Biodiversity and agro-ecology in field margins

During the last decades, structural, floristic and faunistic diversity of the agricultural landscapes in Northern and Western Europe has declined considerably owing to the intensification of agriculture from the 1950’s on. In reaction to biodiversity loss, EU policy pursuited the ecologisation and multifunctionality of agriculture. Field margins do pioneering work in the ecologisation of agriculture since they are the interface between intensive farming practices and the wider environment. The presented multidisciplinary study investigates agro-ecological functions (nature conservation, agriculture, environment) and implications of newly created, unfertilised, sown and unsown field margin strips installed on ex-arable land to increase biodiversity. Margin strips were mown twice a year with a late first cut on 15 June and a regrowth cut on 15 September to meet nature conservation purposes. From conservational concern, species diversity on the long term seemed unaffected by the type of plant community that was installed. The decrease in species diversity was more pronounced under a mowing regime without removal of cuttings. The annual addition of mown roadside herbage significantly enhanced species richness. Convergence in vegetation composition between sown and unsown plots occurred in terms of species importance. From agricultural concern, the importance of economically important weeds Elymus repens Gould, Cirsium arvense L. and Urtica dioica Scop. was significantly higher when cuttings were not removed and in the unsown community. Seed dispersal into the adjacent crop was only of importance one year after installation of the margin strips; seedrain was significantly 8 times higher nearby the unsown community than nearby sown communities. The feeding value of herbage from field margin strips was low compared to the feeding value of herbage harvested in agricultural managed fertilized grassland, limiting its use in rations for highly productive livestock. From environmental concern, the reduction of soil mineral N nearby the boundary by the presence of a margin strip was responsable for the increase in abundance of less competitive species and enrichment of species diversity within the semi-natural boundary

Impact of land use on vegetation composition, diversity and potentially invasive, nitrophilous clonal species in a wetland region in Flanders

In the framework of a nature conservation project in a wetland region of Meetkerke, Belgium, a comprehensive study was conducted to analyse and to compare species composition and diversity among wet grasslands under the six following types of agricultural land use: pastures used at high or low stocking rate, hayfields used at high or low mowing frequency, abandoned hayfields and hay pastures. The focus of the study was on the effects of grassland management on species diversity and on the restriction of occurrence of invasive clonal species. The results show that species importance was strongly related to grassland exploitation parameters and soil hydrological parameters, as shown by the ordination diagram drawn by canonical correspondence analysis (CCA). Species number and importance of non-leguminous dicotyledons were negatively correlated to intensity of use, N supply, water table depth and soil drainage. Phalaris arundinacea, an invasive species which might reduce species diversity, was better suppressed in grazed grassland than in mown grassland. Phalaris arundinacea and Cirsium arvense were most prevalent in abandoned hayfields. Grazing at low stocking rate was the best management technique to maximise plant diversity while restricting invasion by nitrophilous clonal species. Although species-rich and of high complementary value on a landscape scale, haylands mown at low frequency are at higher risk of invasion by clonal species

Differential sensitivity of locally naturalized Panicum species to HPPD- and ALS-inhibiting herbicides

