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1.
Field experiments were carried out in 2004 and repeated in 2005 and 2006 in central Italy to determine the effect of competition from a natural weed flora on growth and yield of French bean (Phaseolus vulgaris L.). Two treatments were applied; weeds were either allowed to infest the crop or plots were kept weed free for an increasing duration of time (0, 7, 21, 28, 35, 45 days) after crop emergence. To assess the critical period of weed competition (CPWC) and the influence of weed infestation on yield, the Gompertz and logistic equations were fitted to data which represented the increasing duration of weed-free and weed-infested periods, respectively. During the three years of the experiment weeds, allowed to interfere for the whole growing season, reduced fresh pods yields up to 60%, 65% and 59% of the weed-free bean plots. Based upon an arbitrary yield loss (AYL) of 5%, the CPWC was from 50 Growing Degree Days (GDD) to 284 GDD, i.e. from 11 days after emergence (DAE) to 28 DAE. These values correspond to the lowest and highest values observed in the three experiments respectively for the weed-infested and weed-free period.  相似文献   

2.
The critical crop-weed competition period in a dry-seeded rice system is an important consideration in formulating weed management strategies. Field experiments were conducted in the summer seasons of 2012 and 2013 at the Punjab Agricultural University, Ludhiana, India, to determine the extent of yield loss in two different rice cultivars (PR 114 and PR 115) with different periods of weed interference. Twelve weed control timings were used to identify critical periods of weed competition in dry-seeded rice. PR 114, a long-duration rice cultivar (145 d) having slower initial growth than PR 115 (125 d), was more prone to yield losses. In both years, 100% yield loss was observed where weeds were not controlled throughout the season. In weed-free plots, the grain yield of PR 114 was 6.39–6.80 t ha−1, for PR 115, it was 6.49–6.87 t ha−1. Gompertz and logistic equations fitted to yield data in response to increasing periods of weed control and weed interference showed that, PR 114 had longer critical periods than PR 115. Critical weed-free periods to achieve 95% of weed-free yield for PR 114 was longer than for PR 115 by 31 days in 2012 and 26 days in 2013. Weed infestation also influenced the duration of critical periods. Higher weed pressure in 2012 than in 2013 increased the duration of the critical period of crop-weed competition in that year. The identification of critical crop-weed competition periods for different cultivars will facilitate improved decision-making regarding the timing of weed control and the adoption of cultivars having high weed-suppressing abilities. This will also contribute to the development of integrated weed management in dry-seeded rice systems.  相似文献   

3.
《Plant Production Science》2013,16(2):228-231
Abstract

In recent years, water and labor shortage in Southeast Asia is driving the farmers towards dry-seeded rice systems. Weed infestation is a serious threat for adoption of these systems. A study was conducted in the wet and dry seasons to evaluate the performance of 10 elite “Green Super Rice” (a recently named group of rice genotypes bred for unfavorable marginal environments) genotypes at two different weed infestation levels (partial and moderate weed control) under dry-seeded conditions. Average yield loss due to weed competition in the partial weed control treatment ranged from 12 – 57% in the wet season and 2 – 23% in the dry season. In the partial weed control plots, the drought pyramiding genotype IR83140-B-11-B performed well, resulting in 2850 and 4610 kg ha–1 of yield in the wet and dry seasons, respectively. The yield loss of this genotype in the partial weed control plots relative to the moderate weed control plots was only 21% in the wet season and 10% in the dry season. Results clearly showed that grain yield in different genotypes were positively correlated with leaf area at an early stage of the crop. The study also found negative and linear correlation between grain yield and weed biomass at harvest, demonstrating the importance of weeds in dry-seeded rice systems. The study suggested that genotypes with a larger leaf area could be integrated with other weed management strategies to achieve sustainable weed control in dry-seeded rice systems.  相似文献   

