共查询到20条相似文献,搜索用时 125 毫秒
1.
对国外农业网站进行了整体调研,以随机抽取的40个国外农业网站为样本,对网站进行了分类总结,分析了典型网站中的内容、现状和问题,对农业网站发展前景进行了展望。 相似文献
2.
农业网站是加快农业信息传递和传播的重要载体,针对当前我国农业网站发展的基本现状,分析了农业网站发展中服务定位不清晰、运营效率不高、盈利模式不明确等发展"瓶颈"问题,指出农业网站的发展壮大需要通过从明晰网站定位、分离网站所有权与经营权和创新网站盈利模式上来解决,对农业网站形成合理的运营机制,更好地服务"三农",具有重要的借鉴和指导意义。 相似文献
3.
4.
本文建立了中国农业网站数量与国内网站总量预测两个回归模型,通过对比分析和实际分析,提出了"中国农业网站数量呈线性增长模式,国内网站总量呈非线性增长模式"的结论。 相似文献
5.
6.
7.
互联网技术的迅速发展推动了科技的进步与信息的迅速传播,农业网站利用现代技术服务"三农"、推动产业升级,是现代农业发展的重要体现和重要标志。通过对当前农业网站建设情况的分析,结合农业行业特点,总结了开展农业网站评价的方法与原则,提出了一套适合农业网站的评价指标体系,为农业网站建设提供参考。 相似文献
8.
比较分析了国内外农业网站建设的成功经验,论述了农业网站在现代农业发展中的作用,全面阐述了目前佛山农业网站的建设现状,提出了佛山农业网站可持续发展的措施。 相似文献
9.
10.
11.
12.
土壤环境质量指导值与标准研究Ⅳ.保护人体健康的土壤苯并[a]芘的临界浓度 总被引:6,自引:0,他引:6
:基于人体健康风险评估制定土壤环境质量指导值或标准是当前国际上广泛采用的方法.本文全面调研了国际上保护人体健康的土壤苯并[a]芘(B[a]P)的各类临界浓度,初步确定了量化土壤中B[a]P暴露剂量的暴露场景和暴露参数,率先提出了制定我国土壤中保护人体健康的B[a]P临界浓度的方法体系,这种方法可用来制定持久性有机污染物的土壤临界浓度.考虑了口腔摄入、皮肤接触、呼吸摄入和取食污染蔬菜摄入四个主要暴露途径,探讨了B[a]P的致癌风险水平为10-5或10-6时,农业用地、居住用地和工业用地方式下土壤中B[a]P的临界浓度,同时制定了保护地下水的土壤B[a]P的临界浓度. 相似文献
13.
14.
Abstract. Simulated estimates of crop yield were made for rainfed rice in a 50 ha dryland rice area. The aim was to investigate how soil units and management units of different sizes with different yields could be used to obtain values for areas of land. Two procedures were applied. First, yields were simulated at six sites, that were representative of six soil mapping units. Second, yields were simulated using soil information from 133 auger sites, and were interpolated over management units using block kriging. Differences between the two procedures for the total area and for a test set of 22 additionally sampled locations were small. A 60% increase in precision was achieved when relatively large management units were defined.
A Geographical Information System was used to identify areas with greatest yield potential for rainfed dryland rice. Statistical analysis showed that the six soil units could be grouped into three yield classes. The largest yields were obtained for a sub-area comprising 11% of the survey area which was associated with a slowly permeable Bg horizon in the soil profile.
It was concluded that the best procedure for the spatial interpolation of simulated rice yield should be based on preliminary simulation of crop yields. A sensitivity analysis of the impact of weather variability and soil heterogeneity on the variation of yield was useful to detect the importance of their contributions. The procedures developed in this study are of value in obtaining a reliable estimate of average yield, and can consequently be used for associated cost-benefit calculations. 相似文献
A Geographical Information System was used to identify areas with greatest yield potential for rainfed dryland rice. Statistical analysis showed that the six soil units could be grouped into three yield classes. The largest yields were obtained for a sub-area comprising 11% of the survey area which was associated with a slowly permeable Bg horizon in the soil profile.
It was concluded that the best procedure for the spatial interpolation of simulated rice yield should be based on preliminary simulation of crop yields. A sensitivity analysis of the impact of weather variability and soil heterogeneity on the variation of yield was useful to detect the importance of their contributions. The procedures developed in this study are of value in obtaining a reliable estimate of average yield, and can consequently be used for associated cost-benefit calculations. 相似文献
15.
《Communications in Soil Science and Plant Analysis》2012,43(12):1417-1424
ABSTRACTSoil salinity and sodicity are two important factors in land degradation, especially in arid and semi-arid regions of the world. Application of soil amendments, such as organic matter, can be a suitable method for improving the fertility of saline-sodic soils. In this research, a saline-sodic soil was chosen, mixed with three levels of 1%, 3%, and 5% (weight) of Cow manure, Vermicompost, and Azolla, and incubated for 5 months at field capacity and a temperature of 20°C. Then, safflower seeds were planted and treatments were placed in a greenhouse for two months. After this period, plant indices were measured. The results showed that the addition of treatments caused differences in safflower growth in comparison to the control treatment. The noted differences were mostly negative for the treatment of cow manure, they were negligible for Azolla, and were positive for Vermicompost. Vermicompost applied at 5% level provided the most suitable substrate for safflower growth in saline-sodic soil. 相似文献
16.
