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1.
CONNELL  C. A.; COUSINS  D. A. 《Forestry》1969,42(2):119-132
The results of development work and practical use of chemicalfire retardants for control of vegetation fires are described.Viscous water, prepared using sodium alginate solution, hasproved highly successful for arresting flame spread in a varietyof fuel types, including heather, grass, and gorse. Field-scaleapplications over a 5-year period at more than 30 forests haveshown that the technique can be used reliably and economicallyfor controlled burning, and has also been used to contain wildfires.A satisfactory mixing/dispensing unit has been developed formixing and applying viscous water. This unit is light and versatileand can be used as a general purpose pump or sprayer for water,herbicides, etc., if required. Extension of earlier trials using herbicides to dry grass vegetationto permit safe and rapid controlled burning during the ‘green’season has confirmed the initial promise. Paraquat has provedthe most effective herbicide for this purpose, and can be usedto considerable practical advantage for fire-break formationin grass, and particularly Molinia vegetation, providing grazinganimals can be excluded for at least 24 hours after spraying.Recommendations are made on practical use of both these methods.  相似文献   

2.
In order to investigate the pyrolytic characteristics of the burning residue of fire-retardant wood, a multifunctional fire-resistance test oven aimed at simulating the course of a fire was used to burn fire-retardant wood and untreated wood. Samples at different distances from the combustion surface were obtained and a thermogravimetric analysis (TG) was applied to test the prrolytic process of the burning residue in an atmosphere of nitrogen. The results showed that: 1) there was little difference between fire-retardant wood and its residue in the initial temperature of thermal degradation. The initial temperature of thermal degradation of the combustion layer in untreated wood was higher than that in the no burning wood sample; 2) the temperature of the flame retardant in fire-retardant wood was 200°C in the differential thermogravimetry (DTG). The peak belonging to the flame retardant tended to dissipate during the time of burning; 3) for the burning residue of fire-retardant wood, the peak belonging to hemicellulose near 230°C in the DTG disappeared and there was a gentle shoulder from 210 to 240°C; 4) the temperature of the main peaks of the fire-retardant wood and its burning residue in DTG was 100°C lower than that of the untreated wood and its burning residue. The rate of weight loss also decreased sharply; 5) the residual weight of fire-retardant wood at 600°C clearly increased compared with that of untreated wood. Residual weight of the burning residue increased markedly as the heating temperature increased when burning; 6) there was a considerable difference with respect to the thermal degradation temperature of the no burning sample and the burning residue between fire-retardant wood and untreated wood. __________ Translated from Journal of Beijing Forestry University, 2006, 28(3): 133–138 [译自: 北京林业大学学报]  相似文献   

3.
Summary Assessments of internal checking and the physical properties of 124 trees of Eucalyptus regnans F. Muell. have shown that for material dried under relatively mild predryer conditions (30 °C, 65% RH) internal checking was highly positively correlated with each of collapse, moisture content and normal shrinkage, and weakly negatively correlated with total external shrinkage. Collapse alone explained 47% of the variation in internal checking. Incidence of internal checking in sample boards could be estimated with moderate success by each of the following properties measured on board ends: collapse, the number of internal checks and initial moisture content. Material with high mean basic density above 530 kg/m3 was associated with low levels of internal checking and collapse. However, the maximum naturally occurring density of E. regnans was not high enough to obviate collapse and internal checking. It was observed that growth rings in 100 × 50 mm backsawn boards in which the earlywood air-dry density was below 450 kg/m3 showed internal checking. The size and number of internal checks increased with a decrease in earlywood density. It was shown that drying E. regnans below temperatures of 24–30 °C does not eliminate collapse, thus raising doubt about the validity of a temperature threshold concept in that range. Received 17 September 1997  相似文献   

