Influence of liquid manure application method on weed control in spring cereals

Summary Injection of liquid manure (slurry) into the soil is an alternative to the traditional surface application. By the injection method, it is possible to place nutrients closer to the crop sown, thus offering the crop a competitive advantage over weeds. This study compares the response in crop yield, weed density and weed biomass to injection vs. surface application of liquid manure through three growing seasons in barley and oats. The manure applications were combined with treatments of weed harrowing or herbicide spraying or no treatment at all. The levels of weed control and crop yield obtained by harrowing and herbicides were larger when slurry was injected compared with surface application. Without any weed control treatments, the injection method decreased the final weed biomass in barley. The influence of nutrient injection on yield and weed control seemed to be modulated by the time of emergence and the early growth rate of the crop relative to weeds. Thus, because of its early root growth and development, barley responded more quickly to the injection treatment than oats. Consequently, barley became a more competitive crop.     

Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

Weed competition and nutrient scarcity often restrict organic cereal production, especially where the availability of livestock manure is limited. While harrowing of annual weeds and legume cover crops can be used, these methods are both executed in early spring and may hinder each other. Two cycles of a 2‐year crop rotation were carried out in south‐east Norway (60°42′N, 10°51′E, altitude 250 m) with weed harrowing and undersown cover crops (WHCC) at two fertiliser rates (40 and 100 kg nitrogen ha^?1). The effect of the WHCC treatments was measured by weed density and species, weed biomass, changes in weed seedbank and grain yield. The weed density depended on the interaction between WHCC, fertiliser and year. On average, pre‐emergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while pre‐ and post‐emergence weed harrowing reduced weed density by 59% and weed biomass by 67% compared with the untreated control. Spergula arvensis became more abundant at low rather than at high fertiliser rates. On average, white clover cover crop sown after pre‐emergence weed harrowing resulted in the highest yields for both oat (+12.1%) and wheat (+16.4%) compared with the untreated control. Despite differences in weed population density and biomass among WHCC treatments within years, the weed biomass, weed density and seedbank increased for all WHCC treatments over the 4‐year period. More research is required into improving the efficacy of mechanical and cultural weed suppression methods that organic systems rely on.     

Evaluation of selected commercial oilseed rape cultivars for early vigour,weed suppression and yield in southern New South Wales

The potential of oilseed rape to suppress weed growth while maintaining optimal yield and quality is not well understood under field conditions in Australia. This study, conducted in Condobolin and Wagga Wagga, New South Wales (NSW), during 2015 and 2016, examined a diverse range of commercial oilseed rape cultivars for their inherent ability to suppress weeds and maintain yields when in competition with natural weed infestations, with and without pre-emergent herbicide treatment. Cultivar differences were observed in oilseed rape canopy architecture and yield; however, early-season biomass, light interception, leaf area index and visual vigour ratings exhibited both year and location interactions. Cultivars with the highest biomass, light interception, leaf area indices and visual vigour were typically also the most weed-suppressive, in particular GT-50 and Hyola 600RR. Although crop and weed biomass accumulation differed significantly among cultivars for both location and year, weed biomass was inversely related to cultivar biomass in both years and locations. Hybrid Hyola and GT-50 cultivars exhibited up to 50% less weed biomass while maintaining consistently high levels of dry crop biomass. In addition, pre-emergent herbicide applications reduced weed infestation and contributed to higher crop yield in both locations and years. Given the consistent aboveground competitive ability of certain oilseed rape cultivars, our study demonstrated that diverse cultivar-dependent competitive traits such as early growth vigour, biomass production, absorption of photosynthetically active radiation and production and retention of crop residue significantly impacted weed establishment and total weed biomass. Our findings suggest that cultivar selection offers potential as a tool for maintaining suitable grain yield in the presence of weeds while potentially delaying the development of herbicide resistance through efficacious weed suppression.     

