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 15 毫秒
1.
This study explores the economic feasibility of several long-rotation afforestation scenarios for southern Ontario, Canada. Three species, red pine (Pinus resinosa Ait.), Norway spruce (Picea abies L.) and black walnut (Juglans nigra L.) are examined. We integrate growth and yield models, site suitability maps, and several management scenarios to investigate the investment attractiveness of these species inclusive and exclusive of carbon sequestration values. We report net present values (NPV), internal rates of return (IRR) and two break-even price metrics. For wood value only scenarios the IRRs range from 4.3 to 4.6% for red pine and 3.4–3.6% for Norway spruce (for the most attractive 10,000 ha, in a single rotation scenario). Black walnut had rates of return 3.5–3.7% for the most attractive 10,000 ha area. Adding carbon valued at Cdn $3.4 per metric ton CO2 − e (roughly 2005 prices in the Chicago Climate Exchange) increases rates of return by about 0.6% for red pine and Norway spruce and 0.4% for black walnut scenarios. Perhaps surprisingly these returns are comparable and better than 20-year rotation hybrid poplar plantations. To achieve a 6% real rate of return break-even carbon prices were $10.7/t CO2 − e for red pine, $12.6/t CO2 − e for Norway spruce and $17.2/t CO2 − e for black walnut (again for the “best” 10,000 ha). Although somewhat unremarkable, the results suggest that these longer-rotation species may be a better investment than perhaps previously expected if landowners have the appropriate site conditions.  相似文献   

2.
In Ethiopia, environmental degradation leads to a reduction of forest areas with economically important tree species like Boswellia papyrifera. In an attempt to reverse this development and assist natural rehabilitation, closing degraded forest from free grazing, fuel wood collection and other interference is practiced in Tigray. Sustainability of this management will, among other things, depend on the resources' tangible benefits. This study aimed to determine and compare net benefits (in Ethiopian Birr (ETB) per ha) from the closed and open Boswellia papyrifera forestlands. Production and household surveys were carried out in Jijike and Siye tabias of Abergelle woreda in northern Ethiopia. Data on costs and benefits of frankincense production were collected from firms trading the product. Net benefits from forestlands and croplands were determined using the Net Present Value criterion. The estimated mean frankincense productions were 127 kg/ha/yr for closed forestland and 84.54 kg/ha/yr for open forestland. A significant difference (p < 0.05) was observed between per tree mean frankincense yield of closed and open sites. The average grass harvest from closed area was 2851 kg/ha/yr. The financial Net Present Values were 8622 ETB/ha for closed and 6468 ETB/ha for open forestlands. These values were by 4574 ETB and 2005 ETB higher than the sum of NPV from crop and crop residuals of a hectare of cropland in the study area of the two sites, respectively. Exporting frankincense could generate foreign exchange of 53.28 and 39.05 USD/ha/yr from closed and open sites, respectively. Rural households earn about 74% of the annual total revenue (ETB/ha) from closed and open area as wage for tapping and collecting frankincense and using of grass. Sensitivity analysis showed that managing degraded Boswellia papyrifera forestland as closed area always generates a higher NPV than the open one in case of changes in discount rate and prices of inputs and outputs. Thus, managing the forest through closed areas is a competitive land-use alternative and provides higher net benefits than both open forestland and agricultural croplands.  相似文献   

3.
Schinus terebinthifolius Raddi (Anacardiaceae) and Rapanea ferruginea (Ruiz & Pavon) Mez (Myrsinaceae) are two neotropical pioneer trees with wide geographical distribution in South America, highly degree of adaptation to different soil conditions and intense regeneration in areas with anthropic activities. With the aim to recommend the use Schinus and Rapanea in gallery forest restoration programs, we conducted an experiment with the objective to analyze the capacity of these two pioneer trees to tolerate soil flooding, mainly by accessing the effects of flooding on leaf gas exchange, growth and dry matter partitioning. Seedling survival throughout the 56-day flooding period were 100 and 90% for Schinus and Rapanea, respectively. The mean values of stomatal conductance (gs) and net photosynthesis (A) observed in the control seedlings were, respectively, 0.4 mol m–2s–1 and 14 mmolm–2s–1, for Schinus, and 0.5 mol m–2s–1 and 14 mmolm–2s–1, for Rapanea. On day 20 flooding reduced gs and A by 36 and 29% in Schinus, and 81 and 61% in Rapanea. At the end of the experiment, significant decreases were also observed for root and whole plant biomass, in both species. Based on the results, we concluded that seedlings of Schinus and Rapanea can survive and grow throughout a medium period of soil waterlogging, in spite of the alterations observed in their physiological behavior, such as the decreases in stomatal conductance and in whole plant biomass.  相似文献   