4.
Weeds are a major constraint to crop production, and are responsible for considerable yield losses in maize production systems throughout the world. Herbicides are widely used for weed control in maize production systems, but can have negative environmental consequences. Researchers have evaluated the use of crop competition and suppression to manage weeds in various crop combinations, including maize-based systems. Crop competition in maize may involve techniques such as reduced row spacing, increased planting density, and the use of competitive cultivars that exhibit weed suppressive potential. In this review, examination of the literature has revealed the considerable value of using crop competition in integrated weed management programs. Research has demonstrated that narrowing row spacing to half the standard distance reduced weed biomass by 39–68%, depending on weed species. Researchers have also demonstrated that increasing maize planting density by up to twice the standard rate achieved a reduction in weed biomass of 26–99%. While little research has been conducted into the use of competitive maize cultivars for weed management, several studies have documented cultivars with potential to suppress weeds. Attributes of weed competitive cultivars include high leaf area index, and other elements of leaf architecture that improve light interception by the crop, so increasing the shading of weeds. Combining crop competition methods with other agronomic practices can increase their effectiveness in controlling weeds. For example, biomass of Setaria italica (L.) Beauv was reduced by 60% when maize planting density was increased by 1.5 times the recommended spacing, and this effect was more pronounced when fertilizer was banded rather than broadcast. In summary, the strategic use of crop competition to control weeds has been a success in many regions, and is an important tool in integrated weed management. The importance of crop competition methods has particular relevance where farmers are unable to afford herbicides, as making use of crop competition is more economical.  相似文献   

5.
H. Nerson 《Crop Protection》1989,8(6):439-442
Field studies were conducted at Newe Ya'ar (northern Israel) during 1986 and 1988 to examine the critical period of weed competition in muskmelon (Cucumis melo L. cv. Galia). The yield of the control (weed free throughout the season) in 1988 was 45% higher than in 1986. In 1988, weed control was required within 6 weeks after seedling emergence in order to maintain fruit quality. Total yield was reduced significantly only if weeding started 7 weeks after emergence or later. Muskmelon remained competitive and maintained optimal yield potential if kept weed free during the first month of crop growth. The critical period for weed control in muskmelon was at the initiation of the rapid fresh-weight accumulation of the weeds and the pistillate flowering peak of the crop. Under Newe Ya'ar conditions this occurred 4–6 weeks after emergence of the crop.  相似文献   

6.
Rice is the most important and staple cereal in Bhutan, currently grown over an area of 19,549 hectares with a total production of 77,038 tonnes. However, its yield is limited in certain regions due to weed competition with losses of up to 50% reported through infestation from both annual and perennial weeds. In this article, we describe the current weed management practices in rice in Bhutan and identify challenges and prospects to guide future weed control research given that weed science in Bhutan is in its infancy. Generally, the most common form of weed control is hand weeding. However, herbicide use is also increasing as farmers face labour shortages on farms and realize the benefits of herbicides, especially in reducing the time taken to weed crops. But the continued use of the single chemical butachlor is a concern given the possible development of herbicide resistance. Research priorities for weed management in rice in Bhutan include a systematic assessment of crop yield losses; prioritization of weed importance and species shifts; mechanical and cultural alternatives to hand weeding; herbicide resistance testing and management; collective community approaches to area-wide management; and weed management options to suit alternative rice production systems. The ecology and management of the perennial semi-aquatic Potamogeton distinctus needs serious attention owing to its prevalence in major rice areas and potential alone to cause significant yield losses of up to 37%. The successful experiences and challenges in neighbouring Asian countries should also help to guide future weed control research in Bhutan.  相似文献   

7.
Weed management in Romaine lettuce (Lactuca sativa L. var. longifolia) is an economic challenge for organic farmers. This study evaluated the effect of weed-free durations on crop yield and quality, weed densities and biomass, and weeding time in two growing seasons. Treatments included weedy entire-season; weed-free for 7 days after transplanting (DAT), 14 DAT, 21 DAT, 28 DAT, 35 DAT, 42 DAT; and weed-free entire season (49 DAT). Weeds were removed by hand-hoes and the time taken to weed each plot was recorded. Weed densities were recorded prior to each weeding and weed biomass was recorded at crop harvest. Total and marketable lettuce heads were recorded and crop quality was estimated. Weed interference up to 21 DAT resulted in approximately 45% total and 58% marketable yield loss. Weed control beyond this period did not result in significant (p < 0.05) increases in crop yield and quality. However, weed densities at the end of the season were 4- to 15-fold and weed biomass approximately 18-fold greater in plots kept weed-free only for 21 DAT compared with plots kept weed-free season-long. This suggested that weed seed-return may be a concern if late-season weeding is not conducted. To minimize weed seed-return, the plots would have to be kept weed-free for about 35 DAT. However, labor costs must be taken into consideration because the time required to hand-hoe was approximately 87 hr ha?1 person?1 greater in plots kept weed-free for 35 DAT compared with plots kept weed-free for 21 DAT.  相似文献   

