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The herbicide, hexazinone, was applied four ways over ponderosa pine, 2–0 seedlings planted in northeast Oregon. The four treatments were two broadcast applications, a single broadcast application, a large spot application, and a small spot application. Seedling survival and growth were monitored for five growing seasons. Results indicate that survival more than doubled with either large or small spot applications compared to no application, and either one or two broadcast applications can increase survival an additional 30% over spot applications. Differences in stem volume were substantial, with two broadcast applications yielding more than twice the volume of a single broadcast treatment and more than five times the volume of seedlings treated with spot applications. Trees in small spots were still three times bigger than surviving seedlings in the control. These results are consistent with the concept of competition threshold. Management implications were considered in terms of cost of established seedlings. Although broadcast applications cost more per acre than spot applications, gains in seedling survival, growth and quality offset the additional cost and translate into lower established seedling costs. The cost effectiveness of broadcast applications also may be seen in the elimination of replanting or in-planting requirements and increases in long-term growth potential of the established trees. 相似文献
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Microbial biomass and mineralization of atrazine [2-chloro-4(ethylamino)-6(isopropylamino)s-triazine] and 2,4-D (2,4-dichlorphenoxyacetic acid) were examined in the top 10 cm of riparian pasture soils and in the litter layer and top 10 cm of mineral soils of riparian forest ecosystems. The riparian forest litter had higher levels of active and total fungal biomass than forest or pasture mineral soils in winter, spring, and fall. Active bacterial biomass was higher in forest litter than in forest and pasture mineral soils in spring and autumn, and higher in forest mineral soils than in pasture soils in summer. Total bacterial biomass was higher in forest mineral soils than in pasture soils during all seasons. In spring, it was also higher in forest litter than in pasture soils. Atrazie and 2,4-D mineralization in pasture soils was exceeded by that in forest litter in spring and autumn and by that in forest mineral soils in summer and autumn. There was no correlation between either active or total fungal and bacterial biomass with pesticide degradation. 相似文献
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Status of uneven-aged management in the Pacific Northwest, USA 总被引：1，自引：0，他引：1
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Resource sharing between tree and forage plant components in silvopastoral systems includes a complex set of facilitative and competitive interactions. To the extent that facilitation exceeds competition, agroforests are expected to outyield monocultures of their components. Pasture and Douglas fir (Pseudotsuga menziesii) tree production of young agroforests was compared to pasture and forest monocultures under both grid and cluster patterns of tree planting near Corvallis, Oregon, USA, during 1983–1987. The height and diameter growth of forest and agroforest trees was similar, regardless of tree planting pattern. Five-year average annual forage production was 6500, 5800, and 2800 kg ha–1 on pasture, agroforest, and forest plots, respectively. The total cumulative 1982–1987 above-ground phytomass yield of forage plus trees was similar for pasture and conventional grid forest monocultures. The total productivity of agroforests, however, was over 30% greater than either pasture or forest components grown in monoculture. Approximately 1.6 ha (0.96 ha forest + 0.64 ha pasture) of monocultures would be needed to equal the productivity of 1 ha of agroforest.Oregon Agricultural Experiment Station Technical Paper No. 10, 825. 相似文献
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The influence of nitrogen on atrazine and 2,4-dichlorophenoxyacetic acid mineralization in grassland soils 总被引：2，自引：0，他引：2
James A. Entry Kim G. Mattson William H. Emmingham 《Biology and Fertility of Soils》1993,16(3):179-182
The influence of fertilizer N on the mineralization of atrazine [2-chloro-4(ethylamino)-6(isopropylamino)-s-triazine] and 2,4-D (2,4-dichlorophenoxyacetic acid) in soils was assessed in microcosms using radiometric techniques. N equivalent to 0, 250, and 500 kg N as NH4NO3 ha-1 was added to three grassland soils. Compared to the control, the 250- and 500-kg treatments suppressed mineralization of atrazine by 75 and 54%, respectively, and inhibited mineralization of 2,4-D by 89 and 30%, respectively. Active fungal biomass responded to the N treatments in an opposite manner to herbicide mineralization. Compared to the control, the 250- and 500-kg treatments increased the active fungal biomass by more than 300 and 30%, respectively. These results agree with other observations that N can suppress the decomposition of resistant compounds but stimulate the primary growth of fungi. The degree of suppression was not related to the amount of N added nor to the inherent soil N levels before treatment. The interaction between the N additions and the active fungal biomass in affecting herbicide mineralization suggests that N may alter microbial processes and their use of C sources and thus influence rates of herbicide degradation in the field. 相似文献