Tolerance of competitive spring barley cultivars to weed harrowing

Two experiments were conducted in 14 spring barley cultivars to investigate if crop tolerance to post‐emergence weed harrowing is related to morphological traits that reflect competitiveness. The experiments were carried out in organically grown fields where low weed densities and biomass production were assumed to be without significant influence on crop growth. The experiments showed that different cultivars responded differently to post‐emergence weed harrowing in terms of yield reduction. Taller and higher yielding cultivars with high leaf area index (LAI) tended to be less tolerant to post‐emergence weed harrowing than shorter and lower yielding cultivars with low LAI. This conclusion, however, is only valid for 13 of 14 cultivars because one very tall cultivar was tolerant to harrowing. Although the tallest and highest yielding cultivars were damaged the most, they remained the highest yielding cultivars after weed harrowing. This study is the first attempt to relate competitiveness of cereal cultivars to tolerance to harrowing, and it is thought provoking that competitiveness and tolerance is found to be counterproductive.     

Influence of intra-row cruciferous surrogate weed growth on crop yield in organic spring cereals

In Northern Europe, inter-row hoeing has become a popular tactic for controlling weeds in organic cereals. Hoeing is highly effective and can be implemented from crop emergence until stem elongation to maintain a nearly weed-free inter-row zone. However, hoeing has a lesser effect on weeds growing in the intra-row zone, where crop–weed proximity results in heightened competition. In the hoed cereal system, it is investigated whether tall-growing, competitive, cruciferous weeds in the intra-row zone affect crop biomass, yield and thousand kernel weight (TKW). An additive experimental design is employed to enable the fitting of rectangular hyperbolas, describing and quantifying the effects of increasing intra-row surrogate weed density on crop growth parameters. Regressions were studied under the influence of crop (spring barley and spring wheat), row spacing (narrow [12.5 or 15.0 cm] and wide [25.0 cm]) and nitrogen rate (50 and 100 kg NH₄-N/ha). Cruciferous surrogate weeds were found to impact crop yield and quality severely. For example, ten intra-row plants/m² of surrogate weed Sinapis alba reduced grains yields by 7%–14% in spring barley and by 7%–32% in spring wheat with yield losses becoming markedly greater in wheat compared to barley as weed density increases. Compared to wheat, barley limited yield and quality losses and suppressed intra-row weed growth more. Row spacing did not have a consistent effect on crop or weed parameters; in one of six experiments, the 25 cm row spacing reduced yields and increased intra-row weed biomass in wheat. Nitrogen rate did not affect crop or weed parameters. Results warrant the implementation of additional tactics to control intra-row weeds and limit crop losses.     

Tolerance of four spring barley (Hordeum vulgare) varieties to weed harrowing

We investigated the tolerance to weed harrowing of four spring barley varieties and examined the possible interactions between varietal weed suppressive ability and two nutrient levels. Tolerance was defined as the combined effect of crop resistance (ability to resist soil covering) and crop recovery (the ability to recover in terms of yield). The weed harrowing strategy was a combination of one pre‐ and one post‐emergence weed harrowing. In terms of yield, the four varieties responded significantly differently to weed harrowing and the response depended on nutrient level. At the lower nutrient level, weed harrowing caused an increase in yield of 4.4 hkg ha⁻¹ for a strong competitor (cv. Otira), while there was no effect on yield at the higher nutrient level. For a weaker competitor (cv. Brazil), weed harrowing caused no change in yield at the lower nutrient level, whereas yield decreased by 6.0 hkg ha⁻¹ at the higher nutrient level. There were marked differences between the weed suppressive ability of the four varieties when not harrowed, with less pronounced but significant differences when harrowed. Weed harrowing did not change the weed suppressive ability of a variety. Varieties that are tall at post‐emergence harrowing and have increased density after pre‐emergence harrowing, are the ones that benefit most from weed harrowing.     