8.
A modeling approach based on weed relative leaf area (RLA) was used to describe the maize yield affected by weed competition and herbicide dose. The change of early RLA with herbicide dose was described using standard dose–response model. The dose response of individual weed species was included in a multivariate rectangular hyperbolic relationship between maize yield and weed relative leaf-area. Final model satisfactorily described the change of the weed relative leaf areas with herbicide dose in a multiple species competition with maize to reach a reasonable estimate of crop yield. Parameter estimates indicated that the maize yield could be about 11.23 t/ha in the absence of weeds. Applying herbicide at 0.29 rate of the recommended dose could decrease the Amaranthus retroflexus leaf area by 50%. For Xanthium strumarium, increasing the dose up to 0.58 rate of the recommended dose caused 50% reduction in early relative leaf area. The relative leaf area of the X. strumarium was 4.2-fold larger than that of the A. retroflexus at the time of herbicide application. Model validation indicated significantly better predictive ability of the leaf area model than that of the density model. Leaf area model permits to monitor the canopy (with considering the relative ground cover of neighboring plants) and decide that if a competitive crop allows reducing the dose. Recommending the precise required amount of herbicide is achieved using models that account for the interactions among crop and weed species, which survive and persist in the competition after herbicide application.  相似文献   

9.
In order to determine the critical period of weed control in winter canola (Brassica napus L. cv. Okapi) an experiment was carried out at research field of Tarbiat Modarres University, Tehran, Iran on 2004-2005 growing season. Fourteen experimental treatments which divided into two sets were arranged in Randomized complete blocks design with four replications. In the first set, the crop was kept weed-free from emergence time to two-leaf stage (V2), four-leaf stage (V4), six-leaf stage (V6), eight-leaf stage (V8), early flowering (IF), 50% of silique set (50% SS) and final harvest (H). In the second set, weeds where permitted to grow with the crop until above mentioned stages. In this study critical period of weed control was determined according to evaluate seed bank emerged weed biomass effect on canola grain yield loss using Gompertz and logistic equations. Result showed a critical time of weed control about 25 days after emergence (between four to six-leaf stages) with 5% accepted yield loss. Therefore, weed control in this time could provide the best result and avoid yield loss and damage to agroecosystem.  相似文献   

10.
Weeds and grain feeding birds are the two main biological causes of yield losses in irrigated rice in Africa. To quantify the single and combined effect of these biological constraints on rice yields, and to investigate whether weeds attract birds and thereby contribute to increased bird damage, a three-year factorial experiment was set-up in the Senegal River Valley. We tested two management factors (bird and weed management), each with two levels (‘complete’ and ‘absent’), and one crop cycle factor also with two levels (Sahel 202, a medium-cycle and Sahel 108, a short-cycle rice cultivar). Season-long competition from weeds resulted in high but predictable yield losses ranging from 50% to 75%, with lower yield losses for the medium-cycle cultivar Sahel 202 in two of the three seasons. Due to the nature of the pest, season-long exposure to birds resulted in less predictable yield losses ranging from 13% to as high as 94%, with high seasonal variation. In two seasons, much lower bird-inflicted yield losses were observed in the short-cycle cultivar Sahel 108, whereas in one season the medium-cycle cultivar Sahel 202 was much less damaged. When rice was exposed to both weeds and birds, the relative yield losses ranged from 80 to 99%. The yield reducing effect of weeds and birds was never additive. Bird visits to a weedy crop were more frequent compared to a weed-free crop at least in the early rice grain filling stages. This attraction of birds by weeds resulted in an additional yield loss in five of the six cases, ranging from 2 to 62%. Bird-inflicted yield losses in irrigated rice may be reduced by keeping the crop, as much as possible, free from weeds.  相似文献   

