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.     

Does weed suppression by high crop density depend on crop spatial pattern and soil water availability?

Size-asymmetric competition, in which larger plants obtain a disproportionally larger share of contested resources, can be applied in agriculture to suppress weeds by increasing crop density and spatial uniformity, as these practices enhance the initial size-asymmetric competitive advantages of crop seedlings over weed seedlings early in the growing season. We do not yet know how agronomic factors influence weed suppression at high crop density. We performed a field experiment to ask how crop density, spatial pattern and irrigation interact to influence weed suppression and grain yield in semi-arid croplands. The experimental was a factorial design with 4 factors: wheat cultivar (Ningchun4, Xihan2), irrigation level (control, irrigated), sowing density (low, 196 seeds m⁻²; moderate, 400 seeds m^-2; high, 625 seeds m⁻²), and spatial sowing pattern (rows, uniform). Weed growth was effectively suppressed by increased crop density and spatial uniformity. Effects of crop density on weed suppression and grain yield were more pronounced in the uniform pattern than in crop rows. Weed biomass was 55.7% lower and grain yield increased 29.7% higher in the high density uniform pattern compared to the low density and row pattern. Crop density interacted with cultivar in determining both weed biomass and grain yield, potentially reflecting different traits regulating crop competitive ability. Irrigation and crop density had additive effects on weed biomass but interacted to influence grain yield. Our findings support the idea that increased crop density and spatial uniformity can make a valuable and environmentally friendly contribution to weed control in wheat, reducing the need for chemical or mechanical weed control. We need a better understanding of the interactions among climate, agricultural management and crop genotype to improve our ability to effectively suppress weeds with high crop density and spatial uniformity.     

Complementing cultural weed control with plant allelopathy: Implications for improved weed management in wheat crop

Wheat (Triticum aestivum L.) is an important cereal crop in Pakistan which is suffering from major grain production loss because of weed infestations. Control of weeds by herbicides is a primary weed management tool in wheat crop which can be detrimental to the environment and grain produce. Development of an efficient and eco-friendly alternate to the herbicidal weed control, testing the effectiveness of cultural weed control (crop row orientation, selected wheat genotypes and hand weeding) and plants water extracts was undertaken for weed control in wheat. An experiment was run under field conditions in winter season in 2016–2017 and in 2017–2018 in Khyber Pakhtunkhwa Province, Pakistan. The repeated experiment was each time undertaken using a randomized complete block design with a double split plot arrangements at the New Developmental Farm, University of Agriculture, Peshawar, Pakistan. The crop row orientations used were assigned to the main plots. The wheat genotypes used were assigned to the sub-plots. The allelopathic water extracts and hand weeding were assigned to the sub-sub plots. The averaged mean values for row orientations of both the years revealed lowest weed density (95.7 weeds m^?2), highest grains per spike (47.3), 1000 grains weight (44.7 g) in north to south row orientation. The averaged mean values of weed density (101.6 weeds m^?2), grains per spike (48.2), 1000 grains weight (45.9 g), crude protein content (12.793%), crude fat content (1.533%) and ash content (1.586%) were greater for the wheat genotype Pirsabaq-2013 and Atta-Habib-2010. Water extract of S. halepense, P. hysterophorus, H. annuus and hand weeding showed significantly lower weed density (84.0 to 93.3), grains per spike (50.9 to 48.3), 1000 grains weight (48.3 to 46.2 g), grains protein content (12.280 to 12.209%), grains crude fat content (1.471 to 1.464%) and grains ash content (1.523 to 1.515%). Interaction effect of different tested weed control treatments i.e. N-S × Pirsabaq-2013 and Atta-Habib-2010 × water extract of S. halepense, P. hysterophorus and H. annuus were found to show further reduction in weed density and enhance grains per spike and grains nutrition contributing parameters. Our results show that sowing wheat genotypes Pirsabaq-2013 and Atta-Habib-2010 in north-to-south row orientation, and application of water extract of S. halepense, P. hysterophorus, H. annuus can give an effective weed management and increased quality grain yield of wheat.     