4.
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   

5.
Some conservation based agroforestry systems (AFS) were developed for possible adoption in place of high risk rainfed farming on land capability classes Ito IV of a typical topo-sequence of foothill north India. The agri-silvi-horticulture system integrating leucaena, lemon, papaya and turmeric on class I irrigated land provided sustainable mean net returns of Rs. 17066 against Rs. 7852 ha.–1 yr.–1 from double cropped agricultural system. The intercropping of cluster beans with leucaena gave the highest net returns of Rs. 3540 ha.–1 yr.–1 in the agri-silvicultural system adopted on class II land. Eucalyptus terettcornis (Smith) in top and Bhabbar grass (Eulaliopsis binata Retz) in the understorey on a sandy loam class III land gave four years (1985–1988) mean air dry grass yield of 4.2 (used for paper pulp) from October and 1.19 t. ha–1 yr.–1 (used for fodder) from June cut. The net returns from grass alone were Rs. 4672 against Rs. 1679 ha.–1 yr.–1 from rainfed field crops raised on an adjoining plot. The returns from trees would be additional. Bhabbar grass raised under Acacia species on a 25 to 30% sloping gravelly class IV land provided yield varying from 2.18 to 4.31 from October cut and 0.50 to 1.1 t. ha.–1 yr.–1 from June cut with 6 years mean of 3.9 t. ha.–1 yr.–1 which at 1988 prices provided net returns of Rs. 2402 ha–1. These AFS proved superior to traditional farming on each land capability class.  相似文献   

6.
Seasonal changes in biomass, net primary productivity and turnover of dry matter of para grass (Brachiaria mutica) under a mixed tree stand and in an adjacent open stand in northern India are presented. Both stands attained peak values of live shoot biomass in September with a higher value under mixed tree stand (665 g m–2) than in the open stand (522 g m–2). The net aboveground production was 590 and 527 g m–2 yr–1 under mixed tree stand and in the open, respectively. The belowground net primary production was also greater under mixed tree stand (100 g m–2 yr–1) than in the open (76 g m–2 yr–1). Maximum aboveground and belowground net primary productions in both stands were obtained during the rainy season. The total net primary production for para grass was about 15% higher under mixed tree stand than in the open. The turnover rates of total plant biomass were greatest in the rainy season and the least during the summer season. The system transfer functions showed that the production of para grass on both stands was aboveground-oriented, accounting for 85–87% of annual total net primary production.  相似文献   

7.
Predictive models were developed for Cordia alliodora branch and Theobroma cacao branch or leaf biomass,based on branch basal areas (r2 0.79) but the model of C. alliodora leaf biomass, although significant, was of very low accuracy (r2 = 0.09) due to annual leaf fall. At age 10 years, shade tree stem biomass accounted for 80% of the total above-ground biomass of either tree. However, between the ages of 6 and 10 years, the biomass increment of T. cacao branches (3–4t.ha–1.a–1) was similar to that of the shade tree stems. During the same period, the net primary productivity was 35 and 28 t.ha–1.a–1, for the Erythrina poepigiana and and C. alliodora systems, respectively.Cocoa production under either of the shade trees C. alliodora or E. poeppigiana was 1000 kg.ha–1.a–1 (oven-dry; ages 6–10 yr). During the same period, C. alliodora timber production was 9 m3.ha–1.a–1 whilst the leguminous shade tree E. poeppigiana does not produce timber. Litterfall over the same 5 years, including crop and/or shade tree pruning residues, averages 11 and 23 t.ha–1.a–1, respectively. The main difference was due to E. poeppigiana pruning residues (10t.ha–1.a–1).Soil organic material reserves (0–45 cm) increased over 10 years from 198 to 240 t.ha–1 in the E. poeppigiana plots and from 168–184 t.ha–1 in the C. alliodora plots. These values, together with the productivity indices presented, provide evidence that the systems are sustainable.For economic reasons, the use of C. alliodora is recommended under the experimental conditions. however, on less fertile soils without fertilization, the greater biomass and hence nutrient return to the soil surface under E. poeppigiana, might make this the preferable shade tree.  相似文献   