11.
Row spacing and weed control timing affect yield of aerobic rice   总被引：2，自引：0，他引：2  
Field experiments were conducted during the wet season of 2009 and dry season of 2010 to determine the effects of row spacing and timing of weed control on weed growth and yield of aerobic rice. Ten weed management treatments were used to identify critical periods of weed competition with aerobic rice grown in three different row spacings (15-cm, 30-cm, and as paired rows 10-20-10-cm). Dominant weed species during both growing seasons were Rottboellia cochinchinensis, Digitaria ciliaris, Echinochloa colona, and Eleusine indica. Rice grown in 30-cm rows had greater weed biomass and less grain yield than in 15-cm and 10-20-10-cm rows; weed growth and grain yields were similar between 15-cm and 10-20-10-cm rows. Rice yields in the wet season ranged from 170 kg ha−1 where weeds were not controlled throughout the crop duration to 2940 kg ha−1 in weed-free treatment, indicating a 94% yield loss with uncontrolled weed growth. Similarly in the dry season, plots with no weed control (140 kg ha−1) compared to weed-free plots (3640 kg ha−1) indicate a 96% yield loss with no weed control. Gompertz and logistic equations were fitted to yield data resulting from increasing durations of weed control and weed interference, respectively. Critical periods for weed control in the wet season, to obtain 95% of a weed-free yield, were estimated as between 18 and 52 days after sowing (DAS) for crops in rows at 15-cm, 20-51 DAS at 10-20-10-cm, and 15-58 DAS at 30-cm. These intervals in the dry season were 17-56 DAS for crops in rows at 15-cm and 17-60 DAS at 10-20-10-cm and 15-64 DAS at 30-cm. Durations of the critical periods in the wet season were 31 days at 10-20-10-cm, 34 days at 15-cm and 43 days at 30-cm, while in the dry season, these were 43 days at 10-20-10-cm, 39 days at 15-cm and 49 days at 30-cm. In both seasons, crops in the wider spacing (30-cm) were vulnerable to weed competition for the longest period. The information gained from this study suggests that the aerobic rice yields better in 15-cm rows and 10-20-10-cm arrangements than in 30-cm rows and there is very little benefit of weed control beyond 8 weeks after sowing.  相似文献   

12.
Knowledge of the crop-weed competition period is vital for designing effective weed management strategies in crop production systems. Field studies were conducted at the Agricultural Research Institute, Kahramanmaras, Turkey in 2013 and 2014 to determine the critical period for weed control (CPWC) in three corn (Zea mays L.) types (field corn, popcorn, and sweet corn). A four parameter log-logistic model described the relationship between relative crop yield to both increasing duration of weed interference and length of weed-free periods. The relative yield of corn was influenced by duration of weed-infested or weed-free period, regardless of corn types. Increasing periods of weed interference significantly reduced corn yields in both years. In field corn, the CPWC ranged from 175 to 788 growing degree days (GDD) in 2013 which corresponded to V2–V12 growth stages, and 165–655 GDD (V1–V10 growth stages) in 2014 based on the 5% acceptable yield loss (AYL) level. In popcorn, the CPWC ranged from 92 to 615 GDD (VE–V10 growth stages) in 2013 and 110–678 GDD (V1–V10 growth stages) in 2014. In sweet corn, the CPWC ranged from 203 to 611 GDD in 2013 (V2–V10 growth stages) and 182–632 GDD (V2–V10 growth stages) in 2014. The practical implication of this study is that weed management should be initiated around V1 stage and maintained weed-free up to V12 stage in all corn types to prevent yield losses greater than 5%. These findings could help corn producers improve the cost effectiveness and efficacy of their weed management programs.  相似文献   

13.
Aerobic rice systems can substitute the conventional rice cultivation system in the wake of water shortage and energy crises. The major constraint in the success of aerobic rice is high weed infestation. Hence, we have discussed the weed flora, yield losses, herbicide-resistant weeds, need for integrated weed management, and approaches to manage weeds in aerobic rice systems. A review of several studies indicated that 90 weed species were competing with rice under aerobic systems, causing 23–100% reductions in grain yield. Weed control in aerobic rice gets difficult due to shifts in weed flora and herbicide resistance development in weeds. A wide increase in grain yield (15–307%) by implementing different weed control practices elaborates the scope of weed management in aerobic rice. Practices, such as soil solarization, sowing of competitive crop cultivars, stale seedbed preparation, mulch application, correct fertilization, and intercropping, were found to have particular significance for managing weeds in aerobic rice systems. Moreover, hand weeding and mechanical control were more effective when combined with other weed control methods. Herbicides, such as pendimethalin, 2,4-D, penoxsulam, ethoxysulfuron, bispyribac-sodium, triclopyr, imazosulfuron, bensulfuron, pretilachlor, and metsulfuron, were found most effective in aerobic rice systems. Keeping in view the severity of weed infestation in these systems and the evolution of herbicide resistance, reliance on a single control method is out of question. Hence, the approach of integrated weed management is the most appropriate for proper weed management and the subsequent success of rice cultivation using aerobic systems.  相似文献   

