Effects of soil depth and aggregate size on weed seed distribution and viability in a silt loam soil

The position of weed seeds within the soil matrix plays an important role in seedling emergence and seed survival. The relationship of weed seeds with soil aggregates and soil depth was evaluated in a Waukegon silt loam soil that had been under a long-term, conventional tillage, annual crop management system. Soil aggregates were separated and classified into eight size classes from ≤5 to >12 mm and weed seeds were extracted from the aggregates. Amaranthus spp., Chenopodium album L. (common lambsquarters), Polygonum pensylvanicum L. (Pennsylvania smartweed), Setaria faberi Herrm. (giant foxtail), and Solanum ptycanthum Dun. (eastern black nightshade) accounted for the majority of seeds recovered. In general, seed viability declined from April to June, but increased in October following seed deposition. Seeds of individual species were most abundant in the aggregate size class most closely matching its seed size. However, seeds were commonly found associated with aggregates larger than 9 mm. Highest seed viability was found in the aggregate fraction closest to the seed size, however, S. faberi viability was also high in the >12 mm aggregate size class. Regardless of aggregate size, seed numbers were generally greatest in the upper 5 cm of soil. The results of this research were species-dependent and variable and demonstrated the complexity of weed seed/soil aggregate associations. However, they did show that seed placement within the soil matrix may play an important role in weed population dynamics.     

入侵植物豚草与本地植物马唐对土壤肥力与酶活性影响的比较

通过同质园试验比较研究了外来入侵植物豚草与本地植物马唐对土壤肥力及3大类酶活性的影响.结果表明: 与本地植物及空白对照相比, 豚草显著提高了入侵地的土壤有效养分含量, 特别是有效钾含量是空白对照区和本地植物马唐区的3.6倍和1.3倍.与空白对照区和本地植物马唐种植区相比, 豚草种植区的土壤酶活性亦显著提高.外来入侵植物豚草在入侵地形成新的关系过程中, 比本地植物马唐能更快地提高土壤有效养分含量及酶活性, 从而实现较短时间内通过提高土壤肥力, 形成对自身生长有利的土壤环境来帮助其竞争入侵.     

强还原土壤处理对再植龙牙百合生长不利因子的消减作用

病害和草害是再植龙牙百合生长的两大关键制约因素。以强还原土壤处理（Reductive soil disinfestation,RSD）为技术手段,以湖南省栽培过龙牙百合的土壤为研究对象,通过设置液体有机物料RSD处理（6 t·hm–2,MO）、固体有机物料RSD处理（15 t·hm–2,SB）和不做任何土壤处理的对照（CK）,研究该技术手段对龙牙百合栽培土壤中土传病原菌和杂草种子库的影响。结果表明,与CK对照相比,RSD处理均能有效杀灭土壤中的尖孢镰刀菌、腐皮镰刀菌和立枯丝核菌等病原真菌,显著降低镰刀菌属在真菌类群中的占比,其杀菌率高达98.8%。同时,RSD处理还能有效抑制土壤杂草种子库中大部分杂草的萌发,显著降低田间杂草的密度和生物量,其对杂草数量和干质量的抑制率分别为94.1%～96.0%和71.0%～94.7%,且MO处理对杂草的防除效果优于SB处理。此外,RSD处理还能显著改变田间杂草的群落结构,并降低其多样性、丰富度和优势度。因此,强还原土壤处理能够显著消减土传病原菌、杂草等再植龙牙百合生长不利因子,是一种具有同时降低田间病害和草害发生潜力的农业措施,且可以为减少农药施用量...     

