Planting & Harvesting

Since Miscanthus x giganteus (MG) is a sterile hybrid, the crop cannot be planted from seeds, but instead must be established with vegetative materials such as seedlings, plantlets or rhizomes (root growths Рshown in Figures). Some other varieties of Miscanthus can be invasive, so it is important to choose true MG rather than other varieties. Using vigorous and healthy planting material is vital. For phytosanitary reasons, MG rhizomes should only be sourced from European or Mediterranean countries. There is currently no rhizome certification or quality standards protocol available anywhere.

MG can be adapted to various kinds of soil conditions, fields need to have well drained soils, and the soil pH level is recommended to be in the range of 5.5-8. A soil test in the year before MG stand establishment can suggest the amount of lime that would be required to attain the recommended pH. Lime needs to be applied at least six months prior to planting of MG.

A plant population of 13,000-15,000 plants per hectare is optimal in an established GM plantation. To achieve the target population, over-planting in the first year is recommended since 20-30% of the plants may not grow, so planting rate of 18,000 rhizomes/ha (0,75 x 075 m) is estimated to give an emergence of 13-15,000 plants/ha. This rate allows for some establishment losses while still providing the plant density required to achieve optimal yields from year three onwards and effective weed suppression through competition.

For good soil contact, rhizomes should be planted at a depth of 5-10 centimeters. Planting is typically done in late spring after the last frost. April – May is the recommended planting time, and a longer growing season in the first year helps rhizome growth. Early planting takes advantage of springtime soil moisture and allows an extended first season of growth and enables larger rhizome systems to develop.

Nitrogen, phosphorus, and potassium are three key nutrients that are vital for growth of MG and can be applied any time before or after planting. Water is also vital for rhizome growth, so irrigation is highly recommended in drier areas. Weed control is very critical for MG, especially in the early establishment stage. Competition from weeds could lower the establishment rate or even cause a complete establishment failure for the MG stand. For land is to be converted from fallow or forage, weed control should be started the year before rhizome planting by pre-planting herbicide tolerant crops followed by a winter cover crop. In the spring of the planting year, tillage, burndown, and application of a pre-emergence herbicide are recommended to help control weeds. Once properly established, the MG stand can outperform weeds and should not require any herbicide application after establishment (year 2 and beyond). Fertilizer amounts in the first year are recommended at the same level as would be applied for growing corn. From the second year forward, fertilizer application is linked to removal of nutrients through harvesting, and there is a recommended rate by USDA (2011) accounting for the removal of each dry ton of MG biomass during harvest.

Based on growing conditions, MG dry-matter yields range from 15-25 t/he with lower yields at more northern latitudes due to harsher winters. Harvest can occur in the second year, and can be carried out for an estimated 20 years before the field needs to be replanted.  After growing vigorously during the summer, MG stops growing during autumn. The leaves drop off the crop and the stems dry as the winter proceeds reaching a moisture content of approximately 30% the following spring. Harvesting is optimal when moisture content is less than 20% and when it is easier to store MG, also the calorific value of biomass increases with decreasing moisture content. Early harvesting can produce a product with high moisture and leaf content which will be unsuitable for many applications. Delayed harvesting can damage the new growth of the emerging crop. Consequently, the optimum time of harvest is between these two extremes. MG can be harvested by mowing and baling, or can be cut and chipped. Harvesting of biomass can be done with a silage harvester or a mower-conditioner, if baled. When harvesting, 5-10 centimeters of stubble should to be left in the field to reduce moisture and soil content in the biomass bales by avoiding contact with the soil and picking up leaf litter. Overall, caution while harvesting is required to produce clean bales to deliver to the energy plant for combustion or processing.