Strip-tilled Cover Cropping for Managing Nematodes, Soil Mesoarthropods, and Weeds in a Bitter Melon Agroecosystem

A field trial was conducted to examine whether strip-tilled cover cropping followed by living mulch practice could suppress root-knot nematode (Meloidogyne incognita) and enhance beneficial nematodes and other soil mesofauna, while suppressing weeds throughout two vegetable cropping seasons. Sunn hemp (SH), Crotalaria juncea, and French marigold (MG), Tagetes patula, were grown for three months, strip-tilled, and bitter melon (Momordica charantia) seedlings were transplanted into the tilled strips; the experiment was conducted twice (Season I and II). Strip-tilled cover cropping with SH prolonged M. incognita suppression in Season I but not in Season II where suppression was counteracted with enhanced crop growth. Sunn hemp also consistently enhanced bacterivorous and fungivorous nematode population densities prior to cash crop planting, prolonged enhancement of the Enrichment Index towards the end of both cash crop cycles, and increased numbers of soil mesoarthropods. Strip-tilled cover cropping of SH followed by clipping of the living mulch as surface mulch also reduced broadleaf weed populations up to 3 to 4 weeks after cash crop planting. However, SH failed to reduce soil disturbance as indicated by the Structure Index. Marigold suppressed M. incognita efficiently when planted immediately following a M. incognita-susceptible crop, but did not enhance beneficial soil mesofauna including free-living nematodes and soil mesoarthropods. Strip-tilled cover cropping of MG reduced broadleaf weed populations prior to cash crop planting in Season II, but this weed suppression did not last beyond the initial cash crop cycle.     

Weed species differ in their ability to emerge in no‐till systems that include cover crops

No‐till cropping systems that include cover crops could lead to important changes in weed communities by decreasing some annual weed populations. In this study, we predicted that seed burial depth and the presence of cover crop would affect the emergence and initial growth success of annual weed species. We tested two factors on 14 weed species in a greenhouse: the seed burial depth of weeds (buried versus soil surface) and the presence/absence of a cover crop (ryegrass). We counted the emerged seedlings and measured the height of weeds and cover crops (Hweed, Hcover), the dry matter content of weeds and cover crops (DMCweed, DMCcover) and the number of leaves of weeds (NLweed) on 1433 weed and 390 ryegrass individuals. Emergence of five weed species (AMBEL, ANGAR, BROST, CENCY and EPHHE) was affected by the seed location (?10.3% on average for unburied seeds), five other weed species (ALOMY, CAPBP, SONAS, VERPE and VLPMY) were affected by cover (on average ?9.5% for seeds emerged in the presence of cover crop), and four weed species (GERDI, LAMPU, POAAN and VIOAR) were not affected by either. Weed growth of all weed species also decreased with the presence of a cover crop (on average Hweed: ?49.9%, DMCweed: ?87.2% and NLweed: ?55.4%) and for unburied seeds (on average Hweed: ?33.7%, DMCweed: ?70.6% and NLweed: ?43.3%), with various responses according to species. This study indicates that annual weeds could be disadvantaged by no‐till systems using cover crops.     

香蕉园施用白花鬼针草的控草增效作用

[目的] 探索香蕉园施用白花鬼针草的可行性。[方法] 采用培养皿萌发试验生物测定法,以发芽率、发芽势、发芽指数、活力指数等化感效应指标评价白花鬼针草对蕉园4种优势杂草的化感作用,同时通过盆栽模拟试验探讨香蕉园施用白花鬼针草后杂草、香蕉和土壤三者的关系。[结果] 当白花鬼针草浸提液浓度为0.0125 g·mL^-1时,对马唐综合化感效应为促进作用,对短叶水蜈蚣、牛筋草、柔弱斑种草综合化感效应为抑制作用,白花鬼针草浸提液浓度为0.025~0.1 g·mL^-1,对4种受体杂草综合化感效应均为抑制作用;白花鬼针草处理具有降低种子发芽率,延缓种子发芽时间的作用,同时对杂草萌发后的鲜重有微弱促进作用,但这种促进作用较弱,综合化感效应表现为抑制作用。随着白花鬼针草茎、叶施用量的增加,控草增效作用不断提升,当施用量为400 g·株^-1时,控草增效作用最佳,对杂草综合株防效为78.99%,综合鲜重防效为70.60%,香蕉苗生物量增加19.79%,土壤有机碳、碱解氮、速效钾依次增加8.72%、10.36%、16.30%。[结论] 本研究初步探明了在香蕉园施用白花鬼针草具有防控蕉园优势杂草、提高土壤肥力和促进香蕉生长的效应。     

