中蜂越夏及秋季繁殖试验

在贵州锦屏进行的中蜂越夏及秋繁试验表明，４框以上的群势越夏较为安全。越夏期间每框足蜂约需补喂白糖１．５公斤。越夏后，蜂群群势约下降１／３左右。蜂群在越夏期间飞逃的主要原因是缺蜜及巢虫危害。当地中蜂在秋季大流蜜初期发生分蜂，分蜂群势均为８框足蜂以上，７框左右不分群。为控制不同起繁群势的蜂群在秋季大流蜜初期正好繁殖到７框左右，不致因分蜂影响秋冬蜜的采集，应分期起步秋繁。根据本试验所建秋季起繁群势（ｘ）与达７框群势所需繁殖天数（ｙ）之间的回归直线方程推算，在起繁群势为１～５框蜂量时，最适的秋繁开始期，１框群为７月３１日，２框群８月１０日……蜂群的基础群势每增加一框，则秋繁开始期应相应推迟１０～１１天。     

Persistence of tebufenozide in aquatic ecosystems under laboratory and field conditions

The persistence and dissipation behaviour of tebufenozide, an ecdysone agonist, were investigated: (1) under laboratory conditions in aquatic models set up in glass aquaria, and (2) under field conditions in in-situ aquatic enclosures deployed in a mixed-wood boreal forest lake. Two models were set up in the laboratory study (Study I), which was conducted at constant conditions of temperature, water pH and photoperiod. In Model I, partitioning of tebufenozide from sediment, treated at a concentration of 1400 μg kg^-1, into untreated water was examined. The results showed that the chemical moved very little from the treated sediment into water. The concentration in sediment and water decreased gradually during the 90-day incubation period. Tebufenozide disappeared faster from the top layer of sediment than from the middle and bottom layers. The half-lives of disappearance were 64 days for the top layer but >90 days for the middle and bottom layers respectively. In Model II, partitioning from water, treated at a concentration of 350 μg litre^-1, into untreated sediment was investigated. The results showed that the chemical moved from treated water into sediment due to adsorption. Little vertical downward movement of the adsorbed residues from the top layer of sediment occurred into layers beneath. The adsorbed residues were also not released readily back into water. The concentration in water and sediment decreased gradually during the 90-day incubation period. The half-life of dissipation from water was 67 days. The field microcosm study (Study II), conducted under fluctuating conditions of temperature, water pH and photoperiod, involved application of tebufenozide onto aquatic enclosures at four concentrations of 0·05, 0·10, 0·26 and 0·5 mg litre^-1. This study also showed that the chemical moved downwards from the applied location and was adsorbed onto sediment. The chemical persisted longer in Study II than in Study I. Tebufenozide, being photo-labile, probably degraded faster after constant exposure to light in Study I than after exposure to fluctuating light in Study II. At 90 days after treatment in Study I, only about 55% of the applied material persisted in the sediment, and there was little accumulation. In Study II, the material not only persisted but also was accumulated in the sediment, since at 92 days post-treatment the residues were about 25 times higher than the applied concentration level. Residues in water also decreased more rapidly in Study I than in Study II, because the concentration at 90 days post-treatment was about 41% of the applied value. In Study II, however, about 65% of the applied chemical persisted in water at 92 days post-treatment. While the long persistence of tebufenozide in both the laboratory and field studies was attributable to its low vapour pressure, low water solubility, high octanol/water partition coefficient etc., the differences in the persistence characteristics observed in the two studies were due to the fluctuating environmental conditions and water pH encountered in the field study, compared with the constant environmental conditions and water pH utilized in the laboratory study. © 1997 SCI.     

