Weed-free Plots Research Articles

Response of Rice Genotypes to Weed Competition in Dry Direct-Seeded Rice in India

The differential weed-competitive abilities of eight rice genotypes and the traits that may confer such attributes were investigated under partial weedy and weed-free conditions in naturally occurring weed flora in dry direct-seeded rice during the rainy seasons of 2011 and 2012 at Ludhiana, Punjab, India. The results showed genotypic differences in competitiveness against weeds. In weed-free plots, grain yield varied from 6.6 to 8.9 t ha−1 across different genotypes; it was lowest for PR-115 and highest for the hybrid H-97158. In partial weedy plots, grain yield and weed biomass at flowering varied from 3.6 to 6.7 t ha−1 and from 174 to 419 g m−2, respectively. In partial weedy plots, grain yield was lowest for PR-115 and highest for PR-120. Average yield loss due to weed competition ranged from 21 to 46% in different rice genotypes. The study showed that early canopy closure, high leaf area index at early stage, and high root biomass and volume correlated positively with competitiveness. This study suggests that some traits (root biomass, leaf area index, and shoot biomass at the early stage) could play an important role in conferring weed competitiveness and these traits can be explored for dry-seeded rice.

Weed Management in Dry-Seeded Fine Rice under Varying Row Spacing in the Rice-Wheat System of Punjab, Pakistan

Direct seeding can curtail water and labor inputs involved in rice production; nevertheless, its large-scale adoption is impeded by heavy weed infestation. A field study was undertaken in 2011 and 2012 to evaluate the effects of crop row spacing (20 and 10 cm) and postemergence herbicides on weed growth and yield of dry-seeded rice. As a herbicide, pyrazosulfuron ethyl at 30 g ha–1, bispyribac-sodium at 30 g ha–1, or penoxsulam at 15 g ha–1 was applied (15 days after sowing, DAS) alone or in combination with fenoxaprop-p-ethyl at 86.25 g ha–1 subsequently (30 DAS). In addition, a partial weedy plot (manually weeded once at 28 DAS), and a weed-free plot were established for each row spacing In the partial weedy plot with 10-cm row spacing, the weed density was only 21 and 25% lower than that in the plot with 20-cm row spacing in 2011 and 2012, respectively. The sole application of an early postemergence herbicide restricted weed growth, while subsequent application of fenoxaprop as late postemergence application suppressed weed growth further, the magnitude of suppression being more pronounced in the plot with narrow row spacing. The density and biomass of weeds were lowest in the plot with 10-cm row spacing applied bispyribac-sodium followed by fenoxaprop . Under weed-free conditions, yields were 29% higher in the plot with 10-cm row spacing (4.18 t ha–1) than in that with 20-cm row spacing (3.23 t ha–1). Grain yield in the herbicide-treated plots was 87 – 188% higher than that in the partial weedy plots. These results suggested that narrow row spacing and sequential herbicide application can help tackle recalcitrant weed flora in dry-seeded rice fields.

Weed management in irrigated castor (Ricinus communis L.) through herbicides

A field experiment was conducted to find out most suitable and cost effective weed management practice for irrigated castor grown on the light textured soils of Western Rajasthan. Ten treatment combinations comprising of four herbicides with or without inter culture along with weedy, weed free check and farmers practice were compared in Randomized Block Design with three replications. Three season's pooled results revealed that pre-emergence application of pendimethalin @ 1.0 kg/ha + inter culture 40 days aftersowing (DAS) produced maximum seed yield of 3652 kg/ha with weed control efficiency of 96.4% besides maximum net return of ` 74,464/ha and B:C ratio of 3.78. The weed competition index was also observed to be lowest in thistreatment (0.4%). However, pendimethalin @ 1.0 kg/ha (pre-emergence) + inter culture 40 DAS, fluchloralin @ 1.0 kg/ha (pre-plant incorporation) + inter culture 40 DAS and weed free plots remained at par with each other. Application of either quizalofop-ethyl or fenoxaprop-p-ethyl @ 50 g/ha at 25 DAS also brought down the weed stand and weed drymatter significantly compared to weedy check though the extent of control was not equivalent to weed free plots. This treatment (preemergence application of pendimethalin @ 1.0 kg/ha + inter culture 40 DAS) validated at five sitesin farmer'sfields recorded higher seed yield and net return compared to farmer's practice of weed control.