黄淮海地区夏玉米田一年生杂草的生态经济防治阈期研究

 本文通过北京和唐山多年多点田间试验,研究了黄淮海地区夏玉米田苗后放任和免除自生一年生杂草生长的相对时间与夏玉米相对产量的函数关系,并据此导出了该区夏玉米田一年生杂草的生态经济防治阈期计算模型。结果发现,该区夏玉米田一年生杂草的生态经济防治阈期约处在夏玉米苗后总生育期的(天)第11.2—50.9%之间。该区夏玉米生长季节中只要此期田间保持无草,便可望以最小的代价和费用,最大限度地使杂草弃害扬利,从而获得较高的生态经济除草效益。     

The conservation of arable weeds at crop edges of barley fields in northeast Spain

The effects of weed control practices and fertilisation on weed flora and crop yield were evaluated in crop edges of barley fields in northeastern Spain. The study was carried out in four organic and four conventional barley fields. In each field, four permanent plots were delimited at the crop edge, and fertilisation and weed control treatments in a factorial design were applied over 3 years. Weed composition and the aboveground biomass of weeds and barley were recorded before the crop harvest in the first and the third year. We found relatively low values of species richness per field, as well as low values of weed biomass, especially in the organic crop edges (3.9% of total biomass). Weeds were significantly reduced by herbicide applications on conventional fields and were not affected by weed harrowing on organic fields or fertilisation. These results demonstrate that specific measures are needed to enhance biodiversity at crop edges both in organic and conventional fields. Our results also suggest that under Mediterranean conditions and among impoverished weed communities, limiting the use of herbicides is crucial to enhancing arable diversity and that, contrary to findings found in previous studies in temperate climates, fertilisation and weed harrowing have little effect on weeds.     

Weed control and cover crop management affect mycorrhizal colonization of grapevine roots and arbuscular mycorrhizal fungal spore populations in a California vineyard

Arbuscular mycorrhizal (AM) fungi naturally colonize grapevines in California vineyards. Weed control and cover cropping may affect AM fungi directly, through destruction of extraradical hyphae by soil disruption, or indirectly, through effects on populations of mycorrhizal weeds and cover crops. We examined the effects of weed control (cultivation, post-emergence herbicides, pre-emergence herbicides) and cover crops (Secale cereale cv. Merced rye, × Triticosecale cv.Trios 102) on AM fungi in a Central Coast vineyard. Seasonal changes in grapevine mycorrhizal colonization differed among weed control treatments, but did not correspond with seasonal changes in total weed frequency. Differences in grapevine colonization among weed control treatments may be due to differences in mycorrhizal status and/or AM fungal species composition among dominant weed species. Cover crops had no effect on grapevine mycorrhizal colonization, despite higher spring spore populations in cover cropped middles compared to bare middles. Cover crops were mycorrhizal and shared four AM fungal species (Glomus aggregatum, G. etunicatum, G. mosseae, G. scintillans) in common with grapevines. Lack of contact between grapevine roots and cover crop roots may have prevented grapevines from accessing higher spore populations in the middles.     