High night temperatures during grain number determination reduce wheat and barley grain yield: a field study

Warm nights are a widespread predicted feature of climate change. This study investigated the impact of high night temperatures during the critical period for grain yield determination in wheat and barley crops under field conditions, assessing the effects on development, growth and partitioning crop‐level processes driving grain number per unit area (GN). Experiments combined: (i) two contrasting radiation and temperature environments: late sowing in 2011 and early sowing in 2013, (ii) two well‐adapted crops with similar phenology: bread wheat and two‐row malting barley and (iii) two temperature regimes: ambient and high night temperatures. The night temperature increase (ca. 3.9 °C in both crops and growing seasons) was achieved using purpose‐built heating chambers placed on the crop at 19:000 hours and removed at 7:00 hours every day from the third detectable stem node to 10 days post‐flowering. Across growing seasons and crops, the average minimum temperature during the critical period ranged from 11.2 to 17.2 °C. Wheat and barley grain yield were similarly reduced under warm nights (ca. 7% °C^?1), due to GN reductions (ca. 6% °C^?1) linked to a lower number of spikes per m². An accelerated development under high night temperatures led to a shorter critical period duration, reducing solar radiation capture with negative consequences for biomass production, GN and therefore, grain yield. The information generated could be used as a starting point to design management and/or breeding strategies to improve crop adaptation facing climate change.     

Competition by, and chemical control of, natural weed populations in spring-sown field beans (Vicia faba)

A field experiment was done in 1974 to determine the effect of the presence of weeds for different periods on the yield of field beans (Vicia faba cv. Maris Bead). A critical period of weed competition of 2 wk duration occurred from 3 to 5 wk after 50% crop emergence. When weeds were not controlled, seed yield was reduced by 46%, from 4–6 to 2–5 t/ha. In another experiment, in 1975, there was no evidence of a critical period. Seed yield was reduced by 48%, from 2–9 to 1–5 t/ha, when weeds were not controlled. Pre-emergence applications of simazine and of dimefuron, a new soil-residual herbicide, effectively controlled weeds and bean seed yields were similar to those of the regularly hand-weeded control. Dinoseb-acetate and early, but not late, post-emergence applications of dimefuron controlled weeds satisfactorily. Dimefuron is potentially useful in spring-sown field beans because it can be applied pre- or early post-emergence without damaging the crop.     

Interactions of two species of the genusChenopodium with two production plants—Sugar beet and spring wheat

TwoChenopodium species (C. album L.,C. suecicum J. Murr) were grown under field conditions with sugar beet to assess the weed-caused crop loss, and with spring wheat in a replacement series experiment. The weeds strongly reduced the growth of sugar beet. Dew's competition indexes for the regressions of sugar beet yield on weed density were 6.81 and 3.78 forC. suecicum andC. album respectively. On the other hand, the yield of spring wheat was not affected by the twoChenopodium species owing to early shading of the weeds by the faster growing crop stand.     

Effects of sowing date and volunteers on the infectivity of soil infested with Gaeumannomyces graminis var. tritici and on take-all disease in successive crops of winter wheat

In a field experiment on winter wheat, take‐all on plants and the infectivity of the soil were studied in crop sequences with different combinations of sowing dates. Take‐all was negligible in the first wheat crop, but thereafter the mean disease intensity (measured using a take‐all rating, TAR, with a maximum of 300) was 108, 190, 118 and 251 in the second to fifth successive crops. In each growing season, the disease differed amongst sequences and built up more rapidly and was more intense on plants sown in mid‐September than on plants sown in mid‐October. In late‐sown plots, where volunteers had been present during the mid‐September to mid‐October period, take‐all reached an intensity intermediate between that in early‐sown plots and that in late‐sown plots that had been kept free of volunteers. Volunteers, therefore, partially offset the expected beneficial effect of decreased disease with later sowing. Differences in take‐all amongst sequences were most pronounced in the second wheat crop and early sowing of the previous wheat increased intensity of disease. In the following (third) crop, differences in disease intensity amongst sequences were smaller. Soil infectivity (measured by seedling bioassay after harvest) built up progressively from a low level after the first crop to peak after the third crop. In this build‐up phase, soil infectivity estimates were always numerically greater after harvest of early‐sown treatments than after later‐sown treatments, although never significant at P= 0.05. The greatest difference (P= 0.06) was recorded in October before sowing of the third crop, where the comparison was between soil after two previous early sowings and soil after two previous later sowings and control of volunteers. In the same autumn, presence of green cover (i.e. volunteers) was associated with a smaller loss of soil infectivity between harvest and later sowing than occurred in an absence of green cover. In 2^nd–4^th crops, where comparisons were available and mean TARs indicated moderate levels of take‐all, sowing later had no yield benefit, despite more take‐all and greater soil infectivity associated with early sowing. Important considerations for the management of crops at risk of take‐all are 1) choosing appropriate sowing dates to minimize take‐all or to encourage take‐all decline and 2) controlling volunteers and weed hosts where crops are sown late to minimise take‐all.     