4.
Reduction in forage production (FP) under trees in the humid tropics is well known, but information on how different levels of nitrogen (N) fertilizer influence FP under trees is meager. The present study reports effects of four N fertilizer levels (0, 60, 80 and 120 kg ha−1 N) on net soil N mineralization rate (NMR) and soil moisture (SM), FP, shoot biomass/root biomass ratio (SB/RB), N concentration in SB, N uptake and nitrogen use efficiency (NUE) of three grasses [guinea (Panicum maximum Jacq.), para (Brachiaria mutica (Forssk) Stapf) and hybrid-napier (Pennisetum purpureum Schumach.)] under three canopy positions [under canopy (UC, representing high shade), between canopy (BC, representing low shade) and open] of coconut trees (Cocos nucifera L.) in a coconut based silvopastoral system in the humid tropical climate of South Andaman Island of India. The study was performed for two annual cycles (2005–2006 and 2006–2007). The hypotheses tested were: (1) FP would decline under tree shades, both in N fertilized as well as no N fertilized conditions, when SM was not growth limiting in the open. However, amount of decline in the FP would depend on grass species and intensity of shades i.e., higher was the shade greater would be the decline; (2) N fertilizer would increase FP under tree shades, but the increase depended on grass species, intensity of shades and amount of N applied. Amount of N applied, however, would not annul the shades effects when SM was not growth limiting in the open. The study revealed that the tree reduced light 59% under UC and 32% under BC positions, but the N fertilizer levels increased NMR by 11–51% under UC and 3–44% under BC positions compared to the open. SM did not differ across the canopy positions. Under all situations, FP of all grasses declined under UC (47–78%) and BC (18–32%) positions compared to the open; the decline was greater in Hybrid-napier than Guinea and Para grasses. Forage production of all grasses increased with N fertilizer increments under all canopy positions reaching 32 t ha−1 dry matters for hybrid-napier at 120 kg ha−1 N in the open. Both guinea and para grasses outyielded hybrid-napier grass under UC but not under BC or in the open. N concentration in the forage (SB) also increased as N fertilizer level increased. These observations support our hypotheses and suggest that forage production under coconut palms can be increased by the application of N fertilizer with both guinea and para grasses being more productive than hybrid-napier grass under the high shade. Where light conditions are better, hybrid-napier would produce more forage than the other species.  相似文献   

5.
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   

6.
This study aimed at evaluating the influence of a silvopastoral system (SPS) composed of “Aroeira” trees (Myracrodruon urundeuva) on the nutritional value of Brachiaria brizantha cv. Marandu forage grass over the rainy season. The experiment was conducted in the SPS located in the “Cerrado” biome in Lagoa Santa County, Minas Gerais state, Brazil, in the agricultural year of 2004–2005. It was evaluated the influence of “Aroeira”, whose density in the area was 140 trees/ha, on the following parameters of the B. brizantha cv. Marandu forage grass: forage mass harvest above stubble height, morphogenic attributes, bromatological composition and nutritional value. The effects of “Aroeira” trees on the micro-climatic conditions were also evaluated. The experiment adopted a randomized block design with five blocks (cutting seasons), two treatments (a shaded pasture—B. brizantha cv. Marandu shaded by M. urundeuva—and a pasture in full sun—B. brizantha cv. Marandu in full sun), and three replicates. The tree component, composed of the tree species M. urundeuva in the experimental density adopted, increased dry matter and crude protein of the forage mass harvest above stubble height, without affecting the concentration of neutral detergent fibre or acid detergent fibre, thus causing dry matter and organic matter in vitro degradability as well as effective degradability of the forage grass to remain the same as those obtained in full sun. Therefore, the results of this study show the possibility of using trees and grass to increase both animal production and environmental services.  相似文献   

7.
Accurate identification of varieties (clones) and knowledge of their genetic relationships are essential for poplar breeding and variety management. In this study, 21 elite poplar varieties of Tacamahaca and Aigeiros in China were fingerprinted using amplified fragment length polymorphism (AFLP) markers. Four AFLP primer pairs developed generated totally 181 AFLP polymorphic fragments, and in particular, each primer pair generated fingerprint profiles specific to each of the tested varieties. The genetic relationships among the varieties were evaluated by dendrograms and multidimensional scaling (MDS). The results showed that the tested poplar can be classified into five groups, and indicated the clear separation of varieties of different sections of poplar and the primary distinction between native and exotic poplar varieties. This study indicated that tested poplar varieties could be identified by their fingerprint profiles and that genetic relationships deduced from the study were consistent with their genealogy. In addition, our results demonstrated that AFLP could be used to construct DNA fingerprints of polar clones at a large-scale level and to determine genetic relationships of poplar varieties. __________ Translated from Acta Botanica Yunnanica, 2006, 28(1): 85–90 [译自: 云南植物研究]  相似文献   