巴图湾水库风沙入库量的估算

风沙入库给干旱、半干旱地区的水库带来了严重的填淤危害。本文通过对内蒙古乌审旗南部巴图湾水库岸边流动沙丘不同部位风速与风沙流的同步观测,计算出库岸流动沙丘表面的平均输沙率。利用巴图湾水库1986~2005年9月份的5期TM遥感影像统计出水库两岸受不同风向影响的流动沙丘断面的平均长度,结合巴图湾水库附近乌审旗河南乡气象站1985~2004年的气象资料,统计出不同风向大于起沙风的风速年均持续时间,初步计算出巴图湾水库的年均入库风沙量。结果表明:(1)巴图湾水库的年均入库风沙量为3.65万t,其中西岸风沙入库量为3.55万t,东岸为0.10万t。西岸风沙危害最为严重,是治沙工作的重点。(2)巴图湾水库的风沙入库具有明显的时间性和方向性。受季风气候的影响,风沙入库的方向会随着风向的变化而改变。东南风与西北风是造成东西两岸风沙入库的主要风向。西北风对风沙入库量的贡献最大。(3)在大于起沙风的风速中,5~12 m/s风速段是风沙入库的主要风速。当风速中7 m/s以上的风速持续时间有一个较小的增加时,入库风沙量将会有一个巨大的增加。(4)库岸半固定沙丘的风沙入库,降尘和风水复合侵蚀引起的库岸坍塌也是入库风沙量的重要组成部分。因此,巴图湾水库的实际年入库风沙量应该大于3.65万t。     

渭河下游水沙变化趋势分析

本文通过对近6年渭河下游水沙量数据的统计和分析得出,渭河下游河段年内多沙期较河流主汛期有所提前;年径流量和年输沙量的变化趋势基本一致,而且自60年代至2005年华县站的水沙量持续呈递减趋势;河流的冲淤情况与该河段的降雨量有着直接的关系,当年平均降雨量小的时候河流以淤积为主,当年平均降雨量大的时候河流以冲蚀为主。针对这些特征,分析了渭河下游目前存在的主要问题。     

陕西黄土高原中南部土壤CO2释放量变化研究

本文根据 NaOH溶液吸收CO_2的方法 ,对陕西黄土高原中南部4个观测点的土壤CO_2释放量时行了昼夜观测。观测结果表明 ,不同地区、不同气候和不同土质土壤CO_2释放量存在差异 ,冷干地区较暖湿地区土壤CO_2释放量少,凉季较暖季土壤CO_2释放量少;粘性硬质土较松散黄土CO_2 释放量少。长武、洛川、西安南郊土壤CO_2释放量变化再次证明 ,在厚层黄土发育的地区 ,土壤CO_2释放量变化相对于大气温度变化具有滞后性,从当日早晨至次日早晨,CO_2释放量具有由低变高再变低的普遍规律。     

秸秆还田及施肥对小麦复种油菜农田土壤呼吸的影响

在甘肃省石羊河绿洲灌区连续3 a的小麦复种油菜田间定位试验的基础上,采用EGM-4密闭式土壤呼吸测量系统,测定了不同施肥水平和不同秸秆还田方式下小麦复种油菜农田的土壤呼吸速率。结果表明：在整个观测期内, 土壤呼吸速率最高值出现在8月下旬（152.06~199.58 mg•m^-2•h^-1）,最低值出现在10月中旬（12.67~19.01 mg•m^-2•h^-1）。土壤呼吸速率日变化呈单峰曲线,最高值出现在12:00-14:00, 4:00左右达最低值;不同秸秆还田方式下, 高茬收割免耕播种油菜的处理明显降低了土壤呼吸速率,且在秸秆处理后的油菜生育期内降低效果更加明显;不同施肥水平下,在N、P减量15%的情况下,土壤呼吸速率显著下降;各试验处理措施下, 土壤呼吸速率与5 cm和10 cm土壤温度、30 cm各层土壤含水量均呈极显著正相关,并且土壤呼吸速率与0~30 cm土壤水分的相关性较土壤温度高;不同处理下土壤呼吸速率与土壤孔隙度基本上呈负相关,但是两者之间相关性并不显著。     

新时期高校财政学课程教学改革思路探讨

本文通过分析高校财政学课程教学与实践中存在的主要问题,分别从该课程的外界交流、教学专业特色、组织方式、教学内容与考核方式等方面进行了改革思路的探讨,旨在为提高高校财政学课程教学质量和深入推动素质教育提供参考。     

山羊高床舍饲配套饲养技术探讨

山羊高床舍饲技术通过修建标准化山羊圈舍，实现山羊饲养过程中对山羊个体的有效控制和辅助，降低饲养劳动量和劳动强度；通过带动种草养羊、养羊与沼气结合，在实现山羊饲养的同时，促进了退耕还草、封山育林等生态建设项目的实施。