Weed Biomass Production Research Articles

Incorporated cover crop residue suppresses weed seed germination

AbstractCover crops have been shown to be important integrated weed management tools. In addition to directly competing with weeds, cover crops can provide weed suppressive effects following incorporation through release of allelopathic compounds and/or changes to nutrient availability. Incorporation of a cover crop mixture may provide a synergistic or antagonistic effect on weed suppression by further altering nutrient dynamics. To investigate this phenomenon, we evaluated the suppressive effects following incorporation of annual ryegrass, buckwheat, brown mustard, and phacelia sown with and without field pea on germination and growth of several pernicious weed species. Further, we used the additive partitioning model to determine if pea synergistically improved biomass production and weed suppression of cover crops. Our results demonstrate that following incorporation, cover crop residues suppress weed germination and weed biomass production. According to the additive partitioning model, the addition of pea had an antagonistic effect on buckwheat and brown mustard biomass production and decreased buckwheat weed suppression by 8%. In contrast, the addition of field pea greatly enhanced biomass production of phacelia at a reduced seeding rate suggesting a positive biodiversity effect. Limited evidence was found for changes to nutrient availability following cover crop incorporation, however, a dose‐dependent effect of cover crop residue on weed suppression suggests allelopathy and/or nutrient availability may have a role on weed seed germination success. Together, our results support the use of incorporated cover crop residues as an integrated weed management tool.

Impacts of two years of autumn cover crops in northwestern Washington on winter annual weed populations

AbstractCover cropping is a suggested soil conservation practice widely investigated in cropping systems. Cover crops suppress weeds and often are part of an integrated weed management plan that could lead to reduced herbicide use and possibly reduce the weed seedbank. Winter brassica cover crops are popular in the eastern Washington potato (Solanum tuberosum L.) production region, but in western Washington, the production of brassica seed crops presents disease issues along with the risk of cross-pollination, which limits the use of brassica cover crops. Research for this article was conducted in two trials from 2018 to 2020 and 2019 to 2021in Mount Vernon, Washington, to identify winter cover crops compatible with regional restrictions and climatic challenges in western Washington cropping systems. Treatments including a no-cover control, eight single species (including brassicas, grasses, and legumes), and a grass–legume mixture were investigated. Cover crop and weed biomass production were measured, and percent ground cover for cover crops and weeds by species was estimated. Cover crop biomass and weed suppression varied by year due to variable environments, but annual ryegrass (Lolium multiflorum Lam.) and the mixture were most consistent in producing large amounts of biomass and reducing weed biomass and cover in all years. The variability of percent weed cover response to environment was ameliorated when weed cover was normalized within each year’s control.

Effect of crimson clover on the critical period of weed control in conservation tillage corn

An increasing number of herbicide-resistant weeds, in addition to troublesome weeds, pose a significant challenge for chemical weed control in corn. Simultaneously, high-biomass cover crop adoption has gained popularity among farmers as an efficient weed control strategy. While the critical period of weed control (CPWC) following conventional tillage has been well documented, there is little knowledge of CPWC following high residue cover crops in corn. A two-year field experiment was conducted to estimate the influence of a high biomass crimson clover cover crop and conservation tillage on the critical period of weed control (CPWC) in corn. The experiment was implemented in a split-plot design in which the main plots were conventional tillage (CVT), conservation tillage following winter fallow (CT + WF), and conservation tillage following crimson clover (CT + CC), and the subplot included multiple durations of weedy plots (estimation of critical timing of weed removal (CTWR), i.e., beginning of weed control) and weed-free plots (estimation of critical weed-free period (CWFP), i.e., end of weed control). The results described that the estimated duration of CPWC in three systems, included CT + CC, CT + WF and CVT equals 2.8 weeks, 3.5 weeks, and 4.9 weeks respectively in 2019. In 2020, the predicted value of CTWR under CT + CC equals 3.8 weeks after planting and the predicted values of CWFP were 5.1 and 5.7 weeks after planting under CT + WF and CVT systems, however, the model did not predict some values within the fitted 8 weeks of time. In conclusion, the presence of a crimson clover cover crop delayed the CTWR and caused the early beginning of CWFP and hence shortened CPWC in 2019. During most of the growing season, weed biomass production was less under CT + CC plots than CVT and CT + WF systems of weedy treatment in both years. While weed biomass production fluctuated in CT + CC, CVT and CT + WF systems in weed-free treatment.

