Influence of compost and digestates on plant growth and health: potentials and limits

Composts can influence soil fertility and plant health. These influences can be positive or negative, depending of the quality of the composts. In order to estimate the potential of Swiss composts to influence soil fertility and plant health, one hundred composts representative of the different composting systems and qualities available on the market were analyzed. The organic substance and the nutrient content of the composts varied greatly between the composts; the materials of origin were the major factor influencing these values. The respiration rate and enzyme activities also varied greatly, particularly in the youngest composts. These differences decreased when the composts become more mature. Maturity, the degradation stage of the organic matter, depended not only on the age of the compost, but also on the management of the process. The Nmineralization potential of compost added to soil showed that a high proportion of young composts immobilized the nitrogen in the soil. Two compost parameters allow to predict the risk of nitrogen immobilization in soil: the NO3- and the humic acids contents. The phytotoxicity of the composts varied very much even in mature composts, showing that the storage of the compost plays a decisive role. While the majority of composts protected cucumber plants against Pythium ultimum, only a few composts suppressed Rhizoctonia solani in basil. With respect to disease suppression, the management of the maturation process seems to play a major role. In field experiments, some biologically immature composts immobilized nitrogen in soil and reduced growth of maize. With additional fertilization, however, it was possible to compensate this effect. Digestates and composts increased the pH-value and the biological activity of soil. These effects were observable also one maize season after compost application. In conclusion, big differences were observed in the quality of composts and digestates, and in their impact on soil fertility and plant health. The management of the composting process seems to influence the quality of the composts to a higher extent than the materials of origin or the composting system. More attention should be paid to biological quality of composts, in order to produce composts with more beneficial effects on crops

Effects of digestate on the environment and on plant production - results of a research project

Composts and digestates can influence soil fertility and plant health. These influences can be positive or negative, depending of the quality of the composts. A currently important question is to know, if digestates differ from composts in these aspects. A Swiss project is concerned with the estimation of the potential of Swiss composts and digestates to influence soil fertility and plant health positively. For this, one hundred composts and digestates representative of the different composting systems and qualities available on the Swiss market were analyzed. The organic matter and nutrient content of the composts varied greatly between the composts and the digestates; the materials of origin were the major factor influencing these values. The respiration rate and enzyme activities also varied greatly; they are particularly important in digestates. The organic matter of digestates is less stable than that of composts. The N-mineralization potential from the majority of the digestates added to soil is high, in comparison to young composts. When digestates are not correctly treated or stored, however, they can immobilize nitrogen in the soil. This problem is hardly correlated with the management of the digestate in the first stage after leaving the fermenter. Especially products which have become too dry during this period lost their ammonia-nitrogen, and hence immobilized nitrogen in the soil. The risk of phytotoxicity is higher in digestates than in composts. This limits the possibility for use of digestate. With a post-treatment of digestate, it is possible to produce high quality compost with a high compatibility with plant growth and with a more stabilized organic matter. In field experiments, digestates increased the pH-value and the biological activity of soil to the same extent than composts. These effects were observable also one season after compost application. No immobilization of nitrogen was observed

Effects of compost and digestate on environment and plant production – results of two research projects

