Initial Effects of Differently Treated Biogas Residues from Municipal and Industrial Wastes on Spring Barley Yield Formation

Soil application of biogas residues (BGRs) is important for closing nutrient cycles. This study examined the efficiency and impact on yields and yield formation of solid-liquid separated residues from biodegradable municipal and industrial wastes (bio-waste) in comparison to complete BGRs, nitrification inhibitor, agricultural BGRs, mineral fertilizer and unfertilized plots as control. The experiment was set up as a randomized block design on silt loam Cambisol. Biogas residues from four biogas plants were evaluated. Plants per m², ears per plant, grains per ear and thousand grain weight (TGW) were measured at harvest. Fertilization with BGRs resulted in similar biomass yields compared with mineral fertilizer. Mineral fertilizer (71 dt/ha) and plots fertilized with liquid fraction (59–62 dt/ha) indicated a trend to higher yields than solid fraction or complete BGR due to its high ammonia content. Liquid fractions and fraction with nitrification inhibitor induced fewer plants per m² than corresponding solid and complete variants due to a potential phytotoxicity of high NH4-N concentration during germination. However, barley on plots fertilized with liquid fraction compensated the disadvantages at the beginning during the vegetation period and induced higher grain yields than solid fraction. This was attributable to a higher number of ears per plant and grains per ear. In conclusion, BGRs from biodegradable municipal and industrial wastes can be used for soil fertilization and replace considerable amounts of mineral fertilizer. Our study showed that direct application of the liquid fraction of BGR is the most suitable strategy to achieve highest grain yields. Nevertheless potential phytotoxicity of the high NH4-N concentration in the liquid fraction should be considered

Biogas residue parameterization for soil organic matter modeling

A variety of biogas residues (BGRs) have been used as organic fertilizer in agriculture. The use of these residues affects the storage of soil organic matter (SOM). In most cases, SOM changes can only be determined in long-term observations. Therefore, predictive modeling can be an efficient alternative, provided that the parameters required by the model are known for the considered BGRs. This study was conducted as a first approach to estimating the organic matter (OM) turnover parameters of BGRs for process modeling. We used carbon mineralization data from six BGRs from an incubation experiment, representing a range of substrate inputs, to calculate a turnover coefficient k controlling the velocity of fresh organic matter (FOM) decay and a synthesis coefficient describing the SOM creation from FOM. An SOM turnover model was applied in inverse mode to identify both parameters. In a second step, we related the parameters k and to chemical properties of the corresponding BGRs using a linear regression model and applied them to a long-term scenario simulation. According to the results of the incubation experiment, the k values ranged between 0.28 and 0.58 d-1 depending on the chemical composition of the FOM. The estimated values ranged between 0.8 and 0.89. The best linear relationship of k was found to occur with pH (R2 = 0.863). Parameter is related to the Ct/Norg ratio (R2 = 0.696). Long-term scenario simulations emphasized the necessity of specific k and values related to the chemical properties for each BGR. However, further research is needed to validate and improve these preliminary results. © 2018 Prays et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Einfluss der Biogasgärreste auf die Ertragsstruktur und organischen Bodenkohlenstoff

