THE EFFECT OF COMPETITION FROM CEREAL CROPS ON THE GERMINATION AND GROWTH OF AVENA FATUA L. IN A NATURALLY-INFESTED FIELD

Summary. The effect of winter wheat, winter rye, winter barley, spring barley, and fallow cultivated as for a winter cereal, on germination and growth of wild oats ( A. fatua ) was investigated on a naturally-infested field. Treatments were continued for 2 years on the same plots and in the third year all plots were cropped with spring barley. Wild oats were not allowed to shed seeds.
A. fatua was controlled by a dense crop of an autumn-sown cereal. The crop genus was unimportant provided it grew well on the site; its effectiveness depended on its density when the wild oats germinated in spring. Winter wheat and winter rye were equally effective. Even in a light crop of barley, wild oats grew much less vigorously than on the fallow plots. Beyond a certain crop density dependent on soil fertility, further increase in crop did not decrease the size of wild oats. The heaviest crop did not completely suppress the wild oats.
The crop affected the wild oats mainly by decreasing growth of the seedlings, but under winter wheat and winter rye some wild oat seeds may have remained dormant, germinating in the spring barley in the third year, perhaps because the crops decreased the soil moisture content. Nitrogenous fertilizer increased the weight of both crops and wild oats. Barley was more severely affected by soil acidity than wild oats and on acid areas of barley plots the wild oats were larger than where the pH was higher. In wheat and rye which were scarcely affected by soil acidity the size of the wild oat plants was unaffected by soil pH.
L'effet du competition des céréales sur la germination et le développement d' Avena fatua dans un champ naturellement infesté .     

COMPETITION OF WILD OATS (AVENA FATUA L.) IN WHEAT AND FLAX*

Summary. This project was designed to study various aspects of wild oat competition in spring wheat and flax. From ten to forty wild oat plants/yd² were sufficient to cause significant yield reductions in wheat when grown on summerfallow land or when ammonium phosphate fertilizer was added to stubble land. However, when wheat was grown on stubble land without the benefit of a fertilizer treatment, seventy to one hundred wild oat plants/yd² were needed to suppress wheat yields significantly. This would suggest that on stubble land, soil fertility was a more important factor than moderate densities of wild oats in determining eventual crop yields. In these experiments, wild oats reduced the number of tillers per plant, but did not significantly affect the protein content of the harvested grain. Only ten wild oat plants/yd² were sufficient to reduce flax yields significantly on both summerfallow and stubble land. The only exception was in 1966, when flax grown on summerfallow land was not significantly affected until the density of wild oats reached forty plants/yd2. This confirms the general observation that flax is a poor competitor with wild oats. The results suggest that wild oat competition had already commenced prior to emergence of wheat, particularly with the higher densities of wild oats. In general, competitive effects increased with time and with wild oat density. In flax, severe competition had already taken place prior to the 2–3-Ieaf stage of the weed in 1964, but did not become severe until after the 2–3-leaf stage of wild oat growth in 1965 and 1966. Again, competitive effects increased with time and with wild oat density. Results of a final series of experiments, suggested that the optimum seeding date for flax in Manitoba is the latter part of May or the first week of June. Yield reductions due to wild oat competition became very severe as seeding dates were delayed. La compétition de la folle avoine (A vena fatua L.) avec le blé et le lin     

The effect of nitrogenous compounds on in vitro germination of Orobanche crenata Forsk.

The effect of nitrogen (ammonium, urea and nitrate), applied during a conditioning or germination phase, on germination of Orobanche crenata Forsk, seeds was investigated in vitro. Ammonium sulphate (8 mM) applied during conditioning in combination with the nitrification inhibitor nitrapyrin, reduced germination of seeds from 46% to 26%. A lower concentration of 4 mM ammonium sulphate or supplying nitrogen as 8 mM urea or 16 mM nitrate did not inhibit germination. Applied after conditioning during the germination phase, 4 mM ammonium sulphate strongly inhibited germination, especially in combination with a nitrification inhibitor: germination was reduced to less than 5%. Urea (8 mM) reduced germination to only a limited extent (from 58% to 40%). When a urease inhibitor (carbon disulfide) was additionally applied, germination percentage was not affected. Nitrate had no effect. It is hypothesized that the inhibition by ammonium of O. crenata germination is connected with a reduced ability to detoxify ammonium, owing to the reduced activities of the enzymes GS and GOGAT. The inhibitory effect of urea may be indirect, occurring through conversion to ammonium. The effect of a short-term exposure to ammonium was largely reversible and no increase in mortality could be detected. The presence of 6 mM phosphate, Hepes or Mops buffer was found to intervene with the inhibition by ammonium.     

