Worked example of DIN reduction using the combination of NiLRI approach and sub-steps
November 2022 release
As no additional modelling is available to represent the additional steps the DIN savings are calculated using a linear interpolation equation. For example, if a site moves halfway to the next existing band, the estimated DIN load reduction will be half of the impact of that change.
In the pre-November 2022 version of P2R Projector, DIN savings are estimated by calculating the difference in DIN loss between the before band and the after band. As an example, the before band of 5 (original bands) might have a DIN loss of 10kg N/ha and the practice change moves the project to band 4 which might have a DIN loss of 6kg N/ha. Hence, a DIN saving of 4kg N/ha (10kg/ha – 6kg/ha).
In the October 2022 version, the DIN loss values for five intermediate steps between the bands must be estimated. This is done using the liner interpolation equation below.
y = interpolated DIN losses
x = given Nitrogen Loss Risk Index (NiLRI)
x1 = lower Nitrogen Loss Risk Index (NiLRI) old band x falls into
x2 = upper Nitrogen Loss Risk Index (NiLRI) old band x falls into
y1 = losses aligned to the Nitrogen Loss Risk Index (NiLRI) old band x falls into
y2= losses aligned to the next Nitrogen Loss Risk Index (NiLRI) old band x falls into
For example:
Before Nitrogen Loss Risk Index (NiLRI) of 1.94
After Nitrogen Loss Risk Index (NiLRI) of 1.81
The before Nitrogen Loss Risk Index (NiLRI) for this example is band 5.0 and the after Nitrogen Loss Risk Index (NiLRI) relates to band 4.3, see the new band calculation table.
Band 5.0 aligns to one of the existing bands and there is an existing DIN loss figure (e.g. 10kg N/ha). Therefore, the before DIN loss is 10kg N/ha. Band 4.3 does not align directly to one of the old modelling bands so the DIN loss must be estimated by interpolating between the major bands.
y = interpolated DIN loss
x = 1.81
x1 = 1.94 (band 5.0)
x2 = 1.62 (band 4.0)
y1 = 10kg/ha (band 5.0)
y2 = 6kg/ha (band 4.0)
After DIN loss for band 4.3 is 8.37kg N/ha
Therefore, the estimated DIN load reduction for this project using the November 2022 method is 10 – 8.37 = 1.63kg N/ha
