Influences of long‐term different types of fertilization on weed community biodiversity in rice paddy fields

In order to provide a scientific basis for developing integrated weed management strategies in rice paddy fields, this study investigated the influences of different types of fertilization on weed biodiversity. The experiment was conducted at Long‐term‐located Monitoring Station for Soil Fertility, Agricultural Science Academy, of Jiangxi Province, China. Five fertilization treatments were set: no fertilization (NOF), PK, NP, NK, and NPK. The results showed that the influence of different fertilization treatments on weed community traits followed the models PK > NOF > NK > NP > NPK for species richness, PK > NOF > NK > NP > NPK for species diversity, NPK > NP > NK > NOF > PK for community dominance, and PK > NOF > NK > NP > NPK for community evenness. Under NPK (i.e. balanced fertilization), the weed species diversity and richness and weed community evenness were the lowest. The principal component analysis showed that the weed community was divided into three groups: (i) NK and a part of NOF; (ii) NP and NPK; and (iii) PK and NOF. The correlation analysis indicated that the influence of each macro‐element on the weed community followed the model N > P > K. The organic content in the paddy soil might have played an equally important role with the amount of available N in determining the weed community's characteristics. Regarding the way by which N, P, and K influenced the weed community, the amount of available P and K mainly influenced the organic content, while the amount of available N influenced both the organic content and light transmittance within the canopy, thereby enhancing the capacity of rice to compete with weeds.     

Effects of Azolla species on weed emergence in a rice paddy ecosystem

The effects of Azolla pinnata R. Br. on weed emergence were evaluated in terms of plot area coverage by an A. pinnata mat, its biomass production and the amount of weed emergence, using fresh and dry weights, in a rice paddy field experiment. The experiment was conducted following a randomized block design with five combinations of fertilizer and A. pinnata treatments (control, A. pinnata  + superphosphate, A. pinnata  + urea, A. pinnata  + compound fertilizer, A. pinnata  + cow manure). The results revealed that after 18 days of inoculation, all superphosphate (T1) and cow manure (T4)-treated plots were fully covered by the A. pinnata mat. However, coverage of the urea (T2) and compound fertilizer (T3)-treated plots were only 80% and 70%, respectively. The full plot area coverage by the A. pinnata mat and the highest biomass production with superphosphate and cow manure-treated plots were able to completely inhibit two weed species ( Scirpus juncoides Roxb. var. hotarui Ohwi and Monochoria vaginalis Burm. f. Presl var. plantaginea (Roxb.) Solms-Laub) and significantly suppressed four other weeds ( Cyperus serotinus Rottb, Echinochla oryzicola Vasing, and Eclipta prostrata L.). In all the treatments, the fresh weight of weeds significantly reduced to 13, 29, 34, and 9%, respectively, for treatments T1, T2, T3, and T4. The dry weights also were significantly reduced to 10.00, 16.00, 22.00, and 7.26%, respectively, for treatments T1, T2, T3, and T4 over the control. The results revealed that there was a significant correlation among plot area coverage by the A. pinnata mat, its biomass production and weed emergence in a rice paddy field over the control. Azolla pinnata did not have any detrimental effect on the growth of rice plants.     

No‐tillage increases nitrogen scavenging by fallow weeds in a double‐season rice cropping system in China

Naturally occurring fallow weeds are an alternative strategy for reducing nitrogen (N) loss from annual cropping systems by scavenging inorganic N from the soil. Soil tillage is a major factor affecting the growth of weed populations. This study was carried out to determine the effect of a no‐tillage (NT) system on the N scavenging capacity of fallow weeds in a double‐season rice cropping system. A fixed field experiment was carried out at the Experimental Farm of Hunan Agricultural University, Hunan Province, China, from 2008 to 2011. The results indicated that NT had 80% greater aboveground biomass of fallow weeds than conventional tillage (CT). There was no significant difference in N concentration in fallow weeds between NT and CT. N uptake by fallow weeds was 82% higher under NT than under CT. The stem density of fallow weeds was 50% higher under NT than under CT. The difference in the single‐stem biomass of fallow weeds was not significant between NT and CT. These results suggest that the N scavenging capacity of fallow weeds in the double‐rice cropping system can be increased by increasing the stem density and aboveground biomass through the adoption of NT farming. Our study identifies a potential new ecosystem service provided by NT farming.     

Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

Weed competition and nutrient scarcity often restrict organic cereal production, especially where the availability of livestock manure is limited. While harrowing of annual weeds and legume cover crops can be used, these methods are both executed in early spring and may hinder each other. Two cycles of a 2‐year crop rotation were carried out in south‐east Norway (60°42′N, 10°51′E, altitude 250 m) with weed harrowing and undersown cover crops (WHCC) at two fertiliser rates (40 and 100 kg nitrogen ha^?1). The effect of the WHCC treatments was measured by weed density and species, weed biomass, changes in weed seedbank and grain yield. The weed density depended on the interaction between WHCC, fertiliser and year. On average, pre‐emergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while pre‐ and post‐emergence weed harrowing reduced weed density by 59% and weed biomass by 67% compared with the untreated control. Spergula arvensis became more abundant at low rather than at high fertiliser rates. On average, white clover cover crop sown after pre‐emergence weed harrowing resulted in the highest yields for both oat (+12.1%) and wheat (+16.4%) compared with the untreated control. Despite differences in weed population density and biomass among WHCC treatments within years, the weed biomass, weed density and seedbank increased for all WHCC treatments over the 4‐year period. More research is required into improving the efficacy of mechanical and cultural weed suppression methods that organic systems rely on.     

上海市水稻田杂草种类组成及群落特征

为明确上海市水稻田杂草种类组成及其群落结构,采用倒置"W"取样法对上海市水稻田杂草进行了调查。结果表明,上海市水稻田杂草共有55种(含变种),隶属于16科35属,其中禾本科和莎草科杂草种类最多。优势杂草有无芒稗、千金子、多花水苋、耳叶水苋等4种,区域性优势杂草有马唐、杂草稻、鳢肠、假稻、稗、空心莲子草、水莎草等7种,这11种杂草是上海市水稻田杂草群落的重要建群种,此外常见杂草有8种,一般杂草有36种。从杂草区域分布来看,上海西部地区水稻田杂草群落的物种多样性最高,但优势种集中性最低;东部地区的物种丰富度和优势种集中性均最高;江中沙洲地区的物种丰富度和多样性均最低。从相似性指数和聚类分析来看,上海市水稻田杂草群落可划分为3组,其中东部地区和江中沙洲地区各一组,西部地区和中部地区的杂草群落结构最类似,为一组。水稻田杂草种类及其群落发生特点与地理区域、耕作制度、栽培方式和除草剂种类等多种因素相关。     

Floristic composition and species diversity of weed community after 10 years of different cropping systems and soil tillage in a Mediterranean environment

Sustainable cropping systems based on low inputs have received much attention, even if they may lead to the establishment of a competitive weed flora. This study, conducted from 2011 to 2014 in a Mediterranean environment, evaluated the changes in weed community composition in two cropping systems [conventional (CONV ) and organic (ORG )] with different soil tillage [inversion tillage (IT ) and non‐inversion tillage (NoIT )] in a wheat–tomato–chickpea rotation that began in 2000. The treatments were replicated three times according to a randomised complete block design. The organic system was managed according to EU regulations. Inversion tillage consisted of mouldboard ploughing to a depth of 30 cm, while NoIT consisted of subsoiling to a depth of 20 cm. Weed control was based on herbicide application in CONV and mechanical weeding in ORG . The organic non‐inversion system showed the highest weed biomass (134, 128 and 195 g dry matter (DM ) m^?2 in wheat, tomato and chickpea, respectively) and weed density (66, 77 and 76 plants m^?2 in wheat, tomato and chickpea, respectively), as well as community richness. However, ORG always increased weed diversity, even if annual dicotyledon species were abundant in ORG ‐IT and perennial dicotyledon species in ORG ‐NoIT . The conventional system enhanced the relative frequency of both annual (CONV ‐IT ) and perennial (CONV ‐NoIT ) grasses. There was a negative correlation between density of perennial weeds and crop yield (r ² = 0.24, P  <  0.001). Therefore, in the Mediterranean environment, combining organic practices with non‐inversion tillage could lead to the establishment of perennial weeds that are difficult to control, thus requiring specific weed management practices.     

