H. Oebel

Hohenheim University, Stuttgart, Baden-Wuerttemberg, Germany

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Publications (5)3.99 Total impact

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    ABSTRACT: Grain yield often varies within agricultural fields as a result of the variation in soil characteristics, competition from weeds, management practices and their causal interactions. To implement appropriate management decisions, yield variability needs to be explained and quantified. A new experimental design was established and tested in a field experiment to detect yield variation in relation to the variation in soil quality, the heterogeneity of weed distribution and weed control within a field. Weed seedling distribution and density, apparent soil electrical conductivity (ECa) and grain yield were recorded and mapped in a 3.5ha winter wheat field during 2005 and 2006. A linear mixed model with an anisotropic spatial correlation structure was used to estimate the effect of soil characteristics, weed competition and herbicide treatment on crop yield. The results showed that all properties had a strong effect on grain yield. By adding herbicide costs and current grain price into the model, thresholds of weed density were derived for site-specific weed control. This experimental approach enables the variation of yield within agricultural fields to be explained, and an understanding of the effects on yield of the factors that affect it and their causal interactions to be gained. The approach can be applied to improve decision algorithms for the patch spraying of weeds.
    No preview · Article · Jun 2008 · Precision Agriculture
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    ABSTRACT: Site-specific weed control requires information on weed infestation and distribution within agricultural fields. For the application of selective herbicides, detailed information on the distribution of all weed species present is needed. Digital image analysis is described as a tool for weed identification. For these purposes, images of the field surface were taken. A high resolution bispectral camera system was developed which simultaneously takes two pixel congruent images in the visible wave band at 610 - 690 nm and in the near infrared wave band > 700 nm. This camera system removed the effect of elements that disturb the images such as organic materials like straw and root residues, stones and shade. Only green plants were represented in the images. This reduced the time for pre-processing of the images and eliminated misclassification due to disturbance. An automatic and dynamic camera control for changing light conditions by atmospheric conditions was developed. Therefore, image acquisition was independent of artificial light and shading. For tests under field conditions, the bi-spectral camera system was mounted on a vehicle equipped with GPS and an on-board computer.
    No preview · Article · Jan 2007
  • R GERHARDS · H OEBEL
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    ABSTRACT: Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Primarily, spatial information allows a potential reduction in herbicide use, when post-emergent herbicides are only applied to field sections with high weed infestation levels. This paper presents a system for site-specific weed control in sugar beet, maize, winter wheat, winter barley, winter rape and spring barley. The system includes on-line weed detection using digital image analysis, computer-based decision making and Global Positioning System-controlled patch spraying. In a 2-year study, herbicide use with this map-based approach was reduced in winter cereals by 6–81% for herbicides against broad leaved weeds and 20–79% for grass weed herbicides. Highest savings were achieved in cereals followed by sugar beet, maize and winter rape. The efficacy of weed control varied from 85% to 98%, indicating that site-specific weed management will not result in higher infestation levels in the following crops.
    No preview · Article · May 2006 · Weed Research
  • H. Oebel · R. Gerhards
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    ABSTRACT: A technology of site-specific weed control using digital image analysis and georeferenced application maps has been applied since 2004 in cereals, rape, maize and sugar beet. For camera-guided weed sampling, bi-spectral cameras took well focused grey scale images with a strong contrast of crops and weeds. For the identification of weed species, characteristic shape features of plants were calculated and compared with a database. With an identification rate from 73 % (malt barley) up to 77 % (sugar beets) application maps were created from classified images for site-specific weed control. Site-specific herbicide application was performed using a GPS-controlled patch sprayer with three separated hydraulic circuits. Herbicide savings ranged from 22 % to 70 % for grass weed species and from 4 % to 80 % for broadleaf weed species. Average savings of site-specific weed control were 27.30 €/ha. Therefore, calculated costs of 16.26 €/ha for camera-guided weed sampling and site-specific weed control using a three-chambered patch sprayer were compensated.
    No preview · Article · Jan 2006
  • R. Gerhards · D. Dicke · H. Oebel
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    ABSTRACT: Field experiments were conducted to test and analyse decision rules for site-specific weed control in malt barley using a geographic information system (GIS). Weed seedling distribution was assessed prior to post-emergence herbicide application. A low and a high weed density threshold were set for site-specific weed management using a GPS-controlled boom sprayer. Application maps were created to direct the sprayer. The sprayer varied the herbicide dosage and mixture depending on the information in the application map. Site-specific weed control resulted in a total reduction of 54 % herbicides directed against Galium aparine and Cirsium arvense, 23 to 96 % herbicides sprayed against grass weeds and 7 to 93 % herbicides applied against broad-leaved weeds. Weed species in the field did not cause significant grain yield reduction. However, C. arvense and A. fatua patches with densities higher than 5 plants/m2 reduced the grain protein content and size sufficiently to result in a complete loss of valuable malting premiums.
    No preview · Article · Sep 2005 · Journal of Plant Diseases and Protection