Weed and wildflower seeds in biogas plants – inactivation of seeds during ensiling

Autor: Hahn, J.; Müller, J.; Westerman, P. R.; Gerowitt, B.
In:

International Plant Science Conference
Book of Abstracts
Herausgeber: Deutsche Botanische Gesellschaft
Seite: 71 - 71
Jahr: 2019

Einordung:
Institut: Professur Grünland- und Futterbauwissenschaften

Abstract:
An alternative to the continuous cultivation of maize for biogas production is to grow "biogas-optimized" mixtures of wildflowers instead. Consequently, seeds of these wildflowers can enter the biogas chain along with the biomass - and weed
seeds. In the case of their survival, the risk occurs that weed and wildflower seeds are spread when the digestate is returned to the fields as a fertilizer. This is problematic, in particular if invasive, non-indigenous or herbicide-resistant species or populations are involved. It has been shown that besides anaerobic digestion in the biogas plant pretreatments like ensiling have the
potential to reduce seed survival (e.g., Westerman & Gerowitt 2013). The factors driving this reduction, however, are still largely unknown. We examined the survival probability of weed and wildflower seeds in ensiling at laboratory scale. Seeds were ensiled for eight months in maize silages manipulated for different qualities (Weissbach & Honig 1992) and in silages with various mixing ratios of maize and wildflower biomass. Selected chemical characteristics of these silages (contents of dry matter and of watersoluble carbohydrates, buffering capacity, nitrate content) were checked for correlations with the probability of seed survival. In
addition, changes in the pH-value (pH 4 – pH 7) with or without the addition of lactic acid (2% v/v) were tested for their effect on seed survival in a water bath setup. Seed survival probability was determined using germination tests and tetrazolium staining. All silage types killed the seeds of species without pronounced physical dormancy and reduced the survival probability of most species that displayed hard-seededness. Seed survival probability did not differ between silage types. The effects of pH and lactic acid were species-dependent. Generally, pH-effects were stronger when lactic acid was added. Our results suggest to (a)avoid hard-seeded species in wildflower-biogas-mixtures and (b) provide high quality silages with low pH-values and high
contents of lactic acid in order to prevent an undesirable spread of plant seeds with the digestate after biogas production.

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