Effect of integrated weed management practices on performance of dry direct seeded rice (Oryza sativa L.)

Weeds are serious problem in dry direct seeded rice (DDSR). A field experiment was conducted during rainy seasons of 2010 and 2011 at research farm of the Regional Agricultural Research Station (RARS) Parwanipur, to study the effect of integrated weed management practices on the performance of dry direct seeded rice. Ten treatment combinations viz; weedy, weed free (weekly), Pendimethalin fb (followed by) Bispyribac, Pendimethalin fb two hand weeding, Stale seedbed fb Bispyribac, Stale seedbed fb Pendimethalin fb Bispyribac, Mulch 4 t/ha fb Bispyribac fb one hand weeding, Stale seedbed fb mulch 4 t/ha fb Bispyribac, Pendimethalin and Sesbania co-culture fb 2,4-D Na salt fb one hand weeding and Pendimethalin fb 2,4-D fb one hand weeding were tested in a randomized complete block design and replicated thrice. Observations were taken on weed, plant growth and yield attributes, yield, and socio-economic parameters. All weed control treatments significantly reduced the weed density and dry weight of weed resulting significant increase in yield of DSR over weedy check in both years. Weed free treatment resulted the highest yield, however, it was not economical due to high cost of cultivation. The use of Pendimethalin fb 2,4-D fb one hand weeding produced yield (5161 in 2010 and 6160 kg/ha in 2011) which were statistically at par with yield (5305 in 2010 and 6319 kg/ha in 2011) obtained under the weed free treatment. Further, the highest benefit cost ratio (CBR) 1.77 and 2.22 and net return Rs 47700 and 75084/ha during 2010 and 2011, respectively, were obtained under this treatment indicating its superiority over other treatments. The grain yield, yield attributing characters viz. panicles per m2, panicle weight, filled grain per panicle, thousand grain weight as influenced by different weed management practices revealed that higher yield resulted from weed free plot followed by Pendimethalin followed by two hand weeding and Pendimethalin followed by 2,4-D followed by one hand weeding. However, the net return per unit investment resulted highest in Pendimethalin followed by 2,4-D followed by one hand weeding. This proved that amid increasing wage rate and labor scarcity integrated weed management through Pendimethalin 30 EC (stomp) @ 1 kg a. i./ha as pre- emergence herbicide application followed by 2,4-D sodium salt 80 WP @ 0.5 kg a.i./ha followed by one hand weeding or stale seed bed followed by Pendimethalin 30 EC (stomp) @ 1 kg a. i./ha followed by Bispyribac (nominee gold) @ 25 g a. i./ha 10 % @ 200 ml/ha at 20 days of seeding resulted best alternative for manual hand weeding practices giving higher net return per unit investment. Agronomy Journal of Nepal (Agron JN) Vol. 3. 2013, Page 53-63 DOI: http://dx.doi.org/10.3126/ajn.v3i0.9006

Effects of different densities of wild oat (Avena fatua L.) and nitrogen rates on oilseed rape (Brassica napus L.) yield

Abstract A Two-year field experiment was carried out in 2009 and 2010 to evaluate the effects of different densities of wild oat and nitrogen (N) rates on oilseed rape yield and yield components. Experimental design was split plot with three replications. Increased nitrogen rates up to 150 kg N/ha caused an increase in oilseed rape grain yield in weed-free plots (4.26 t/ha; 1t = 10 3 kg), while even at the lowest density of wild oat (15 plants/m 2 ), increasing N fertilizer only up to 50 kg/ha led to a significant increase in grain yield. Wild oat growth was favored by high levels of N. Intraspecific competition reduced biomass, 100-seed weight and number of tillers of wild oat. Both lower N rate and intraspecific competition had negative effect on wild oat growth but the weed was still able to produce a considerable number of tillers and vigorous seeds. It showed that wild oat possess a no table adaptive plasticity and can allocate a greater proportion of its resource toward re -productive organs even under resource shortage conditions and, thus, it may increase the competitive ability of the weed over the crop.Our results suggest that effective weed management should be done to prevent wild oat seed production in crops preceding oilseed rape as well as to control the weed at early season in oilseed rape fields.

