首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 485 毫秒
1.
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.  相似文献   

2.
Weeds are the main problem with turmeric (Curcuma longa L.) cultivation where herbicides are not allowed. This is because herbicides cause water contamination, air pollution, soil microorganism hazards, health hazards, and food risks. Considering turmeric's medicinal value and the environmental problems caused by herbicides, various agronomic practises have been evaluated for non‐chemical weed control in turmeric. One additional weeding is required before turmeric emergence and weed infestation is much higher when turmeric is planted in February and March, as compared to April, May or June planting. A similarly higher yield of turmeric is achieved when it is planted in February, March, and April, compared to late plantings. Weed emergence and interference are not affected by planting depth, seed size, planting pattern, planting space, ridge spacing, and the row number of turmeric until 60 days after planting. This is because turmeric cannot develop a canopy structure until then. Thereafter, weed infestation reduces similarly and significantly when turmeric is planted at depths of 8, 12, and 16 cm, compared to shallower depths. The yield of turmeric at these depths is statistically the same, but the yield for the 16 cm depth is difficult to harvest and it tends to decrease. Turmeric grown from seed rhizomes (daughter rhizomes) weighing 30–40 g reduces weed infestation significantly and obtains a significantly higher yield compared to smaller seeds. The mother rhizome also can suppress weed infestation and increase the yield markedly. Around 9% weed control and 11% higher yield are achieved by planting turmeric in a triangular pattern compared to a quadrate pattern. The lowest weed infestation is found in turmeric grown in a 20 or 30 cm triangular pattern and the highest yield is obtained with the 30 cm triangular pattern. Turmeric gown on two‐row ridges spaced 75 cm apart shows excellent weed control efficiency and obtains the highest yield. This review concludes that turmeric seed rhizomes of 30–40 g and/or the mother rhizome could be planted in a 30 cm triangular pattern at the depth of 8–12 cm on two‐row ridges spaced 75–100 cm apart during March to April in order to reduce weed interference and obtain a higher yield. Mulching also suppresses weed growth and improves the yield. The above agronomic practises could not control weeds completely; biological weed management practises could be integrated in turmeric fields using rabbits, goats, sheep, ducks, cover crops or intercrops.  相似文献   

3.
Notices     
Abstract

Seed‐bed types, fertilizers, cassava stem portions, planting time and yam cultivars were studied for the incidence of termites in cassava and yam fields. Planting cassava on ridges reduced the incidence of termites and significantly (P<0.05) increased tuber yield. The bottom stem portion of cassava stick was the least attacked by termites. Planting cuttings when rains became steady reduced termite incidence. NPKMg (12:12:17:2) suppressed termites in yam and improved yield significantly. Delay in harvesting yam tubers increased termite infestation. Yield loss was highest for Dioscorea rotundata cv. Nwopoko, with losses of more than 5 metric tonnes/ha when harvest was done after December in termite infested soil. Chinese yam showed the greatest resistance to termites.  相似文献   

4.
Effects of density and period of competition by Solanum nigrum L. on direct seeded tomatoes in relation to weed control The effects of density and period of competition from Solanum nigrum L. were measured in direct seeded tomatoes given weed control treatments currently used in south-east France. S. nigrum emerging after a diquat treatment at the 2–3 leaf stage of the crop and thinned to low densities (<12.8 plants ha?1) at the 5–6 leaf stage of the crop caused significant yield loss if left to compete with the crop until harvest. Yield reduction was smaller if the same weed densities were present only until the onset of flowering. The regression curves of yield on weed density differed as annual climatic variations affected sowing date and plant growth; a comparison between years was made using the relation ‘crop yield × weed biomass/crop biomass’. Significant interactions between weed density and period of competition were found with yield of both green and red fruit. For late sown crops with low densities of S. nigrum two weed control treatments at the 5–6 leaf stage and at the onset of flowering were sufficient to prevent yield loss.  相似文献   

5.
Abstract

Field surveys were conducted in 2012 and 2013 to evaluate the distribution and virulence of fungal isolates associated with tuber rot disease among yam (Dioscorea spp.) producing agroecological zones (AEZs) of Nigeria. A total of 70 and 66 farmers’ fields were surveyed in 2012 and 2013, respectively among three yam species, Dioscorea rotundata, D. alata and D. cayenensis. Fifteen rotted samples were randomly collected per each yam species in fourteen districts across the humid rainforest (HF), the derived savanna (DS) and the southern Guinea savanna (SGS) agroecologies. Twenty-one fungal species were isolated in the HF, 18 species in the DS and 16 in the SGS. The highest rot severity was in HF agroecology in the D. rotundata which varied from 27.2% to 65.7% in 2012 and from 21.1 to 57.4% in 2013, while the SGS agroecology had the least severity. Lasiodiplodia theobromae was the most virulent pathogen with lesion diameter of 26.8–42.1?mm at 14?days after inoculation. Findings provide baseline information for the formulation of management strategies for yam tuber rot disease in Nigeria.  相似文献   

