Germination base temperature and relative growth rate of 13 weed species - comparing populations from two geographical origins

Es wurden zwei Experimente durchgeführt, um die Validität von Modellparametern eines Unkraut-Simulationsmodells für norddeutsche Bedingungen zu testen. Es umfasst zurzeit Parameter zum Lebenszyklus von 25 annuellen Unkräutern, die entweder durch Experimente in der Region Burgund erhoben oder aus der Literatur entnommen wurden. Solche Parameter können sich in Populationen verschiedener geographischer Herkunft erheblich unterscheiden.Im Experiment zur Basistemperatur für die Keimung wurden norddeutsche Samen von zehn Arten untersucht. Die meisten von Ihnen wiesen Basistemperaturen auf, die ca.1.5-2.7 °C höher lagen, als die Basistemperaturen der französischen Experimente. Das Experiment zur Relativen Wachstumsrate mit 19 Arten zeigte für die meisten Arten ähnliche Werte in französischen und deutschen Populationen.Für eine Nutzung des Modells in Norddeutschland sollten die Basistemperaturen angepasst werden. Wachstumsraten können beibehalten werden, wobei für einen kleinen Teil an Arten zu klären ist, ob Unterschiede durch saisonale Verschiebungen bei Samenernte und Experiment zu erklären sind.Two experiments were conducted to test parameter validity of a simulation model under North German conditions. At the moment, the model is stocked with life cycle parameters of 25 annual weed species. These were obtained from experiments in the region Burgundy and from literature. Such parameters may vary strongly between geographical regions. Base temperature for germination was studied in one experiment for North German seeds of ten species. Mostly, base temperatures were between 1.5 and 2.7 °C higher than the parameters from French experiments. The second experiment, on Relative growth rate of 19 species, yielded similar values for most species in French and German seed populations.In respect to using the model for simulations under North German conditions, adaptations should be undertaken for the germination base temperature. Growth rates can be kept unchanged, but for some species it needs to be clarified whether differences between parameters can be explained through seasonal variations in seed collection or experiment

Neutral modelling of agricultural landscapes by tessellation methods—Application for gene flow simulation.

International audienceNeutral landscape models are not frequently used in the agronomical domain, whereas they would be very useful for studying given agro-ecological or physical processes. Contrary to ecological neutral landscape models, agricultural models have to represent and manage geometrical patches and thus should rely on tessellation methods. We present a three steps approach that aimed at simulating such landscapes. Firstly, we characterized the geometry of three real field patterns; secondly, we generated simulated field patterns with two tessellation methods attempting to control the value of some of the observed characteristics and, thirdly, we evaluated the simulated field patterns. For this evaluation, we considered that good simulated field patterns should capture characteristics of real landscapes that are important for the targeted agro-ecological process. Real landscapes and landscapes simulated using either a Voronoi or a rectangular tessellation were thus compared when used as input data within a gene flow model. The results showed that neither tessellation method captured field shapes correctly, thus leading to over or (small) under estimation of gene flow. The Voronoi tessellation, though, performed better than the rectangular tessellation. Possible research directions are proposed to improve the simulated patterns, including the use of post processing, the control of cell orientation or the implementation of other tessellation techniques

Measuring the effectiveness of management interventions at regional scales by integrating ecological monitoring and modelling

Background: Because of site‐specific effects and outcomes, it is often difficult to know whether a management strategy for the control of pests has worked or not. Population dynamics of pests are typically spatially and temporally variable. Moreover, interventions at the scale of individual fields or farms are essentially unreplicated experiments; a decrease in a target population following management cannot safely be interpreted as success because, for example, it might simply be a poor year for that species. Here, we argue that if large‐scale data are available, population models can be used to measure outcomes against the prevailing mean and variance. We apply this approach to the problem of rotational management of the weed Alopecurus myosuroides. Results: We derived density‐structured population models for a set of fields that were not subject to rotational management (continuous winter wheat) and another group that were (rotated into spring barley to control A. myosuroides). We used these models to construct means and variances of the outcomes of management for given starting conditions, and to conduct transient growth analysis. We show that, overall, this management strategy is successful in reducing densities of weeds, albeit with considerable variance. However, we also show that one variant (rotation to spring barley along with variable sowing) shows little evidence for additional control. Conclusion: Our results suggest that rotational strategies can be effective in the control of this weed, but also that strategies require careful evaluation against a background of spatiotemporal variation