A Comparison of Methods for Evaluating the Suppressive Ability of Winter Wheat Cultivars against Italian Ryegrass (Lolium perenne)

Infestations of Italian ryegrass are problematic in both conventional and organic wheat production systems. The development of wheat cultivars with superior competitive ability against Italian ryegrass could play a role in maintaining acceptable yields and suppressing weed populations. Research was conducted in North Carolina to identify indirect methods of selection for Italian ryegrass suppressive ability (hereafter referred to as weed suppressive ability) of winter wheat cultivars that correlate well with Italian ryegrass-to-wheat biomass ratios. Two winter wheat cultivars (Dyna-Gro Baldwin and Dyna-Gro Dominion) and one experimental wheat line (NC05-19684) with differing morphological traits were overseeded with varying densities of Italian ryegrass. Wheat height measured throughout the growing season in weed-free plots was strongly associated with weed suppressive ability, but high wheat tillering capacity had no significant effect on weed suppressive ability in the lines tested in this study. Italian ryegrass seed head density during grain fill was strongly correlated (r= 0.94) with Italian ryegrass-to-wheat biomass ratio, the generally accepted measure of weed suppressive ability. Visual estimates of percent Italian ryegrass biomass relative to the plot with the highest level of Italian ryegrass infestation in each replicate were also strongly correlated with weed suppressive ability at all growth stages, especially during heading (r= 0.87) (Zadoks growth stage [GS] 55). Measurements from nonimaging spectrophotometers and overhead photographs taken from tillering (Zadoks 23 to 25) to early dough development (Zadoks 80) were unreliable estimates of end-of-season Italian ryegrass-to-wheat biomass ratios because they failed to account for wheat cultivar differences in biomass, color, and growth habit. Italian ryegrass seed head density and visual estimates of Italian ryegrass biomass during grain fill are appropriate indirect methods of selection for weed suppressive ability in breeding programs.

Determination of the best weeds control period in a soybean (Glycine max) new released hybrid:Williams

In order to determine the critical period of weeds control in soybean in semi-arid regions two experiments were conducted at Tabriz, Iran, on soybean hybrid Williams, based on randomized complete block design. For weedinfested plots, weeds were hand removed after 20, 40 and 60 days after emergence (DAE) and were kept weed free thereafter. For weed-free plots, weeds were allowed to compete with crop plants from 20, 40 and 60 DAE thereafter. Weeds interference duration of 40 DAE or more and weed-free period of less than 40 DAE greatly reduced the number of pod bearing branches per plant. Significant reduction in soybean yield up to 50% with increasing of weeds interference duration indicates that weeds is highly competitive with crop, and their competition beyond 40 WAE, results in greater crop yield loss than 24%, compared to control. A Gompertz model provided the best fit for the maximum weed-infested experiment. The relationship of crop yield with weed-free period was best described by the Logistic equation. The best weeds control period in soybean field using 5% permissible yield loss was between 40-60 DAE.

English

Luxuriant weed growth destroying rice crops is a major problem in tropical Africa. The objective of this study was to determine the critical period of weed infestation in upland rice varieties in order to enable the development of more precise weed management recommendations for farmers. The effects of 10 differing periods of weed management on upland rice yield were studied in experiments with five rice varieties (three interspecific NERICA: NERICA1, NERICA2, and NERICA4) and the parents (Oryza sativa WAB 56-104 andOryza glaberrima CG 14) during the 2004 and 2005 rainy seasons at Farako (Mali). INTERCOM model was used to explore the relationship between duration and timing of weed competition and rice crop yield loss, and the applicability of the model in rice cropping based weed management. The critical period of weed infestation determined from the field experiment was similar for the three New Rice for Africa (NERICA) varieties and theO. sativa parent (WAB 56-104), and was between 14 and 42 days after seeding (DAS). For the O. glaberrimaparent (CG 14), the critical period was between 28 and 42 DAS. Weed competition either before or after these critical periods had negligible effects on crop yield. During the 2 years, yields of NERICA varieties and WAB 56-104 averaged 2700 and 400 kg ha-1 under weed-free plots and no weed control plots, respectively, indicating a yield loss of 85%. For GG 14, yields averaged 900 and 300 kg ha-1 under weed-free plots and no weed control plots, respectively, resulting in a 66% yield loss. The occurrence and composition of weeds during the two years were similar with a mean of 40% broadleaves, 35% grasses and 25% sedges. The most important weeds were Imperata cylindrica, Cyperus sphacelatus and Digitaria longiflora. During both calibration and testing efforts, the INTERCOM model satisfactorily simulated rice NERICA1 LAI, shoot dry weight and yields (r2 ranging from 0.71 to 0.87). There appears to be room for improvement in the model with regard to the assumption that nutrients are not limiting to crop growth, but the use of the model for simulating the interactions between rice crop yield losses, weed density, and duration of weed competition appears promising. Results of this study can serve as a guide for optimum timing of weed control to maximize upland rice yield in West Africa.   Key words: Critical period, northern Guinea savanna, upland rice, New Rice for Africa (NERICA), INTERCOM.

