Effect of tillage systems and herbicide treatments on weed abundance and diversity in a glyphosate resistant crop rotation

The effect of exclusive application of glyphosate and glyphosate in combination with residual herbicides on weed species density and composition in summer crops was studied over 2 years. Field experiments consisted of three rotations including soybean and maize glyphosate-resistant cultivars in two tillage systems. Regardless of the tillage system, both glyphosate application alone and in combination with residual herbicides had a pronounced impact on the reduction in density and richness of summer herbaceous annual weeds, but the effect was greater with glyphosate in combination with residual herbicides.     

Weed management in maize using crop competition: A review

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.     

Managing crop losses from plant diseases with foliar fungicides, rotation and tillage on a Black Chernozem in Saskatchewan, Canada

The impact of tillage system, rotation sequence and foliar fungicides on diseases and seed yield and quality of wheat, barley, pea, canola and flax was determined in the second cycle of three, 4-year rotations from 1998 to 2001 on a Black Chernozem (Udic Boroll) at Melfort, Saskatchewan, Canada. The objective of the study was to evaluate the impact of reduced-tillage production systems, broadleaf cropping intensity and fungicide use on cereal, oilseed and pulse crops in northeastern Saskatchewan, a sub-humid region of the northern Great Plains. A split-split plot design was used with three tillage systems (conventional, minimum and no-till) as main plots, three rotations of increasing broadleaf crop intensity (1. canola-wheat-barley-barley; 2. canola-barley-pea-wheat; and 3. canola-pea-flax-barley) as sub-plots, and fungicide treatments (treated or untreated) as sub-sub-plots. Fungicides appropriate for the diseases of concern were applied at recommended crop development stages and application rates, followed by assessment of diseases. Tillage system had little impact on diseases of any crop, although seed yield was usually greater under no-till for most crops under dry conditions. Rotation was not a major factor in disease severity of most of the crops, except barley in the rotation where it was grown for two consecutive years. Under dry conditions, barley yield was reduced when it followed flax compared with other crops, most likely due to less available soil moisture after flax. Fungicide application had the greatest impact on disease control and seed yield increase, although results varied among crops and years. In conclusion, the findings indicate that tillage system had little effect on disease severity, rotation contributed to greater disease severity only when a crop was grown intensively, such as on its own stubble, and fungicide application had variable effects on both disease control and seed yield.     

Spatial distribution of nutsedge (Cyperus spp. L.) seed bank in rice growth cycle using geostatistics

A field experiment was conducted to investigate the spatial distribution of nutsedge (Cyperus spp L.) seed bank in rice growth cycle using geostatistics in 2010–11. The sampling from seed banks were performed prior to rice farm preparation and after rice harvest; also weeds density was determined in three different dates during the growing season. The results showed that the highest amount of weed population was belonging to nutsedge (Cyperus spp. L.) including Cyperus difformis, C. rotundus and C. esculentus species. Nugget/sill ratios for all variogram models ranged from 15.2 to 46.9%, indicated that there was strong and moderate spatial correlation as spherical and exponential variograms models between weed and seedling nutsedge at all stages of sampling. Visual assessments of the weed growth in these field indicated that the weed exist in patches, but mapping results showed that the size and morphology of these patches varied within field. In the present study, seed bank patchy pattern was roughly in accordance with seedling germination pattern. Generally the provided seed bank maps can be used not only as information database of seedling germination, but also for predicting of seed bank dynamics and weed management programs.     

