Phytosociological and conservational study of the arable weed communities in western Hungary

Abstract

The present study surveyed the weed vegetation on extensively managed arable fields and unsprayed field edges in western Hungary, based on 1698 phytosociological relevés collected between 1995 and 2005. The separation of the 15 vegetation units was conducted with the traditional comparative tabular method, and the diagnostic species were determined with statistical fidelity measures. The numerical analyses show that the most important factor in the separation of weed communities is the fluctuating proportions of winter and summer annuals and cosmopolitan elements throughout the year. Soil chemical properties are the second most important whereas soil texture and climatic factors also contribute to the development of weed communities. The surveyed vegetation units support 41 red list weed species. Across all associations, the average proportion of insect-pollinated plant species is 68%, and the average proportion providing weed seed food sources for farmland birds is 47%. These factors illustrate the importance of weed communities in agro-ecosystem function and the need for their conservation.     

Towards the archaeobotanical identification of intensive cereal cultivation: present-day ecological investigation in the mountains of Asturias, northwest Spain

The region of Asturias, northwest Spain, is highly unusual in that a cereal crop (spelt wheat) is cultivated on a garden scale using horticultural methods. A floristic survey was made of the weeds in 65 spelt plots in this region. The ecological attributes of the weed species were then measured and compared to an earlier study of the functional characteristics of weeds associated with pulse crops on the Greek island of Evvia. In this earlier study, it was possible to distinguish between plots cultivated intensively on a garden-scale and plots cultivated extensively in fields, on the basis of a suite of functional attributes of the weed species. The cereal plots from Asturias were correctly identified as gardens on the basis of the same suite of attributes. The Asturias plots were also compared to weed associations from autumn- and spring-sown crops in Germany, using a different suite of attributes, and were classified either as autumn-sown or ambiguously. This is consistent with the sowing time in Asturias, which is spread over late autumn to winter. These results demonstrate that the suites of functional attributes identified to distinguish intensive and extensive cultivation, and to recognise sowing time, can be applied in another geographical area and to another crop type. This paves the way for the application of these attributes to the identification of past agricultural practices from archaeological weed assemblages. Received September 12, 2001 / Accepted December 12, 2002     

Diversity of coevolved weeds in smallholder maize fields of Mexico and Zimbabwe

Theory and empirical data suggest the areas of origin of a crop to be the general area of origin of its coevolved weeds. These longer evolved weeds would have an advantage over species with a shorter evolutionary time and migrate more successfully. We seek to identify patterns by comparing two regions with a shared crop, similar physiographic traits, but little direct contact, one of which is the area of origin of the crop. We compared the diversity of the maize weed flora and its edible components between two rural villages each of Oaxaca, Mexico, and Honde Valley, Zimbabwe, using vegetation sampling, interviews and participatory observation. The Mexican fields had higher species richness and diversity than the Zimbabwean ones. Species richness and densities were higher in the villages that receive more rainfall. Mexican fields had a mainly native weed flora with almost 80% American species and very few of African origin, whereas Zimbabwe had 32% of American and 50% of African origin. The regions shared seven American species and one of African origin. American/Mesoamerican agrestal weeds appear to be more successful in maize. Subsistence farmers in both study areas consumed about 19 edible weed species of which four were common to all villages. Our results also suggest that the presence of 3–4 species of edible weeds per field may be a general pattern in the maize-based systems, and that people not necessarily want or need more, so usefulness—at least as an edible plant—would have a limited influence on migration success.     

Weed species composition and distribution pattern in the maize crop under the influence of edaphic factors and farming practices: A case study from Mardan,Pakistan

Weeds are unwanted plant species growing in ordinary environment. In nature there are a total of 8000 weed species out of which 250 are important for agriculture world. The present study was carried out on weed species composition and distribution pattern with special reference to edaphic factor and farming practices in maize crop of District Mardan during the months of August and September, 2014. Quadrates methods were used to assess weed species distribution in relation to edaphic factor and farming practices. Phytosociological attributes such as frequency, relative frequency, density, relative density and Importance Values were measured by placing 9 quadrates (1 × 1 m²) randomly in each field. Initial results showed that the study area has 29 diverse weed species belonging to 27 genera and 15 families distributed in 585 quadrats. Presence and absence data sheet of 29 weed species and 65 fields were analyzed through PC-ORD version 5. Cluster and Two Way Cluster Analyses initiated four different weed communities with significant indicator species and with respect to underlying environmental variables using data attribute plots. Canonical Correspondence Analyses (CCA) of CANOCO software version 4.5 was used to assess the environmental gradients of weed species. It is concluded that among all the edaphic factors the strongest variables were higher concentration of potassium, organic matter and sandy nature of soil. CCA plots of both weed species and sampled fields based on questionnaire data concluded the farming practices such as application of fertilizers, irrigation and chemical spray were the main factors in determination of weed communities.     

