Possibilities of plant nutrient recycling in energy grass plantations = Augu barības elementu reciklācijas iespējas enerģētisko zālaugu plantācijās

To develop the scientific work, field trials were performed at the Research Institute of Agronomy of the Latvia University of Life Sciences and Technologies, in Skriveri in the time period from 2012 to 2016. Hypothesis of the thesis By using by-products of bioenergy production in fertilisation - fermentation residues or digestate and wood ash, it is possible to partially cover the requirements of energy grasses for nutrients, as well as to ensure their reuse. The aim of the thesis To find out the possibilities of growing reed canary grass (Phalaris arundinacea L.) 'Bamse' and festulolium (× Festulolium pabulare) 'Felina' for energy production by using bioenergy production by-products in fertilisation – fermentation residues or digestate and wood ash, as well as to study possibilities of plant nutrient reuse in the system: soil – plants – digestate / ash – soil – plants. Research tasks 1. To evaluate digestate and wood ash as energy grasses fertilisers. 2. To find out the optimal norm and the regime of use of digestate in reed canary grass fertilisation. 3. To study the nitrogen, phosphorus, potassium circulation cycle in the system: soil – plants – digestate / ash – soil – plants. 4. To perform economic evaluation of reed canary grass and festulolium fertilisation. The structure of the research paper Chapter 1 - The literature review includes five subchapters. The chapter provides a brief overview of bioenergy production technologies, examines perennial grasses in the context of bioenergy production, evaluates agrotechnical measures to ensure adequate grass biomass yield and quality for biogas and fuel feedstock production, examines plant nutrient circulation in bioenergy crop production systems, and provides agronomic assessment of by-product – digestate and ash fertiliser for use in energy grass plantations. Chapter 2 - Materials and Methods includes two subchapters. The chapter describes the methodology of test establishment, the studied material, the observations and analyzes performed, describes the meteorological conditions and describes the statistical analysis of data. Chapter 3 - The results and discussion include six subsections. The chapter analyzes the obtained results on reed canary grass and festulolium yield and changes in yield structure and quality due to the use of different fertilisers, norms and regimes, performing grassland dry matter yield inventory by mowing once and twice a year. The remove of plant nutrients from soil with dry matter yield, as well as changes in soil agrochemical parameters due to fertilisation were evaluated. An economic evaluation of reed canary grass and festulolium fertilisation has been performed. The conclusions include answers to the research tasks. The paper contains 34 tables, 41 figures, 53 annexes and 353 scientific source references.