Weed emergence as affected by maize (Zea mays L.)-cover crop rotations in contrasting arable soils of Zimbabwe under conservation agriculture

Weed control in smallholder farming systems of sub-Saharan Africa is labour intensive or costly. Many researchers have therefore advocated for the use of cover crops in weed management as an affordable alternative for smallholders. Cover crops may be grown in rotations to suppress weeds and reduce the reliance on herbicides. The use of cover crops creates microenvironments that are either conducive or inhibitive to the emergence of certain weed species. A study, initiated in 2008 in contrasting soils at four different locations of Zimbabwe, investigated the effect of maize (Zea mays L.)-cover crop rotations on the emergence of weeds that showed dominance in those soils. Weed assessments were however, carried out from 2011 to 2014. The weed species Galinsoga parviflora Cav., Commelina benghalensis L., and Richardia scabra L. showed dominance in all four locations with weed densities as high as 500 plants m⁻² being recorded for R. scabra L. in a sandy soil. Maize-cover crop rotations resulted in higher densities of Bidens pilosa compared with maize monocropping (control treatment) due to its high nitrogen (N) requirement to produce more seeds. On the other hand, the integration of cover crops such as pigeon pea [Cajanus cajan (L.) Millsp.] that had poor shading qualities, due to large gaps or spaces and slower initial growth, had limited effects on competitive weeds such as Cyperus esculentus L. which tend to dominate exhausted soils. The density of C. esculentus was 38% greater in maize–pigeon pea rotations compared with the control treatment. Variability between seasons and sites affected emergence of all weeds in the present study, which masked long-term trends. The results suggest that there is need to identify the germination and emergence requirements of specific weeds and select cover crops best suitable for their control. The study provides useful information for farmers and advisors on the best cover crops for control of certain problematic weeds in different soil types of Zimbabwe.     

Weed control and crop tolerance to propane flaming as influenced by the time of day

Time of day has been observed to affect flaming efficacy. The basis for the differential plant response is not well understood; however, daily variation in leaf relative water content (RWC) is thought to contribute to the response. Leaf RWC is the ratio of the amount of water in the leaf tissue compared to when fully turgid. To determine the influence of leaf RWC in plant response to propane flaming, greenhouse experiments were conducted during April and repeated in September of 2009. Two crops [4-leaf maize (Zea mays) and second trifoliate soybean (Glycine max)] and two weed species [5-leaf velvetleaf (Abutilon theophrasti) and 6-leaf green foxtail (Setaria viridis)] were flamed with four propane doses of 0, 29, 43 and 87 kg ha⁻¹ at 0, 4, 8 and 12 h after sunrise-HAS. Leaf RWC was measured before treatment application. Flaming treatment was conducted utilizing a hand flamer with one VT 2-23 C vapor phase burner positioned 20 cm above soil surface and angled horizontally at 30°. The propane pressure was 120 kPa and the application speeds were 1.6, 3.2 and 4.8 km h⁻¹. The plant responses evaluated were plant injury and fresh weight at 7 days after treatment (DAT). All plant species were more susceptible to flaming during the afternoon when they had lower leaf RWC at 8 HAS; however, the response of these plants did not differ with the plants flamed at 12 HAS. Green foxtail flamed at 87 kg ha⁻¹ at 0, 8 and 12 HAS had injury of 62, 76 and 82%, respectively. The same response was observed in velvetleaf which had 80% injury when flamed with 87 kg ha⁻¹ at 0 HAS and 93% injury when flamed at 12 HAS with the same propane dose at 7 DAT. Similar trends occurred for maize and soybean suggesting that leaf RWC could be one of the factors affecting plant response to flaming. Practical implication is that flaming operation should be conducted in the afternoon in order to improve efficacy of weed control and reduce propane consumption rate.     