Weed development in spring wheat after contrasting soil tillage and nitrogen management

Soil tillage and nitrogen (N) management effects on weed species composition were evaluated in 2013 and 2014 on a clayey soil after 5‐years of organic management at the Royal Agricultural University's Harnhill Manor Farm, UK. Three tillage systems – Conventional Tillage (CT), and High and Low Intensity Non‐inversion Tillage (HINiT & LINiT) – were compared at four N fertiliser rates of 0, 70, 140 and 210 kg N ha^?1. Broad‐spectrum herbicide was applied before soil operations across the site in both years. Previous organic management legacy of high weed biomass promoted greater weed prevalence in 2013 while 2‐years of herbicide inclusion reduced weed biomass. Contrasting weather conditions across the seasons affected weed incidence. In the 2014 wet season, early weed dry weight (DM) was higher under HINiT than CT and LINiT, while no differences were observed in the 2013 dry year. At midseason, weed DM was higher under HINiT than CT and LINiT in both years, which was related to higher DM of the dominant weeds Stellaria media (L.) Vill. and Sinapis arvensis L. Grass weed DM was higher under non‐inversion tillage than CT. N fertilisation increased midseason total weed DM and weed prevalence at harvest. Spring wheat yield was the highest under CT while LINiT produced 17% higher yields than HINiT. Despite higher but still tolerable weed prevalence under both non‐inversion tillage systems and with the application of N, weeds alone was not the only yield‐limiting factor. However, results show that CT is the most reliable option for weed control in changing weather, while N fertilisation rates needs to be considered.     

Study of soil algae

Summary Algal techniques were used to study the soil factors affecting the toxicity of herbicides. It was found that the organic matter adsorbed 18 times more herbicide than clay. The inherent phytotoxicity of different herbicides was tested by these methods and the results obtained compared favourably to those of higher plants. The order of toxicity as tested by algae was: diuron >neburon>monuron>atrazine>simazine>atratone. The prediction of application rates of diuron and simazine by algal methods was tested in the field with wheat as cereal crop. The data obtained testified that the predictions were correct and better than the commercial recommendation. Good chemical control of weeds was achieved by herbicide at the early stage of crop growth. At later stages of crop development the toxicity of the chemical was reduced to insignificance and the crop plants were then capable to compete successfully against the emerging weeds. Thus a biological weed control was obtained. Such combined chemical-biological weed control technique should be regarded as the most desirable practice in agriculture.     

Interactions of maize and Italian ryegrass in a living mulch system: (1) Shoot growth and rooting patterns

It has been demonstrated that the use of living mulches solves some of the environmental problems associated with the conventional cropping of maize (Zea mays L.). However, plant growth and yield are often reduced in such a cropping system. Since shoot competition between the main crop and the cover crop can be avoided by regular cutting of the cover crop, it was hypothesized that decreases in maize growth and yield in a living Italian ryegrass (Lolium multiflorum Lam.) mulch must be related to below ground interactions between the two species and that these may be traced back to the characteristics of their root systems. Two cropping systems, maize grown alone in bare soil (conventional cropping, BS) or together with a living Italian ryegrass mulch (LM), were studied in lysimeters (1.0 m² surface area and 1.1 m depth) placed outdoors, near Zurich Switzerland, for a duration of three years. In the LM treatment a strip, 0.3 m wide, in the center of the plot around the maize row was free of grass. For comparison, an Italian ryegrass (RG) treatment, managed as the LM treatment but without maize plants, was also included in the study. Minirhizotrons (54 mm inner diameter) were horizontally installed at ten soil depths between 0.0 and 1.0 m, perpendicular to the orientation of the maize rows. The development of the maize shoot and the rooting patterns were observed non-destructively. LM strongly modified the maize crop by decreasing growth and duration of the leaf area, and thus biomass and grain yield at harvest by as much as 78 and 72%, respectively. Maximum root densities in the three treatments were observed around the time of maize anthesis. However, BS maize was unable to build up root densities similar to those observed in Italian ryegrass plots at the time of maize sowing. The root densities of the LM and the RG treatments were usually similar. The inability of the maize plants to establish a competitive root system in the LM limits the supply of nutrients and water and therefore reduces growth and yield. Improving the productivity of maize in living mulches will depend on the ability to achieve a better separation of the rooting volumes of the two species, so that specific steps to facilitate the main crop and control the living mulch can be taken.     

