1. Environmental Considerations of Phosphorus Use Rich. McDowell

2. 69-78% of sites P-limited Control + N + P What does phosphorus do?

3. Distribution and significance of the issue Caspian Sea Potomac River Maharakeke Stream Effects: - Increased algal biomass (toxic) - Reduced water clarity - Taste and odour problems - Poor habitat - Increased probably of fish kills - Decrease aesthetic/recreation Costs: - £75-114M/yr UK water treatment - >$1B decreased fishing revenue over 10 yrs in Chesapeake Bay - 100M/yr lost recreation revenue NZ

4. Sources: Soil Low (5) Medium (25) High (50) V. high (85)

5. Sources: Fertiliser, Manure, Grazing Rate Placement Timing

6. In an equal world… 2005 2004 Runoff 7 days after application Losses would reflect amount of P available for loss

7. 86 L Albrights soil fragipan Berks soil no fragipan 21,757 L 0.1 g 4 g Soil P = 78 mg kg -1 Soil P = 177 mg kg -1 Hydrology and runoff can control P loss Source: Buda et al. (2009)

8. Source + Transport = risk Risk Low (clear) Medium High 80% of losses come from 20% of area Concentrating mitigation and P use efficiency on critical source areas is the most cost-effective method of reaching an environmental target Management of source & transport

9. A policy response… Laggards: Prohibit detrimental practice Leaders: Advance good practice 1. Intensive regulatory approach could miss losses stifles innovation 2. Voluntary approach relies on good will hard to pin-point effect 3. Combined model (must be based on good system knowledge and targeting e.g. cost-effectiveness)

10. Example of poor regulation via stream fencing 20042009 – after fencing Target

11. PUBLIC called 30% less periphyton in the river and tributaries. POLICY is that median DRP during summer-autumn should not be > 0.02 mg/L, down from 0.07 mg/L Combined model: define problem

12. Combined model: define main leakage Too much effluent applied at too high a rate

13. Low rate irrigator 100 80 60 90 70 50 40 30 20 10 Total P NH 4 + -NE. coli Concentration relative to effluent applied High rate irrigator Combined model: prescribe mitigation to fix mian leakage

14. Strategy Effectiveness (%) Cost ($/kg P conserved) Optimum soil test P Management 5-20highly cost-effective Split grass-clover pastures0-40Highly cost-effective Low solubility P fertilizer0-200-25 Restricted grazing30-50125-200 Tile drain Amendment 5020-75 Alum to pasture / cropland5-30125->400 Buffer strips Edge of field 0-10>200 Stream fencing10-304-55 Sorbents in and near streams20300 Natural and constructed wetlands-426-77>400 Combined model: educate on cost-effectiveness of applying next mitigation to CSAs

15. Example: Ryegrass produces well at low soil test P. However, higher soil test P (and loss?) is required to maintain clover. Olsen P (mg/L) 1540 Ryegrass yield Phosphorus loss from soil Clover yield Mixed model: innovative management of CSAs

16. Answer: Place clover in areas of a catchment unlikely to contribute runoff to the stream. Mixed model: innovative management of CSAs D ECREASES DRP LOSS BY 45%

17. $0-$30$15 $429 Change in profit ($/ha/yr) Reference condition Proposed target Mixed model: management of CSAs at farm scale

18. For a 1-2 kg P/ha loss, common sources are: Soil 40-60%; Fertiliser = 10-15%; Manure/Grazing = 25-50% Much P loss comes from critical source areas SUMMARY A good policy response would be: 1.Set clear objectives (including anthropogenic load) 2.Target mitigation strategies to CSAs 3.Allow flexibility in strategies (educate on cost-effectiveness) Challenge that critical source areas of P loss can be identified and treated successfully (with time) to minimise compliance costs.