不同牧草混播方式对冬闲田杂草发生及种类的影响

为了解冬闲田播种的不同种类牧草田的杂草群落发生动态，调查了30％黑麦草＋70％白三叶，30％黑麦草＋70％紫云英，30％黑麦草＋70％紫花苜蓿，3种不同牧草混播处理下冬闲田杂草的生长特点。结果表明：牧草混播种类的变化使冬闲田杂草的发生有差异，主要表现为杂草种类和危害程度不同，其中以30％黑麦草＋70％紫云英处理下的冬闲田杂草危害程度最低。     

Effects of alfalfa leaf extracts and phenolic allelochemicals on early seedling growth and root morphology of alfalfa and barnyard grass

Alfalfa (Medicago sativa L.) plants contain water-soluble substances that are autotoxic as well as allelopathic to other plants. Laboratory experimentation through a petri dish assay with imbibed seeds was conducted to evaluate the phytotoxic effects of alfalfa cv. “Vernal” leaf extracts, coumarin, trans-cinnamic acid, o-coumaric acid, and hydro-cinnamic acid on the seedling growth and anatomical responses of 6 day-old alfalfa and barnyard grass. With increasing concentration, the alfalfa leaf extracts significantly reduced root lengths of alfalfa and barnyard grass (Echinochloa crus-galli, Beauv. var. oryzicola Ohwi). Coumarin, trans-cinnamic acid, o-coumaric acid, and hydro-cinnamic acid at 10⁻⁴ M significantly reduced root lengths of alfalfa and barnyard grass. The root systems, especially root tips of alfalfa, were stunted and swollen by the aqueous alfalfa leaf extracts at 30 g l⁻¹ and coumarin at 10⁻³ M. This research suggests that alfalfa plant extracts significantly affected root growth and morphological differentiation of susceptible plants, resulting in reduction of their biomass in the presence of either autotoxic or allelopathic compounds. The results may have value in enabling weed control based on natural plant extracts.     

The effect of insecticide treatment on the establishment and growth of Italian ryegrass under different sowing conditions

Italian ryegrass, Lolium multiflorum Lam., cv. RvP., was broadcast in spring on to fine and coarse seedbeds at seed rates of either 2 or 20 kg ha^-1. Each of the four combinations of sowing condition was either left untreated or treated with fungicide or insecticide. The establishment of the sown species and of weeds under each regime was measured and their relative contribution to dry matter assessed in four cuts during the sowing year. Seed rate affected weed invasion and yield more than seedbed condition. Insecticide treatment increased the establishment and yield of ryegrass and its contribution to total herbage yield under all four sowing conditions. The fungicide treatment had no effect. The improvements caused by insecticide treatment were associated with a reduction in the level of infestation by shoot flies, Oscinella spp. (Diptera: Chloropidae): the effect of a single treatment in April was still detectable in October.     

Inhibitory effects of cover crop mulch on germination and growth of Stellaria media (L.) Vill., Chenopodium album L. and Matricaria chamomilla L.

Cover crops may suppress weeds due to their competitive effects and the release of inhibitory compounds. We examined the inhibitory influence of 11 cover crop mulches on the germination and growth of weed species (Stellaria media (L.) Vill., Chenopodium album L. and Matricaria chamomilla L.) in laboratory, greenhouse and field experiments. In the laboratory, cover crop extracts were tested in germination bioassays at six concentrations (0–500 mg ml⁻¹). The germination rate and root length (i) were measured 10 days after treatment (DAT). Pot experiments were carried out in the greenhouse to investigate the effects of cover crop mulch (ii) incorporated into the soil on weed germination and weed dry mass. Field trials measured the suppressive effects of cover crops and cover crop mixtures on weeds (iii). Correlations were determined between the experiments to quantify the competition and the biochemical effects of cover crops separately. Cover crop extracts at a concentration of 125 mg ml⁻¹ (i) significantly reduced the weed germination rate by 47% and the root length by 32% on average. M. chamomilla showed a lower susceptibility to the extracts of S. alba, R. sativus var. niger and H. annuus compared to C. album and S. media. The mulch-soil mixtures (ii) significantly reduced the germination rate by 50% and the dry mass by 47% on average across all three weed species, while M. chamomilla showed the highest tolerance to the mulches of V. sativa and A. strigosa. The correlation analysis revealed a strong positive correlation between extract toxicity and field weed suppression and, thus, indicated a high impact of the biochemical effects of the tested cover crops on weed suppression, especially for S. media and M. chamomilla.     