Field margins enhance weed seed predation in adjacent fields in early spring

Seed depletion by granivorous organisms can regulate weeds in arable agriculture. Enhancing this regulation can be achieved by adopting farming practices that favour seed predators. Here, we test the hypothesis that the presence of grassy field margins along field edges will increase in-field weed seed predation, in comparison to situations where no grassy field margin is present. Predation cards with Poa annua were exposed in 15 wheat fields in May and June 2018 along 57 transects at distances of 4, 8, 16, 32 meters from the field edge. Cards were either caged (predation by invertebrates) or uncaged predation byall seed predators). We found that in May, the presence of grassy field margins led to higher in-field predation rates at all distances from the field edge, with a very high contribution of invertebrates to seed predation. In June, the presence of grass margin had no impact on in-field seed predation, to which invertebrates and vertebrates contributed equally. This preliminary study provides some support to the hypothesis that grassy field margins augment in-field weed seed predation in early spring. It is plausible that these habitats are emergence sites for invertebrates, with a subsequent high abundance of adults nearby grass margins in early spring, before they disperse more widely across fields and/or switch to alternative prey. These results call for further comparative research on the impact of grass margins on seed predation, seed predators and alternative prey during the whole cropping season

Combining a weed traits database with a population dynamics model predicts shifts in weed communities

A functional approach to predicting shifts in weed floras in response to management or environmental change requires the combination of data on weed traits with analytical frameworks that capture the filtering effect of selection pressures on traits. A weed traits database (WTDB) was designed, populated and analysed, initially using data for 19 common European weeds, to begin to consolidate trait data in a single repository. The initial choice of traits was driven by the requirements of empirical models of weed population dynamics to identify correlations between traits and model parameters. These relationships were used to build a generic model, operating at the level of functional traits, to simulate the impact of increasing herbicide and fertiliser use on virtual weeds along gradients of seed weight and maximum height. The model generated ‘fitness contours’ (defined as population growth rates) within this trait space in different scenarios, onto which two sets of weed species, defined as common or declining in the UK, were mapped. The effect of increasing inputs on the weed flora was successfully simulated; 77% of common species were predicted to have stable or increasing populations under high fertiliser and herbicide use, in contrast with only 29% of the species that have declined. Future development of the WTDB will aim to increase the number of species covered, incorporate a wider range of traits and analyse intraspecific variability under contrasting management and environments

Evidence that wheat cultivars differ in their ability to build up inoculum of the take-all fungus, Gaeumannomyces graminis var. tritici, under a first wheat crop

The effect of wheat cultivar on the build-up of take-all inoculum during a first wheat crop was measured after harvest using a soil core bioassay in field experiments over five growing seasons (2003-2008). Cultivar differences in individual years were explored by analysis of variance and a cross-season Residual Maximum Likelihood (REML) variance components analysis was used to compare differences in those cultivars present in all years. Differences between cultivars in the build-up of inoculum were close to or at significance in two of the five trial years (2004 P < 0 center dot 05; 2006 P < 0 center dot 07), and current commercially listed cultivars were represented at both extremes of the range. In 2007 and 2008, when environmental conditions were most favourable for inoculum build-up, differences were not significant (P < 0 center dot 3). In 2005 the presence of Phialophora spp. at the trial site restricted the build-up of take-all inoculum under all cultivars. The cross season REML variance components analysis detected significant differences (range: 3 center dot 4-47 center dot 8% roots infected in the soil core bioassay; P < 0 center dot 01) between the nine cultivars present in all years (excluding 2005). This is the first evidence of relatively consistent differences between hexaploid wheat cultivars in their interactions with the take-all fungus, and this could give an indication of those cultivars that could be grown as a first wheat crop, in order to reduce the risk of damaging take-all in a second wheat crop. This phenomenon has been named the take-all inoculum build-up (TAB) trait