Manipulation of Pinus elliottii Seedling Growth through Regulation of Mineral Nutrient Supply

An N-P-K fertilizer trial with Pinus elliottii was analysed to provide regression equations of height and dry mass on soil nutrient levels. Response surfaces and isoquants were plotted. The technique is used to demonstrate the derivation of fertilizer recommendations for the raising of seedlings to predetermined standards.     

Weed Allelopathy,Its Ecological Impacts and Future Prospects

Summary

The importance, characteristics, positive and negative impacts, and future role of weeds as an integral part of the natural and agroecosystems are evaluated and discussed. Interference between plants in nature and the importance of differentiating between competition and allelopathy are interpreted. Allelopathy as one component of weed/crop interference, allelochemicals from weed species and their possible mechanism of action are listed and discussed. Weed species with inhibitory action against cultivated crops, other weed species, and plant pathogens, as well as self-inhibitory (autopathic) species are reviewed. Stimulatory or inhibitory allelopathic effects of different crop plants, trapping and catching species, and the potential of allelopathic weeds in inhibiting or stimulating certain parasitic weed species are discussed and evaluated. Allelopathy as a mechanism and future strategy for agricultural pest control and farm management and the potential use and development of some allelochemicals as natural pesticides or plant growth regulators are also considered and discussed.     

Potential allelopathic influence of certain pasture weeds

Laboratory and growth chamber research was conducted to determine the potential allelopathy of tissue harvested from certain weeds commonly found in pastures. Results of bioassays indicated that the weeds dogfennel and mayweed chamomile are potentially allelopathic to alfalfa and Italian ryegrass seedlings. Leaf-tissue extracts from the two weed species reduced seedling growth more than stem and root extracts. In most experiments alfalfa seedlings were influenced more than Italian ryegrass seedlings and seedling growth was influenced more than seed germination. Leaf tissue from the weed species mixed into potting soil at a concentration as low as 0.25% (w/w) significantly reduced alfalfa and Italian ryegrass plant development and foliage production. Extract and tissue concentration used in this research were estimated to be similar to concentrations expected to occur within the pasture ecosystem and below concentrations that would result in hypertonicity in the bioassays.     

北京地区草坪杂草防治的初步研究

在摸清北京地区不同类型草坪中不同杂草种类的基础上，选择了一定效果的除草剂对这些优势种进行了２个生长季节的防治试验。结果表明，不同除草剂对草坪草敏感程度和防治效果不一样。在使用除草剂防治草坪杂草时一定要谨慎，否则将出现较大药害。     

Direct infection of potato tubers by the root parasite Orobanche aegyptiaca

Parasitic plants of the Orobanchaceae are known as obligate root parasites that develop haustoria that connect to roots of various host plants. This article describes, for the first time, a case where the root parasite successfully connected to potato tubers, i.e. to the swollen portion of an underground stem rather than to a root. The rhizosphere of Orobanche aegyptiaca and of its host Solanum tuberosum (potato) was carefully examined. In anatomical studies, the adventitious roots were directly connected to potato tubers. Numerous secondary haustoria, which developed along the adventitious roots in close vicinity to the potato tuber, penetrated the tuber epidermis and the perimedullary tuber parenchyma and developed xylem strands that are presumably connected to the minor xylem strands within the tuber cortex. These findings indicate that parasites of the Orobanchaceae that normally attack host roots may also parasitise underground stem tubers.     

紫花苜蓿对氟乐灵除草剂的抗性试验

利用氟乐灵除草剂，在苜蓿播种前对土壤进行地下处理，灭除杂草，提高苜蓿产草量。结果表明，苜蓿幼株长势良好，氟乐灵对杂草杀灭率为９０％以上，使用氟乐灵灭草剂成本低，效果好，可在生产中推广应用。     

武当山地区野生有毒植物资源的开发利用研究

经调查,湖北武当山地区共有野生有毒维管植物71科156属206种。本文分析和讨论了它们的经济价值、在本地区的开发利用现状及存在的问题,提出了保护与开发对策。     

紫红短须螨生物学特性初步观察

利用紫红短须螨（Brevipalpus phoenicis)控制薇甘菊，是生物控制杂草的一种新方法，文章着重介绍了紫红短须螨的生物学特性及形态特征。卵椭圆形。卵椭圆形，长约0.10mm，宽约0.07mm。红色，多单产在植物茎叶的裂缝或凹陷处，或叶片背面的主脉两边，成块成串堆聚在一起，幼螨桔红色，长约0.17mm，宽约0.11mm。若螨2龄，背上有黑色斑纹，雌成螨长约0.30mm，宽约0.16mm，身体椭圆形，扁平，多桔红色。背上有一个“H”形标记，紫红短须螨1年6-8代，世代重迭，从孵发育到成虫，恒温30℃为18.6d,20℃为48.8d。当湿度低于30%，平均温度高于30℃或者低于20℃时，紫红短须螨不能完成生活史，室内11.0-28.5℃的自然变温，湿度58%-97%条件下，紫红短须螨发育完成一个世代为28-55d。     

A diagnostic survey of shifting cultivation in northern Laos: targeting research to improve sustainability and productivity

About 25% of Laos' four million people practise shifting cultivation (mainly of rice) on a third of the country's cropped area. Official policy is to eliminate shifting cultivation by the year 2000. Diagnostic surveys of shifting cultivation were conducted in Luang Prabang and Oudomsay Provinces in northern Laos to understand the practice from a farmer's perspective, to observe fields, and to identify and give priority to problems and research to address problems. Weeds, low and possibly declining soil fertility, intensification of the cropping cycle, rats (plus birds, wild pigs), and insects lowered rice yields or reduced system sustainability. The forest ecosystem has been degraded by logging, burning, and rice monocropping; and potentials for environmental rehabilitation through natural succession are minimal. Farmers cannot adopt high labor and cash cost innovations; and improved fallow is needed as an intermediate step prior to crop diversification, adoption of agroforestry technologies, and sedentary agriculture.