Relationship Between Miscanthus x Giganteus Growth and Soil Properties in Response to Residual Fertility and Time.

Miscanthus x giganteus is a high yielding, cellulosic biofuel crop of increasing popularity. The objective of this study was to measure the responses of Miscanthus x giganteus and soil properties to residual fertility in the first five years of crop establishment. The hypothesis was that, over time, the relationships between M. giganteus growth, soil properties and residual soil fertility treatments would change. In 2010, M. x giganteus was planted in an existing study with eight replications of each of five composted manure rates (0, 2.2, 4.5, 9.0 and 18.0 Mg/ha), applied annually between 2000 and 2005, and with the forty plots laid out in a completely randomized design. The plots were sampled annually between 2011 and 2015 for plant (vigor and tissue composition) and soil (organic matter, bulk density, wet and dry aggregate stability as Geometric Mean Diameter [GMD], and bioavailable nutrient levels) properties. Results indicated that as time progressed, M. x giganteus growth curves and vigor showed less response to the residual fertility treatments. Soil properties were becoming more similar as well. In 2011, there were significant differences in bulk density (1.39, 1.32, 1.32, 1.19 and 1.23 g/cm³ for 0, 2.2, 4.5, 9.0 and 18.0 Mg composted manure/ha, respectively) and dry aggregate stability (GMD=13.79, 6.52, 8.89, 4.55, 5.31 mm for 0, 2.2, 4.5, 9.0 and 18.0 Mg composted manure/ha, respectively), as well as wet aggregate stability. However, in 2015 plant vigor and growth were not significantly different due to the residual fertility treatments, nor were bulk density (averaged 1.32), wet aggregate stability (GMD averaged 5.19 mm), or dry aggregate stability (GMD averaged 7.03 mm). These results support the hypothesis - the relationship between Miscanthus x giganteus growth/vigor and residual fertility changed with time, as did the responses of other soil properties.