Allelopathic effect of Bromus spp. and Lolium spp. shoot extracts on some crops

Allelopathy is an untapped resource for weed control in crops that could give good possibilities for environmentally sound, integrated crop production. Allelopathy is defined as the direct or indirect harmful or beneficial effects of one plant on another through the production of chemical compounds, called allelochemicals, which escape into the environment. Allelochemicals can be produced by weeds and affect crops, and the reverse is also true. Allelopathic interactions include weed-weed, weed-crop, and crop-crop. Allelopathy offers potential for selective biological weed control for instance weed-suppressing crops and the use of plant residues in cropping systems, allelopathic rotational crops, or companion plants with allelopathic potential. Bromus species occur in many habitats in temperate regions of the world, including America, Eurasia, Australia, and Africa. The genus Lolium is one of the most important forage grasses. The weed species usually grow in the same production zones as wheat and are considered weeds since they parasitize wheat fields. Some of the weed species in these two genus have been reported to have allelopathic effect. One of the methods that has been successful in studying allelopathic activity are bioassays. Laboratory experiments were conducted to determine allelopathic effect of watery shoot extracts of four weed species of the Poaceae family, namely Bromus rigidus, Bromus diandrus, Lolium multiflorum and Lolium temulentum on germination and growth of winter wheat (Triticum aestivum L.), spring barley (Hordeum vulgare L.), corn (Zea mays L), perennial ryegrass (Lolium perenne L.), bean (Phaseolus sp.) and sunflower (Helianthus annuus L.) and on each other. The experiment was carried out during the period March 2010 to October 2010. Twenty five seeds were put into one Petri-dish on filter paper, adding 15ml of extract to each in four repeats. The germination took place in a Binder-type thermostat in the dark. The timing of germination was checked in every two days and the rate of growth was estimated after a week, by counting the number of germinated seeds and measuring the length of the radicle and plumule. The measured data was statistically analyzed and the effect of the extracts on germination percentage and seedling length was evaluated.     

Composting One Invasive Species to Control Another

The need for research and development of effective approaches to weed control continues to increase globally. Adaptive protocols using diverse control methods are often required in ecological restoration as recruitment of native species is highly site‐specific, species‐specific, and experimental. The use of composted weed refuse to control other weeds may be a practical option; yet, the option is not well studied due to the accompanied risk of introducing weed propagules to areas where weed control is desired. Here, we tested the effectiveness of different physical control techniques including the use of mulch made by composting weed refuse on‐site. English ivy (Hedera helix), a non‐native, invasive species in the Pacific northwestern United States, was removed from a heavily invaded site, shredded, and composted. The mulch was compared with other methods of suppressing herb Robert (Geranium robertianum), another invasive species on‐site. Five treatments were tested: flame‐weeding, hand‐pulling, mulching, hand‐pulling followed by mulching, and flame‐weeding followed by mulching. The mulch and pull/mulch treatments were the most effective, reducing G. robertianum cover by 92 and 86% of pre‐treatment levels, respectively, and suppressing G. robertianum 2.9 and 1.6 times more than the control, respectively. The mechanism behind the effectiveness of the mulch is uncertain, but may be related to weed seed burial or the allelopathic potential of the mulch. Composting one invasive species to use as mulch to control another can be effective and merits trial elsewhere.     

Influence of crop background on aphids and other phytophagous insects on Brussels sprouts

More Brevicoryne brassicae and other alate aphids were caught in yellow water-traps in a weed-free crop of Brussels sprouts than in a crop with a weedy background. More B. brassicae colonized Brussels sprout plants in bare soil than in weeds; very few alatae were attracted to cruciferous weeds in the crop. Results in 1 yr suggest that initially larger populations on the weed-free sprouts became smaller than populations on the weedy sprouts because the larger aphid population attracted more natural enemies. Aleyrodes brassicae and certain Lepidoptera were also more abundant on sprout plants in bare soil than on sprouts surrounded by weeds; more adult A. brassicae were caught in water traps over the bare soil. More A. brassicae were present on sprout plants surrounded by a green than by a brown cloth background but the differences were not significant (P < 0–05). Numbers of B. brassicae on sprout plants with green and brown backgrounds varied greatly and did not differ significantly. In field cages, B. brassicae alatae were more attracted to potted sprout plants surrounded by bare soil than to ones surrounded by rings of living or cut grass or by artificial green rings. This effect was greater with small than with large sprout plants surrounded by grass rings. The maintenance of a limited weed cover is considered potentially useful in integrated control of some brassica pests.     