8.
A feeding experiment was conducted to study the effects of supplementation with dried Gliricidia sepium leaves on dry matter (DM) intake, digestibility and nitrogen retention in sheep fed KW4 elephant grass. Four mature rams were fed elephant grass ad libitum supplemented with four levels of gliricidia leaves (0, 4, 8 and 12 g DM kg−1 lwt day−1) in a 4 × 4 Latin square design. Supplementation with gliricidia leaves decreased elephant grass DM intake (g DM day−1 or g DM kg−1 BW0.75 day−1). However, the effect of supplementation on total DM intake of the rations was not significant (P >; 0.05). Total crude protein intake significantly (P < 0.001) increased with increasing levels of gliricidia supplementation. Total DM digestibility and body weight changes were significantly (P < 0.05) improved by gliricidia supplementation; with the highest digestibility coefficient (60.5%) and body weight gain (89.3 g/day) obtained at 8 g DM kg−1 lwt day−1. Gliricidia supplementation significantly (P < 0.001) improved nitrogen intake, absorbed nitrogen and retained nitrogen but with no significant difference at 8 and 12 g DM kg−1 lwt day−1 level of supplementation. The highest efficiency of N retention by sheep (44.9%) was obtained at 8 g DM kg−1 lwt day−1 level of gliricidia supplementation. The results indicated that supplemention of KW4 elephant grass with small quantities of gliricidia leaves up to 8 g DM kg−1 lwt day−1 enhance utilisation efficiency of the total ration. Further increases in the level of gliricidia supplementation, under the conditions of this experiment, reduced the intake of elephant grass leading to substitution effects of the basal. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

9.
Techniques for encouraging natural tree regeneration are of increasing interest to managers of Scots pine Pinus sylvestris forests. We tested prescribed fire at a management scale, with deer present or excluded, as a means of increasing rates of Scots pine forest expansion on heathland. At a semi-natural pinewood in Scotland, ten experimental blocks were established, within range of pine seed-fall. Each block comprised four, 100 m2 plots. Two plots at each site were burnt and two fenced, allowing the effects of burning on pine regeneration to be measured at two levels of deer abundance. We monitored pine seedlings, seed-fall, deer dung and vegetation for 5 years following treatment. Differences in seedling detection rates between treatments were quantified using dummy seedlings, and analyses corrected accordingly. Mean new pine seedling establishment was 9.8 times higher on burnt ground than unburnt ground (confidence intervals 3.2–30). Differences were even more pronounced in a year of high seed-fall, and following fires with low rates of spread. Establishment rates varied strongly between experimental blocks. Exclusion of deer increased establishment rates, but only in the first 2 years after fire. There was evidence that both seedling survival, and cumulative recruitment of older (over 12 months) seedlings, were improved by prescribed burning. Our results support the use of prescribed fire as a tool to promote increased Scots pine seedling establishment. This technique is likely to give strong fine-scale variation in seedling densities, and so would most suit areas where a variable spatial pattern of regeneration is sought, for landscape or naturalness reasons. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

10.
Multi-species tree-shrub-grass riparian buffer systems have been recognized as one of the most cost-effective bioremediation approaches to alleviate nonpoint source agricultural pollution in heavily fertilized systems. However, highly concentrated herbicides in surface and subsurface water and shade cast by trees along the stream bank usually compromise the effectiveness of these systems. Greenhouse trials and field lysimeter studies were conducted to evaluate the tolerance of orchard grass (Dactylis glomerata), smooth bromegrass (Bromus inermis), tall fescue (Festuca arundinacea), timothy (Phleum pratense), and switchgrass (Panicum virgatum) ground covers to atrazine and Balance™ (isoxaflutole) plus their capacity to sequester and degrade these herbicides and their metabolites. Their ability to remove soil nitrate was also quantified. Concentrations of atrazine, Balance™ and their metabolites in the leachate, soil and plant samples were determined by solid phase extraction followed by high performance liquid or gas chromatographic analyses. Distribution of the herbicides and metabolites in the system was calculated using a mass balance approach. Herbicide bioremediation capacity of each lysimeter treatment was determined by the ratio of metabolites to parent herbicide plus metabolites. Bioremediation of nitrate was quantified by comparing nitrate reduction rates in grass treatments to the bare ground control. Based on this herbicide tolerance, bioremediation data and shade tolerance determined in a previous study, it was established that switch grass, tall fescue and smooth bromegrass are good candidates for incorporation into tree-shrub-grass riparian buffer systems designed for the bioremediation of atrazine, Balance™ and nitrate.  相似文献   