Short‐term impacts of cover crops in maritime potato (Solanum tuberosum) systems

AbstractCover cropping is a soil conservation practice widely investigated in agronomic crops, but less is known about cover crop implications in specialty cropping systems, particularly in a high disturbance system like potato (Solanum tuberosum L.). Brassica cover crops are popular in eastern Washington potato production, but brassica seed crop production in western Washington presents issues with use of brassica cover crops in the region's fresh‐market potato systems. To identify winter cover crops compatible with regional restrictions and climatic challenges in western Washington potato systems, trials including a no‐cover control, eight single species (including brassicas, grasses, and legumes), and a grass–legume mixture were conducted in Mount Vernon, WA, in 2018–2019 and 2019–2020. We examined cover crop and weed biomass production, potato yield and quality, and short‐term soil health impacts by measuring permanganate oxidizable carbon (POXC) and inorganic nitrogen before cover crop incorporation and at midseason. Cover crop biomass and weed suppression varied by year, with annual ryegrass (Lolium multiflorum Lam.) producing the most biomass in both years despite poorer weather conditions and reduced cover crop biomass in other treatments in 2020, making it a good cover crop candidate for western Washington. Both POXC and inorganic nitrogen were greater at midseason but did not vary among cover crop treatments, suggesting that temporal variation influences POXC and inorganic nitrogen more than a single winter of cover crops. Potato yield and tuber wireworm damage varied by year, but not across cover crop treatments, and tuber symptoms resembling black scurf did not vary by year nor treatment.

Weed suppression versus water use: Efficacy of cover crops in water‐limited agroecosystems

AbstractWinter cover crops (CC) may facilitate weed management by inhibiting weed seed germination and seedling emergence and suppressing weed growth within the cash crop. In southern New Mexico, with scarce winter precipitation and limited irrigation water, producing sufficient CC biomass for effective weed suppression while conserving water resources is challenging. This study assessed the water requirement to produce a CC with enough biomass for weed suppression benefits during cash crop growth at two locations in New Mexico. Three winter CC species, barley, Austrian winter pea and mustard, grown singly and in a three‐way mix, under three differential irrigation treatments (one, two or three irrigations after emergence) were evaluated for their weed‐suppressive potential. Maize was planted as a cash crop four weeks after winter CC termination. Number of irrigations had no effect on the CC and weed biomass production. All CCs had lower weed density prior to maize planting compared with fallow. Barley and the three‐way mix reduced weed density by 56–96% and 68–95%, respectively. All CC treatments had lower weed biomass at the end of critical period for weed control in maize compared with fallow. Weed biomass at maize harvest did not differ between treatments. The maize yield was consistently higher in conventionally managed, weed‐free subplots, than in unsprayed weedy subplots, suggesting that CCs did not suppress weeds throughout the maize growing season. Except for barley, CCs did not cause reductions in maize yield compared with fallow. Overall, the study suggested that with adequate winter precipitation, weed‐suppressive winter cover crop stands can be produced with just one irrigation at seeding and one supplemental irrigation, making them a viable option in water‐limited agroecosystems.

Intercropping organic field peas with barley, oats, and mustard improves weed control but has variable effects on grain yield and net returns

Interest in intercropping semi-leafless field peas (Pisum sativum L.) is increasing as a means of weed control in organic production. We evaluated field pea (cv. CDC Amarillo) grown alone or intercropped with three seeding rates of either barley (Hordeum vulgare L.), mustard (Brassica juncea L.), or oat (Avena sativa L.). A full seeding rate of field pea was used in each instance, resulting in an additive intercropping design. Each crop combination was conducted in a separate experiment, three times over two years (2019 and 2020) in Carman, MB. Measurements included crop and weed biomass production, grain yield and quality, and net return. Intercrops reduced weed biomass at maturity from 17% to 44% with barley and oat being more suppressive than mustard. Intercrops also reduced field pea yield from 6% to 26%, but increased field pea seed mass. Barley at the high seeding rate provided the most weed suppression per unit of field pea yield loss (2.62 kg of weed suppression per kg of field pea yield loss) compared with oat (1.29) and mustard (0.87). Barley and mustard intercrops decreased net return compared with monoculture field pea. Under low weed pressure (1150 kg·ha−1 weed biomass at maturity) and earlier seeding, oat intercrops reduced net return. However, under weedy conditions (2649 kg·ha−1) and later seeding, field pea-oat intercrops significantly increased net return. In conclusion, while all three intercrop mixtures reduced weed biomass, reductions in field pea yields were observed, and net return benefits were observed only in certain circumstances.