Effects of duck activities on a weed community under a transplanted rice–duck farming system in southern China

Rice–duck farming is one of the traditional, but current and gradually popularized, ecological farming techniques for paddy rice production in China. In comparison to rice monoculture farming, we investigated a weed community and weed infestation in a transplanted rice–duck farming system and examined the effects of duck activities on the weeds. Three treatments were imposed in the experiment: a rice–duck coculture with duck grazing and disturbance effects, a rice–duck coculture with duck disturbance effects only, and a control (rice monoculture, no duck effects). Rice seedlings were nursed and transplanted in this experiment. The total number of weed species was significantly lower in the treatment with both duck grazing and disturbance and in the treatment with duck disturbance only than in the monoculture rice treatment (control). The Shannon‐Wiener Biodiversity Index of the weed species decreased but the Pielou Evenness Index increased in both treatments with ducks compared to the monoculture control. Sorensen's coefficient of similarity of the weed communities was low between the treatments with ducks and the monoculture control, implying that the weed communities diverged. The total density and biomass of the weed community in both the treatments with ducks were significantly lower compared to the monoculture control. However, compared to the rice monoculture control, the weed biomass was reduced by 98% in the treatment with duck grazing and disturbance and by 84% in the treatment with duck disturbance only, implying that only 14% of the weeds were controlled by duck grazing and that 84% of the weed biomass was inhibited by duck activities in the rice field with ducks. The rice grain yield increased in the treatments with ducks compared to the control. The results suggested that duck activities, like grazing weeds and disturbance of the soil and water, had a significant effect on the weed community structure and that weeds could be well controlled without herbicide application under a rice–duck farming system.     

Effects of loosing Aigamo ducks on the growth of rice plants, weeds, and the number of arthropods in paddy fields

Aigamo duck farming has been noticed as one of the techniques of environmental conservation agriculture. This study was carried out to investigate the effects of loosing Aigamo ducks on the growth and production of rice plants, the quantity of weeds and arthropods, and the balance of nitrogen (N) in paddy fields by changing the density of the Aigamo ducks. A paddy field was divided into three test plots: a 10-Aigamo-duck plot, a five-Aigamo-duck plot, and a weeding plot. The results show that the height, number of culms, and yield crops of the rice plants increased more in the 10-Aigamo-duck plot and the five-Aigamo-duck plot than that of the weeding plot. Millet ( Echinochloa oryzicola ) remained in both the Aigamo duck plots. The weeding plot was covered with monochoria ( Monochoria vaginalis ). In both the Aigamo duck plots, the outbreak of total arthropods was lower than that of the weeding plot, but the number of rice plants damaged by grass leaf rollers ( Cnaphalocrocis medinalis ) was increased. The number of spiders, regarded as useful insects, did not differ that much between the experimental plots. The N content of the soil did not differ as an effect of loosing the Aigamo ducks. The rice plants in the 10-Aigamo-duck plot absorbed more N than the rice plants in the other plots.     

Impact of crop management on weed species diversity and community composition of winter wheat fields in Iran

The aim of this study was to assess the effects of crop management practices on the diversity, structure, and composition of weed communities. A total of 30 fields (15 fields each) in low‐input and conventional farming systems were surveyed in north‐eastern Iran. In the conventional cropping system, both mineral fertilizers and herbicides were applied, while in the low‐input cropping system, the fertilizer was mainly manure and herbicides were avoided. The results showed that the pool of species, species richness, number of unique species, and Shannon's diversity index were greater in the low‐input system than in the conventional system. Both cropping systems had more broad‐leaved species than grasses and more annual species than perennial species. All the multivariate methods of analysis that were applied revealed that the weed community composition was significantly different between the two management types. The low‐input cropping favored herbicide‐susceptible broad‐leaved weeds, legumes, and weeds with biodiversity value, whereas a high proportion of herbicide‐tolerant grasses was found in the conventional fields. The results suggest that low‐input cropping can sustain high weed diversity and abundance.     

Application of bispyribac‐sodium provides effective weed control in direct‐planted rice on a sandy loam soil

An increasing water crisis, as well as the unavailability and high cost of labor, in Pakistan has forced rice‐growers to plant rice directly into the field. However, severe weed infestation causes disastrous effects on the productivity of this rice system. In this study, three herbicides (pendimethalin, penoxsulam and bispyribac‐sodium) were evaluated for weed control in direct‐planted rice on a sandy loam soil. Weedy check and weed‐free plots were established for comparison. Weed infestation decreased the rice yield by 75.2%. However, the application of herbicides suppressed the weed infestation, with a simultaneous increase in the rice yield. The postemergence application of bispyribac‐sodium was the most effective herbicide in reducing the total weed density and dry weight over the weedy check, followed by penoxsulam and pendimethalin, respectively. Bispyribac‐sodium increased the number of productive tillers, 1000‐grain weight, number of grains per panicle and grain yield over the control, as well as improved the water productivity and economic returns of direct‐planted rice. The weeds' proliferation increased the number of unproductive tillers and decreased the plant height. In conclusion, the postemergence application of bispyribac‐sodium can be used effectively to control weeds, increase water productivity and improve the economic returns and yield of direct‐planted rice on a sandy loam soil in Pakistan.     

