The importance of reduced light intensity on the growth and development of six weed species

Crops limit light for photosynthesis and growth of weeds. We studied the effect of reduced light on performance of six weed species [one invasive species (Amsinckia micrantha), three common species (Veronica persica, Capsella bursa‐pastoris, Viola arvensis) and two less common weeds (Anagallis arvensis and Scleranthus annuus)]. In two glasshouse experiments, six light levels were achieved aiming at 0%, 20%, 50%, 80%, 90% and 95% reduction of light and corresponding with daily light integrals (DLI) of 12.4, 9.63, 7.13, 2.74, 0.95 and 0.69 mol m^?2 day^?1 in experiment 1 and 21.2, 18.0, 10.7, 3.71, 1.64 and 1.20 mol m^?2 day^?1 in experiment 2. The number of leaves was strictly controlled by DLI. Chlorophyll content index, maximum photochemical efficiency of photosystem II (F_v/F_m), stomatal conductance, flowering and dry matter were strongly reduced when DLI was reduced to 0.69–3.71 mol m^?2 day^?1 for all species. Threshold DLI for flowering was ca. 3.71 mol m^?2 day^?1 for S. annuus, V. arvensis, A. arvensis and V. persica, while C. bursa‐pastoris deviated by flowering at DLI of 0.95 mol m^?2 day^?1. This may explain why C. bursa‐pastoris is common in the seedbank of Danish arable soils in spite of intensive farming with well‐fertilised and dense crops.     

You cannot fight fire with fire: a demographic model suggests alternative approaches to manage multiple herbicide‐resistant Avena fatua

Multiple herbicide‐resistant (MHR ) weed populations pose significant agronomic and economic threats and demand the development and implementation of ecologically based tactics for sustainable management. We investigated the influence of nitrogen fertiliser rate (56, 112, 168, or 224 kg N ha^?1) and spring wheat seeding density (67.3 kg ha^?1 or 101 kg ha^?1) on the demography of one herbicide susceptible and two MHR Avena fatua populations under two cropping systems (continuous cropping and crop‐fallow rotation). To represent a wide range of environmental conditions, data were obtained in field conditions over 3 years (2013–2015). A stochastic density‐dependent population dynamics model was constructed using the demographic data to project A. fatua populations. Elasticity analysis was used to identify demographic processes with negative impacts on population growth. In both cropping systems, MHR seedbank densities were negatively impacted by increasing nitrogen fertilisation rate and wheat density. Overall, MHR seedbank densities were larger in the wheat‐ fallow compared with the continuous wheat cropping system and seedbank densities stabilised near zero in the high nitrogen and high spring wheat seeding rate treatment. In both cropping systems, density‐dependent seed production was the most influential parameter impacting population growth rate. This study demonstrated that while the short‐term impact of weed management tactics can be investigated by field experiments, evaluation of long‐term consequences requires the use of population dynamics models. Demographic models, such as the one constructed here, will aid in selecting ecologically based weed management tactics, such as appropriate resource availability and modification to crop competitive ability to reduce the impact of MHR .     

The role of models for multicriteria evaluation and multiobjective design of cropping systems for managing weeds

Weeds are both harmful for crop production and important for biodiversity, while herbicides can pollute the environment. We thus need new cropping systems optimising all cultural techniques, reconciling agricultural production, herbicide reduction and biodiversity conservation. Here, we show how to (i) develop models quantifying the effects of cropping systems on weed dynamics, (ii) integrate interactions between weeds and other organisms, (iii) predict the impact on production and biodiversity and (iv) use the model for multicriteria evaluation and multiobjective design of cropping systems. Among the existing weed dynamics models, we chose the one closest to our requirements to illustrate these different steps, that is, FlorSys which predicts multispecific weed dynamics as a function of cultural techniques and pedoclimate. We have illustrated the development of interaction submodels with the example of a crop pathogen whose propagation is increased when infecting grass weeds. To evaluate the weed flora impact, predicted weed densities were translated into indicators of harmfulness (crop yield loss, technical harvest problems, harvest pollution, field infestation, crop disease increase) and biodiversity (weed species richness and equitability, trophic resources for birds, insects and pollinators). Simulations were run over several years and with different weather scenarios (i) to optimise cultural techniques to control harmful weeds, (ii) to analyse the impact of changing agricultural practices (e.g. simplified tillage and rotations, no‐till, temporary crops) on weed density, species and trait composition and (iii) to evaluate cropping systems for their ability to reconcile agricultural production and biodiversity, thus identifying levers for designing sustainable cropping systems.     

Changes in functional diversity and intraspecific trait variability of weeds in response to crop sequences and climate

How weed communities assemble represents one the key issues of weed science. For a decade, functional approaches have been applied to investigate the processes that govern weed community assembly. In most previous studies, trait values have been generally averaged over multiple populations and habitats. Consequently, conspecifics display similar trait values while neglecting the considerable influence of intraspecific variability to detect changes in functional diversity in response to environmental drivers. However, this influence has been shown to be critical, especially, at local scales. Here, we studied changes in weed functional diversity at the field scale in four crop sequences. We focused on intra‐ and interspecific variability of four key functional traits involved in response to resource acquisition processes, the latter being modified by climate, management and competition. The relative influence of intra‐ and interspecific variability among the crop sequence types was highlighted using a diversity partitioning approach. It provides evidence for substantial amount of intraspecific variability in the weed community and underlines its essential role in response to fine‐scale environmental drivers. In addition, we investigated the response of the three most abundant species to competition with the crop, the growing season and the crop sequence type. We highlighted that these species showed a wide range of combinations of trait values, suggesting the co‐existence of several successful strategies. Based on these results, we emphasise that neglecting intraspecific variability can lead to substantial underestimations of the functional weed response to management and crop‐weed competition at the field scale.     