Component yields and quality of binary mixtures of lucerne and perennial, Italian or short rotation hybrid ryegrass

Studies were conducted to characterize sward dynamics of lucerne ( Medicago sativa L.) and perennial, Italian or short rotation hybrid rye-grass ( Lolium perenne L. and L. multiflorum Lam.) binary mixtures under hay management. Lucerne/timothy ( Phleum pratense L.) mixtures were included as controls. The study was conducted on two farms in central Pennsylvania, USA on Hagerstown silt loams (fine, mixed, mesic hapludalf). Total dry matter yield, grass yield and yield of digestible dry matter were higher for tetraploid perennial and tetraploid Italian ryegrass mixtures than for timothy mixtures. Seasonal production differed for the three kinds of ryegrass. Italian ryegrass dry matter yields were higher in cuts 2 and 3 than perennial ryegrass yields. Grass yields represented 34%, 24% and 12% of total yields of the Italian, perennial or short rotation, and timothy mixtures, respectively. However, herbage in vitro dry matter digestibility of Italian was lower than that of perennial ryegrass.
The tetraploid perennial ryegrasses Grimalda and Reveille had high-ranking N concentrations more frequently than other cultivars, while Bar-vestra and Reveille tetraploid perennials and Bison short rotation ryegrass had high-ranking dry matter digestibility values more frequently than the other cultivars. Perennial ryegrass cultivars and Lipo tetraploid Italian ryegrass persisted well for 4 years and produced higher yields with a lower weed content than timothy mixtures. It is concluded that perennial ryegrasses and Lipo Italian ryegrass should be recommended over timothy, as companion grasses with lucerne.     

Effects of Application of Alfalfa Pellet on Germination and Growth of Weeds

Summary

Allelopathy is well known as an interaction among plants (including microbes) through chemicals produced by plants. Recently, many investigations have evaluated the possibility of the use of allelo-pathic substances as a natural herbicide. Alfalfa (Medicago sativa L.) is reported to contain allelopathic chemicals that inhibit the growth of weeds. Experiments were conducted in Laboratory of Crop Science, Experimental Farm of Miyazaki University and Kobayashi city in Miyazaki Prefecture, Japan to determine the allelopathic impact of alfalfa pellet (commercial forage fodder) on germination and growth of lowland weeds, and its potential as a natural herbicide in paddy field. The results indicated that alfalfa pellet significantly inhibited germination and growth of 4 weed species, viz., Echinochloa orygicola, Digitaria ciliaris, Cyperus difformis and Monocholia vaginalis in rice paddies. Among the 4 tested weeds, the maximum inhibitory effect of alfalfa pellet was seen against Cyperus difformis. The degree of inhibition of weed growth by alfalfa pellet became stronger as the application of concentration increased. The results showed that alfalfa pellet might be used as a natural herbicide in rice paddies and might reduce the amount of herbicide used in paddy fields.     

