Seed dynamics in populations of A vena sterilis ssp. ludoviciana

Seed populations of Avena sterilis ssp. ludoviciana (Durieu) Nyman were monitored in a naturally occurring infestation throughout its life cycle. Considering the large weed population present (298panicles m^?2), total seed production was relatively low: 3838 seeds m^?2. Only 68% of these seeds were recovered from the soil surface and a further 3% were removed with wheat grain and straw during harvest operations. The numbers of seeds from the stubble between mid-July and mid-September were relatively low (10%). Ploughing the stubble in October buried most of the recently produced seed rain and resulted in a relatively uniform vertical distribution of the seedbank. Maximum seed persistence in the soil ranged from 27 to 43 months (depending on the experimental technique used to do the study). Seed decline followed an exponential pattern on a yearly basis, with the greatest decline taking place between October and April (57–90% in year 1 and 10–40% in year 2), Between May and September the buried seed populations remained practically constant. Seedbank depletion was primarily due to seedling production (25%) and ‘lethal’ germination (24%). Although the depth of burial had very little effect on seed survival, the mode of seed disappearance was closely related to their depth in the soil. Seed depletion through ‘lethal’ germination increased with increasing depth in the soil, whereas depletion through seedling emergence decreased with increasing depth.     

Apera spica-venti population dynamics and impact on crop yield as affected by tillage, crop rotation, location and herbicide programmes

Apera spica‐venti is a winter annual grass and, increasingly, a severe weed problem in autumn‐sown crops. Non‐inversion tillage has become more common in Denmark in recent years, but may accentuate problems with A. spica‐venti. These problems may be avoided, if selected preventive and cultural weed management practices are adopted. To this end, we conducted a 4‐year field study investigating the effects of crop rotation, tillage method, location and limited herbicide input on A. spica‐venti population dynamics and crop yield. Additionally, detailed studies were performed on the fate of A. spica‐venti seeds when incorporated to different soil depths. The location with a lighter soil texture, cooler climate and higher rainfall favoured A. spica‐venti growth and consequently crop yield loss, especially in the crop sequence comprised only of autumn‐sown crops and with non‐inversion tine tillage. Incorporating A. spica‐venti seeds in the soil improved their survival, explaining the higher A. spica‐venti proliferation seen with tine tillage as opposed to direct drilling. The rotations including an even mixture of spring‐ and autumn‐sown crops did not lead to noteworthy changes in the A. spica‐venti population, irrespective of tillage method. Thus, in many regions, management of A. spica‐venti will require rotations that balance autumn‐ and spring‐sown crops.     

Spatial stability of Avena sterilis ssp. ludoviciana populations under annual applications of low rates of imazamethabenz

Long‐term experiments were conducted in two winter barley fields in central Spain to determine the spatial stability of Avena sterilis ssp. ludoviciana populations under annual applications of low rates of imazamethabenz herbicide. Weed density was sampled every year (over 5 years in the first field and over 3 years in the second) on the same grid locations prior to herbicide application. Although weed patches were stable in their location, weed density decreased in most of the years. In the first field, the populations decreased exponentially over the 5‐year period. The rates of population decline were dependent on the initial density of the population, being higher for the central core of the patches and lower for the low‐density areas. Under the conditions present in this experiment, it was possible to reduce heavy weed patches (up to 1200 seedlings m^?2) down to relatively safe levels (18 seedlings m^?2) in a period of 3 years using a density‐specific control programme, applying low rates of herbicides when weed densities were below a given level (1000 seedlings m^?2). However, under adverse environmental conditions, half rates of the herbicide failed to control the weed populations adequately. The stability of the location of patches of A. sterilis ssp. ludoviciana suggest that weed seedling distributions mapped in one year are good predictors of future seedling distributions. However, the actual densities established each year will depend on the control level achieved the previous year and the climatic conditions present during the establishment period.     

