Nitrogen-fixation dynamics in a cut-and-carry silvopastoral system in the subhumid conditions of Guadeloupe, French Antilles

This paper summarizes several studies on N recycling in a tropical silvopastoral system for assessing the ability of the system to increase soil fertility and insure sustainability. We analyzed the N₂ fixation pattern of the woody legume component (Gliricidia sepium), estimated the recycling rate of the fixed N in the soil, and measured N outputs in tree pruning and cut grass (Dichanthium aristatum). With this information, we estimated the N balance of the silvopastoral system at the plot scale. The studies were conducted in an 11-year-old silvopastoral plot established by planting G. sepium cuttings at 0.3 m × 2 m spacing in natural grassland. The plot was managed as a cut-and-carry system where all the tree pruning residues (every 2-4 months) and cut grass (every 40-50 days) were removed and animals were excluded. No N fertilizer was applied. Dinitrogen fixation, as estimated by the ¹⁵N natural abundance method, ranged from 60-90% of the total N in aboveground tree biomass depending on season. On average, 76% of the N exports from the plot in tree pruning (194 kg [N] ha^–1 yr^–1) originated from N₂ fixation. Grass production averaged 13 Mg ha^–1 yr^–1 and N export in cut grass was 195 kg [N] ha^–1 yr^–1. The total N fixed by G. sepium, as estimated from the tree and grass N exports and the increase in soil N content, was about 555 kg [N] ha^–1 yr^–1. Carbon sequestration averaged 1.9 Mg [C] ha^–1 yr^–1 and soil organic N in the 0-0.2 m layer increased at a rate of 166 kg [N] ha^–1 yr^–1, corresponding to 30% of N₂ fixation by the tree. Nitrogen released in nodule turnover (10 kg [N] ha^–1 yr^–1) and litter decomposition (40 kg [N] ha^–1 yr^–1) contributed slightly to this increase, and most of the recycled N came from the turnover or the activity of other below-ground tree biomass than nodules. This revised version was published online in June 2006 with corrections to the Cover Date.     

缓坡山地林牧复合经营的桉树生长性状研究

通过对广西防城港市防城区缓坡山地宽行窄株种植模式下桉树生长性状进行调查,结果表明：宽窄行种植模式的桉树生长量明显高于对照林,其蓄积量比对照高31.86%。桉牧模式3年生桉树的收益为12923.7元·hm-2,比对照林（8317元·hm-2）高4606元·hm-2以上。缓坡山地实行林牧经营模式达到林业和牧业共同发展的双赢局面,具有一定的推广意义。     

Variability in feeding ecology of a South American cichlid: a reason for successful invasion in mediterranean‐type rivers?

Abstract –  Ecological attributes behind the success of the South American cichlid Australoheros facetus in mediterranean-type rivers remain unclear. This study addresses this issue, by analysing its abundance and feeding patterns in the lower Guadiana drainage (Portugal), during the dry season of 2003. Despite slight spatial variations in abundance and individual size, A. facetus seemed well established in the Guadiana, Vascão and Ardila rivers. No seasonal or size-related changes in feeding intensity were found, but the diet changed across rivers, over time and throughout ontogeny. Feeding seemed highly generalist, with fish apparently reacting to both spatial and temporal changes in food supply and tending to use the most abundant and easily accessible food items. Overall prey breadth was broad relative to that of other native and non-native species. It is suggested that a generalist feeding strategy may play a significant role in the establishment of non-native fish in mediterranean-type rivers.     

真空堆载联合预压法在某工程中的应用分析

本文通过对某工程孔隙水压力及水平位移资料的观测，分析了通过真空一堆载联合预压法加固软上地基，土颗粒所受侧压力、渗流力、抗剪力的变化，揭示了真空一堆载联合预压法在地基水平位移方面的相互作用．以及地下水位的变化对其加固效果的影响。     

