Browsing by Subject "Bildanalyse"

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Development of a sensor-based harrowing system using digital image analysis to achieve a uniform weed control selectivity in cereals
(2021) Spaeth, Michael; Gerhards, Roland
Using intelligent sensor technology for site-specific weed control can increase the efficacy of traditional weed control implements. Several scientific studies successfully used intelligent sensors for automatic harrow control by taking many different parameters into account such as weed density, soil resistance factor, and plant growth. However, none of the systems was practically feasible because these factors made the control system too complex and unattractive for farmers. Defining only one parameter (crop soil cover) instead of many provides a new and simple approach which was investigated in this work. The first scientific publication focuses on the development, practical implementation and testing of the automatic harrow control system. Two RGB-cameras were mounted before and after the harrow and constantly monitored crop cover. The CSC was then computed out of these resulting images. The image analysis, decision support system and automatic control of harrowing intensity by hydraulic adjustment of the tine angle were installed on a controller which was mounted on the harrow. Eight field experiments were carried out in spring cereals. Mode of harrowing intensity was changed in four experiments by speed, number of passes and tine angle. Each mode was varied in five intensities. In four experiments, only the intensity of harrowing was changed. Modes of intensity were not significantly different among each other. However, intensity had significant effects on WCE and CSC. Cereal plants recovered well from 10% CSC, and selectivity was in the constant range at 10% CSC. Therefore, 10% CSC was the threshold for the decision algorithm. If the actual CSC was below 10% CSC, intensity was increased. If the actual CSC was higher than 10%, intensity was decreased. The new system was tested in an additional field study. Threshold values for CSC were set at 10%, 30% and 60%. Automatic tine angle adjustment precisely realised the three different CSC values with variations of 1.5% to 3%. The next publication discussed and assessed the site-specific field adaptation of the development in cereals. In 2020, three field experiments were conducted in winter wheat and spring oats to investigate the response of the weed control efficacy and the crop to different harrowing intensities, in southwest Germany. In all experiments, six levels of CSC were tested. Each experiment contained an untreated control and an herbicide treatment as a comparison to the harrowing treatments. The results showed an increase in the WCE with an increasing CSC threshold. Difficult-to-control weed species such as Cirsium arvense (L.) and Galium aparine (L.) were best controlled with a CSC threshold of 70%. With a CSC threshold of 20% it was possible to control up to 98% of Thlaspi arvense (L.) The highest crop biomass, grain yield, and selectivity were achieved with an CSC threshold of 20–25% at all trial locations. With this harrowing intensity, grain yields were higher than in the herbicide control plots and a WCE of 68–98% was achieved. The last scientific article compares pairwise a conventional harrow intensity with automatic sensor-based harrowing intensity. Five field experiments in cereals were conducted at three locations in southwestern Germany in 2019 and 2020 to investigate if camera-based harrowing resulted in a more homogenous CSC and higher WCE, biomass, and crop grain yield than a conventional harrow with a constant intensity across the whole plot. For this purpose, pairwise comparisons of three fixed harrowing intensities (10 °, 40 °, and 70 ° tine angle) and three predefined CSC thresholds (CSC of 10%, 20%, and 60%) were realized in randomized complete block designs. Camera-based adjustment of the intensity resulted in 6-16% less standard deviation variation of CSC compared to fixed settings of tine angle. Crop density, WCE, crop biomass and grain yield were significantly higher for camera-based harrowing than for conventional harrowing. WCE and yields of all automatic adjusted harrowing treatments were equal to the herbicide control plots. In this PhD-thesis, a sensor-based harrow was developed and successfully investigated as an alternative to conventional herbicide application in cereals. A permanent, equal replacement of chemical weed control in arable farming systems can only be achieved using modern, sensor-based mechanical weed control approaches. Therefore, the efficacy of the mechanical weed control method can be improved and increased continuously. It has been shown that the precise adjustment of mechanical weed control methods to site-specific weed conditions allows similar WCE results as an herbicide application without causing yield losses. These findings contribute towards modern plant protection strategies to reduce the herbicide use and to establish the acceptance of technical progress in society.
Untersuchungen zum Herbizidstress in Zuckerrüben mit drei feldtauglichen optischen Sensoren und Methoden der Bildanalyse
(2014) Roeb, Johannes
Weed management in sugar beets is based on the repeated use of herbicide mixtures after crop emergence. Due to the limited selectivity of active ingredients, herbicide treatments not only control the weeds but will reduce the growth of sugar beets also. Yield losses due to herbicide stress are expected to range between 5-15%. Using optical sensors is a nondestructive method to assess changes in reflection, leaf fluorescence or chlorophyll fluorescence kinetics induced by herbicides. To evaluate the applicability of three optical sensors for assessing herbicide stress and to measure the influence of herbicides and herbicide mixtures on sugar beets, a pot experiment was performed at the University of Hohenheim, Germany. Sugar beets were grown under natural light and temperature conditions and treated with the active ingredients metamitron, phenmedipham, desmedipham, ethofumesate, triflusulfuron-methyl and dimethenamid-P in their commercially available formulation and practical dosage. In total five single herbicides as well as five different herbicide mixtures were applied in the cotyledon stage (EC 10), the two-leaf stage (EC 12) or the four- to six-leaf stage (EC 14/16) of sugar beets. Stress reactions were monitored with three optical sensors: Images of a digital camera (Canon EOS 1000D) were used to determine leaf coverage area, plant shape and leaf color. Measurements were performed about every second day and a growth index had been calculated. A multispectral fluorometer (FORCE-A MULTIPLEX®) was used to detect the blue-green fluorescence, red fluorescence and far-red fluorescence and to calculate fluorescence indices. A portable imaging sensor of chlorophyll fluorescence kinetics (WALZ IMAGING PAM) was used on a daily basis to determine changes in the maximum quantum efficacy (Fv/Fm) induced by herbicide treatments. Four respectively two weeks after the treatment sugar beets were harvested for dry matter analysis. For each of the herbicide treatments and for each of the three application dates five Mitscherlich pots were used for replication. Each pot had about four sugar beet plants. Based on digital imaging it was possible to measure leaf coverage area and determine growth depressions induced by herbicide treatments containing mixtures of the active ingredients phenmedipham, desmedipham and ethofumesate. Herbicide mixtures with more active ingredients increased the stress reaction of sugar beets. Differentiation between untreated plants and sugar beets treated with different herbicides or mixtures was possible a few days after application. Results were correlated with dry matter. Changes in plant shape parameters indicated a delayed development of herbicide treated plants. Higher red content of leaf color was attributed to a relative loss of chlorophyll. Measurements with the FORCE-A MULTIPLEX® fluorometer detected an increase in red and far-red fluorescence but not blue-green fluorescence within 1-2 days after treatments with the aforementioned mixture of active ingredients. About the same trends were found at all application dates. Most fluorescence values were affected by growth stage and leaf area of sugar beets. Thus, although differences between treated and untreated plants were strong, it was not possible to discriminate between stress reactions on different herbicide treatments. Based on the maximum quantum efficacy (Fv/Fm) measured with the WALZ IMAGING-PAM chlorophyll fluorescence sensor previous studies, describing the time course of stress reaction on application of PSII-inhibitors in sugar beets were confirmed. After a strong decrease of Fv/Fm within one day, recovery to the initial value was observed within ten days. Quantification of herbicide stress induced by PSII-inhibitors was possible due to different intensities and durations of the stress reaction. Photochemical stress response to treatments with metamitron or chloridazon was lower than with products containing phenmedipham or desmedipham. Stress reaction on herbicide mixtures not only depended on content of PSII-inhibitors but also on formulation. Weather conditions were more important than the sugar beet development stage considering the stress reaction. Observations from previous studies, indicating an increase in herbicide stress after precipitation and at low temperatures, were also confirmed in this study. Differences in stress reactions of cotyledons and first true leaves can be explained by a higher uptake of herbicides in young tissues. The influence of other herbicides, mixtures, dosages and formulations on herbicide stress in sugar beets has to be further investigated. Moreover the complex interrelations between sugar beet development stage, weather conditions and stress reaction could only be investigated in systematic field trials. For the measurement of stress reactions on herbicides the described optical sensors and methods can be used, each having different advantages and disadvantages.