The impact of crop processing on the reconstruction of crop sowing time and cultivation intensity from archaeobotanical weed evidence

Reconstruction of crop sowing time and cultivation intensity, based on arable weed ecology, can resolve archaeological questions surrounding land use and cycles of routine activity, but crop processing may introduce systematic ecological biases in the arable weeds represented in products and by-products. Based on previous ethnoarchaeological work, there is a predicted bias against indicators of spring sowing and intensive cultivation in fine sieve products (and a corresponding over-representation of such species in by-products). Recent work on modern weed floras using functional weed ecology has identified distinctive functional attributes associated with different sowing regimes and cultivation intensity levels. Evaluation of the predicted biases using functional attribute data for modern weed survey studies of different sowing regimes (in Germany) and cultivation intensity levels (in Greece) suggests that there is a likely bias against spring sowing indicators in fine sieve products but not (apparently) against intensive cultivation indicators. An archaeological case study is presented in order to illustrate how bias relating to crop sowing time may be identified and interpreted.     

Impact of Fertilizing Pattern on the Biodiversity of a Weed Community and Wheat Growth

Weeding and fertilization are important farming practices. Integrated weed management should protect or improve the biodiversity of farmland weed communities for a better ecological environment with not only increased crop yield, but also reduced use of herbicides. This study hypothesized that appropriate fertilization would benefit both crop growth and the biodiversity of farmland weed communities. To study the effects of different fertilizing patterns on the biodiversity of a farmland weed community and their adaptive mechanisms, indices of species diversity and responses of weed species and wheat were investigated in a 17-year field trial with a winter wheat-soybean rotation. This long term field trial includes six fertilizing treatments with different N, P and K application rates. The results indicated that wheat and the four prevalent weed species (Galium aparine, Vicia sativa, Veronica persica and Geranium carolinianum) showed different responses to fertilizer treatment in terms of density, plant height, shoot biomass, and nutrient accumulations. Each individual weed population exhibited its own adaptive mechanisms, such as increased internode length for growth advantages and increased light interception. The PK treatment had higher density, shoot biomass, Shannon-Wiener and Pielou Indices of weed community than N plus P fertilizer treatments. The N1/2PK treatment showed the same weed species number as the PK treatment. It also showed higher Shannon-Wiener and Pielou Indices of the weed community, although it had a lower wheat yield than the NPK treatment. The negative effects of the N1/2PK treatment on wheat yield could be balanced by the simultaneous positive effects on weed communities, which are intermediate in terms of the effects on wheat and weeds.     

Reintroduction of rare arable plants by seed transfer. What are the optimal sowing rates?

相似文献   

长期不同施肥方式对麦田杂草群落的影响

以太湖地区农业科学研究所31a的长期肥料定位试验田为材料,分别于2011—2012年小麦苗期、拔节期和收获期进行了杂草群落调查,研究杂草类型与密度的分布、杂草多样性指数的变化,并对杂草种群分布与土壤养分因子进行冗余分析。结果表明:小飞蓬、看麦娘、大巢菜、稻槎菜、通泉草是本地区小麦生长期的主要杂草类型;随着小麦的生长以及氮肥、有机肥的施入,杂草密度呈下降趋势;施入有机肥降低了麦季杂草的群落多样性指数,在小麦生长的不同时期均衡施肥的CNPK处理以及不施肥的C0处理的群落各项多样性指数能维持在一个较高的水平。RDA分析显示土壤氮含量以及有机质含量与第一排序轴相关性大,是对杂草分布影响最大的两个土壤养分因子。太湖地区稻麦两熟制条件下,长期有机无机肥料单一或配合投入可显著影响麦田杂草的群落组成,其中氮肥和有机肥的施入能显著降低杂草密度;土壤养分的差异影响田面杂草密度和优势种群,均衡施肥能降低优势杂草种群的优势地位,抑制其发生危害程度,提高农田生态系统的生产力及稳定性。     