Arable weeds identified as new sources of beet mosaic potyvirus in Greece

Field and laboratory studies were carried out between 1992 and 1994 to assess the potential for arable weeds to act as reservoirs of beet mosaic potyvirus (BtMV) in fields where sugar beet is cultivated for seed. 933 weed samples were collected and tested by biological methods, while a representative number of weeds were tested by serological methods. The results showed that 97 samples, representing 14 weed species from eight families, were infected with BtMV. The following weeds were found to be naturally infected with BtMV for the first time: Bilderdykia convolvulus, Nonea pulla, Cerastium glomeratum, Galium aparine, Conyza (Erigeron) spp., Fumaria officinalis, Heliotropium europaeum and Rumex spp. The most common weeds found to be infected with BtMV in high percentage were members of the Papaveraceae.     

Seed-transmission in the ecology of nematode-borne viruses

Virus-free populations of vector nematodes can acquire tomato black ring (TBRV), raspberry ringspot (RRV) and arabis mosaic (AMV) viruses from weed seedlings grown from virus-carrying seed. When soils from fields where nematode-borne viruses occurred naturally were air-dried to kill vector nematodes and then moistened, TBRV and RRV occurred commonly in the weed seedlings that grew, but AMV occurred only rarely. Similar tests did not detect tobacco ringspot, grapevine fanleaf or tobacco rattle viruses in weed seeds in the single soil studied in each instance, although these three viruses are also seed-borne in some of their hosts. Many weed species, when infected experimentally, readily transmit TBRV and RRV to their seed, but the viruses were much commoner in naturally occurring seed of some of these species than of others. These discrepancies between the frequency of seed-transmission of viruses from experimentally infected plants and the extent of natural occurrence of infected seed seem largely to reflect the host preferences of the vectors. Infective Longidorus elongatus kept in fallow soil retained TBRV and RRV only up to 9 weeks. When weed seeds in the soil were then allowed to germinate, the nematodes reacquired virus from the infected seedlings. Some weed species were better than others as sources of virus. Persistence of these viruses in fields through periods of fallow or fasting of the vector therefore depends on a continuing supply of infected seedlings produced by virus-containing weed seeds. This is probably less true of viruses like AMV and grapevine fanleaf, which persist for 8 months or more in their vectors (Xiphinema spp.). A few seeds containing TBRV and RRV were found in soils free of vector nematodes, suggesting that the viruses are disseminated in weed seed. This probably explains how TBRV and RRV have reached a large proportion of L. elongatus populations in eastern Scotland.     

Changes in size and composition of weed communities during planted and natural fallows