绿肥对咖啡园杂草多样性及功能群的影响

为揭示绿肥对咖啡园杂草多样性及功能群的影响,调查了云南省保山市常规种植咖啡园（CK）、种植绿肥田菁咖啡园（SC）、种植绿肥硬皮豆咖啡园（MU）的杂草群落,探讨种植绿肥对咖啡园杂草群落的生态位、多样性、群落结构相似性及功能群的影响。结果表明：CK有杂草12科21种,SC有杂草10科16种,MU有杂草7科10种。3种类型咖啡园杂草生态位宽度大于0.600的杂草有10种,其中,CK有6种,SC有2种,MU有3种。种植绿肥的咖啡园杂草的物种丰富度、个体数、ACE估计值、Fisher α指数、Shannon-Wiene指数及生物量均低于常规种植咖啡园（CK）,其中,杂草物种丰富度、ACE估计值和鲜重具有显著性差异。常规种植咖啡园与种植绿肥咖啡园杂草群落结构不相似。3种类型咖啡园杂草单子叶一年生或越年生植物功能群占据最大优势,但种植绿肥咖啡园的占比更高。种植绿肥改变了咖啡园杂草群落的生态位、群落结构及功能群,降低了咖啡园杂草群落多样性,对咖啡园杂草群落产生了影响。     

The silage yield potential of hybrid ryegrass over a 5-year period in Northern Ireland relative to other ryegrasses and timothy

The yield and persistency of grass species within a managed sward are a major consideration when determining species mixtures for either long-term or short-term sward management systems. Perennial ryegrass is lower yielding but more persistent than Italian ryegrass. Hybrid ryegrass, an interspecies cross between perennial and Italian ryegrass, may be higher yielding than perennial ryegrass and more persistent than Italian ryegrass. Therefore, the yield and persistency of hybrid ryegrass was investigated in Northern Ireland in five experiments, each harvested over five consecutive years, and compared with that of Italian ryegrass, perennial ryegrass and timothy. The performance of the five grass species were in the expected order; Italian ryegrass was higher yielding than hybrid ryegrass, which was higher than perennial ryegrass, with timothy the lowest, whereas perennial ryegrass and timothy had significantly higher sward densities than the hybrid and Italian ryegrasses. In addition, it was found that the rate of decline in yield and sward density with age was the same for all species. Consequently, this study indicated that the higher yielding Italian and hybrid ryegrasses could continue to out-perform perennial ryegrass for 5 years, opening the possibility of more extensive farming use of these species, particularly in Northern Ireland.     

Growth Stage of Cyperus esculentus Influences Its Allelopathic Effect on Ectomycorrhizal and Higher Plant Species

Summary

Live plants and plant material in various forms have important roles in ecological processes. Weeds may be involved in interactions with desirable species at different trophic levels through the production and release of allelochemicals. The allelopathic potential of the weed Cyperus esculentus (yellow nutsedge) was assessed by preparing aqueous extracts from tubers and foliage from immature or mature plants, and testing their effects on an ectomycorrhiza and two higher plant species. The extracts from tubers and both foliage types significantly reduced the colony diameter of the ectomycorrhiza Boletus maxaria, which was isolated from roots of the forestry species Pinus patula, on agar medium. Extracts (2% m/v) from C. esculentus tubers and the foliage of immature plants inhibited the germination of lettuce (Lactuca sativa) seeds significantly. At 5% concentration, the extracts from foliage of immature weed plants completely inhibited the germination of lettuce seeds at the end of the 7-day trial period. The emergence of corn (Zea mays) was retarded in soil where C. esculentus tubers were planted 28 days before planting the crop, irrespective of whether the weeds continued to grow or were physically removed at the time the corn was sown. In contrast, where weed tubers and corn seeds were planted at the same time, emergence of corn was not affected. It is suggested that the growth stage of weeds be considered in the assessment of their direct and indirect allelopathic effects, and in predictions for their impacts on crop development and yield.     

Can winter cover crops influence weed density and diversity in a reduced tillage vegetable system?

Weeds are a major constraint for organic crop production. Previous research has found that cover crops in reduced tillage systems can provide weed interference, subsequently reducing inputs and improving crop yield. However, questions remain about effects of cover crop species identity and cover crop biomass on weed suppression and crop yield. This four-year study investigated how winter cover crops grown alone or in mixture influenced weed presence and crop yield in a reduced tillage organic vegetable system. Treatments were barley (Hordeum vulgare L.), crimson clover (Trifolium incarnatum L.), mixed barley + crimson clover, and a no-cover crop control. Plots were flail-mowed and strip-tilled prior to planting main crops (2011 and 2012: broccoli Brassica oleracea L.; 2013 and 2014: crookneck squash Cucurbita pepo L.). We measured density, diversity, and community composition of weeds and viable weed seeds, changes in weed percent cover within growing seasons, and crop yield. We found that the presence of barley, crimson clover, or barley + crimson clover reduced weed density by 50% relative to the control. Cover crop biomass negatively influenced weed density and weed seed diversity, and positively influenced squash yield. Weed percent cover within growing seasons did not respond differentially to cover crop treatment. Cover crop treatment and cover crop biomass had no influence on weed or weed seed community composition. These results suggest that reduced tillage winter cover crops in mixture or monoculture can similarly suppress weeds and improve yield, primarily due to biomass effects.     