Narrow rows reduce biomass and seed production of weeds and increase maize yield

Smallholder farmers in southern African countries rely primarily on cultural control and hoe weeding to combat weeds, but often times, they are unable to keep up with the weeding requirements of the crop because of its laboriousness, causing them to incur major yield losses. Optimisation of crop planting pattern could help to increase yield and suppress weeds and to reduce the critical period of weed control and the weeding requirements to attain maximum yield. Experiments were carried out in Zimbabwe during two growing seasons to assess the effect of maize density and spatial arrangement on crop yield, growth and seed production of weeds and to determine the critical period for weeding. Planting maize at 60 cm row distance achieved higher yields and better weed suppression than planting at 75 or 90 cm row distance. Increasing crop densities beyond the customary three to four plants m⁻² gave modest reductions in weed biomass but also diminished crop yields, probably because of increased competition for water and nutrient resources. Maize planted in narrow rows (60 cm) intercepted more radiation and suffered less yield reduction from delaying hoe weeding than those planted in wider rows (75 or 90 cm), and the duration of the weed-free period required to attain maximum grain yield was 3 weeks shorter in the narrow spacing than that in the 75- and 90-cm row spacings. Weeding was more effective in curtailing weed seed production in the narrow row spatial arrangements than in the wide row planting. The results of these studies show that narrow row spacings may reduce weeding requirements and increase yields.     

Assessing broomrape risk due to weeds in cropping systems with an indicator linked to a simulation model

Integrated crop protection tolerates residual weed floras if they are not harmful for crop production. These weeds can host harmful crop pests, among which parasitic plants such as branched broomrape (Phelipanche ramosa). This holoparasite is responsible for large yield losses in French crops such as oilseed rape. To date, there are no herbicides available to control it. To evaluate ex ante the impact of crop management practices on weed-mediated parasite infection of crops, we developed an indicator calculated from outputs of the weed dynamics model FlorSys. It consists of three components assessing weed impact on (1) stimulation of parasite germination during the whole cropping season, i.e. the potential risk reduction for future crops via a reduction of the parasite seed bank, (2) the stimulation of parasite germination in host crops, i.e. the potential risk increase for the current crop, (3) parasite reproduction on weed plants, i.e. the potential risk increase for future crops. This indicator was then used to predict weed-mediated broomrape risk in cropping systems from six regions from France and one from Spain. Antagonisms and synergies with other indicators of weed-harmfulness for crop production and weed contribution to plant and functional biodiversity were investigated with Pearson correlation analyses. For instance, cropping systems with a high parasite risk also had a high functional biodiversity (e.g. weed-based food offer for bees). Effects of crop management practices on the weed-mediated parasite risk indicator were identified with linear models; regression trees were used to identify the combinations of management practices that maximised or minimised weed-mediated broomrape risk. Parasite risk depended on crop rotation, sowing and harvest dates, tillage, herbicides and mechanical weeding. The lowest risk was observed in fields that were last tilled less than 21 days before sowing, with more than 0.6 herbicides per year (i.e. 3 applications in 5 years) with multiple entry modes into the weeds (e.g. leaves and roots) and the last herbicide sprayed no later than 127 days before harvest. RLQ analyses were used to identify correlations between weed species traits (Q matrix) and simulated parasite risk (R matrix), via simulated weed densities (L matrix). Early summer-emerging weed species increased parasite risk. No other notable correlations were found, indicating that parasite risk results from a weed community of interacting species, and not simply from individual weed species. An advice table was built to summarize and explain the effects of crop management practices on weed-mediated parasite risk.     

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。     

An ecological approach to study the physical and chemical effects of rye cover crop residues on Amaranthus retroflexus, Echinochloa crus-galli and maize

Weeds can be suppressed in the field by cover crop residues, extracts of which have been demonstrated to exert chemical inhibition of crop and weed germination and early growth in bioassays. In this study, two complementary bioassays were developed with soil and mulch material originating from a long‐term maize–cover crop experiment to determine the relative physical and chemical effect of rye cover crop residues on weed and maize germination and early growth. This was compared with the effect exerted by residue material from the natural vegetation that developed in the crop stubble during the winter before maize sowing. Germination percentage and early growth of maize and two maize weeds, Amaranthus retroflexus and Echinochloa crus‐galli, were assessed in a seed incubator in tilled (green manured) and nontilled (surface mulched) soil, with and without N fertilisation, at various dates after cover crop destruction. Responses were compared to those of the same species in a standard soil without mulch or with an inert poplar mulch. A second bioassay was set up in a glasshouse to determine the effect of different quantities of fresh residue material and additional N fertilisation on emergence speed and percentage and on plant vigour during the first 22 days after cover crop destruction. These results were compared with no‐mulch controls and poplar mulch controls. Results of these trials were compared with weed density and biomass that developed in the maize crop sown after cover crop destruction. Soil and mulch chemical and biological properties were determined for material collected in the field at different times after cover crop destruction. Chemical properties of the mulch differed only occasionally between the treatments, but variation in cover crop biomass production led to significantly different soil chemical properties. Although soil total phenolic acid content did not always correlate to weed and maize germination and early growth inhibition, soil microbial activity did. In suboptimal conditions, as is often the case in the field, plant residue material exerted both a physical and a chemical effect on maize and weed emergence and early growth. Nitrogen fertilisation and application timing can give the maize crop a competitive advantage with respect to the weeds, but the final response and the practical consequences depended largely on the weed species involved.     