6.
The outcome of crop-weed competition should be predicted as early as possible in order to allow time for weed control measures. Maize grain yield losses caused by interference from Amaranthus retroflexus L. (redroot pigweed) were determined in 1991 and 1992. The performance of three empirical models of crop-weed competition were evaluated. Damage functions were calculated based on the weed density or relative leaf area of the weed. In the yield loss-weed density model, values of I (percentage yield loss at low weed density) were relatively stable for similar emergence dates of A. retroflexus across years and locations. Estimated maximum yield loss (A) was more variable between locations and may reflect environmental variation and its effect on crop-weed competition, at least in 1991. The two-parameter yield loss-relative leaf area model, based on m (maximum yield loss caused by weeds) and q (the relative damage coefficient) gave a better fit than the single-parameter version of the model (which includes only q). In both relative leaf area models, the values of q varied between years and locations. Attempts to stabilize the value of q by using the relative growth rate of the leaves of the crop and weed were successful; however, the practical application of such relative leaf area models may still be limited owing to the lack of a method to estimate leaf area index quickly and accurately.  相似文献   

7.
Common lambsquarters (Chenopodium album) is one of the world's worst weeds. In order to study the competitive potential of single‐cross 704 corn (Zea mays) in competition with common lambsquarters at different relative times of emergence and density levels of the weed, an experiment was conducted in 2006 at the farm of the Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran. This experiment was designed as a split plot based on a randomized complete block design with three replications. The emergence time of the weed was considered at three levels (7 days and 14 days earlier than corn and simultaneously with corn) as the main plot, while the density of the weed was considered at six levels (0, 4, 8, 12, 16, and 20 plants per m2) as the subplot. The results showed a decrease in the grain yield and biomass of corn, as the emergence time of corn was delayed in comparison with the weed in a way that the maximum reduction was observed at the earlier emergence of the weed, compared to corn, and also at a high density of the weed. As the weed emerged earlier than corn, the rate of yield loss resulting from the first flush of weeds was not that high. However, with every few days that the weed emerged earlier than corn, the rate of yield loss became higher as the density of the weed increased to its maximum. The maximum reduction in the yield components was observed at 14 days earlier emergence of the weed, compared to corn, and at high densities, as the corn plants were overshadowed by the weed canopy and no ear was produced.  相似文献   

8.
Interspecific competition between wheat (Triticum aestivum L.) and Chenopodium album L., was studied in pots using the replacement series design of de Wit. Competitive interference for phosphorus, and to some extent for nitrogen, between the two species was noted. This played a major part in limitation of growth of wheat plants by C. album, whereas wheat exhibited greater non-competitive interference in restricting potassium uptake by the weed. Increasing interference from the weed resulted in significant reductions in wheat grain size and yield.  相似文献   

9.
In India, wheat is prone to being heavily infested with weeds, which cause considerable yield losses. Agronomic practices, including sowing method, influence weed interference in wheat growth. A herbicide mixture is usually more effective than a single herbicide for controlling a broad-spectrum of weeds. It may prevent weed species shift and delay resistance development in weeds. This study attempted to develop an integrated approach, combining a modified sowing method with applying a herbicide mixture for efficient weed management in wheat. We found that flat bed missing-row sowing resulted in significant reductions in: (i) the three-year mean population densities of grassy, broad-leaved and total weeds at 40 days after sowing (d.a.s), (ii) total weed population density and biomass (dry weight) at 60 d.a.s., compared to a mainly, furrow-irrigated raised bed system. Applying a tank-mix of fenoxaprop-p-ethyl at 0.08 kg/ha and isoproturon at 0.4 kg/ha applied 30 d.a.s. resulted in significant reductions in total weed population density and biomass, leading to a significant improvement in wheat growth and yield compared to either a weedy check or a regime of fenoxaprop-p-ethyl applied at 0.10 kg/ha. However, a combination of the flat bed missing-row sowing and tank-mix application of fenoxaprop-p-ethyl 0.08 kg/ha and isoproturon 0.4 kg/ha 30 d.a.s. resulted in higher wheat yield through better management of weeds compared with other sowing/ weed control combinations.  相似文献   

