Miscanthus: Planting and Growing (PB5421)

Fertiliser Requirements

The annual fertiliser demands of the crop are low. This is due to good nutrient use efficiency and the plants capability to re-cycle large amounts of nutrients into the rhizomes during the latter part of the growing season. As a consequence, nutrient off-take at harvest is low, as shown in Table 1. Since the leaves predominately remain in the field it is only necessary to account for the amount of nutrients removed in the stems. The nutrient requirements during the following seasons are met by leaf litter decomposition, natural soil nutrient reserves, rhizome reserves and atmospheric depositions. Mature rhizomes tend to store more nutrients than the crop needs, so after the first 2 years, only a small quantity of additional micro-nutrients may be required. For good miscanthus yields a minimum phosphorus and potassium soil index of 1 should be aimed for and soil nitrogen supply should exceed 150 kg/ha in each of the first 2 seasons. When nutrients are needed in the first 2 seasons, this could come from farmyard manure or sewage sludge.

Codes of Good Fertiliser Practice should always be followed.

Table 1: Nutrient off-take (kg/ha) for an average crop consisting of
13.5 t/ha of stems and 4.5 t/ha leaf litter

  Stem Leaf Litter
Nitrogen 88 47
Phosphorus 11 2
Potassium 95 14

 

Weed Control

Weeds compete with the crop for light, water and nutrients and can reduce yields. Weed control in the establishment phase of the crop is essential because poor control can severely check the development of the crop. It is vital that proposed sites should be cleared of perennial weeds before any planting takes place. DEFRAs Pesticides Safety Directorate has given off-label approval for herbicides used for cereals,grass and maize to be used on miscanthus. Write to PSD (see page 18) or see http://www.pesticides.gov.uk/psd_databases/solaweb/solaweb_search.asp.

Herbicide application must not be made on miscanthus crops greater than 1 metre in height and the crop cannot subsequently be used for food or feed. A wide range of herbicides have been used effectively with no visible damage to the crop in Denmark and the UK. Following the establishment year, an annual spring application of a broad-spectrum herbicide may be needed to control grass weeds such as common couch and annual meadow-grass and broad-leaved weeds with early season vigour. Glyphosate and paraquat have been used in this dormant period between harvest and initiation of spring growth but they will cause severe damage to any new shoots which might have emerged. Once the crop is mature (i.e. from the summer of the second year), weed interference is effectively suppressed. This is initially due to the leaf litter layer on the soil surface and subsequently due to the closure of the crop canopy, which reduces the light penetrating into the under-storey.  Weeds that do survive offer little competition to the crop. Since there are no labelled recommendations, all products used are at the users own choosing and the commercial risk is entirely theirs.

Table 2: Herbicides which have been used successfully to control weeds in miscanthus
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