14.
Grain yields of a soft white winter wheat cultivar, cv. Ionia, susceptible to cereal leaf beetle (Oulema melanopus (L.)), were determined when the crop was subjected to four controlled infestation levels of the beetle in caged plots over a 3-year period in Michigan. Although identical infestation procedures and insect numbers were used each year, the intensity of larval infestation and feeding damage varied with the year. Significant (P < 0·01) grain losses occurred in plots that had at least 9·0 larvae per stem. The greatest yield loss was 45% and occurred with 15 larvae per stem and 85% feeding damage. Beetle damage had a greater effect on kernel weight than on the other yield components. Although economic thresholds should be conservative to allow for environmental variations, it appears that soft white winter wheat can often withstand beetle infestation levels greater than the current economic threshold of three or more eggs and largae per stem before the boot stage or one or more large larvae per flag leaf during heading.  相似文献   

15.
During the period from 2011 to 2013, several plant diseases repeatedly occurred in vegetable crops grown in Yuanmou County, Yunnan Province, China. Affected plants included cowpea, sword bean, string bean, tomato, lettuce, and water spinach. The diseased plants exhibited symptoms of witches'-broom growth and floral deformations, linking each disease to phytoplasmal infection. Phylogenetic and virtual RFLP analyses of the phytoplasmal 16S rRNA gene sequences amplified from DNA of diseased plants revealed that all of the individual strains present in the diverse vegetable plants were affiliated with a single ‘Candidatus Phytoplasma’ species (‘Ca. Phytoplasma aurantifolia’) and a single ribosomal subgroup (16SrII-A). While presence of subgroup 16SrII-A phytoplasma in this geographic region was reported previously, such widespread infections in diverse plant hosts are unveiled for the first time in this study. In pursuing the source of the infections, we found that areas surrounding the affected vegetable fields were extensively invaded by parthenium weeds (Parthenium hysterophorus); and many of the weed plants exhibited abnormal morphologies that were suspicious of, and later diagnosed with, phytoplasmal infections. Results from genotyping of 16S rRNA and lineage-specific immunodominant membrane protein genes revealed that the vegetable-infecting phytoplasmas and the parthenium weed phytoplasma belong to the same genetic lineage. The findings indicate that parthenium weed poses a substantial risk as a reservoir of phytoplasmal infection of nearby agricultural crops in the geographic region since the ecosystems of Yuanmou are insect-rich, and parthenium weed is known to attract diverse leafhoppers. Further studies are warranted to assess the impact of farmland invasions by the noxious weed and to devise practical measures for improved weed control.  相似文献   