The use of trees and herbaceous cover crops for weed management in smallholder farms is a promising alternative to the unsustainable traditional shifting cultivation system. The reported experiment was conducted from 1993 to 1996 in fallow plots established in 1989 to rehabilitate a degraded Alfisol after 10 years of continuous cultivation of maize/cassava. Treatments consisted of four plots each of woody legume species (Acacia auriculiformis, A. leptocarpa, Leucaena leucocephala, and Senna siamea), and a herbaceous legume cover crop (Pueraria phaseoloides). Two controls (natural bush fallow and continuous maize/cassava) were included. Each treatment was cleared and cultivated in 1993 and 1995 (after 4 and 6 year fallow). Cultivation was repeated in 1994 for plots cleared in 1993 and in 1996 for subplots cleared in 1995. In all the years, weed density and dry weight was lower in planted fallows than in the controls. Per capita weed population growth rate decreased in all the fallow treatments most notably in A. auriculiformis and S. siamea fallow. All fallow species except A. auriculiformis would require more than 6 years of fallow to prevent growth of the weed population over the long term. The weed seed bank was 75% lower in A. auriculiformis and P. phaseoloides fallow than the control plots. Canonical correspondence and redundancy analysis indicated differences in species composition between treatments in the aboveground weed flora and in the weed seed bank. Cynodon dactylon and Digitaria horizontalis dominated continuously cultivated maize/cassava plots. Chromolaena odorata occurred more in natural bush fallow. In contrast, annual broadleaf weeds dominated the planted fallow treatments.Die Einsatz von stickstoffbindenden Bäumen und Bodenbedeckungspflanzen zur Unkrautbekämpfung in kleinbäuerlichen Anbausystemen ist eine vielversprechende Alternative zum traditionellen Wanderfeldbau. Zwischen 1993 und 1996 wurde auf einem degradierten Alfisol ein Feldversuch durchgeführt, mit dem Ziel, den Einfluss von verschiedenen Brachesystemen auf den Unkrautbefall zu ermitteln. Die Versuchsfläche hatte seit 1989 brachgelegen, zwischen 1979 und 1989 wurde die Fläche alljährlich zum Anbau von Mais und Maniok genutzt. Der Versuch beinhaltete fünf Behandlungen mit verbesserter Brache: Acacia auriculiformis, A. leptocarpa, Leucaena leucocephala und Senna siamea als Baumleguminosen and Pueraria phaseoloides als stickstoffbinden Bodenbedecker. Als Kontrollbehandlungen dienten Naturbrache und jährlicher Anbau von Mais/Maniok. Alle Parzellen wurden nach 4- und 6-jähriger Brache in 1993 and 1995 kultiviert, die Bodenbearbeitung auf diesen Parzellen wurde jeweils im folgenden Jahr wiederholt. In allen Jahren waren die Unkrautdichte und Unkrauttrockenmasseerträge in den Baum- und P. phaseoloides Parzellen geringer als in den Kontrollparzellen. Die Abnahme war deutlich niedriger in A. auriculiformis und in S. siamea. Mit Ausnahme von A. auriculiformis, würden alle verbesserten Brachesysteme mehr als 6 Jahre benötigen, um die Wachstumrate der Unkrautpopulation zu hemmen. Die Unkrautsaatgutdichte im Boden war 75% niedriger in A. auriculiformis und in P. phaseoloides Parzellen als in der Kontrolle. Canonical Korrespondenz- und Redundanzanalysen zeigten, dass die Behandlungen die Zusammensetzung der Unkrautarten sowie die Unkrautsaatgutdichte beeinflussten. Cynodon dactylon und Digitaria horizontalis waren die dominanten Arten in den Parzellen, auf denen jährlich Mais/Maniok angebaut wurde. Chromolaena odorata war die dominante Art in Parzellen mit Naturbrache während einjährige, zweikeimblättrige Unkrautarten in den verbesserten Bracheparzellen vorherrschend waren.     

Effects of environmental factors on weed species composition of cereal and stubble fields in western Hungary

Multivariate analysis of data obtained from 184 cereal and stubble fields in low-input agricultural systems located in western Hungary was undertaken in order to asses environmental factors affecting weed species composition. For each variable, the gross and net effect on weed species composition was calculated. All variables considered in this study had a significant effect on weed species composition and explained 26.99% of the total variation. Most variation in species composition was explained by the aspect (cereal vs. stubble), followed by soil pH, mean annual precipitation, soil texture, mean annual temperature, and altitude. Separating the cereals and stubbles soil pH became the most important factor. Our results suggest that during the long vegetation period, cereal weed communities dominated by winter annuals are replaced by stubble-field weed communities dominated by summer annuals. This seasonal change may also have the same important effect on weed species composition as crop types.     

Dynamics of buried seed population and seedling cohorts of two dominant weeds in a hill agroecosystem of the humid subtropics of India

Dynamics of the buried seeds and plant population of two dominant weeds, viz.,Emilia sonchifolia (Linn.) DC. andRichardsonia pilosa HBK were studied in the crop fields of Meghalaya, north-east India during radish and maize cropping and intervening fallow periods. The total buried seed population ofR. pilosa was always larger than that ofE. sonchifolia, but the germinable fraction was invariably greater in the latter. A major portion (39–41%) of the viable (germinable+dormant) seed population in both weeds was confined to the surface soil layer (0–5 cm). The viable seed population ofE. sonchifolia peaked during April, while that ofR. pilosa showed two peaks (during August and December). The survival pattern and half-lives of seedling cohorts showed, some differences in the two weed species, but both being summer annuals, their populations behaved in a similar manner by showing higher seedling recruitment (K) and survivorship (p) rates in the summer crop (maize) than in the winter crop (radish). However, the density of plants that could attain adulthood was significantly higher inE. sonchifolia thanR. pilosa which might have resulted in greater seed input of the former to the soil leading to its greater abundance in the crop fields.     