Winter Wheat (Triticum aestivum L.) Tolerance to Mulch.

Mulch from cover crops can effectively suppress weeds in organic corn (Zea mays L.) and soybean (Glycine max L.) as part of cover crop-based rotational no-till systems, but little is known about the feasibility of using mulch to suppress weeds in organic winter small grain crops. A field experiment was conducted in central NY, USA, to quantify winter wheat (Triticum aestivum L.) seedling emergence, weed and crop biomass production, and wheat grain yield across a gradient of mulch biomass. Winter wheat seedling density showed an asymptotic relationship with mulch biomass, with no effect at low rates and a gradual decrease from moderate to high rates of mulch. Selective suppression of weed biomass but not wheat biomass was observed, and wheat grain yield was not reduced at the highest level of mulch (9000 kg ha−1). Results indicate that organic winter wheat can be no-till planted in systems that use mulch for weed suppression. Future research should explore wheat tolerance to mulch under different conditions, and the potential of no-till planting wheat directly into rolled-crimped cover crops.

Weed Suppression, Biomass and Nitrogen Accumulation in Mixed-Species and Single-Species Cover Crops in a Tropical Sugarcane Fallow

While mixed-species cover crops are gaining worldwide popularity, their utility in the ‘plough-out’ period in tropical sugar cane systems has not been investigated. Field trials investigating weed suppression (one season only), biomass production and nitrogen accumulation of single-species and mixed-species cover crops were conducted over two seasons on a commercial sugarcane farm in the Australian tropics. Mixed-species cover crops showed strong weed suppression, and were among the top treatments for biomass production each year, but did not yield the highest biomass in either season. Sunn hemp (Crotalaria juncea cv. Global sunn) produced the most biomass in the drier-than-average 2016–2017 season (>10 t dry matter ha−1), while soybean (Glycine max cv. Leichardt) produced the most biomass (5.3 t dry matter ha−1) in the wetter-than-average 2018–2019 season, highlighting the influence of seasonal conditions on species’ biomass production. The inclusion of multiple species in a short-term cover crop in the tropics where extreme weather events can occur can thus be seen as a risk mitigation strategy given the risk of failure of any given species in a given season.

Improving weed control in sustainable agro-ecosystems: Role of cultivar and termination timing of rye cover crop

Alternative strategies to control weeds are required at the field level to reduce herbicides and derived pollution. As cover crop, rye (Secale cereale L.) is adopted mainly because of its allelopathic weed control, which takes place through a strong inhibition of germination and seedling growth in several types of grass and broad-leaved weeds. The present study consisted of: i) a field trial, focused on the evaluation of biomass production and allelochemical concentration in the biomass, and in situ weed control at 30 days after termination (with two termination timings: T1 - heading phase and T2 - 10 days later) of 8 rye varieties; ii) a pot experiment, focused on the inhibition effect of mulches derived by those 8 rye varieties on four summer weeds: velvetleaf (Abutilon theophrasti Med.), lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and common purslane (Portulaca oleracea L). Results showed that biomass production was the highest with Protector, closely followed by Primizia, Sito 70, Hellvus, Forestal, and Hymonta. In any case, rye mulching always reduced the weed biomass, especially with Fasto and Forestal. The allelochemical concentration in the biomass was the highest with Fasto and Forestal and decreased on average from T1 to T2 (–38% for total benzoxazinoids and –57% for isovitexin). Conversely, the rye biomass production increased (on average +77%), passing from T1 to T2. We also found that the reduction of weed biomass, compared with the control, is highly correlated with the allelochemical content in rye biomass in the case of T1 termination, while with the biomass production in the case of T2. In pots, a strong inhibitory effect on seedling growth due to rye mulching was observed for C. album (–76%), A. retroflexus (–56%), and P. olearcea (–84%), while not for A. theophrasti. We concluded that, regardless of the variety, adopting rye as a cover crop may be considered as a suitable practice to reduce weed pressure at the field level. Among all the varieties tested, Forestal and Protector showed the most significant weed suppression potential, due to the high amount of allelochemicals production for Forestal and high biomass production for Protector. Highlights - One month after rye termination, the weed biomass under mulching is reduced by 4 times, compared with the control. - When rye is terminated early, the allelochemical content in rye tissues reduces the weed biomass production. - When rye is terminated late, the weed biomass production is reduced by the amount of rye biomass. - Lambsquarters, redroot pigweed and purslane growth is inhibited by rye mulching, while velvetleaf is not affected.