8.
Casearia sylvestris methanolic extract (MCE) was screened at doses of 125–500 mg/kg for its antihyperlipidemic activity. The antihyperlipidemic effect was evaluated in olive oil-loaded mice. Acute treatment caused inhibition in the triglyceride (TG) and serum lipase elevation-induced by 5 ml/kg of olive oil.  相似文献   

9.
A study was made on the effect of an east-west tree line of years old Eucalyptus tereticornis on soil physical parameters and adjoining mustard and wheat crops as a function of distance from the tree-crop interface in north- and south-facing sides. Maximum soil temperature, pan evaporation, moisture extraction, number of plants/m2, and yields of mustard and wheat did not differ significantly on the two sides of plantation. Plant growth parameters decreased linearly with distance from the plantation. Mustard yield, Y (kg/ha) was linearly related to moisture extraction, ME (mm) as Y = 1914–120.3 ME. Eucalyptus tereticornis was found to extract 5 times more water than mustard from 0–150cm soil profile. Mustard and wheat yield reductions in adjoining 10 meter strips on both sides of the plantation were 47 and 34 per cent, respectively. Eucalyptus tereticornis is, therefore, not a suitable species for row plantations in agro-forestry systems in deep water table conditions of semi-arid regions.  相似文献   

10.
Seasonal fodder production responses of five shrubs (Centrosema arenarium, Desmodium strigillosum, Desmodium velutinum, Phyllodium pulchellum, and Tadehagi triquetrum)and five trees (Albizia gummifera, Berlinia grandiflora, Albizia niopoides, Bauhinia monandra, and Inga edulis) to pruning heights ranging from 15 to 75 cm were evaluated during the main-wet, minor-wet, and dry seasons of 1993 and 1994 in the forest-savanna transition zone of West Africa. Fodder from the main-wet season was analysed for nitrogen (N) and phosphorus (P), and dry matter degradation characteristics after 6, 12, 24, 48, 72 and 96 h of incubation in rumen-fistulated N'Dama steers. In the minor-wet season, fodder production of all species increased in response to increasing pruning height with the exception of P. pulchellum and A. gummifera. Highest fodder production was attained at a pruning height of 45 cm for the Desmodium species, 50 cm for P. pulchellum, and 75 cm for the rest of the species. Concentrations of N and P varied significantly among the species; for N the ranges were 28.7–38.8 g kg–1 (shrubs) and 25.3–44.5 g kg–1 (trees), while for P the ranges were 3.26–7.04 g mg–1 (shrubs) and 3.58–6.76 g mg–1 (trees). Dry matter degradation characteristics differed significantly among shrubs and trees; ranges for shrubs were: soluble fraction (a), 128–185; degradable fraction (b), 664–703; potential degradability (PD), 793–857, as g kg–1; rate of degradation (c), 0.0241–0.0308 as % h–1 while for trees ranges were: (a), 139–160; (b), 651–826; (PD), 824–970, as g kg–1; (c), 0.0143–0.0227 as % h–1. Based on fodder production and quality, C. arenarium, D. strigillosum, D. velutinum, B. monandra, I. edulis, and A. niopoides were the most promising species for the development of animal agroforestry technologies in the west African forest-savanna transition zone and similar environments in the tropics.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

