Phosphorus bioavailability of fertilizers recycled from sewage sludge and their suitability for organic crop production

Phosphorus (P) nutrition of plants is a key production factor in agriculture. In an approach to recycle P from urban areas back to agriculture, technologies have been developed to produce mineral P fertilizers out of municipal sewage sludge. In this study, different P fertilizers recycled from sewage sludge have been investigated in pot and field experiments for their bioavailability to maize and several plant species of a crop rotation. It was also investigated, if bioavailability of recycled P fertilizers can be enhanced either by a soil inoculation with different bacteria strains that are efficient in P solubilizing, or by a cultivation of red clover in the crop rotation. As there is a lack of bioavailable P fertilizers in organic cropping systems, P fertilizers recycled from sewage sludge were evaluated for their suitability to be used in organic crop production. It has been shown that most of the investigated fertilizers recycled from sewage sludge have a higher P bioavailability than Phosphate Rock (PR). Fertilizer efficacy seems very dependent from specific production conditions which are decisive for the final product. Among the tested fertilizers, struvite (MgNH4PO4 . 6 H2O) was most efficient in increasing plant P offtake of maize (+ 27.5% in the field, and more than sixfold in a pot experiment, compared to the unfertilized control). Struvite and calcined sewage sludge ash (SSA) are efficient fertilizers at both acidic and neutral soil pH. Other fertilizers (e.g. untreated incineration ashes) have low solubility at soil with pH > 6, and thus, might be used on acidic soil only, or as raw material for fertilizer production. In the field experiment, the overall response to P fertilizer input was low, which probably can be attributed to a sufficient inherent P supply on the used site. An immobilization of fertilizer P over time could be shown in all experiments. Thus, recycled P fertilizers should be applied to responsive crops in the rotation. An improved P supply of maize could be shown when grown after red clover in the crop rotation. This might be attributed to a combination of different factors, such as a solubilization of sparingly soluble P forms in recycled fertilizers, following a drop in soil pH due to biological N2 fixation of clover. A recycling of P to maize via decomposed clover roots might in addition have contributed to an increased P supply of the subsequent maize. Despite this promising effect, P mobilization by clover cultivation was not sufficient to cover the entire P demand of maize. Thus, additional fertilizer P inputs to maize might still be necessary to ensure optimal plant growth on P deficient soils. With one exception, an application of different bacteria strains generally did not affect P supply of the plants. Applied bacteria seem very dependent on the environmental conditions. It is conceivable, that especially in organic systems, a soil application with external bacteria does not enhance the beneficial effects of a high microbial abundance and activity which often is already present in organic cropping systems. From an agronomic point of view, P fertilizers recycled from sewage sludge are better alternatives for organic crop production than PR. A recycling of nutrients generally fits well with basic organic principles. By introducing those fertilizers, the organic system could make a decisive contribution to the ongoing effort of closing the P cycle, and, once more, develop towards a farming system of the future.So wie alle anderen Lebewesen, sind