Weed Management in Mechanized-Sown, Zero-Till Dry-Seeded Rice

Weeds are the main constraint in the adoption of zero-till, dry-seeded rice systems because weeds and rice emerge simultaneously in these systems, and there is no standing water at crop establishment to suppress weeds. A study was conducted during the wet season of 2011 and the dry season of 2012 at the International Rice Research Institute to evaluate the performance of different herbicides in mechanized-sown, zero-till dry-seeded rice. Among the treatments evaluated, oxadiazon followed by penoxsulam + cyhalofop followed by one hand-weeding at 42 d after sowing, provided 23 to 35% higher yield than the nontreated control. The yields in the oxadiazon-treated plots were similar to those in the weed-free plots. Some weed species, including eclipta and doveweed, were not controlled by the evaluated herbicides. Therefore, there is a need to evaluate additional herbicides and to integrate them with cultural weed management strategies to manage such problematic weeds.

Determination of the Critical Period for Weed Control in Corn

Field experiments were conducted in western Atakora, Benin, to determine the critical time period of weed competition in hand-weeded corn. Weeds were removed until different crop growth stages and then allowed to reemerge. Other treatments began weed control at different growth stages (four-, eight-, and ten-leaf stages and flowering) and were maintained until harvest. One treatment was permanently kept weed-free and one treatment was uncontrolled until harvest. Yields without weed competition ranged from 2.8 to 3.4 t ha−1. As expected, yield loss increased with duration of weed infestation and ranged from 38 to 65% compared to permanent weed-free plots. In three out of four site-years, the critical period for weed control started at the four- to six-leaf stage and continued until ten-leaf stage or flowering of corn. Approximately four hand-weeding applications were required in this critical period of weed control.

Implications of plant geometry and weed control options in designing a low-seeding seed-drill for dry-seeded rice systems

Farmers in many Asian countries are moving from puddled-transplanted rice to dry-seeded rice systems as they respond to increased costs or decreased availability of labor or water. Hybrid rice has the potential to grow in dry-seeded conditions and can perform well even if seeds can be planted at low seedling rates. A field study was conducted in the wet season of 2011 and dry season of 2012 to evaluate the effect of plant-to-plant spacing (10 or 20cm), the number of rice seeds planted per spacing (2 or 3), and weed control methods (42 days weedy, weed-free, and oxadiazon followed by penoxsulam+cyhalofop) on the growth and yield of rice under a dry-seeded rice system. The crop was planted at 20-cm row spacing. Herbicide-treated plots had fewer rice plants than the 42 days weedy and weed-free plots when rain occurred before crop emergence. However, the herbicide treatment provided 81–93% better weed control than the 42 days weedy treatment, which resulted in 54–125% yield advantages over no weeding for 42 days. Grain yield in the herbicide-treated plots was only 75–88% of the grain yield in the weed-free plots, suggesting further scope to improve rice yield in dry-seeded systems. Grain yield was similar across plant-to-plant spacing and the number of seeds planted per spacing. Our study suggests that hybrids can be grown at low seeding rates or at 20-cm plant-to-plant spacing, provided that there is no herbicide phytotoxicity on crop emergence and rice plant density is uniform. These results may help manufacturers in designing sowing drills with precise seed-metering systems for dry-seeded rice systems in Asia.

