Dynamics of C, N and C/N ratio in substrates based on miscanthus straw in container production of Spiraea japonica 'Macrophylla'

Peatlands, as non-renewable resources, are under international and EU legal protection supported by many acts from member countries. Therefore, peat substrates will have to be replaced and new alternatives for this material are being sought. Tested organic compounds, such as pine bark or straw, have high C/N ratios, thus there is a need for compensatory N application. The aim of this research was to assess the dynamics of C, N and C/N ratio during the cultivation of Spiraea japonica 'Macrophylla' in substrates based on miscanthus straw with the use of different fertilizers. Analysis was performed on three dates: at the end of April, July and October 2016. The results show that C and N content on all the dates increased with increasing miscanthus straw content in the tested substrates. However, N content increased in July in comparison to April and then decreased in October, while C content increased with each date. In July and October, the highest N content was noted in substrates treated with B+YM fertilizers, while there was no clear fertilization effect for C content. Also the C/N ratio showed a tendency to increase in July with the increase of miscanthus straw content in substrates, while in October neither the substrate nor the fertilizer had a significant effect on this parameter. Moreover, despite the C/N ratio being higher in October in comparison to July, on both dates the C/N ratio was lower than in April. The results indicate that initial C/N ratio decreases to a level suitable for decomposition, but the competition for nitrogen between the microorganisms and plants leads to a deceleration of this process and an increase in C content. These findings suggest that substrates based on the miscanthus straw used can be suitable for nursery production.