不同氮水平下玉米苗期根系形态和氮吸收量的 QTL 定位 总被引:4,自引:2,他引:2
17.
Alexander Bruckner John Wright Christian Kampichler Roswitha Bauer Ellen Kandeler 《Biology and Fertility of Soils》1995,19(2-3):257-262
Equipment and handling methods for the preparation of soil mesocosms were developed. The mesocosms were used to investigate the interrelationships between mesofauna and microflora in a coniferous forest soil. Soil monoliths were taken from the ground, defaunated by deep-freezing, wrapped in nets to control reimmigration of different faunal size-classes, and replanted in the field for 8 months. in a practical test the technique described here proved to be an inexpensive field method for producing a replicated series of mesocosm in a short time. Deep-freezing is appropriate for defaunating soil monoliths. The fine nets effectively exluded meso-and macrofauna. No significant differences were found in the abundance of Enchytraeids and Collembola between recolonized mesocosms and the undisturbed control at the end of the study period. In contrast, oribatid mite abundace was still greatly reduced in the recolonized esocosms. Dominance structure and species composition of the more dominant oribatid species in the different treatments were apparently similar. To compensate for the low colonization ability of oribatids, a reintroduction of selected animal size-classes to defaunated monoliths is recommended. 相似文献
18.
Sophie Chaperon 《Soil biology & biochemistry》2007,39(9):2329-2338
A study of the individual and mixture toxicities of the trace metals Ag, Cu, Hg, Zn to the soil enzymes dehydrogenase and urease was undertaken. An agricultural soil and a sandy forest soil were spiked with metal salts, individually and in combinations. The anion additions to the various treatments and controls were normalized for added anions using Ca salts. The soils were then left to equilibrate and leached to reduce the excess metals and anions. Total and dissolved metal concentrations were measured concurrently in order to consider the effect of soil chemistry on the enzyme activities. Dose-response relationships for total soil metals and soil solution metals were estimated for each metal separately following a log-logistic curve fitting. Ag and Hg were the most efficient metals to reduce soil enzyme activities. The Bliss independence model was used to predict the toxicity of metal combinations. The enzyme responses in relation to the total soil metal combinations were synergistic for the agricultural soil and antagonistic for the forest soil; possibly as a result of a higher organic matter content and higher pH in the latter soil. Enzyme activities expressed in relation to the dissolved metal concentrations were more variable than against the total metal contents and consequently we observed both synergistic and antagonistic interactions. 相似文献
19.
通过样地实测生物量和采用重铬酸钾法测定植物碳索含量,研究了思茅松中幼龄人工林生物量碳密度的分配特征及随林龄的动态变化规律。结果表明:1)林龄为3-5、6-10、11 -20和21 -30 a思茅松人工林的生物量碳密度分别为(20.15 ±3.09)、(27. 24 ±2.25)、(94. 89 ±9. 90)和147. 58 t/hm2。随林齡增长,乔木层、枯落物层和林分的碳密度显著增加,灌木层和草本层的碳密度有所减少。林分、乔木层和枯落物层的生物量碳密度随林龄的变化用逻辑斯蒂模型可实现良好拟合,而灌木层和草本层拟合效果差。2)林龄为3-5、6-10、11 -20和263思茅松人工林的年均固碳量分别为(4. 92 ±0.63)、(3. 52 ±0.25〉、(6. 44 ±0.30)和5. 68 t/(hm2·a)0乔木层的年均固碳量与林龄存在显著正相关,灌木层和草本层的年均固碳请与林龄存在显著负相关,林分年均固碳量与林龄呈较弱的正相关。乔木层和草本层的年均固碳量与林龄的关系以逻辑斯蒂模型拟合效果较好,灌木层年均固碳量和林龄关系以Gauss模型拟合效果较好,林分的年均固碳量与林龄的拟合效果差。 相似文献
20.
Random amplified polymorphic DNA markers were used to assess relatedness and genetic diversity for 15 lingonberry (Vaccinium vitis-idaea) populations. Seven primers yielding 59 polymorphic bands were used to analyse 13 populations, representing ssp. vitis-idaea from Sweden, Finland, Norway, Estonia and Russia, and two populations, representing ssp. minus from Japan and Canada. A cluster analysis and a multidimensional scaling analysis (MDS) showed similar phenetic patterns
among populations, with a pronounced geographic grouping in most cases. Significant correlations were obtained between geographic
and genetic distances for the entire set of populations as well as for the 13 ssp. vitis-idaea populations. Mean within-population diversity was 0.206 when estimated with Lynch and Milligan's index, and 0.431 when estimated
with Shannon's index, which is in agreement with the mixed mating system reported for lingonberry. Within-population variability
accounted for 68.6% of the total variance when all populations were included, and for 78.8% when only populations of ssp.
vitis-idaea were analysed. Two different approaches were applied to the selection of plant material for a potential gene bank: (1) a
hierarchical sampling strategy based on a cluster analysis and (2) the Maximum genetic diversity program, developed for the
establishment of core collections. Random sampling was undertaken for comparisons with the selected data sets. The most diverse
and representative set of lingonberry specimens was obtained when samples were selected with the Maximum diversity program. 相似文献