Download as a PDF - CiteSeerX

A e
= 0.39 . S W S
TA + TA ) W (0.39 . W +
e
W TA TA )
e
From (1) and (2): =
(3)
A e
S
TA
For 1999 (default year): = 0.954 and for flat slope the minimum A e = 0.40.
So, from (3) we get W e = 0.957 and from (2) S e = 0.373.
Using W e and S e , as they were calculated based on 1999’s data, and the relative
areas of winter and spring cereals for 1989, 1994 and 2004 we get from (1) A e * for
each of the previous years.
A e
*
A correction factor = is used in order to reproduce the series of export
A e
coefficients according to land slope.
Where: A e
is the export coefficient for the default year, and
A e
* is the export coefficient for arable land representative of the proportion of winter–
spring cereals of the year that data are used in the equation (1).
Second Scenario’s Description and Assumptions
This scenario investigated how sensitive the model is to changes in the P export
coefficients table used in the PLUS application. Specifically, the P loss coefficients
that correspond to arable land, which is one of the biggest contributors to TP in the
lochs, were improved and afterwards the effect that this change had on the model’s
TP calculation, was examined.
Table 1 summarizes export coefficients for arable land, as they were collected from
literature research. Based on the figures listed in Table 1, P export coefficients for
cereals are lower compared with other arable crops.
Table 1:
Summary of P export coefficients from literature review
Land cover type
P (kg/ha)
Min
max
Location
PLUS Arable 0.4 2.0 -
Agriculture (general) 0.1 1.0 Scotland
0.1 6.8 UK
Arable (general) 0.8 2.5 Scotland
0.5 5 UK
Cereals 0.22 0.9 Scotland
0.06 0.9 UK
233