Panicum schinzii (Transvaal millet), P. dichotomiflorum (Fall panicum) and P. capillare (Witchgrass) are alien panicoid grasses that have gradually spread and are now locally naturalized in corn fields in Belgium. One of the possible reasons for their expansion in corn fields might be a lower sensitivity to post-emergence herbicides acting against panicoid grasses, in particular those inhibiting 4-hydroxyphenyl pyruvate dioxygenase (HPPD) and acetolactate synthase (ALS). Dose-response pot experiments were conducted in the greenhouse to evaluate the effectiveness of five HP-PD-inhibiting herbicides (sulcotrione, mesotrione, isoxaflutole, topramezone, tembotrione) and two AILS-inhibiting herbicides (nicosulfuron, foramsulfuron) for controlling populations of P. schinzii, P. dichotomiflorum and P. capillare (all naturalized Belgian populations except for P. capillare). In another dose-response pot experiment, sensitivity of five local P. dichotomiflorum populations to HPPD-inhibitors and nicosulfuron was investigated. Finally, the influence of growth stage at time of herbicide application on efficacy of topramezone and nicosulfuron for Panicum control was evaluated. Large interspecific differences in sensitivity to HPPD-inhibiting herbicides were observed. Panicum schinzii was sensitive to tembotrione but moderately sensitive to topramezone and poorly sensitive to mesotrione and sulcotrione. However, P. dichotomiflorum was sensitive to mesotrione and topramezone but moderately sensitive to tembotrione. All Panicum species were sensitive to low doses of nicosulfuron and foramsulfuron. Naturalized P. dichotomiflorum populations exhibited differential herbicide sensitivity profiles. All species tested showed a progressive decrease in sensitivity to topramezone and nicosulfuron with seedling age. A satisfactory post-emergence control of Panicum species in the field will require appropriate choice of herbicide and dose, as well as a more timely application (i.e. before weeds reach the four leaves stage)

Hyperspectral classification of Cyperus esculentus clones and morphologically similar weeds

Cyperus esculentus (yellow nutsedge) is one of the world's worst weeds as it can cause great damage to crops and crop production. To eradicate C. esculentus, early detection is key-a challenging task as it is often confused with other Cyperaceae and displays wide genetic variability. In this study, the objective was to classify C. esculentus clones and morphologically similar weeds. Hyperspectral reflectance between 500 and 800 nm was tested as a measure to discriminate between (I) C. esculentus and morphologically similar Cyperaceae weeds, and between (II) different clonal populations of C. esculentus using three classification models: random forest (RF), regularized logistic regression (RLR) and partial least squares-discriminant analysis (PLS-DA). RLR performed better than RF and PLS-DA, and was able to adequately classify the samples. The possibility of creating an affordable multispectral sensing tool, for precise in-field recognition of C. esculentus plants based on fewer spectral bands, was tested. Results of this study were compared against simulated results from a commercially available multispectral camera with four spectral bands. The model created with customized bands performed almost equally well as the original PLS-DA or RLR model, and much better than the model describing multispectral image data from a commercially available camera. These results open up the opportunity to develop a dedicated robust tool for C. esculentus recognition based on four spectral bands and an appropriate classification model

Impact of the quality of organic amendments on size and composition of the weed seed bank

In addition to improving the soil quality, organic amendments of soils may affect weed seed survival, emergence, growth and reproduction. This study evaluated the effects of applications of different qualities of organic amendments on size and composition of the weed seed bank in a field under sequential cropping over 4 years. Fertilisation systems tested included farmyard manure, vegetable fruit and garden waste compost, two types of farm compost differing in carbon:nitrogen (C:N) ratio, cattle slurry and mineral fertiliser. All organically amended plots received equal amounts of C. Crop growth was equalised on all plots by applying supplemental mineral N. Seed bank sampling took place in May 2009 to a depth of 10 cm. The weed seed bank was analysed using the seedling emergence method. Despite equal crop growth in fertilised plots, total seed bank density was lowest in plots amended with compost with low C:N ratio and highest in slurry-amended plots. Observed differences in seed bank densities reflected differences in soil organic carbon content and microbial biomass. At plot level, hard-coated seeds in the seed bank (e.g. Chenopodium spp.) were inversely related to soil microbial activity. Observed differential responses of species to applied fertilisers might be attributed to interspecific differences in resistance against microbial seed degradation. Compost-based fertilisation systems could be sustainable tools for incorporation into integrated weed control strategies aiming at depleting the weed seed bank

Dry matter yield and herbage quality of field margin vegetation as a function of vegetation development and management regime

AbstractDry matter (DM] yield and herbage quality of unfertilized mown field margin strips were studied during early succession in a field experiment over a period of three years. The experiment aimed to maximize botanical diversity and was conducted at two different locations with contrasting soil type and comprised four vegetation types (spontaneously regenerated versus sown vegetation) and three herbage removal strategies (herbage left versus herbage removed). The experimental factors investigated were location, vegetation and herbage removal. Margin strips were mown twice a year with a late first cut around 15 June and a regrowth cut around 15 September to meet nature conservation objectives. Average DM yield over the first three years was not significantly affected by herbage removal but increased significantly over time, irrespective of vegetation or herbage removal. Initially, sown margin strips significantly outyielded unsown margin strips, but differences in DM yield converged over time. The mid-June cut yielded significantly more than the regrowth cut but its herbage quality was significantly lower. Herbage from the unsown margin strip had a significantly better forage quality than herbage from sown margin strips. Forage quality decreased over time, irrespective of location or vegetation. Changes over time in DM yield and quality were attributed to changes in species composition. The herbage quality of field margins was lower than the herbage quality of intensively managed grassland, limiting its use in rations for highly productive livestock

Differences in growth and herbicide sensitivity among Cyperus esculentus clones found in Belgian maize fields

Cyperus esculentus is an invasive troublesome neophyte in many arable crops in Belgium. Applied weed control varies from field to field. One of the possible reasons for this variability might be a differential vegetative and reproductive behaviour among Belgian C.esculentus clones. In this study, growth characteristics and herbicide sensitivity of C.esculentus clones collected in Belgian maize (Zea mays) fields were evaluated. In a morphology Experiment, 25 clones were screened for growth characteristics and ability to set viable seeds under outdoor conditions. Dose-response experiments were conducted in the glasshouse to evaluate the effectiveness of two foliar-applied herbicides (bentazon and glyphosate) and two pre-sowing soil-incorporated herbicides (S-metolachlor and dimethenamid-P) for controlling 14 C.esculentus clones. Response variables were aboveground dry biomass, tuber number, tuber dry biomass and individual tuber dry weight. Clones exhibited large differences in shoot number (up to 3.1-fold), tuber dry biomass (up to 4.7-fold), tuber number (up to 3.4-fold), individual tuber dry weight (up to 4.8-fold), inflorescence number and capacity to set viable seeds. Large interclonal differences in herbicide sensitivity (up to 8.3- and 4.0-fold for aboveground dry biomass and tuber dry biomass, respectively) were observed. Contrary to foliar-applied herbicides, soil-incorporated herbicides were very effective and provided season-long C.esculentus control at doses below the recommended maximum field dose. However, low doses stimulated tuber formation. Future C.esculentus management strategies should take into account differential growth characteristics and herbicide sensitivity of C.esculentus clones

Optimisation of weed control in organic processing spinach (Spinacia oleracea l.) : impacts of cultivar, seeding rate, plant spacing and integrated weed management strategy

Weed control in organic spinach for the processing market is challenging because of the low tolerance of weed contamination in the harvested produce and the limited physical weeding options. Optimisation of weed control systems is therefore urgently needed. Three field experiments with autumn spinach were carried out in organic fields to evaluate the impact of cultivar choice, seeding rate (300 and 400 seeds m(-2)), plant spacing management (10.5-cm-wide single rows and 21-cm-wide single or twin rows) and integrated weed management strategy (combinations of pre-sowing, pre-emergence and post-emergence tactics) on weed biomass and spinach yield and quality. Spinach cultivars with a planophile growth habit and a high growth rate were more weed suppressive than the cultivar with an erectophile growth habit and a slower growth rate. Spinach density was significantly negatively correlated with weed biomass and weed biomass fraction in the harvested produce, but significantly positively correlated with (marketable) spinach biomass and petiole fraction in the harvested produce. Narrow row spacing systems with post-emergence broadcast harrowing had the lowest weed biomass and weed biomass fraction but also the lowest (marketable) spinach biomass as a result of the thinning action of harrowing. Post-emergence harrowing is of key importance for reducing weed biomass in any integrated weed control strategy. Weediness was lowest in systems comprising flaming on false seedbed or in pre-emergence followed by post-emergence harrowing. To mitigate the risk of crop failure, the field should preferably be cropped with quickly growing spinach plants arranged in narrow spaced rows at high plant density and weeded by pre-sowing or pre-emergence flaming followed by post-emergence harrowing