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Based on a detailed distribution of the different land uses in Lunan catchment and
according to agricultural census data per parish for 1999, 52.8% of the total arable
land in Lunan catchment was under cereals crops. This fact combined with the
conclusion that cereal crops have lower export coefficients compared with other
arable crops allowed us to accept the assumption that P export coefficients for
arable land used for the default application could be reduced by 40% and still be
representative of the Lunan catchment.
So, applying this scenario involved reducing arable land P export rates by 40% and
creating a new P export table for the application.
Third scenario’s description and assumptions
This scenario was based on two main assumptions:
• First assumption: Buffer strip efficacy concerning prevention of phosphorus
losses is 40%, based on literature search (Vinten et al., 2004).
• Second assumption: In order for the buffer strip to be effective, the slope should
be less than seven degrees (Vinten et al., 2004).
The only way to implement a BMP, like a buffer strip, in the PLUS model, is by trying
to include the effect of such practice in the P loss coefficients. Figure 1 shows the
fields that were assumed to be influenced by the installation of the buffer strip.
Figure 1: Fields that were assumed to be influenced from the installation of
the buffer strip (dotted area across both sides of the Lunan Burn
depicts buffered fields)
After identifying the buffered fields, P loss coefficients that corresponded with those
fields were reduced by 40% from their initial value, according to the first assumption.
This new P export table was then used in order to run the PLUS model.
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