一步法RT—PCR检测大缸奶在BVDV清除计划中的应用

本文利用一步法RT—PCR对28个牛场共计50份大缸奶样进行了BVDV核酸检测。在与全群抗原检测结果对比后发现．9个已知存有PI牛的泌乳牛群,其大缸奶核酸检测均为阳性,其余41个已知无PI牛的泌乳牛群．除1个因为存在急性感染牛造成阳性结果外,其余40个均为阴性。由此可见,本方法对与泌乳牛群内是否存在PI牛可以做出准确判断,其检测灵敏度和特异性均为100％,阳性预测结果可信度为0．9（9／10）,阴性预测结果可信度为0．98（40／41）。此外．针对50个大缸奶样进行的抗体检测表明,对于已感染牛场,泌乳牛群是否存在PI牛,抗体水平没有明显差异（OD1．12±0．12vsOD1．34±0．23,P〉0．05）。实验室条件下,本试验使用的RT—PCR方法对于阳性乳的最低检出限为50uL/头,因此理论上,最多可从1000份样品中检出阳性乳成分（总体积为50mL）。综上可知,本试验确立的RT—PCR方法灵敏度高、特异性强,可对泌乳牛群是否存在PI牛进行准确预测,相比大缸奶抗体检测更具实际指导意义,联合ELISA—Ag使用时还可大幅度降低泌乳牛群BVDV清除计划的检测成本,因而值得推广使用。     

生物质能在烟叶烘烤中的应用前景

生物质能是一种新型的高效清洁能源。简述了生物质能在烟叶烘烤中的应用现状,分析了生物质能在烟叶烘烤应用中存在的问题,介绍了最新的研究进展并展望了发展前景。     

混合方式对泡沫砂与土壤混合均匀性的影响

通过设置常规混合+风干态泡沫砂(CK)、常规混合+水浸态泡沫砂(1T)、常规混合+泥浆态泡沫砂(2T)、分层混合+风干态泡沫砂(3T)和分层混合+水浸态泡沫砂(4T) 5个处理,研究了不同混合方式对泡沫砂和土壤混合均匀性的影响,并采用容重的标准差和变异系数表征混合均匀性。结果表明:泡沫砂形态显著影响了混合均匀性。采用常规混合时,水浸态泡沫砂显著增加了0～10 cm和0～20cm土层混合均匀性,容重的标准差比风干态泡沫砂分别降低了188%和105%,容重的变异系数分别降低了62.1%和50.1%;与风干态泡沫砂相比,泥浆态泡沫砂不仅显著降低了不同土层的混合均匀性,还显著降低了混合物内部的混合均匀性,0～10 cm土层容重的标准差和变异系数分别比10～20 cm土层显著增加68.1%和50.8%。单变量分析表明,混合方式对混合均匀性无显著性影响,混合方式和泡沫砂形态之间无交互效应,泡沫砂形态是影响泡沫砂和土壤混合均匀性的主要因素。采用水浸态泡沫砂在常规混合方式下与土壤混合,不仅提高了混合物整体以及不同土层的混合均匀性,而且还降低了不同层次之间混合均匀性的差异。因此,建议采用常规混合+水浸态...     

不同放牧强度下奶牛对多年生黑麦草/白三叶草地土壤特性的影响

本文作者在湖南南山牧场通过放牧试验研究了不同放牧强度下奶牛对多年生黑麦草／白三叶人工草地土壤物理和化学特性的影响。结果表明：放牧强度直接影响着多年生黑麦草／白三叶人工草地土壤的物理结构。随放牧强度增加，奶牛对草地土壤的践踏加剧，导致土壤紧实度增加，容重上升，通气性变差，含水量下降。放牧强度对土壤物理特性的影响随土层深度增加而减轻。土壤中全磷、速效磷、碱解氮和有机质随放牧强度的增加而减少，而全氮、速效钾则随放牧强度的增加而增加。土壤中各养分含量随季节变化波动很大。     

Comparisons of quantitative trait locus mapping properties between two methods of recombinant inbred line development

Theoretical comparisons for quantitativetrait loci (QTL) mapping properties wereconducted among simulated recombinantinbred (RI) populations developed bysingle-hill (SH), complete bulk, and singleseed descent (SSD) procedures by MonteCarlo simulations based on variouspopulation sizes, heritabilities, and QTLeffects. Our simulations includedestimation of QTL effects, QTL positions,and statistical testing power in the RIpopulations by comparing the estimates withpreset values. The simulation resultsshowed that the single hill (SH) bulk andsingle seed descent RI populations weregenerally not significantly different withrespect to quality of estimated QTL effectsand positions. Furthermore, when each RIpopulation had 150 lines, each couldprovide desirable properties for QTLmapping. The results implied that a SH RIpopulation consisting of 75 or moreF₂-derived families with two lines perfamily (corresponding population size of150 or above) was appropriate for QTLmapping and was not significantly differentthan a SSD RI population of 150. Thus, theSH method could be used to develop largenumbers of RI lines for achieving betterresults in QTL mapping. Simulations alsoshowed that there was no significantdifference between means using SH methodswith 10 and 100 fruits per family. However, RI populations developed by thecomplete bulk method where F₂identities are lost were not suitable forQTL mapping.     