The effect of nitrogen fertilizers on the germination and seedling emergence of wild oat (A. fatua L.) seed in different soil types

Ammonium-containing fertilizers such as granular limestone ammonium nitrate (LAN) and liquid ammonium nitrate (AN) proved to be most effective in stimulating germination and emergence of wild oat in sandy and loamy soil. In pot experiments, rates as low as 25 kg N ha^?1, significantly increased seedling emergence of wild oat. In sandy soil percentage emergence increased with increasing levels of LAN-fertilizer up to 125 kg N ha^?1 which gave 76·1 % emergence after 60 days. In control pots where no nitrogen was applied, only 21·6% of seeds planted emerged after 60 days, In loamy soil, as for AN in both soil types, high levels of LAN initially delayed seedling emergence. This negative effect disappeared approximately 15 days after seeding, resulting in no significant difference in emergence of wild oat where 25 to 125 kg N ha^?1 was applied as LAN or AN. All these rates, however, increased seedling emergence between 25 and 35% compared to the no-nitrogen treatments. Since the same rate of ammonia gas is not equally effective in breaking dormancy of semi- and deeply dormant wild oat seed, results of these experiments are not necessarily applicable to wild oat seeds differing in dormancy status.     

Application method of nitrogen fertilizer affects weed growth and competition with winter wheat

The management of crop fertilization may be an important component of integrated weed management systems. A field study was conducted to determine the effect of various application methods of nitrogen (N) fertilizer on weed growth and winter wheat yield in a zero-tillage production system. Nitrogen fertilizer was applied at 50 kg ha⁻¹ at the time of planting winter wheat over four consecutive years to determine the annual and cumulative effects. The nitrogen treatments consisted of granular ammonium nitrate applied broadcast on the soil surface, banded 10 cm deep between every crop row, banded 10 cm deep between every second crop row, and point-injected liquid ammonium nitrate placed between every second crop row at 20 cm intervals and 10 cm depth. An unfertilized control was also included. Density, shoot N concentration and the biomass of weeds was often lower with subsurface banded or point-injected N than with broadcast N. The winter wheat density was similar with all N fertilizer application methods but wheat shoot N concentration and yield were consistently higher with banded or point-injected N compared with broadcast N. In several instances, the surface broadcast N did not increase the weed-infested wheat yield above that of the unfertilized control, indicating that it was the least preferred N application method. Depending on the weed species, the weed seedbank at the conclusion of the 4 year study was reduced by 29–62% with point-injected N compared with broadcast N. Information gained from this study will be used to develop more integrated weed management programs for winter wheat.     

The use of undisturbed soil cores to study methods of controlling rhizoctonia patch of cereals

Methods of controlling rhizoctonia patch including cultivation, compaction and fertilizer were investigated using undisturbed soil cores removed from patches. Root rot on wheat seedlings was reduced by deep mixing (5 and 10.5 cm) but not shallow mixing (2.5 cm); deep mixing increased root dry weight from 6 mg per plant in undisturbed soil to 15 and 21 mg respectively. Mixing dry and mixing moist gave similar results. Compaction of undisturbed soil from bulk density 1.45 to 1.74 had no measurable effect, but the same level of compaction on soil mixed to 10.5 cm did cause a significant reduction in root weight. Top dressings of sodium nitrate, ammonium sulphate or urea had no effect on root rot. None of the treatments affected the root growth of seedlings grown in cores from adjacent non-patch sites.     

Herbicide-resistant crops: yield penalties and weed thresholds for oilseed rape (Brassica napus L.)

