Christian Andreasen

Weed Mapping with Co-Kriging Using Soil Properties

Our aim is to build reliable weed maps to control weeds in patches. Weed sampling is time consuming but there are some shortcuts. If an intensively sampled variable (e.g. soil property) can be used to improve estimation of a sparsely sampled variable (e.g. weed distribution), one can reduce weed sampling. The geostatistical estimation method co-kriging uses two or more sampled variables, which are correlated, to improve the estimation of one of the variables at locations where it was not sampled. We did an experiment on a 2.1ha winter wheat field to compare co-kriging using soil properties, with kriging based only on one variable. The results showed that co-kriging Lamium spp. from 96 0.25m2 sample plots ha−1 with silt content improved the prediction variance by 11 % compared to kriging. With 51 or 18 sample plots ha−1 the prediction variance was improved by 21 and 15 %.

Survival of weed seeds and animal parasites as affected by anaerobic digestion at meso- and thermophilic conditions

Anaerobic digestion of residual materials from animals and crops offers an opportunity to simultaneously produce bioenergy and plant fertilizers at single farms and in farm communities where input substrate materials and resulting digested residues are shared among member farms. A surplus benefit from this practice may be the suppressing of propagules from harmful biological pests like weeds and animal pathogens (e.g. parasites). In the present work, batch experiments were performed, where survival of seeds of seven species of weeds and non-embryonated eggs of the large roundworm of pigs, Ascaris suum, was assessed under conditions similar to biogas plants managed at meso- (37°C) and thermophilic (55°C) conditions. Cattle manure was used as digestion substrate and experimental units were sampled destructively over time. Regarding weed seeds, the effect of thermophilic conditions (55°C) was very clear as complete mortality, irrespective of weed species, was reached after less than 2 days. At mesophilic conditions, seeds of Avena fatua, Sinapsis arvensis, Solidago canadensis had completely lost germination ability, while Brassica napus, Fallopia convolvulus and Amzinckia micrantha still maintained low levels (~1%) of germination ability after 1 week. Chenopodium album was the only weed species which survived 1 week at substantial levels (7%) although after 11 d germination ability was totally lost. Similarly, at 55°C, no Ascaris eggs survived more than 3h of incubation. Incubation at 37°C did not affect egg survival during the first 48 h and it took up to 10 days before total elimination was reached. In general, anaerobic digestion in biogas plants seems an efficient way (thermophilic more efficient than mesophilic) to treat organic farm wastes in a way that suppresses animal parasites and weeds so that the digestates can be applied without risking spread of these pests.

Use of Image Analysis to Assess Color Response on Plants Caused by Herbicide Application

Abstract In herbicide-selectivity experiments, response can be measured by visual inspection, stand counts, plant mortality, and biomass. Some response types are relative to nontreated control. We developed a nondestructive method by analyzing digital color images to quantify color changes in leaves caused by herbicides. The range of color components of green and nongreen parts of the plants and soil in Hue, Saturation, and Brightness (HSB) color space were used for segmentation. The canopy color changes of barley, winter wheat, red fescue, and brome fescue caused by doses of a glyphosate and diflufenican mixture, cycloxydim, diquat dibromide, and fluazifop-p-butyl were described with a log-logistic dose–response model, and the relationship between visual inspection and image analysis was calculated at the effective doses that cause 50% and 90% response (ED50 and ED90, respectively). The ranges of HSB components for the green and nongreen parts of the plants and soil were different. The relative potencies were not significantly different from one, indicating that visual and image analysis estimations were about the same. The comparison results suggest that image analysis can be used to assess color changes of plants in response to some herbicides and may have the potential to provide an objective measurement of symptoms. Nomenclature: Cycloxydim; diflufenican; diquat dibromide; fluazifop-p-butyl; glyphosate; brome fescue, Vulpia bromoides (L.) S.F. Gray; barley, Hordeum vulgare L; red fescue, Festuca rubra L; wheat, Triticum aestivum L. Resumen En experimentos de selectividad de herbicidas, la respuesta puede ser medida mediante inspección visual, conteo de plantas establecidas, mortalidad de plantas y biomasa. Algunos tipos de respuesta son relativos al testigo no-tratado. Nosotros desarrollamos un método no-destructivo que analiza imágenes digitales a color para cuantificar cambios en el color de las hojas causados por herbicidas. El rango de los componentes de color de partes verdes y no-verdes de las plantas y el suelo en el ámbito de tono, saturación y brillo (HSB) de color fue usado para la segmentación. Los cambios en el color del dosel de cebada, trigo de invierno, Festuca rubra y Vulpia bromoides causados por dosis de una mezcla de glyphosate y diflufenican, cycloxydim, diquat dibromide, y fluazifop-p-butyl fueron descritos con un modelo log-logístico de respuesta a dosis, y la relación entre la inspección visual y el análisis de imagen fue calculada a dosis efectivas que causaron una respuesta del 50% y 90% (ED50 y ED90, respectivamente). Los rangos de los componentes de HSB para las partes verdes y no-verdes de las plantas y el suelo fueron diferentes. Las potencias relativas no fueron significativamente diferentes de uno, indicando que las estimaciones del análisis visual y del de imagen fueron casi las mismas. Los resultados de la comparación sugieren que el análisis de imagen puede ser usado para evaluar los cambios de color de las plantas en respuesta a algunos herbicidas y podría tener potencial para brindar una medida objetiva de los síntomas.

Controlling Grass Weeds on Hard Surfaces: Effect of Time Intervals between Flame Treatments

Abstract An experiment was conducted on a specially designed hard surface to study the impact of time interval between flaming treatments on the regrowth and flower production of two grass weeds. The goal of this experiment was to optimize the control of annual bluegrass and perennial ryegrass, both species that are very difficult to control without herbicides. Aboveground biomass from 72 plants per treatment was harvested and dry weights were recorded at regular intervals to investigate how the plants responded to flaming. Regrowth of the grasses was measured by harvesting aboveground biomass 2 wk after the second flaming treatments that were implemented at different time intervals. Flaming treatments decreased plant biomass of both species and also the ratio of flowering annual bluegrass plants. However, few plants were killed. The first flaming treatment affected aboveground biomass more than the second flaming treatment. A treatment interval of 7 d provided the greatest reduction in regrowth of perennial ryegrass, whereas the effect of treatment interval varied between the first and second repetitions of this experiment for annual bluegrass. In general, short treatment intervals (3 d) should be avoided, as they did not increase the reduction of aboveground biomass compared with the 7-d treatment interval. Knowledge on the regrowth of grass weeds after flaming treatments provided by this study can help improve recommendations given to road keepers and park managers for management on these weeds. Nomenclature: Annual bluegrass, Poa annua L.; perennial ryegrass, Lolium perenne L.

The Effect of Reduced Light Intensity on Grass Weeds

The effect of reduced light intensity on the growth and development of three common grass weeds, blackgrass, silky windgrass, and annual bluegrass, was studied. Two identical greenhouse experiments displaced in time were performed with six light levels aiming at 0%, 20%, 50%, 80%, 90%, and 95% shade corresponding to a mean daily light integral (DLI) of 12.4, 9.63, 7.13, 2.74, 0.95, and 0.69 mol m?2 d?1 in experiment 1 and 21.2, 18.0, 10.7, 3.71, 1.64, 1.20 mol m?2 d?1 in experiment 2. Climate screens of acrylic fabric were used to create the light levels. A DLI of 0.69 to 3.71 mol m?2 d?1 substantially reduced the plant height, the number of leaves, leaf chlorophyll content index, stomatal conductance, maximum photochemical efficiency of photosystem II, and dry matter of blackgrass. It also reduced plant height, the number of leaves, and dry matter and delayed flowering of windgrass and annual bluegrass. Annual bluegrass reacted most rapidly when light levels increased from the lowest levels by producing more leaves. DLI thresholds for blooming were estimated to be about 7.13 mol m?2 d?1 for windgrass and 1.64 mol m?2 d?1 for annual bluegrass. Annual bluegrass was able to bloom and sustain biomass even at a DLI of 1.64 mol m?2 d?1. This ability may contribute to an explanation of why annual bluegrass is among the most common weed species in highly competitive and well-fertilized crops even though it is much smaller than the two other grass species. Nomenclature: Blackgrass, Alopecurus myosuroides Huds.; silky windgrass, Apera spica-venti (L.) Beauv.; annual bluegrass, Poa annua L.

A note on the analysis of germination data from complex experimental designs

In recent years germination experiments have become more and more complex. Typically, they are replicated in time as independent runs and at each time point they involve hierarchical, often factorial experimental designs, which are now commonly analysed by means of linear mixed models. However, in order to characterize germination in response to time elapsed, specific event-time models are needed and mixed model extensions of these models are not readily available, neither in theory nor in practice. As a practical workaround we propose a two-step approach that combines and weighs together results from event-time models fitted separately to data from each germination test by means of meta-analytic random effects models. We show that this approach provides a more appropriate appreciation of the sources of variation in hierarchically structured germination experiments as both between- and within-experiment variation may be recovered from the data.

Effect of reduced oxygen concentration on the germination behavior of vegetable seeds

Oxygen (O2) in the soil is necessary for the germination of seeds, but it can be reduced by excessive water contents, compaction, compression, and hard surfaces. Reduced O2 concentrations may change the germination success (proportion of seeds germinated; d) and speed (time to reach 50% germination; t50) of seeds. Independent laboratory experiments tested the germination of nine economically valuable vegetable species at five O2 concentrations (20.9, 15, 10, 5, and 2.5%). Members of the Asteraceae (butterhead lettuce and iceberg lettuce) and Brassicaceae (broccoli and white cabbage) families germinated best at 20.9% O2 and 15% O2, but were also able to germinate at 5-2.5% O2. Members of the Apiaceae (carrot, celeriac, and parsley) were sensitive to 5-2.5% O2 concentrations, which reduced their d and increased their t50. The germination rate of Swiss chard (Amaranthaceae) consistently declined as O2 concentrations reduced from 20.9% O2 to 2.5% O2. There was a slight variation in the germination response to O2 concentration between the morphotypes of Brassica oleracea, (white cabbage, broccoli and cauliflower), although it was unclear whether this was related to seed age, genetic variation, or the conditions experienced during seed production or storage. The seeds of the Brassicaceae (broccoli and white cabbage) and Asteraceae (butterhead lettuce and iceberg lettuce) were less sensitive to reduced O2 concentrations and therefore may be more suitable for soils suffering from low O2 concentrations, such as compacted soils with hard surfaces or waterlogged soils.

Image analysis as a non-destructive method to assess regrowth of weeds after repeated flame weeding

Abstract Efficient non-chemical weed control like flame weeding often requires repeated treatments. In weed control experiments the effect of each treatment may be estimated by removing and weighing the remaining weed biomass after the treatment, but the method influences the weed plants ability to regrow, and therefore it may influence the long-term effect of repeated treatments. Visual assessment of weed cover or image analysis do not affect the remaining parts of the weed plants after treatment, but the methods may have other disadvantages. In order to evaluate and compare three methods we measured changes in vegetation cover of perennial ryegrass after flaming by (1) a simple image analysis programme counting green pixels, (2) visual assessment of images and (3) by taking biomass samples. Plants were flame treated with eight different dosages (0, 20, 30, 35, 45, 60, 90 and 180 kg propane ha−1) and with various treatment frequency (2, 4, 6, 8 and 10 yearly treatments). Image analysis and visual assessment of images were easy methods to measure vegetation cover. The experiments showed that increasing dosages and frequent treatments resulted in increasing reduction of plant weight and vegetation cover. However, there were significant differences in the estimated effective doses (e.g., ED50 and ED90 values) depending on assessment method and treatment frequency. One reason could be that image analysis and visual assessment did not affect the remaining weed parts after treatment and therefore gave a more realistic picture of the long-term effect of repeated treatments. Image analysis was most useful for assessing the effect of repeated treatments when weed cover was relatively low (below 40%) and when plots contained relatively much withered plant material. However, when weed cover is close to 100%, dry weight measurements reflected the effect of the treatment better.

Trends and drivers of on-farm conservation of the root legume ahipa (Pachyrhizus ahipa) in Bolivia over the period 1994/96–2012

The leguminous Andean root crop ahipa has become scarce and the current status of in situ conservation in Bolivia is concerning. Agro-biodiversity changes affect the use, conservation and socio-economic trends for ahipa (Pachyrhizus ahipa) and to substantiate this, a comparison of two cropping periods were made. Aspects of root production and the shift from cultivation of ahipa to cash crops such as maize were compared for two periods: (a) 1994/96 and (b) 2012. Our study showed that the price of ahipa had not increased in 70% of the urban markets; hence, there is little incentive to retain the cultivation of ahipa. We found that rural ahipa growers selected the largest seeds, but did not select seeds by colour. The mixed seed colour predominated the conservation of ahipa. Laborious yield enhancing practices required in field management and low market value endanger future conservation of the ahipa. We conclude that additional research is needed in order to safeguard the extant variation of ahipa, i.e. nutritional value, taste, stress tolerance and market potential.

Hypoxia Improves Germination of the Problematic Invader Garlic Mustard (Alliaria petiolata) of North American Forests

Abstract Garlic mustard [Alliaria petiolate (M. Bieb.) Cava & Grande] is a problematic European invader of temperate Eastern North American forests. We studied its germination response at reduced oxygen (O2) concentrations. Seeds of garlic mustard were exposed to different O2 concentrations (20.9, 15, 10, 5, and 2.5 %) in two laboratory experiments. Germination rate increased, and it took fewer days to attain 50 % germination (t50) at 15 % O2 than at 20.9 % O2. Germination declined at 5 % O2, and seedlings became stunted at 2.5 % O2. The ability of garlic mustard to thrive under low O2 concentrations may allow it to invade a wide variety of suboptimal habitats, such as shady understories where leaf litter cover the forest floors and on compressed and compact soils. Its ability to grow at low O2 levels may contribute to its invasiveness.