Seeding depth and soil packing affect pure live seed emergence of cuphea

Cuphea viscosissima Jacq. × C. lanceolata f. silenoides W.T. Aiton is a new crop being developed in the north-central USA as an industrial oilseed crop. Adequate plant stand is essential for successful commercial production of cuphea. The objective of this study was to determine the effect of seeding date, depth and soil packing on stand establishment and subsequent crop performance. The study was conducted at Carrington and Prosper, ND, in 2005 and 2006. The experimental design was a randomized complete block with four replicates, with a split–plot arrangement, where the whole plot was a factorial arrangement (2 × 2) of two seeding dates, optimum and late, with or without soil packing after seeding. The subplot treatments were three seeding depths (surface, 13, and 25 mm). The same plot planter was used to adjust seeding depth to 13 and 25 mm. Each experimental unit had six rows 4.6-m long with a between-row spacing of 0.31 m. Traits evaluated were pure live seed emergence (PLSE), plant stand, plant height at harvest and seed yield. The main effect for seeding date did not have an effect on PLSE and resulted in adequate stands from both late May and mid June plantings averaged across environments. The seeding depth by soil packing interaction was significant for PLSE, plant stand and seed yield. Pure live seed emergence, plant stand, and seed yield were greater if the soil was packed compared with non-packed for the surface seeded treatment. The soil packing treatment did not influence PLSE, plant stand, or seed yield at the 13- and 25-mm seeding depths. Plant stands obtained from the non-packed surface and 13-mm seeding depths was adequate for high seed yield, as the plants branched to compensate for the lower plant density. Although surface seeding with packing produced satisfactory plant stands, reliance on timely rainfall is required for this to be successful. For this reason, the recommendation for seeding at the 13-mm depth without soil packing would ensure a better chance for sufficient soil water absorption by the seed to initiate germination. If surface seeding is practiced, a roller-packer to incorporate seeds and firm the seedbed after planting is recommended.     

Longevity of seeds of Poa pratensis and Lolium perenne as affected by simulated soil tillage practices and its implications for contamination of herbage seed crops

In grass-seed production, the purity of the product is of major importance and high purity can only be obtained by preventing contamination with other species and cultivars during the whole crop rotation. In this context, seeds of previously grown grass species or varieties are particularly important. This study investigated the influence of different soil tillage practices on persistence of newly shed seeds of two grass species, Poa pratensis and Lolium perenne . Leaving the seeds at or close to the soil surface reduced seed survival of both species to low levels compared with strategies that involved a deep incorporation of the seeds shortly after seed-shedding. Survival rate of seeds of P. pratensis after 1 year was reduced to a low level when seeds were left at the soil surface for 2–3 months before incorporation. Seeds of L. perenne were less persistent and survival rate after 1 year was generally very low if the seeds were left near the soil surface for approximately 1 month before deeper incorporation. Use of the stale seedbed technique to reduce the seedbank of the two species in the autumn ahead of a spring-established grass-seed crop was also found to be effective in reducing the potential risk of contamination.     

Effects of crop density and tillage system on grain yield and N uptake from soil and atmosphere of sole and intercropped pea and oat

Pea (Pisum sativum L.) and oat (Avena sativa L.) were grown as sole and mixed crops in various densities under two different tillage systems on a loess soil near Göttingen/Germany in a 2-year field experiment (2002/2003). In the conventional tillage system a mouldboard plough (CT) was used and in the minimum tillage system a rotary harrow (MT) was employed. The effect of crop density and tillage system on the grain dry matter and grain N yields, N₂ fixation and soil N uptake were determined to address the following questions: (i) which mixture compositions exhibit the highest grain yields compared to the sole crops, (ii) which mixture compositions also fix a high level of N₂ and leave low levels of residual inorganic soil N after harvest, and (iii) whether the intercrop advantage is influenced by the tillage system. For (i) the result in 2002 showed that the highest grain yields of both sole cropped pea and oat and intercropped pea and oat were achieved at the highest densities. In 2003, when the inorganic soil N content was higher and weather conditions were warmer and drier, grain yields were significantly higher than in 2002, but sole as well as intercropped pea and oat gave their highest grain yields at lower densities. For both years and tillage systems, the highest intercrop advantages were achieved in mixtures with densities above the optimal sole crop densities. The result for (ii) was that a distinctly higher proportion of nitrogen was derived from the atmosphere (Ndfa) by intercropped pea than by sole cropped pea. However, the uptake of soil N by intercropped pea and oat was not reduced in comparison with that of sole cropped oat as the decrease in the uptake of N from the soil by oat at lower oat densities in the mixture was compensated for by the soil N uptake of pea. Additionally, the N_min-N content of the soil following the mixtures and sole cropped oat did not differ, especially in the deeper soil layers because oat in mixture was forced to take up more soil N from deeper layers. Therefore, the risk of soil N losses through leaching after mixtures was lower compared to sole cropped pea. The tillage system (iii) had no significant influence on grain yield and soil N uptake, but N₂ fixation and the competitive ability of intercropped pea were higher under CT than with MT. An additional result was that intercropping led to a significantly increased grain N content of both pea and oat compared to the sole crops. The increase in grain N content from sole to intercrop was from 3.30 to 3.42% for pea and from 1.73 to 1.96% for oat as a mean for both years and tillage systems. The present study confirms that growing pea and oat as intercrops highlights potential economic and environmental benefits which still need to be understood in more detail in order to exploit intercropping to a greater extent.     