Weed seedbank diversity and sustainability indicators for simple and more diverse cropping systems

AbstractStorkey and Neve (2018) hypothesised that weed seedbank diversity could be used as an indicator of agroecosystem sustainability, with cropping systems associated with higher weed seedbank diversity being more agronomically and environmentally sustainable than those with lower weed diversity. We evaluated their hypothesis using multiple years of empirical data collected from a long‐term field experiment in Iowa, USA, and life cycle assessment models parameterised with data from that experiment. We found that diversifying a 2‐year maize–soyabean rotation with two additional crop phases, oat and lucerne, to form a 4‐year rotation (a) increased Simpson's diversity index for weed species in the soil seedbank, while (b) increasing maize and soyabean productivity, (c) maintaining total crop energy production and profitability, and (d) reducing herbicide‐related aquatic toxicity, fossil energy consumption, greenhouse gas emissions, damage to human health due to fine particulate matter, and discharge of soil sediment, nitrogen, and phosphorus. Increased weed biomass production and greater weed species diversity that occurred within oat and lucerne phases of the 4‐year rotation sequence did not result in a loss of weed control within maize and soyabean phases of the rotation. We suggest that while there was no cause‐and‐effect relationship between greater weed seedbank diversity and improved agroecosystem sustainability in agronomic, economic and environmental dimensions, all of these responses were driven in a parallel manner by cropping system diversification. Consequently, weed seedbank diversity may indeed be a useful agroecosystem sustainability indicator. Further evaluation of this hypothesis in more systems is warranted.

Soil Nitrogen and Weed Biodiversity: An Assessment under Two Orchard Floor Management Practices in a Nitrogen Vulnerable Zone in Italy

Nowadays, understory vegetation along the tree row is considered a vital source of agroecosystem services and functional biodiversity improvement in the fruit orchard. Hence, current orchard floor management systems encourage practicing a more sustainable approach that supports vegetation cover rather than keeping bare soil herbicide use, or tillage. A two-year field trial was conducted using two different ground management techniques; integrated mowing (mower and brush or disc) and herbicide (glyphosate) in two commercial apple and peach orchards in a nitrogen vulnerable zone (NVZ) of the Marche region, Italy. This study aimed to evaluate the effects of these practices on soil N status, weed abundance, percent of soil cover, and dry weed biomass production. Weed management systems had no significant effect on soil organic matter and N availability; however, an improvement was noticed under integrated mowing when compared to the one treated with herbicides. Integrated mowing had a significant effect on species richness, soil coverage, and weed biomass production, which was approximately 2-times higher than in the herbicide-treated plots. The overall results showed that integrated mowing maintained a balance in the soil N status of both orchards, while supporting above-ground weed biodiversity and soil protection.

Influence of Farming System on Weed Infestation and on Productivity of Narrow-Leaved Lupin (Lupinus angustifolius L.)

