Sirvi Autor "Astover, Alar (advisor)" järgi
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Kirje Mitigation of nitrous oxide emissions from arable soils(Estonian University of Life Sciences, 2022) Escuer Gatius, Jordi; Shanskiy, Merrit (advisor); Soosaar, Kaido (advisor); Astover, Alar (advisor); Institute of Agricultural and Environmental Sciences; Butterbach-Bahl, Klaus (opponent)The need to reduce emissions of greenhouse gases responsible for global warming of the planet is generally acknowledged. Agriculture is the main anthropogenic source of non-CO2 emissions, which include N2O and CH4. Anthropogenic emissions represent approximately half of the total global N2O emissions, and agriculture is responsible for around two-thirds of those emissions. This is especially important because N2O has a global warming potential 273 times that of CO2 and is currently the main stratospheric ozone-depleting substance. The aim of this PhD thesis was to contribute to the understanding mechanisms behind N2O emissions and in the mitigation potential of N2O emissions of biochar and the nitrification inhibitor DMPP. Field emissions were driven by organic fertilization and freeze-thaw events. Organic fertilization increased N2O emissions in all cases, but mineral fertilization did not immediate increase emissions. Fresh rapeseed and rye residues incorporation into the soil increased N2O emissions with similar emissions to those measured for organic fertilization, while wheat straw incorporation did not increase emissions. The studied mitigation tools did not reduce N2O emissions. Emissions coming from denitrification, due to the environmental and field conditions, resulted in ineffectiveness of the nitrification inhibitor, with differences in N2O emissions attributable to differences in soil water content. High temperature hay biochar application, on the other hand, increased N2O emissions, which is explained by the release of C and N from the applied biochar. This research highlights the importance of the relationships between soil amendment properties and soil N2O emissions, and finally the moment of application. Research on mitigation tools should focus on developing effective farmer-oriented tools that consider amendment characteristics, soil properties and weather conditions.Kirje Pathogenic and arbuscular mycorrhizal fungi in potato fields in Estonia(Eesti Maaülikool, 2021) Loit, Kaire; Astover, Alar (advisor); Tedersoo, Leho (advisor); Öpik, Maarja (advisor); Timonen, Sari (opponent); Koppel, Mati (reviewer)Soil fungi have fundamental ecological roles as decomposers, mutualists, and pathogens of plants. Roots of agricultural plants are hosts for various microorganisms. These include many harmful, often soilborne, pathogens, as well as beneficial organisms such as plant growth- and health‐promoting arbuscular mycorrhizal (AM) fungi. Potato (Solanum tuberosum L.) yield and quality is very sensitive to various pathogens. Soils contain distinct AM fungal communities and most crops (including potato) naturally become colonized by AM fungi in the absence of inoculation. In the current thesis, diversity, abundance, and community composition of putative pathogenic fungi and symbiotic AM fungi in potato fields in Estonia is studied. We found that potato roots have higher AM fungal colonization levels under organic, rather than conventional, farming. However, colonization of potato roots by AM fungi is extremely low in both of these management types. Relative abundance of AM fungi is significantly higher at the end of the growing season compared to the beginning. Seasonal and cultivar-driven changes of soilborne phytopathogenic fungal communities in conventional potato production, both within roots and in soil, were studied for the first time on a large number of potato cultivars using high-throughput sequencing. Cultivar influenced root-pathogenic fungal richness and community composition more than sampling time or sampling time x cultivar interaction. Additionally, cultivar had a significant effect on root fungal pathogen relative abundance. In soil, the community composition of putative pathogenic fungi changed significantly over time. Under increasing threat of plant disease outbreaks, the speed of detection of plant disease agents is essential for avoiding large-scale crop losses. This thesis work demonstrated that the third-generation sequencing device MinION is well suited for rapid, PCR-free diagnosis of fungal pathogens and other eukaryotic organisms. However, care should be taken due to a number of possible limitations that might lead to misdiagnosis. Our findings demonstrate that AM fungi are present in Estonian conventional potato fields, but studied potato cultivars exhibit low AM root colonization levels. In