Effect of three contrasting onion (Allium cepa L.) production systems on nitrous oxide emissions from soil

 N₂O emissions were measured from three contrasting onion (Allium cepa L.) production systems over an 8.5-month period. One system was established on soil where a clover sward had 3 months earlier been ploughed in (ploughed clover site). This production system followed conventional production management practices. The other two systems were established on soil where a mixed herb ley had 3 months earlier been either ploughed or rotovated. These last two production systems followed the guidelines of the International Federation of Organic Agriculture Movements (IFOAM). Cumulative N₂O emissions were significantly greater from the ploughed clover site compared to the ploughed ley site (3.8 and 1.6 kg N₂O-N ha^–1, respectively), while cumulative N₂O emissions from the ploughed ley and rotovated ley sites were not significantly different from each other. Emissions from all sites were dominated by episodes of high N₂O flux activity following seedbed preparation and drilling, when soil water suction (SWS) was shown to be the rate-controlling variable. The decline in the N₂O fluxes after these peak emissions followed clear exponential relationships of the form F=Ae^{– kt} (r≥0.91), where F is the daily flux and A is the y-intercept. First-order decay constants (k) during these periods of declining N₂O fluxes (corresponding to half-lives of 2.6–3.0 days) were not significantly different in magnitude from the first-order rate constants that characterised the increasing SWS. Gross differences in cumulative emissions between the clover and ley sites were attributed to the influence of differing soil pHs at the two sites on the N₂O:(N₂O+N₂) ratio in the denitrification products. It also appeared that fertiliser applications to the clover site had both direct and indirect effects on N₂O emissions by: (1) enhancing N₂O emissions via potential nitrification, (2) increasing the NO₃ ^– supply for enhanced N₂O emissions via denitrification, and (3) influencing the N₂O:(N₂O+N₂) ratio by lowering soil pH and increasing NO₃ ^– concentrations. Onion crop yields were greater at the clover site, mainly due to the higher density of planting made possible under a conventional production philosophy. Expressing the yield on the basis of net N₂O emissions, 23 t onions kg^–1 N₂O-N was obtained from the ploughed clover, which was double that obtained for the two systems based on the ley site. However, when the N₂O emissions from the cultivation of the soils prior to the sowing of the onions was included, all three systems produced a similar yield per kilogram of N₂O-N emitted, averaging 10 t kg^–1. Received: 6 January 1999     

屋顶花园栽培基质中添加海泡石的效果研究初报

在屋顶花园条件下,以葱兰和佛甲草为实验材料,对它们的栽培基质中添加海泡石,通过与未加海泡石的实验作对照,发现,将适量海泡石加入屋顶花园的栽培基中,可明显改良植物的根际环境,提高土壤肥力,提高基质保水供水的能力,使植物生长旺盛,提高抗病能力。但大雨时,加入海泡石的基质,水分下渗慢,基质表层留水量及流水量增大,易冲走混合基质中的轻型材料部分,在坡面屋顶使用时,不宜加入过多。     

广东重要农林有害外来生物飞机草入侵的历史阶段与特点

飞机草是世界上危害严重的100种有害外来入侵物种之一,是我国公布的第一批入侵植物之一,也是广东主要的入侵植物之一。本文介绍了飞机草对入侵地农田、牧草、生态等会造成严重危害,归纳了飞机草入侵广东的3个历史阶段,从防治和利用两方面总结了飞机草入侵广东的历史特点,指出了飞机草的入侵应引起社会的广泛关注,政府的高度重视,防止进一步扩散蔓延。     

Notes on neglected and underutilized crops Current taxonomical overview of cultivated plants in the families Umbelliferae and Labiatae

A comprehensive list is given of cultivated plants in the families Umbelliferae and Labiatae. Major uses are indicated for every species by commodity groups. Numerous neglected and underutilized crops interesting for breeding activities in the future are included in this overview as well as many lesser known possibilities of utilization.     