Effects of inter-row hoeing and fertilizer placement on weed growth and yield of winter wheat

Inter‐row hoeing is known to control tap‐rooted and erect weed species more effectively in winter wheat than weed harrowing. However, little is known about its effectiveness for use in the spring in winter wheat grown at wide row spacing (240 mm) under the influence of different placement of fertilizer. Two field experiments, one in 1999 and one in 2000, were conducted to study the influence of fertilizer placement, timing of inter‐row hoeing, and driving speed on the weeding effect on different weed species and crop growth. Placement of fertilizer below the soil surface improved crop growth and grain yield in both years compared with placement on the surface, but the more vigorous crop did not give any better suppression of the weeds surviving hoeing. Timing was not important in one experiment, whereas hoeing twice beginning in early April was more effective in the other experiment where weed growth over the winter had been vigorous. Driving speed had no influence on either the weeding effect or the yield, except for one case where increasing speed reduced the control of well‐developed weeds. Compared with unweeded reference treatments, inter‐row hoeing reduced total weed biomass by 60–70% and tap‐rooted and erect weed species in particular by 50–90%. Sowing at 240 mm row spacing yielded less than 120 mm (Danish standard), and inter‐row hoeing for winter wheat needs to be adapted to narrower row spacing to avoid such yield decreases.     

Consequences of narrow crop row spacing and delayed Echinochloa colona and Trianthema portulacastrum emergence for weed growth and crop yield loss in maize

Echinochloa colona and Trianthema portulacastrum are weeds of maize that cause significant yield losses in the Indo‐Gangetic Plains. Field experiments were conducted in 2009 and 2010 to determine the influence of row spacing (15, 25 and 35 cm) and emergence time of E. colona and T. portulacastrum (0, 15, 25, 35, 45 and 55 days after maize emergence; DAME) on weed growth and productivity of maize. A season‐long weed‐free treatment and a weedy control were also used to estimate maize yield and weed seed production. Crop row spacing as well as weed emergence time had a significant influence on plant height, shoot biomass and seed production of both weed species and grain yield of maize in both years. Delay in emergence of weeds resulted in less plant height, shoot biomass and seed production. However, increase in productivity of maize was observed by delay in weed emergence. Likewise, growth of both weed species was less in narrow row spacing (15 cm) of maize, as compared with wider rows (25 and 35 cm). Maximum seed production of both weeds was observed in weedy control plots, where there was no competition with maize crop and weeds were in rows 35 cm apart. Nevertheless, maximum plant height, shoot biomass and seed production of both weed species were observed in 35 cm rows, when weeds emerged simultaneously with maize. Both weed species produced only 3–5 seeds per plant, when they were emerged at 55 DAME in crop rows spaced at 15 cm. Infestation of both weeds at every stage of crop led to significant crop yield loss in maize. Our results suggested that narrow row spacing and delay in weed emergence led to reduced weed growth and seed production and enhanced maize grain yield and therefore could be significant constituents of integrated weed management strategies in maize.     

Effects of pre- and post-emergence weed harrowing on annual weeds in peas and spring cereals

To assess the effects of timing and frequency of weed harrowing on weed abundance and crop yield, different pre- and post-emergence weed harrowing sequences were applied to spring cereals and peas in field experiments performed during 2003 and 2004 in Sweden. Post-emergence harrowing was performed at crop growth stages 2–3 and 5–6 true leaves respectively. The best weed control was obtained by a combination of pre- and post-emergence harrowing, but these treatments also caused yield losses of 12–14% in spring cereals, while no yield losses were observed in peas. Pre-emergence weed harrowing treatments alone or combined with weed harrowing shortly after crop emergence proved to be most effective against the early emerging annual weed species Sinapis arvensis and Galeopsis spp. Post-emergence harrowing alone in peas had no effect on S. arvensis . The late emerging annual weed species Chenopodium album and Polygonum lapathifolium were most effectively controlled when pre-emergence weed harrowing was combined with one or two weed harrowing treatments after crop emergence.     

