摘要:

SummaryThe growth and competition of wild oats(Avena fatuaL.) 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−2respectively 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 m2, and in the other where they were 295 and 294 m2respectively, 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 cr

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1984.tb00592.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SummaryThe critical period of weed competition was determined in three vegetable crops: early cabbage (Brassica oleraceavar.capitataL.), pickling cucumbers (Cucumis sativusL.), and field‐seeded processing tomatoes (Lycopersicon esculentumL.). There were significant interactions between weed‐removal treatments, year, and row width. Cabbage yields were reduced if plots were not kept weed‐free for at least 3 weeks after transplanting or if weeds which emerged with the crop were allowed to remain longer than 4–5 weeks, Cucumber yields were reduced if plots were not kept weed‐free for up to 4 weeks after seeding or if plots remained weed‐infested longer than 3–4 weeks. Higher crop population densities (narrower row widths) in cabbage and cucumbers resulted in smaller plants, earlier competition from weeds, and therefore a shorter period that the crop could remain weed‐infested without suffering reduced yields. Yields of direct‐seeded tomatoes were reduced if plots were not kept weed‐free for up to 9 weeks after seeding or if weeds which emerged with the crop were allowed to remain longer than 5 weeks. In each crop the timing of the critical period of competition was verified by weed removal only during this interval. There was a true critical period in direct‐seeded tomatoes, but not in cabbage or cucumbers where a single weeding was sufficient to

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1984.tb00593.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SummaryThe relative potencies of analytical‐grade lenacil (99% ai) and its commercial formulation, Venzar® (80% ai), technical‐grade ethofumesate (96%) and its commercial formulation Nortron® (21% ai) were evaluated using oats (Avena sativaL. cv. Selma) as test plant.In all experiments the dose‐response curves of the pure herbicide and its commercial product were parallel. The average potency of Venzar relative to lenacil, assayed twice in a sandy loam, was 0⋅80 and thus equal to the expected 0⋅80. The average potency of Nortron relative to ethofumesate, assayed in a sandy loam and a loamy sand, was 0⋅25 and close to the expected value of 0⋅21.The implication of using the technique of parallel‐line assay in herbicide studies is discussed and its potential use in other contexts than the present

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1984.tb00594.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SummarySpring‐produced seeds ofLamium amplexicauleL. were dormant at maturity in May and after‐ripened when buried and stored over a range of temperatures, becoming conditionally dormant at low (5, 15/6 and 20/10°C) and non‐dormant at high (25/15, 30/15 and 35/20°C) temperatures. Conditionally dormant seeds germinated to high percentages at 5 and 15/6°C, and non‐dormant seeds germinated to high percentages at 5, 15/6, 20/10, 25/15 and 30/15°C. Seeds that became conditionally dormant at 5°C afterripened completely (i.e. became non‐dormant) after transfer to 30/15°C. Buried seeds that became non‐dormant in a non‐temperature‐controlled glasshouse during summer were still non‐dormant after 12 weeks of storage at 30/15°C, while those stored at 5°C for 12 weeks had entered conditional dormancy. Thus, low temperatures cause reversal of the afterripening that takes place at high temperatures, but not that which takes place both at low and at high temperatures. Low winter temperatures cause dormant autumn‐produced seeds and non‐dormant seeds in the soil seed pool to become conditionally dormant. The ecological consequences of these responses to temperature are discussed in relation to the timing

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1984.tb00595.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SummaryFresh seeds ofLamium purpureumL. were dormant at maturity, and when buried and exposed to natural seasonal temperature changes they exhibited an annual dormancy/non‐dormancy cycle. During burial in summer, fresh seeds and those that had been buried for 1 year afterripened and thus were non‐dormant by September and October; light was required for germination. During autumn and winter seeds re‐entered dormancy, and during the following summer they became non‐dormant again. Dormant seeds afterripened when buried and stored over a range of temperatures, becoming conditionally dormant at low (5, 15/6°C) and non‐dormant at high (20/10, 25/15, 30/15 and 35/20°C) temperatures. Conditionally dormant seeds germinated to high percentages at 5, 15/6 and 20/10°C, while non‐dormant seeds germinated to high percentages additionally at 25/15, 30/15 and 35/20°C. Low temperatures caused non‐dormant seeds to re‐enter dormancy, while high temperatures caused a sharp decline in germination only at 30/15 and 5°C. The temperature responses ofL. purpureumseeds are compared to thos