The effects of herbicides, applied atone and in sequence, on the control of wild-oats (Avena fatua) and broad-leaved weeds, and on yield of winter wheat

Experiments were done to examine the effects of controlling wild-oats and autumn-germinating broad-leaved weeds in winter wheat, early in winter or late in spring. The herbicides used were barban (winter), chlortoluron or isoproturon (winter), and benzoylprop-ethyl, at the recommended doses and at half doses. Sequential treatments of two herbicides at half doses were also examined. All treatments were given a routine broad-leaved herbicide treatment in spring. Yields of wheat were influenced more by the time of weed removal than by the degree of control achieved. Grain yields at three sites with dense autumn broad-leaved weed populations were greatest following the use of chlortoluron or isoproturon. At three other sites with moderate to dense wild-oat populations (60 to 240 plants/m¹), the use of barban at the crop three-leaf stage gave larger yields than benzoylprop-ethyl in late spring at the early stem elongation stage of the crop. Seed formation from surviving A. fatua was similar with both wild-oat herbicides. The treatment which reduced seed production of A. fatua and maintained crop yield most consistently was barban followed by benzoylprop-ethyl, each at half the normal recommended dose.     

Crop/weed gene flow:Chenopodium quinoa Willd. andC. berlandieri Moq.

Introduction of the Andean grain chenopod (Chenopodium quinoa) into North America placed this crop within the distributional range of a related wild species,C. berlandieri. This wild species, native to the North American flora, is cross-compatible withC. Quinoa. Isozyme analysis of progeny fromC. berlandieri plants growing within and at the periphery of theC. Quinoa fields, combined with fertility assessment and phenetic comparison among putative hybrids and parental types, indicates that over 30% of progeny from wild plants growing as weeds withC. quinoa in 1987 were crop/weed hybrids. This high incidence of interspecific gene flow from crop to weed appears to be the result of asymmetric pollen flow to free-living plants from high-density cultivated populations. The observed level of crop/weed hybridization, combined with heterosis and partial fertility of F₁ crop/weed hybrids, suggests that repeated annual cycles ofC. quinoa cultivation within the North American range ofC. berlandieri could produce introgressive change among sympatric wild populations. In terms of risk assessment for biotechnology, these results suggest that the breeding system may not provide an accurate indication of the potential for genetic interaction among predominately self-pollinating grain crops and their free-living relatives.     

Identifying the critical period for waterlogging on yield and its components in wheat and barley

Background and aims

Crop tolerance to waterlogging depends on factors such as species sensitivity and the stage of development that waterlogging occurs. The aim of this study was to identify the critical period for waterlogging on grain yield and its components, when applied during different stages of crop development in wheat and barley.

Methods

Two experiments were carried out (E1: early sowing date, under greenhouse; E2: late sowing date, under natural conditions). Waterlogging was imposed during 15–20 days in 5 consecutive periods during the crop cycle (from Leaf 1 emergence to maturity).

Results

The greatest yield penalties occurred when waterlogging was applied from Leaf 7 appearance on the main stem to anthesis (from 34 to 92 % of losses in wheat, and from 40 to 79 % in barley for E1 and E2 respectively). Waterlogging during grain filling reduced yield to a lesser degree. In wheat, reductions in grain number were mostly explained by reduced grain number per spike while in barley, by variations in the number of spikes per plant.

Conclusions

The time around anthesis was identified as the most susceptible period to waterlogging in wheat and barley. Exposing the crop to more stressful conditions, e.g. delaying sowing date, magnified the negative responses to waterlogging, although the most sensitive stage (around anthesis) remained unchanged.