Diet selection by hares (Lepus europaeus) in arable land and its implications for habitat management

Populations of European hares (Lepus europaeus) have experienced a dramatic decline throughout Europe in recent decades. European hares are assumed to prefer weeds over arable crops, and weed abundance was reduced by the intensification of agriculture. Therefore, modern agriculture has been blamed as a major factor affecting European hare populations. However, it is questionable whether European hares select weeds at all, as previous studies had major methodological limitations. By comparing availability and use of plants with Chesson’s Electivity Index, we investigated whether the European hare actually feeds selectively on different plants in arable land. Food availability and use were dominated by cultivated crops (e.g. winter wheat, spring barley and sugar beet). Diet selection analysis revealed that in autumn and winter, European hares predominantly preferred cultivated crops (winter wheat) and food items provided by hunters (tubers of sugar beet and carrot). In spring and summer, apart from soy, only weeds (e.g. clover and corn poppy) were positively selected, especially after cereal crops were harvested. We suggest that the decline in European hare populations throughout Europe was facilitated by the decrease in weed abundance. Wildlife-friendly set-asides in arable land have the potential to reconcile the European Union’s Common Agricultural Policy with wildlife conservation.     

不同施肥方式对稻麦两熟制小麦田杂草群落的影响

为揭示不同施肥方式对稻麦两熟制区麦田杂草的影响,以连续4年固定施肥田为对象,于2014年小麦收获前进行了杂草群落调查,研究不同施肥、秸秆还田小麦田间杂草种类、密度、高度、杂草多样性指数的差异,并对杂草种群分布与肥料因子进行典范分析. 结果表明：36个试验小麦田中共记录杂草20种,分属11科19属. 其中,菵草、泥胡菜、牛繁缕、蛇床广泛分布于各试验田块. 长期施肥可减少麦田杂草种类及发生密度,但会增加麦田杂草高度,其中阔叶杂草在试验设定的各施肥措施下种类及发生密度均显著下降;纯施化肥、有机肥配施化肥,特别是施用有机无机复混肥的田块中,杂草群落多样性指数和均匀度指数低,优势度指数较高,容易使单一优势杂草种类暴发,造成严重危害;秸秆还田配施有机肥化肥处理麦田环境中杂草多样性指数、均匀度指数相对较高,优势度指数相对较低,杂草群落的结构较复杂,群落相对稳定,且杂草密度较低,对小麦生长危害较轻.     

Weeds as crops: The value of maize field weeds in the valley of Toluca, Mexico

Maize field weeds or agrestals are widely used in central Mexico as potherbs (quelites) and forage. This work presents quantitative data on these uses from the village of San Bartolo del Llano, Municipio de Ixtlahuaca, Valley of Toluca, an area with a relatively intensive, semicommercial agriculture. We interviewed 24 families of the village and 10 vendors at the market of Ixtlahuaca regularly during one rainy season (1995) on type and quantity of weed use. Also, the weed vegetation was surveyed and we interviewed 49 farmers on their farming practices and on costs. All of the 74 weed species found in maize fields were useful as forage, potherb, medicinal, or ornamental. Within the village, 11 species were eaten; an average family consumed 4.5 kg of wild potherbs per month during the rainy season. In Ixtlahuaca, 2150 kg of 10 species were sold, worth 3054 pesos (US $611). For quantity and gross economic value, forage was much more important. On the average, 1 ha of maize field produced a harvest of 1.5 t of green forage, worth about 25% of the gross value of the maize harvest, and 55% of its net value. The combination of maize with forage weeds for stabled animals constitutes an interesting integrated farming system. The weeds increase the useful biomass of the field, improve nutrition of the farmers, do not reduce the yield of the main crop, as the fields are kept weed free during the critical period, and provide erosion control, shade, and green manure.     