Weed control and sweet maize (Zea mays L.) yield as affected by pyroxasulfone dose

Pyroxasulfone is a new herbicide being considered for registration in sweet maize in Canada; however, there is still little information on the doses required to provide 90% control of annual grass and broadleaved weeds found in southwestern Ontario. The objective of this study was to determine pyroxasulfone doses that would provide at least 90% control of several economically important weeds, without impacting final sweet maize yield by more than 5% in comparison to a weed-free control. Six field trials were conducted over a two-year period (2007 and 2008) at three Ontario locations to evaluate the effectiveness of pyroxasulfone at doses ranging from 31.25 to 1000 g a.i. ha⁻¹. The doses required to reduce weed biomass by at least 90% (I₉₀) varied by weed species. Doses of 93, 499, and 111 g a.i. ha⁻¹ were required to reduce the biomass by 90% of redroot pigweed, common lambsquarters and green foxtail, respectively. There was greater than 95% control of velvetleaf, large crabgrass and barnyardgrass with 31.25 g a.i. ha⁻¹, the lowest dose tested. Sweet maize yield could not be consistently maintained within 5% of the weed-free control. There are several factors that may have contributed to the reduced yield, including soil texture effects, competition as a result of poor common lambsquarters control, and hybrid sensitivity. These results show that biologically effective weed control with pyroxasulfone may be achieved at lower than proposed doses for several weed species; it remains unclear if this is economically sustainable due to the potential impacts on yield.     

Seed quality as affected by nitrogen during true potato seed production and moisture conditions during storage

The objective was to investigate the effects of moisture conditions in storage at 21 C (± 3) on true potato seed (TPS) germination and seedling vigor. The influence of supplemental nitrogen (N) during seed production on these effects was also studied. One set of TPS was stored exposed to ambient humid (> 80% RH) air; the other was stored dry (sealed with silica gel). Germination tests were performed at 7, 11, and 14 months of seed storage. Seedling vigor tests were made at 14, 20, and 23 months. The rate of germination was mostly affected by the moisture conditions during storage. Seed stored dry germinated faster than TPS stored in humid ambient air. The rate of germination increased with time in storage and the percentage of germination was always high (≥ 95%) in dry seed produced with high N. Seedling vigor was mostly affected by N treatments during seed production. High-N seed had a much higher rate and percentage of emergence and seedling dry-weight levels than low-N seed, particularly when stored dry. Seedling vigor criteria decreased with time in storage in low-N seed; in high-N seed, the rate of emergence increased and the percentage of emergence was always high (≥ 95%). In conclusion, the TPS should be produced with high N and stored dry for sowing under unfavorable conditions.     

