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101.
采取清水浸泡、药物蒸煮、干燥和PC树脂浸渍处理等措施,对易裂难干、易发生翘曲变形、使用价值较低的枫香木材进行改性处理,可以显著降低其干缩差异,减少翘曲变形,实现均匀干燥.从而大大改善其加工性能和耐腐程度,提高利用价值.实践证明,以浸泡时间为6个月,蒸煮时间为48h,药量配比为1号药液:2号药液=0.5%:1.5%进行改性处理的效果最为理想. 相似文献
102.
M.E.?Isaac A.M.?GordonEmail author N.?Thevathasan S.K.?Oppong J.?Quashie-Sam 《Agroforestry Systems》2005,65(1):23-31
The conversion of forests to agroecosystems or agroforests comes with many changes in biological and chemical processes. Agroforestry,
a tree based agroecosystem, has shown promise with respect to enhanced system nutrient accumulation after land conversion
as compared to sole cropping systems. Previous research on tropical agroforestry systems has revealed increases in soil organic
matter and total organic nitrogen in the short term. However, research is lacking on long-term system level sustainability
of nutrient cycles and storage, specifically in traditional multi-strata agroforestry systems, as data on both the scope and
duration of nutrient instability are inconclusive and often conflicting. This study, conducted in Ghana, West Africa, focused
on carbon and nitrogen dynamics in a twenty-five year chronosequence of cacao (Theobroma cacao Linn.) plantations. Three treatments were selected as on-farm research sites: 2, 15 and 25-year-old plantations. Soil carbon
(C, to a depth of 15 cm) varied between treatments (2 years: 22.6 Mg C ha−1; 15 years: 17.6 Mg C ha−1; 25 years: 18.2 Mg C ha−1) with a significant difference between the 2- and 15- and the 2- and 25-year-old treatments (p < 0.05). Total soil nitrogen in the top 15 cm varied between 1.09 and 1.25 Mg N ha−1 but no significant differences were noted between treatments. Soil nitrification rates and litter fall increased significantly
with treatment age. However, photosynthetically active radiation (PAR) and soil temperature showed a significant decrease
with age. No difference was found between decay rates of litter at each treatment age. By 25 years, system carbon sequestration
rates were 3 Mg C ha−1 y−1, although results suggest that even by 15 years, system-level attributes were progressing towards those of a natural system. 相似文献
103.
日光温室内作物干物质积累预测新方法研究 总被引:2,自引:0,他引:2
介绍了一种有效结合神经网络和作物生长模型预测目光温室内作物干物质积累的方法,该方法既解决了经验模型的解释性和广适性差的缺点,又解决了机理模型难以理解和使用、输入多而输出欠稳定的不足。以有效光照积累和有效积温作为输入参数,以作物的干物质积累作为输出参数建立神经网络,利用大量实测数据对神经网络结构进行训练,建立作物干物质积累与有效光照累积和有效积温之间的关系,从而对干物质积累进行预测。并以目光温室内黄瓜为例,采用此方法对其进行干物质积累的预测,与实际测量结果相比较,误差率不超过10%。 相似文献
104.
The performance (survival and growth) of Douglas-fir (Pseudotsuga menziesii Mirb. Franco.) seedlings planted in minimally disturbed, scalped, and bedded soils, both with and without herbicidal control of weeds, were compared. Douglas-fir growing for 3 years in bedded soils treated with herbicide were heavier, taller, and had deeper root systems than trees growing in other preparations. Scalping did not improve seedling performance when compared to minimally disturbed soils. Soils rich in organic matter benefited tree growth. Competing vegetation in raised beds was detrimental to seedling performance. 相似文献
105.
Field trials were carried out on an Oxic Paleustalf in the humid zone of southwestern Nigeria withLeucaena leucocephala (Lam.) de Wit,Gliricidia sepium (Jacq.) Steud. andSesbania grandiflora (L.) Pers. alley cropped with maize and cowpea. The three leguminous woody species were grown in hedgerows spaced at 2 m. Trials were carried out one year after establishment of the hedgerows using a split-plot design with four replications. TheLeucaena trial had twenty pruning combinations consisting of five pruning heights (25, 50, 75, 100 and 150 cm) and four pruning frequencies (monthly, bi-, tri- and six-monthly). TheGliricidia andSesbania hedgerows were subjected to nine pruning intensities consisting of three pruning heights (25, 50 and 100 cm) and three pruning intensities (monthly, tri- and six-monthly).For the three woody species, biomass, dry wood and nitrogen yield from the hedgerow prunings increased with decreasing pruning frequency and increasing pruning height. Biomass, dry wood and nitrogen yields were in the following orderLeucaena >Gliricidia >Sesbania.The various pruning intensities had no effect on survival ofLeucaena plants. Pruning frequency had a larger effect than pruning height on survival ofGliricidia andSesbania plants. With monthly pruning, about 25 percent of theGliricidia and all of theSesbania plants died within six months of repeated pruning. Even with lower pruning frequencySesbania plants showed lower survival rates thanGliricidia orLeucaena.The various pruning intensities of all the hedgerow species had more pronounced effects on the grain yield of the alley cropped cowpea than on maize grain yield. Higher maize and cowpea yields were obtained with increasing pruning frequency and decreasing pruning height.IITA Journal paper number 335 相似文献
106.