Legumes have become important crops, due to an increasing global population and its demand for feed protein. Furthermore, legumes can improve the characteristics of the soil, improve biodiversity levels in crop rotations, and be cultivated in both organic and sustainable farming systems. In this study, a two-factor field experiment was conducted in Gorzyń, Poland in 2011–2015. The first factor was the farming system: low-external inputs (LI; without fertilization and chemical protection), medium-input (MI; medium fertilization level and chemical protection), and high-input (conventional—CONV; high fertilization level and chemical protection). Narrow-leaved lupin cultivar was the second factor; the indeterminate cv. Kalif and the determinate cv. Regent. We evaluated (a) weed infestation levels, (b) seed and protein production, and (c) the economic effects of narrow-leaved lupin cultivation under different farming conditions. A total of 12 weed species were identified, with the lowest weed density level and biomass production observed in CONV, and the greatest weed density level observed in LI. Seed yield was determined by the farming system; the greatest in CONV and significantly lower in LI (by 0.73 t h−1) and MI (by 0.18 t ha–1). Little difference was observed in seed yield between cultivars. The greatest production values for the Kalif and Regent cultivars (996€ and 949€ ha–1, respectively) were recorded in CONV, although LI proved to be the most profitable (with the highest gross agricultural income and lowest total cost of production). LI farming systems, in conjunction with chemical weed control, should be investigated in future studies.

Integrated Weed Management in High Density Fruit Orchards

Despite the productivity, achieving long-term sustainability and maintaining plant biodiversity have become the pivotal goals in orchard floor management, especially along tree rows. Thus, the paradigm of eradicating weeds in the tree row using chemical herbicide or repeated soil tillage needs to be substituted with more sustainable alternatives. This study was conducted in two commercial apple and peach orchards in Marche region (Italy). Two integrated mechanical approaches, integrated mowing (mower and brush or disc) and integrated tillage (blade weeder and integrated mowing), were compared with the standard herbicide system in a 2-year trial. Weed species diversity, soil coverage, and weed biomass production, including, gas exchange parameters, trunk cross-sectional area (TCSA), fruit yield and quality were measured. Overall, both integrated practices demonstrated approximately 82%, 91% and 113% more species diversity, soil coverage, and weed biomass production, respectively, than herbicide systems. No significant differences were found in terms of tree gas exchange parameters, growth and fruit yield. However, a few fruit quality parameters such as fruit firmness, soluble solids content (SSC) and dry matter content responded positively to the integrated practices. These results suggest that the integrated mechanical approaches of weed management increased orchard biodiversity, and had no adverse effects on tree growth, fruit yield, and quality. The average costs per hectare associated with chemical weed control were 66.5% and 72% lower, respectively, compared to integrated tillage and integrated mowing. However, the government subsidies provided to the orchardists to encourage sustainable management practices were able to offset such additional costs.

Effect of irrigation and weed management practice on available nutrients, nutrient concentration and their uptake by weeds and wheat

A field experiment was conducted in sandy loam soil during winter season of 2017-18 and 2018-19. Significantly the lowest weed biomass production, highest available nutrients in soil and the maximum N and K content in weeds and crop was recorded with the application of irrigation at CRI+ active tillering stage. Whereas, irrigation at CRI+jointing+ booting+ flowering+milking stage was recorded maximum P content. Application of broadway (carfentrazone ethyl 20% + sulfosulfuron 25%WG) 100 g a.i. ha-1 at 35 DAS recorded significantly lowest weed biomass and the highest nutrient content in weeds and crop. Application of irrigation at CRI+jointing+ booting+ flowering+milking stage was recorded significantly the highest nutrients depletion by weeds and their uptake by crop. Significantly the lowest nutrients depletion by weed and their highest uptake of crop and the maximum available nutrients in soil were recorded with the application of broadway (carfentrazone ethyl 20% + sulfosulfuron 25%WG) 100 g a.i. ha-1 at 35 DAS. Grain (9.79 kg ha-1) and straw yield (4.54 kg ha-1) will be reduced by an increased in unit of nutrients depletion by weeds.

Impact of Diverse Annual Forage Mixtures on Weed Control in a Semiarid Environment