11.
Growth and production in the first year, as additional selection criteria, were assessed for nine poplar clones to be used as short rotation woody crops (SRWC) in the production of biomass for energy purposes. In order to identify the most promising clones in terms of growth and yield and also to assess their stability, trials were established at different locations in Spain. The majority of these clones, which form part of the European list of base materials, have frequently been used in plantations aimed at timber production but not for biomass in Mediterranean conditions. Others, such as those selected in Italy specifically for biomass production (currently provisionally admitted), are being tested for the first time under different soil and climatic conditions in Southwest Europe. The early selection of clones for rapid juvenile growth provides a valuable additional input to the clonal selection process, especially where very short rotations are desired (no more than 3 years). In any case, determining clonal stability in terms of growth is of great use not only when deciding on the clones to be used in plantations but also when developing breeding programs. ANOVA and Genotype plus Genotype × Environment (GGE) biplot analyses were used to analyse the growth and stability of the clones, which were then ranked according to mean performance and stability. Differences were detected between clones as well as between the different environments tested. The biplot analysis allowed different groups of clones to be identified according to their performance and degree of interaction displayed, thus providing useful information for the selection process. The production of aboveground biomass in the first vegetative period ranged from 1.7 to 8.0 Mg DM ha−1 at the different sites. ‘Monviso’, ‘Guardi’, ‘AF2’ and ‘2000 verde’ were the most productive clones whereas ‘Unal’, ‘Pegaso’ and ‘USA 49-177’ were the least productive. The stability analysis identified ‘AF2’, ‘Guardi’, ‘I-214’ and ‘MC’ as more stable clones while ‘Monviso’, ‘2000 verde’, ‘Unal’, ‘Pegaso’ and ‘USA 49-177’ were found to be specifically adapted to certain environments. This implies that where information on site conditions is not available, the ‘AF2’ and ‘Guardi’ clones offer greater assurance of successful establishment and higher initial growth. The growth of ‘Monviso’ ‘2000 verde’ ‘Unal’ ‘Pegaso’ and ‘USA 49-177’ clones is highly dependent on site conditions during the establishment phase. Similarly, the SH (Shore Henares river) and LT (La Tallada) sites were identified as the most highly discriminative environments for the set of clones while CS (Cubo de la Solana) and AR (Atarfe) were identified as those where performance levels were average.  相似文献   

12.
THOMAS  P. H. 《Forestry》1967,40(2):139-164
This paper describes some recent experimental and theoreticalwork on the growth and spread of fire in the open and discussessome examples of field data in terms of the theoretical calculationspresented. The lengths of flames from laboratory fires have been relatedto the size and rate of burning of the fuel by formulae derivedfrom a simplified dimensional analysis. The effects of a windblowing across a long fuel bed on the length and orientationof flames are also described. The scaling laws for flame heightsuggest that in the horizontal spread of fire, heat transferfrom the flames above the fuel bed is important primarily withshallow fuel beds. It is suggested that the main effect of a wind on crib firesis aerodynamic. The wind deflects the advancing fire front fromthe vertical, but perpendicular to this deflected front therate of spread of fire, at least for cribs, is roughly the sameas in still air. However, a theory of spread allowing for heattransfer through the fuel bed and radiation from the flamespredicts that there can be a stable ‘fast‘ spreadas well as a ‘slow’ spread. In ‘fast’spread the flames are thick and control the spread. In ‘slow’ spread radiant heat transfer from theburning zone is usually responsible for the spread. The flamesare thin and of low emissivity. The most important factors determiningthe rate of ‘slow’ spread R are pb the bulk densityof the fuel bed and ø the deflection from the verticalof the front of burning fuel which varies with wind speed. Rpb cos ø is approximately constant over a wide rangeof conditions with an order of magnitude of 5–10 mg cm–2s–1.  相似文献   