Weed abundance and soil seedbank responses to tillage systems in continuous maize crops

Weed abundance in crops undergoes frequent changes, often due to changes in tillage practices. Annual species, with quick germination, a short vegetative stage, profuse seed production and long-lived seeds become problematic under zero-tillage systems. Portulaca oleracea L. and Amaranthus blitoides L. are widespread weeds in the Mediterranean area, prominent in irrigated crops. We studied the total weed abundance in the field, and specifically these two species (Portulaca oleracea and Amaranthus blitoides) with high frequency of occurrence in monoculture maize, from 2012 to 2014, in the field and soil seedbank. Results showed significant differences between zero-tillage (ZT) and conventional tillage (CT) systems on total weed abundance and relative abundance of Portulaca oleracea. Total weed abundance decreased in ZT plots (from 136 plants m^?2 to 25 and 46 plants m^?2, in 2013 and 2014 respectively). The same trend was observed in Portulaca oleracea recorded in ZT plots, but the abundance of Amaranthus blitoides did not vary in this system. Weed seedling germination and weed seed numbers both of total weed seedbank and Portulaca oleracea, were greater in ZT plots compared to CT, regarding Amaranthus blitoides seedling germination and seed count, the values did not increase with ZT, in continuous maize crops.     

Effect of tillage intensity on weed infestation in organic farming

Conservation tillage is not yet widely accepted by organic farmers because inversion tillage is considered to be necessary for weed control. Three long-term experiments were established with combinations of reduced and conventional plough tillage and stubble tillage to determine weed infestation levels in organic farming, i.e. herbicide application being excluded. Experiment 1 (with very low stocking density of perennial weeds) showed that in presence of primary tillage by mouldboard ploughing the number of annual weeds was nearly unaffected by the mode of stubble tillage. In experiment 2, however, with Canada thistle (Cirsium arvense) being artificially established, thistle density was significantly affected by stubble tillage and by a perennial grass–clover forage crop. Experiment 3 combined two levels of stubble tillage (skimmer plough, no stubble tillage = control) with four implements of primary tillage in the order of decreasing operation depth (deep mouldboard plough, double-layer plough, shallow mouldboard plough or chisel plough). Primary tillage by chisel plough resulted in significantly highest annual weed density compared to all other treatments. The natural C. arvense infestation in experiment 3 showed highest shoot density in the “skimmer plough/chisel plough” treatment compared to the lowest infestation in the “skimmer plough/double-layer plough” treatment. The poor capacity of the chisel plough for weed control was also reflected by the soil seed bank (5500 m⁻² C. arvense seeds for chisel plough, <300 seeds for all other primary tillage). A reduced operation depth of the mouldboard plough (“shallow mouldboard plough”) seemed to have an insufficient effect in controlling C. arvense infestation as well. Stubble tillage by the skimmer plough in addition to nearly any primary tillage operation largely reduced both annual weeds and thistle shoots. Most effective in controlling C. arvense was also a biennial grass–clover mixture as part of the crop rotation.Double-layer ploughing is a compromise between soil inversion and soil loosening/cutting and can be regarded as a step towards conservation tillage. In terms of controlling annual weeds and C. arvense, the double-layer plough was not inferior to a deep mouldboard plough and seems to be suitable for weed control in organic farming. Tilling the stubble shallowly after harvest can support weed control in organic farming remarkably, particularly in reducing C. arvense. If no noxious, perennial weeds occur and primary tillage is done by soil inversion, an omission of stubble tillage can be taken into consideration.     

Mexican poppy (Argemone mexicana) control in cornfield using deep learning neural networks: a perspective

Mexican poppy (Argemone mexicana) is a widespread noxious annual weed associated with crops such as corn (Zea mays L.), and this weed is persistent because it produces a seed bank. This invasive weed species must be controlled even in the dry season because Mexican poppy has a deep-reaching root system, which taps water from deep soil layers. Cases of a human death caused by Mexican poppy seeds in South Africa, India, and other Eastern countries were reported from the early years of the twentieth century. However, when weeds are controlled uniformly instead of site-specific or precision farming method across the spatially variable fields, there are environmental pollution challenges. Site-specific weed control techniques have gained interest in the precision farming community over the last years mainly because of Global Positioning System (GPS) applications, and a controlled measure of herbicides are applied where there are weeds in the field, and areas with more clusters of weeds receive the correct amount of herbicide application. Mexican poppy has prickles and is a nuisance to farmers, and herbicides represent a severe health hazard to humans due to chemical concentrations in water. For that reason, we propose the design of a site-specific weed control plan to use a row-guided robot to detect and identify weeds with accuracy, control speed timeously, and spray herbicides with a high level of precision and automation. These robotics methods are reported to be environmentally conscious, and economically efficient with less labour and management. The proposed method of deep learning neural networks, which use row-guided robots, a machine is trained on multiple images to identify weeds automatically from the main crop, and release a controlled measure of herbicides based on weed location and density, and spray weeds on-the-go upon emergence.     

