Nutrient allocation: Two modelled examples

1. Nutrient allocation:Two modelled examples Darran.Austin@mpi.govt.nz Thanks to Adam Daigneault (Landcare), Levi Timar (Motu & GNS), and Dan Marsh (Waikato Uni)

2. Lake Rotorua • Over-allocated in N, ~60% reduction to meet final cap • Motu modelled trading, with grandparenting versus sector average allocation • EBoP benchmarked farms (~25 dairy, >100 dry stock) Sector average Sector average Classification?

3. Most mitigation is carried out on dry stock farms (afforestation), and is “purchased” by dairy farmers • Grandparenting results in a tighter distribution of costs across farms

4. Hinds management zone • Over-allocated in terms of N • 45% reduction in N (after new irrigation) to protect 80% of species in lowland streams (90% in Hinds River) • Landcare modelled a range of policies, MacFarlanes mitigation costs

5. Allocation methods • Grandparenting and equal allocation • Nutrient vulnerability • Based on soils ability to “filter” N • Base set to dryland S&B • Rest of load proportional to soil filtering, • more filtering = more allocation • or high vulnerability = less allocation • Land use capability • Based on lands carrying capacity • Allocation proportional to a theoretical deficit irrigated, zero fert, dairy farm’s leaching in each class

6. Trading is cheaper, should be in a frictionless optimisation model • Without trading, overall impact of allocation depends on specifics of mitigation costs and amount to mitigate

7. 45% reduction in N • Except grandparenting, costs are concentrated with dairy and dairy support on lighter soils, small gains in S&B revenue through land use change