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1984.tb00596.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SummaryA simple bioassay is described in which the increase ofin vivochlorophyll fluorescence of unialgal continuous, cultures is related to the concentration of photosynthetic inhibitors by a hyperbolic function. Concentrations of the herbicide terbutryne detected by the bioassay in an aquarium microcosm were generally within 2 μg 1−1of estimates by gas chromatography. A multispecies bioassay approach is proposed, which combines high sensitivity with a wide operating range of concentratio

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1984.tb00597.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ZusammenfassungAn drei Versuchsstationen in Rumänien, die unterschiedliche Klima‐ und Bodeneigenschaften aufweisen, wurde die Verlustrate von Atrazin und Simazin, die mit jeweils 1 und 3 kg AS ha−1in Parzellen mit und ohne Mais (Zea maysL.) appliziert wurden, in der oberen 10‐cm‐Schicht analysiert. Unabhängig von Dosierung und Pflanzenbewuchs konnte eine weitgehend vergleichbare 50%ige Konzentrationsabnahme am jeweiligen Standort festgestellt werden, die bei Atrazin zwischen 36 und 68 Tagen und bei Simazin zwischen 48 und 70 Tagen lag.Mit Bodenproben der verschiedenen Standorte wurden weiterhin mit Atrazin Laborversuche durchgeführt, um das Abbauverhalten unter standardisierten Bedingungen und durch Sorptions‐ und Einwaschungsuntersuchungen das Verhalten von Atrazin in diesen Böden zu charakterisieren.Mit Hilfe von Klimadaten für die entsprechende Periode der Freilandversuche und den entsprechenden Konstanten aus den Laborversuchen bzw. aus Literaturdaten wurde mit einem Computerprogramm die Herbizidpersistenz für Feldbedingungen simuliert. Mit dem Modell konnten im Vergleich zu den gemessenen Werten in fast allen Fällen recht gute Übereinstimmungen festgestellt werden, wobei in einigen Fällen das Modell die Tendenz einer geringfügigen Unterschätzung der tatsächlichen Wirkstoffverluste zeigt. Bei der Anwendung des Simulationsmodells ist eine Vorhersage der Persistenz von Atrazin und Simazin auch unter den extremeren Bedingungen der rumänischen Standorte mit ausreichender Genauigkeit für praktische Belange möglich, ohne aufwendig

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1984.tb00598.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ZusammenfassungVon drei Versuchsstationen in Rumänien, die unterschiedliche Klima‐ und Bodeneigenschaften aufweisen, wurden 1982 120 Tage nach Applikation von 3 kg Atrazin ha−1in Mais (Zea maysL.) Proben aus 0–10 cm Bodentiefe auf ihre Gesamtrückstände und pflanzenverfügbaren Anteile mit einer Wasserextraktions‐ und Biotestmethode untersucht. An einem Standort wurden zudem die gleichen Bestimmungen 3,5 Jahren nach Anwendung von 100 kg AS ha−1durchgeführt.In Abhängigkeit von der unterschiedlichen Atrazinverlustrate und der prozentualen Verfügbarkeit bei den drei Standorten konnten 30–120 μg 1−1Boden an potentiell pflanzenverfügbarem Atrazin ermittelt werden.In Langzeit‐Biotesten in Hydroponik wurde die Aktivität dieser Konzentrationen auf die für Rumänien wichtigsten Folgekulturen nach Maisanbau—Sonnenblume, Winterweizen, Sojabohne und Lein—überprüft. Die ED50‐Werte und die Einteilung der Wirkung in fünf Aktivitätskategorien erfolgte mit der Probit‐Analyse, wobei die Sonnenblume mit 22 μg 1−1die höchste und die Sojabohne mit 78 μg 1−1die niedrigste Empfindlichkeit zeigte.Mit Hilfe der ermittelten Verfügbarkeitswerte kann für jeden Standort anhand einer Verträglichkeitsliste abgelesen werden, ob und wie stark Atrazin‐Rücks

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1984.tb00599.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY