hydraulic conductivity (K sat) were measured after scanning the cores. Image-J software was used to analyze five equally spaced images from each core. Bulk density was 5.9% higher and saturated hydraulic conductivity (K sat) values were five times lower for pasture treatments relative to buffer treatments. For the 0–10 cm soil depth, CT-measured soil macroporosity (>1,000 μm diam.) was 13 times higher for the buffer treatments compared to the pasture treatments. Buffer treatments had greater macroporosity (0.020 m3 m−3) compared to pasture (0.0045 m3 m−3) treatments. CT-measured pore parameters were positively correlated with K sat. The project illustrates benefits of agroforestry and grass buffers for maintaining soil porosity critical for soil water and nutrient transport.  相似文献   

13.
Whole catchment liming or forest liming has been proposed and implemented as a countermeasure to the effects of elevated sulphur deposition. Since the end of the 1980s the Swedish Forest Agency has undertaken experimental forest liming experiments in selected catchments in southern Sweden. These studies were with low doses (3 tonnes ha−1) of lime (CaCO3) and dolomite (CaMg(CO3)2). Data from both soil samples and stream water samples have been collected for the 16 years following treatment. The stream data has been complemented with data from untreated catchments, from the Swedish monitoring stream network. Significant differences due to treatment were seen for Ca, cation exchange capacity (CEC) and base saturation (BS) in the humus layer, none of these variables showed a statistically significant change in the mineral soil due to treatment alone. Soil samples from both the treated and untreated sites showed temporal changes in both the humus layer and the mineral soils with increases in pH, Ca and CEC and decreases in BS and Al which were independent of treatment. A combination of treatment and time, gave significant changes in BS and TA down to 10 cm in the mineral soil. In the stream water samples no statistically significant differences were observed between treated and untreated sites. Regardless of treatment, the streams exhibited a general pattern of declining concentrations of SO4, Ca, sum of base cations (BC) and increasing acid neutralizing capacity (ANC). In summary, the application of a low dose of lime (3 tonnes ha−1) did not result in significant changes in surface water chemistry in the study catchments and changes in soil chemistry were mainly restricted to the humus layer during the 16 years following treatment. The natural recovery, as a result of reductions in sulphur deposition, dominated the effects and was clearly seen in both the treated and untreated study sites. MAGIC simulations indicate that this recovery will continue in the coming decades.  相似文献   

14.
In 1984, a liming experiment with a surface application of 4 t ha−1 of dolomitic limestone was started at the acidic N-saturated Norway spruce forest “Höglwald” in southern Germany and monitored until 2004. The decay of surface humus due to the accelerated mineralisation accounted for 18.5 ± 2.7 t ha−1 C or 50% of the initial pool and 721.6 ± 115.0 kg ha−1 N or 46% for N. Due to some translocation of organic material to the mineral soil the values to 40 cm depth are slightly lower (13.5 ± 4.4 t ha−1 C or 15% of the initial pool and 631.6 ± 192.8 kg ha−1 N or 13% for N). In the control plot NO3− concentrations at 40 cm depth were above the European level of drinking water (0.8 mmolc l−1 or 50 mg NO3− l−1) for nearly the whole investigation period. Liming increased NO3− concentrations in seepage water for approximately 15 years, and accelerated leaching losses by 396.2 NO3−–N kg ha−1 from 1984 to 2003. The increase in pH of the soil matrix was more or less restricted to the humus layer and the upper 5 cm of the mineral soil during the whole time span, while the base cations Ca and Mg reached deeper horizons with seepage water. From 1984 to 2003, an amount that nearly equalled the applied Mg, was leached out of the main rooting zone, while most of the applied Ca was retained. The time series of the elemental concentrations in needles showed minor changes. Ca concentrations in needles increased with liming, while Mg remained nearly unchanged, and P decreased in older needles.  相似文献   