Flowers for better pest control? The effects of apple orchard ground cover management on green apple aphids (Aphis spp.) (Hemiptera: Aphididae), their predators and the canopy insect community

Effects of habitat diversification through ground cover management on green apple aphids (Aphis spp.) (Hemiptera: Aphididae), woolly apple aphid (Eriosoma lanigerum [Haussmann]) (Hemiptera: Aphididae), their insect natural enemies and the most abundant canopy insects (in the Neuroptera, Fulgoromorpha, Cicadomorpha, Heteroptera, Coleoptera and Formicidae) were studied in an apple orchard over 6 years. The composition and diversity of the main functional groups of canopy insects was also compared. Habitat diversification was achieved by changing ground cover conditions within the orchard. In the treatment termed FLOWER, annual and/or perennial flowering plants were sown in the alleys of an apple orchard. Other ground cover treatments were weed-free bare ground (termed BAREgr) and orchard plots with alleys of mowed grass (termed GRASS), which served as control treatments. We found no evidence that habitat diversification enhanced the biological control of green apple aphids compared to the control treatments. However, the greater plant cover in FLOWER resulted in increased woolly apple aphid infestations compared to BAREgr or GRASS. The abundance of various beneficial or neutral canopy insects – Chrysoperla carnea sensu lato (Neuroptera, Chrysopidae) adults, leafhoppers and treehoppers, planthoppers, herbivorous (non-apple feeding) beetles, dipterans and parasitoid wasps – also increased in FLOWER as compared to BAREgr, with GRASS being intermediate between the other treatments. Significantly greater species richness and diversity was found in FLOWER than in BAREgr for most of the functional groups sampled, although the number of predacious insect species was similar among treatments. The composition of the studied functional groups showed high similarity in FLOWER and GRASS, but these treatments were different from BAREgr. Effects of groundcover management on the dominant insect species are discussed.

Fertilizer Placement Affects Weed Growth and Grain Yield in Dry-Seeded Rice (<i>Oryza sativa</i> L.) Systems

A study was conducted in a split-plot design to evaluate the effect of fertilizer placement method on weed growth and grain yield in a dry-seeded rice (DSR) system. Main-plot treatments were four fertilizer placement methods: between narrow rows (between 15-cm-wide rows of the pattern 25-15-25 cm), between uniform rows (between 20-cm-wide rows), within uniform rows, and surface broadcast. Subplot treatments were three weed control methods: herbicide-treated, nontreated, and weed-free. Weed biomass was greater in the nontreated plots than in the herbicide-treated plots. Herbicide application reduced weed biomass by 89% to 99% compared with the nontreated control. Fertilizer placement did not influence weed biomass in the herbicide-treated plots; however, it greatly influenced biomass in the nontreated plots. Fertilizer placement on the surface increased weed biomass (69 -71 g·m–2) compared with the placement of fertilizer below the soil surface (37 -57 g·m–2). Fertilizer placement did not influence weed density and biomass at 60 days after planting. Nontreated plots yielded 700 to 2080 kg·ha–1. Grain yield was similar between the herbicide-treated (2660-3250 kg·ha–1) and weed-free (2620-3430 kg·ha–1) plots. Grain yield was not influenced when basal fertilizer was banded within (2390-2500 kg·ha–1) or between rows (2530-2650 kg·ha–1). However, grain yield decreased when basal fertilizer was broadcast on the soil surface (2200 kg·ha–1). The results of our study demonstrated that rice yield was usually lower with surface broadcast of fertilizer than with subsurface fertilizer treatments. In conclusion, surface broadcast of basal fertilizer may result in high weed pressure in DSR systems.

Competition for Nutrients between Cold-Tolerant Maize and Weeds

Maize is a significant crop in Hungary, cultivated on about 1.3–1.5 million ha, approximately 25% of the total arable land. Dense weed infestation of maize can result in significant yield reduction because of the competition for water and nutrients. Adequate fertilization is an important factor for the development of maize but it also enhances weeds growth. Therefore, strong competition for nutrients can occur between the crop and weeds. Recently, hybrid maize, which is tolerant to the cold weather, has been introduced in Hungary. In a field experiment, we assessed the weed cover, development of the weeds, and the rate of the infestation of weeds in competition with this cold-tolerant hybrid. The field trial was conducted in 2010 in Hungary, Zala County, close to the town of Keszthely in field conditions with plot size of 0.1 ha in four replicates. Plant samples were taken from crop and weeds at different intervals of growth. The fresh weight, dry biomass, and nutrient content of maize and weeds were measured. The early development of weeds was very dynamic and strong in the cold-tolerant maize cultures. On the 12th week after sowing, the maize biomass was 64% less than the weed-free maize as a result of the competition. Threefold difference was found in the biomass production of maize between the weedy and the weed-free experimental plots. The difference in potassium (P) content was also similar to that of the biomass production. The P content of maize was 3.17 times greater and the calcium (Ca) content was 3.24 times greater in samples collected from weed-free areas. The biggest difference was observed in the case of nitrogen (N) content. It was 4.73 times greater in the weed-free maize than in the weedy plots. This result shows that the competition for N was very strong between the maize and the weeds.

