ARCHIVE: Fertiliser Manual (RB209)

Willow

Typical offtakes of nutrients in wood harvested from willow SRC after 3 years growth following the previous coppicing are.

Nutrient

per tonne of dry biomass

In a typical crop yielding 14
tonne dry biomass per ha

 

kg/t

kg/ha

Nitrogen (N)

3

90

Phosphate (P2O5)

1.8

55

Potash (K2O)

2.4

72

For SRC willow there is even less experimental data on nutrient requirements than for Miscanthus. So the provisional recommendations given here are based a combination of nutrient offtakes measured at a very small number of sites and experience of growers. No fertilisers are required during the establishment year; so the recommendations below refer to the three year periods after the initial cutback (in the winter after establishment) and the subsequent three year periods after each harvest. With SRC it is almost impossible to enter the plantation to apply fertilisers or manures in the second or third year after cutback or harvesting unless specialist equipment is available. It is therefore necessary to determine nutrient requirements, and make any appropriate applications, in the first year after a cutback, normally during spring in preparation for the period of rapid growth.

In situations where biomass crops are used for bioremediation of biosolids or bio filtration of effluents, levels of nutrient application in excess of those highlighted above may be justified, recognising the relatively low environmental risks associated with this approach, relative to alternative methods of disposal. In such circumstances, careful monitoring of ground and surface water is required to demonstrate absence of leaching and/or surface runoff of N and P.

Phosphate

Maintain soil at P Index 1. Check every 3 years (i.e. each harvesting cycle) by soil testing (see Section 1 and Appendices 3 and 4). 

Potash

Maintain soil at K Index 1- 2. Check every 3-5 years by soil testing (see Section 1 and Appendices 3 and 4).

Nitrogen

As with Miscanthus, a combination of nitrogen mineralised from soil organic matter plus that from atmospheric deposition and rain will supply much of the modest nitrogen requirement of about 30 kg N/ha per year for a typical UK crop yielding 30 t dry biomass during a three year cycle, i.e. 90 kg N/ha total offtake. However, larger offtakes have been observed in some situations and, as a grower gains experience of yields in specific soil types and different environments, nitrogen applications can be adjusted using the values in the table above for nitrogen removed per tonne dry biomass.

Applications of organic materials such as FYM, slurry or sewage sludge are an ideal way of maintaining a suitable supply of nitrogen and other nutrients throughout the three year growth cycle from a single application made in the first year. But amounts applied should be determined on the basis of estimated crop requirement, or within the limits described above for bioremediation or bio filtration systems.

ADLib logo Content provided by the Agricultural Document Library
© University of Hertfordshire, 2011