An expérimental procedure was designed to provide a simple model for types of analyses necessary to determine weed density thresholds for advantageous use of crop plants engineered for herbicide resistance. Oilseed rape (Brassica napus L., cv. Tower) biotypes resistant (RES) and susceptible (SUS) to atrazine were used as model crop plants, and wild oat (Avena fatua L.) was used as the model weed. Along a wild oat density gradient equivalent to 0–128 plants m^?2, RES plants consistently experienced biomass and yield reductions of approximately 10–20% compared to SUS plants. When atrazine was applied at 1.5 kg ha^?1 to control wild oats competing with RES plants, RES biomasses and yields were stabilized at the same level as that where 25–30 wild oats m^?2 reduce yields of SUS plants. This implies that with wild oat densities of 25–30 plants m^?2, it becomes agronomically advantageous to crop with RES plants plus atrazine rather than to crop with higher-yielding SUS plants.     

Interactions between barban and benzoylprop etbyl, flamprop metbyl or flamprop isopropyl applied at two growtb stages for wild oat control in cereals

Barban was combined with benzoylprop ethyl, flamprop methyl, or flamprop isopropyl, and the eflects of the combinations on wild oat control and crop yield were assessed, tn greenhouse experiments, the interaction in all three combinations was synergistic, following application at the 2- or 4-leaf stage of wild oats. Under field conditions, combinations of barban + benzoylprop ethyl applied at the 2- or 4-leaf stage of wild oats were as eflective for wild oat control and wheat yield response as barban at 028 kg/ha applied at the 2-leaf or benzoylprop ethyl at 14 kg/ha applied at the 4-leaf stage of wild oats. Mixtures of barban + flamprop methyl applied at the 2- or 4-leaf stage of wild oats provided excellent wild oat control and wheat yield increases. Mixtures of barban + flamprop isopropyl applied at the 2- or 4-leaf stage of wild oats provided comparable wild oat control and barley yield increases to barban (028 kg/ha) applied at the 2-leaf or flamprop isopropyl (14 kg/ha) applied at the 4-leaf stage of wild oats.     

Asulam mixtures for weed control in flax

Five field experiments were conducted from 1972 to 1975 to evaluate weed control in flax (Linum usitatissimum L.) using post-emergence treatments of asulam [methyl (4-aminobenzenesulphonyl) carbamatel alone and in combination with other herbicides. The ¹⁴C-asulam absorption by leaf segments and roots of glasshouse grown wild oats (Avena fatua L.) was also investigated. Asulam at 1.12 kg/ha gave good wild oat control and acceptable control of green foxtail (Setaria viridis (L.) Beauv.). However, wild oat control was poorer when asulam was combined with other herbicides: on a 3-year average, as compared with asulam alone at equal rates, the asulam+MCPA mixture resulted in a greater antagonism and a significant 6% reduction in flax seed yield, whereas the asulam+bromoxynil/MCPA mixture gave the least antagonistic effect, improved broadleaf weed control and increased yield by 13%. In mixtures, the potassium salt of MCPA was more compatible with asulam for weed control than the amine form. Both leaf segments and roots of wild oats absorbed and distributed less ¹⁴C-asulam from solutions containing MCPA than from those containing bromoxynil or bromoxynil/MCPA.     

Time of onset of competition and effects of various fractions of an Avena fatua L. population on spring barley

The growth and competition of wild oats (Avena fatua L.) emerging at different times, and the time of onset of competition by them were studied using natural populations in spring barley. In one experiment in 1972, wild oats emerging in the 0–0?5, 0?5–2?5, 2?5–4 crop leaf stages at densities of 54, 46, 15 m ^?2 respectively were allowed to compete all season with the crcp. These gave rise to 82, 17 and l% of all seed shed and caused 16%, and two non-significant yield losses respectively. In two other experiments in 1973, nearly all the wild oats that caused yield losses had emerged by the crop 2˙45 leaf stage. Where wild oats emerging up to the crop 2?5 leaf stage were removed, the later ones did not compensate by making extra growth. In one of these experiments in which densities of crop and weed were 416 and 414 m ², and in the other where they were 295 and 294 m ² respectively, grain yield losses were significant if the wild oats remained in the crop until the crop had 2?5–4?5 leaves and 4?5–6?5 leaves respectively. In a third experiment in 1973 with initial densities of 464 wild oats and 336 barley plants m ^?2, and where a top dressing of nitrogen was given at the crop 3–4 leaf stage, unlike the other two experiments in 1973 where all nitrogen was applied at sowing, no yield losses resulted unless the wild oats remained in the crop until after the crop 6 leaf stage.     