15.
Precipitation of mineral phosphate is often recognized as a factor of limiting the availability of P in acidic soils of tropical and subtropical forests. For this paper, we studied the extractable P pools and their transformation rates in soils of a tropical evergreen forest at Xishuangbanna and a subtropical montane wet forest at the Ailao Mountains in order to understand the biogeochemical processes regulating P availability in acidic soils. The two forests differ in forest humus layer; it is deep in the Ailao forest while little is present in the Xishuangbanna forest. The extractable P pools by resin and sodium-bicarbonate decreased when soil organic carbon content was reduced. The lowest levels of extractable P pools occurred in the surface (0–10 cm) mineral soils of the Xishuangbanna forest. However, microbial P in the mineral soil of the Xishuangbanna forest was twice that in the Ailao forest. Potential rates of microbial P immobilization were greater than those of organic P mineralization in mineral soils for both forests. We suggest that microbial P immobilization plays an essential role in avoiding mineral P precipitation and retaining available P of plant in tropical acidic soils, whereas both floor mass accumulation and microbial P immobilization function benefit retaining plant available P in subtropical montane wet forests. Translated from Acta Ecologica Sinica, 2006, 26(7): 2,294–2,300 [译自: 生态学报]  相似文献   

16.
The Mn, Zn and Cu contents of litter, soil fauna and soil in Pinus koraiensis and mixed broad-leaved forest in Liangshui Nature Reserve of Xiaoxing’an Mountains were analyzed in this paper, results showed that the tested microelement contents in the litter, soil fauna and soil followed the order: Mn>Zn>Cu, but varied with environmental components, for Mn the order is soil>litter>soil fauna, for Zn is soil fauna>litter and soil, and for Cu is soil fauna>soil>litter. The change range of the tested microelement contents in litter was larger in broad-leaved forest than those in coniferous forest. Different soil fauna differed in their microelementenrichment capability, the highest content of Mn, Zn and Cu existed in earthworm, centipede and diplopod, respectively. The contents of the tested microelements in soil fauna had significant correlations with their environmental background values, litter decomposition rate, food habit of soil fauna, and its absorbing selectively and enrichment to microelements. The microelements contained in 5–20 cm soil horizon were more than those in 0–5 cm humus layer, and their dynamics differed in various horizons. __________ Translated from Chinese Journal of Applied Ecology, 2007, 18(2): 277–282 [译自: 应用生态学报]  相似文献   

17.
Forest fires are known to influence nutrient cycling, particularly soil nitrogen (N), as well as plant succession in northern forest ecosystems. However, few studies have addressed the dynamics of soil N and its relationship to vegetation composition after fire in these forests. To investigate soil N content and vegetation establishment after wildfire, 13 sites of varying age class were selected in the Sub-Boreal spruce zone of the central interior of British Columbia, Canada. Sites varied in time since the last forest fire and were grouped into three seral age classes: (a) early-seral (<14 years), (b) mid-seral (50–80 years) and (c) late-seral (>140 years). At each site, we estimated the percent cover occupied by trees, shrubs, herbs and mosses. In addition, the soil samples collected from the forest floor and mineral horizons were analyzed for the concentrations of total N, mineralizable N, available NO3−-N and available NH4+-N. Results indicated that soil N in both the forest floor and mineral horizons varied between the three seral age classes following wildfire. Significant differences in mineralizable N, available NO3−-N and available NH4+-N levels with respect to time indicated that available soil N content changes after forest fire. Percent tree and shrub cover was significantly correlated to the amount of available NH4+-N and mineralizable N contents in the forest floor. In the mineral horizons, percent tree cover was significantly correlated to the available NH4+-N, while herb cover was significantly correlated with available NO3−-N. Moss cover was significantly correlated with total N, available NO3−-N and mineralizable N in the forest floor and available NO3−-N in the mineral horizons. We identified several unique species of shrubs and herbs for each seral age class and suggest that plant species are most likely influencing the soil N levels by their contributions to the chemical composition and physical characteristics of the organic matter.  相似文献   