Field evaluation of a decision support system for herbicidal control of Avena sterilis ssp. ludoviciana in winter wheat

Two field studies were conducted in Central and Northern Spain over a total of five seasons to assess the usefulness of a decision support system (AVENA-PC) from agronomic, economic and environmental points of view on herbicidal control of Avena sterilis ssp. ludoviciana in winter wheat. The control treatments evaluated were: (i) AVENA-PC-based recommendations, (ii) full herbicide dose (standard farmer practice), (iii) half herbicide dose and (iv) no herbicide. The herbicide rates used in the AVENA-PC treatment averaged 65% and 30% lower than the full and half dose treatments respectively. AVENA-PC implementation controlled A. ludoviciana with similar efficacy as standard herbicide treatments. Nevertheless, it did support a reduction in relation to the non-herbicide treatment. Yields obtained with AVENA-PC were, in general, not statistically different to those obtained with herbicide treatments and were on average 69% higher than those in the no herbicide application strategy. Comparing AVENA-PC economic performance with the other treatments there were, in general, no significant statistical differences in Central Spain. In Northern Spain, all herbicide treatments had similar net returns, with there being no statistical differences between AVENA-PC and the herbicide treatments. However, there were differences recorded with the non-herbicide treatment. The results of this research indicate that AVENA-PC, due to its flexibility, may recommend less herbicide than the standard farmer practice, providing clear environmental benefits and adequate weed control with maintained crop yield and net returns similar to standard farmer practice.     

Field emergence of Avena fatua L. and A. sterilis ssp. ludoviciana (Dur.) Nym. in Aragón, Spain

Emergence of Avena fatua and A. sterilis ssp. ludoviciana infesting winter cereals during two years and at two sites in Aragon began after sowing in late October and continued for 23 weeks, with 75% of seedlings appearing in the first 9 weeks. The start of emergence was associated with a fall in minimum air temperature to below 9°C and a maximum of less than 20°C. Soil moisture was not limiting, and during winter flushes of seedlings tended to be associated with rises in mean temperature. In contrast with results from other latitudes, A. fatua emerged mainly in autumn at the same time as A. sterilis ssp. ludoviciana.     

Effect of tillage, cover crop and crop rotation on the composition of weed flora in a sandy soil

The development of integrated weed management strategies requires knowledge of mechanisms that influence compositional changes in weed flora. A 9-year study was initiated in 1988 at Delhi, Canada, on a loamy sand soil to evaluate the effect of tillage systems [conventional (CT) and no-till (NT)] and cover crops (only in NT) on weed density, species composition and associations, and crop yield in a winter wheat ( Triticum aestivum L.)/bean/winter wheat rotation. Three bean types: soyabean ( Glycine max L. Merr.), white bean ( Phaseolus vulgaris L.) and kidney bean ( P . vulgaris L.) were included. The NT system included variations: rye ( Secale cereale L.) or maize ( Zea mays L.) cover crop, volunteer wheat disked after harvest and wheat stubble. Data were collected in 1994, 1995 and 1996. Tillage systems, cover crops and crop type had differential effects on weed densities, species composition and associations. Weed densities were not affected by tillage or cover crops in wheat but, in the beans, densities were greater in the CT than in the NT systems. Various associations of weed species with tillage system, cover crop and crop type were observed. Crop yields were not affected by tillage type or cover crop, except that soyabean yields were highest in plots with cover crops.     

Influence of herbicide treatments on the population dynamics of Avena stériles ssp. ludoviciana (Durieu) Nyman in winter wheat crops

A long-term study was conducted during 4 consecutive years to determine the effects of herbicides on the major demographic parameters and on the dynamics of the populations of Avena sterith ssp. ludoviciana (Durieu) Nyman growing in winter wheat crops in Central Spain. The three herbicides tested bad different effects on the life cycle of the plant. Tri-allate was moderately effective in reducing seedling recruitment and seedling survivorship, but it resulted in adult fecundities similar to or higher than, those of the check plots. Difenzoquat was highly effective in reducing plant survivorship and it consistently reduced the reproductive capacity of the survivors. Flamprop-isopropyl L was not very effective in reducing plant survivorship, but it had the largest influence on adult fecundity. Overall, although the three herbicides were able to reduce substantially (59–95%) the production of new seeds, large numbers of seeds were returned annually to the soil in all the treatments. The annual application of any of the three compounds during 4 consecutive years had a marked effect on the long-term evolution of the populations of buried seeds in the soil, emerged seedlings, mature plants and new seeds produced. Continuous herbicide application resulted in a gradual depletion of the seed bank of A. sterilis in the soil. At the end of the 4-year period, buried seed populations in the herbicide-treated plots were (61–81%). lower than those at the beginning of the experiment, and 92–95% lower than those of the check plots at the same lime. However, the seed reserves present in the treated plots were Mill high enough to require some type of control programme.     