Crop stand density enhances competitive ability of spring barley (Hordeum vulgare L.)

Abstract

The aim of the research was to establish weediness, competitive ability and productivity of the crop. The experimental object was agrophytocenoses of spring barley – Hordeum vulgare L. – crop of spring barley ‘Aura’ and unsown soil, and weeds growing in them. The crop was formed sowing 0, 120, 200 and 280 kg ha^?1 (0, 2.7, 4.5 and 6.2 million seeds per ha^?1 respectively) seeds of spring barley ‘Aura’. Spring barley crop was not harrowed and herbicides were not applied. In the field experiment estimates were made of changes of weeds and spring barley inter- and within- species competition optimizing crop density. During three years of field experiment in the crop of spring barley annual weeds prevailed at 88–99%, such as Chenopodium album, Stellaria media, Erysimum cheiranthoides. Perennial weeds formed 1–12% of the crop weeds, such as Sonchus arvensis, Cirsium arvense, Equisetum arvense. General number of weed species in spring barley crops varied from 13 to 21. Weed abundance proportionally declined in the crops of higher density, hence, higher seed rate should be recommended for organic agriculture where weeds are controlled in non-chemical ways. Consistently increasing barley stand density, the competition between species (spring barley with weeds) gradually turned into competition within species (between barley plants) when a higher number of weaker and non-productive stems started forming. Spring barley yield did not significantly depend on the stand density. Increasing stand density enhanced cultivated crop yield to a certain level (200 kg ha^?1), since an increase in spring barley plant number resulted in the reduction in weight per plant and 1000 grain weight, which was compensated by an increase in the number of spring barley plants. Different spring barley density had an essential influence on the chemical composition of weeds which was similar to that of spring barley. Weeds accumulated the greatest amount of crude proteins, crude fat and crude fibre growing without spring barley.     

Effect of soil tillage and weed control methods on weed biomass and yield of lentil (Lens culinaris Medic.)

Abstract

The study was carried out in dryfarming areas in Ankara, Turkey, over 2 years (2001 – 2002 and 2002 – 2003). The objective was to determine different soil tillage and weed control methods on weed biomass and yield components, yield of lentil (Lens culinaris). This study compared the effects of two tillage systems (shallow minimum tillage and traditional tillage) and three weed control methods (weedy check, hand weeding and herbicide) on weed biomass, growth characteristics, seed yield and some yield components of lentil. Significant differences were found among weed control methods for weed biomass and yield parameters of lentil. Tillage systems had no significant effect on weed biomass or yield of lentil. The highest yield and lowest weed biomass was found in the hand-weeded treatment compared to the other weed control methods. Results of this research indicate that weeds are a main constraint for lentil growing under dryland conditions. Grain yield of lentil was reduced more than 60% due to uncontrolled weeds.     

Changes in the weed communities as affected by different primary soil tillage and deep loosening

Long-term soil cultivation at the same depth affects soil characteristics and crop productivity. The aim of the study was to investigate the impact of a long-term different intensity soil tillage methods and deep loosening on weed number, weed agrobiological group and soil seed bank changes in till Bathygleyic Dystric Glossic Retisol soil under the climatic conditions of the Western Lithuania (geographical coordinates 55°43′38″N, 21°27′43″E). The study included different soil tillage methods (conventional ploughing, shallow ploughing and shallow ploughless tillage) and deep loosening. During investigational years, the greatest weed number in crops and the greatest weed seed number in the seed bank were determined in the soil reduced tillage (shallow ploughing and shallow ploughless tillage). The weed number in crops of conventional ploughing soil was 35.8% lover compared to reduced tillage soil. The weed seed number in the seed bank of conventional ploughing was 49.6% lover compared to reduced tillage Decreasing soil tillage intensity resulted in weed seeds concentration in the upper topsoil. A one-time deep loosening had a significant effect during the crop rotation: the weed number in crops and weed seed number in the seed bank were determined to have increased by 26.6% and 51.6% in conventional ploughing soil and by 11.9% and 23.2% shallow ploughless soil respectively. However, after deep loosening, the number of Poa annua in crops decreased 2.9 times in plots of conventional ploughing and 1.7 times – in plots of shallow ploughing soil.     