13.
Mechanical properties and the visible and near infrared (NIR) (350–2500 nm) spectra obtained from longitudinal and transverse face of 155 small clear wood samples of Chinese fir (Cunninghamia lanceolata) were measured, and 103 of them were used to establish calibration models. Calibrations were tested on an independent set (52 samples). Differences between calibrations developed by using the longitudinal and transverse face were small. The calibrations developed by using NIR spectra (350–2500 nm) collected from transverse face were slightly inferior to those developed by using NIR spectra collected from longitudinal face. When reducing the spectral range to between 780 and 1050 nm, the calibrations developed by using NIR spectra collected from longitudinal face were slightly inferior to those developed by using NIR spectra collected from transverse face, and reducing the spectral range causes no decrease in the quality of the models developed using NIR spectra collected from transverse face. Partial lease square (PLS) modeling and test showed that calibrations developed using the visible and NIR spectra from transverse and longitudinal faces and calibrations developed by using the reducing spectral range (780–1050 nm) from the transverse face were moderate, and have a RPD range from 1.51 to 1.90. It is concluded that NIR spectroscopy can be used as an initial screening. __________ Translated from Journal of Northwest Forestry University, 2007, 22(5): 149–154 [译自: 西北林学院学报]  相似文献   

14.
Abies nordmanniana and Abies lasiocarpa, established for Christmas tree production in southwestern Norway (58°44′N, 5°38′E), were treated with different weed control methods, including chemicals, use of black plastic mulch, grass or clover as ground cover, living mulch and mechanical hoeing. Ground cover with black plastic mulching resulted in the best growth and quality in A. lasiocarpa; the least favourable treatment was when grasses were allowed to grow close to the trees. Unless measures were taken to remove this competing vegetation, the ground cover grew over the trees, smothering 94% of them. A. nordmanniana plants grew to the same height on plots with no weed control as on plots with thorough weed eradication. Stem diameter decreased on plots with ground vegetation compared to seedlings grown in the weed-free environment. The use of Trifolium repens as ground cover decreased height growth by 30% compared to thorough weed control. Both grasses and clover sown as living mulch, damaged the trees more than did natural weed vegetation.  相似文献   

15.
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   

16.
We conducted a two-factor experiment in randomized com- plete block design with four replications during 2004 in El Demokeya Forest Reserve and El Himaira Natural Forest, North Kordofan State, Sudan. The objective was to develop an understanding of the ecological effects of under-story vegetation and tapping date on the productivity of gum arabic from Acacia senegal as over story cover. The first factor was grass cover which was tested in four levels (100% and 50% grass cover in addition to bare and burnt). The second factor, date of tapping was tested in three levels namely (1st Oct, 15th Oct and 1st Nov). The first picking was done after 45 days from tapping and the gum yield up to seven pickings was collected at intervals of 15 days. Gum yield from each picking was collected and weighed using sensitive balance. Analysis of variance was carried out using MSTAT-C statistical package, and the Tukey test was applied for mean comparisons. The results showed highly significant differences (p<0.01) of grass cover on gum arabic yield in the two sites for most of the first consecutive pickings (1st-4th out of seven) in addition to total yield (kg/ha). With exception to the 4th pickings, the interaction effect between the grass densities and tapping date was not significantly different. The total gum yield was significantly (p<0.05) increased in only two pickings (third and fourth) in El Demokeya Forest Reserve and two pickings (1st and 2nd) at El Himaira Natural Forest. The density of grass cover significantly (p<0.05) affected the number of pickings at both sites; the number of gum pickings was directly proportional to grass density. The number of gum pickings was found to be significantly (p < 0.05) increased at the early date of tapping.  相似文献   

17.
土壤消毒处理是一种被广泛采用、积极有效的防治温室病虫草害的方法。目前普遍采用的甲基溴等化学试剂熏蒸方法对人类健康和自然生态环境有害，为解决这一问题，对微波消毒土壤进行了探索。采用不同功率的微波辐射进行土壤消毒处理，并与常规加热处理效果对比，对处理后土样中微生物的杀灭效果进行检测。结果表明，采用自动控温的微波消毒温室土壤装置可以有效杀灭土壤中的微生物和草籽，控制病虫草害，改善土壤环境。采用自动控温的微波消毒温室土壤装置消毒土壤是替代甲基溴等化学试剂熏蒸及其他物理消毒土壤的较好方法。  相似文献   

18.
Since the shelterbelt systems of 1,092,260 hm~2have been established for thirteenyears from 1978,have formed 526,541 networks and protected 13,619,400 hm~2 land in westernpart of Northeast region of China.According to the research work we did in the last five years,the results of research project showed that the shelterbelts had improved the environmentsignificantly.A parameter of comprehensive effects of temperature,moisture and wind in thenetworks(E_c=246.52-12.17E+0.58T+6.58U)which is an active method to estimate the effects ofshelterbelt on farmland,is around 21.1-30.9mm/month improving the moisture state in dryseason,helping the crop yield increasing on the average by 19.8%.The effective accumulatedtemperature(≥10℃)incrcases by 71℃;the cropland area which suffered from wind and frostdamage decreases by 80-90%,the grass coverage on the pastureland and grass production in-creases by 13% and by 49.4-72%,rough protein,rough fat and nitrogen-free extract of grassincrease by 3.34%,2.4% and 8.4%separat  相似文献   

