Crop Production

Site Selection & Crop Requirements

Soils: Miscanthus Giganteus (MxG) has been reported growing and producing high or reasonable yields on a wide range of soils, from sands to high organic matter soils. It is also tolerant of a wide range of pH, but the optimum is between pH 5.5 and 7.5. MxG is harvested in the winter or early spring and therefore it is essential that the site does not get excessively waterlogged during this period, as this may limit accessibility for harvesting machinery and cause damage to the soil structure. Growing MxG on heavy clay soils in certain circumstances should therefore be avoided.

Temperature:  The potential cropping zones for MxG are quite widespread. MxG does not grow at low temperatures below a threshold of 6°C. This is considerably lower than for maize and therefore the potential growing season is longer. MxG photosynthetic mechanism appears to be better adapted to low temperatures than that of many other C4 crops, equipping it for high productivity under relatively cool temperatures. Late spring frosts which destroy early spring foliage and effectively reduce the duration of the growing season can be a constraint to long season growth in MxG. The commercially available clones of MxG can survive low winter temperatures of -20°C based on recent years’ experience.

Water Availability:  Annual rainfall and soil water retention will strongly influence the yield of MxG at any site (≥700 mm average annual precipitation). MxG possesses good water use efficiency when considered based on the amount of water required per unit of biomass and miscanthus roots can penetrate and extract water to a depth of around 2m. Limited soil water availability during a growing season will prevent the crop from reaching full potential yield in that year. In times of severe drought, the foliage of miscanthus will first show leaf rolling and then die back from the leaf tip. This will reduce yield in the year of drought but in all cases experienced in Europe to date the crop will survive and re-grow the following year.

 

Pre-Planting Site Preparation

Thorough site preparation is essential for good establishment, ease of subsequent crop management and high yields. As the crop has the potential to be in the ground for at least 20 years, it is important that it is established correctly to avoid future problems. If it’s a grassland site, the first step, before planting, is to spray the site with an appropriate broad-spectrum herbicide (e.g. glyphosate) for controlling perennial weeds. The site should be sprayed and then ploughed in late autumn to control perennial weeds. This will allow frost activity to break down the soil further. In the case of low soil pH (below 5.5) before plowing there should be applied 2-3 t / ha of calcium fertilizers based on CaO. Later in the spring from March to April the site should be rotovated or power harrowed immediately prior to planting. This will not only improve establishment by aiding good root development, good soil root contact and improved soil aeration but will also improve the effectiveness of any residual herbicides, applied after planting.

Planting Material & Planting Density

Since MxG is a sterile hybrid, the crop cannot be planted from seeds, but instead must be established with vegetative materials such as seedlings or rhizomes (root growths). Some other varieties of Miscanthus can be invasive, so it is important to choose true MxG rather than other varieties. Using vigorous and healthy planting material is vital. For phytosanitary reasons, miscanthus rhizomes should only be sourced from the European Union countries. There is currently no rhizome certification or quality standards protocol available anywhere. Rhizome pieces must have at least 2 to 3 shoot initials, (buds with sharp points)’ and must be kept moist before re-planting.

A planting rate of 13,400 – 17,800 rhizomes/ha is recommended to give an emergence of 10-15,000 plants/ha. This rate allows for some establishment losses while still providing the plant density required to achieve optimal yields from year three – four onwards and effective weed suppression through competition. Rhizomes need to be planted at a depth of 5-10 cm. The optimal planting time for rhizomes is from March to April but planting can continue into May and still be successful. Early planting takes advantage of spring-time soil moisture and allows an extended first season of growth. This is important, because it enables larger rhizome systems to develop and allow the crop to tolerate drought and frost better in the next years. We recommend the optimal planting rate 17,800 rhizomes per hectare (0,75 x 0,75 m spacing) in order to get a guaranteed plantation establishment and allow for some rhizome losses during the establishment phase. Also, the higher density will secure higher biomass yields on second and third year of crop lifetime and more rapid achievement of plantation maturity.

Weed Control: Pre-Planting, Post Planting, Post Emergence & Year 1 Weed Control

Weeds if not controlled, will compete with the crop for light, water and nutrients and thus reduce yields. The level of weed interference will depend on the stage of maturity of the crop (i.e. its ability to out-compete weeds), the degree of weed infestation at the site and the diversity of the weed species (affected by location, season, climate and previous land use). Weed control is essential in the establishment phase of the crop because the slow initial growth of miscanthus reduces its ability to compete. The planting process causes soil disturbance which promotes seed germination. Furthermore, the low planting densities which are used results in large unoccupied spaces where weed growth can occur. At this stage the young MxG plantlets can easily become overwhelmed by weeds. As the MxG crop becomes more established, a range of selective herbicides can be used for weed control. Once the full canopy develops, the germination of new weed seedlings is dramatically reduced, and only shade tolerant varieties.