Während der Klimarahmenkonvention der Vereinten Nationen einigte man sich auf die Bekämpfung des Klimawandels und die Einhaltung des globalen Temperaturanstiegs in diesem Jahrhundert auf unter 2°C des vorindustriellen Niveaus. Eine der Maßnahmen, um dieses Ziel zu erreichen, ist die Erhöhung des Anteils der erneuerbaren Energien, z.B. den Anteil des Biogases, das durch anaerobe Vergärung der Biomasse erzeugt wird. Während der anaeroben Vergärung setzen die Mikroorganismen die Biomasse zu Methan (CH4) und Kohlenstoffdioxid (CO2) um. Die verbleibende organische und anorganische Substanz wird Gärrest genannt. Da während der anaeroben Vergärung ca. 60% des Kohlenstoffs zu CH4 und CO2 umgewandelt werden, kann er nicht zum Aufbau der organischen Bodensubstanz zurückgeführt werden, die als eine essentielle Komponente im Boden die Bodenfunktionen verbessert und damit diverse Ökosystemleistungen unterstützt. Die Entnahme des Kohlenstoffs aus dem landwirtschaftlichen System durch die Vergärung bekräftigt die Annahme, dass im Vergleich zu unvergorenem Dünger dies zu einer Abnahme des organischen Bodenkohlenstoffs (Teil der organischen Bodensubstanz) im Boden und damit zu einer Bodendegradierung führen kann. Gärreste sind zwar als Pflanzendünger und Bodenverbesserer mit überwiegend positiven Eigenschaften bekannt. Nichtdestotrotz, ist ihre Anwendung in der Landwirtschaft ein relativ neues Konzept. Da die Biogasproduktion global expandiert, ist es notwendig Ihre Auswirkungen auf die Umwelt zu verstehen. In diesem Zusammenhang war das übergreifende Ziel dieser Doktorarbeit zu einem verbesserten Verständnis des Gärresteinflusses in landwirtschaftlichen Systemen beizutragen. Ziele dieser Arbeit waren: a) Bestimmung der Wirkung der separierten Gärreste aus industriellen und kommunalen Abfällen auf Kornertrag und Ertragsstruktur, b) Bestimmung des Einflusses der Biogasproduktion auf organischen Bodenkohlenstoff auf der Betriebsskala, c) Bestimmung des Flächenbedarfs der Biogasproduktion und ihres Einflusses auf die Kohlenstoffflüsse auf der Landschaftsskala. Um diese Ziele zu erreichen, wurde im ersten Schritt ein Feldexperiment angelegt, um Information über den Effekt verschiedener Gärreste (separiert / unsepariert, landwirtschaftliche / industrielle und kommunale Abfälle) auf den Boden und Pflanzen (Kornertrag, Ertragsstruktur) zu bekommen. Im nächsten Schritt, wurde eine Studie auf der Betriebsskala durchgeführt, um den Einfluss der Biogasproduktion auf den organischen Kohlenstoff im Boden zu untersuchen. Hier wurde der Fokus auf landwirtschaftliche, unseparierte Gärreste gelegt aufgrund ihrer Relevanz und deren Verbreitung. Hierfür wurde ein System mit einem landwirtschaftlichen Betrieb und einer Biogasanlage betrachtet. Ein Prozessmodell (CANDY: Carbon and Nitrogen Dynamics) wurde angewandt, um Vorhersagen zu treffen. Inkubationsexperimente wurden verwendet, um für Gärreste die Parameter des Umsatzes der organischen Bodensubstanz zu bestimmen. Im nächsten Schritt wurden die bestimmten Parameter auf der Landschaftsskala angewandt. Hier wurde eine quantitative und qualitative Analyse der Kohlenstoff-Flüsse, die durch die Biogasanlage verändert wurden, durchgeführt. Zusätzlich wurde eine Methodik zur Berechnung des Flächenbedarfs einer Biogasanlage, der so genannte „Biogas Fingerabdruck“ ausgearbeitet. Folgende Ergebnisse wurden erzielt: a) kurzfristige Düngewirkung der separierten Gärreste aus industriellen und kommunalen Abfällen ist vergleichbar mit der Düngewirkung der landwirtschaftlichen Gärreste sowie des Mineraldüngers. Flüssigphase der Gärreste führte zu weniger Pflanzen pro m² verglichen mit der Festphase oder dem gesamtem Gärrest, was dem phytotoxischen Potential der Flüssigphase auf die Keimung zugeschrieben werden kann. Nichtdestotrotz, führte Flüssigphase zu höherem Kornertrag als die Festphase. Die Gerste kompensierte die ursprünglichen Nachteile im Laufe der Vegetationsperiode durch die höhere Anzahl von Ähren pro Pflanze sowie Körnern pro Ähre. b) Parameter des Umsatzes der organischen Substanz für das Prozessmodell CANDY wurden bestimmt und ein linearer Zusammenhang zwischen ihnen und den chemischen Gärresteigenschaften (pH und C/Norg) wurde gefunden. Die Ergebnisse auf der Betriebsskala zeigen, dass der Ersatz der unvergorenen organischen Dünger mit Gärresten während eines 10-jährigen Gärrest-Einsatzes zu keiner Abnahme des Kohlenstoffs im Boden geführt hat. Des Weiteren, wurde gezeigt, dass der organische Kohlenstoff im unter getesteten Anbauverhältnissen nicht abnimmt. c) in Sachsen können die Biogasanlagen im Hinblick auf den organischen Bodenkohlenstoff nachhaltig betrieben werden. Der Flächenbedarf, welcher für die Versorgung der Biogasanlage und Gärrestausbringung notwendig ist, nimmt durchschnittlich nur ca. ein Fünftel der landwirtschaftlichen Fläche ein. Der gesamte Kohlenstofffluss in den Boden ist in der Untersuchungszeit angestiegen und der Beitrag verschiedener Kohlenstoffquellen hat sich geändert. Flächen, die durch die Biogasproduktion betroffen sind, zeigten aufgrund des hohen Beitrags der Gärreste und der Koppelprodukte höhere Kohlenstoff-Reproduktionsraten