A STUDY OF THE COMPETITION BETWEEN BARLEY AND OATS AS INFLUENCED BY BARLEY SEEDRATE, NITROGEN LEVEL AND BARBAN TREATMENT

Summary. The object of the work described in this paper was to obtain information on the relationship between the effects of crop competition and barban treatment on oats growing in another cereal. The work was carried out on barley cross-drilled with cultivated oats. Variation in crop competition was obtained by using different barley seed-rates and nitrogen levels. Increasing the seedrate of barley without applying barban resulted in a reduction of the initial oat population. This reduction applied to weight of individual shoots, number of shoots and panicles per unit area and number of spikelets per panicle. The application of barban at selective rates gave an independent reduction of oats of the order of 80%. This value proved almost constant at each seedrate of barley. Crop competition and barban accordingly seem to art independently and their effects appear to be simply additive. The barley fresh weights per unit area increased substantially when oat competition was reduced by barban treatment. The highest increase occurred on the plots with the lowest barley seedrate in spite of the fact that these plots still appeared infested with oats at harvest time. Nitrogen application stimulated the growth of barley and oats to a similar degree and did not in consequence lead to a selective suppression of oats.
Etude de l'influence de la densité du Semis, du taux de fertilisation azotée et du traitement au barbane, sur la concurrence entre une Orge et une Avoine     

灌溉量和氮肥增效剂对夏玉米产量及水肥利用的影响

为探究水分和氮肥增效剂对夏玉米生长及水肥利用的综合影响，通过设置40 mm（W1）和60 mm（W2）两个灌水水平下不施氮肥（N0）、施用氮肥（U）、氮肥+硝化抑制剂（U+DCD）、氮肥+脲酶抑制剂（U+NBPT）、氮肥+双效抑制剂（U+N+D）5种氮肥施用措施，开展夏玉米田间试验。结果表明：相较于施用氮肥处理，氮肥配施增效剂可以显著提高夏玉米产量、成熟期地上生物量、净收益、水分利用效率和氮肥偏生产力，增幅分别为5.92%~13.82%、5.85%~18.07%、11.12%~24.30%、12.35%~41.83%和5.93%~13.80%，其中氮肥配施双效抑制剂效果较优；氮肥配施脲酶抑制剂和双效抑制剂可以降低夏玉米农田土壤氨挥发累积量和成熟期土壤硝态氮残留量，前者效果最优。相比于W1，W2水平下氮肥配施双效抑制剂处理玉米产量、成熟期地上生物量、净收益、水分利用效率和氮肥偏生产力分别提高10.54%、15.51%、19.40%、20.31%和27.36%；氮肥配施脲酶抑制剂处理农田土壤氨挥发累积量和硝态氮残留量分别降低11.33%和48.46%。综合考虑夏玉米施肥灌水方案的经济效益、环境效益、水肥利用效率和玉米植株生长，构建模糊综合评价体系，得到最优处理为灌水量60 mm下氮肥配施双效抑制剂。     

Phosphorus fertilizer effects on the competition between wheat and several weed species

Information on phosphorus (P) fertilizer affecting crop–weed competitive interactions might aid in developing improved weed management systems. A controlled environment study was conducted to examine the effect of three P doses on the competitive ability of four weed species that were grown with wheat. Two grass and two broad-leaved weed species were chosen to represent the species that varied in their growth responsiveness to P: wild oat (medium), Persian darnel (low), round-leaved mallow (high), and kochia (low). Wheat and each weed species were grown in a replacement series design at P doses of 5, 15, and 45 mg P kg⁻¹ soil. The competitive ability of the low P-responsive species, Persian darnel and kochia, decreased as the P dose increased, supporting our hypothesis that the competitiveness of species responding minimally to P would remain unchanged or decrease at higher P levels. As expected, the competitiveness of the high P-responsive species, round-leaved mallow, progressively improved as the P dose increased. However, wild oat's competitive ability with wheat was not affected by the P fertilizer. The results suggest that fertilizer management strategies that favor crops over weeds might deserve greater attention when weed infestations consist of species known to be highly responsive to higher soil P levels. The information gained in this study could be used to advise farmers of the importance of strategic fertilizer management in terms of both weed management and crop yield.     

