The National Freshwater Standard cap synthetic nitrogen use at 190kg N/ha. This rule came into effect on the 1st July this year and every farmer with 20ha or more will need to report their N usage to Council annually. 

For a full explanation go to
https://environment.govt.nz/publications/ncap-dairy-farms/ 

Some key points are: 

Synthetic nitrogen may be applied at a rate of no more than 190kg/ha/year to each hectare of land not used to grow annual forage crops and as an average rate over all of the land. This essentially means that nitrogen can be applied to cropping areas at a higher rate but must be lower over other farm areas to meet the 190kg average. The use of over 190kg/ha/year of synthetic nitrogen as an ongoing activity requires resource consent. 

Nitrogen fertiliser is calculated based on contiguous landholdings ie a separate support block is reported separately 

The first reporting period is the current season 1st July 2021 to 30th June 2022 and needs to be reported to council by the 31st of July 2022. 

The regulations set out a list of information that needs to be reported, but not a specific way to present it. A good amount of the data you will have recorded already but it would be advisable to make sure you have kept the records and rin a way that can be put together.