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881.
Designing pest-suppressive multistrata perennial crop systems: shade-grown coffee in Central America
During most of its cultivation in Central America, coffee (Coffea arabica L.) suffered few serious pest problems. However, over the past three decades, three factors contributed to significantly
increase pest levels and losses: the recent introduction of new pests; more favorable conditions for existing pests, diseases,
and weeds due to lower shade levels; and secondary pest problems caused by pesticide use. The strategy of maximizing coffee
production with pest control dominated by synthetic pesticides has not only increased yields substantially, but also production
costs, pesticide resistance, and both human health and environmental risks. An analysis of the response of the food web in
coffee plantations to varying levels of light and humidity associated with different shade levels provides the basis for identifying
the optimum shade conditions which minimize the entire pest complex and maximize the effects of beneficial microflora and
fauna acting against it. These optimum shade conditions for pest suppression differ with climate, altitude, and soils. The
selection of tree species and associations, density and spatial arrangement, as well as shade management regimes are critical
decisions for shade strata design. Site-specific knowledge of the seasonal food web dynamics permits growers to determine
the appropriate seasonal shade management in order to further suppress pest levels. For example in a low-elevation dry coffee
zone, 35 to 65% shade promotes leaf retention in the dry season and reduces Cercospora coffeicola, weeds, and Planococcus citri; at the same time, it increases the effectiveness of microbial and parasitic organisms without contributing to increased
Hemileia vastatrix levels or reducing yields. In these conditions, shade should be at a maximum early in the dry season and at a minimum by
the middle of the rainy season. Further research is needed on: the effects of individual tree species on the food web; the
role of canopy architecture for coffee vigor, photosynthesis, leaf drying, pest susceptibility, and pruning regimes; and on
simple observation methods and decision criteria for farmer management of tree-coffee-food web interactions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
882.
沙柳的材性对刨花板生产工艺的影响 总被引:1,自引:2,他引:1
论述了沙柳的材性对刨花板生产工艺和产品质量的影响,并根据分析结果讨论了目前沙柳刨花板的生产工艺,测试了沙柳刨花板的物理力学性能,针对测试结果提出了改善刨花极性能的措施。 相似文献
883.
884.
The effect of compression and incision on wood veneer and plywood physical and mechanical properties
Maija Kymäläinen Akio Yamamoto Kasperi Sokka Lauri Rautkari 《Wood material science & engineering》2020,15(2):97-103
ABSTRACTDrying takes the largest share of energy in plywood production, and varying moisture content of veneers necessitates re-drying that often leads to over-dry veneers with deactivated surfaces, which may promote imperfect bonding. In order to decrease the drying time, reduce the need for re-drying of veneers, and improve the quality of plywood, birch and spruce veneers were subjected to pre-treatment by cold compression, incision, or a combination of the two. The effects of pre-treatment on the veneer and plywood quality were assessed by standard tests. Compression had a beneficial effect on water removal of the wettest veneers (spruce sapwood (SW) and birch), but some thickness reduction was observed in the veneers as well as the finished birch plywood. Compression led to thickness reduction of spruce veneers, but had no effect on SW plywood thickness likely due to higher viscoelasticity. Both compression and the combination of incising and compression levelled the moisture variation within the compressed stacks. Incision improved the modulus of elasticity of birch plywood, shear strength of SW plywood, and both bending and shear strengths of heartwood plywood. Higher surface pressure decreased the drying time of spruce SW in both plain compression and combined incision and compression pre-treatment. 相似文献
885.
南方铁杉与长苞铁杉物理力学性质研究 总被引:1,自引:0,他引:1
本文对产于福建省武夷山市的南方铁杉和连城县的长苞铁杉进行了较系统的材性试验研究,提供了必要的该铁杉属木材的物理力学性质指标。 相似文献
886.
不同树龄福建马尾松KP法制浆性能的评价 总被引:5,自引:1,他引:5
为了合理采伐、有效利用资源,对3种不同树龄的福建戏剧性以进行性制浆性能比较。测定了它们的纤维形态和化学组成;优选出各自的最佳蒸煮工艺;测定了浆物理强度;并对漂白性能作了研究;最后用卒 标评定法全面评价它们的制浆性能。得出20年树龄马尾松制浆性能优良,10年次之,30年较差的结论。 相似文献
887.
888.
通过对北京低山地区土壤的理化性质和脲酶、过氧化氢酶以及多酚氧化酶的分析,探讨了供试土壤中3种酶活性状况及其与土壤理化性质的关系。研究结果表明:3种土壤酶活性均表现出随土壤深度增加而降低的规律性;3种土壤酶活性间具有良好相关性,显示了3种酶在土壤生物化学过程中的共性关系;土壤酶活性同多种土壤性质呈现良好相关性,其中,土壤有机质含量和土壤全氮量对酶活性影响最大。 相似文献
889.
890.
经调查纳曼干脊虎天牛(Xylotrechus namanganensis Heydel.)在新疆北部危害钻天榆等近20种阔叶树,造成严重危害,在克拉玛依市一年发生1代,以老熟幼虫在树干内越冬,每年4月中旬至7月中下旬都能见到成虫,卵和幼虫,各龄幼虫终年可见,在该天牛上发现了3种寄生蜂;脊虎天牛菜洛茧蜂,长腹盾长茧蜂(国内新记录)和酱色齿足茧蜂;3种寄生真菌:球孢白僵菌=腐皮镰孢和亮白曲霉。 相似文献