18.
Soil properties were compared in adjacent 50-year-old Norway spruce, Scots pine and silver birch stands growing on similar soils in south-west Sweden. The effects of tree species were most apparent in the humus layer and decreased with soil depth. At 20-30 cm depth in the mineral soil, species differences in soil properties were small and mostly not significant. Soil C, N, K, Ca, Mg, and Na content, pH, base saturation and fine root biomass all significantly differed between humus layers of different species. Since the climate, parent material, land use history and soil type were similar, the differences can be ascribed to tree species. Spruce stands had the largest amounts of carbon stored down to 30 cm depth in mineral soil (7.3 kg C m−2), whereas birch stands, with the lowest production, smallest amount of litterfall and lowest C:N ratio in litter and humus, had the smallest carbon pool (4.1 kg C m−2), with pine intermediate (4.9 kg C m−2). Similarly, soil nitrogen pools amounted to 349, 269, and 240 g N m−2 for spruce, pine, and birch stands, respectively. The humus layer in birch stands was thin and mixed with mineral soil, and soil pH was highest in the birch stands. Spruce had the thickest humus layer with the lowest pH.  相似文献   

19.
Soil moisture content from 0 to 2 m depth was monitored under 2–6 year old radiata pine (Pinus radiata) with three understoreys of bare ground, lucerne (Medicago sativa) and ryegrass/clover (Lolium perenne/Trifolium spp.) and under adjacent open-grown lucerne and ryegrass/clover pastures. By the fifth year soil moisture depletion/recharge pattern under the trees alone was similar to that under open pasture and under trees with pasture understoreys. Maximum plant available moisture storage was 207–223 mm in the top meter of this Templeton silt loam soil but only 69–104 mm at 1–2 m depth where coarse textures often predominated. Lucerne reduced soil moisture content (SMC) to lower levels during drier summers and extracted more water from 1 to 2 m depth than ryegrass/clover. Evapotranspiration (ET) during early summer when soil moisture was high was close to the Penman potential evapotranspiration (E p ), but the difference increased when SMC in the top meter dropped below 200 mm. The silvopasture treatments had higher ET in winter than pasture alone but this was still less than E p . Soil moisture deficits (SMD) at the end of each summer were sufficiently large to require slightly higher than normal winter rainfall and ET < E p to recharge the soil to field capacity before the next summer. The soil moisture results, taken together with root and growth data, suggest that trees and understorey pastures are complementary in the first three or four growing seasons but this balance subsequently declines in favor of the pine trees. Management options, to extend the period that understorey pastures are productive, include reducing tree stockings, more vigorous pruning, using competitive understoreys and changing from pines to deciduous trees. Research on new silvopastoral combinations is suggested.  相似文献   

20.
Soil water characteristics were determined in 6 soil profiles along a Norway spruce forested sandy‐loamy till hillslope in Southern and Northern Sweden, respectively. The soil moisture class was mesic at both sites, i.e. having well drained soil water conditions. Two different Podzols; Leptic and Orthic, were developed at each site respectively. The vertical distribution of soil water retention capacity (SWRC) was similar in the different profiles at each site respectively. The SWRC of the mineral soil was significantly higher in the spodic B horizon compared to the other horizons. In concordance with the vertical distribution of SWRC, the largest amount of organic matter in the mineral soil, measured as ignition loss, was also found in the spodic B horizon. The significantly higher SWRC in the spodic B horizon, i.e. the ¡lluvial horizon, was suggested to depend on the accumulated organic‐sesquioxide material in this horizon. As SWRC reached maximum values in the spodic B horizon at all tensions applied, it was further suggested that soil formation in the studied profiles enhanced the formation of both micro‐ and macropores in the spodic B horizon. The variation of SWRC, at a certain level in the soil, was often larger within a profile than between the profiles at each site respectively.  相似文献   

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