高等级公路建设测量监理工程师的素质与职责

本文叙述了高等级公路建设过程中测量监理工程师的职责、作用、应具备的素质，说明了测量监理的工作流程，具有参考价值。     

南沙群岛重要珊瑚礁水域鱼类资源数量分布

1998年3—5月和1999年5—6月．采用手钓、延绳钓和流刺网3种作业方式在南沙群岛的渚碧、南薰、东门、美济、赤瓜、永署和华阳等7座珊瑚礁水域进行了2个航次的鱼类资源调查。结果表明,7座珊瑚礁水域不同作业方式的鱼类资源相对丰盛度差别较大,其中刺网以永暑礁最高,手钓以华阳礁最高,延绳钓以南薰礁最高;同时．刺网和手钓不同水深区域鱼类资源的相对丰盛度也不相同．其中刺网以11～30m区域最高．手钓以10m以浅和51～80m区域较高;分析认为,造成礁区之间鱼类相对丰盛度差异的主要原因不是初级生产力．而是生态环境因素,主要是礁盘形态和大型海藻的数量。另外．各礁区水域的优势类群有明显不同．这主要与洞穴的大小和数量、大型海藻及珊瑚的种类和数量等生物和非生物环境有关。     

黑龙江省部分玉米杂交种的综合评价

玉米杂交种的综合评价是新品种选育、审定和推广的重要依据。以黑龙江省种植的部分玉米杂交种为试验材料,测定其产量（14%含水量）、籽粒含水量、容重、秃尖长、出籽率、轴粗/穗粗、百粒重和穗长8个性状,采用灰色关联度法对28个供试玉米杂交种的8个性状进行综合评价。结果表明,德美亚3号、先玉696和先玉335加权关联度排在前3位,综合表现好。     

27个木槿品种的数量分类和主成分分析

通过观测27个木槿品种的17个数量和质量性状,探究了木槿品种分类的等级和标准,便于为木槿品种的选育与资源研究等提供参考依据。首先对17个性状指标进行R型聚类分析和主成分分析,根据分析结果再对27个木槿品种进行Q型聚类分析。R型聚类分析结果表明,各性状选取是合理的;主成分分析结果表明,17个性状可综合为6个主成分,其累计贡献率达88.096%。Q型聚类结果表明,27个木槿品种根据有无丹心、花型、丹心基部形状、花瓣指数、花径、叶形、丹心线与丹心的关系可被分为2大类、3大类或8大类。16个性状对木槿品种的划分贡献较大。综合而言,有无丹心、花型、花瓣指数、丹心线与丹心的关系是木槿品种分类的主要标准和依据。     

东北地区杨树烂皮病气象预报模型研究

为了研究东北地区杨树烂皮病气象预报预警技术,以2002-2008年东北地区杨树烂皮病发生程度为研究对象,利用相应气象资料,在相关分析、逐步回归和逐步判别分析方法的基础上,构建东北地区杨树烂皮病气象适宜度预报模型,并将气象适宜度指数划分为非常适宜、适宜、基本适宜、不适宜4个级别,以反映气象条件对杨树烂皮病发生发展的适宜程度。结果表明：东北地区杨树烂皮病发病面积与冬季气温日较差≥15℃的天数、春季和初夏平均气温呈正相关,冬季气温日较差越大、春季和初夏气温越高,越有利于杨树烂皮病发生发展;入冬冻害、春季温湿条件对东北地区杨树烂皮病发生发展起主导作用,气温、空气湿度与杨树烂皮病发生程度关系最为密切;影响东北地区杨树烂皮病发生发展的关键气象因子分别是3月下旬风速、3月空气相对湿度、4月温湿系数、3月和5月及4月上下旬气温、上年11-12月气温日较差≥15℃的天数。预报模型对2002-2008年的历史拟合和重发生年2009年预报取得了较好的效果,分级和分省外延预报平均准确率均在75%以上,3省预报准确率顺序为：黑龙江>吉林>辽宁。     

浅圆仓多功能中心系统的应用与研究

为降低浅圆仓入库过程中产生的自动分级,减小破碎率的增加等现象,解决中心部位在通风过程中产生的通风死角,实现安全储粮,我库与河南工业大学及郑州筒仓公司合作开发研制了浅圆仓气浮式降分级、减破碎多功能中心系统。通过实仓试验发现,该系统在降低分级、减小破碎率方面效果明显,并实现了中心部位的径向通风,提高了储粮稳定性。