Miscanthus x giganteus yield in a REpeated PLAnting Year (REPLAY) experiment across three sites in Iowa, USA.
Research objectives were to study nitrogen (N) fertilization and age effect on Miscanthus x giganteus (mxg) yield and their interaction. In addition, we studied how establishment conditions affected mxg yield response to N fertilization. This is the first repeated planting year experiment conducted on perennial bioenergy grasses. Data showed that mxg yield response to N fertilization was highly variable. Establishment effects were an important driver of this variability and caused significant changes on the magnitude and direction of one-year-old stands’ response to N fertilization. With repeated planting we compared yield gain from first to second year of growth of different single starts. Yield gain of each single start was different within and between sites. This site-specific response suggests that important biases could be introduced when comparing results across studies if repeated planting is not utilized. Biomass from mxg plots was sampled annually in winter or early spring after multiple days with freezing temperatures (Table 1). At each harvest, two 1-m2 quadrats per plot were collected by hand at 0.10 m above the soil surface and weighed. In 2016 and 2018, we used a composite subsample to estimate dry matter content. In 2017, the dry weight subsamples were made of 15 randomly collected stems from each plot. Subsamples were weighed in the field and dried to constant mass at 60 °C in a forced air drier. The final mass was recorded and dry matter content was calculated for each plot.