auch Pflanzen auf das Element Phosphor (P) angewiesen. Es ist umstritten, wie lange die natürlichen Rohphosphat (PR) Reserven noch ausreichen, um den P-Bedarf der Landwirtschaft zu decken. Vor diesem Hintergrund haben sich verschiedene Technologien entwickelt um P-Düngemittel aus kommunalem Klärschlamm zu gewinnen. Angesichts des Mangels an pflanzenverfügbaren P-Düngemitteln im Ökologischen Landbau wurde evaluiert, ob diese Recycling-P Düngemittel aus agronomischer Sicht für die Ökologische Pflanzenproduktion infrage kommen. Dafür wurden in dieser Studie verschiedene Recycling-P Düngemittel in Gefäß- und Feldversuchen mit mehreren Pflanzen einer Fruchtfolge auf ihre Pflanzenverfügbarkeit hin untersucht. Darüber hinaus wurde untersucht, ob durch eine Beimpfung des Bodens mit verschiedenen Bakterienstämmen, oder den Anbau von Rotklee in der Fruchtfolge, die Pflanzenverfügbarkeit der Recycling-P Düngemittel erhöht werden kann. Es konnte gezeigt werden, dass die meisten Recycling-P Düngemittel eine höhere Pflanzenverfügbarkeit aufweisen als PR. Offenbar wird die P-Düngewirkung dabei insbesondere von den jeweiligen Produktionsbedingungen bestimmt. Von allen untersuchten Recycling-P Düngemitteln hatte Struvit (MgNH4PO4 . 6 H2O) die höchste P-Düngewirkung. Im Vergleich zur ungedüngten Kontrolle erhöhte eine Düngung mit Struvit die P Aufnahme von Mais um 27.5% im Feldversuch und um mehr als das sechsfache im Gefäßversuch. Struvit und kalzinierte Klärschlammasche (KSA) sind effektive P Düngemittel, unabhängig von den jeweiligen Bodenbedingungen. Andere Düngemittel, wie etwa unbehandelte KSA, weisen bei einem pH der Bodenlösung von > 6.0 hingegen eine niedrige Pflanzenverfügbarkeit auf. Diese kommen daher nur für eine Nutzung auf sauren Böden, oder aber als Rohmaterial für die Düngemittelproduktion infrage. Die allgemein geringe Wirkung der P-Düngung im Feldversuch ist wahrscheinlich auf eine ausreichende P-Versorgung des Versuchsstandorts zurückzuführen. In allen Versuchen konnte mit der Zeit eine Immobilisierung von Dünger-P im Boden gezeigt werden. Recycling-P Düngemittel sollten daher innerhalb einer Fruchtfolge zu Kulturen mit hohem P-Bedarf gedüngt werden. Eine gesteigerte P-Versorgung von Mais konnte durch einen vorherigen Anbau von Rotklee in der Fruchtfolge erzielt werden. Die Absenkung des pH in der Bodenlösung infolge biologischer Stickstofffixierung hat vermutlich zu einer erhöhten Pflanzenverfügbarkeit schwerlöslicher P-Verbindungen aus Recycling-P Düngemitteln geführt. Darüber hinaus hat möglicherweise auch eine Freisetzung von P aus zersetzten Kleewurzeln zu einer verbesserten P-Versorgung des darauffolgenden Maises beigetragen. Die durch den Anbau von Klee mobilisierte P-Menge war jedoch nicht hoch genug um den gesamten P-Bedarf von Mais zu decken. Zu Mais sind daher vermutlich zusätzliche P-Düngegaben erforderlich. Eine P-Mobilisierung durch die Applikation verschiedener Bakterienstämme konnte in nur einem Fall erzielt werden. Möglicherweise bleibt der gewünschte Effekt einer P-Mobilisierung durch zusätzlich applizierte Bakterien gerade im Ökologischen Landbau aus, für den eine hohe mikrobielle Aktivität im Boden charakteristisch ist. Aus agronomischer Sicht sind Recycling-P Düngemittel aus Klärschlamm geeignetere Alternativen als PR für die ökologische Pflanzenproduktion. Ein Nährstoffrecycling wird von ökologischen Leitlinien grundsätzlich befürwortet. Mit der Aufnahme dieser neuartigen Düngemittel kann der Ökologische Landbau einen entscheidenden Beitrag zur Schließung des P Kreislaufes leisten und sich - einmal mehr - zu einem Bewirtschaftungssystem der Zukunft weiterentwickeln