江苏省主要农田杂草种子库物种组成和多样性及其与环境因子的相关性分析

采用水洗镜检法对江苏省31个农田样点(包括旱田和水田)0～15 cm土层土壤杂草种子库的种类组成和物种多样性进行了调查研究;采用典范对应法分析了杂草种子库种类与环境因子(包括淹水天数、土壤有机质含量、土壤pH、年降水量、年均温、样点经度和样点纬度)的相关性并绘制了样点和种类与环境因子的二维排序散点图.调查结果表明:在31个样点的土壤杂草种子库中共检测到杂草种子15科54种,旱田和水田各有41和45种,二者共有种类占多数但优势种有差异,通泉草[ Mazus japonicus (Thunb.) Kuntze]、异型莎草(Cyperus difformis L.)、水苋菜(Ammannia baccifera L.)、千金子[Leptochloa chinensis (L.) Nees]、棒头革(Polypogon fugax Nees ex Steud.)和牛繁缕[ Malachium aquaticum (L.) Fries]等种类为二者的共有优势种;杂草种类最多的为禾本科(Gramineae)和莎草科(Cyperaceae),分别占种类总数的22.6％和20.8％.旱田不同样点杂草种子库的优势种类变化较大,而水田杂草种子库优势种较稳定;二者优势种频度差异较大,旱田中频度高于0.30的杂草有19种,水田中频度高于0.50的杂草有20种;旱田和水田中平均重要值大于0.03的杂草各有11和9种,这些频度高的种类重要值也较大.旱田和水田土壤种子库种子密度分别为21 015和37 847 m-2,平均为31 008 m-2;旱田3层土壤中种子密度差异不显著,而水田上、中层土壤的种子密度显著高于下层.旱田以夏熟和秋熟杂草为主,而水田则以水田和夏熟杂草为主.按形态类型划分,水田及旱田中杂草种类数和密度从大到小均依次排序为阔叶草类、禾草类、莎草类,且水田中这3类杂草的种类数和种子密度均高于旱田.与旱田相比,水田杂草种子库的物种丰富度指数(S)、Shannon-Wiener 指数(H')和Simpson指数(D)较高,但Pielou均匀度指数(E)较低;旱田杂草种子库的S、H'和D指数随土层深度增加而降低、E指数逐渐升高,水田各土层的物种多样性指数则无明显变化趋势.第1种类排序轴与淹水天数负相关性最高(R=-0.8143),第2种类排序轴与年降水量和经度也有较高的负相关性;相关性分析和CCA分析结果均表明淹水天数是影响杂草种子库群落构成的最大因素.通过二维排序可将31个样点分为旱田和水田2大类,旱田可划分为长期旱连作和水旱轮作2个亚类;水田可划分为淮河以北地区和淮河以南长江流域地区2个亚类.研究结果说明:杂草种子库潜群落优势种与地上部农田杂草显群落优势种具有一致性,通过土壤杂草种子库的研究可以预测地上杂草的发生和危害情况.     

Soft rot Erwinia bacteria in the rhizosphere of weeds and crop plants in Colorado, United States and Scotland

The soft rot coliform bacteria Erwinia carotovora subsp. carotovora and E. carotovora subsp. atroseptica were isolated by an enrichment method from the rhizosphere of many weed species and crop plants, collected in commercial potato fields either currently in potatoes or in a different crop as part of the rotation. Erwinia carotovora was isolated from 24 plant species in Colorado and 47 species in Scotland. Weeds contaminated with E. carotovora were found in fields growing other crops in which potatoes had not been grown for 1–2 and sometimes much longer. Weeds collected from virgin land in Colorado were not contaminated with E. carotovora but in Scotland virgin soils containing weed roots yielded E. carotovora subsp. carotovora . In general, the numbers of contaminated weeds rose from nil or low levels in spring and early summer to considerably higher levels during mid-season, and fell to progressively lower levels later. Erwinia carotovora subsp. carotovora was the predominant organism recovered from the rhizosphere, but E. carotovora subsp. atroseptica was less common, especially in Scotland, and its incidence varied in different seasons depending on factors such as temperature and moisture conditions. The bacteria could apparently persist in the root zone for an extended period of time and may be a source of inoculum to contaminate soft rot erwinia-free seed potato stocks; the origin of the bacteria was uncertain.     

Weed-crop competition studies in swedes.