预处理对废旧人造板再生材料化学特性的影响

对粉碎后的废旧人造板原料进行冷水、热水、1％NaOH处理，通过测定预处理后材料的pH值、缓冲容量、胶固化时间，探讨预处理对废旧人造板材料化学特性的影响。试验结果表明：（1）相对于冷水和热水处理来说，1％NaOH处理使得3种木质材料的pH值极显著升高，最高可达10．41；（2）酸碱缓冲容量、UF胶固化时间在3种预处理方式间均有较显著差异，即随酸缓冲容量的增加UF胶固化时间缩短，而随碱缓冲容量的增加固化时间则延长。     

烘烤工艺、成熟度和取样方式对烤烟CB-1中部叶石油醚提取物含量的影响

测定了2种烘烤工艺、3个成熟度和2种取样方式的CB-1品种中部叶烤后石油醚提取物的含量.结果表明,慢烤烘烤工艺下石油醚提取物的含量高于快烤的,在5%水平上差异显著;随着成熟度的提高,石油醚提取物的含量降低,在快烤工艺下的差异不显著,在慢烤工艺下的差异显著(P＜0.05);混合样品的石油醚提取含量高于C3F的,在快烤工艺下的差异不显著,在慢烤工艺下的差异显著(P＜0.01).     

Spatial distributions of soil chemical and physical properties prior to planting soybean in soil under ridge‐, no‐ and conventional‐tillage in a maize–soybean rotation

Detailed information on the profile distributions of agronomically important soil properties in the planting season can be used as criteria to select the best soil tillage practices. Soil cores (0–60 cm) were collected in May, 2012 (before soybean planting), from soil transects on a 30‐yr tillage experiment, including no‐tillage (NT), ridge tillage (RT) and mouldboard plough (MP) on a Brookston clay loam soil (mesic Typic Argiaquoll). Soil cores were taken every 19 cm across three corn rows and these were used to investigate the lateral and vertical profile characteristics of soil organic carbon (SOC), pH, electrical conductivity (EC), soil volumetric water content (SWC), bulk density (BD), and penetration resistance (PR). Compared to NT and MP, the RT system resulted in greater spatial heterogeneity of soil properties across the transect. Average SOC concentrations in the top 10 cm layer were significantly greater in RT than in NT and MP (P = 0.05). NT soil contained between 0.8 and 2.5% (vol/vol) more water in the top 0–30 cm than RT and MP, respectively. MP soil had lower PR and BD in the plough layer compared to NT and RT soils, with both soil properties increasing sharply with depth in MP. The RT had lower PR relative to NT in the upper 35 cm of soil on the crop rows. Overall, RT was a superior conservation tillage option than NT in this clay loam soil; however, MP had the most favourable soil conditions in upper soil layers for early crop development across all treatments.     

密集烘烤关键温度点稳温时间对烟叶颜色和色素降解的影响

为优化密集烘烤工艺，提升烟叶质量特色，对密集烘烤关键温度点不同稳温时间的烟叶颜色参数和质体色素变化进行了研究。结果表明，烘烤过程变黄期关键温度点时间延长，烟叶亮度值、黄度值和叶片饱和度增加；随着定色期关键温度点时间的延长，亮度值降低，但对烟叶黄度值和叶片饱和度影响较小；红度值则随着各关键温度点稳温时间的延长而增加，主脉红度值只有在延长54℃稳温时间时能明显提高；色度角随着稳温时间的延长而降低，烟叶颜色偏向橘黄；在42℃和54℃延长时间有利于降低烟叶正背面色差值；叶绿素和类胡萝卜素随着烘烤时间的延长降解转化更彻底。因此，密集烘烤关键温度点延长稳温时间，在38℃稳温24 h，42℃稳温16 h，47℃稳温20 h，54℃稳温16 h，烟叶内质体色素降解更充分，烤后烟叶颜色和色度增强。     

Field evaluation of soil moisture deficit thresholds for limits to trafficability with slurry spreading equipment on grassland

This study investigated the extent of soil damage caused by field traffic associated with different levels of soil moisture deficit (SMD). The hybrid SMD model was used for computing temporal patterns of SMD which can be accurately predicted for a range of soil types in Ireland. The aim of this study was to determine SMD threshold limits to trafficability for incorporation into a decision support system for safe slurry spreading. A tractor and a fully loaded single‐axle slurry tanker (total weight ca. 18 tonnes) were driven over well, moderate and poorly drained soils at SMD values of 0, 5, 10 and 20 mm during drying phases. The change in soil bulk density (SBD) was used as an indicator of soil compaction, and rut profile measurements were taken to determine soil deformation indicative of surface damage. The effect of traffic on the grass crop was determined by measuring dry matter yield at 30 and 60 days posttraffic in the wheel‐rut and nontrafficked area. Results showed that the SMD at the time of traffic had a significant (P < 0.05) effect on the magnitude of the changes in SBD on soils of different drainage status, and on rut dimensions following traffic. DMY was significantly (P < 0.05) reduced on the wheeled compared with the nonwheeled soil. No differences in the magnitude of DMY loss were identified between the sites having different drainage status. An SMD value of 10 mm was suggested as an SMD threshold for trafficability for safe slurry spreading purposes.