不同轮作模式下小麦禾谷孢囊线虫的发生动态和种群密度

轮作是防治小麦禾谷孢囊线虫的重要农业措施,为了明确青海省春麦区不同轮作模式对小麦禾谷孢囊线虫的控制效果,采用田间大区试验法对生产中应用的6种轮作模式进行了研究。结果表明:不同轮作模式下,小麦禾谷孢囊线虫种群密度变化差异极显著,其中小麦与马铃薯、油菜、蚕豆轮作两年或以上能有效降低小麦禾谷孢囊线虫种群密度,土壤中的孢囊量减少39.31%~84.39%,单孢虫口数量减少73.21%~95.35%,虫口密度减少83.76%~97.82%;不同作物间,小麦与马铃薯或蚕豆的轮作效果(虫口密度减少74.39%~79.37%)显著优于小麦与油菜的轮作效果(虫口密度减少67.16%)。在同一地块相同条件下,种植油菜、蚕豆、马铃薯、小麦4种作物,小麦禾谷孢囊线虫均能正常孵化,4月底土壤中的2龄幼虫(J2)量增加,5月上旬达到高峰期,5月中旬开始,土壤中的J2、孢囊量、虫口密度和单孢虫口数量均急剧下降,6月至7月份下降幅度小,趋于稳定;田间空孢囊率于5月中旬至6月中旬急剧增加,7月份趋于稳定,8月份以前,4种作物田禾谷孢囊线虫的孵化动态和种群密度变化趋势一致,8月中旬,小麦田随着新孢囊脱落到土壤中,禾谷孢囊线虫种群密度开始上升,小麦收获后土壤中的孢囊量比播种前增加28.62%,虫口密度增加41.30%;而油菜、蚕豆、马铃薯田土壤中的孢囊量比播种前减少32.27%~48.36%,虫口密度减少70.91%~81.73%,8月中旬至10月份小麦田禾谷孢囊线虫种群密度极显著高于油菜、蚕豆、马铃薯田。     

Effects of crop rotation and removal of crop debris on the soil population of two isolates of Verticillium dahliae

Microsclerotia of Verticillium dahliae are produced in large numbers on senescing parts of host plants and remain viable in the soil for many years. Changes in the population density, i.e. density of microsclerotia, in the soil were measured in micro-plots using two isolates of V. dahtiae , specific to either field bean or potato, several crop sequences comprising potato, field beans and barley, and either the removal of aerial debris of the crops or incorporation into soil.
Potato was more susceptible to the potato isolate and field bean more susceptible to the field bean isolate. Removal of debris of potato and field bean reduced numbers of microsclerotia in the soil in the subsequent years, but removal of barley straw had no effect. Initially non-infested control micro-plots became infested, probably by the growth of potato roots into the naturally infested subsoil. The rate of increase of the microsclerotial population in the non-infested control micro-plots was larger than in the initially infested treatments, because more colonized debris was produced. It is concluded that removal of aerial debris of host crops is important to reduce the soil population of V. dahtiae.     