Hand-weeding experiments were conducted over a three-year period in field-grown crops of swedes in north-east Scotland. When weeds were left to grow all season they reduced the dry matter yield of swede roots by 62% in 1980 and 79% in 1981 but by only 42% in the dry year 1982, in comparison with a weed-free crop. In all three years there was at least one time when a single removal of all weeds was sufficient to prevent yield loss by weed competition. In 1980 this was 6 wk after crop sowing, but the intervals between weed removal times were too great to reveal how critical this timing was. With shorter intervals in 1981 the timing of a single removal of weeds to achieve maximum crop yield was found to be highly critical at 6 wk after sowing, but in 1982 when weed biomass was much lower a single weeding any time from 4–7 wk after sowing gave as high a yield as a crop kept weed-free all season. Earlier weeding allowed subsequently emerging weeds to become competitive and reduce crop yield, while delaying weeding until after the optimum time allowed early competition from weeds emerging with the crop to depress final yield. In all years if weed removal was delayed until 12 wk after sowing, the crop yield was only slightly or no higher than if weeds were left to grow all season. It is concluded that swedes, unlike red beet or sugar beet, are incapable of recovery from the severe restriction to growth caused by weeds competing with the crop from 6–12 wk after sowing.     

Evaluation of the bioherbicide Myrothecium verrucaria for weed control in tomato (Lycopersicon esculentum)

An isolate of the fungus Myrothecium verrucaria was evaluated for its biocontrol potential against common purslane, horse purslane, spotted spurge, and prostrate spurge, all serious weed pests in commercial tomato fields in the southeastern US. In greenhouse and field tests, M. verrucaria was highly virulent against these weeds when applied as conidial sprays formulated in 0.2% Silwet L-77 surfactant, even in the absence of dew. In field test plots naturally infested with these weeds, seedlings in the two-to-three leaf growth stage treated with M. verrucaria at 2×10⁷ conidia mL^-1 in 0.2% Silwet, exhibited leaf and stem necrosis within 24 h following inoculation, with mortality occurring within 96 h. After 7 days, M. verrucaria had killed 90-95% of both purslane species and 85-95% of both spurge species. Tomatoes that were transplanted into plots treated with M. verrucaria remained healthy and vigorous throughout the growing season. Since M. verrucaria effectively controlled several common weeds under field conditions, this fungus appears to have potential as an effective bioherbicide for pre-plant weed control in production systems with transplanted tomato.     

Interference of horse purslane (Trianthema portulacastrum L.) and other weeds affect yield of autumn planted maize (Zea mays L.)

To assess comparative losses of Trianthema portulacastrum (HP) relative to other weeds, the experiment was set during consecutive summer seasons 2018 and 2019 at the Research Farm MNS-University of Agriculture, Multan, Pakistan. Experiment consisted three replications which were laid out under randomized complete block design. Experiment consisted of ten treatments viz: weeds free (whole season), HP free till 20 Days after emergence (DAE), HP free till 40 DAE, HP free till 60 DAE, all weeds free 20 DAE, all weeds free 40 DAE, all weeds free 60 DAE, weedy check (all weeds), weedy check except HP and weedy check containing only HP. During 2018 in all weeds weedy check, maximum HP relative density (33.33%) was observed while in 2019, plot where weeds were controlled from growing till 20 DAE showed (80%) relative density at 30 DAE. HP maximum frequency (66.67%, 77.78%) and relative frequency (66%, 100%) was recorded at 45 DAE in plots where HP was kept controlled till 20 DAE and all weeds kept controlled till 20 DAE, respectively. Maximum number of grains per cob (738, 700.68), 1000 grain weight (306.66, 271.51 g) and grain yield (6150, 8015 kg hec^-1) were recorded in plots which were kept all weed free till 60 DAE. As the competition period of weeds increased over 40 DAE, it substantially reduced yield of maize. Keeping the plots HP free till 40 DAE in the maize fields with HP as the major dominating weed, likely increase in maize grain yield is up to 30% compared to the fields where HP left un attended throughout the growing season. However, if maize field is infested with a mix of weeds with more than one dominating weeds including HP, compared to weedy situation the whole season, 30% higher grain yield can be obtained if all weeds are kept controlled till 40 DAE. Hence it can be concluded that whether the farmers face heavy HP infestation only or the mix of weeds as dominating weeds, in either case farmer should control weeds within first 40 days in maize field for better grain yield.     

