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How legacy nutrients affect farm conservation measures

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Full proceedings available at: http://www.extension.org/72868

There has been a tremendous amount of activity and funding of conservation programs with regional and watershed-specific cost-share initiatives. While there have been some successes, water quality response in many areas has not been as great as expected. This has led many to question the efficacy of these measures and to call for stricter land and nutrient management strategies. In many cases, this limited response has been due to the legacies of past management activities, where sinks and stores of phosphorus along the land-freshwater continuum mask the effects of reductions in edge-of-field losses of phosphorus.

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How legacy nutrients affect farm conservation measures

  1. 1. How Legacy Nutrients Affect Farm Conservation Measures Andrew Sharpley Crop, Soil,& Environmental Sciences Water to Worth 2015 Advancing Sustainability in Animal Agriculture Seattle, WA
  2. 2. Dealing with a 10-ton gorilla Legacy P & system response  Soil  BMPs  Hydro-chemistry  Fluvial Where do we go from here?
  3. 3. Soil Hydro-chemBMPs System
  4. 4. Uptake & release of P by sediments affects waterbody response Decline in soil P with crop offtake is slow Adoption of BMPs by farmers is variable BMPs can take time to decrease P runoff Soil processes Hydro-chemical response System response BMP response Wetlands trap & buffers can trap then recycle P Time for ground water to reach stream can vary from days to years
  5. 5. 0 100 200 300 400 500 1988 1992 1996 2000 2004 2008 2012 Available soil P (Mehlich-3), mg/kg Grazed pasture Dairy manure added 75 kg P/ha/yr Pasture cut for hay Crop response
  6. 6. Land use Location Decline Time Decline mg P/kg years mg P kg-1 yr-1 Pasture OK. 260 - 190 15 4.7 Corn NC 100 – 20 16 4.7 Wheat Canada 125 – 109 4 4.0 Soybean IA 95 - 10 27 3.2
  7. 7. BMPs can take time to effectively decrease P runoffPonds trap P Time for buffer to become effective Wetlands trap P But are not infinite sinks for P Can eventually release P
  8. 8. • 1.2 billion broilers produced annually in AR • In 2003  Judge set 300 mg/kg Mehlich-3 P threshold  Litter rates went from 3 to 1.3 tons/acre/yr • In 2014  Most of the litter exported out of watershed  85% in Eucha-Spavinaw & 45% in Illinois River Watershed  Judge reduced STP threshold to 150 mg/kg
  9. 9. AR Water Resources Center, 2012 Diss. P Total P 2000 0.224 0.377 2003 0.148 0.244 2011 0.070 0.130 Mean annual concentration, mg/L
  10. 10. Time for water body to biologically respond to P input Response to BMPs takes time Variable delivery time from source to point of impact
  11. 11. 36 48 15 Baseflow dissolved P, µg/L 27 Stormflow dissolved P, µg/L 170 124 304 202 I mile
  12. 12. 0 50 100 150 200 250 300 1990 1995 2000 2005 2010 Lake P µg/L Recovery phase Internal recycling of ‘legacy’ P (10-15 y) Water quality target met P input reduced 60% Water quality target 40 µg/L Loch Leven, Scotland; Linda May & Bryan Spears, CEH
  13. 13. Lakes (c.5-30 yr) Groundwater (<1 – 50 yr) In-channel (<1 yr) Riparian & floodplains (<1 – 1000 yr) Soils & hillslopes (c.5-30 yr)
  14. 14. Maumee River watershed Sandusky River watershed MICHIGAN Lake Erie OHIO Richards et al., 2002
  15. 15. 3 4 5 6 7 1975 1980 1985 1990 1995 15 20 25 30 35 40 1975 1980 1985 1990 1995 Conservation measures reduced fertilizer P inputs Maumee Sandusky Fertilizer P, 103 tonnes P/yr
  16. 16. 1975 1980 1985 1990 1995 2000 2005 2010 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Maumee River 1975 1980 1985 1990 1995 2000 2005 2010 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Sandusky River Baker et al (2014) J. Great Lakes Research Mean total P mg/L 1975 1980 1985 1990 1995 2000 2005 2010 0.0 0.2 0.4 0.6 0.8 Maumee River 1975 1980 1985 1990 1995 2000 2005 2010 0.0 0.2 0.4 0.6 0.8 Sandusky River Mean dissolved P, mg/L
  17. 17. Some of the drivers Increased DP input & blooms result of… Same annual rainfall but more intense spring rains  Prior to 2008 – 12% of annual rains  2008 to 2011 – 30% of annual rains Surface soil P buildup with no-till Increased tile drainage of soils created more critical source areas Solutions need to consider day-day farm management decisions
  18. 18. Conservation initiatives, metrics, & outcomes should account for & adapt to legacy impacts  Legacies mask/delay water quality improvements  Some practices will transition from sinks to sources of P – no-till soils & buffers
  19. 19. Model fluvial processing of P  Move from delivery coefficients & distance functions to process-based model
  20. 20. Legacy P will likely become a resource  As costs of fertilizer production increase  Market forces & govt. intervention will determine how quickly legacy P stores are tackled
  21. 21. Need better understanding of  Spatial & temporal aspects of watershed response to nutrient load reductions  Scale at which responses may occur in a more timely fashion Local water quality & quantity benefits evident more quickly at a smaller scale Important to demonstrate change & foster accountability & ultimately wider adoption of conservation practices

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