Early-season nutrient competition between weeds and soybean

Abstract

Soybean [Glycine max (L.) Merr.] yield losses may be attributable to early-season nutrient competition with weeds; however, research investigating macro- and micronutrient accumulation of weeds in soybean is scarce. Field experiments were conducted across eight site-years in Illinois, USA to determine which soybean nutrients are most susceptible to weed competition. Weeds were controlled by applying glyphosate at 10-, 20-, 30-, or 45-cm weed heights during which accumulation of 11 nutrients were measured in soybean and broadleaf and grass weeds. For both weed groups, K and Fe were the macro- and micronutrient, respectively, with the greatest rate of accumulation. Variations in nutrient uptake between broadleaf and grass weeds were largely explained by differences in weed density, except for Ca and B, which were greater in broadleaf weeds regardless of density. Canonical discriminant analysis (CDA) identified soybean accumulation of N, P, K, Fe, and Cu as the nutrients most affected by weed competition, with P, K, and Fe uptake being particularly susceptible during droughty conditions. The weed height causing a 10% reduction in uptake was 11, 12, 12, 7, and 10?cm for N, P, K, Fe, and Cu, respectively. Soybean grain yield, seed weight, pods plant^?1, and seed oil content were identified through CDA as the yield parameters most affected by weed competition. Results indicate weeds should be removed before reaching 18?cm (V2 to V3 soybean) to avoid a 5% loss in grain yield. Early-season weed control preserves yield potential and may improve efficiency of nutrient management programs in soybean.     

Characterization of ammonia oxidizing bacteria associated with weeds in a Japanese paddy field using amoA gene fragments

Abstract

Ammonia oxidizing bacteria (AOB) are important microorganisms in rice paddy field ecosystems because they play a key role in the nitrogen (N) cycle by converting ammonia (NH₃) to nitrite (NO^? ₂). In this study, we investigated AOB associated with three types of weeds in a Japanese paddy field (semi-aquatic Echinochloa oryzicola Vasing, floating Lemna paucicostata Hegelm and submerged Najas graminea Delile) using molecular techniques polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and DNA sequencing targeting ammonia monooxygenase (amoA) gene. This work confirmed that rice paddy weeds harbor AOB and that the community composition is different for each type of weed. However, all AOB sequences associated with the tested weeds were closely related to known species of Nitrosospira-like AOB isolated from soil, suggesting that AOB associated with weeds were not specific to weeds and can also be found in the soil. Nitosomanas-like AOB were not detected on any of the weeds tested. In addition, the most dominant AOB strains present in the tested weeds were closely related to Nitrosospira sp. Ka3 and Nitrosospira sp. CT2F. The phylogenetic tree revealed that most of the AOB detected in the present study belonged to amoA cluster 1.     

Allelopathic effect of some essential oils and components on germination of weed species

Abstract

In this study, allelopathic effects of some essential oil plants (Carum carvi L., Coriandrum sativum L., Foeniculum vulgare Mill., Lavandula stoechas L., Mentha spicata L.,Origanum onites L., Pimpinella anisum L., Rosmarinus officinalis L., Salvia officinalis L. and Thymbra spicata L.) were investigated against some common weed species (Alcea pallida Waldst. & Kit., Amaranthus retroflexus L., Centaurea salsotitialis L., Raphanus raphanistrum L., Rumex nepalensis Spreng., Sinapis arvensis L. and Sonchus oleraceus L.) that grow in field and horticultural crops. Different concentrations (3, 6, 10 and 20 µl) of the essential oils were tested against weed seeds in vitro and their effect on germination was determined. Inhibitory effects of essential oils and concentrations were analysed with Freadman's test and they were found significant. Essential oils from Carum carvi, Mentha spicata, Origanum onites and Thymbra spicata showed high inhibitory effect against weed seeds at lower concentrations. The main components (carvacrol, thymol, carvone, limonene) of these four essential oils were tested for seed germination at four different concentrations (500, 250, 125 and 62.5 µg/ml) against the same weeds.Thymol, carvacrol and carvone showed high inhibition even at low concentrations against weed seeds. Only Alcea pallida seeds showed resistance against all essential oils and components.     