稻田水面漂浮的杂草种子种类及动态

为了揭示杂草种子的漂浮动态,并为探寻生态控草方法提供理论依据,我们于2005年6-11月,在南京沧波门稻作区调查了水稻种植前及生长后期田问杂草群落以及稻田灌水期间水面漂浮的杂草种子的种类及漂浮时间.结果表明,在水稻种植前及生长后期田间出现有15科24种杂草;可漂浮于水面的杂草种子有17科26种,与田间发生的杂草种类相同的共有18种,占所有32种杂草的56.25%.这些杂草主要隶属于禾本科、蓼科、毛茛科、报春花科、莎草科、菊科和雨久花科.田埂附近漂浮的杂草种类及种子数量均高于田中间;各类杂草种子的漂浮能力不一,其中菵草(Beckmannia syzigachne)、泽珍珠菜(Lysimachia candida)、茴茴蒜(Ranunculus chinensis)、齿果酸模(Rumex dentatus)、蛇床(Cnidium monnieri)、鳢肠(Eclipta prostrata)和看麦娘(Alopecurus aequalis)等在田间水面漂浮能力较强.漂浮期间杂草种子除多集中于田埂附近,也附着于稻稞周围,并有互相结联的趋势.从整体上看,杂草种子漂浮2天后骤降,8天后基本全部沉降.显然,稻田生境的杂草种子大多可以漂浮于水面传播扩散.因此在灌水早期采取过滤或清除水上漂浮杂草种子可以减少杂草种子的输入和加速杂草种子从田间输出,减少杂草发生基数.     

长期稻鸭共作对稻田杂草群落组成及物种多样性的影响

2000~2003年连续4年研究了稻鸭共作条件下田间杂草群落的特征及其动态变化规律。结果表明,在长期稻鸭共作条件下,田间杂草密度逐年降低,下降趋势符合阻滞模型y=k+a·e^bx,模型参数b反映了杂草种群的下降速率。在稻田6种主要杂草中,水虱草(Fimbristylis miliaceae)、陌上菜(Lindernia procumbens)、丁香蓼(Ludwigia prostrata)种群数量降低较快,鸭舌草(Monochoria vaginalis)、异型莎草(Cyperus difformis)次之,稗(Echinochloa crusgalli)最慢。稻鸭共作使稻田杂草群落的物种多样性持续降低,群落均匀度提高,群落相似性与稻鸭共作前相比逐年降低。说明稻鸭共作改变了田间杂草的群落结构,有利于限制杂草的发生危害。随着稻鸭共作的连年进行,对田间杂草的控制效果逐渐上升,4年后达99%以上。稻鸭共作是稻田替代化学除草的一种非常有效的生物、生态控草措施,具有显著的经济和生态效益。     

红薯对农田杂草群落及其多样性的影响

为了解红薯(Ipomoea batas)对农田杂草群落和生物多样性的影响, 作者研究了云南省东南部红河州建水县5种不同覆盖度红薯田的杂草种类、密度、重要值及多样性。结果表明, 5种红薯田共统计到25种杂草, 隶属18科。其中4种入侵植物藿香蓟(Ageratum conyzoides)、鬼针草(Bidens pilosa)、牛膝菊(Galinsoga parviflora)、牛筋草(Eleusine indica)和2种本地植物马齿苋(Portulaca oleracea)、马唐(Digitaria sanguinalis)的密度较高, 为红薯田杂草群落的优势物种。随红薯覆盖度增加, 杂草优势物种的密度和重要值显著降低(P<0.05), 然而2种本地物种打碗花(Calystegia hederacea)和早熟禾(Poa annua)密度却显著增加, 2种本地物种铁苋菜(Acalypha australis)和稗(Echinochloa crusgalli)重要值与红薯覆盖度成正相关(P<0.05)。红薯覆盖度为1-25%和26-50%时, 杂草群落的物种丰富度(23.5、24.5)、Simpson指数(0.89、0.85)、Shannon-Wiener指数(2.36、2.35)和Pielou均匀度指数(0.75、0.73)较高, 说明中低水平的红薯覆盖度有利于提高群落的物种多样性。可以推断, 红薯种植改变了农田杂草的群落结构, 有利于限制优势杂草和入侵杂草的发生危害, 中低水平的红薯覆盖度可作为一种有效的旱田替代化学除草剂的生态控草措施。