L. Alpízar Professor H. W. Fassbender Coordinator J. Heuveldop Professor H. Fölster G. Enríquez 《Agroforestry Systems》1986,4(3):175-189
The agroforestry systems of cacao (Theobroma cacao) under laurel (Cordia alliodora) and cacao under poro (Erythrina poeppigiana) were studied at CATIE, Turrialba, Costa Rica. An inventory was taken of the organic matter and nutrients (N, P, K, Ca, and Mg) separating the species into their compartments (leaves, branches, trunks and roots). Studies of the litter and of the mineral soil (0–45 cm) yielded these results:
Patterns of nutrient accumulation are discussed in relation to the characteristics of these agroforestry systems. 相似文献
107.
Variations in soil chemical properties and microbial biomass in artificial gaps in silver fir stands
Changes in soil chemical and microbiological parameters in small (185 m2) and medium (410 m2) gaps, created in mature silver fir (Abies alba Mill) stands (mean height 30 m) in the Calabrian Apennines (Southern Italy), were studied over 2 years. Medium gaps had high
soil temperature and photosynthetically active radiation (PAR) transmittance and low soil moisture. Within small gaps we detected
a greater amount of organic matter, with respect to under canopy cover sites and medium gaps. Moreover, a different trend
of the organic matter between small and medium gaps was observed. In the medium gaps, with respect to under canopy cover sites
and small gaps, we found a relatively low content of organic matter, associated to a lower amount of humic acid, which suggested
that the organic substrate undergoes a mineralization rather than a humification process. An opposite trend was observed in
small gaps, where the increase of organic matter content, associated to an increase of humic acid and microbial biomass, suggested
a better humification process. Moreover, in small gaps the highest level of urease and the greatest fluorescein diacetate
(FDA) hydrolysis were observed. The different trend of organic matter observed in small and medium gaps may be related to
changes in the environmental conditions. PAR transmittance, significantly higher in medium gaps, contributed to increase soil
temperature and decrease soil moisture, affecting soil microbial populations and organic matter trend. These results suggest
that the creation of small gaps represents the silvicultural practice with minor environmental impact. 相似文献
108.
109.
The relationship of branch cross sectional area (CS) to leaf biomass (LM) and leaf area (LA) was studied in three agroforestry tree species,Calliandra calothyrsus Maissn.,Erythrina berteroana Urban andErythrina poeppigiana (Walpers) O.F. Cook, to develop a non-destructive method for the estimation of LM and LA for trees managed with periodic pruning. Variation in these relationships was observed according to the bifurcation level and, in theErythrina spp., by clone. All the relationships were linear except the CS-LM relation in small branches ofE. poeppigiana, where it was initially exponential. At main branch level the relationship of CS to LM and LA was linear in all cases but the regression parameter values varied between species and clones, with determination coefficient (R2) 0.88–0.99. It was concluded that the ratio of main branch CS to LM and LA can be used for non-destructive estimation of the latter variables. The method has the additional benefit that the regression parameter value reflects the allocation of dry matter within a tree and, consequently, may give indications about its possible uses in different agroforestry systems.Work carried out at the Centro Agronómico Tropical de Investigación y Enseñanza (CATIE), Turrialba, Costa Rica. 相似文献
110.
不同母岩母质上土壤特性的分析与研究 总被引:1,自引:0,他引:1
不同的母岩母质,一般形成不同性质的土壤。分析研究不同母岩母质上发育的土壤特性,对于指导农林业生产具有重要的意义。本文仅就河北省西陵地区几种主要母岩质上发育的土壤做了初步的分析。经研究发现,不同母岩母质上发育形成的土壤,其物理化学性质都存在很大的差异。 相似文献