Ecological studies on Echinochloa crus-galli and the implications for weed management in direct-seeded rice

Echinochloa crus-galli, a C₄ grass, is one of the world’s most serious weeds. Weed management decisions for this species can be derived from knowledge of its seed biology. Studies were conducted to determine the effects of light on germination; seed burial depth and rice residue on emergence and growth; and flooding time and depth on emergence, survival and growth of this species. Light stimulated seed germination but it was not an absolute requirement for germination. The proportion of seeds germinating was greatest for seeds placed on the soil surface (92%), and emergence declined with increasing burial depth in soil; no seedlings emerged from the depth of 8 cm. A burial depth of only 0.4 cm reduced seedling emergence by 50%. Seedling emergence and seedling biomass were reduced by the addition of high level (6 ton ha⁻¹) of rice residue to the soil surface. Early and deep flooding significantly suppressed growth of E. crus-galli seedlings. In flooded conditions, with increased water depth the weed allocated more biomass to shoots at the expense of roots. The information gained from this study could contribute to improve weed control approaches. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence, use of crop residue as mulch and early flooding of the crop could serve as important tools for managing E. crus-galli and other weed species with similar germination requirements. These management options, however, would need to be compatible with other crop management requirements.     

Sward maintenance of Lolium multiflorum by slurry seeding

A field investigation into the effect of slurry seeding on the dry-matter yield and persistence of an Italian ryegrass sward was assessed over a 3-year period (1984–86) under a regime of three cuts per season combined with sheep grazing in early spring and late autumn. Results showed that slurry plus seed treatments produced up to 30% more herbage dry matter and a significantly higher tiller density than where no slurry or seed were used. Slurry application with and without seed also reduced the proportion of weed grasses ( mainly Poa spp.) in the sward. It is concluded that slurry seeding is a useful technique for extending the productive life of an Italian ryegrass sward.     

Presence of Drechslera species in certified ryegrass seed-lots

Samples of 39 perennial ryegrass ( Lolium perenne L.) and 24 Italian ryegrass ( Lolium multiflorum Lam.) commercial seed-lots used at the Grassland Research Institute between 1974 and 1978 were examined for the presence of seed-borne Drechslera species. The five species of Drechslera isolated from the seeds were D. andersenii, D. siccans, D. nobleae, D. sorokiniana and an unidentified Drechslera sp.
A high proportion of the seed-lots were infected but levels of infection were low except in the perennial ryegrass cv. S24. Infection was located more commonly inside the caryopses than externally on the lemmas and paleae, and about 12% of the seedlings growing from infected seeds were infected. The species recovered in the seedlings were the same as those observed on the seeds.
There was no relationship between level of seed infection and level of damage observed in the field in the autumn of the first harvest year.     

Allelopathic Research in Permanent Improved Pastures of Inland Temperate Australia

Summary

Agricultural productivity is very dependent upon the successful establishment of crops and pastures. High populations of vigorous seedlings enable the crop or pasture to withstand competition from weeds and infection from diseases as well as providing good utilisation of nutrient inputs and water. Residues of weed and pasture species can interfere with crop establishment and pasture regeneration. Research at Charles Sturt University (CSU) and elsewhere in Australia has focused on a better understanding of these relationships and the management of each situation to advantage the pasture and to minimise the impact of the allelopathic effects. Such effects include poor germination and early seedling growth and are influenced by the variety and species of agricultural plants being grown.     