Mycorrhizae,biocides, and biocontrol. 4. Response of a mixed culture of arbuscular mycorrhizal fungi and host plant to three fungicides

The effects of three commonly used fungicides on the colonization and sporulation by a mixture of three arbuscular mycorrhizal (AM) fungi consisting of Glomus etunicatum (Becker & Gerd.), Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, and Gigaspora rosea (Nicol. & Schenck) in symbiosis with pea plants and the resulting response of the host-plant were examined. Benomyl, PCNB, and captan were applied as soil drenches at a rate of 20 mg active ingredient kg^-1 soil 2 weeks after transplanting pea seedlings in a silty clay-loam soil containing the mixed inocula of AM fungi (AM plants). Effects of fungicides were compared to untreated plants that were inoculated with fungi (AM control). The effect of mycorrhizal inoculation on plant growth was also examined by including nonmycorrhizal, non-fungicide-treated plants (non-AM control). Fungicides or inoculation with AM fungi had only a small effect on the final shoot weights of pea plants, but had greater effects on root length and seed yield. AM control plants had higher seed yields and lower root lengths than the corresponding non-AM plants, and the fungicide-treated AM plants had intermediate yields and root lengths. Seed N and P contents were likewise highest in AM control plants, lowest in non-AM plants, and intermediate in fungicide-treated AM plants. All three fungicides depressed the proportion (%) of root length colonized by AM fungi, but these differences did not translate to reductions in the total root length that was colonized, since roots were longer in the fungicide-treated AM plants. Pea plants apparently compensated for the reduction in AM-fungal metabolism due to fungicides by increasing root growth. Fungicides affected the population of the three fungi as determined by sporulation at the final harvest. Captan significantly reduced the number, relative abundance, and relative volume of G. rosea spores in the final population relative to the controls. The relative volume of G. etunicatum spores was greater in all the fungicide-treated soils, while G. mosseae relative volumes were only greater in the captan-treated soil. These findings show that fungicides can alter the species composition of an AM-fungal community. The results also show that AM fungi can increase seed yield without enhancing the vegetative shoot growth of host plants.     

Annual warm-season grasses vary for forage yield,quality, and competitiveness with weeds

Warm-season annual grasses may be suitable as forage crops in integrated weed management systems with reduced herbicide use. A 2-year field study was conducted to determine whether tillage system and nitrogen (N) fertilizer application method influenced crop and weed biomass, water use, water use efficiency (WUE), and forage quality of three warm-season grasses, and seed production by associated weeds. Tillage systems were zero tillage and conventional tillage with a field cultivator. The N fertilization methods were urea broadcast or banded near seed rows at planting. Warm-season grasses seeded were foxtail (Setaria italica L.) and proso (Panicum mileaceum L.) millets, and sorghum–sudangrass (Sorghum bicolor (L.) Moench × Sorghum sudenense Stapf.). Density of early emerging weeds was similar among treatments, averaging 51 m^?2. Millets exhibited higher weed density and weed biomass than sorghum–sudangrass. At harvest, sorghum–sudangrass produced significantly greater biomass and N accumulation than either millet. Water use (157 mm) and WUE (25.1 kg mm^-1 ha^?1) of total biomass did not vary among treatments or grass entries. Weed seed production by redroot pigweed and green foxtail was respectively 93 and 73% less in sorghum–sudangrass than proso millet. Warm-season grasses offer an excellent fit in semiarid cropping systems.     