verglichen mit der umliegenden landwirtschaftlichen Fläche. Zusammenfassend zeigt die vorliegende Doktorarbeit, dass Gärreste zu der Produktivität sowie der Erhaltung des organischen Kohlenstoffs im Boden in landwirtschaftlichen Anbausystemen beitragen können.The United Nations Framework Convention on Climate Change (UNFCCC) reached an agreement to combat climate change by keeping a global temperature rise this century less than 2 °C above pre-industrial levels. One of the measures to achieve this goal is to increase the share of renewable energy, e.g. the share of biogas which is produced by anaerobic degradation of biomass. During this process microorganisms transform biomass into methane (CH4) and carbon dioxide (CO2). The remaining organic and inorganic matter is a secondary product which is called biogas residue (BGR), which is usually used in the agriculture as organic fertilizer. As during the anaerobic digestion process about 60% of carbon is transformed into CH4 and CO2, it cannot be returned to the soil to rebuild soil organic matter (SOM). This supports the presumption that compared to undigested fertilizer this carbon extraction from the agricultural system can lead to soil carbon decrease and soil degradation. Soil organic carbon (SOC) is a part of SOM which is an essential component of soil that improves the soils functions thereby supporting several ecosystem services. Although BGRs are known as a predominantly positive crop fertilizer and soil conditioner, the effects on SOC are rarely studied, because the application of these substances within agriculture is a relatively new concept. As biogas production expands globally, it is necessary to understand its environmental consequences. In this context, the overarching goal of this thesis was to contribute to an improved understanding of the BGR effects in agricultural systems. The objectives of this thesis were: a) to identify the effects of separated BGRs from industrial and municipal wastes on yield formation and grain yields, b) to determine the impact of the implementation of biogas production on the SOC on the farm scale, c) to identify the areal demand for biogas production and its impact on carbon fluxes on the landscape scale. To reach these objectives in the first step a field experiment was conducted to derive the information about the effect of different BGRs (treated / untreated, agricultural / industrial and municipal waste) on soil and crops (grain yields, yield formation). In the next step, a farm scale study was performed to determine the impact of the implementation of biogas production implementation on the SOC. Here the focus was on agricultural and untreated BGRs due to their relevance and wide distribution. Therefore a system with a farm and an agricultural biogas plant (BGP) was regarded. A process model (CANDY: Carbon and Nitrogen Dynamics) was applied to make predictions for the SOC development over time. Incubation experiments were used for estimation of SOM turnover parameter for BGRs. In the next step the estimated parameters were applied on a landscape scale (Saxony). Here a quantitative and qualitative analysis of the SOC fluxes which were changed through BGP was conducted. Additionally a methodology of a BGP areal demand calculation, so called “biogas fingerprint area” was worked out. The following results were obtained: a) the initial short-term fertilization effect of soil treated with BGRs from industrial and municipal wastes is similar to agricultural BGRs and mineral fertilizer. Liquid fractions of BGRs caused less plants per m² than solid or complete BGRs, what was attributed to phytotoxic potential of the liquid fractions on the germination. Despite that, liquid fractions caused higher total grain yields than solid fractions. Here, barley compensated the disadvantages at the beginning during the vegetation period with higher number of ears per plant and grains per ear. b) the values for the SOM turnover parameters for the process model CANDY were determined and a linear relationship between those parameters and chemical properties of BGRs (pH and C/Norg) was found. The findings at the farm scale suggest that the replacement of undigested organic fertilizers with BGR did not lead to a decrease in SOC within ten years of BGR application. Furthermore, the model indicated that, despite carbon removal during anaerobic digestion, the SOC did not decrease under the tested cropping conditions (until 2050). c) in Saxony, BGPs can be operated sustainably with regard to SOC recycling. The “biogas fingerprint area” which is required to supply the BGPs and dispose of their BGRs, is on average only approximately the fifth part of the agricultural land. Overall, the total C flux into the soil increased in the observed time and the contribution of different C sources changed. Areas affected by biogas production showed higher SOC reproduction rates than the surrounding agricultural land due to high contributions from BGR and crop residues. In conclusion, the present thesis shows that BGRs can contribute to productivity as well as to the maintenance of SOC in agricultural cropping systems