10.
Variations in climate are widely recognized as central factors governing the competitive balance in mixed‐species plant communities. In agricultural systems, highly variable patterns of crop yield reduction as a function of weed density have been documented across sites and among years at the same site for several crop–weed combinations. This variation is typically attributed to contrasting environmental conditions. Despite broad acknowledgement of their importance, experimental and temporal limitations have constrained the investigation and systematic understanding of environmental controls on the dynamics of competition. For several well‐studied crop–weed associations, aggregating historical data from similar competition experiments provides an opportunity to explore interference relationships over an array of conditions. In this study, 19 site‐years of maize –Abutilon theophrasti (velvetleaf) data were compiled and the weather characterized (i.e. average ambient temperature and moisture regime) for discrete portions of each growing season. These features were then related to patterns of maize yield loss from A. theophrasti interference at high weed densities. Results of this analysis suggest that temperatures following establishment, together with the presence or absence of water stress during the maize crop's exponential growth phase, account for over 60% of the observed variation in relative yield loss.  相似文献   

11.
Planning effective weed control in cropping systems requires exact appraisal of the weed intensity and duration of their competition with the crops. This 2‐year study was carried out in order to determine the critical weed control period in sesame fields. Related and relative crop yields were monitored and analyzed using a four‐parametric log‐logistic model. We recorded data from weed‐free plots and compared these with data from different periods of weed interference. In both the study years, the longer period of weed interference decreased the relative yield of sesame, whereas the yield was increased with increasing duration of the weed‐free period. A 51–78.7% decline in sesame yield was noted if the weeds were allowed to compete with the crop from planting to harvest. In the first year, the duration of the critical period for weed control (CPWC) was 177–820 growing degree days (GDD), which corresponded to 14–64 days after crop emergence (DAE), and between 170 and 837 GDD (13–64 DAE) in the second year; this was based on a 5% acceptable yield loss. The results of this study clearly elaborated that maintaining weed‐free conditions is compulsory from as early as the second week after the emergence of sesame plants, and this should be maintained at least until the ninth week to avoid sesame yield losses by more than 5%. These findings show that growers can benefit from CPWC to improve weed control in sesame production, including the efficacy of a weed control program and its cost.  相似文献   

12.
B Bukun 《Weed Research》2004,44(5):404-412
Field studies were conducted over 4 years in south‐eastern Turkey in 1999–2002 to establish the critical period for weed control (CPWC). This is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. A quantitative series of treatments of both increasing duration of weed interference and of the weed‐free period were applied. The beginning and end of CPWC were based on 5% acceptable yield loss levels which were determined by fitting logistic and Gompertz equations to relative yield data representing increasing duration of weed interference and weed‐free period, estimated as growing degree days (GDD). Total weed dry weight increased with increasing time prior to weed removal. Cotton heights were reduced by prolonged delays in weed removal in all treatments in all 4 years. The beginning of CPWC ranged from 100 to 159 GDD, and the end from 1006 to 1174 GDD, depending on the weed species present and their densities. Practical implications of this study are that herbicides (pre‐emergence residual or post‐emergence), or other weed control methods should be used in Turkey to eliminate weeds from 1–2 weeks post‐crop emergence up to 11–12 weeks. Such an approach would keep yield loss levels below 5%.  相似文献   

13.
Summary. Since 1961 the Weed Research Organization has been testing and developing herbicides for weed control in potatoes. Inthe three experiments which are reported, herbicides were compared with other forms of weed control. The first experimentin 1961 was exploratory and compared yields following hand-weeding versus no weed control versus several promising herbicides. The highest yield was produced by the hand-weeded crop. Several herbicide treatments applied before crop emergence gave useful selective weed control.
Assuming weed control to be necessary, selected herbicides were then compared in 1962 and 1963 with conventional mechanical cultivations. In both years successful weed control by herbicide resulted in a higher yield of potatoes than did mechanical cultivation although the soil-acting chemical used in 1962 caused some crop damage. The 1963 experiment included triangular planting patterns, at normal and high plant densities. Increases both in gross and marketable yield were obtained at normal plant density with the triangular arrangement as compared with the row crop. The high plant population resulted in the largest gross yield but a lower yield per plant and smaller average tuber size.  相似文献   