Weed Interference in the Sugarcane (Saccharum officinarum L.) Plantations of Ethiopia

Field experiments involving sprawling and erect cultivars of sugarcane and 12 weed competition periods were conducted in randomized complete block design in four replications for two cropping seasons at three sugarcane plantations of Ethiopia. Sugarcane was either kept free of weeds or weeds were allowed to grow for 0, 3, 6, 9, 12 and 15 weeks after planting (WAP). The sprawling sugarcane cultivars (‘B41227’ and ‘N14’) suppressed weed growth more and gave higher cane yield than the erect cultivar ‘NCo334’. The cane yield loss in unweeded plots compared to weed free plots ranged from 69.7% for sprawling cultivar ‘B41227’ at Methara to 83.5% at Wonji-Shoa for the erect cultivar ‘NCo334’. The beginning and end of critical periods of weed interference on 5% acceptable cane yield loss levels ranged from about 2.5 to 14 WAP for the erect cultivar and from 3 to 13.5 WAP for the sprawling cultivars implying the need to use herbicides or other weed control methods in sugarcane plantations of Ethiopia during these periods to keep cane yield loss levels below 5%.

Weed management and grain yield of rice sown at low seeding rates in mechanized dry-seeded systems

Because of the rapid depletion of water and shortage of labor, farmers in many Asian regions are moving from puddled transplanted rice to dry-seeded rice. However, weed infestations are a serious problem in dry-seeded rice systems because dry cultivation practices and aerobic soil conditions are conducive to the germination and growth of weeds. A field study was conducted in the wet season of 2011 and the dry season of 2012 to evaluate the effect of two rice cultivars and different herbicides on weed growth and rice yield under dry-seeded rice. The rice cultivars (one hybrid and one inbred) were dry-seeded at 20–22kgseedha−1 with a combine drill fitted with knife-point openers. Rice plant densities ranged from 44 to 56plantsm−2 in the first season and from 67 to 77plantsm−2 in the second season. Weed density, weed biomass, rice panicle number, and rice yield were not influenced by the cultivars; however, they were strongly influenced by the weed control treatments. In terms of percent, the hybrid cultivar had 11–12% higher yield than the inbred cultivar. Weed competition in the control plots (one hand-weeding) lowered yield by 39–41% compared with the weed-free plots. All herbicides significantly reduced weed biomass compared with the control treatment, providing 75–93% weed control. Herbicide-treated plots had similar grain yield and the yield in these plots was 76–86% of the yield of the weed-free plots (4.2–4.4tha−1), suggesting further scope to improve rice yield in dry-seeded systems. Compared with the control treatment (one hand-weeding), herbicide-treated plots had 27–41% greater yield. Future research in dry-seeded rice systems should focus on the integration of appropriate agronomic practices with herbicide application timing and combinations to improve the effectiveness of weed management practices.

Influences of Different Nitrogen Levels on Competition between Spring Wheat (Triticum aestivum L.) and Wild Mustard (Sinapis arvensis L.)

A field experiment was carried out to investigate the effects of different nitrogen levels on interspecific competition between wild mustard and spring wheat. The experiment was laid out in randomized complete block design under a split plot arrangement, with three replications. The experiment comprised of three nitrogen levels (90, 150 and 210 kg ha-1) assigned to main plots and four wild mustard densities such as 0, 5, 10 and 15 plants m-2 kept in sub-plots. The results revealed that yield, yield components and nitrogen use efficiency of wheat were decreased with increasing wild mustard density. The density of 5, 10 and 15 wild mustard plants m-2 reduced the grain yield of wheat by 21.4, 32.2 and 40.2% respectively as compared to control. Increasing nitrogen level increased the grain yield of wheat in weed free plots, while in the presence of wild mustard, increasing nitrogen level led to increase the competitive ability of wild mustard and increased the yield losses of wheat. The density of 15 wild mustard plants m-2 had decreased the grain yield of wheat by 31.6, 34.4 and 53.3 % under 90, 150 and 210 kg N ha-1 respectively.

