Effect of Balanites glabra canopy cover on grass production,organic matter and soil moisture in a southern Kenyan rangeland

A study was undertaken in Kenya's southern savanna rangelands to determine the seasonal effect of Balanites glabra canopy cover on aboveground grass biomass, grass species composition, soil organic matter and soil moisture content. The study was conducted during the period June to December 1999 in order to capture both the dry and wet season effects. The grass biomass in the sub-canopy zone (2-4m from tree trunk) was found to be significantly higher than in the mid-canopy (0-2m from tree trunk) and open grassland zones (4-6m from tree trunk) during the dry season. However, the difference between the sub-canopy and the open grassland was not significant during the wet season, implying that the role of a tree canopy in enhancing grass biomass is greater during the dry than the wet season. Variations in percent grass species composition from the mid-canopy to the adjacent open grassland were observed, indicating that while B. glabra canopy cover favours certain grass species, other species find the micro-climatic conditions under the canopy unfavourable. Soil organic matter in the mid-canopy zone was significantly higher than in the sub-canopy and adjacent open zones during both dry and wet season. Although the sub-canopy zone exhibited significantly higher soil moisture content than the mid-canopy and open grassland zones during the dry season, the difference between the sub-canopy and the adjacent open grassland during the wet season was not significant, suggesting that the tree canopy influence on soil moisture is more pronounced in the dry than the wet season.     

The contribution and direct-use value of livestock to rural livelihoods in the Sand River catchment,South Africa

The productive functions of livestock ownership in communal areas are multipurpose in character, comprising a mix of stock types and a range of goods and services used. When all these multiple uses are accounted for, the cash and direct-use returns of livestock in communal areas can be comparable to commercial systems, although temporally and spatially variable. Yet previous work has generally excluded small stock from such analyses, as well as benefits and costs to non-owning households. This paper presents empirical results of a study in the Sand River catchment, assessing the benefits and costs accruing to owners and non-owners for both cattle and goats within a livelihoods analysis framework. Results indicate that cattle are used for a greater variety of goods and services than are goats. The savings value represented the most important function, followed by milk and then manure. Even if savings value was excluded, cattle ownership made a significant contribution to local livelihoods. Goats also provided a net positive benefit, represented largely by the savings value, followed by meat and cash sales. Non-owners also benefited through donations of manure, milk, draught and meat for free, or at a cheaper rate than alternatives. The majority of non-owners aspired to livestock ownership, although the risk of theft of animals was of growing concern. Averaged across the whole catchment, the net value of goods and services from livestock was just over R400 per hectare, with an annual return to capital of 36%. Cattle contributed the bulk of the value by virtue of their greater numbers and larger size, but on a per kilogramme basis goats provided higher value. Many of the goods and services obtained from livestock were not enumerated in regional or national economic statistics.     

Pilot survey to assess sample size for herbaceous species composition assessments using a wheel-point apparatus on the Zululand coastal plain

A pilot survey to determine sub-sample size (number of point observations per plot) for herbaceous species composition assessments, using a wheel-point apparatus applying the nearest-plant method, was conducted. Three plots differing in species composition on the Zululand coastal plain were selected, and on each plot 2 000 point observations were collected. Thirty sets of N point observations were produced, where N = 10, 20, 30, 40 to 300. For each 30 sets of N points, percentage replicate similarities were calculated. To the mean percentage replicate similarity, a Chapman-Richards function was fitted, and the asymptotic value (β₀) was used to assess the increase in mean replicate similarity with increasing sample size. Efficient sample sizes were ≤ 200 point-observations per plot, and in some situations, ±150 points might suffice. The sample size selected depends on the goals, species diversity and equitabilities (for species contributing >10% to sward composition), and the financial and time resources available.     

林分结构聚类及水土保持效应分析

本文在判明低效林分改造试验林的现实林分结构具有趋同性的情况下，采用主成份分析和谱系聚类法进行聚类，依据聚类的结果作了水土保持效应的分析。通过逐步回归分析，揭示了林分结构要素在控制水土流失方面的作用。     

鸭瘟鸭病毒性肝炎二联弱毒疫苗的研究 Ⅳ、疫苗的田间免疫试验

本文报道鸭瘟鸭病毒性肝炎二联弱毒疫苗的田间免疫试验。试验采用不同品种鸭群首次免疫（30日龄）后不同日龄和加强免疫（168日龄）后不同时间（天）的鸭抵抗1万倍最小致死置鸭瘟病毒（DPV）强毒攻击的能力以及鸭首次免疫后不同日龄鸭血清中抗DHV中和抗体液度和加强免疫后不同时间（天）所产的蛋孵出的1日龄雏鸭抵抗1万倍LD60鸭肝炎病毒（DHV）强毒攻击的能力。试验结果表明：30日龄的雏鸭进行首次免疫，其对鸭病毒性肝炎的免疫期达5．5－6个月，对鸭瘟的免疫期达9个月；产蛋前（23-24周龄）进行加强免疫，则对鸭瘟和鸭病毒性肝炎的免疫期均达到9个月。经过1990－1995年大面积对天府肉鸭（曾祖代、祖代和父母代）、樱桃谷鸭（祖代和父母代）四川麻鸭、建昌鸭和奥日星鸭（祖代和父母代）共1千余万羽份的免疫注射，免疫效果良好，深受使用单位的欢迎。     

云阳县坡耕地作物产量低的原因及对策

为了合理利用旱地资源，发展贫困落后山区经济。本文详述了云阳县坡耕地的特点，着重分析了作物产量低的原因，并对坡耕地的综合治理和合理利用提出了建议。     

玉米雄性不育系的质、核对农艺性状的影响

选用一组同核异质、四组同质异核不育系及保持系分别与测验系组成不完全双列杂交。对测交Ｆ１的吐丝期、株高、穗粒重等农艺性状进行了考察分析。结果表明：①同核异质组呈现出不同程度的胞质效应；同质异核组不同核背景之间表现出的差异较为明显。大多数性状的核基因组变异大于胞质基因组变异。②不育系在对农艺性状的影响上存在有质核互作效应。     

四川盆地低山丘陵区县级最佳防护效益森林覆盖率定量研究

本文以四川盆地低山丘陵区68个县为对象，科学定义了最佳防护效益森林覆盖率的概念，系统探讨了相应的理论与方法，揭示了森林面积数量、内涵质量及空间分布格局的综合防护效应，并计算出各县最佳防护效益森林覆盖率，为持续发展林业，优化土地利用结构提供了科学依据。     

岷江上游干旱河谷的水土流失现状和原因

岷江上游茂县,汶川一带的干旱河谷是优质苹果的生产区。目前该区水土流失极为严重。表现为:沟蚀强烈,片蚀普遍,滑坡频繁,泥石流时有发生,河谷底部风蚀作用强。导致水土流失的原因是:植被稀疏,河谷幽深,土层松散,乱砍滥伐与陡坡垦殖。     

遗传与环境的互作对蛋鸡异常蛋产生的影响

本文研究了蛋鸡产蛋期的异常蛋（双黄蛋、软完蛋、破裂蛋）现象。试验用三个品种进行三种不同处理（光照、饲养、舍温），分析了遗传和环境因素对异常蛋产生的影响及其互作效应．结果表明，异常蛋的产生在产蛋期不同阶段有较大差异。不同品种鸡异常蛋出现率有显著差异（P＜0．05），采用不同光照对异常蛋的产生有显著影响，而饲养制度和舍温则无明显影响。遗传与环境的互作效应在品种X光照、品种X饲养X会温之间有一定显著性。