Needs for and effectiveness of slow release herbicide seed treatment Striga control formulations for protection against early season crop phytotoxicity

Imidazolinone resistant maize seed dressed with imazapyr has been successfully used to control the parasitic weed Striga in many locations, and has begun to be commercially successful in Africa. Despite this, occasionally poor effectiveness of control had been documented in some sites that required explanation. Analysis of the data against rainfall patterns suggested that: 1. poor maize emergence occurred when there was limited rainfall at germination, possibly due to inhibition by a very high herbicide concentration too near the maize seed; 2. there was poor Striga control in seasons of very high rainfall, possibly due to herbicide washout away from the maize root zone where Striga germinates and attaches. These field assessments were matched by experiments suggesting that slow release formulations might alleviate the problems. A series of slow release formulations were synthesized based on binding imazapyr to high capacity anion exchangers and using them to coat maize seed. The best seems to be a polyethyleneimine gel. Epidemiological field data from a multitude of sites support the conclusion that the slow release formulations increased stand establishment across sites and seasons compared to the control where there was low rainfall.     

Biology and management of Phalaris minor in rice–wheat system

Phalaris minor Retz. (Littleseed canarygrass) is a pernicious weed, which infests several crops during the winter season, particularly the wheat crops in rice–wheat sequence. Considering the limitations of cultural and chemical methods of weed control, the understanding of its biology with respect to different environmental, edaphic and management factors may offer a useful key to strengthen weed management strategies. This review considers various aspects on dormancy, viability and agro-ecology with emphasis on management practices in host and succeeding crops. Due attention has been given to the approaches required to manage the resistant biotypes under present conditions and hence to avoid further escalation of the epidemic. The various studies indicate that P. minor utilizes beneficially the prevailing environmental and management conditions of both the wheat and succeeding rice crop in rice–wheat system for its survival and growth. Its seed is highly sensitive to variable moisture and temperature regimes for germination and exhibits tolerance to anoxia during anaerobic respiration in rice. Tillage options, residue management, spatial–temporal considerations and other factors influence the seed dynamics, pattern and depth of emergence and growth of P. minor. A comprehensive and conceptual understanding of these aspects may provide useful guidelines in formulating cautious and opportunistic weed management strategies.     

Ludwigia hyssopifolia emergence and growth as affected by light, burial depth and water management

Experiments were conducted to evaluate the effects of light, seed burial depth, and flooding on germination, emergence and growth of Ludwigia hyssopifolia. Germination was strongly stimulated by light, suggesting that seeds of this species are positively photoblastic. Seeds sown on the soil surface gave the greatest percentage of seedling emergence in plastic trays, and no seedlings emerged from seeds buried in soil at depths of ≥1 cm. Intermittent or shallow flooding suppressed emergence and growth of L. hyssopifolia. Flooding to a depth of 2 cm for 4 days out of 7 days reduced seedling emergence by more than 71% and seedling dry matter by 97% compared to where the soil had not been flooded. Flooding up to a depth of 10 cm however, when delayed to 21 days after sowing, did not significantly suppress growth of this species. This study illustrates the role of seed burial by tillage and flooding as two important tools for the management of L. hyssopifolia.     

Persistence and productivity of orchardgrass and orchardgrass/alfalfa mixtures as affected by cutting height

Cutting height is an important factor controlling the yield and persistence of grass swards harvested for conserved feed. The objective of this experiment was to determine the effect of four cutting heights (5, 10, 15 and 20 cm) on the yield, composition and productivity based on deviation from a size/density compensation line for swards of orchardgrass (Dactylis glomerata L.) and an orchardgrass/alfalfa (Medicago sativa L.) mixture harvested nine times over three growing seasons. Yield was greatest for the 5 cm cutting height through the course of the experiment but ground cover of orchardgrass declined. Prior to the final harvest, tiller weight and density were determined. The 10‐, 15‐ and 20‐cm treatments fell on an apparent size/density compensation line with slope ‐1·779 (R² = ·99; p = ·008) while the 5‐cm treatment fell considerably below that line indicating a reduction in productivity or relative persistence. Harvest at 10 cm appears to optimize yield while maintaining stand productivity in infrequently harvested orchardgrass swards.     