14.
Weeds that emerge along with or immediately after crop plants usually can reduce the yield of those crops. Two randomized complete block design experiments were conducted during 2006 and 2007 in Tabriz, Iran to determine the critical period of redroot pigweed control in the green bean hybrid “Cantander”. The treatments were weed‐infested and weed‐free plots at 2, 4, 6, 8, 10, and 14 weeks after bean emergence (WABE). The green bean biomass was affected by the early emergence of redroot pigweed, but it was not reduced when redroot pigweed emerged at 10 weeks after crop emergence, along with crop emergence, and grew with green bean until 4 WABE. The redroot pigweed biomass decreased by 2.7 g m?2 per day when weed emergence was delayed. Each 100 g m?2 of weed biomass that was produced resulted in a 1.4 kg ha?1 loss in the green bean yield. When redroot pigweed interference lasted for ≥4 weeks after green bean emergence, the green bean yield was reduced significantly. Weeds, which emerged 2 weeks after green bean and thereafter were controlled, did not decrease crop productivity significantly. The highest crop yield was obtained when the weed emerged at 14 WABE. The critical period of redroot pigweed control, considering a 10% yield loss, was between 19 and 55 days after green bean emergence. Thus, weed control practises should be begun no later than 3 WABE and should continue until at least 8 WABE in order to obtain the maximum green bean yield.  相似文献   

15.
Field experiments were conducted in the early and late cropping seasons of 1979 on a loamysand Oxic Ustropept in a subhumid environment in Nigeria, using 40000, 50000 and 30000 + 40000 plants ha?1 of maize (Zea mays L. cv. TZB), cowpea (Vigna unguiculata (L.) Walp. cv. VITA-5) and maize/cowpea intercrop respectively. These indicated that weed interference effects on crops under no-tillage depended on cropping season, cropping pattern and crop species. In the early and late seasons respectively, thirty-five and twenty-nine different weed species were recorded and weed dry weights of approximately 10·4 and 5·7 t ha?1 from the plots kept weedy throughout the season reduced corresponding food energy yields by 60 and 82%. Except for the intercrop, which in the early season showed significant yield reduction when exposed to 4 weeks’ weed interference after sowing, all cropping patterns needed more than 4 weeks’ interference to show significant yield reductions, regardless of cropping season. In the early season, weed interference accounted more for the yield reductions in monocultures than it did for those in the intercrop, but in the late season all cropping patterns were equally sensitive to weed association. Maize, which performed much better in the early season, showed greater yield reductions than cowpea under early weed interference but less under full-season interference irrespective of cropping pattern and season. Cowpea seed quality was more reduced by intercropping than by weed interference in the early season but neither of these factors affected seed quality significantly in the late season.  相似文献   

16.
To assess the potential contribution of growing highly competitive crops to control Cyperus esculentus in the Netherlands, the influence of silage maize, hemp, winter barley and silage winter rye on emergence, growth and reproduction of this weed was studied in two field experiments. Growth and reproduction of C. esculentus (determined both as tuber production per plant and density of the weed in the subseuent crop maize) was reduced by each crop, compared to plots in which no crop was grown. In hemp, hardly any tuber production was observed. By growing a green manure crop after harvest of the winter barley the tuber production of the weed was reduced to about 40% of that in winter barley followed by fallow. Decreasing the light regime in a greenhouse experiment in the same order as was observed in the crops winter barley, maize and hemp, caused a similar reduction of tuber production to that found in the field. Therefore, it is suggested that competition for light is the main factor explaining the observed crop effects on the population dynamics of the weed. It is concluded that growing competitive crops as hemp in rotation may effectively complement chemical control of C. esculentus.  相似文献   

17.
Weeds are a major constraint to increasing production of lentil (Lens culinaris Medik.) in Sudan, Field studies were conducted to determine the yield loss due to weeds, to identify the critical period of weed interference, to evaluate the activity of different herbicide mixtures in controlting weeds and their selectivity for lentil, and to evaluate different methods of weed control for developing an integrated weed management practice. At Rubatab. unrestricted weed growth accounted for up to 84% loss in yield. The critical period of weed control was between 2 and 4 weeks after sowing. However, a weeding regime experiment at Dongola, a cooler location with a longer growing season, indicated that the critical period was between 4 and 6 weeks after sowing. suggesting that the critical period might vary with the environmental conditions. The herbicides imazethapyr (0.05 kg a.i. ha-1), terbutryn (1.0 kg a.i. ha-1) and prometryn (1.0 kg a.i. ha-1), each in a tank mixture with pendimethalin (1.2 kg a.i. ha-1), were tolerated by lentil, controlled weeds effectively and significantly increased yields at Wad Hamid. Their efficacy in controlling weeds at Rubatab was low, however, because of the presence of Tephrosia apollinea (Del.) DC. and Melilotus indica (L.) All., which tolerated these herbicides. Efficacy was also reduced in heavier soils. One supplementary hand-weeding at 4 weeks after sowing enhanced the performance of these herbicides under such conditions. A tank mixture of oxyfluorfen (0.24 kg a.i. ha-1) with either terbutryn (1.0 kg a.i. ha-1) or prometryn (1.0 kg a.i. ha-1) also provided good weed control and increased yield of lentil at Wad Hamid. Application of a higher dose (1.5 kg a.i. ha-1) of terbutryn and prometryn caused phytotoxicity. Irrigation before seed-bed preparation reduced grass and broad-leaved weeds by 58% and 40% respectively, and gave a 30% increase in grain yield over no irrigation. Pre-emergence application of oxyfluorfen (0.24 kg a.i. ha-1) and a supplementary hand-weeding at 4 weeks after sowing gave excellent control of weeds and increased lentil yield by 57% over the weedy control. Thus, use of presowing irrigation, pre-emergence herbicide and one hand-weeding form an effective integrated package for controiling weeds in northern Sudan.  相似文献   

