Oak and red maple seedling survival and growth following periodic prescribed fire on xeric ridgetops on the Cumberland Plateau

To test the hypothesis that repeated prescribed fires alone can improve the status of oak regeneration, a long-term seedling population study was established to follow permanently tagged chestnut oak (Q. prinus L.), scarlet oak (Q. coccinea Muenchh.), and red maple (Acer rubrum L.) seedlings over 8 years in sites where fire was excluded, and where fire was applied either three (3×) or four (4×) times.     

掌叶覆盆子优株的复选及繁殖示范推广研究

[目的]为掌叶覆盆子（Rubus chingii Hu）的优株选育和推广种植提供科学依据。[方法]对初步选育的10株掌叶覆盆子优株进行植株性状、生长习性、开花习性及结果习性进行调查,结合掌叶覆盆子优株爱选标准,淘汰不符合标准的单株,再进行株间比较,选育出不同熟期的掌叶覆盆子优良单株。[结果]选育出的优良单株有7号（晚熟、长果型）、6号（早熟、圆果型）及4号（中熟,圆果型）。[结论]复选的3株优良掌叶覆盆子单株具有广阔的推广应用前景。     

Restoration of rooting competence in mature Faidherbia albida,a Sahelian leguminous tree,through serial root sucker micrografting

Faidherbia albida is an essential leguminous tree of arid areas of Africa which is widely used in agroforestry. This species naturally produces root suckers. Their morphogenetic ability has been used to initiate a rejuvenation/reinvigoration process in mature subjects. The proposed method contains two stages. The first stage generates the first ramets : our results have shown that suckers picked from root cuttings are more vigorous than explants taken directly from the crown of adult subjects. The second stage furthers the rejuvenation process through cycles of repeated micrografting onto juvenile rootstock, which have been grown in vitro. As early as the third cycle, a significant increase in reactivity is gained. This is determined by growth of the scion and the rooting competence of microcuttings severed from the scions after each micrografting cycle. At that point, the rooting competence is completely restored. So, this sequential method, (i) suckers from root cuttings, (ii) repeated micrografting, seems valid as a technique for the restoration of rooting competence in mature F. albida with a view to its cloning.     

用物种专化DNA重复序列作分子标记检测导入小麦的大赖草染色质

ｐＬｒ ＮＡＵ３４４，ｐＬｒ ＮＡＵ４２６和ｐＬｒＮＡＵ６４７是我们新近从大赖草中克隆到的３个特种专化ＤＮＡ重复序列。它们都大量存在于赖草属，而小麦中却很少。Ｓｕｏｔｈｅｒｎ杂交证明，ｐＬｒＮＡＵ４２６和ｐＬｒＮＡＵ６４７对导入小麦的８条不同的大草染色体（其中３条携带有小平麦赤霉病抗性基因）和两条染色体臂部都有检测效果，据此可用其作为赖草属染色质的分子标记进一步研究和利用。     

Critical state parameters from intact samples of two agricultural topsoils

The critical state parameters of intact samples of a sandy loam (Eutric Cambisol) and a clay loam (Gleysol) were estimated in a constant cell volume triaxial apparatus. Samples were taken under wet and dry conditions. The parameters describing the clay loam were the more variable. This was true of both its initial condition and its response to deformation. Under dry conditions, the sandy loam was less sensitive to increasing stress but compacted more at low stress than the clay loam. Isotropic stress compacted the wet soils until the percentage saturation reached about 85–95% and axial loading caused little further compaction. The difference in strength between soils was greater for the wet samples, whereas the corresponding compactibility differences were greater under dry conditions. The sandy loam was stiffer than the clay loam and the shear modulus decreased exponentially with increasing specific volume before deformation. The rebound slope was about one-twentieth of the compression index for the dry soils and about one-third of the compression index for the wet soils. A simple model of recompression accounted for plastic deformation below the virgin compression line, where the critical state model usually assumes elasticity. The proposed model reproduced the main observed features of repeated isotropic loading.     

多菌灵重复施药对其持久性及土壤微生物群落功能多样性的影响

选择浙江大学华家池校区大棚蔬菜试验田,研究了多菌灵(以active ingredient,a.i.计)0.94、1.88和4.70 kg hm-2三种剂量重复施药对其持久性及土壤微生物功能多样性的影响。结果表明,第1次施药后,多菌灵在土壤中的降解速率分别为0.11、0.25、0.74 mg kg-1d-1;第4次施药后,多菌灵在土壤中的降解速率分别达到0.18、0.39、1.00 mg kg-1d-1。随着施药次数的增加,多菌灵的降解速率逐渐增大。初次施药后,土壤微生物群落AWCD值明显低于对照,土壤微生物群落的Shannon、Simpson和McIntosh指数也均低于对照水平。第4次施药后,三个处理土壤微生物群落的AWCD值、Shannon、Simpson和McIntosh指数均恢复到对照水平。     

单因素随机区组试验中重复测量数据分析及其SAS实现方法

结合两个实例,讨论了单因素随机区组试验中重复测量数据的分析方法,并用SAS程序进行了统计计算。对于不同地点的重复测量数据,在其变异来源中增加了一个地点取样误差,其SAS程序中,采用了Proc Anova语句,巧妙地在Model语句后加入了Test语句。对于不同时间点的重复测量数据,可以将单因素随机区组设计转化为裂区设计,单因素为主区因素,时间因素为副区因素,其SAS程序中,采用了Proc Mixed语句,并进行了同质性检验。     

长期借贷关系下农户与金融机构信用机制研究

社会主义新农村建设时期,我国农户面临着严重的信贷约束,农村经济的发展受到制约。从＂信任匮乏＂的视角,基于借贷农户间信用机制的形成机理,运用博弈论的知识,研究长期借贷关系下农户与金融机构信用机制的形成,并提出该机制形成与运用的条件。     

The effect of an outbreak of respiratory disease on herd-level milk production of Norwegian dairy farms

This study was done to evaluate the effect of an outbreak of acute respiratory disease associated with bovine respiratory syncytial virus (BRSV) on the daily milk yield per cow in Norwegian dairy-cattle farms. Retrospective data from 184 dairy herds located in two neighbouring veterinary districts during the study period (December 1994–May 1995, during which an epidemic of acute respiratory disease associated with BRSV occurred in this area) were analysed. Data on the bulk-milk deliveries and the date of the outbreak were collected at herd level, whereas information on calving dates and parity was collected at cow-level. The effect of the herd outbreaks on the daily milk yield was analysed with a repeated-measurement approach. The average daily milk loss was estimated to be 0.70 kg per cow for 7 days after a herd outbreak (compared with the period >1 week prior to an outbreak), adjusted for the herd-level lactation stage, parity and their interaction term. We consider the estimated milk loss associated with a herd outbreak of epidemic respiratory disease to be of minor importance.     

不同超排方案以及重复超排对犊牛超排效果的影响

本试验选择北京奶牛中心良种场36头9~12月龄的犊牛进行超排采卵,研究了不同超排方案以及重复超排对犊牛超排的效果。结果表明,超排方案以埋植CIDR的同时,第5天、第6天注射FSH,第7天手术采卵获得的可用卵母细胞数最多。两次重复超排对犊牛平均卵泡数和平均卵母细胞数没有显著影响,但三次超排后的平均卵泡数和平均卵母细胞数显著低于一次和二次超排。