Long-term tillage and crop rotation effects on weed seedbank size and composition

Size and composition of the weed seedbank was assessed after 12 years of application of four tillage systems in two crop rotations. Mouldboard and chisel ploughing at 45 cm, minimum tillage at 15 cm and no tillage were compared in continuous winter wheat and a pigeon bean/winter wheat 2-year rotation. Weed control was based upon post-emergence herbicide application. Weed seedling emergence from soil samples taken at 0–15, 15–30 and 30–45 cm depths was assessed in a non-heated glasshouse for 12 months. The tillage system influenced weed seedbank size and composition to a much greater extent than crop rotation. Total weed seedling density was higher in no tillage, minimum tillage and chisel ploughing plots in the 0–15, 15–30 and 30–45 cm layers respectively. Density in the whole (0–45 cm) layer did not differ significantly among tillage systems. With no tillage, more than 60% of the total seedlings emerged from the surface layer, compared with an average 43% in the other tillage systems. Crop rotation did not influence either weed seedbank size or seedling distribution among soil layers, and only had a small influence on major species abundance. The weed seedbank was dominated (>66%) by Conyza canadensis (L.) Cronq. and Amaranthus retroflexus (L.), which thrived in chisel ploughing and no tillage respectively. Results suggested that crop rotation and substitution of mouldboard ploughing by non-inversion tillage (especially by minimum tillage) would not result in increased weed problems, whereas use of no tillage might increase weed infestations because of higher seedling recruitment from the topsoil.     

Interactions between the tillage system and crop rotation on the crop yield and weed populations under arid conditions

Field experiments were conducted in Iran in order to determine the interactions between the tillage system and crop rotation on weed seedling populations and crop yields from 2002 to 2005. No tillage, shallow tillage and deep tillage were the main plots and three crop sequences comprising continuous wheat (W‐W), wheat–canola–wheat–canola (C‐W) and wheat–safflower–wheat–safflower (S‐W) were the subplots. Bromus japonicus, Carthumus lanatus, Polygonum aviculare, Lolium temulentum and Avena ludoviciana were found to be the dominant species. The initial weed population in 2002 was estimated at 65 seedlings per m² and B. japonicus (～35 seedlings per m²) was the most abundant species, followed by A. ludoviciana and L. temulentum. The dominant weed species mostly did not favor the combination of S‐W and C‐W with any tillage type. For the B. japonicus population, S‐W in combination with moldboard plowing indicated the lowest seedling population. In conclusion, the crop sequence in combination with tillage would help to control troublesome weed species. Safflower and canola were determined to be effective in reducing the grass weeds. The inclusion of these crops in rotation also increased the total revenue of the cropping systems because of the higher sale price of canola and safflower.     

Competition between Avena sterilis ssp. macrocarpa Mo. and cultivars of wheat

A pot experiment was done in the glasshouse to study the competition between Avena sterilis ssp. macrocarpa Mo. and six wheat cultivars of different lengths of growth cycle. The competitiveness of wild oat was similar for all six wheat cultivars with respect to grain weight, straw weight, number of ears and total accumulation of nitrogen. The cultivar with the longest cycle was the most affected by wild oat competition as regards height, because a large part of its stem extension and some of the heading took place after the panicles of wild oat had expanded. Wild oat competition with wheat plants was greater than the competition among wheat plants themselves. The wild oat had a similar tolerance to all the wheat cultivars.     

Influence of tillage, straw disposal system and seed return on the population dynamics of Alopecurus myosuroides Huds. in winter wheat

Alopecurus myosuroides Huds. was studied over a 2-year period in winter wheat established after tine cultivations or direct drilling. Straw was removed by baling or spread and burnt. Seed production was either allowed or prevented by cutting and removing all vegetation at the end of the first year. Cultivation differences had no consistent effect on plant or seed populations. Straw burning destroyed about 50% of seeds and encouraged the germination of surviving seeds. Weed populations in the crop were lower on burnt than on baled areas. Where seed shedding was allowed, populations of seeds in soil and plants increased by up to nine-fold per year. Straw burning resulted in smaller population increases. Seed decline in the soil averaged about 80% per year, so that less than 6% of the weed seeds sown were still viable after 2 years’burial in the soil. Most of the seed decline occurred between July and October and was slightly greater on burnt than on baled areas. Only part of this seed loss was accounted for by germination and emergence of seedlings during summer and autumn. Plants emerging in the crop represented less than 26% of viable seeds present in the soil at time of drilling the crop. Few seedlings emerged in spring. The viability of shed seeds varied with year and with weed density. High infestations were associated with lower seed viability and also fewer heads per plant.     

