Straw yield and quality parameters of wheat for bio-refineries as affected by nitrogen application
Research output: Book/Report › Ph.D. thesis › Research
Most of global energy production is currently facilitated by use of fossil fuels. Uncertain supply of ever declining fossil fuel reserves and climatic changes associated with their use demand a transition towards sustainable alternatives for energy production in the future. The use of lignocellulosic bio–masses has the potential to dramatically reduce carbon footprint for energy production. The challenge therefore is to increase agricultural output in order to feed the world’s growing population and simultaneously manage the transition to a bio–based society without devastating effects to the environment. A renewable "dual purpose" biomass like wheat can yield grain for food and fodder as well as straw for energy (burning, gasification, or ethanol production) and/or chemical production. The aims of this Ph.D. thesis were to evaluate the performance of wheat cultivars in terms of grain and straw yield as well as molecular components (cell wall components, nitrogen containing substances) in order to select a suitable "dual purpose cultivar" for bio–refining purposes. The focus was set on nitrogen fertilisation as the main driver of plant growth and productivity. Furthermore, the amount and composition of residual nitrogen in mature wheat straw was investigated. This might help to find possible targets on how to improve nitrogen use efficiency. In order to find a suitable "dual purpose cultivar", a field trial with one triticale and14 modern elite wheat cultivars was conducted over a three–year period at three nitrogen regimes (100, 160 and 220 kg ha1). The influence of nitrogen application on straw and grain yield, straw and grain nitrogen concentrations and straw cell wall composition (cellulose, lignin, and silicon) as well as their influence on sugar release (glucose and xylose) by enzymatic saccharification was investigated. It is concluded that increased nitrogen application up to 160 kg ha1 significantly increased straw and grain yield whereas grain and straw nitrogen concentrations significantly increased even up to 220 kg ha1. It was not possible to detect an overall significant effect of nitrogen fertilisation on straw quality parameters directly relevant for bio–refining purposes, i.e. carbohydrate concentration and conversion efficiency. Furthermore, no consistently significant differences between cultivars in terms of cell wall composition, apart from silicon, and sugar release potential were observed. However, the triticale cultivar Trilobit showed the highest sugar potential on a hectare basis since it outperformed all tested wheat culitivars in terms of straw and grain yield. Therefore, Trilobit was identified as the ideal "dual purpose cultivar". The selection and breeding of "dual purpose cultivars" should be focused on higher total above ground biomass yield (straw and grain) rather than higher cellulose content or reduced recalcitrance. Further research should include more genetically diverse wheat cultivars and focus on improving their nitrogen use efficiency to boost total above ground biomass output. In a second part, nitrogen which has not been re–mobilised to the grain during plant maturation, and therefore remained unutilised as residual nitrogen in mature straw was investigated. The reduction of residual nitrogen in mature wheat straw is an essential challenge not only in order to boost grain protein and nitrogen use efficiency but also to improve the quality of the straw for bio–energy purposes, since residual straw nitrogen contributes to the production of gases such as nitrous oxides (NOx, N2O) during thermochemical degradation, which results in pollution of the atmosphere. In order to reduce residual nitrogen a thorough understanding of its nature is required. However, very limited information is available on the composition of residual nitrogen pools and how they are affected by nitrogen fertilisation. iTherefore, a field trial in which the winter wheat variety Evolution was grown at five different nitrogen fertilisation levels ranging from 60 to 280 kg ha1 was conducted to elucidate the effect of nitrogen fertilisation on the composition of the residual nitrogen pools in winter wheat straw fractions. For this, a high–throughput method to analyse amino acids in a range of plant materials was developed. This method was used to investigate the influence of nitrogen fertilisation on the concentration and composition of amino acids in mature wheat straw fractions.It was concluded that nitrogen fertilisation significantly incr eased residual straw nitrogen concentrations, which were mainly derived from non–re–mobilised proteins (e.g. amino acid–derived), whereas non–protein nitrogen (DNA, chlorophyll and nitrate-derived) contributed only minor to the overall pool of residual nitrogen. Most of the amino acid nitrogen was associated with cell walls rather than cellular proteins, indicating that cellular proteins were efficiently re–mobilised. Finally, a considerable part of residual nitrogen seemed to be lignin associated. However, further research in order to decipher the formation and role of lignin associated nitrogen is required. Given the relatively small variety differences in straw quality parameters and the minor influence of nitrogen fertilisation on this, it is concluded that future breeding programs should focus on achieving greater biomass yields of straw and grain, than on increased cellulose content per unit of straw biomass or increased straw degradability to release sugars by enzymatic saccharification. Nitrogen supply, through increasing biomass yields, increases the potential for larger yields of bio–refining components such as sugar and lignin in the straw. As part of this, it will be a key objective to improve the nitrogen utilisation efficiency of wheat.
|Publisher||Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen|
|Publication status||Published - 2019|