SURVIVAL OF SEEDS OF WILD OATS (AVENA FATUA L, AND AVENA LUDOVICIANA DUR.) AND CHARLOCK (SINAPIS ARVENSIS L.) IN SOIL UNDER LEYS

Summary. Survival of wild oat seeds (mainly Avena fatua ) under leys on clay soils was investigated in two field experiments. During the first year under ley the number of seeds decreased by 41 % and 86% respectively. Subsequent decreases were less, and after 5 years under ley there were still enough of the original seeds left to produce infestation of a cereal crop. These results suggest that a long ley is not an efficient way of eliminating wild oat seeds from soil, and that a 1-year ley may be almost as effective as one of 5 years.
When a ley was ploughed, the number of wild oats germinating decreased as the number of years under ley and the age of the seeds increased, but was scarcely affected by the weather. In contrast, charlock ( Sinapis arvensis ) germination did not decrease with increasing age of seeds up to 5 years, but was greatest in years with most rain during April and May.
Survivance de semences de Folle Avoine (Avena fatua L . et A . ludovieiana Dur.) et de Moutarde des champs (Sinapis arvensis L.) dans le sol sous prairie temporaire     

Night‐time tillage revisited: the delayed soil desiccation process in night‐time tilled plots may promote unexpected weed germination

Night‐time tillage and sowing (photocontrol of weeds, soil cultivation in darkness) can reduce the germination and subsequent density of light‐sensitive weeds by excluding the short light flash during soil disturbance. In most experiments conducted from 1990 to 2004 worldwide, total weed density was reduced in night‐time tilled plots as expected. However, in a few field experiments, total weed density was significantly increased in night‐time compared with daytime tilled plots. We hypothesise that the desiccation process of the upper soil layer (roughly about 0–30 mm), from where most small seeded weeds emerge, may have been delayed in night‐time compared with daytime tilled plots, with significant effects on early seed germination processes. Daytime tillage was usually performed around noon, to capture high light intensities during soil tillage. However, around noon soil desiccation can be much higher than during the night. A few hours of relatively higher water availability for seeds in the upper soil layer during the night, before the next morning when soil desiccation usually increases again, may have favoured seed germination and subsequent weed emergence compared with daytime tillage, finally resulting in higher weed density in night‐time tilled plots. On the other hand, crop germination and emergence may also be higher under such conditions.     

The effect of sowing date, stale seedbed, row width and mechanical weed control on weeds and yields of organic winter wheat

Three field experiments were carried out in organically grown winter wheat in Denmark. The treatments were sowing time (normal or late sowing) and false seedbed, row width (12 and 24 cm) and weed control method [untreated; mechanical weed control (weed harrowing at 12 cm supplemented with inter‐row hoeing at 24 cm); and herbicide weed control]. Weed biomass in midsummer was greatest on plots sown at the normal sowing time (compared with delayed sowing) and was reduced by mechanical or chemical weed control (compared with untreated plots). Row width alone had no influence on weed biomass, but in the experiment with high weed pressure, the more intensive mechanical weed control used at a row width of 24 cm reduced weed biomass. Normal sowing time tended to give higher yields, but this was only statistically significant in one of the three experiments. Wide rows gave a yield decrease in the experiment with low weed pressure. The effect of weed control on yield was dependent on the weed pressure. At low weed pressure, mechanical weed control caused a yield decrease compared with untreated or herbicide treated. At intermediate weed levels there were no differences, whereas at high weed pressure, mechanical weed control and herbicide treatment caused a yield increase compared with untreated. False seedbeds were shown to contribute to a decrease in the soil seed reserve.     