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Livestock may provide important service and production functions in agroforestry systems. However, use of livestock in conifer/improved pasture agrosilvopastoral systems is currently limited by concerns about potential damage to trees by livestock. Effects of sheep grazing on Douglas-fir (Pseudotsuga menziesii) trees in two patterns of sheep/pasture/conifer agroforest (cluster and grid plantations) were studied from 4 years after planting (1983) until the first precommercial thinning at age 10 years (1988). Trees averaged over 1 m in height when grazing began in summer 1983. Some browsing of tree lateral branches by sheep occurred regardless of grazing season in 1983–1985. However, the 2 to 10% of current year's lateral branch growth removed by grazing sheep was too low to impact tree growth. Sheep removed the terminal leaders from only 3 to 9% of trees each year during 1983–1985. Most browsing of terminals occurred in the summer when other forages had become mature and were relatively unpalatable to sheep. Less than 13% of agroforest trees were debarked by sheep each year during 1983–1987. By the end of grazing in 1987, less than 8% of agroforest trees had sustained a level of debarking likely to impact future growth (>50% of tree circumference debarked). Grazing had no discernible effect upon tree diameter or height in any year (P > 0.05). Total tree mortality attributable to sheep grazing during 1983–1987 was only 0.9%, including three trees girdled by sheep and two debarked trees which were subsequently attacked by insects. Overall, grazing had no detrimental impact on timber stand growth or mortality.Submitted as Oregon Agricultural Experiment Station Technical Paper No. 9628. 相似文献
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Underplanting conifers beneath thinned hardwood stands could shorten conversion to a more valuable crop species. Thinning the hardwoods to final crop-tree spacing could increase growth and marketable volume while releasing the site resources necessary to support conifers planted in the understory. In western Oregon, an experimental thinning of a 14-year-old red alder (Alnus rubra Bong.) stand provided an opportunity to test this concept. Initial efforts were directed toward testing survival and growth of wilding seedlings of western hemlock (Tsuga heterophylla [Raf.] Sarg.) planted in thinned and unthinned alder stands. Survival averaged 78% and 52% after the first and fifth growing seasons. Fifth-year height growth of surviving seedlings averaged from 38 to 49 cm under various thinning regimes but only 9 cm in the unthinned. Wildlife browsing and the pinning of seedlings by falling debris reduced growth and survival. 相似文献
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Plant-soil-water relations of a silvopastoral system composed of a Douglas-fir (Pseudotsuga menziesii) timber crop, subterranean clover (Trifolium subterraneum) as a nitrogen-fixing forage, and tall fescue (Festuca arundinacea) as a forage crop were investigated near Corvallis, Oregon, during 1983–1986. Treatments included all possible combinations of two tree-planting patterns (trees planted 2.4 m apart in a grid, and groups of five trees spaced 7.6 m between clusters) and two grazing/understory management systems (agroforests were seeded to subclover and grazed by sheep; forests were unseeded and ungrazed).Mean twig xylem water potential (XWP) for Douglas-fir trees ranged from –0.3 to –1.5 MPa on forest plots and from –0.3 to –1.2 MPa on agroforest sites. Pre-dawn and sunset XWP were more negative for forest than for agroforest plots during dry summer periods. Midday XWP was similar for both agroforest and forest plots on all dates. Soil water content at 50–100 cm depth was greater under agroforest plots as compared to forest plots in 1984, but not in 1985 (unusually dry spring). Average foliage nitrogen content of tree needles was 1.54% vs. 1.43% for agroforests vs. forests, respectively.Our data are consistent with the hypotheses that: (1) grazing of understory vegetation may reduce water stress of trees during dry periods by reducing transpirational water use by the forage plants; and (2) nitrogen-fixing vegetation combined with grazing increases nitrogen uptake of associated trees. However, neither mean foliar N nor average XWP differences experienced by trees in agroforest versus forest plantations were sufficient to have an effect on tree growth. Our data demonstrate that it is possible to produce a second crop (i.e. forage grazed by sheep) in timber plantations without reducing the growth of the main tree crop.Submitted as Oregon Agrocultural Experiment Station Technical Paper No. 10109. 相似文献
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