Effects of cover crops, weeds and plant debris on development of Mycocentrospora acerina in caraway

This paper reports on the search for inoculum sources of Mycocentrospora acerina on caraway (Carum carvi L.). Obvious suspects are cover crops of biennial caraway and preceding crops of annual caraway. Other suspects are weeds in or alongside the field. Finally, survival structures of the fungus, chlamydospore chains, packed in plant debris or naked, are suspected. M. acerina is able to infect many plant species, including cover crops of caraway such as spinach for seed production and peas. However, the agronomical suitability of a crop to serve as a cover crop of biennial caraway proved to be a more important factor in determining caraway yield than the susceptibility of the cover crop to M. acerina. This finding was corroborated by the fact that spinach and peas as preceding crops had no significant effects on M. acerina development in spring caraway sown the next year. Dill, barley and four weed species were found as new hosts of M. acerina. The role of weed hosts, susceptible crops and plant debris in the survival of the fungus in years without caraway is discussed. Caraway sown on soil containing infested caraway straw, infested debris of other plant species or chlamydospores grown in pure culture, became infected by M. acerina. Only high inoculum densities of chlamydospores in the soil caused severe damping-off of caraway seedlings. The opportunity for disease management by agronomical means is quite limited.     

The role of weed invasion in controlling sand dune reactivation in abandoned fields in semi-arid Inner Mongolia, China

The growth of crops and invading weeds were examined at six sites under different cultivation conditions in semi-arid Inner Mongolia, where sand dune reactivation has been controlled by weed invasion. The soil moisture content was not sufficient for crop growth in over-cultivated farmland. The shortage of moisture in the soil suppresses the growth of both crops and weeds. Accordingly, farmers carry out weeding to maintain better soil moisture conditions for crop growth. Over-cultivated farmland is often abandoned when the crop yield decreases to an economically unprofitable level. If weed vegetation before abandonment remains, it becomes a core of vegetation expansion and recovers the entire soil surface. While weedy vegetation is lacking or has been grazed by livestock, sand dune reactivation occurs.     

三裂叶豚草的化感作用研究

 本文研究了在我国东北地区广泛蔓延的菊科杂草—三裂叶豚草(Ambrosia trifida)对大豆、玉米、小麦、水稻的化感作用(Allelopathy)。通过对三裂叶豚草的不同部位(挥发物、茎叶、根、根区土壤)的化感活性的研究,发现三裂叶豚草的挥发物和根区土壤对作物无明显的作用;茎叶部分的水浸液对实验作物的种子萌发和幼苗的幼根伸长有明显的抑制作用,同时使根系形态发生较大的变化;根的水浸液对作物的幼芽伸长有一定的促进作用。在上述的研究基础上,对不同的活性组分进行了GC、GC/MS分析．结果表明主要的化感成分可能为α-蒎烯、β-蒎烯、2-冰片烯、里那醇、冰片、4-萜品醇、樟脑、α-萜品醇、马鞭烯酮、橙花叔醇、法尼烯、勺叶桉醇等。由此我们分析三裂叶豚草主要是通过雨水淋溶的方式向周围环境释放化感物质,从而对其它植物产生影响,加强自身在自然界的竞争力。     

Allelopathic influence of Vigna mungo (black gram) seeds on germination and radical growth of some crop plants

Intercropping of Vigna mungo (black gram) isprevalent for varied crop regimes in subtropical northern plains of India. Insugarcane, the negative impacts of a black gram intercrop on crop yields,rhizosphere soil properties and benefit: cost ratio have been reported. Thepossible allelopathic potential of black gram seeds on the germination,seedlingemergence and root elongation of other commercial crops is reported here. Theeffects of imbibed seeds of black gram, their aqueous leachate and seedextractson the germination and root elongation of seeds of four test crops viz. wheat,maize, gram and lentil, both under aseptic and soil conditions, wereinvestigated. Inhibitory effects were evident in all the bioassays of seeds ofthese crops. The black gram seeds directly and leachates were highly inhibitorybut the aqueous seed extract was less so. The observations indicate a releaseofinhibitory substances from black gram seeds leading to the observed inhibitoryeffects.     

Inhibitory effects of redroot pigweed and crabgrass on switchgrass germination and growth—from lab to field

Interactions between weeds and crops often occur by resource competition or allelopathy. However, it is still unknown how local weed species influence artificially introduced switchgrass. In this study, four experiments were conducted to evaluate the inhibitory effects of redroot pigweed (Amaranthus retroflexus) and crabgrass (Digitaria sanguinalis) on germination and growth of the lowland tetraploid switchgrass cultivar ‘Alamo’ (Panicum virgatum cv. Alamo). Switchgrass germination was significantly inhibited in Petri dishes, with 48.1% and 33.9% inhibitions on germination rate by redroot pigweed and crabgrass root aqueous extracts, respectively, at 0.1 g mL^?1 concentration. Significant inhibitory effects on switchgrass seedling biomass were observed at 5:5 ratio with redroot pigweed and crabgrass in glass jars, with 61.6% and 53.4% inhibitions on plant biomass, respectively. Under the same root segregation, redroot pigweed had a stronger inhibitory effect on switchgrass seedling growth than crabgrass. Growth of transplanted switchgrass seedlings was significantly inhibited by local weeds in the field, with 46.2% and 11.7% inhibitions on shoot biomass during the first and second growing seasons, respectively. However, no significant growth reduction in switchgrass was detected in the third growing season. These findings further our understanding of weed–crop interactions and could help develop weeds management strategies with ecological security.

     

Screening methods for the evaluation of crop allelopathic potential

There is increasing interest in the development of allelopathic crop varieties for weed suppression. Allelopathic varieties are likely to be able to suppress weeds by natural exudation of bioactive allelochemicals, thereby reducing dependence upon synthetic herbicides. Screening bioassays are essential tools in identifying crop accessions with allelopathic potential. A number of crops have been screened for this allelopathic trait, and key issues in selecting and designing screening bioassays are reviewed. It is recommended that a combination of different bioassays be used in the evaluation of crop allelopathic potential. Laboratory bioassays, field testing, and chemical screening are important steps, and none of them can be precluded if conclusive evidence of crop allelopathy is to be established. More concerted efforts are needed in screening crop germplasm before the development of allelopathic varieties occurs.     

Measuring the ecological preference for growth of 150 of the most influential weeds in weed community structure associated with agronomic and horticultural crops

The phytosociological researches which intent for studying the performance of weeds and the structure of weed assemblages associated with different crops derives their importance mainly from the adverse effect of weeds on crop productivity. Consequently, it is worth questioning about the ecological preferences of the weed growth in response to three main drivers for weed community structure associated with agronomic, and horticultural crops: crop diversification, crop seasonality, and soil type. A study area was selected comprising farmland of Nile Delta and its adjoining east and west territories, Egypt. A total of 555 species were recorded in 30 agroecosystems monitored and depending on species frequency/abundance values, 150 species were designated as the most influential weeds in weed community structure associated with agronomic and horticultural crops. The ecological preference of species for crop seasonality was evident through the results of Agglomerative hierarchical clustering. Three weed assemblage groups (WAG) identified: WAG A associated with winter agronomic crops, WAG B associated with summer agronomic crops, and WAG C associated with perennial agronomic crops and horticultural crops (orchards). Their diversity evaluated at different levels. The growth preference of the 150 species which were assigned as most influential weeds was gauged in response to the three environmental variables. 61 species were faithful to WAG A, 45 to WAG B, and 44 to WAG C. Concerning crop diversification, 34-species were significantly affected and scored coefficient of variation ≥ 100%. As for soil type, indicator species analysis revealed that 66-species show growth preference in fine grained soil while 84-species prefer coarse grained soil. In the three vegetation units (WAG A – C), 12 within-group associations (alliances) were specified of less-common (differential) species. The record of these alliances match to a specific environmental condition (ecological niche) and in them 29 strong indicators are identified. Redundancy analysis was used to extract and summarize the variation in species records in the response matrix (species vs. sites) that can be explained by the three different types of growth preference (explanatory variables), and the partial linear effect of them was evaluated by variation partitioning.