A yearly amount of 9.3x106t compost and digestate derived from separately collected organic waste is produced in the 25 European Union member states. The improvement of soil properties is a major benefit of compost application. However, little is known about the occurrence of organic pollutants in compost. In order to estimate the potential of Swiss composts and digestates to influence soil fertility and plant health, one hundred products representative for the different composting systems and qualities available on the Swiss market were analyzed in two research projects. In the first study, polycyclic aromatic hydrocarbons (PAHs), ortho substituted and dioxin-like polychlorinated biphenyls (PCBs, DL PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), tetrabromobisphenol A (TBBPA), perfluorinated alkyl substances (PFAS), pesticides, chlorinated paraffins (CPs), phthalates and nonylphenol (NP) were analyzed. All compound classes were detected except for NP. PFAS, HBCD, TBBPA, some compounds out of PBDEs and pesticides were found in compost and digestate for the first time. Concentrations of most compounds were in the low ppb range. Contents of PAHs were between 600 and 12473 μg/kg dry weight (dw) and contents of HBCD and CPs between 17 and 384 μg/kg dw. Tests with springtails (Folsomia candida) have been shown to be a versatile tool for ecotoxicological assessment. Within these tests, inhibiting and stimulating effects due to compost application were observed. Except for high PAHs contents, no major problem with regard to contamination of compost and digestate was identified. In the second study, the physical, chemical and biological properties of the composts and digestats, and their influence on soil fertility and plant growth, were characterized. The organic substance and the nutrient content of the composts varied largely between the composts with the feedstock materials as major influencing factors. The respiration rate and enzyme activities exhibited large variations as well, particularly in the youngest composts. These differences decreased when the composts became more mature. Maturity, the degradation stage of the organic matter, depended not only on the age of the compost, but also on the management of the process. The N-mineralization potential of compost added to soil showed that a high proportion of young composts immobilized the nitrogen in the soil. Two compost parameters allowed to predict the risk of nitrogen immobilization in soil: the NO3- and the humic acids contents. The phytotoxicity of the composts varied largely even in mature composts, showing that the storage of the compost plays a decisive role. While the majority of composts protected cucumber plants against Pythium ultimum, only a few composts suppressed Rhizoctonia solani in basil. With respect to disease suppression, the management of the maturation process seems to play a major role. In field experiments, some biologically immature composts immobilized nitrogen in soil and reduced growth of maize. With additional fertilization, however, it was possible to compensate this effect. Digestates and composts increased the pH-value and the biological activity of soil. These effects were observable also one maize season after compost application. In conclusion, the management of the composting process seems to influence the biological quality of the composts and digestats to a higher extent than the feedstock materials or the composting system. More attention should be paid to this biological quality, in order to produce composts with more beneficial effects on crops

Auswirkungen von Komposten und von Gärgut auf die Umwelt, Bodenfruchtbarkeit, sowie die Pflanzengesundheit: Ökologische Bewertung der organischen Substanz

Bisher war es für Kompost und Gärgut in Ökobilanzen üblich, die Nährstoffe als Substitute von Mineraldüngern und die Schwermetalle als Belastungen einzusetzen. Im Vergleich zur Verbrennung, wo die organische Substanz vollständig mineralisiert und energetisch genutzt wird, gibt es bei Kompost und Gärgut eine Lücke: wie soll die organische Substanz bewertet werden? Zur Bewertung der organischen Substanz in Ökobilanzen gibt es zwei grundlegend verschiedene Vorgehensweisen: 1. Einsetzen der einzelnen Effekte wie Erosionsreduktion, weniger Zugkraftbedarf, bessere Wasserhaltekapazität, weniger Krankheitsanfälligkeit etc. mit jeweils entsprechenden LCA-Modulen 2. Globales Einsetzen von Substituten, welche die Effekte möglichst gut abbilden. Gegen die erste Vorgehensweise sprechen die lückenhafte Datenbasis, der hohe Aufwand für die einzelnen Module und die Problematik der Interaktionen zwischen einzelnen Effekten. Das globale Einsetzen gibt ein rasterartiges Bild, das die physikalischen Effekte relativ gut abbildet, aber die biologischen Effekte (z.B. Krankheitsunterdrückung) nicht vollständig abdecken kann. Der Vorteil dieses Ansatzes besteht darin, dass man mit bestehenden Modulen arbeiten kann und diese gleichzeitig die Interaktionen nicht stören (die alternative organische Substanz wird nur einmal angewendet und erzeugt die Effekte). Aufgrund von Machbarkeitsüberlegungen gelangt die Studie zum Schluss, dass im Moment nur das globale Einsetzen von Substituten zum Erfolg führen kann. Als Substitut werden für die landwirtschaftliche Anwendung Stroh und für die gärtnerische Anwendung Torf gewählt. Es wird angenommen, dass zwei Drittel der Menge von Kompost und Gärgut in der Landwirtschaft eingesetzt wird. Das dritte Drittel, das im Gartenbau Anwendung findet, kann durch den dort üblichen Torf ersetzt werden. Die Mengen der Substituten werden aufgrund der Fähigkeit Humus zu reproduzieren berechnet. Ein Reifkompost kann fast viermal so viel Humus ersetzen wie frische organische Substanz in Stroh oder Gründüngung. Es wird auf viele Wissenslücken in diesem Bereich hingewiesen

