Lake Rotorua

Lake Rotorua

Reference Files

What are Reference Files?

Reference files are OVERSEER® files that have been built to represent the average benchmarked farm. Each reference file represents the average benchmark management practices (i.e. stock type, stocking rate, fodder cropping, etc.) together with the geophysical characteristics (i.e. soil, slope, rainfall) of the benchmarked areas to form an average sector file. The intent is that the predicted nitrogen discharge from these reference files track the average benchmarked sector losses through OVERSEER® versions as closely as possible. There are five reference files representing six sectors: dairy, drystock, grazed trees, house, forestry and bush and scrub. 

How are they used?

Reference files are used to proportionally adjust the allocations of each block to reflect nitrogen loss changes that occur with each new version of OVERSEER®. Each block in the catchment has been assigned a sector and a percentage. The sector reflects the landuse that occurred on the block of land during 2001-2004, and the percentage is the blocks allocation relative to the reference file for the given sector. If the drystock reference file in the new version of OVERSEER® was to increase its discharge prediction by 10 % then all drystock block allocations will increase by 10 %

For example:

If under OVERSEER® 6.2.0 Farm A has an output of 50 and the reference file output under the same version is 40 then Farm A’s NDA is 125 % of the reference file. For any future changes to OVERSEER® the NDA target remains constant for Farm A (at 125 %).

OVERSEER® version

Reference File N loss (kg N/ha/y)

% of Reference File = NDA expressed as a %

Block allocation (NDA) (kg N/ha/y)

Allocation version


= (50/40)x100

= 125 %




N loss output obtained by running reference file through latest OVERSEER version

Fixed % post allocation version

New Block NDA calculated by ref. file N loss x %

Version X


125 %

43 x 125 % = 53.75

Version Y


125 %

51 x 125 % = 63.75

Version Z


125 %

33 x 125 % = 41.25


The start point (benchmarks) and managed reduction targets can all be expressed as a % of the reference file. A further example is provided in Schedule Five of the rules.

What do reference files mean to me?

When the OVERSEER® version updates, the reference file outputs will change. If you need to know what your  allocation is in the new version of OVERSEER®, you multiply your block percentage allocations by the new reference file output to give a new block discharge that works with the new version of OVERSEER®. By summing the individual block allocations your property allocation can be determined.

What happens with future OVERSEER® change?

As OVERSEER® continues to improve and incorporate new research into the model the reference file outputs will change. This table shows the outputs of the reference files in the current version of OVERSEER® and will be updated as OVERSEER® versions are released.          


OVERSEER® version


Released  November 2016


Release in March 2018

Dairy 95.45 87.72
Drystock, grazed trees    34.24 27.99
House 78 78
Bush and scrub, wetland          3.0 3.0
Forestry 2.5 2.5