Influence of sowing density and spatial pattern of spring wheat (Triticum aestivum) on the suppression of different weed species

To better understand the potential for improving weed management in cereal crops with increased crop density and spatial uniformity, we conducted field experiments over two years with spring wheat ( Triticum aestivum ) and four weed species: lambsquarters ( Chenopodium album ) , Italian ryegrass ( Lolium multiflorum ), white mustard ( Sinapis alba ), and chickweed ( Stellaria media ). The crops were sown at three densities (204, 449, and 721 seeds m⁻²) and in two spatial patterns (normal rows and a highly uniform pattern), and the weeds were sown in a random pattern at a high density. In most cases, the sown weeds dominated the weed community but, in other cases, naturally occurring weeds were also important. There were strong and significant effects regarding the weed species sown, the crop density, and the spatial distribution on the weed biomass in both years. The weed biomass decreased with increased crop density in 29 out of 30 cases. On average, the weed biomass was lower and the grain yield was higher in the uniform compared to the row pattern in both 2001 and 2002. Despite the differences in weed biomass, the responses of L. multiflorum , S. media , and C. album populations to crop density and spatial uniformity were very similar, as were their effects on the grain yield. Sinapis alba was by far the strongest competitor and it responded somewhat differently. Our results suggest that a combination of increased crop density and a more uniform spatial pattern can contribute to a reduction in weed biomass and yield loss, but the effects are smaller if the weeds are taller than the crop when crop–weed competition becomes intense.     

Competition of sorghum cultivars and densities with Japanese millet (Echinochloa esculenta)

Field studies were conducted at two locations in southern Queensland, Australia during the 2003–2004 and 2004–2005 growing seasons to determine the differential competitiveness of sorghum (Sorghum bicolor L. Moench) cultivars and crop densities against weeds and the sorghum yield loss due to weeds. Weed competition was investigated by growing sorghum in the presence or absence of a model grass weed, Japanese millet (Echinochloa esculenta). The correlation analyses showed that the early growth traits (height, shoot biomass, and daily growth rate of the shoot biomass) of sorghum adversely affected the height, biomass, and seed production of millet, as measured at maturity. “MR Goldrush” and “Bonus MR” were the most competitive cultivars, resulting in reduced weed biomass, weed density, and weed seed production. The density of sorghum also had a significant effect on the crop's ability to compete with millet. When compared to the density of 4.5 plants per m², sorghum that was planted at 7.5 plants per m² suppressed the density, biomass, and seed production of millet by 22%, 27% and 38%, respectively. Millet caused a significant yield loss in comparison with the weed‐free plots. The combined weed‐suppressive effects of the competitive cultivars, such as MR Goldrush, and high crop densities minimized the yield losses from the weeds. These results indicate that sorghum competition against grass weeds can be improved by choosing competitive cultivars and by using a high crop density of >7.5 plants per m². These non‐chemical options should be included in an integrated weed management program for better weed management, particularly where the control options are limited by the evolution of herbicide resistance.     

Improved management of Avena ludoviciana and Phalaris paradoxa with more densely sown wheat and less herbicide

Summary The effectiveness of crop competition for better weed control and reducing herbicide rates was determined for Avena ludoviciana and Phalaris paradoxa . Four experiments, previously broadcast with seeds of the two weeds in separate plots, were sown with three wheat densities, and emerged weeds were treated with four herbicide doses (0–100% of recommended rate). The measured crop and weed traits were first analysed across experiments for treatment effects. Grain yield and weed seed production data were then analysed using cubic smoothing splines to model the response surfaces. Although herbicide rate for both weeds and crop density for P. paradoxa had significant linear effects on yield, there was a significant non-linearity of the response surface. Similarly, herbicide rate and crop density had significant linear effects on weed seed production, and there was significant non-linearity of the response surface that differed for the weed species. Maximum crop yield and reduction in seed production of P. paradoxa was achieved with approximately 80 wheat plants m⁻² and weeds treated with 100% herbicide rate. For A. ludoviciana , this was 130 wheat plants m⁻² applied with 75% herbicide rate. Alternatively, these benefits were achieved by increasing crop density to 150 plants m⁻² applied with 50% herbicide rate. At high crop density, application of the 100% herbicide rate tended to reduce yield, particularly with the A. ludoviciana herbicide, and this impacted adversely on the suppression of weed seed production. Thus, more competitive wheat crops have the potential for improving weed control and reducing herbicide rates.     