An on-farm approach to investigate the impact of diversified crop rotations on weed species richness and composition in winter wheat

Weed species diversity may benefit from organic farming due to enhanced temporal diversification of crop species in a rotation and omission of herbicide applications. However, in intensively managed conventional systems, little evidence exists as to what extent diversified crop rotations contribute to higher weed species richness. Using an on-farm approach, the effect of crop rotation (organic, conventional diverse (CD) and conventional simple (CS) crop rotations) and weed control (with vs. without) on weed species richness, cover, community composition and crop biomass, was analysed in 24 winter wheat fields. Weed species with beneficial functions for invertebrates and birds were analysed separately. Weed species richness was higher in the organic crop rotation, but did not differ between CD and CS crop rotations. Weed control treatment reduced species richness in both conventional rotations, but not in the organic one. Redundancy analyses revealed that crop rotation intensity accounted for the largest part of the explained variation in weed species composition. Results from the study indicate that the maintenance of weed species richness and conservation of species with important ecological functions requires not only temporal diversification of crop species in the rotation, but also an adjustment of weed control strategies.     

Effects of soil and crop management practices and pedo‐hydrological conditions on the seedbank size of Galinsoga spp. in organic vegetable fields

Galinsoga quadriradiata and Galinsoga parviflora are very troublesome weeds in many organic vegetable crops in Europe. A very straightforward method to keep Galinsoga infestations under control is by targeting the Galinsoga seedbank. To identify cropping systems able to reduce the seedbank size in vegetable‐based cropping systems, the relationships between the seedbank size of Galinsoga species and prevailing soil/crop management practices and pedo‐hydrological conditions were investigated. Hereto, the seedbank of the 0–20 cm topsoil layer was sampled in 50 organic vegetable fields and analysed according to the seedling emergence method. Field history data were collected for the past 5 years, and physical, chemical and microbial soil quality was determined. Galinsoga quadriradiata was the most frequent and abundant Galinsoga species in the weed seedbank. The genus Galinsoga was present in 90% of the soil weed seedbanks of organic vegetable fields but displayed wide variation in abundance. Smallest Galinsoga seedbanks were found in fields that were predominantly tilled with non‐inversion implements or rotationally ploughed, and continuously cropped with competitive crops during the entire growing season (April 15‐November 15). Contrary to G. quadriradiata, seedbank size of G. parviflora was closely related to soil organic carbon content and sand fraction. Remarkably, soils with a low level of easily plant‐available phosphorus and concomitant high activity of arbuscular mycorrhizae had smaller G. quadriradiata seedbanks. To reduce Galinsoga infestations, fields should preferably be tilled without soil inversion, fertilised with organic amendments with low content of readily plant‐available phosphorus and cropped with competitive crops all season long.     

Long‐term changes in weed occurrence,yield and use of herbicides in maize in south‐western Germany,with implications for the determination of economic thresholds

In 393 field experiments in Baden‐Württemberg region in south‐western Germany, herbicide efficacy, yield loss and crop tolerance of maize (Zea mays) were investigated between 1981 and 2011. The collected data served to determine changes in weed frequencies, in herbicide use, yield loss functions and economic thresholds (ETs). Over 60 weed species were reported. Chenopodium album and Galium aparine were the most frequent broad‐leaved weeds, the former becoming more frequent over time. Species of the genera Lamium, Polygonum, Veronica and Matricaria occurred in about every fifth trial. Alopecurus myosuroides and Echinochloa crus‐galli were the most frequent grass weeds; the former declining in frequency by 1.1% per year, the latter increasing by 1.5%. Results suggest a weed population shift towards thermophilic species. aceto‐lactate‐synthase and 4‐HPPD‐inhibitor herbicides became important in the 1990s. Pendimethalin and bromoxynil have been integral components of weed control since the 1980s. ETs, the point at which weed control operations provide economic returns over input costs, ranged between 3.7% and 5.8% relative weed coverage. Without weed control, no yield increase was found over 24 years. Yield increased by 0.2 t ha ^{? 1} year ^{? 1}, if weeds were controlled chemically. Despite intensive use of effective herbicides in maize, problematic weed species abundance and yield losses due to weed competition have increased in Baden‐Württemberg over a period of 30 years.