11.
A simple, sensitive and accurate liquid chromatographic method with photodiode-array detection was developed for determination of dehydroevodiamine with detection wavelength at 368 nm and column temperature at 30 °C. The separation was carried out on an Agilent Zorbax SB-C18 column (250 mm × 4.6 mm, 5 µm) together with a C18 guard column. The mobile phase was acetonitrile–water (containing 30 mM sodium acetate trihydrate and 0.15% acetic acid) in the ratio of 30:70 (v/v) delivered at a flow rate of 1 mL/min. Excellent linear behavior was observed over the concentration range investigated, with correlation coefficient (R2) = 0.9998. This validated method was applied to determine the contents of dehydroevodiamine in 36 samples from different regions of China, and hierarchical clustering analysis was firstly used to classify and differentiate Evodia rutaecarpa samples. The analysis is specific and can be successfully applied to analyze E. rutaecarpa which is helpful for quality control of the herb.  相似文献   

12.
Two species of Japanese subterranean termite, Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe), were used in an investigation of the optimum temperature–relative humidity (RH) combination for their feeding activities. Daily wood consumption per worker and survivals were measured, and the protozoan fauna in the hindgut were observed under 15 temperature–RH combinations for 1 week. Five temperatures (20°, 25°, 30°, 35°, and 40°C) and three RH conditions (50%, 70%, and 90% RH) were examined. The activities of the workers were highest at around 30°C for both species, and workers died at 40°C within 5 days and 2 days for C. formosanus and R. speratus, respectively. The optimum RH condition for feeding activity was 90% RH for C. formosanus and 70%–90% RH for R. speratus. The optimum temperature–RH combinations for feeding activities were 30°C at 90% RH for C. formosanus and 30°C at 70%–90% RH for R. speratus.  相似文献   

13.
To meet their wood, fodder and fruit needs, resource-poor farmers with only small land holdings are forced to mix trees in their food crop plots. An experiment was conducted to study the effect of nine tree species planted at 312.5 trees ha–1 (4×8 m) on the yield of bananas planted at 625 stools ha–1 (4×4 m) and beans (80000 plants ha–1) as well as the wood production of the trees when intercropped. In addition, an economic analysis was done to compare the different tree/banana/bean associations.After three and one-half years, wood volume (in m3 ha–1) ofGrevillea robusta (18.1), was highest and that ofErythrina poeppigiana (2.7),Cedrela odorata (2.4) orMarkhamia lutea (0.8) was the lowest. Volume ofCedrela serrata (13.7) was not significantly different from that ofAlbizia chinensis (12.8) but was significantly higher than that ofLeucaena diversifolia (6.8),Acrocarpus fraxinifolius (6.7) orCalliandra calothyrsus (6.0).None of the tree species had a significant influence on the yields of the bananas and none affected the yield of the bean crops until the seventh cropping season, three years after the trees were planted. In that year, Grevillea reduced bean yield by 29%, Albizia by 34% and Leucaena by 36%. From the economic analyses, all the treatments except Leucaena and Markhamia had positive net benefits relative to the control (banana/bean) but the results were highly variable.C. serrata was found to be the best tree to be intercropped in a banana/bean system.  相似文献   

14.
A new withanolide identified by spectroscopic analysis as 12β-acetoxy-4-deoxy-5,6-deoxy-Δ5–withanolide D and Withanolide D, were isolated from the leaves of Acnistus arborescens. Cytotoxic activity of these two compounds against human tumor cell lines HT-29, MCF-7, MKN-45, HEp-2, HeLa, U-937 and two human normal fibroblast cultures, Fib04 and Fib05, were assessed. Withanolide D presented in vitro cytotoxic activity against tumor cell lines at the low micromolar range (LC50:1.0 to 1.69 µM) and showed a slightly lower activity against Fib04, suggesting moderated selectivity among tumoral and normal cells. No cytotoxic effect was observed for 12β-acetoxy-4-deoxy-5,6-deoxy-Δ5–withanolide D.  相似文献   

