Research paperHarvest date of Miscanthus x giganteus affects nutrient cycling, biomass development and soil quality

- Nutrient recycling of Miscanthus was intensely reduced by early harvest dates.
- Element-specific reduction of nutrient recycling by early harvest dates.
- Internal and external recycling pathways were both affected.
- Premature harvest of Miscanthus reduces soil quality due to reduced C and N inputs.

Anaerobic digestion is the most advanced technology allowing the production of methane as flexible energy carrier. Recently, in view of mitigating the ecological drawbacks of maize as predominantly used feedstock, perennial energy crops were introduced in European agriculture, which implicated reduced resource input and improved landscape diversity. The biogas potential of Miscanthus x giganteus is high when harvested in autumn, prior to lignification. However, the effects of autumn harvest on carbon and nutrient recycling depict a gap of research. A two-year field experiment was conducted to compare autumn harvest with the commonly conducted harvest date in spring. Below and aboveground plant fractions were analysed to quantify pathways of nutrient recycling and contrasting different harvest dates. Additionally, crop biomass development and soil quality parameters were monitored.This study indicates that autumn harvest increase biomass yields by up to 30%, whilst nutrient exports were several times higher than in spring. Our results further show that pathways of nutrient recycling were element-specific and that recycling of specific elements was influenced to a varying extent by autumn harvest. Significantly reduced deposition of storage proteins in rhizomes resulted in weaker biomass development in subsequent years. The degradation of the mulch layer, resulting from drastically reduced input of organic material to the soil, led to changed soil conditions, which were reflected in reduced soil microbial biomass and activity.Consequently, the ecological benefits of Miscanthus cultivation, such as low nutrient demands, perennial soil cover and high potential for carbon sequestration, would be distinctly reduced.