Yield loss prediction models based on early estimation of weed pressure

Weed control thresholds have been used to reduce costs and avoid unacceptable yield loss. Estimation of weed infestation has often been based on counts of weed plants per unit area or measurement of their relative leaf area index. Various linear, hyperbolic, and sigmoidal regression models have been proposed to predict yield loss, relative to yield in weed free environment from early measurements of weed infestation. The models are integrated in some weed management advisory systems. Generally, the recommendations from the advisory systems are applied to the whole field, but weed control thresholds are more relevant for site-specific weed management, because weeds are unevenly distributed in fields. Precision of prediction of yield loss is influenced by various factors such as locations, yield potential at the site, variation in competitive ability of mix stands of weed species and emergence time of weeds relative to crop. The aim of the review is to analyze various approaches to estimate infestation of weeds and the literature about yield loss prediction for multispecies. We discuss limitations of regression models and possible modifications to include the influential factors related to locations and species composition in context of their implementation in real time patch spraying.     

Does Allelopathy Play a Role in Suppression of Mugwort (Artemisia vulgaris) by Alfalfa?

Abstract

Alfalfa suppresses mugwort growth in the field. In the present study, the allelopathic effect of alfalfa on mugwort was examined using the above-ground (AGAB) and under-ground alfalfa biomasses (UGAB), and their water extracts. The sprouting of mugwort rhizomes or seed germination, growth of seedlings and leaf color changes in mugwort seedlings were evaluated in pot experiments. AGAB mixed into soil highly inhibited sprouting of mugwort rhizome fragments and growth of seedlings. The inhibitory effect was increased, and gradual leaf discoloration (yellowing) was observed in response to a higher dose of AGAB. However, UGAB affected neither sprouting of mugwort rhizome fragments nor growth of seedlings. The growth of mugwort seedlings was not significantly affected by water extracts of either AGAB or UGAB applied after emergence. The seed germination and seedling growth were significantly reduced by water extracts of AGAB and UGAB in the petri dishes experiments. These results indicated that the allelopathic effect of alfalfa along with the competitive ability and harvesting regime may play an important role in suppressing mugwort growth.     

Allelopathic effects of Ambrosia artemisiifolia L. in the invasive process

Ambrosia artemisiifolia (common ragweed), an annual native to North America, is now present in many European countries where it causes summer hay fever and interferes with several important crops. We investigated if common ragweed invasiveness could be explained by its leaf tissue and root exudate allelopathic potential on indicator crops (alfalfa, barley, maize, lettuce, tomato, and wheat), weeds (Echinochloa crus-galli, Solanum nigrum, Portulaca oleracea, and Digitaria sanguinalis), and common ragweed itself in laboratory and greenhouse conditions. Different residue substrates were prepared for soil incorporation and trials were conducted under both laboratory (1, 2, and 3 g residues/Parker dish) and greenhouse conditions (1.28 g residues/pot). The effect of the preparations on the germination and growth of the indicator crops and weeds were evaluated relative to soil previously used to grow A. artemisiifolia. Results showed tomato was the most sensitive indicator crop species as growth was reduced by more than 50% in both laboratory and greenhouse experiments. Lettuce root and shoot growth were also inhibited, but only when common ragweed residues, and not root exudates, were added to the substrate. Among the weeds, E. crus-galli was not affected by common ragweed while D. sanguinalis suffered a large germination reduction (90%) after incorporation of 3 g of residues. If common ragweed occurred as weed in a field, the cultivation of a less sensitive crop such as winter wheat should be considered before the cultivation of a more susceptible crop.     