Effects of different irrigation intervals and weed control on yield and yield components of safflower (Carthamus tinctorius L.)

A two-year (2008–2009) field experiment was conducted to determine the effect of irrigation management and weed control on yield and yield components of safflower. The experiment was conducted as a split-split plot arranged in a randomized blocks design with three replications. There were two treatments (weedy and weed free) and four irrigation interval water managements (7 days for all stages, 15, 22 and 28 days after six-leaf stages). The results indicated that grain yield was 29% higher in weed-free plots than in weedy plots. Weed competition reduced yield components such as primary branches, petal weight and number of capitulum per plant. Increasing the irrigation interval to 15 days at the six-leaf stage had no significant effects on grain yield, but grain yield decreased by 18 and 29.8% with increases in the irrigation interval to 22 and 28 days, respectively. An increased irrigation interval >15 days had negative effects on yield components like number of capitulum per plant, petal weight and number of primary branches. The highest grain yield (3703 kg ha−1) was obtained in the weed-free plot, and there was no significant difference between 7- and 15-day irrigation intervals.

Effect of tillage systems and herbicides on weed emergence, weed growth, and grain yield in dry-seeded rice systems

Farmers in many Asian countries are moving from puddled-transplanted rice to dry-seeded rice systems. Dry-seeded rice can be sown after land preparation or under zero-till conditions. Weeds, however, are the major constraint to the production of dry-seeded rice. A study was conducted during the wet season of 2011 and dry season of 2012 at the farm of the International Rice Research Institute to evaluate the effect of tillage systems (zero-till and conventional tillage) and herbicides on weed emergence, weed growth, and grain yield in dry-seeded rice systems. In the zero-till system, the densities of Digitaria ciliaris, Eleusine indica, Eclipta prostrata, and Ludwigia octovalvis increased many-fold from the first season to the second. The efficacy of herbicides (oxadiazon followed by fenoxaprop+ethoxysulfuron and oxadiazon followed by penoxsulam+cyhalofop) was lower in the zero-till system than in the conventional tillage system. Grain yield in the herbicide-treated and weed-free plots was similar between the tillage systems and this response was consistent during both the seasons. However, grain yield in the zero-till-control (one hand-weeded) plots was lower (0.9–1.5tha−1) than in the conventional tillage-control plots. The information gained from this study suggests that yields in zero-till systems similar to those in conventional-tilled systems can be achieved if weeds are effectively controlled. In the absence of effective weed control, zero-till systems may result in poor grain yield.

Weed harrowing in organically grown cereal crops avoids yield losses without reducing weed diversity

This report shows that weed harrowing in organic cereal fields is an efficient alternative to herbicides since weed harrowing does not reduce yields compared to weed-free plots. Arable weeds provide resources and habitat to many organisms. However, weeds are the most important constraint to crop production. Indeed, the potential crop losses of the eight major crops due to weed–crop competition amount to about 30 %. New ways of food production are needed due to the current severe biodiversity decline, about 1,000 times higher than the natural rate of species loss, and the growing food demands. Herbicides are highly efficient at reducing crop losses due to weed–crop competition, but at the expense of declining biodiversity. Studies have shown a poor efficiency of weed harrows in terms of weed reduction in organic farming systems. Here, we evaluated the feasibility of weed harrows in organic fields to reduce weeds to a threshold that does not limit crop production, while maintaining a rich flora. The results were compared to results obtained using herbicides in conventionally managed fields. Eleven organic and conventional cereal field pairs in Catalonia, Spain, were evaluated for one season in 2006–2007. Three different weed control treatments were applied: weed-free plots; weed-controlled plots, using herbicide in conventional fields and weed harrowing in organic ones and non-weeded plots. Crop yield and the abundance, richness and composition of the weed flora, which was dominated by ryegrass and poppies, were evaluated. Our results show that weed harrowing prevents weeds from being a limiting factor of crop productivity in organic cereal fields, since weed-controlled plots did not reduce yields compared to weed-free plots. A similar trend was observed in herbicide-controlled plots. However, herbicides diminished weed species richness in approximately 47 % and changed the species composition whereas harrowing allowed the maintenance of high levels of weed diversity in the organic fields.