Potential of different composts to improve soil fertility

Composts can influence soil fertility and plant health. These influences can be positive or negative, depending of the quality of the composts. Some practitioners already make use of the positive effects on plant health. For example, they use composts to protect their plants against soil borne diseases in substrate, or to detoxify and reactivate soil after steaming. In order to estimate the potential of Swiss composts to influence soil fertility and plant health positively, we analyzed one hundred composts representative of the different composting systems and qualities available on the market. The organic substance and the nutrient content of the composts varied greatly between the composts; the materials of origin were the major factor influencing these values. The respiration rate and enzyme activities also varied greatly, particularly in the youngest composts. These differences become smaller when the composts become more mature. Maturity, the degradation stage of the organic matter, depended not only on the age of the compost, but also on the management of the process. The N-mineralization potential from compost added to soil showed that a high proportion of young composts immobilized the nitrogen in the soil. This problem was hardly correlated with the materials of origin, but with the management of the first stage of the composting process. Especially composts which had become too dry in this period lost their ammonia-nitrogen, and hence immobilized nitrogen in the soil. Also composts with a low NO3/NH4 ratio, as a rough indicator for an immature compost, immobilized nitrogen in the soil. By contrast, the phytotoxicity of the composts varied very much also in matured composts, showing that the storage of the compost plays a decisive role. While the majority of compost protected cucumber plants against Pythium ultimum, only a few composts suppressed Rhizoctonia solani in basil. With respect to disease suppression, the management of the maturation process seems to play a major role. In conclusion, big differences in compost quality and of their impact on soil fertility and on plant health were observed. The management of the composting process seems to influence the quality of the composts to a higher extent than the materials of origin or the composting system. More attention should be paid to biological quality of composts, in order to produce composts with more beneficial effects on crops

Velocity profiles and interface instability in a two-phase fluid: investigations using ultrasonic velocity profiler

In the present study the velocity profiles and the instability at the interface of a two phase water-oil fluid were investigated. The main aim of the research project was to investigate the instability mechanisms that can cause the failure of an oil spill barrier. Such mechanisms have been studied before for a vast variety of conditions (Wicks in Fluid dynamics of floating oil containment by mechanical barriers in the presence of water currents. In: Conference on prevention and control of oil spills, pp 55-106, 1969; Fannelop in Appl Ocean Res 5(2):80-92, 1983; Lee and Kang in Spill Sci Technol Bull 4(4):257-266, 1997; Fang and Johnston in J Waterway Port Coast Ocean Eng ASCE 127(4):234-239, 2001; among others). Although the velocity field in the region behind the barrier can influence the failure significantly, it had not been measured and analyzed precisely. In the present study the velocity profiles in the vicinity of different barriers were studied. To undertake the experiments, an oil layer was contained over the surface of flowing water by means of a barrier in a laboratory flume. The ultrasonic velocity profiler method was used to measure velocity profiles in each phase and to detect the oil-water interface. The effect of the barrier geometry on velocity profiles was studied. It was determined that the contained oil slick, although similar to a gravity current, can not be considered as a gravity current. The oil-water interface, derived from ultrasonic echo, was used to find the velocity profile in each fluid. Finally it was shown that the fluctuations at the rearward side of the oil slick head are due to Kelvin-Helmholtz instabilitie

Influence of Operational Timing on the Efficiency of Venting Turbidity Currents

Reservoir sedimentation is gaining growing attention as dams are aging, due to economic and environmental consequences. Venting of turbidity currents is one of many sediment management techniques, highly recommended when water is in shortage. The venting operation is experimentally investigated using two reservoir bed slopes. The main research questions concern the opening timing of bottom outlets and the duration of venting. The timings tested are relative to the arrival of the current at the outlet. The results showed that in-time venting, synchronized with the arrival of the turbidity current at the outlet, is more efficient than early or late venting. It is recommended to start opening the gates when the turbidity current is around 300 m upstream of the outlet, so that the evacuation is synchronized with the arrival of the current at the dam. Additionally, venting should not be stopped immediately after the end of the turbidity current flow but should instead last for a certain time in order to evacuate the muddy lake depending on the outflow discharge