Weed management in maize using crop competition: A review

Weeds are a major constraint to crop production, and are responsible for considerable yield losses in maize production systems throughout the world. Herbicides are widely used for weed control in maize production systems, but can have negative environmental consequences. Researchers have evaluated the use of crop competition and suppression to manage weeds in various crop combinations, including maize-based systems. Crop competition in maize may involve techniques such as reduced row spacing, increased planting density, and the use of competitive cultivars that exhibit weed suppressive potential. In this review, examination of the literature has revealed the considerable value of using crop competition in integrated weed management programs. Research has demonstrated that narrowing row spacing to half the standard distance reduced weed biomass by 39–68%, depending on weed species. Researchers have also demonstrated that increasing maize planting density by up to twice the standard rate achieved a reduction in weed biomass of 26–99%. While little research has been conducted into the use of competitive maize cultivars for weed management, several studies have documented cultivars with potential to suppress weeds. Attributes of weed competitive cultivars include high leaf area index, and other elements of leaf architecture that improve light interception by the crop, so increasing the shading of weeds. Combining crop competition methods with other agronomic practices can increase their effectiveness in controlling weeds. For example, biomass of Setaria italica (L.) Beauv was reduced by 60% when maize planting density was increased by 1.5 times the recommended spacing, and this effect was more pronounced when fertilizer was banded rather than broadcast. In summary, the strategic use of crop competition to control weeds has been a success in many regions, and is an important tool in integrated weed management. The importance of crop competition methods has particular relevance where farmers are unable to afford herbicides, as making use of crop competition is more economical.     

Growth and weed suppression ability of common and new cover crops in Germany

Cover crops have a wide-ranging influence on the agroecosystem and create multiple benefits for farmers. A major benefit of cover crops is the suppression of weeds during fall and winter, which can help to reduce soil tillage and herbicide use. However, only a small number of cover crop species are currently grown in Germany. To enlarge this number, four new cover crop species including tartary buckwheat, forage radish, red oat and grain amaranth were tested in comparison with common cover crop species such as white mustard, oilseed radish and phacelia. Emergence, soil coverage, dry matter production and weed suppression ability was assessed for all cover crop species. White mustard emerged faster than all other cover crops and produced the highest amount of shoot dry matter at both locations in southwest Germany twelve weeks after planting (WAP). Oilseed radish was the only cover crop that reduced the weed dry matter in all experiments eight WAP. Phacelia was able to reduce weed density by 77% at Meiereihof twelve WAP. Tartary buckwheat offered the highest soil coverage four WAP, produced the greatest shoot dry matter eight WAP and reduced weed dry matter by more than 96% at Meiereihof and Ihinger Hof twelve WAP. Forage radish produced the highest root dry matter and reduced spring weed density by more than 81% in all experiments. Red oat and grain amaranth emerged slowly, produced less biomass than other cover crops and did not suppress weed growth. The results show that tartary buckwheat and forage radish are well suited as new cover crops in Germany due to their fast growth and good weed suppression ability.     

Effects of water-saving irrigation on weed infestation and diversity in paddy fields in East China

The purpose of the article is to investigate the effects of water-saving irrigation on weed infestation and diversity in paddy fields; a two-year field experiment was conducted in Gaoyou Irrigation District, China. The responses of two irrigation treatments, controlled irrigation (CI) and traditional irrigation (TI), were observed and compared. The irrigation water use, yield, weed density, coverage ratio, height, species richness, density, dominant species, Shannon–Wiener index, and Pielou index were examined to analyze the water productivity, weed infestation, and diversity in paddy fields under the two treatments. The results showed that the water conditions were similar before the late tillering stage, and thereafter the CI fields were alternatively dry and wet with shallow standing water and low soil water content, while the TI fields were mostly continuously flooded by deep standing water and high soil water content. Irrigation water use for CI was 46.8% lower than TI. The CI treatment reduced weed density by 38.0%, decreased coverage ratio by 13.8%, and resulted in a 39.0% increase in weed height. Fewer species were found in CI fields than TI fields. The Shannon–Wiener index decreased by 11.5%, and the Pielou index increased by 3.2%. The changed water regime under CI not only impeded the growth of dominant species but also placed the whole weed community at a relatively stable level with reduced weed density. Meanwhile, aquatic weeds were well controlled; however, semi-aquatic weeds became the dominant species. In general, CI effectively reduced the risk of weed outbreaks, and weed diversity also decreased when it reduced irrigation water use.