order to benefit from AM fungi in potato cultivation, a potato growing technique that involves less soil disturbance could be used. The results of this thesis work also indicate the importance of plant breeding, concerning disease resistance; and offer implications for rapid pathogen diagnostics that may help to avoid large-scale crop losses caused by new, emerging pathogens that are undetectable from symptoms.Kirje Prediction models of soil organic carbon and bulk density of arable mineral soils(Eesti Maaülikool, 2016) Putku, Elsa; Astover, Alar (advisor); Ritz, Christian (advisor)Measuring soil properties is often not reasonable and financially possible. Therefore, prediction of soil properties is used more frequently by pedotransfer functions and predictive models. Legacy soil data can be used for predictive modelling, e.g., soil monitoring data, soil map. Soil organic carbon (SOC) concentration and bulk density are important indicators of soil quality and they are also necessary for SOC stock calculation. The aim of the thesis was to develop prediction models to predict SOC and soil bulk density in the humus horizon of Estonian arable soils from other more easily measured and available soil properties. The prediction quality between the grey-box models (multiple linear regression, median approach, linear mixed model) and a black-box model (random forests) was compared. It was important that the predictor variables were compatible with the Estonian large-scale Soil Map. Additionally, SOC stock was calculated based on predicted SOC and bulk density values. The highest prediction accuracy was for the linear mixed-model-predicted SOC (%) and bulk density (RMSE 0,22% and 0,09 g cm-3). Higher prediction accuracy can be expected as the competitor models did not incorporate any nested structure: transects are nested within plots, which are again nested within sites. Mixed model-based kriging for SOC concentration had a very modest gain in prediction accuracy. The best prediction accuracy for SOC stock was achieved by the mixed model-predicted values (RMSE 7 t C ha-1) compared to linear regression and median approach. The results were implemented into Estonian Soil Map in a specific area of Tartu County. Average estimated SOC stock of mineral arable soils in Tartu County is 54,8 t C ha-1 and total topsoil SOC stock 1,8 Mt. The methodology outlined in this thesis is general and applicable to situations with more candidate models in similar data structures renewing legacy soil data and using it efficiently addressing current scientific and practical soil use questions.Kirje Response of root fungal communities to fertilisation, crop species and cultivar(Estonian University of Life Sciences, 2021) Soonvald, Liina; Mänd, Marika (advisor); Astover, Alar (advisor); Tedersoo, Leho (advisor); Institute of Agricultural and Environmental Sciences; Peltoniemi, Krista (opponent)As the human population increases exponentially, intensification of agriculture is inevitable. Thus, there is an ongoing need for further research towards sustainable agriculture. Soil is a habitat with great microbial diversity. Many of these microorganisms interact with plants, promoting plant growth, improving nutrient uptake, and making plants less susceptible to pathogens. Therefore, it is important to study microorganisms and their coexistence with plants. The aim of this thesis was to study the root fungal community structure across different fertilisation treatments, crop species and cultivars. Fertilisation treatment had no effect on overall root fungal community composition and richness. However, changes occurred when pathogenic and mutualistic fungi were studied separately. Both manure amendment and alternative organic fertilisation decreased mutualists and increased pathogen richness in comparison to mineral fertilisation. Fertilisation is not the only factor affecting the root mycobiome; the results of this thesis suggest crop species as the most important factor. When the effects of fertilisation treatment and crop species were studied together, the effect of crop species was greater than both fertilisation treatment and the species−treatment interaction. Species richness and diversity were highest in wheat roots and lowest in potato roots. Crops species was the main factor determining differences in root fungal community composition. These results suggest that the root mycobiome is selectively recruited from the soil and related to host-plant physiological or morphological traits. In addition, potato cultivars differed in root fungal community composition and richness, again indicating the importance of host genotype in structuring the root mycobiome. This thesis improves our knowledge of how agricultural practices can shape root fungal