氮肥对保水剂吸水保肥性能的影响

测定保水剂在不同氮肥(尿素、碳酸氢铵、硝酸铵、硫酸铵、氯化铵)溶液中的吸水倍率和对肥料养分的吸持量,分析不同氮肥对保水剂吸水、保肥性能的影响。结果表明:保水剂在各种氮肥溶液中吸水倍率显著下降,并随肥料浓度的增加下降幅度增加;受影响程度聚丙烯酸钠盐型保水剂大于聚丙烯酰胺-丙烯酸盐型保水剂;不同氮肥对保水剂吸水倍率的影响按尿素、碳酸氢铵、硝酸铵、硫酸铵、氯化铵顺序递增。保水剂在大量吸水的同时,也对溶液中的肥料分子或者离子有吸持作用,吸持量均随肥料浓度的增加而增加;保水剂和肥料品种不同,吸持量也不同;除尿素外,保水剂对肥料的吸持率随肥料浓度的增加而降低,最高浓度下,吸持率按硝酸铵、碳酸氢铵、氯化铵、硫酸铵、尿素次序依次增大。     

燕麦叶斑病病原菌鉴定及其生物学特性

为明确内蒙古、河北地区燕麦叶斑病病原菌种类及其生物学特性,采用组织分离法对病原菌进行分离,通过形态学特征及18SrDNA序列分析进行分类鉴定,以离体和活体叶片接种进行致病性测定,并采用十字交叉法对病原菌的生物学特性进行研究。结果表明,共分离到3株菌株R1、H44和B8,根据形态学特征和18SrDNA序列分析将3株菌株均鉴定为燕麦内脐蠕孢菌Drechslera avenacea(M.A.Curtis ex Cooke)Shoemaker,有性态为燕麦核腔菌Pyrenophora avenae S.Ito et Kurib.。3株菌株均为致病菌,在离体和活体叶片上均能产生腐烂坏死病斑。3株菌株的菌丝在5~30℃、pH 5~11范围内均可生长,其中菌株R1和H44的最适生长温度为25℃、最适生长pH为8,菌株B8的最适生长温度为20~25℃、最适生长pH为7~8。3株菌株对碳源的利用效果中均以淀粉最好,对乳糖利用效果最差;菌株R1的最适氮源是硝酸铵,对蛋白胨和尿素利用效果最差;菌株H44和B8的最适氮源是蛋白胨,菌株H44对硫酸铵利用效果较差,3株菌株都不能利用碳酸铵,且菌株B8也不能利用尿素。     

Predicting the risk of weed infestation in winter oilseed rape crops

Chemical weed control before crop and weed emergence is a systematic practice in winter oilseed rape crops in France. It would be profitable both for farmers and the environment to predict the level of weed infestation early on in the growing season and to control weeds only when necessary using post‐emergence weed control. The objective of this paper was to develop and evaluate simple models to predict weed biomass in oilseed rape crops. The model input variables were related to weed population characteristics and farmers’ practices. The models can be used to classify oilseed rape plots into two categories: plots with a level of weed infestation above a threshold or those with level of weed infestation below a threshold. A data set including 3 years of experiments, conducted across several regions in France, was used to estimate the parameters and to evaluate the models. High values of sensitivity and specificity were obtained when weed biomass was predicted as a function of sowing date, type of soil tillage, soil mineral nitrogen, crop density, weed density at emergence, and main characteristics of the most abundant weed species. Model performance strongly decreased when input variables related to the weed population were not taken into account. The best models correctly classified 90% of the plots with high weed infestation and 64% of the plots with low weed infestation.     

江苏省镇江市麦田杂草发生情况调查

为了摸清江苏省镇江市麦田杂草种类、分布状况、出草规律、草相变化、防除情况等,通过倒"W"形九点取样法对镇江市麦田杂草进行了调查。调查结果显示镇江市麦田杂草有29科99种,日本看麦娘、菵草、猪殃殃、看麦娘、稻槎菜、硬草、繁缕、大巢菜、荠菜、涩荠、野老鹳草、牛繁缕、早熟禾为该地区主要危害性杂草,其中菵草、日本看麦娘、猪殃殃为麦田杂草群落优势种。不同地形区域杂草种类和优势种不同。镇江市麦田杂草由20世纪90年代初以看麦娘、日本看麦娘和猪殃殃等为主演变为以菵草、日本看麦娘、猪殃殃为主,稻槎菜、硬草、繁缕等发生较重。出草高峰集中在小麦播后15 d左右,具体到镇江来说11月底至12月上旬为杂草发生高峰期。针对镇江本地杂草发生情况,制定了以土壤封闭和茎叶处理相结合的防控技术方案。