Nutrient Summary calculation details

Sometimes the spread rate displayed in HawkEye may show as more or sometimes less than the rate you ordered. So why is that? The below information will explain this and reinforce the importance of an accurate farm map.

If fertiliser spreaders overlap any areas on a paddock, or leave gaps or holes, the rates can end up being different to what was requested when averaged over the paddock. So, if an area of a paddock is not spread, that portion of the paddock has a rate of 0 kg/ha of product, and likewise anywhere that overlaps of spread fertiliser happen will create double (or more) the requested rate for that particular area.

The descriptions below will help you understand how these calculations take place to provide the important information regarding rate of product spread.

Proportion overlap

This is the area of the paddock that the spread took place over. It also considers the overlaps of that area.

The calculation is:
The intersected dissolved application area (spread area) divided by the calculated area of the LAU (paddock). 

Total amount

The total accumulated applied amount including overlapped applications.

Average rate

This is the rate of product applied when we consider the amount (including any overlaps) and just the area of the paddock it was applied on.

The calculation is:
The total applied amount divided by dissolved area of the applied portion of the application.

So, for the scenario above, the values should be:

Proportion overlap = 40ha / 100ha = 0.4

Total amount = 850kg

Average rate = 850kg / 40ha = 21.25kg/ha (slightly higher than the requested spreading rate due to overlaps).

Calculations when a spread crosses a paddock boundary

When running a nutrient summary, we specify a negative buffer for LAU's (paddock) boundaries and intersect that with the spread centreline to determine whether the LAU would be included in the calculation. So if the centreline of a spread crosses over a paddock boundary by 3 metres, the paddock with the small intersection will not show any evidence of that fertiliser spread in a report.

The negative buffer is 4 metres.

Spread area Intersection rule

Along with the above rule, for each paddock that a spread area intersects, any intersection with any paddock less than 100m2 will be ignored, as these are not considered to be a requested spread.