Distribution of proteins and amino acids in milled and brown rice as affected by nitrogen fertilization and genotype

A field experiment involving six japonica rice cultivars with contrasting agronomic traits and seven nitrogen (N) fertilizer treatments was performed to determine the effects of N and genotype on distribution of four kinds of grain proteins and amino acids in milled and brown rice. For brown and milled rice, albumin and globulin were controlled more by genotype than N treatments, whereas prolamin and glutelin were largely determined by N. Substantial genotypic differences in response of milled/brown (M/B) ratios of proteins to N treatments were detected. In comparison with large panicle cultivars, small panicle cultivars such as Wuyujing3 had the lower ratio and exhibited more stability under contrasting N treatments. N had significant influence on amino acid composition of brown and milled rice, with contents of the 17 amino acids measured increasing with elevated N rate. However, cysteine and methionine in brown rice and lysine and methionine in milled rice were not significantly affected by N. In addition, N had little effect on ratios of M/B for most of the amino acids.     

超临界CO_2提取人参籽油工艺研究及人参籽油脂肪酸组成分析

该研究以人参籽为原料,采用超临界CO2流体技术萃取人参籽油,通过正交试验优化了萃取人参籽油工艺参数,再将其与通过冷榨法及溶剂法提取的人参籽油进行对比,测定和比较了不同工艺制取的人参籽油的脂肪酸组成。试验结果表明,在萃取压力26MPa、萃取温度50℃、萃取时间2 h工艺条件下,人参籽油得率为16.2%。经检测,人参籽油脂肪酸组成为不饱和脂肪酸占99%以上,其中油酸含量极高,可达73.93%。通过不同制取方法所得到的人参籽油的脂肪酸组成分析表明,超临界CO2萃取法与溶剂萃取法所提取人参籽油的脂肪酸明显多于压榨法的脂肪酸成分;且超临界CO2萃取法具有无有机化学试剂残留的明显优势,因此,是未来人参籽油提取中可以应用的一种绿色环保的提取工艺和技术。     

Emissions of CH4 and CO2 from paddy fields as affected by tillage practices and crop residues in central China

A field experiment was conducted to investigate effects of tillage practices [no-tillage (NT) and conventional intensive tillage (CT)] and oilseed rape residue returning levels (0, 3000, 6000, 9000 kg dry matter ha^?1) on methane (CH₄) and carbon dioxide (CO₂) emissions and grain yield from paddy fields during the 2011 rice growing season after 2 years oilseed rape-rice rotation in central China. The experiment was established following a split-plot design of a randomized complete block with tillage practices as the main plots and residue returning levels as the sub-plots. NT significantly decreased CO₂ and CH₄ emissions by 38.8 and 27.3 % compared with CT, respectively. Residue returning treatments released significantly more CO₂ and CH₄ by 855.5–10410 and 51.5–210.5 kg ha^?1 than no residue treatments, respectively. The treatments of 3,000 and 6,000 kg ha^?1 residue returning significantly increased rice grain yield by 37.9 and 32.0 % compared with the treatment of no residue returning, respectively. Compared with NT, CT increased yield-scaled emissions of CH₄ and CO₂ by 16.0 %. The treatments of 6,000 and 9,000 kg ha^?1 residue returning significantly increased yield-scaled emissions of CH₄ and CO₂ by 18.1 and 61.5 %, respectively, compared with the treatment of no residue returning. Moreover, the treatment of NT in combination with 3,000 kg ha^?1 residues had the lowest yield-scaled emissions of CH₄ and CO₂ across tillage and residue treatments. In this way, this study revealed that the combination of NT with 3,000 kg ha^?1 residues was a suitable strategy for optimizing carbon emissions and rice grain yield.