Soil and weed management for enhancing arbuscular mycorrhiza colonization of wheat

Tillage and weed control are critical components of cropping systems that need to be combined such that crops benefit from reduced competition. However, weeds may also contribute to the biological diversity within the agro‐environment. This greenhouse study investigated whether common weeds of arable cropping systems were suitable host plants for arbuscular mycorrhizal fungi (AMF), allowing the development of extraradical mycelium (ERM) that can contribute to the early colonization of a following wheat crop, especially in the absence of soil disturbance. Weeds were allowed to grow for up to 2 months before being controlled by soil disturbance or herbicide application (glyphosate or paraquat). Pregerminated wheat seeds were then planted. Chemical control of the weeds prior to sowing enhanced the early arbuscular mycorrhiza (AM) colonization rate of wheat roots, whereas mechanical disturbance was less acceptable as a method of weed control for rapid AM colonization. The type of herbicide (contact or systemic) had no impact on colonization of the wheat crop. Enhanced AM colonization promoted early P acquisition and growth of the crop. Appropriate management of weeds emerging between two consecutive cropping seasons coupled with no‐till soil management could ensure a quick and efficient AM colonization of the following wheat plants.     

Effects of repeated clover undersowing,green manure ley and weed harrowing on weeds and yields in organic cereals

Abstract

Cover crops can be used to reduce leaching and erosion, introduce variability into crop rotation and fix nitrogen (N) for use by the main crops, less is however known about effects on weeds. The effects on weed seed bank, weed growth and grain yield of 4 years of annual undersown clover and ryegrass alone and in combination, and one of the 4 years with clover or clover + grass as green manure, were studied in oat and spring wheat at two experimental sites in south-eastern Norway. These treatments were compared with no undersown crop (control) and with weed harrowing. In contrast to many results in the literature, the undersown clover in this study did not suppress annual weeds, but fertilized the weeds as well as the cereals. Undersown clover resulted in a statistically significant increase of grain yield at the two sites to 116% and 121% of control. During the 4-year period relative seed bank and density of emerged weed (dominated by Spergula arvensis) increased significantly about 4.5 and 10 times respectively in the undersown clover plots at Apelsvoll. At Kise both ryegrass alone and ryegrass mixed with clover significantly suppressed the weed biomass to 70% and 74% of control respectively. It is concluded that fertilization effects of undersown clover may have dominated and overriden the competitive effects. One whole-season clover green manure did not increase the mean yield, but resulted in a significant drop in seed bank size the following year, because of limited weed establishment in an established ley. Only a slight increase in average weed biomass was observed at one of the two experimental sites. The weed seed bank and the weed biomass were essentially kept at steady state during the experimental period in harrowed plots, but harrowing decreased grain yield significantly at both sites.     

Weed seed bank composition under three long-term tillage regimes on a fine sandy loam in Atlantic Canada

Tillage systems can influence weed seed viability and the distribution with depth of weed seeds in soil. To investigate this ‘tillage effect’, weed seed bank composition was determined at two soil depths (0–10 and 10–20 cm) in three tillage systems [mouldboard plough (MP), shallow tillage (ST), and direct drilling (DD)] established for 14 years on a sandy loam (Podzol) in Prince Edward Island, Atlantic Canada. The cropping system was a cool-season soybean (Glycine max L. Merr.) in rotation with barley (Hordeum vulgare L.). The objectives were to evaluate the size and composition of the viable soil seed bank, using the seedling germination method, and to determine if the adoption of non-inversion tillage practices (DD and ST) influence seed bank parameters relative to the conventional full inversion MP. The diversity of weed species was slightly lower for MP (17 species) compared to the ST (21 species) and DD treatments (22 species). The population for most weed species was relatively low with only three common species [low cudweed (Gnaphalium uliginosum L.), creeping buttercup (Ranunculus repens L.), common lambsquarters (Chenopodium album L.)] above 5 m⁻². For the total soil depth sampled (0–20 cm), weed seed population was significantly greater under DD (56 weeds m⁻²) and ST (66 weeds m⁻²), compared to MP (25 weeds m⁻²), and mainly related to changes in the number of annual broadleaf weeds, compared to perennial broadleaf and grasses. Comparison of the 0–10 with the 10–20 cm soil depth showed a relatively uniform weed seed distribution for the MP treatment, while a greater proportion of weed seeds was found at the lower soil depth for DD and ST. This distribution tended to be weed species dependent. Soil texture and weed seed characteristics were considered to have a critical impact on the total weed seed bank size, specifically for the 10–20 cm soil depth. Overall, the weed bank size was relatively small indicating that adoption of conservation tillage practices for sandy loams in Atlantic Canada should not cause a major change in weed community and weed populations, or present a need for significant changes in weed control management.     

