MANAGING PHOSPHORUS LOSSES. Rich. McDowell, AgResearch

Transcription

1 MANAGING PHOSPHORUS LOSSES Rich. McDowell, AgResearch

2 BIOAVAILABILITY: N-, CO-, OR P-LIMITATION Co-Limited Co-Limited 14% 19% N-Limited 13% P-Limited 73% N-Limited 17% P-Limited 64%

3 Where does it come from? Rain Dung Fertilizer & feed Infiltration excess Overland flow Erosion of particulate P Release of dissolved P Effective depth of interaction Deposition Percolation; > P retention Infiltration & saturation excess overland flow Preferential flow via macropores; < sorption Drainage Ground water Subsurface flow Variable source area

4 LOSSES FROM DIFFERENT SYSTEMS Catchment losses (1970-present) Phosphorus loss (kg P ha -1 yr -1 ) Wide range due to: climate soil type topography management 0 Native Sheep Mixed Deer Dairy n =7 n = 8 n = 9 n = 6 n = 22 Land use

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6 SOIL OLSEN P Yield

7 FERTILISER Phosphorus concentration (mg/l)

8 FERTILISER Soil Dung Fertiliser Runoff 7 days after application Soil Dung Fertiliser

9 GRAZING

10 DIRECT DEPOSITION Enriched source of phosphorus, nitrogen and faecal bacteria

11 FENCING The impact of fencing-off and planting? after fencing Guideline

12 EFFLUENT Rotating twin gun travelling irrigators - soil water deficits low in spring & autumn - poor control of application depth & application uniformity - high rate of application (potential to be > infiltration) Effluent applied, mm Distance from centre of irrigator

13 EFFLUENT Direct contamination of surface water via: - mole-tile drainage - surface runoff - other (e.g. infrastructure failure) 450 mm Macropores Trench soil 600 mm Mole drain Gravel backfill Intercepting pipe drain

14 FLOOD IRRIGAITON OUTWASH Olsen P mg/kg Photo courtesy of Bob Wilcock, NIWA

15 TRACKS/LANES Used each day Concentrated source of faecal deposits

16 TRACKS/LANES E Coli Location of collectors Raw effluent NH4-N Close to Shed Bridge crossing TP % of water quality guidelines

17 WINTERING BLOCK P N loss per ha N/P loss on a farm scale Restricting grazing to 3-4 hr can decrease losses by 30%

18 FENCE-LINE PACING Associated with stress Denudes pasture + compacted soil = increased runoff mg/l or log 10 E. coli /100 ml ANZECC limits

19 SELF FEEDING Low cost and labour, but high losses NOx-N Total P Self feeding silgae pit Bottom Middle Top DRP SS E. coli Percent of water quality guideline

20 MITIGATION STRATEGIES NEED TO BE FULLY ASSESSED Strategy Effectiveness (%) Cost ($/kg P conserved) Optimum soil test P Management 5-20 highly cost-effective Low solubility P fertilizer Effluent pond storage / low rate application Restricted grazing Tile drain amendments Amendment Alum to pasture / cropland >400 Phoslock/red mud Buffer strips Edge of field 0-10 >200 Stream fencing Sorbents in and near streams Natural and constructed wetlands >400 Increasing cost = stop at source

21 DEFINING THE MANAGEABLE LOSS Business as usual Managed decrease In losses Concentration (mg L -1 ) Consensus target Anthropogenic loss Reference conditions

22 POMAHAKA CATCHMENT c km 2 30% dairy, 55% S&B, 15% Forestry.

23 WHERE IS THE P COMING FROM?

24 MITIGATION STRATEGIES THAT MATCH THE FARM SYSTEM Strategy Effectiveness (%) Cost ($/kg N/P conserved) Optimum soil test P 5-20 highly cost-effective Effluent pond storage / low rate application Management Restricted grazing Tile drain Amendment Alum to pasture / cropland >400 Phoslock/red mud Buffer strips 0-10 >200 Stream fencing Sorbents in and near streams Natural and constructed wetlands >400 Edge of field Increasing cost = stop at source

25 USE LOW RATE EFFLUENT APPLICATION Concentration relative to effluent applied High rate irrigator Low rate irrigator Total P NH 4+ -N E. coli

26 ESTIMATED EFFECTS: TARGETED + FARM-WIDE $0 -$30 $15 $129 Change in profit ($/ha/yr) Proposed target Natural baseline

27 SUMMARY Soil Decrease soil Olsen P to mg kg -1 unless in top 20% of producers for the region Redistribution of soil P by cultivation as part of farm re-grassing program and/or addition of P sorption agents Fertiliser Use RPR or serpentine super. Avoid applying superphosphate if rain forecast within the next 7 days. Dung Avoid set stocking wet paddocks. Effluent apply little and often (and have storage). Other areas Restricted grazing of forage crops Irrigation management (prevent outwash water recycling) Amendments Fencing, buffer strips, sediment traps

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