The growth pattern of the Miscanthus Giganteus (MG) crop is simple. From the underground rhizomes new shoots are produced annually. These shoots develop into erect, robust stems, which reach 0.5 – 1m in height by late August of the first year of planting, with a diameter of up to 10mm. The stems, which have an appearance like bamboo canes, are usually unbranched and contain spongy pith. From the third season onwards, the crop can be expected to achieve a maximum height of 3 — 3.5m.
From late July the lower leaves senescence as canopy closure prevents sufficient light penetration. Following the first air frost in autumn senescence accelerates and nutrients move back to the rhizome. Leaves then fall and a deep leaf litter develops. Any remaining foliage dies, and the stems dry to relatively low moisture content (30-50%) during winter. By March, free standing, almost leafless, canes remain and moisture content in the biomass decrease to less than 20% and it is these which are harvested mechanically. This growth cycle is repeated once spring-time temperatures increase again.
First year MG grows to approximately waist height producing 3-5 canes, year 2 it grows to approximately head height with probably 15-25 canes, in year 3 it grows to about 2,5 meter height with about 50 canes. MG is on a yield building phase over the first 3 years. Growth potential is dependent in temperature, sun, the water capacity within soil and the rainfall levels. Therefore, sunlight and moisture are important.
The agricultural system for MG biomass cultivation is described below:
The system boundaries include the production of input substrates (e.g., fertilizers, propagation material) and the whole cultivation process (from soil preparation through planting and establishment to harvest over a twenty-year cultivation period) to subsequent re-cultivation. Yields will vary according to age of the crop and environmental factors specific to any one particular site. The crop will take three to four years to reach a mature yield (up to five years on marginal sites). After this initial yield-building phase, MG will continue for at least 20 years. The yield from the first season’s growth, at 3-5 t/ha, is not worth harvesting, however, if spring-time applications of translocated herbicides are planned then, the MG stems should be flailed/mulched in order to avoid any risk of crop uptake. From the year 2 onwards the crop is harvested annually. The second-year harvestable yields may range from 8-12 t/ha, and those in the third year may achieve between 18-25 t/ha or more at 20% moisture content. Harvestable yields reach a plateau after 3-4 years. The reasons for the variation in the yield building phase duration and yield in the plateau phase depends on planting material, planting density, soil type, climate. Where moisture supply or exposure limits yield there may be a longer ‘yield-building’ phase.