community structure. This expertise is important for both scientists and agricultural practitioners. Understanding fungal communities allows us to use them to our advantage, and offers a promising strategy for improving soil quality and crop productivity. Without a fundamental understanding of how fungi respond to different agricultural practices at the field scale, it is not possible to develop these mycobiome-based sustainable farming practices.Kirje Site-specific energy crop planning: potential land resource, pedo-climatic and economic risks(Eesti Maaülikool, 2012) Kukk, Liia; Astover, Alar (advisor); Shanskiy, Merrit (advisor)In recent decades, renewable energy production has become the focus of energy policy. For meeting the target of increasing the share of renewable energy, biomass use is claimed to be essential. Since there has been a decrease in the use of agricultural areas after the restoration of independence in Estonia, abandoned agricultural land resource may have a potential in increasing bio-energy production. However, bio-energy sustainability should be analysed. Furthermore, there is a need for site-specific assessments, i.e. the inclusion of pedo-climatic conditions in bio-energy analyses. The aims of the study were: to develop a methodology for quantifying and locating abandoned agricultural areas, to assess bio-energy potential on abandoned fields and to develop the methodology for site-specific yield analysis in Tartu County as an example; to analyse fertilisation and energy efficiency dependence on soil properties and to model reed canary grass yield dependence on soil nitrogen content and nitrogen fertilisation; to compile multi-criteria analysis, i.e. energy efficiency (net energy yield, energy use efficiency) and profitability of reed canary grass production; and to analyse fibre hemp and energy sunflower biomass production grown on different nitrogen treatments. The conclusions of the study were: 1. In 2007, abandoned agricultural land in Tartu County formed 24% of the total agricultural area. Land resource soil analysis indicated a clear tendency of soil effect on land-use decisions. The proportion of abandoned areas in Tartu County is higher on soils with low soil fertility. 2. Total abandoned areas are not equally suitable for energy crop production. Soil-crop suitability analysis indicated that reed canary grass and grey alder have the highest re-use potential for abandoned parcels of compared dedicated energy crops (i.e. reed canary grass, Caucasian goat’s rue, willow, grey alder, hybrid aspen) with each re-using more than 80% of the available abandoned land in Tartu County. In the case of a combined land-use strategy, potential bio-energy production could provide a quarter (667 GWh) of county’s annual energy demand. 3. The yield of reed canary grass varies from 0.9 to 6.9 Mg ha-1 depending on the soil total nitrogen content and the climatic conditions. Nitrogen fertilisation decreases yield variability of reed canary grass on soils with a low soil nitrogen content. By contrast, on soils with a high soil nitrogen content, reed canary grass yield variability, i.e. production risks, increases with increasing fertiliser application. Nitrogen fertilisation efficiency decreases with increasing soil nitrogen content and mineral nitrogen application. 4. Irrespective of fertiliser application rates, also nitrogen treatment influences energy crop yield. From mineral and organic fertilisers in current study, the more favourable treatment for fibre hemp biomass formation was mineral nitrogen and sewage sludge and for energy sunflower, highest yield formed on sewage sludge treatment. 5. The integration of the yield model to the Estonian large-scale soil map approves spatial variability of reed canary grass biomass production. Approximately 81% of Tartu County`s agricultural area is capable of producing an average reed canary grass yield without fertilisation below 4 Mg ha-1, and the yields of 4 to 6 Mg ha-1 are achievable in a limited number of fields. 6. The current study provides the first evidence of an energy use efficiency curve dependent on soil nitrogen content in reed canary grass production. Energy use efficiency decreases on Histosols. On humus-poor soils, a quadratic curve relationship between energy input and energy use efficiency occures, i.e. to reach the optimum energy use efficiency level, nitrogen fertiliser inputs should be 198 kg ha-1. Detailed analyses on Haplic Albeluvisol indicated that an optimum energy use efficiency could be achieved by reducing the nitrogen application norm twofold to reach a production minimum net cost. Therefore, knowledge-based bio-energy production requires the inclusion of multiple characteristics and site-specific information in analysis.