摘要:

Summary.Solanum ptycanthum(Dun.) vegetative and reproductive growth was evaluated under shade and in the field with soybean interference. In full sunlight without soybean interference, aS. ptycanthumplant produced 243 g shoots and 5957 berries in 20 weeks, but only 38 g and 576 berries in 11 weeks. Plants grown in 94% shade produced 3 g of shoots and 23 berries in 20 weeks, and 1 g and 1 berry in 11 weeks.S. ptycanthumplants that emerged with the soybeans and were positioned between 75‐cm rows produced 43 g shoots and 264 berries, whereas plants positioned in 75‐cm rows and emerging 6 weeks after the soybeans produced 1 g and 16 berries. When grown between 37·5‐cm rows for the same period of time this weed produced 12 g and 2 berries plant−1; plants positioned in 37·5‐cm rows produced shoots less than 1 g in weight and one berry plant−1. Shoot growth and berry production ofS. ptycanthumincreased from 80 to 200% in a 2‐week period between the initiation of soybean leaf abscission and maturity. In a season about 50 000 seeds weed−1were produced in full sunlight; 20 000 or less were produced under soybean interference. When grown in irradiance levels from full sunlight to 94% shade, viable seeds were first detected 10 days after anthesis and essentially all seeds in the berry were viable 24 d

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01300.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.Most freshly‐matured seeds ofThlaspi arvenseL. (Brassicaceae) were dormant at maturity in May. Seeds sown on soil germinated in autumn and spring, but mostly in autumn. Buried seeds exhumed at monthly intervals and tested in light and darkness over a range of thermoperiods exhibited annual dormancy/non‐dormancy cycles. However, the dormant period was short, usually only in April, but sometimes May, and in some years 1–6% of the seeds remained conditionally dormant. After‐ripening occurred during summer, and seeds were non‐dormant during autumn. Seeds entered conditional dormancy in winter and dormancy in late winter or early spring. When buried dormant seeds were kept at 25/15, 30/15 or 35/20°C for 12 weeks, they gained the ability to germinate to 95–100% at 15/6, 20/10, 25/15, 30/15 and 35/20°C. After burial for 12 weeks at 15/6 and 20/10°C, seeds germinated to 80–100% at 15/6, 20/10 and 25/15°C. but to only 11–64% at 30/15 and 35/20°C. After 4 weeks at 5°C, initially‐dormant seeds germinated to 100% at all thermoperiods except 35/20°C, where only 15% of them germinated. However, after 18 weeks at 5°C, only 0–1% of the seeds germinated at all thermoperiods. Most non‐dormant seeds exposed to 1, 5 and 15/6°C for 16 weeks were induced into dormancy; 1–15% entered conditional dormancy and thus germinated only at 15/6, 20/10 and 25/15°C. This study indicates that seeds of winter annual plants ofT. arvenseare non‐dormant in autumn and enter dormancy in winter, while those from summer annuals are dormant in autumn a

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01301.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.When sequential single‐node shoot segments (third to fifteenth node, counting from the apex) of the perennial grass weedPaspalum distichumL. were buried in soil, new shoot growth was significantly correlated with initial segment length. Growth from the youngest segment (third), which was about 2 cm long, was only half as great as that from segments 8 to 15, which were initially 2–3·5 times longer. When 14‐node shoot segments were buried in soil, the apical bud exerted a dominating influence on shoot emergence and new shoot growth of axillary buds. The degree of suppression increased gradually up to node 8 and then decreased as the distance from the apex increased. A similar result was obtained in these shoot segments following decapitation. However, the degrees and patterns of apical and bud dominance varied in shoots collected during different seasons and also in shoots with different node numbers, node position, cutting and chilling treatments. A possible role of apical and bud dominance inP. distichumin keeping aerial shocks in reserve under adverse conditions, thus providing a survival mechanism for this weed, is dis

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01302.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.Bud sprouting, shoot height, and fresh and dry weights of plants arising from single‐node stem segments ofPaspalum distichumL. decreased as the depth of burial in the soil increased. Sprouting, rooting and shoot growth of single‐node segments submerged in 5–15 cm of water were reduced significantly in the dark. Light alleviated this water‐induced reduction in 1‐, 3‐ and 7‐node segments. Submergence actually promoted sprouting of the proximal bud and shoot growth from the distal bud in 3‐node segments, and shoot growth of the first two buds from the distal end in 7‐node segments, Flooding the roots of 3‐week ‐old plants for one month had no effect, but markedly reduced tiller production and dry weights after 2 and 3 months. Treatment at 100% relative humidity promoted new shoot production in 4‐month old plants only if all shoots were decapitated (clipped) but not in plants with 6 shoots left intact. Submergence of the whole plant in water drastically reduced new shoot production regardless of clipping treatment. Effects of flooding varied with its duration. It is concluded that thoughP. distichum, a wetland perennial weed, survives root flooding and submergence conditions, these conditions do not support maxim