Weather conditions and soil water content during the experiment.

<p>Weather conditions and soil water content during the experiment.</p

Experimental design.

<p>Abbreviations are explained in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0154232#pone.0154232.t001" target="_blank">Table 1</a>.</p

Yield formation, grain and straw yields, N content in grain and aboveground biomass N uptake.

<p>Biogas residue abbreviations are explained in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0154232#pone.0154232.t001" target="_blank">Table 1</a>. mean ± sd = mean value ± standard deviation, LSD = Least Significant Difference t-Test. Means with the same letter are not significantly different.</p

Soil properties before fertilization and after harvesting.

<p>mean ± sd = mean value ± standard deviation, n.a. = sd is not possible, TC = total carbon, TN = total nitrogen, N_min = mineral nitrogen.</p

Chemical properties of used BGRs and mineral fertilizer.

<p>TKN = total Kjeldahl nitrogen; NH₄-N = ammonia nitrogen, FM = fresh matter, DM = dry matter, oDM = organic dry matter, BGP = biogas plant.</p

Biogas production and changes in soil carbon input - A regional analysis

The inclusion of biogas production into the agricultural system has modified crop management and as a result the soil organic carbon (SOC) cycle of the agricultural landscape. To evaluate the effects for the German federal state of Saxony this study determines: (1) the share of agricultural land required for biogas production, (2) the change in regional carbon input fluxes to soil during the time of the establishment of the biogas production considering also the quality of sources of different fresh organic matter (FOM) for the formation of SOC and (3) the differences in carbon input to SOC between the area influenced by biogas production (here “biogas fingerprint area” (BFA)) and the surrounding arable land. Based on the location of biogas plants the region was subdivided into biomass providing units (BPUs) where a part of the arable land was considered as affected by biogas production (BFA). We hypothesized that each biogas plant uses a specific substrate mix according to its capacity. The carbon fluxes for each BPU were estimated for the years 2000 (without biogas plants) and 2011 (with biogas plants). For the year 2011, the analysis included the area demand for production of biogas feedstock and digestate recycling. On average 17.6% of the BPU agricultural land was required to supply the biogas plants and dispose of their digestate. Per kilowatt installed electrical capacity this equates to 2.0 ha, including inter alia 0.4 ha for energy crops. Highest area requirements have been observed for biogas plants with <500 kW installed capacity. Between 2000 and 2011 the total carbon flux into soil increased by 2.1%. When considering the quality of different FOM sources the gain in carbon input was 2.8%. The BFAs showed higher carbon input to soil than the surrounding agricultural land due to high contributions from digestate and crop residues (esp. agricultural grass). This compensated the low carbon input from crop by-products (e.g. straw)