15.
Fine root dynamics of shaded cacao plantations in Costa Rica   总被引：1，自引：0，他引：1  
Root turnover may contribute a significant proportion of recycled nutrients in agroforestry systems and competition between trees and crops for nutrients and water may depend on temporal fine root regrowth patterns. Fine root biomass ( 2 mm) and fine root productivity were measured during one year in plantations of cacao (Theobroma cacao) shaded by Erythrina poeppigiana or Cordia alliodora planted on a deep alluvial soil in Turrialba, Costa Rica. Fine root biomass of approximately 1.0 Mg ha–1 varied little during the year with maximum values at the beginning of the rainy season of 1.85 Mg ha–1 in the cacao-C. alliodora system compared to 1.20 Mg ha–1 for cacao-E. poeppigiana. Fine root productivity of C. alliodora and E. poeppigiana (maximum of 205 and 120 kg ha–1 4 week–1, respectively) was greatest at the end of the rainy season, while for cacao it was greatest at the beginning of the rainy season (34–68 kg ha–1 4 week–1), which suggests that if nutrient competition occurs between the shade trees and the cacao, it could be minimized by early fertilization during the beginning of the rains immediately after pruning the shade trees. Annual fine root turnover was close to 1.0 in both systems. Assuming that fine root biomass in these mature plantations was constant on an annual basis, nutrient inputs from fine root turnover were estimated as 23–24 (N), 2 (P), 14–16 (K), 7–11 (Ca) and 3–10 (Mg) kg ha–1 year–1, representing 6–13% and 3–6% of total nutrient input in organic matter in the C. alliodora and E. poeppigiana systems, respectively.  相似文献   

16.
Studies on tree crop interaction under rainfed condition in Dehradun valley were conducted for 13 years during 1977 to 1990. Grewia optiva (Bhimal), Morus alba (Mulbery) and Eucalyptus hybrid were tried along with rice (CV: Akashi) — wheat (CV: RR-21) rotation. One-year-old tree seedlings of the above tree species were planted in line, 5 m apart in N-S direction, in July 1977, in the middle of the plot (size 20 m × 20 m). Eucalyptus was first harvested in 1987. Grewia optiva, Morus alba and coppice of Eucalyptus were harvested in 1990. All tree species had depressing effect on crop yields. Eucalyptus had maximum effect in depressing crop yield till the first harvest and had least effect thereafter. From 1987 onwards, Morus alba affected rice most, while wheat was mostly affected by Grewia optiva. The depressing effect on an average varied from 28 to 34% depending upon the species.Distance of tree line from the crop significantly affected the crop yield upto a distance of 5 m and there was 39% decrease in crop yield upto 1 m, 33% from 1–2 m, 25% from 2–3 m and 12% from 3–5 m distance. Annual removal of lops and tops from trees partly compensated the deficit. Grewia optiva could produce 1.08 t ha–1 yr–1 of branches and 0.26 t ha–1 yr–1 of leaves (air dry) and 1.28 t ha–1 yr–1 of branches and 0.28 t ha–1 yr–1 of leaves were obtained from Morus alba. Wood (ADT) produced by the trees was 33.6 t ha–1 from Eucalyptus, 9.5 t ha–1 from Grewia optiva and 11.6 t ha–1 from Morus alba.  相似文献   

17.
The willows Salix matsudana x alba and S. kinuyanagi, and the leguminous shrub Dorycnium rectum, are used for soil conservation in New Zealand and have potential value as browse plants. Two experiments were conducted in the lower North Island to ascertain the effect of selected establishment and cutting practices on their browse yield and nutritive value. A hill site experiment determined the effect of rooted and unrooted stem cuttings on establishment and initial production of the Salix species. A flat site experiment determined the effect of cutting height (0.10–0.30 m, 0.80 m, and 1.20 m above ground) and cutting frequency (once or twice per year) on yield of the Salix species and D. rectum. The establishment and dry matter (DM) yields of the Salix species were unaffected by the type of stem cutting. S. matsudana x alba (1.2 kg DM/tree) plants yielded more edible DM than S. kinuyanagi (0.9 kg DM/tree) and D. rectum (0.4 kg DM/tree). Cutting height had no effect on edible DM yield but affected total DM yield of the Salix species. Nitrogen concentration in edible DM, of all species, was 18–22 g/kg DM. In vitro organic matter digestibility of S. matsudana x alba (648–691 g/kg DM) and D. rectum (664–666 g/kg DM) was greater than S. kinuyanagi (611–615 g/kg DM). The condensed tannin concentration in edible DM of S. kinuyanagi was four-fold higher than in S. matsudana x alba (255 vs. 59 g/kg DM). It was concluded that S. matsudana x alba had the greatest potential as a browse species and D. rectum the least.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

18.
The transgenic rice lines Kemingdao 1 (KMD1) and Kemingdao 2 (KMD2) contain a synthetic cry1Ab gene derived from Bacillus thuringiensis Berliner and are highly resistant to rice stem borers and foliage-feeding lepidopterans. Propylea japonica (Coleoptera: Coccinellidae) is an important predator of rice insect pests; it also uses rice pollen as a food source under natural conditions. In the present study, the effects of KMD1 and KMD2 pollen expressing Cry1Ab protein on the fitness of P. japonica were assessed in the laboratory. P. japonica larvae and adults were provided with the following four diets: KMD1 pollen with the aphid Myzus persicae, KMD2 pollen with M. persicae, nontransgenic Xiushui 11 (parent variety of KMD1 and KMD2) pollen with M. persicae, and M. persicae only (KMD1–pollen, KMD2–pollen, XS11–pollen, and aphid treatments, respectively). The results showed that the longevity of female adults in the KMD1–pollen treatment was significantly lower than that in the XS11–pollen treatment, but was not significantly different from that in the KMD2–pollen and aphid treatments. Newly emerged males in the KMD2–pollen treatment were evidently less vital than those in the XS11–pollen treatment, but not significantly different from those in the KMD1–pollen and aphid treatments. The development, survival and reproduction indices for the three pollen treatments did not differ significantly from one another. In short, Bt toxin expressed in Bt rice pollen had no evident negative impacts on P. japonica fitness when the pollen was used as a food by this beetle.This revised version was published in March 2005 with corrections to the names of the authors.  相似文献   

19.
In 1987–89 the CATIE-GTZ Agroforestry Project set up experiments with five timber tree species planted in single lines on twelve farm boundaries in cooperation with local farmers. When the trees were five years old, their height, diameter and total stem volume were: Acacia mangium 17 m, 19 cm and 67 m3 km–1, Cordia alliodora 14 m, 20 cm and 46 m3 km–1, Eucalyptus deglupta 22 m, 24 cm and 85 m3 km–1, Tectona grandis 17 m, 20 m and 64 m3 km–1, Terminalia ivorensis 18 m, 23 cm and 104 m3 km–1. Considering these excellent growth rates, planting of Cordia alliodora, Eucalyptus deglupta and Tectona grandis in lines on farm boundaries should be promoted. T. ivorensis and A. mangium are not recommendable for sites with impeded drainage because of mortality caused by root rot, mostly due to Rosellinia sp.  相似文献   

20.
A study on the biomass of fine roots and its relationship with water-stable aggregates (WSA) was conducted in two herbaceous models, triploid Populus tomentosa + Lolium multiflorum (TL) and triploid P. tomentosa + natural grass (TN). Both of the model triploid P. tomentosa stands were four years old converted from agriculture. Unconverted steep slope farmland was used as a control site. Results showed that the biomass of fine roots (⩽ 1 mm) in different layers varied in the following descending order: upper layer, middle layer and lower layer, at approximate ratios of 50:30:20. The average annual biomass of fine roots in ryegrass was twice that of the mixed natural grass-forest land. The total amount of natural grass roots was 4.4 times that of the ryegrass model. Water-stable aggregates of the upper, middle and lower layers and the unconverted farmland did not show any significant differences, whereas the amounts of water-stable aggregates of big-particles in the upper and middle layers were much larger than those of unconverted lands. The amounts of water-stable aggregates of natural grass-forest lands (TN model) were higher than those of managed grass-forest lands (TL model). Two-way analysis of variance indicated that fine roots (≤ 1 mm) could significantly enhance water-stable aggregates and total water-stable aggregates. We conclude that the program of converting agricultural lands to forest-grass lands is an effective way in improving soil anti-erosion capability. __________ Translated from Scientia Silvae Sinicae, 2007, 43(5): 24–29 [译自:林业科学]  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