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01303.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.The main techniques and the common experimental methods used in studying allelopathy are reviewed. Problems associated with both methodology and conclusions drawn based on certain techniques are discussed. The accuracy obtained using these techniques is evaluated and show that some of the techniques could be a misleading tool. Some changes are suggested.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01304.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.The allelopathic effect ofChenopodium albumL. (fat‐hen) andSenecio vulgarisL. (groundsel) on tomato (Lycopersicon esculentumMill cv. Ailsa Craig) plants was investigated under glasshouse conditions. A new technology was used to separate competitive from allelopathic effects. These experiments suggested thatC. albumhad an effect on tomato through allelopathy.C. albumleach‐ates significantly reduced shoot fresh and dry weights and the accumulation of N, P, K, Ca and Mg of tomato shoots. No effect was found on the quantities of these elements in tomato roots. Leachate of five plants ofC. albumper pot was sufficient to reduce tomato growth. Addition of 10 or 20 g kg−1ofC. albumdried shoots to the soil mixture significantly decreased the fresh and dry weights of tomato plants.S. vulgarisleachates did not show significant effects on the growth or nutrient accumulation of tomato p

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01305.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.Seed coat structures may play a major role in determining the germination of seeds. The involvement of seed coat characteristics in the inhibition of germination observed when dry seeds ofDatura feroxL. andD. stramoniumL., were rinsed or soaked in water for 1–5 min (‘soaking effect’) was investigated. Germination was inhibited by soakingD. feroxseeds even at late stages of the germination process up to one day before root protrusion. Simulation of the ‘soaking effect’ was achieved by blocking the hilum with lanolin, enamel lacquer or agar during imbibition. Blocking the hilum did not prevent water uptake by the seeds. Seed coat integrity was necessary for the ‘soaking effect’ since germination inhibition was eliminated by removing or cracking the seed coat. Drying the seeds up to 12 h after soaking reversed the inhibitory effect. SEM observations of both species revealed a loose outer parenchymatous tissue covering the hilum, an inner spongy tissue between the nucellus and the hilum and a space between the seed coat and the nucellus. We concluded that during soaking, water is trapped in the space between the seed coat and the nucellus, and in the intracellular spaces of the spongy tissue within the hilum. This water ‘plug’ may limit the diffusion of gas(es) to and from the embryo through the hilum, thus inhib

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01306.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.Post harvest soil samples taken during the autumn of 1985 and 1986 were split and estimates made of the weed seedbank using two methods: (1) a physical separation of seed from the soil mineral fraction by a sieving/flotation procedure and (2) by placing soil in shallow containers in a greenhouse where seeds could germinate and be periodically counted over a period of eight months. Seedbank estimates derived from each procedure were analysed to determine the suitability of each technique for detecting treatment differences from an experiment evaluating tillage/herbicide effects on weed populations. Both techniques were suitable for determination of seedbank changes due to different tillage treatments and herbicide inputs. The two techniques also proved effective for detection of individual species in the seedbank and the two techniques provided comparable estimates of the relative density of individual weed species in the seedbank. Weed seedbank estimates obtained by the physical extraction procedure from the autumn 1985 soil samples were correlated with weed seedling counts made in the spring of 1986. In most cases, weed seedlings represented less than 10% of the number of seeds estimated by physical extraction the preceding autumn. Individual species seed estimates and subsequent weed counts were poorly correlated which indicated that the seed count estimates alone were poor predictors of weed flora.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01307.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.Adsorption and degradation rates of triasulfuron in 8 different soils were negatively correlated with soil pH and were generally lower in subsoils than in soils from the plough layer. The half‐life at 20°C varied from 33 days in a top soil at pH 5·8 to 120 days in a subsoil at pH 7·4. Adsorption distribution coefficients in these two soils were 0·55 and 0·19, respectively. Movement and persistence of residues of chlorsulfuron, triasulfuron and metsulfuron‐methyl were compared in a field experiment prepared in spring 1987. Triasulfuron was less mobile in the soil than the other two compounds. Residues of all three herbicides were largely confined to the upper 40–50 cm soil 148 days after application. With an initial dose of 32 g ha−1, residues in the surface soil layers were sufficient to affect growth of lettuce and sugar‐beet sown approximately one year after application. Laboratory adsorption and degradation data were used with appropriate weather data in a computer model of herbicide transport in soil. The model gave good predictions of total soil residues during the first five months following application, and also predicted successfully the maximum depth of penetration of the herbicides into the soil during this period. However, more herbicide was retained close to the soil surface than was predicted by the model. The model predicted extensive movement of the herbicides in the soil during winter but did not predict that residues sufficient to affect crop growth could be present in the upper 15–20 cm soi

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01308.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary.Fluroxypyr‐MHE (methylheptyl ester) was hydrolysed to fluroxypyr in soil/water suspensions at rates several thousand times that in distilled, deionized water at similar pH and temperature: the pH 7, 25°C half‐life in water was 454days, compared to 2, 5, and 5·5 hours in 1 : 100 soil/water suspensions of a Barnes loam, Catlin silt loam, and Mhoon clay. The catalysed hydrolysis did not occur in decanted, aqueous supernatants of centrifuged Barnes soil suspensions, nor in Barnes soil/water suspensions which had been autoclaved. In soils incubated (26·1°C) at field moist conditions, only 1 to 2% of the fluroxypyr‐MHE had not hydrolysed after three days. An extracellular enzyme was suggested as the

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb01309.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY