Anneli Lundkvist

Comparison of monocultures of perennial sow-thistle and spring barley in estimated shoot radiation-use and nitrogen-uptake efficiencies

Abstract Shoot radiation-use efficiency (RUE) and nitrogen-uptake efficiency (UPE) of monocultures of perennial sow-thistle (Sonchus arvensis L.) and spring barley (Hordeum distichon L.) were quantified to assess the significance of these traits for the relative performance of the two species. RUE and UPE were derived for shoot growth and N uptake by calibrating a mechanistic model to above-ground biomass and N observations in an outdoor box experiment, conducted during two years at two soil nitrogen levels in Central Sweden. The model, which is driven by climate variables, predicts above-ground biomass and nitrogen increment as a function of intercepted radiation, temperature, and nitrogen availability. Observed values of leaf area and root development are used as input. Shoot RUE in S. arvensis was only 56% of the RUE in spring barley (1.35 and 2.40 g dry weight MJ−1, respectively). On the other hand, shoot UPE in S. arvensis at low N supply during early season was seven times higher than in barley (0.07 and 0.01 d−1, respectively). For S. arvensis, UPE was higher at the low soil nitrogen level than at high level, while the reverse was found for barley, at a given amount of biomass per area unit. We suggest that the higher shoot UPE in S. arvensis at low nitrogen supply, in comparison with the low UPE of annual small grain crops at low soil nitrogen levels, is a contributing cause for the observed increase in S. arvensis in organic farming.

Modelling species competition in mixtures of perennial sow-thistle and spring barley based on shoot radiation use efficiency

Abstract Perennial sow-thistle (Sonchus arvensis L.) may be a serious weed in organic and conventional farming. To assess the effects of radiation acquisition and resource allocation on competitive ability, S. arvensis was grown together with spring barley (Hordeum distichon L.) in six mixtures in a replacement series with initial above-ground biomass proportions of S. arvensis ranging from 2% to 96%. A one-season experiment was made outdoors in boxes in Uppsala, Sweden, at a low level of nitrogen supply (5 g N m−2). The study tested the predictability of shoot biomass of each species based on two principal assumptions: (i) growth model parameters derived from species in monocultures could be applied in mixtures, and (ii) radiation in the mixed stand was partitioned between species proportional to their leaf area. Calibration of two parameters, for scaling of shoot radiation use efficiency and radiation partitioning respectively, were the base for the evaluation. When the coefficients were close to unity, which was the case for all mixtures dominated by barley, and for one of the mixtures with high proportion of S. arvensis in the early season, observed and predicted shoot biomass coincided well. For the evenly composed mixtures, total shoot biomass was underestimated (the scaling coefficient of shoot radiation use efficiency was>1), whereas the relative composition among species was predicted well. In the late season the principal model assumptions were not applicable to S. arvensis, likely due to increasing root allocation not accounted for in the model. Sonchus arvensis in mixtures with high proportions was planted early in relation to sowing of barley, which resulted in a comparably late development stage of S. arvensis. Consequently the relation between species development stages varied with species composition suggesting a need to introduce effects of differences in development stage into the model.

Selection in Cirsium arvense (L.) Scop. and Sonchus arvensis L.: Susceptibility to MCPA on different types of farmland in Sweden

Abstract During the past century, changes in cropping systems have led to selective pressure on weed flora. The number of competitive species with decreased susceptibility to herbicides has increased, at the cost of more susceptible species. For a long period, the economically important perennial weed species Cirsium arvense (L.) Scop. and Sonchus arvensis L. have mainly been controlled by the herbicide MCPA (phenoxy-acetic acid), which stimulates the weed plant to abnormal growth. However, it has been reported from Sweden, Great Britain, Hungary and North America that C. arvense has become less susceptible to MCPA since the 1950s. Therefore, two greenhouse experiments were performed at Uppsala, Sweden with clones of C. arvense and S. arvensis. The purpose was to study whether ecotypes (clones) from high input farmland, where herbicides had been used intensively and regularly for a long time, were less susceptible to herbicide (MCPA) treatment than ecotypes from low input farmland. Sixty clones of C. arvense and 36 clones of S. arvensis were treated with nine different doses of MCPA. The results supported the suggestion that a shift towards less MCPA-susceptible ecotypes of C. arvense had occurred on high input farmland. Clone material from such farmland had, on average, significantly higher dry matter content after herbicide treatment than ecotypes from low input farmland. Similar decrease in susceptibility was not detected for S. arvensis. This was probably due to S. arvensis generally being less susceptible to MCPA than C. arvense. Sonchus arvensis has therefore being exposed to a lower selection pressure than C. arvense.

Weed Biology and Weed Management in Organic Farming

Weed biology, including the ecology, physiology and population dynamics of weed species, does not differ from plant biology apart from the notion that the plants under investigation are considered to be “unwanted”. Weeds are unwanted and undesirable plants which interfere with the utilization of land and water resources and thus adversely affect human welfare (Rao, 1999). Weed biology research consequently aims to generate knowledge that is expected to be applied in the practical control of weeds, and should include integrated research, from basic to applied, with all elements contributing to real improvements in weed management (Moss, 2008). Management of weeds is performed for the benefit of different interests, ranging from clean and non slippery pavements, to minimizing yield losses in agriculture. The occurrence of weeds in agricultural crops leads to substantial yield reductions causing economic losses all over the world. Crop damage from weeds generally is larger than from other pests (Oerke, 2006). According to FAO (the Food and Agriculture Organization of the United Nations) and the environmental research organization, Land Care of New Zealand, weeds caused yield losses corresponding to

Selective pressure on Cirsium arvense (L.) Scop. and Sonchus arvensis L. growth characteristics on different types of farmland in Sweden

95 billion in 2009. This may be compared with yield losses caused by pathogens (

Effects of selective cutting and herbicide use in spring barley on seed production of Cirsium arvense

85 billion), and insects (

Population dynamics and nitrogen allocation of Sonchus arvensis L. in relation to initial root size

46 billion). The economic losses may even be larger if the costs for weed control measures are included (FAO, 2011). The main reason for controlling weed abundance in agricultural crops is the risk for qualitative and quantitative reductions in crop yields. Black Nightshade (Solanum nigrum L.) is a problematic weed in crops such as peas (Pisum sativum L.), beans (Vicia faba L.) and soybean (Glycine max (L.) Merr.), where it not only causes a yield reduction in the crop, but also reduces crop quality by means of contamination with its poisonous seeds (Defelice, 2003). Common ragwort (Senecio jacobaea L.) is another poisonous species which does occur in temperate grasslands and pastures where it may lead to death of cattle and other livestock (Suter et al., 2007). Not only the fresh herbage is poisonous, but also its hay and silage remains toxic (Luthy et al., 1981; Candrian et al., 1984). A quantitative reduction in crop yield due to weeds foremost is ascribed to the ability of weeds to compete for resources such as light, water and nutrients, at the expense of the crop. The relative competitive ability of weed species is determined by two groups of interacting factors. The first one consists of species characteristics, such as propagation and dispersal features and other life cycle characteristics, and potential growth rate. The second

Modelling below-ground shoot elongation and emergence time of Sonchus arvensis shoots

Abstract Changes in cropping systems during the past century have led to selective pressure on weed flora. Species and ecotypes with characteristics enabling them to survive in high-input farmland have increased in numbers, at the cost of plants lacking these characters. Since the 1950s, the perennial weed species Cirsium arvense (L.) Scop. and Sonchus arvensis L. have mainly been controlled by the herbicide group synthetic auxins like MCPA. During recent decades, C. arvense seems to have become less susceptible to MCPA in both Europe and North America but the reasons are unclear. To study the importance of selective pressure on weed ecotypes, both short- and long-term studies were carried out in Uppsala, Sweden. The first consisted of two growth-characteristic greenhouse experiments. The hypothesis was that ecotypes of C. arvense and S. arvensis from high-input farmland were different and displayed a more competitive growth pattern than did ecotypes from low-input farmland. The second study was a field experiment with four ecotypes of C. arvense from low-input farmland to study if selective pressure was in force, over a period of six years. The four ecotypes had different growth characteristics and herbicide sensitivity and they were exposed to crop competition and MCPA treatments during the experimental period. The hypothesis was that ecotypes with a more competitive growth pattern and MCPA tolerance would survive to a greater extent than would other ecotypes. For C. arvense, the results from the growth-characteristic experiment showed that the growth pattern of ecotypes from high-input farmland differed, showing a more directly elongated growth pattern with fewer spines on the leaves compared with ecotypes from low-input farmland, which usually were of rosette-type. Results from the field experiment with C. arvense showed that after six years MCPA-sensitive and/or rosette-type ecotypes had almost disappeared while ecotypes with a more directly elongated growth pattern and less sensitive to MCPA survived to a much greater extent. The conclusion was therefore that when exposed to selective pressure like crop competition and herbicide treatments, ecotypes of C. arvense with a more directly elongated growth pattern and less sensitive to herbicide treatment survived to a greater extent compared with ecotypes missing these traits. Ecotypes from high-input farmland had generally fewer leaf spines than did ecotypes from low-input farmland. This may suggest a trade-off between spine formation and rapid competitive growth. In the growth-characteristic experiment with S. arvensis, no differences between ecotypes from high- and low-input farmland regarding growth characteristics or leaf spines could be detected. This might partly be due to a lower exposure of S. arvensis to selective pressure compared with C. arvense, since S. arvensis generally is less sensitive to MCPA.

Effects of Cutting Phenology (Non-dormant Versus Dormant) on Early Growth Performance of Three Willow Clones Grown Under Different Weed Treatments and Planting Dates

ABSTRACT A field experiment was performed in Sweden to evaluate the effect of herbicide treatment and selective cutting on the seed production of Cirsium arvense. Four treatments (control (C), selective cutting (S), early (H1) and late (H2) herbicide application) were laid out in a randomized block experiment. The field was sown with spring barley and contained a natural population of the weed. Treatments were first applied 2015 and repeated 2016. Changes in the number of seeds per flower receptacle and average seed weight were measured over time in 2016 from the onset of seed production until crop harvest. At harvest, number of shoots per area and cumulative numbers of flower receptacles, which had shed mature seeds over the season, were counted. These data were used to assess total seed production over the season. Treatment H2 led to a significantly decreased number of seeds per receptacle (49) compared to S (59), H1 (64) and C (67). Over time and treatment, number of seeds per flower receptacle was lowest in the second week (47) and increased over the third week to 69 in week four. Average weight per seed was about constant over time (0.91 mg) while H1 and S (0.63 and 0.78 mg, respectively) had lower seed weights compared to H2 and C (1.04 and 1.19 mg, respectively). Total seed production over the season in terms of number of seeds per square meter was greatly reduced by all treatments (5–20 seeds m−2, or 3–14 mg m−2) compared to the control (6600 seeds m−2, or 7800 mg m−2). We conclude that seed production of C. arvense is inhibited a thousand-fold and equally well by selective cutting as by early or late herbicide treatments.

Effects of root fragmentation on generative reproduction of Sonchus arvensis

To develop better mechanical management strategies, more information on the impact of root partitioning on changes in the population dynamics of Sonchus arvensis is needed. Therefore, the effects of root fragmentation of S. arvensis on shoot height frequency distributions, biomass production and nitrogen allocation were studied in an outdoor experiment in Sweden in 2008. Three artificial populations of S. arvensis of different initial root lengths but with the same total root length per area were planted. Shoot heights were measured at the onset of flowering and dry weight and nitrogen content of leaves, stems, buds and roots were quantified twice during the season. Height frequency distributions of the populations were bimodal, indicating the existence of two generations distinctly different in height growth pattern. Shorter root fragments produced shoots with a lower mean height compared to longer fragments. Plants originating from longer root fragments had higher dry weight and more nitrogen compared to plants from shorter root fragments. Dry matter production per square meter did not differ between the populations. The proportion of dry matter and nitrogen allocated to the different plant components (leaves, stems, buds and roots) at harvest did not differ between the populations. Over time, nitrogen was reallocated from leaves and stems to roots. Our results show that initial root length of S. arvensis per square meter, rather than the number of root fragments per square meter, is a good predictor of biomass at harvest, and that the degree of root fragmentation does not affect nitrogen allocation patterns. Root fragmentation, however, leads to a lower average canopy height for S. arvensis, and thus may be an effective weed control measure in combination with a crop which is competitive for light.