Biogas im Rahmen einer nachhaltigen Landwirtschaft zu erzeugen bedeutet u. a., die anfallenden Gärprodukte als Dünger zu verwenden, um die Verluste im Nährstoffkreislauf zu minimieren. Die vorliegende Arbeit geht der Frage nach, welche Wirkungen Gärprodukte aus der Biogasproduktion bei der Verwendung als Dünger auf Boden und Pflanzen haben. Die Ergebnisse von Parzellenfeld- und Praxisversuchen, in denen Gärprodukte aus der Mono- und Kofermentation von Energiepflanzen im Vergleich zu N-Mineraldünger untersucht wurden, werden vorgestellt und diskutiert. Zur Beurteilung der Wirkungen auf den Boden wurden bodenchemische und bodenbiologische Parameter herangezogen sowie die Abbaustabilität der organischen Substanz der Gärprodukte gemessen. Zur Untersuchung der Wirkungen auf die Pflanzen wurden verschiedene Wachstums-, Entwicklungs-, Ertrags- und Qualitätsparameter erfasst und ausgewertet. Die Gärprodukte zeichnen sich durch relativ hohe Ammoniumgehalte sowie durch hohe pH-Werte aus. Das Pflanzenwachstum und die Erträge werden durch die Düngung mit Gärprodukten gesteigert, wobei die Wirkung trotz der hohen Ammoniumgehalte deutlich hinter denen des N-Mineraldüngers zurückbleibt. Die berechneten Nährstoffbilanzen weisen auf deutliche Unterschiede zwischen den untersuchten Gärprodukten und Kulturarten, aber auch zwischen den beiden Versuchsjahren hin. Die Ergebnisse zeigen jedoch, dass durch die Verwendung von Gärprodukten als Dünger wichtige Pflanzennährstoffe rezykliert werden können, wodurch der Einsatz von Mineraldüngern reduziert werden kann. Hinsichtlich der Wirkungen von Gärprodukten auf den Boden zeichnen die umfangreichen Analysen ein differenziertes Bild. Die mikrobiologischen Umsetzungsprozesse im Boden werden insbesondere in den ersten Tagen nach der Ausbringung gefördert. Weiterer Forschungsbedarf wird insbesondere hinsichtlich der Wirkungen auf die Bodenmakrofauna aufgezeigt. / Producing biogas in a sustainable agricultural system means using digestates as fertilizers, in order to minimize leaks in nutrient cycles. The aim of this work is to investigate effects on soil and plants after field application of digestates. In this respect, results from plot- and practical fieldexperiments are analyzed to compare digestates from mono- and from co-fermentation of energy crops in comparison to mineral N-fertilizer. Soil chemical and biological effects were assessed on the basis of selected parameters, one of which was the stability of the organic matter applied. Effects on crops have been evaluated by measuring growth, development, yields, and quality of the crops. The digestates have been analyzed and showed especially high amounts of ammonium and a high pH-value. Plant growth and yields increased as a result of fertilization. However, despite high amounts of ammonia present in digestates, fertilizing effects have been much lower compared to mineral N-fertilization. The calculated nutrient balances showed obvious differences between the digestates analyzed, crops, and also between the two experimental years. Generally, the results demonstrate that nutrients can be recycled by using digestates as fertilizers and thus the use of mineral fertilizers can be reduced. The extensive soil analyses presented in this work show diverse results. Microbial metabolic processes in the soil are increased especially during the first few days after digestate application. More research is needed with respect to effects on macro fauna.

Questa tesi di dottorato analizza l’utilizzo del sorgo (Sorghum bicolour (L.) Moench) al fine di produrre energia elettrica, tramite combustione diretta della biomassa. Il focus della tesi è stato quello di sottolineare i benefici ed i rischi associati all’uso di tre genotipi di sorgo caratterizzati da diversa lunghezza del ciclo culturale (precoce, medio-tardivo e tardivo). La dinamica e la durata del processo di essicazione in campo sono state simulate attraverso un modello ad hoc (“sorghum haying model”), il quale integrato a CropSyst, è stato utilizzato per realizzare un’analisi del rischio produttivo stimando le perdite di biomassa (respirazione e meccanizzazione), ed i mancati affienamenti. Nell’analisi del rischio vengono stimati il numero di ettari necessari e la probabilità di eccedere la soglia di 64.000 ton ss anno-1 necessari per l’alimentazione di una centrale nell’Oltrepò pavese . Inoltre uno studio di Life Cycle Assessment è stato condotto per la valutazione dell’impatto ambientale dell’utilizzo del sorgo integrato a quello della paglia per il completamento del fabbisogno totale della centrale 94.000 ton ss anno-1. Particolare attenzione inoltre è stata data alla variazione del contenuto di C organico del suolo dovuto alla rimozione della paglia ed all’interramento dei mancati affienamenti di sorgo. Il genotipo precoce mostra le migliori performance produttive ed energetiche oltre che la più alta probabilità di eccedere la soglia di 64.000 ton ss anno-1. Lo studio di LCA non ha mostrato differenze significative tra i genotipi anche se il minor impatto ambientale, è stato evidenziato dal genotipo tardivo conseguenza dell’interramento della più alta quantità di mancati affienamenti. / This PhD thesis explores the use of sorghum (Sorghum bicolour (L.) Moench) as a dedicated bio-energy crop and highlights the benefits and risks associated with the use of early, medium-late and late sorghum genotypes to generate electricity by direct combustion in a biomass power plant. The dynamics and duration of the field drying process were simulated through the development of a specific model ("sorghum haying model"), which integrated with CropSyst, was used to perform a production risk assessment analysis estimating the biomass losses (respiration and mechanical), the haymaking failures and consequently to quantify the amount of dry baled biomass available for the power plant. In addition, the number of hectares needed to plant sorghum and the probability to exceed the threshold of 64000 Mg DM y-1, necessary to feed a biomass power plant in Oltrepò Pavese, were estimated. A complete Life Cycle Assessment (LCA) study was carried out in order to evaluate the environmental impact of the three sorghum genotypes involved in this study. The LCA study takes into consideration the use of winter wheat straw as an additional biomass source to satisfy the total biomass power plant needs (94000 Mg DM y-1). Particular attention was given to the soil organic C change (ΔSOC) due to straw removal and haymaking failures soil incorporation. Early genotype showed the best biomass production and energy performance as well as the highest probability to exceed the threshold of 64000 Mg DM y-1. The LCA results did not show significant differences between genotypes although the lower environmental impact, has been achieved by the late genotype due to the highest amount of haymaking failures incorporated in the soil.