16.
Large within-field variation in rice growth often causes production loss in broadcast-seeded (BC) rainfed lowland rice. The spatial variability of direct-seeded rainfed lowland rice was evaluated in 2004, 2005, and 2007 in on-station experiments at Ubon Ratchathani, northeast Thailand, in relation to soil water content and weed infestation, by adopting semivariogram and block kriging, including comparisons among BC with harrowing (BCH; no weeding), BC with no harrowing (BCNH; no weeding), and row-seeded (RS; interrow weeding once) fields. BCH and BCNH were also compared in 11 farmers’ fields in 2006 and 2007, to assess the effect of harrowing on rice growth and weed infestation. During most of the rice growing periods, flooded and non-flooded portions existed simultaneously in the fields, with different proportions among years and among seeding methods in the on-station experiment. BCH and BCNH rice had large within-field variation in seedling density, heading date, shoot dry matter, grain yield, harvest index, panicle density, and filled spikelet per panicle, as well as in weed infestation, measured by a quick visual estimation. Many of the measured variables (except mean soil water content in RS in 2007, seedling density in BCH in 2005 and 2007, shoot dry matter in BCH and BCNH in 2007, and panicle density in BCH in 2007) were spatially dependent (i.e., data from nearby locations were most similar) by geostatistical analysis. Analysis of correlations using the 420 data sets of BCH plots in 2005 and BCH, BCNH, and RS plots in 2007 revealed a positive correlation between soil water content and grain yield and negative correlations between weed infestation and soil water content and grain yield. Compared with BCH, in 2007 BCNH had much lower grain yield because of lower soil water content after establishment and more weed infestation. BCH had higher grain yield than BCNH in weedy fields in the farmers’ fields experiment. RS with interrow weeding resulted in a smaller coefficient of variation, smaller sill value, and higher grain yield than BCH, due to less weed infestation and a higher proportion of flooded water. These results indicated that reducing the spatial variability in rice growth requires careful field preparation, such as harrowing to level the soil surface and to reduce the uneven distribution of standing water and the variability in soil water content, combined with effective crop and weed management (i.e., harrowing and row-seeding). This is the first study that examined spatial variability in the growth of direct-seeded rice as a function of soil water content and weed infestation in a rainfed lowland environment.  相似文献   

17.
Crop rotation and tillage systems have important implications for weed infestation and crop productivity. In this study, five tillage systems viz. zero tillage (ZT), conventional tillage (CT), deep tillage (DT), bed sowing (60/30 cm with four rows; BS1) and bed sowing (90/45 cm with six rows; BS2) were evaluated in five different crop rotations viz. fallow-wheat (FW), rice-wheat (RW), cotton-wheat (CW), mungbean-wheat (MW) and sorghum-wheat (SW) for their effect on weed infestation and productivity of bread wheat. Interaction between different tillage practices and cropping systems had significant effect on density and dry biomass of total, broadleaved and grass weeds, agronomic and yield-related traits, and grain yield of bread wheat. The un-disturbed soils (ZT) under fallow-wheat or mungbean-wheat rotations favoured the weed prevalence (a total weed dry biomass of 72.4–109.6 and 105.6–112.1 g m−2 in first and second year, respectively). Contrary to this, the disturbed soils (CT, DT, BS1 and BS2) had less weed infestation with either of the rotations (a total weed biomass of 0.4–7.1 and 1.1–5.4 g m−2 in first and second year, respectively). Sorghum-wheat rotation had strong suppressive effect on weed infestation in all tillage systems. The impact of crop rotation was more visible during second year of experimentation. Bed sown wheat (BS1 and BS2) in mungbean-wheat rotation had the highest wheat grain yield (6.30–6.47 t ha−1) compared to other tillage systems in different crop rotation combinations.  相似文献   

18.
Weed management is a major issue in organic farming systems. Although interseeding cover crops is one alternative to herbicides, cover crops often suppress not only weeds but also main crops. Therefore, using cover crops for weed control without adverse effects on main crop growth is important. To verify the effect of cover crops on competition between main crops, cover crops and weeds in a snowy-cold region, main crops soybean (Glycine max Merr.) in 2005 and maize (Zea mays L.) in 2006 were grown with cover crops winter rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth), respectively. The cover crops were sown on three sowing dates: before main crop planting (Pre-MC), on the same date of main crop planting (Syn-MC) and after main crop planting (Post-MC). A plot without cover crops (Sole-MC) was used as a control. The dry weight (DW), vegetation cover ratio (VCR), vertical community structure and chlorophyll content were measured to estimate the competition between main crops, cover crops and weeds. Weed DW was suppressed significantly by sowing cover crops in both soybean and maize. This weed suppression was associated with the increase of VCR of main crops plus cover crops at the early growth stage of main crops. Soil seed banks of dominant weed also became lower by sowing cover crops, implying the importance of proper weed management for suppressing weeds successively. In addition, the sowing dates of cover crops had large effects on main crops DW especially in maize, i.e., it was significantly lower in Pre-MC and Syn-MC than in Post-MC. Although the cover crop height was markedly shorter than the main crop height, the chlorophyll content of the main crops was significantly lower when cover crops were sown earlier. These results suggest that the growth inhibition of main crops by cover crops was partly caused by competition for nutrients between main crops and cover crops, and this growth inhibition was alleviated when cover crops were sown after the establishment of main crops. Consequently, soybean yield was the highest in Post-MC and decreased by 29%, 18% and 7% in Sole-MC, Pre-MC and Syn-MC, respectively, and maize yield was also the highest in Post-MC and decreased by 68%, 100% and 24% in Sole-MC, Pre-MC and Syn-MC, respectively. It was concluded that weeds could be controlled effectively by sowing cover crops after planting main crops in organic farming systems in a snowy-cold region.  相似文献   