Ecological factors affecting durian production in the forest gardens of West Kalimantan,Indonesia

Whereas a natural ecosystem is stochastically created by mechanism of natural selection, an agroecosystem is systematically fashioned by farmers in response to specificperceived ecological and economic constraints. In this paper, I employ a geographical information systems (GIS) based analysis to examine the beliefs of forest garden owners in West Kalimantan, Indonesia, regarding ecological factors involved in maximizing durian fruit (Durio zibethinus) production. Factors that I tested included individual tree characteristics (age, size, color), microsite factors (on or off ridge, near stream, slope, proximity to rock outcrops, in dry or swampy site), species associations (with other types of trees, spacing to nearest large tree), and the overall position of the garden (on flat land or hill, distance to natural forest). I first conclude that respondents generally had accurate perceptions as to how ecological factors influence durian production. I then briefly discuss how the findings of this study could be used to improve existing and future durian gardens. Finally, I discuss the potential for studying slow-growing agroforestry systems using cross-sectional data collected from plots owned and managed by individual house-holds through the use of a GIS and statistical control.In spite of the high specific richness of the gardens' vegetation ... the place of each plant is carefully chosen, and often corresponds to its ecological niche in the natural forest. Enauiries have shown that people have a certain ecological knowledge in individual care towardseach plant that is in contradicion to the mass treatment of cultivated crops in monoculture.-G.Michon (1983, p.19)     

农业生态多维绩效评价研究进展

【目的】 农业生态多维绩效包括农业生态效率、农业生态承载力、农业生态敏感性、农业生态环境质量和可持续发展能力等,对其进行客观全面的评价能够有效管理农业生产经营方式,为农业决策系统提供支持,有助于可持续发展战略的落实。【方法】 文章分别从评价体系构建、评价指标获取和评价方法选择三方面总结现阶段农业生态多维绩效评价研究进展,并结合国内外实证研究,探究其成果在农业信息化中的应用潜力。【结果】 研究结果表明,农业生态多维绩效研究在国内倾向于作为农业生产者管理农业生产经营方式的数据基础,在国外则偏重农业生态信息系统的创新与模拟。【结论】 该文从适用于小农耕作特点的体系构建,研究结果的完善与推广和农业信息技术的具体应用3个角度提出展望,旨在为我国农业管理与决策以及农业信息化进程提供新思路。     

Increasing weed flora in Danish arable fields and its importance for biodiversity

A number of political initiatives have been implemented to meet growing concerns about negative side effects of the intensification of land‐use practice over the past 25 years. Declining species diversity and abundance and pollution of the environment have been reported worldwide. In order to assess the overall effect on wild flora of the changing management of arable land, national surveys are necessary. Surveys of the weed flora in Danish arable fields were conducted in 1987–89 and 2001–04. The frequency of common weed species in spring barley, spring rape, winter rye, winter wheat and grass leys was compared between time periods. Weed frequency increased overall during the interval. Species that are of particular importance as food sources for invertebrates and birds increased considerably in some of the crops. The frequency of some grass species increased remarkably, possibly because of increased areas of winter crops. Some perennial weeds also became more frequent, probably caused by less mechanical weed control and a reduction in the use of specific herbicides. The dominant weed species in 2001–04, with frequency higher than 10%, were largely the same as in 1987–89, but included three new species in 2001–04. Only a few species occurred less frequently in 2001–04 than in 1987–89 and only in some crops. As common weed species make up an important food reservoir for wildlife, new trends in the management of arable land in Denmark seem to have led to more biodiversity.     

The effect of crop,cultivation and seed addition for birds on surface weed seed densities in arable crops during winter

Weed seeds present an agronomic threat, but are also an important food resource for wildlife in winter. Weed seed densities on the soil surface in winter were examined from 1999 to 2002 in 105 fields on three different farms in UK. The effect of the preceding crop, cultivation, position within the field and the application of seed for birds (bird seed) on surface seed abundance and species composition was tested. Six or fewer species comprised c. 80% of the weed seeds. By January of each study year, the densities of seeds important for farmland birds (key seeds) were 73% or 87% lower compared with early winter on two of the farms, but were stable on the third where seeds were incorporated through cultivation. At the edge and mid‐field, seed densities only exceeded 400 m^?2 in 17%, 10% and 12% of fields for total, key and dicotyledonous seeds respectively. The preceding crop only affected seed densities at one site; stubbles of winter barley had fewer seeds compared with winter wheat or spring barley. Seed densities varied between the edge and mid‐field, but trends were inconsistent between sites. The density of the larger seeds (Atriplex patula, Viola arvensis, Polygonum aviculare and Chenopodium album) were reduced in fields receiving bird seed. The objectives of weed control and conservation may not be mutually exclusive because seed return was most reduced where the ground remained uncultivated through the winter, yet this also provided the best foraging opportunities for surface feeding seed predators.