One Plan update and Nitrogen leaching

I attended an update by Horizons earlier this week about Proposed Plan 2 of the One Plan, and specifically a technical update to the vexed One Plan Table 14.2 which set out the cumulative nitrogen leaching maximums for the various Land Use Classes.

One Plan N-leaching limits were calculated using Overseer 2007. Since that date a lot of revisions have taken place to Overseer and more knowledge applied.  Proposed Plan 2 see’s N-loss calculated using Overseer 6.3.0 with this version now taking into account that some of the Nitrogen leached from farmland is lost to atmosphere as well as some as dissolved N into groundwater and ultimately finding it’s way into waterways.

Horizons measures N in the waterways. And knowing what goes onto the land and what is in the waterways, there is a significant difference which is explained by atmospheric loss.

As an example, under the previous Overseer model, LUC II land in the Tararua was required to meet a N-leaching target of 21 by Year 5. Using the new model, that number is 40. Now, this higher number does not mean more N is reaching the rivers compared to the lower limit – the actual N-loss to water is exactly the same so the intent of One Plan remains on track to reduce Nitrogen in our waterways. But these new calcs will provide a lot more ability for farmers to develop systems that meet or exceed the targets.

See the draft detail below:

 

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