19.
Narrow row planting has potential to increase crop growth and yield by increasing radiation interception (RI) and minimizing intra-specific competition in the crop. It reduces weed growth and competitiveness, making resources that are normally taken up by weeds available for crop uptake. The objective of this study was to assess the effect of row spacing on weed biomass, bean growth and yield in a semi arid agro-ecology at Nyagatare, Rwanda. The study was set up as a randomized complete block design in October–December 2009 and repeated in 2011. Planting patterns at a constant bean population density of 111 000 plants ha−1 random planting (normal practice), narrow row planting (30 cm × 30 cm), medium row planting (45 cm × 20 cm) and wide row planting (60 cm × 15 cm) were treatments tested in this study. The narrow row square planting pattern significantly (P < 0.01) out-yielded the wide and random planting patterns by 22–31% in the wet 2009 season and by 27–70% in the dry 2011 season. Bean plant dry weight (P < 0.01) and number of pods per plant (P < 0.01) was highest in the narrow row and lowest in the random planting pattern in the dry 2011 season. Bean plant dry weight was not significantly affected (P > 0.05) in the wet 2009 season but number of pods plant−1 (P < 0.001) was highest in the narrow row and lowest in the random planting pattern. Weed biomass was significantly lower (P < 0.05) in the narrow row and the random than in the medium and wide row planting patterns at 3, 6 and 9 weeks after emergence in 2009, but the random planting had the highest weed biomass in 2011. The results suggest that the effects narrow row planting in alleviating the negative impact of inter- and intra-specific competition were more strongly expressed in the dry 2011 season than the wet 2009 season when water was probably not a limiting factor to crop growth and yield. The results also indicate that narrow and equidistant planting has potential to increase bean yield by 30%–70%, when compared to random planting (normal practice) while at the same time suppressing weed growth and is recommended for smallholder farmers in Rwanda and other semi-arid areas in sub-Saharan Africa.  相似文献   

20.
《Field Crops Research》1999,61(2):97-107
Crotalaria (C. ochroleuca G. Don.) used as a green manure may improve the productivity of maize–bean cropping systems in eastern Africa. To test this hypothesis, three field studies were conducted over three consecutive cropping seasons at Kawanda Agricultural Research Institute in Uganda. In the first season, crotalaria biomass was produced in pure stands or in intercrop systems with either common beans (Phaseolus vulgaris L.) or maize (Zea mays L.) as companion crops. Crotalaria was sown at planting and three weeks after planting the food crops. The biomass of early planted crotalaria was mulched, that of late planted crotalaria was incorporated into the soil at planting of the following crop. The first subsequent crop was maize, and the second was either beans (in two seasons) or maize (in one season). In the crotalaria production season, mean yield losses of maize through intercropping with early or late sown crotalaria were 40 and 22%, respectively; the corresponding values for beans were 45 and 14%. In the first cropping season after crotalaria production, the increase in maize grain yield on account of crotalaria averaged 39%; the best response (68% increase) to crotalaria was obtained with early sown sole crotalaria applied as mulch. Major differences in soil mineral nitrogen content among the treatments occurred at the six-leaf stage of maize only. In the second cropping season following crotalaria production, the mean increases in seed yields of beans or maize, due to crotalaria, were 23 and 19%, respectively, indicating a considerable residual effect of crotalaria green manure. The decrease in bulk density, and the increase in water infiltration capacity of the soil suggest that the yield stimulation because of crotalaria not only resulted from the increased nitrogen supply, but also from more favorable soil physical properties. Considering the competitive effect of crotalaria with the food crops and the positive effect on yields of subsequent crops, two options are especially promising: incorporation of crotalaria produced by relay intercropping with beans and mulching of early sown crotalaria produced in pure stands.  相似文献   

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