Intercropping with different crop species and different spatial patterns is suggested to lead to increased competition with weeds and reduced weed abundance and biomass. In this study, our objective was to explore the ability of multi-species annual forage crop mixtures to control weeds while providing productive forage. We utilized field and greenhouse trials to evaluate the impact of different crop mixtures and row spacing on weed control in the semi-arid Brown soil region of southwestern Saskatchewan, Canada. Seven different mixtures of up to eight annual forage crops were grown with row spacing of 15 cm or 30 cm in a replicated field trial. Weed abundance and biomass was significantly affected by crop species mixtures. Crop mixtures that contained radish and barley generally had higher weed suppression. Row spacing did not significantly impact weed abundance or biomass across the treatments. Results were similar over both years in spite of drastically different precipitation conditions. Forage production was significantly different between cropping mixtures in July in both years. The barley-radish mixture had the highest crop biomass in July, and this early crop production was linked to weed suppression because crop biomass had a significant effect on weed abundance and biomass in July, but not August. A greenhouse experiment was used to further evaluate the crops (i.e., barley and radish) that demonstrated the highest weed suppressive activity in the field trial. Crop identity and row spacing were both significant factors affecting weed and crop biomass production. Radish exhibited stronger control of common lamb’s quarters (Chenopodium album) compared to barley, but the binary mixture of the two species produced the highest crop biomass and equivalent weed control compared to the radish monoculture. This research suggests that cropping with multiple species (particularly forage radish) may be an effective way to control weeds in semiarid environments.

Alternative performance targets for integrating cover crops as a proactive herbicide-resistance management tool

AbstractIntensified cover-cropping practices are increasingly viewed as a herbicide-resistance management tool but clear distinction between reactive and proactive resistance management performance targets is needed. We evaluated two proactive performance targets for integrating cover-cropping tactics, including (1) facilitation of reduced herbicide inputs and (2) reduced herbicide selection pressure. We conducted corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] field experiments in Pennsylvania and Delaware using synthetic weed seedbanks of horseweed [Conyza canadensis (L.) Cronquist] and smooth pigweed (Amaranthus hybridus L.) to assess winter and summer annual population dynamics, respectively. The effect of alternative cover crops was evaluated across a range of herbicide inputs. Cover crop biomass production ranged from 2,000 to 8,500 kg ha−1 in corn and 3,000 to 5,500 kg ha−1 in soybean. Experimental results demonstrated that herbicide-based tactics were the primary drivers of total weed biomass production, with cover-cropping tactics providing an additive weed-suppression benefit. Substitution of cover crops for PRE or POST herbicide programs did not reduce total weed control levels or cash crop yields but did result in lower net returns due to higher input costs. Cover-cropping tactics significantly reduced C. canadensis populations in three of four cover crop treatments and decreased the number of large rosettes (>7.6-cm diameter) at the time of preplant herbicide exposure. Substitution of cover crops for PRE herbicides resulted in increased selection pressure on POST herbicides, but reduced the number of large individuals (>10 cm) at POST applications. Collectively, our findings suggest that cover crops can reduce the intensity of selection pressure on POST herbicides, but the magnitude of the effect varies based on weed life-history traits. Additional work is needed to describe proactive resistance management concepts and performance targets for integrating cover crops so producers can apply these concepts in site-specific, within-field management practices.

Monthly nutrient uptake by weeds in different land use systems at two locations of Punjab, India

In present study, biomass production and nutrient status (NPK) of weeds in three land use systems (canal bunds, fallow land and in cultivated land) at two locations (Ludhiana and Sangrur) of Punjab was analyzed throughout year (Jan-Dec 2017) at monthly interval. In case of land use systems fallow land (Sangrur) was recorded to have maximum total biomass (5.73 t/ha), nitrogen (96.9 kg/ha), phosphorus (21.5 kg/ha) and potassium (85.9 kg/ha). With respect to months, total maximum weed biomass production (7.40 t/ha), nitrogen (147.8 kg/ha), phosphorus (27.8 kg/ha) and potassium (125.8 kg/ha) was recorded in July. Thus from present data it is revealed that weeds which grow lavishly in fallow lands of Punjab possess high nutrient value and dry matter production of weeds in this land use system increased with heavy rainfall.