18.
The influence of no-tillage and conventional tillage on the outcome of early weed interference in maize (Zea mays L., cv. TZB), cowpea [Vigna unguiculata (L.) Walp, cv. VITA-5] and their intercrop at populations of 40000, 50 000 and 30 000 + 40 000 plants ha?1 was investigated on a loamy sand Oxic Ustropept in a subhumid tropical environment between April and July 1980. Both tillage treatments received 60 kg N, 30 kg P2O5 and 30 kg K2O ha?1. Although the weed spectrum was wider under no-tillage, weed weight was only 52% of the weight recorded under conventional tillage 6 weeks after sowing and the average food energy yield reductions caused were 28 and 65%, respectively. Cropping pattern had no effect on plot weediness. With minimum or no weed interference, maize performance was better in conventional than no-tillage but worse with prolonged weed interference. Cowpea responded more to weed interference than to tillage practice. Regardless of tillage practice and weed interference duration (up to 6 weeks) after sowing, maize monoculture produced the highest food energy yield, followed by maize/cowpea intercrop and cowpea monoculture in that order.  相似文献   

19.
The performance of three empirical models describing white bean yield loss (YL) from common ragweed competition was compared using field experiments from Staffa and Woodstock, both in Ontario, Canada, in 1991 and 1992. One model was based upon both weed density and relative time of emergence. The other two models described yield loss as a function of weed leaf area relative to the crop. The model based on both weed density and relative time of emergence best described the data sets. The predicted maximum yield loss (A) and the parameter for relative time of weed emergence (C) varied across locations and years whereas the yield loss at low weed density (I) was relatively more consistent across locations and years. Use of thermal time (base temperature=10oC) rather than calendar days did not change the overall fit of the model, but reduced the value of the parameter for the relative time of weed emergence (C). The two parameter leaf area model accounting for maximum yield loss (m) gave a better fit to the data compared with the one parameter model. The relative damage coefficient (q) varied with time of leaf area assessment, location and year. Values of q calculated from relative leaf area growth rates of the crop and weed were similar to observed values. The relationship between q and accumulated thermal time was linear but varied with location and year. As management tools, models based upon relative leaf area have advantages over models based on density and relative time of emergence since the level of weed infestation needs only to be assessed once, whereas density and emergence time require frequent observations. The ability to assess accurately and quickly both the crop and weed leaf area, however, may limit the practical application of models based on leaf area. The inability of empirical models to account for year–to–year variation in environmental conditions was observed.  相似文献   

20.
Field experiments were carried out in Northern Greece from 1994 to 1997 to study interference between Avena sterilis L. or Phalaris minor Retz. and five autumn-sown barley cultivars. Weed:crop interference began in early April. Avena sterilis at 120 plants m−2 showed greater interference against barley than P. minor at 400 plants m−2. The greatest grain yield and ear number reduction due to interference by either weed was recorded for cvs Klipper and Plaisant, and the least for cv. Athinaida; with cvs Carina and Thermi intermediate. Yield reduction due to A. sterilis for cvs Athinaida, Carina, Thermi, Klipper and Plaisant was 8, 16, 27, 61 and 67%, respectively, while corresponding losses to P. minor were 1, 8, 14, 45 and 55%. These results clearly indicate that growth and consequently yield components of cv. Athinaida were unaffected by the presence of either weed species, while those of cv. Carina were affected by A. sterilis , but not by P. minor . However, dry weight and panicle number of both weed species were severely reduced by interference with cvs Carina, Athinaida and Thermi compared with cvs Klipper and Plaisant. The order of interference of the five barley cultivars tested against A. sterilis and P. minor was Athinaida > Carina > Thermi > Klipper ≥ Plaisant.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号