The influence of climatic factors on metoxuron activity on Bromus sterilis L.

Metoxuron was more active when Bromus sterilis L. (sterile brome) plants were kept under cool (10/6°C day/night) compared with warm (26/16°C) temperatures after spraying. The effect of warmer temperatures required exposure for more than 3 days. Metoxuron activity was unaflected by a cold exposure (0/-2°C or 4/2°C) for a 24-h period shortly before or after spraying. Greater damage occurred when plants were kept in high relative humidity (r.h.) (95/98% r.h. day/nighl) after spraying than at 75/86% r.h. or at 50/75% r.h. Increasing soil moisture from 11.5 to 21.5 g water 100 g^?1 dry soil also resulted in increased metoxuron activity. Metoxuron was less active under severe shading. There was little evidence in these studies that metoxuron activity resulted from foliar uptake. Results are discussed with reference to field reports of metloxuron use against B. sterilis. L.     

Dispersal of Avena fatua and Avena sterilis patches by natural dissemination, soil tillage and combine harvesters

The dispersal of Avena spp. (A. fatua and A. sterilis) by natural dissemination and by agricultural operations was studied in four experiments conducted in Spain and Britain. Natural dispersal was very limited, with a maximum dispersal distance of 1.5 m. Dispersal was higher in the geographic direction that was downwind than in any of the other three geographic directions. Although plant movement was very small under no‐tillage, an annual patch displacement of 2–3 m in the tillage direction was observed under conventional soil tillage. Ploughing downhill resulted in much larger dispersal distances than ploughing uphill. In the crops studied, combine harvesters dispersed few Avena spp. seeds, because of the fact that the plants had shed most of their seeds (>90%) before harvest. The percentage of seeds available to be dispersed by the combine was dependent on the harvest time. Although combine harvesting may not contribute much to short‐distance dispersal, it may play an important role in long‐distance dispersal. In our studies, isolated plants were located up to 30 m from the original sources. This small proportion may have a significant effect on the distribution of the weed within a field, acting as foci for new patches.     

The implication of stubble tillage for weed population dynamics in organic farming

In practical farming, early and shallow stubble tillage is carried out post‐harvest to stimulate germination of freshly ripened crop and weed seeds, to kill the resulting seedlings and hence to reduce the input into the soil seedbank. Additionally, it aims at reducing perennial weeds by mechanical damage. In this paper, field experiments and laboratory studies are presented which show that stubble tillage can reduce perennial weeds. However, it had a variable effect on annual weeds. After 5 years of experimentation, no effect of stubble tillage was seen on the aboveground vegetation. In contrast, the soil seedbank of the control was roughly doubled where the stubble had been left uncultivated until autumn ploughing. These results indicate that practical experience which assumes that stubble tillage reduces annual weed populations may be correct, despite the fact that in other published studies stubble tillage exerted no control on annual weeds or had a variable effect. This will have practical application in organic arable production systems.     