It is vital that proposed sites should be cleared of perennial weeds before any planting takes place. It is important that this is carried out effectively particularly on old pasture land where the presence of perennial weeds such as docks and nettles is more likely. A translocated (systemic) herbicide (e.g Glyphosate at 4-6 l/ha) should be applied to actively growing vegetation in autumn prior to the year of planation establishment. To allow the herbicide to fully translocate, a period of ten days post herbicide application should be allowed before ploughing. Within 14 days of planting, spray a pre-emergence weed killer and if necessary, an insecticide onto a moist soil.  Once MxG shoots have emerged, selective herbicides may be used for the control of vigorous annual dicotyledonous weeds. From May to August walk the fields on a weekly basis. Monitor weed populations and take remedial action in worst case scenarios. Spring cereal broad leaf weed herbicides can generally be used on miscanthus. Weed control is likely to be relatively intensive after planting and during the establishment phase. However, once the crop has become established, the demand for weed control is low.

Nutrition and Fertilization

MxG does not require a high level of fertilization, because this crop is very efficient in the way it uses nutrients. There are several reasons for this high level of efficiency:

  • MxG is deep rooted and can abstract nutrients from a large area of soil
  • MxG has a high nutrient efficiency compared to arable crops (wheat, barley) and native grasses (ryegrass). Less nutrients are needed for each kilogram or unit mass of biomass produced by the crop.
  • Excess nutrients are exported from the above ground parts to the rhizome during the autumn as the leaves senesce (die). The nutrients are stored in the rhizome during the winter and are used to support early growth of shoots during the following spring.
  • Leaves fall off the MxG stems as winter progresses and accumulate as a litter layer on the surface of the soil. The litter layer is broken down over time and the nutrients find their way back into the soil where they can be once again absorbed by the root system. Additional nutrition is available to the crop through atmospheric deposition and soil mineralization.

Nutrient off-takes are confined to the amount of nutrients in the stems at harvest as nutrients in the leaves are returned to soil. Final harvest yields and consequent nutrient offtake will depend on crop productivity. Crop productivity will depend largely on rainfall and temperature. The proposed doses of fertilizer and the date of their application are as follows:

  1. In plantation establishment year (not necessary on fertile soils or after the adoption of the seedlings before spring systems):
  • Nitrogen — 30 kg/ha,
  • Phosphorus – 20 kg/ha,
  • potassium — 40 kg/ha,
  1. In the next few years (in the spring after the dry field it can be mixed with the soil tool used for weeding between rows):
  • Nitrogen — 60-90 kg/ha,
  • Phosphorus — 30-50 kg/ha,
  • potassium — 80-100 kg/ha,
  • magnesium — 20-25 kg/ha,
  • Calcium (if necessary, every 4 years).

In the late fall and winter liquid organic fertilizer can be used on the MxG plantation in the form of slurry, to a maximum of 30 m3 / ha (or sludge), which practically can replace mineral fertilization. It is generally not recommended that any fertilizer be applied in the first two years as offtakes are low and there are generally enough nutrients in the soil. Typically, fertilizer application during these years will only promote weed growth which will compete with the growth of the young MxG plants and incur additional expenditure on herbicides.

Pests and Diseases

Miscanthus species are susceptible to pests and diseases in the areas to which they are native (Asia) but, yet, none of these has been reported in the EU. Stem basal diseases may infect stems in the autumn or winter, reducing stem strength. There are no reported insect pests in Europe that have significantly affected the production of miscanthus. However, two ‘ley pests’, the common rustic moth and ghost moth larvae feed on miscanthus and may cause problems in the future. Rabbits can also be a problem in establishing a new MxG crop as they like to feed on the fresh emerging leaf as the crop grows initially.

Harvesting

MxG is harvested annually during spring, typically with conventional farm machinery. After growing vigorously during the summer, MxG 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. Harvested biomass with lower moisture content is easier to store and the calorific value of biomass increases with decreasing moisture content. Early harvesting of Miscanthus (January, February) can produce a product with high moisture and leaf content which will be unsuitable for many applications. In contrast, delayed harvesting (late April) can damage the new growth of the emerging crop. Consequently, the optimum time of harvest is between these two extremes, generally in March or early April. MxG can be harvested by mowing and baling. Once harvested, bales should be stored inside a shed or outside under cover. Covered storage will ensure that bales will continue to dry whereas bales stored without cover will deteriorate particularly if conditions are poor. Alternatively, the crop can be cut and chipped using a forager equipped with a Kemper header. This method of harvesting involved one operation whereas two operations are involved when the crop is mowed and baled. Cutting and chipping produces a product in chip form which is suited for combustion in boilers and power stations. Smaller chip sizes have a greater tendency to heat during storage while larger chip sizes are likely to be unsuitable for the intake systems of boilers and power stations.