水稻秸秆-薄膜连续叠加覆盖对三叶鬼针草的控制效果

入侵植物三叶鬼针草(Bidens pilosa L.)严重危害我国农林畜牧业的生产。为探究生态高效控制三叶鬼针草的方法,开展了水稻秸秆与塑料薄膜相结合覆盖控制入侵杂草的研究。试验在以三叶鬼针草和马唐[Digitaria sanguinalis(L.)Scop.]为主的自然杂草荒地进行,设置不同稻秆覆盖量(0kg·m~(-2)、1kg·m~(-2)、1.5kg·m~(-2)),于冬季进行稻秆覆盖,春季在稻秆覆盖的基础上覆盖薄膜。通过测定秸秆覆盖中期(2月12日)和薄膜覆盖中期(4月12日)的午间土壤温度、土壤相对含水量和近地表空气温湿度等环境指标和杂草生物量、种子萌发量、杂草群落结构和土壤种子库等群落指标,探究该方法控制入侵杂草的效果和机制。结果表明:冬季水稻秸秆覆盖显著降低了草地午间土壤温度、近地表空气温度、三叶鬼针草生物量和种子萌发量、优势杂草盖度和从属种的种类和数量;覆盖1.5 kg·m~(-2)稻秆的处理对各类指标的影响程度均大于1 kg·m~(-2)的处理。春季叠加薄膜覆盖导致浅层土壤高温干燥、近地表空气高温高湿;叠加薄膜覆盖处理使三叶鬼针草的土壤种子密度在0～5cm的土层内显著低于未做覆盖处理的对照,降低了79.49%;叠加薄膜覆盖处理的入侵杂草全部死亡且无种子萌发。说明冬季采用水稻秸秆覆盖,春季再叠加覆盖薄膜能有效防控三叶鬼针草的生长蔓延,在薄膜覆盖之前,覆盖1.5 kg·m~(-2)稻秆的处理对三叶鬼针草的防控效果要好于1 kg·m~(-2)的处理,在薄膜覆盖处理后,两个稻秆覆盖量处理对三叶鬼针草的防控效果均达到100%。本研究结果可为不同季节采用不同的控制方法及其组合模式防控入侵杂草的扩散提供参考。     

Einfluss von Bodeneigenschaften auf die Segetalflora von Ackerflächen

Impact of soil properties on weed distribution within agricultural fields Occurrence and distribution of weeds on agricultural fields are often heterogenous. The influence of various soil properties on the spatial structure and density of weed populations was investigated on two agricultural fields with special regard to three weed species (Polygonum amphibium, Cirsium arvense, Veronica hederifolia). Based on field specific sampling grids, weed counting and soil sampling were done. For all grid points, soil analysis was carried out (texture, organic C, total N, pH, soil nutrients P, K, Mg). Soil texture, soil organic C, and soil nutrients are the factors with the highest influence on the occurrence of the species studied.     

The role of imbibition on seed selection by Harpalus pensylvanicus

Invertebrate weed seed predation is an important component of weed seed loss in agricultural fields. This study investigated the role of seed imbibition on the selection and consumption of the seeds of seven common agricultural weed species by Harpalus pensylvanicus De Geer, a granivorous carabid beetle (Coleoptera: Carabidae) that is found throughout North America. The volatile organic compounds released by ambient dry and imbibed weed seeds were quantified, and Y-tube bioassays were conducted to determine if H. pensylvanicus individuals responded to volatile compounds released from weed seeds. H. pensylvanicus individuals were found to consume higher masses of seeds for each weed species examined in imbibed versus ambient dry trials (P < 0.05). Larger seeded species had the greatest increase in mass consumption between dry seed and imbibed seed trials. The seeds from the seven weed species examined released carbon dioxide and ethylene when ambient dry and imbibed, but H. pensylvanicus adults were only able to detect weed seeds through olfaction when volatile release was highest as a result of imbibition. These results demonstrate that seed imbibition is important in determining seed detection and consumption by invertebrates and may affect seed banks in agricultural fields.