Critical periods of weed competition in cotton in Greece

Four experiments were conducted in central Greece during 1997 and 1998 to determine the late-season presence of weeds in cotton (Gossypium hirsutum L.) and the critical times for removing weeds. Experiments were conducted in natural, heavily infested cropland. The presence of weeds for more than 3 weeks after crop emergence caused significant reductions in crop growth and lint yields. However, weeds that emerged 11 weeks or more after crop emergence did not adversely impact yields. Total weed biomass increased with increasing time prior to weed removal. A weed-free period of 11 weeks after crop emergence was needed to prevent significant reductions in cotton height, biomass, number of squares, and yield. These results indicated that postemergence herbicides or other control measures should be initiated within 2 weeks after crop emergence to avoid significant yield reduction. For greater efficiency, soil-applied herbicides in cotton should provide effective weed control for at least 11 weeks. Curvilinear regression equations were derived to describe the relationship between critical periods of weed presence and cotton growth and fruit development.     

Effect of crop density on competition by wheat and barley with Agrostemma githago and other weeds

The effect of Agrostemma githago L. and other naturally occurring weeds on biomass production and grain yield was studied in winter wheat and winter barley. Naturally occurring weeds had only a negligible effect on barley, but reduced wheat grain yield by 10% at a quarter of normal crop density. The interaction between the cereals and A. githago was studied in additive series employing different crop densities. Growth of this weed species was strongly dependent on crop density, which was more important for controlling weed growth than it was for obtaining a normal grain yield. Wheat and especially barley had a better competitive ability than A. githago. Wheat and A. githago utilized resources for growth better when grown in mixture than when grown in pure stands as the relative yield totals were significantly larger than unity.     

A model for prediction of yield response in weed harrowing

A model is presented to describe crop yield response in weed harrowing. The selectivity of harrowing, crop yield response to soil covering, and the competitive strength of the weeds are all variables in the model, which is derived from the hyperbolic yield-density relationship, and therefore accounts for the effects of weed density. An advantage of the modelling approach is that the yield response can be separated into two parts, one derived from the positive weed-killing effect of harrowing, and the other derived from the negative crop-covering effect. Simulation runs based on experimental data showed that crop damage, when it occurs, cannot be ignored, and may sometimes even dominate the positive weed-killing effect. Possible scientific and practical applications of the model are discussed.     

Early vigour and allelopathy – two useful traits for enhanced barley and wheat competitiveness against weeds

The objectives of this study were to identify traits in spring barley (Hordeum vulgare) and spring wheat (Triticum aestivum) related to the competitive ability of the crop and to determine their importance. Weed biomass 1–2 weeks prior to ear emergence was used as a measure of genotypic differences in competitiveness against weeds. Crop trait measurements comprised early crop biomass, early shoot height, straw length, heading and maturity. Early crop biomass 1–2 weeks prior to ear emergence was used as an overall trait for the various characters related to early vigour. In addition to these morphological traits, the potential allelopathic activity of the tested cultivars was determined using an agar-based bioassay with Lolium perenne (ryegrass). In both barley and wheat, multiple regression analysis revealed that early crop biomass and potential allelopathic activity were the only parameters that significantly contributed to competitiveness. In barley, early crop biomass explained 24–57% of the observed genotypic variance across 4 years, allelopathic activity explained 7–58% and combined they explained 44–69% of the observed genotypic variance. In wheat, the corresponding figures were lower: 14–21% for early biomass, 0–21% for allelopathic activity and 27–37% when combined. Model predictions suggested that new cultivars with increased early vigour and allelopathic activity offer a potential to further reduce weed interference.     