Allelopathic Effects of Different Plant Water Extracts on Yield and Weeds of Wheat

ABSTRACT: Use of synthetic herbicides to control weeds poses serious threats to sustainable agricultural production around the globe. The phytotoxic effect of different plant water extracts (i.e., sorghum, sunflower and mulberry) against weeds has been previously studied; however, their combined effects at different rates are yet to be explored. In this study, mixtures of allelopathic water extracts of sorghum + sunflower and sorghum + sunflower + mulberry were sprayed each at 12, 15, 18 and 21 L ha-1 at 40 and 55 days after sowing in wheat to control wild oats (Avena fatua), little seed canary grass (Phalaris minor), lamb’s quarters (Chenopodium album) and swine cress (Coronopus didymus). A synthetic herbicide Affinity 50 WP (Carfentrazone-ethyl 0.75% + Isoproturon 50% applied at 1000 g a.i., ha-1) and a weedy check were kept as a control treatment. The increasing order of water extract dose 12-21 L ha-1 showed substantial reduction in total weed density and their dry biomass production of both narrow and broad-leaved weeds in all the treatment combinations. Mixture of sorghum + sunflower + mulberry water extracts each at 18 L ha-1 applied at 40+55 DAS resulted in an 87.14% decrease in total weed dry matter with a 19.5% increase in grain yield of wheat and higher net benefits of Rs. 100525 with 777.5% marginal rate of return. Nonetheless, application of sorghum + sunflower water extracts each at 12 L ha-1 at 40+55 DAS was more economical than the other treatments in terms of higher marginal rate of return of 799.82%. Based on this study, it can be suggested that the use of allelopathic plant water extracts in a mixture may act as a potential weed control strategy in wheat.

Crop competition in winter wheat has a higher potential than farming practices to regulate weeds

AbstractManagement of biotic interactions has been recognized as a potential substitute for costly agrochemical inputs. Competition is one of the most important biotic interactions known to regulate populations and govern species assemblages. However, although theoretical and empirical work has been produced on competition, in situ experimental evidence is much scantier, mainly because of the difficulty of manipulating competition in the field. Arable weeds offer an outstanding opportunity to meet this challenge, because of the relative ease of in situ experimental manipulation and because of the urgent need to find sustainable weed management strategies. Here, we assess the importance of crop competition and two main conventional farming practices (N fertilizer and weed control) on weed species richness, abundance, and biomass. We set up an experiment with a design with two factors, presence/absence of crops and presence/absence of N fertilizer and weed control, in working farm fields with winter cereals as the target crop. We found that the crop competition reduced weed biomass production by almost 65%, as a result of the crop's competitive advantage from its greater ability to take up N, while the effect on weed species richness was less important. Our results also show that the effect of crop competition on the weed assemblage was much stronger than the effect of N fertilizer and weed control. The decrease in weed abundance and biomass mainly resulted from a strong effect of the crop on the dominant species, while the abundance of intermediate species tended to be much less affected, a result consistent with studies in grasslands where the removal of the dominant species provides a competitive release for subordinate ones. Our results further give experimental support for crop competition as a way to reduce costly agricultural inputs for weed control. Conducting experiments with farmers in their field is a valuable approach to generate knowledge for the future delivery of sustainable management.

Is mulching an efficient way to control weeds? Effects of type and amount of crop residue in rainfed rice based cropping systems in Madagascar

Weeds are a major constraint to crop yields in tropical production systems, especially for smallholder farmers who cannot afford to purchase herbicides. It has been argued that the practice of mulching with crop residues can suppress weeds in conservation agriculture systems. However, few data are available on the effect of crop residue mulching on weed infestation. In this study we quantified the effect of increasing amounts of surface crop residues on weed emergence, weed biomass production and rice yield. The experiment was conducted during four growing seasons in the Lake Alaotra region, Madagascar. Two types of mulch were applied on a no-tilled soil, Stylosanthes guianensis and a mixture of maize and Dolichos lablab, with different amounts ranging from 0 to 45Mg dry matter ha−1. Weed emergence was measured every week from the day of the first rain that triggered weed germination to 100days thereafter, and weed biomass was monitored at four dates during the cropping season. Our results show that weed emergence and weed biomass decreased with increasing amount of residue. More than 10Mgha−1 was, however, needed to significantly reduce weed emergence and weed biomass as compared to the bare soil treatment without surface residues. Rice grain yields decreased by 16% for an increase in weed biomass of one Mgha−1. Our results indicate that mulching is not a viable option of weed control for smallholder farmers, given the low amounts of residue currently retained on their fields, which is at best about 4Mgha−1 in the case of a stylosanthes crop and about 5Mgha−1 in case of dolichos intercropped with maize.