19.
In direct-seeded woodlands and nursery seed-beds, weeds canrapidly invade newly sown areas, leading to death or suppressionof tree seedlings. Hand weeding is usually expensive, and thesafe use of broad-spectrum contact herbicides is seldom possible.Hence in the work reported here, the tolerance of young treeseedlings to the potentially more selective, post-emergenceherbicides clopyralid, cycloxydim and metazachlor, was tested.Seedlings of Fraxinus excelsior L. (ash) with two to four expandedtrue leaves (2–4 ETL), Fagus sylvatica L. (beech) (2–4ETL), Acer pseudoplatanus L. (sycamore) (4–6 ETL), Prunusavium L. (cherry) (6–8 ETL) and Quercus robur L. (oak)(6–8 ETL) appeared to tolerate applications of cycloxydimat a rate of 0.45 kg a.i. ha–1. Applications of 0.2 kga.i. ha–1 clopyralid or 1.25 kg a.i. ha–1 metazachloralso appeared to be generally tolerated, but did cause somesuppression of annual growth increment in Q. robur, P. avium,F. sylvatica and A. pseudoplatanus, particularly where repeatapplications were made to the earliest growth stages. Seedlingsurvival was unaffected by any herbicide treatment. Mixturesof all three herbicides were no more damaging than the sameherbicides applied separately. Therefore, depending on treespecies and growth stage, it appears that clopyralid could potentiallybe safely used to control a range of herbaceous weed species,metazachlor a variety of seedling or germinating weeds and cycloxydima range of established grass weed species, in direct sown woodlandsor nursery seed-beds, although further research is advisableto confirm crop safety.  相似文献   

20.
The potential for agricultural soils to act as a sink and sequester carbon (C) or a source and emit carbon dioxide (CO2) is largely dependent upon the agricultural management system. The establishment of permanent vegetation, such as trees and grass contour buffer strips, may cause accumulation of above- and below-ground C over time, thereby acting as a sink for tropospheric CO2. However, the effects of contour grass strips and grass-tree strips (agroforestry) on soil CO2 emissions have not been extensively studied in row-crop watersheds in the temperate regions. The objective of this study was to determine the effects of agroforestry and grass contour buffer strips and landscape position on soil surface efflux rate of CO2 in three adjacent agricultural watersheds with claypan soils in northeast Missouri. The three watersheds were in a corn-soybean rotation, and contained (1) cropped only (CR), (2) cropped with grass contour strips (GR), or (3) cropped with tree-grass contour strips (AF) management systems. Soil surface CO2 efflux was measured throughout the 2004 growing season at the upper (UBS), middle (MBS), and lower (LBS) backslope landscape positions within the three watersheds. The cumulative soil CO2 production was lowest in the CR (0.9 kg CO2-C m−2) compared to the AF (1.5 kg CO2-C m−2) and GR watersheds (1.5 kg CO2-C m−2). The lower backslope position (1.6 kg CO2-C m−2) across all three watersheds produced 32 and 40% greater cumulative soil CO2 than the upper and middle backslope positions, respectively. A 72-day incubation study determined the effects of 40, 60, 80, and 100% soil water-filled pore space (WFPS) and N rate (0 and 1.39 g KNO3 kg soil−1) on soil CO2 efflux from bulk soil collected under each management system. The cumulative CO2 production was highest in the grass soil (1,279 mg CO2-C kg soil−1) compared to the agroforestry (661 mg CO2-C kg soil−1) and cropped (483 mg CO2-C kg soil−1) soils regardless of WFPS and N rate. The highest cumulative CO2 production for the grass soil (1,279 mg CO2-C kg soil−1) occurred at 80% WFPS, and was approximately 2 to 2.6 times greater than the agroforestry and cropped soils at 80% WFPS. The results of this study indicate that conservation management practices, such as grass and grass-tree contour buffer strips, and landscape position affect soil surface CO2 production and accumulation of soil organic C that may influence soil C sequestration.  相似文献   

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