Browsing by Person "Schumacher, Matthias"

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Facilitation of weed seed predation by living mulch and cover crops
(2022) Schumacher, Matthias; Gerhards, Roland
Weed seed predation (WSP) is an important agro‐ecosystem service that naturally suppresses weed populations. Disturbances directly interfere with the activity of the seed predators, for example, harvest and soil tillage during a peak in weed seed availability (around cereal harvest). Plant soil cover and reduced soil tillage are factors that might positively affect WSP. We investigated cover crops and living mulch along with soil disturbance (no‐till and conventional seeding) in comparison to a fallow and repeated stubble tillage with a chisel plough in terms of WSP, activity‐density of carabid beetles and soil cover. A field experiment with a randomised complete block design and four replications was conducted at two sites from 2017 until 2019. WSP rates were assessed with seed cards and exclosure cages from July until November during a period of eight consecutive days each month. Living mulch exhibited the highest WSP rates of 72% with a maximum of 95% immediately following cereal harvest in August and September of 2017 and 2019, while the remainder of the treatments ranged from 2% to 5% WSP. In October and November mustard showed on average twice as high WSP rates compared to the other treatments (50% vs. 10%–25%). Seeding and soil tillage did not significantly influence carabid beetle activity‐density and WSP, except for living mulch. Predator groups (invertebrates and vertebrates) were not influenced by the various treatments, rather year and month determined the predator groups dominance. Besides their weed suppressive effects, living mulches and cover crops also facilitate WSP.
Interactions of farming and plant biodiversity in weed control related ecosystem service provision and weed conservation
(2020) Schumacher, Matthias; Gerhards, Roland
There is evidence that diverse plant communities in terrestrial ecosystems are either more stable or more productive in terms of food web support and ecosystem service provision. In agro-ecosystems, characterized by high disturbance and external inputs, plant diversity and their services can only be provided by weeds. In the first study, vegetation recordings and farmer surveys were conducted in on-farm experiments in two regions of Southwestern Germany. The aim was to examine the effects of agricultural management on weed community composition, weed biodiversity and occurrence of rare arable weed species in cereal fields. Weed biodiversity was influenced mainly by crop species, herbicide use and farming system as well as nitrogen and light availability. Weed communities were quite similar in both study regions and dominated by Alopecurus myosuroides, Galium aparine, Viola arvensis, Polygonum convolvulus and Veronica persica. A redundancy analysis revealed that the weed community was mainly shaped by crop species, tillage, location in the field and timing of herbicide application. The results highlight the erosion of weed communities due to intensive agricultural practices and emphasize the conservation of weed biodiversity per se and rare arable weed species in particular. The next aim was to examine if this biodiversity is able to support weed control related ecosystem services, like the predation of weed seeds. The objectives of this study were to investigate the connection between weed biodiversity, Carabid beetle diversity and weed seed predation as well to evaluate the role of farming intensity in this sequence. For this purpose, on-farm experiments were performed on the Eastern Swabian Alb. A positive correlation between weed biodiversity and Carabid beetle diversity was identified as well as a pattern of medium Carabid beetle diversity providing the highest weed seed predation. There was no consistent influence of farming intensity on weed seed predation. The revealed connection between weed diversity, Carabid beetle diversity and weed seed predation highlights the role of plants in food web support and subsequent ecosystem service provision. The utilization of these services depends on the promotion of biodiversity by designing appropriate management strategies. In the next step, the general principles underlying ecosystem service provision by biodiversity, were conveyed to a cover cropping system. The aim was to test single sown cover crops and species mixtures in terms of weed suppression efficacy and reliability. For this purpose, cover crop species were sown singly and as mixtures in a field experiment. Lower weed dry matter and weed densities were found predominantly in treatments with favorable establishment and above-average biomass production. Mixtures performed much more homogeneous in regard to the measured parameters compared to single sown cover crops. The results suggest that, although particular single sown cover crops are more effective to control weeds than mixtures, mixtures are more reliable under changing conditions. Altering the species composition of cover crop mixtures according to more complementary traits might further improve their weed control efficacy. The results of this dissertation demonstrate the importance of plant biodiversity in the provision and reliability of weed control related ecosystem services, either by weeds themselves or by specifically designed cover crop mixtures. Furthermore, management factors influencing weed biodiversity were determined, which can aid in the creation of more sustainable management strategies for a diverse agroecosystem and the conservation of rare arable weed species.