Soil erosion potential of organic versus conventional farming evaluated by USLE modelling of cropping statistics for agricultural districts in Bavaria

Abstract. Organic agriculture (OA) aims to identify a production regime that causes less environmental problems than conventional agriculture (CA). We examined whether the two systems differ in their susceptibility to soil erosion by water. To account for the large heterogeneity within the rotations practised on different farms, we chose a statistical evaluation which modelled erosion using the USLE method from the cropping statistics for 2056 districts in Bavaria (70 547 km²; 29.8% arable). Physical conditions of erosion were determined in a rectangular grid yielding 13 125 grid-cells of c. 5 km² each. For validation, erosion was measured in 10 sub-watersheds on two neighbouring OA and CA farms over 8 years (287 erosive events). On average, about 15% less erosion on arable land was predicted for OA than for CA due to the larger area of leys, although OA occupies areas that are susceptible to erosion more often than CA. The same conclusions could be drawn from the validation data. These data also demonstrated that erosion could be reduced considerably below 1 t ha⁻¹ yr⁻¹ with best management practices under both farming systems. In contrast, at the countrywide scale, cropping did not change adequately with site conditions favouring erosion. The need for erosion control seems not to influence crop rotation decisions on erosion-prone sites.     

石蒜花粉萌发与贮藏性研究

以石蒜盛花期的花粉为试验材料,采用液体培养基法研究了培养基组成、贮藏温度和时间对花粉萌发特性的影响。结果表明院石蒜花粉萌发的最适培养基为150 g/L蔗糖+10 mg/L硼酸,花粉萌发率达41.07%;石蒜花粉生活力随贮藏时间的延长而下降,适宜的贮藏温度为-20℃,可保持生活力达28 d。     

中国石蒜SSR体系的建立及性状对应分析

 为开发利用石蒜属球根花卉资源和开展分子标记辅助选择育种,利用正交试验和单因素试验建立了中国石蒜的SSR分子标记体系：20 μL含Taq酶0.5 U、Mg ²⁺ 1.5mmol · L^-1、dNTP 0.125 mmol · L^-1、Primer 0.5 mmol · L^-1、DNA 50 ng。利用该体系对石蒜属的8个物种和中国石蒜种内35个无性系进行扩增,每对引物在种间平均得到7个多态性位点,在中国石蒜种内得到9.5个多态性位点,反映出该体系具有较好的通用性和稳定性。利用对应分析法对中国石蒜的花葶高度、开花期等性状和SSR扩增条带之间的对应关系进行关联分析,初步得到与迟花期‘Oct’性状相关的Ly97和Ly98条带,与中矮花葶高度‘Mid’、‘Low’性状相关的Ly84、Ly87和Ly97条带等,并提出开展进一步的杂交和遗传测定,对辅助选择标记的可靠性进行验证。     

鸢尾蒜化学成分的研究(1)

鸢尾蒜石油醚提取物,用毛细管气相色谱和GC/MS联用技术,从鸢尾蒜石油醚提取物中鉴定出α-侧柏烯、β-水芹烯、3-蒈烯、β-蒎烯、枯茗醛、番红花醛、正十二烷醇、廿四烷、廿五烷、廿六烷、廿七烷和廿八烷等30种组分。而其大部分组分经药理实验表明,具有重要的生理活性。     

中草药鸡痢灵镇痛和止血作用的研究

本文以200%的鸡痢灵水煎液用热板法和扭体法对小鼠进行镇痛实验,有明显的镇痛作用(P<0.01);用玻片法进行止血实验,其凝血时间给药组110±2.5秒和空白对照420±20秒相比,差异显著(P<0.01)。     

河西走廊草本花卉引种试验及栽培技术

在河西走廊中部对一串红，万寿菊等14个品种的草本花卉进行引种栽培试验，其结果表明：一串红，万寿菊，红头鸡冠等9个品种可作为河西走廊主要品种推广，同时还对这些花卉的育苗方法，移植，摘心，水肥管理和病虫害防治等技术环节进行了研究。