Assessment of Alternative Phosphorus Fertilizers for Organic Farming: Sewage Precipitation Products

The application of sewage sludge to agricultural land is currently prohibited in organic farming due to the risk of soil contamination from harmful compounds. Incineration or disposal to landfill of sludge is costly, leads to increased greenhouse gas emissions, and neglects the possibility of nutrient recovery. There are various technologies to recover P by crystallization or precipitation from waste water and sewage sludge. Depending on the input material, nutrient concentrations and concentration of contaminants can vary widely. Regarding the content of potentially toxic elements, the trade-offs between (potentially) toxic element concentrations and potential benefits may be more favorable for treated sewage products than for several natural phosphate rocks or even animal manures or bio waste compost. This fact sheet describes the most important aspects to assess the suitability of sewage sludge precipitation products for use in organic farming

Re-visiting Meltsner: Policy Advice Systems and the Multi-Dimensional Nature of Professional Policy Analysis

10.2139/ssrn.15462511-2

Recycling Phosphor Düngemittel für den Ökologischen Landbau

Phosphorus is an essential, non-substitutable nutrient for all living organisms, and global resources are getting depleted. Cycling of nutrients is a main principle in organic farming, which can make P fertilizers recycled from sewage sludge a suitable alternative. Several Recycling P fertilizers from sewage sludge processing, combined with two different Bioeffector products, were investigated for their P availability in pot experiments with red clover and maize. No significant effects could be shown due to Bioeffector applications. Promising effects of Recycling P-fertilizers could be shown concerning dry matter and plant P-uptake for both maize and red clover. Treatments with struvite reached values comparable with the superphosphate control while sewage sludge ash and the pyrolysis-coal performed in the lower range of the unfertilized and Phosphate Rock (PR) control. Remaining products lied in between. Further research on Recycling P-fertilizers is a promising approach in search of an alternative P supply of crops in the future

Increased phosphorus availability from sewage sludge ashes to maize in a crop rotation with clover

A recycling of Phosphorus (P) from the human food chain is mandatory to secure the future P supply for food production. However, many available recycled P fertilizers from sewage sludge do not have an adequate P bioavailability and, thus, are not suitable for their application in soils with pH >5.5–6.0, unless being combined with efficient mobilization measures. The aim of the study was to test the P mobilization ability of red clover (Trifolium pratense L.) from two thermally recycled P fertilizers for a subsequently grown maize. Two sewage sludge ashes (SSA) were investigated in a pot experiment at soil pH 7.5 with red clover differing in its nitrogen (N) supply (added N fertilizer or biological N2 fixation (BNF)), followed by maize (Zea maize L.). Shoot dry matter of maize was almost doubled when N supply of previous grown clover was covered by BNF, instead of receiving added N fertilizer. Similarly, shoot P removal of maize following clover with BNF was significantly increased. It is suggested that the P mobilization is related to the BNF, and a proton release of N2 fixing clover roots led to the measured decrease in soil pH and thereby increased P availability of the tested fertilizers.CORE Organic I

Phosphorus bioavailability of sewage sludge-based recycled fertilizers

Six phosphorus (P) fertilizers recycled from sewage sludge [Struvite SSL, Struvite AirPrex,P-RoC, Mephrec, Pyrolysis coal and Ash (Mg-SSA)] were tested for their plant availability in potted soil of pH 7.2 under greenhouse conditions. The crop sequence simulated a rotation of red clover (Trifolium pratense L.), maize (Zea maize L.), and ryegrass (Lolium perenne L.). Other P fertilizer treatments included: Phosphate Rock (PR), Calcium dihydrogen phosphate [Ca(H2PO4)2], and an unfertilized control. Additionally, soil was regularly inoculated with two strains of plant growth-promoting rhizobacteria (PGPR; Pseudomonas sp. Proradix, and Bacillus amyloliquefaciens) to test their ability to increase P availability to plants. Sequential P fractionation was conducted to link the amount of readily available P in fertilizers to plant P acquisition. Shoot P content and dry matter of maize decreased in the following order: Struvite SSL >= Ca(H2PO4)2 > P-RoC >= Struvite AirPrex >= Mephrec > Pyrolysis coal >= Mg-SSA >= PR >= unfertilized. Rhizobacteria did not affect shoot biomass or P content. The results show that red clover might have mobilized substantial amounts of P. Sequential P fractionation was not suitable to predict the efficacy of the fertilizers. Generally, the sewage sludge-based fertilizers tested proved to be suitable alternative P sources relevant to organic farming systems. However, the efficacy of recycled fertilizers is strongly dependent on their specific production conditions

Sensitivity of Three Phosphate Extraction Methods to the Application of Phosphate Species Differing in Immediate Plant Availability