轮耕条件下土壤改良及春玉米增产增收效果研究

针对旱作区长期采用单一的土壤耕作方式造成的土壤结构变差及作物生长发育受限等问题,研究由免耕、深松及翻耕组成的不同轮作模式对干旱区春玉米土壤肥力及产量的影响具有重要生产意义。于2014—2016年在兰州市榆中县清水驿乡孟家山村玉米田开展连续免耕(NT)、连续深松(ST)、连续翻耕(PT)、深松、免耕及深松轮耕(ST/NT/ST)、免耕、免耕和深松轮耕(NT/NT/ST)、翻耕、免耕及翻耕轮耕(PT/NT/PT)、翻耕、免耕及深松轮耕(PT/NT/ST)和深松、翻耕及深松轮耕(ST/PT/ST) 8种耕作模式试验,测定8种耕作模式下的土壤孔隙度、土壤养分、干物质和玉米产量,并分析其经济效益。结果表明:在0～60 cm土层,随着土层的增加土壤孔隙度表现为先降后增,以20～40 cm土层的土壤孔隙度最低。5种轮耕措施较耕作前均能增加土壤孔隙度,以ST/PT/ST轮耕模式最优,其次为ST/NT/ST,较PT提高了1.24%、0.25%;土壤养分含量在0～20 cm土层均高于20～40 cm土层,其中,0～20 cm土层免耕与深松进行轮耕下土壤全氮、全磷含量较高,以ST/NT/ST全氮、磷含量最高,20～40 cm土层,对土壤全氮、全磷含量无显著影响,翻耕与深松轮作促进了速效氮、磷、钾的提高,以ST/PT/ST速效氮、磷、钾含量高,免耕土壤有机质含量较其它耕作方式低,其余土壤养分指标为表层富集,下层匮乏;轮耕模式较单一的耕作方式更能促进玉米干物质的累积,其中以ST/NT/ST与PT/NT/PT耕作下玉米干物质高,频繁的翻耕(PT)不利于玉米的生长; 3年产量相比,8种耕作模式中,ST/NT/ST处理下玉米产量显著高于其它处理(ST/NT/STNT/NT/STST/PT/STSTNTPT/NT/ST PT/NT/PT PT)。较单一耕作(NT、ST、PT),ST/NT/ST处理下玉米产量提高了5. 97%、3. 56%、15.75%;且以ST/NT/ST经济效益最高。结论:深松、免耕及深松轮耕有利于改善耕层结构和提高土壤养分,增产增效显著,为旱作区春玉米农田适宜的轮耕模式。     

A study on seed population dynamics of three weedy species of Eupatorium

The data on seed population dynamics of three weedy species of Eupatorium, viz. E. adenophwrum Spreng., E. riparium Regel and E. odoratum L. have been presented and discussed in the paper. The seed production and seed populations in soil seed bank were estimated, and the fate of buried seeds in soil was followed over a 2-year period. All the three species of Eupatorium produced a large number of seeds. The seed production of E. riparium per unit area was higher than that of the other two species because of its high population density. In all the three species most of the seeds were found to be present in the top 2 cm of the soil. The viable seed population of the three species of Eupatorium declined exponentially alter their burial in soil showing almost similar mortality patterns. A large proportion of seeds of all the Eupatorium spp. remained under enforced dormancy during their burial in soil with only a small fraction exhibiting induced dormancy. The longevity of the buried seeds increased on account of the dormancy imposed on them. The loss of seeds through degeneration and/or decomposition was rather low.     

耕作措施对宁南山区缓坡地土壤团聚体及作物产量的影响

为探讨不同耕作措施对宁南山区缓坡耕地轮作体系土壤团聚体特征及作物产量的影响,在2015—2016年期间,开展了玉米-马铃薯轮作条件下传统平作(CK)、垄沟不覆膜(NH)、垄沟半覆膜(HP)和垄沟全覆膜(WP)4种不同耕作措施试验研究。结果表明:不同耕作措施对表层0～20 cm土壤机械稳定性团聚体和水稳性团聚体影响均较为显著,对20～40 cm土层影响不显著;CK、WP和HP处理下0～20 cm土层范围内均为>5 mm和2～5 mm土壤机械稳定性团聚体含量高,而NH处理下为1～2 mm和0.5～1 mm土壤机械稳定性团聚体含量高,分别为16.25%、13.38%。CK处理下>5 mm土壤机械稳定性团聚体占比为30.99%,显著高于其他三种耕作方式,而NH处理下1～2 mm、0.5～1 mm和0.25～0.5 mm的土壤机械稳定性团聚体含量显著高于其他三种耕作方式。水稳性团聚体则表现为各处理>5 mm所占比例急剧下降。CK处理下显著低于其他处理,含量为1.96%。土壤机械稳定性团聚体平均重量直径(MWD)在NH、HP和WP处理下表层0～20 cm和底层20～40 cm显著...