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.

A two-year lysimeter study was undertaken to compare the environmental effects (e.g. nitrate leaching and nitrous oxide emissions) of soil applied lactose-depleted dairy factory effluent (LD-DFE) with lactose-rich DFE. The aim of this experiment was to determine the fate of nitrogen from LD-DFE and dairy cow urine applied to a Templeton fine sandy loam soil (Udic Ustrochrept), supporting a herbage cover of ryegrass (Lolium perenne) and white clover (Trifolium repens). Measurements were carried out on the amount of nitrogen lost from the soil via leaching, lost by denitrification, removed by the pasture plants, and immobilized within the soil organic fraction. Further, a comparison between the fate of nitrogen in LD-DFE irrigated onto land under a "cut and carry" system, as opposed to a "grazed" pasture system was undertaken. Lactose-depleted dairy factory effluent was applied at three-weekly intervals during the summer months at rates of 25 and 50 mm, until nitrogen loading targets of 300 and 600 kg N ha⁻¹ yr⁻¹ had been achieved. Measured leaching losses of nitrogen averaged 2 and 7 kg N ha⁻¹ yr⁻¹ for Control 25 and Control 50 treatments; 21, 20 and 58 kg N ha⁻¹ yr⁻¹ for 25 and 50 mm "cut and carry" treatments respectively; and 96 kg N ha⁻¹ yr⁻¹ for the 25 mm "grazed" treatment. The range of nitrate-N leaching loss from LD-DFE plus urine is no different from the lactose-rich DFE nitrate leaching loss. Uptake of nitrogen by the growing pasture averaged 153, 184,340,352,483, and 415 kg N ha⁻¹ yr⁻¹ for Control 25, Control 50, LD-DFE 25 and LD-DFE 50 mm "cut and carry" treatments, and the LD-DFE 25 mm "grazed" treatment, respectively. Denitrification losses were 0.06, 4.4, 1.69, 19.70, and 7.4 kg N ha⁻¹ yr⁻¹ for Control 25, the LD-DFE 25 "cut and carry" treatments, the LD-DFE 25 mm "grazed" treatment, and calculated "paddock losses", respectively. Isotopic nitrogen studies found that 29.4 and 25.8% of applied LD-DFE nitrogen was immobilised in the LD-DFE 25 and LD-DFE 50 "cut and carry" treatments. The results of this experiment confirm the findings of the previous lactose-rich DFE study, in that the effects of grazing stock are of greater environmental concern than the removal of lactose from the effluent waste stream.

<p>Current watershed-scale, nonpoint source (NPS) pollution models do not represent the processes and impacts of agricultural best management practices (BMP) on water quality with sufficient detail. To begin addressing this gap, a novel process-based, watershed-scale, water quality model (WEPP-WQ) was developed based on the Water Erosion Prediction Project (WEPP) and the Soil and Water Assessment Tool (SWAT) models. The proposed model was validated at both hillslope and watershed scales for runoff, sediment, and both soluble and particulate forms of nitrogen and phosphorus. WEPP-WQ is now one of only two models which simulates BMP impacts on water quality in ‘high’ detail, and it is the only one not based on USLE sediment predictions. Model validations indicated that particulate nutrient predictions were better than soluble nutrient predictions for both nitrogen and phosphorus. Predictions of uniform conditions outperformed nonuniform conditions, and calibrated model simulations performed better than uncalibrated model simulations. Applications of these kinds of models in real-world, historical simulations are often limited by a lack of field-scale agricultural management inputs. Therefore, a prototype tool was developed to derive management inputs for hydrologic models from remotely sensed imagery at field-scale resolution. At present, only predictions of crop, cover crop, and tillage practice inference are supported and were validated at annual and average annual time intervals based on data availability for the various management endpoints. Extraction model training and validation were substantially limited by relatively small field areas in the observed management dataset. Both of these efforts contribute to computational modeling research and applications pertaining to agricultural systems and their impacts on the environment.</p>