Extractive tests for determining the plant-availability of soil phosphorus (P) give varying results due to the inherently different characteristics of the extraction solution. Generally, classical soil P tests such as the Olsen or calcium acetate/lactate (CAL) method do not give an indication on the total amount of plant available P, but merely give an indication of the equilibrium between soil and extraction solution. It is also not entirely clear which fractions of P are directly determined through the various methods of extraction, i.e., determined P must not be immediately plant available, as is the case for rock phosphate. It is therefore possible that extraction methods either over or under estimate the amount of P available for plant consumption. In this research, we compared three methods of soil P determination (CAL, Olsen and diffusive gradients in thin films (DGT)) with regards to their ability to determine P species (Ca(H2PO4)2, CaHPO4, Ca3(PO4)2 and Inositol-6-hexakisphosphate) added to soils of high sorption capacity, immediately after as well as two weeks after application. For each of the methods, it could be shown that sorption processes in the soil immediately (0 days incubation) fix P to a point where it is not extractable through any of the described methods. These sorption processes continue over time, leading to a further decrease of determined P. The acidic CAL extraction method gives higher results of extractable P compared to the Olsen method. Due to the extraction of Ca3(PO4)2, the CAL method may overestimate immediately plant-available P. The most suitable methods for the determination of immediately plant available P may therefore be the Olsen and DGT methods. Organic IP6 is not determined by any of the extraction methods. At low concentrations of soil P, the DGT method may fail to give results

The Oncolytic Virus VSV-GP Is Effective against Malignant Melanoma

Previously, we described VSV-GP, a modified version of the vesicular stomatitis virus, as a non-neurotoxic oncolytic virus that is effective for the treatment of malignant glioblastoma and ovarian cancer. Here, we evaluate the therapeutic efficacy of VSV-GP for malignant melanoma. All of the human, mouse, and canine melanoma cell lines that were tested, alongside most primary human melanoma cultures, were infected by VSV-GP and efficiently killed. Additionally, we found that VSV-GP prolonged the survival of mice in both a xenograft and a syngeneic mouse model. However, only a few mice survived with long-term tumor remission. When we analyzed the factors that might limit VSV-GP’s efficacy, we found that vector-neutralizing antibodies did not play a role in this context, as even after eight subsequent immunizations and an observation time of 42 weeks, no vector-neutralizing antibodies were induced in VSV-GP immunized mice. In contrast, the type I IFN response might have contributed to the reduced efficacy of the therapy, as both of the cell lines that were used for the mouse models were able to mount a protective IFN response. Nevertheless, early treatment with VSV-GP also reduced the number and size of lung metastases in a syngeneic B16 mouse model. In summary, VSV-GP is a potent candidate for the treatment of malignant melanoma; however, factors limiting the efficacy of the virus need to be further explored

Investigating of a three-mirror multipass waveguide laser resonator for a compact CO2 laser with radio frequency pumping

Phosphorus (P) is an essential element for all living organisms. At the current rate of extraction, global reserves of mineable deposits will be exhausted within the next few centuries. This publication aims to summarize the current knowledge on P recycling for organic farming. The evaluation of recycled P fertilizers (RPFs) includes (i) a chemical characterization, (ii) assessment of their plant P availability and added effects in the soil, (iii) life cycle assessments, (iv) a risk assessment of their long-term impacts on soil pollution, and (v) the compilation of other environmental impacts of different treatment approaches to produce RPFs.The highest nutrient recovery rates for P are achieved by rather simple process approaches of P recycling, while more sophisticated approaches often result in lower P recovery rates (e.g., chemical approaches for P precipitation), lower plant P availability in the final product (e.g., most thermal approaches), and losses of organic matter and nutrients like nitrogen and sulfur (e.g., thermal approaches). The plant P availability of many RPFs is higher than that of phosphate rock. Each P recycling approach has strengths and weaknesses. We conclude that any decision not to use a potential recycled P source or to introduce sophisticated treatments may have consequences compromising the ability of future generations to meet their needs. Nevertheless, we need to minimize risks for current and future generations caused by contamination linked to fertilization. Therefore, any management of nutrient recycling requires navigation between constraints. The challenge for the organic agriculture sector is to assess RPFs using a balanced approach that compromises neither the principle of ecology nor the principle of care