Effect of different weed management systems on the weed populations, and seedbank composition and distribution in tropical coconut plantations

Weeds are a perennial problem in coconut plantations and cause significant losses in the nut yield. The occurrence of a wide range of weeds also causes difficulties in their eradication. The influence of five different weed management practises on the distribution and composition of the soil weed seed bank in coconut plantations in the low-country dry zone of Sri Lanka was evaluated. The treatments imposed included the application of glyphosate (N-[phosphonomethyl]-glycine), cover cropping with Pueraria phaseoloides , tractor harrowing, tractor slashing, and tractor plowing. All the treatments were applied twice per year, except for the cover cropping treatment. In terms of a reduction in the weed biomass, the application of glyphosate and cover cropping ( Pueraria ) were more efficient in reducing the ground weed population. These methods were very effective in reducing the weed seed density in the top soil layers. Plowing and harrowing significantly reduced the seed bank in the top soil layers and shifted significant numbers of weed seeds to deeper soil profiles. However, the total germinated weed seed count increased by 123.5, 691.4, 1133.1, and 1216.5% in the 10–15, 15–20, 20–25, and 25–30 cm soil depths, respectively, compared with the initial germinated weed seed count in the plowing treatment. Considering all the soil layers, the decline in the germinating weed seed count was very high in the treatment plots with cover cropping and the application of glyphosate; thus, these are considered to be the best practises to reduce the germinating weed seed count in the soil of coconut plantations.     

Critical period of weed interference in chickpea

The critical period of weed interference in one variety of chickpea was determined in field experiments carried out at two sites, Tabriz 2002 and Kermanshah 2003, Iran. Chickpea culture was either kept free of weeds for 0, 12, 24, 36, 48 and 60 days after crop emergence (DAE) or weeds were allowed to grow for 0, 12, 24, 36, 48 and 60 DAE. In these experiments, chickpea yield increased with increasing duration of weed-free period and was reduced by increasing duration of weed-infested period. Unweeded conditions for the entire growing season caused 66.4% and 48.3% seed yield reduction when compared with the treatment that was weed-free throughout the growing season, at Tabriz 2002 and Kermanshah 2003, respectively. The results indicated that chickpea must be kept weed-free between the five-leaf and full flowering stages (24–48 DAE) and from the four-leaf to beginning of flowering stages (17–49 DAE) at the two sites, respectively, in order to prevent >10% seed yield loss. At both sites, reduction in seed yield, because of the increased weed interference period, was accompanied by simultaneous reduction in plant dry weight, number of branches, pods per plant and 100-seed weight. This was supported by significant and positive correlations between these traits and chickpea seed yield. There was no significant correlation between the number of seeds per pod and seed yield. A linear regression model was used to describe the relationship between weed dry weight and seed yield loss.     

发展化学除草重视综合治理

我国农田杂草有２５０多种，全国农田受草害面积４３００多万ｈｍ２，平均受草害减产１３．４％，每年减产粮食１７５０万ｔ，皮棉２５．５万ｔ和大豆５０万ｔ。传统农业生产采用机械作业及人力等除草。随着农村经济的发展，化学除草面积迅速扩大，全国农田化学除草面积从１９７５年的１７０万ｈｍ２增加到１９９５年的４１３３万ｈｍ２。但是，长期化学除草也带来了除草剂土壤残留对后茬作物药害、农田杂草种群更替和产生抗药性等新问题。必须重视农田杂草综合治理，通过采用各种有效的农业技术措施，为农作物保持良好的生态条件，结合化学除草才是最有效的防除杂草方法     

Effects of tropical weeds on yield in white yam (Dioscorea rotundata Poir)

The effects of tropical weeds on the yield of while yam were studied outdoors in wooden boxes. When the foliage and roots of weeds were in physical contact with the crop until harvest (full interference), tuber yield of yam was reduced by 76–79% of that obtained under weed-free conditions over 3 years of study. When there was no physical contact between roots of crop and weeds, the leachate from the weed zone caused tuber yield reductions of 42, 40 and 38% in 1978, 1979 and 1980, respectively, when it was applied to the yam zone. This leachate also reduced leaf area index (LAI) in the yam crop but the adverse effects on yam root and shoot biomass were less pronounced. This technique made it possible to separate competitive interference from allelopathic interference of tropical weeds with the yam crop.